JP7852804B2 - Multilayer resin sheet - Google Patents

Description

This invention relates to a multilayer resin sheet. Furthermore, it relates to a multilayer resin sheet with a support, a printed circuit board, and a semiconductor device obtained using the multilayer resin sheet. This invention also relates to a method for manufacturing a printed circuit board using the multilayer resin sheet.

As a manufacturing technology for printed circuit boards, a build-up method is known in which insulating layers and conductive layers (circuit layers) are stacked alternately. In the build-up method, the insulating layer is generally formed by laminating resin composition layers onto a circuit board using a resin sheet containing resin composition layers, and then curing the resin composition layers. For example, Patent Document 1 discloses a technique in which resin composition layers are laminated onto a circuit board using a resin sheet having multiple resin composition layers, the resin composition layers are heat-cured to obtain a cured product, and then the cured product is roughened to form a thin insulating layer with excellent mechanical strength.

International Publication No. 2009/119621

Regarding the technology described in Patent Document 1, when forming via holes with a laser for wiring formation, it is necessary to perform desmear treatment to remove resin residue (smear) inside the via holes. However, if the intensity of the desmear treatment is increased to improve the smear removal efficiency inside the via holes, the resin surface may become roughened, impairing the smoothness of the insulating layer surface. If the insulating layer surface is not smooth, when forming a conductor layer (wiring layer) on the insulating layer, the adhesion between the pattern-forming dry film and the insulating layer tends to decrease, which can lead to defects in the formation of fine wiring.

As a technique to solve this problem, a method has been proposed in which via holes are formed with a laser while the insulating layer surface is protected by a support, and then the support is peeled off after desmearing (for example, Japanese Patent No. 6322885). According to this technique, the insulating layer surface remains smooth while smearing from within the via holes can be removed. However, this technique has the drawback of requiring the removal of the support after desmearing, which necessitates a change from the conventional process. Furthermore, since a release agent remains on the insulating layer surface after the support is peeled off, a separate process for cleaning the release agent is required, which also presents a challenge.

The present invention provides a novel technique that can yield an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes, even when desmearing is performed after peeling off the support.

As a result of diligent research into the above-mentioned problems, the inventors of this invention have found that the above-mentioned problems can be solved by a multilayer resin sheet having the following configuration, and have completed the present invention.

In other words, the present invention includes the following:
<1>
A multilayer resin sheet comprising two or more resin composition layers, each consisting of a first resin composition layer which is the outermost layer and layers other than the first resin composition layer,
When the etching rate of the cured product of the first resin composition layer by desmear treatment is denoted as RA, and the etching rate of the cured product of the outermost resin composition layer on the opposite side of the first resin composition layer by desmear treatment is denoted as RD, then RD/RA is 5 or more and less than 100.
A multilayer resin sheet in which the arithmetic mean roughness Ra of the cured product of the first resin composition layer after desmear treatment is less than 50 nm.
<2>
The multilayer resin sheet according to <1>, wherein D1 is the average particle size (μm) of the inorganic filler in the first resin composition layer, and D2 is the average particle size (μm) of the inorganic filler in the layers excluding the first resin composition layer, and D1 < D2.
<3>
The multilayer resin sheet according to <1> or <2>, wherein the content of inorganic filler in the first resin composition layer is 5% by mass or less when the non-volatile components in the first resin composition layer are taken as 100% by mass.
<4>
A multilayer resin sheet as described in any of <1> to <3>, wherein the etching rate RA is 0.1% or more and less than 1%.
<5>
A multilayer resin sheet according to any one of <1> to <4>, wherein the thickness of the multilayer resin sheet (μm) is T, and the thickness of the first resin composition layer (μm) is t, such that t < (T - t).
<6>
A multilayer resin sheet according to any one of <1> to <5>, which is used by laminating it onto a member to be laminated such that the surface opposite to the first resin composition layer is bonded to the member to be laminated.
<7>
A multilayer resin sheet described in any of <1> to <6>, for use as an insulating layer in printed circuit boards.
<8>
A multilayer resin sheet with a support, comprising a multilayer resin sheet according to any one of <1> to <7> and a support that is bonded to the first resin composition layer of the multilayer resin sheet.
<9>
A method for manufacturing a printed circuit board, comprising the following steps (I) to (IV).
(I) Laminating a multilayer resin sheet described in any of <1> to <7> onto an inner layer substrate such that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the inner layer substrate; (II) Curing the multilayer resin sheet to form an insulating layer; (III) Forming via holes in the insulating layer with a laser and performing desmear treatment; (IV) Forming a metal film on the surface of the insulating layer after desmear treatment <10>
A printed circuit board comprising an insulating layer made of a cured multilayer resin sheet as described in any of <1> to <7>.
<11>
A semiconductor device including the printed circuit board described in <10>.

According to the present invention, even when desmearing is performed after peeling off the support, a novel technique can be provided that can yield an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes.

Furthermore, according to the present invention, even when desmearing is performed after peeling off the support, it is possible to obtain an insulating layer with little change in film thickness before and after desmearing.

The present invention will be described in detail below with reference to its preferred embodiments. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with modifications as appropriate without departing from the scope of the claims and equivalents of the present invention.

[Multilayer resin sheet]
The multilayer resin sheet of the present invention comprises two or more resin composition layers, each consisting of a first resin composition layer which is one of the outermost layers and layers excluding the first resin composition layer. When the etching rate of the cured product of the first resin composition layer by desmear treatment is denoted as RA, and the etching rate of the cured product of the resin composition layer on the opposite side of the first resin composition layer by desmear treatment is denoted as RD, the ratio RD/RA is 5 or more and less than 100, and the Ra of the cured product of the first resin composition layer after desmear treatment is less than 50 nm.

The multilayer resin sheet of the present invention has a structure in which two or more resin composition layers are laminated together. Here, in a multilayer resin sheet having a structure in which two resin composition layers, a first resin composition layer and a second resin composition layer, are laminated together, both the first resin composition layer and the second resin composition layer are the outermost layers. Furthermore, in a multilayer resin sheet having a structure in which N layers (where N is an integer of 3 or more) of resin composition layers are laminated together, if the layers are numbered in ascending order from the outermost layer of one to the outermost layer of the other as the first, second, ..., N, then the first resin composition layer and the Nth resin composition layer are the outermost layers.

The multilayer resin sheet of the present invention is used by laminating it onto a target member (for example, an inner layer substrate described later). In this case, the surface opposite to the first resin composition layer, which is one of the outermost layers (the other outermost layer; in the case of a multilayer resin sheet consisting of two resin composition layers, this corresponds to the second resin composition layer, and in the case of a multilayer resin sheet consisting of N resin composition layers, this corresponds to the Nth resin composition layer), is used in such a manner that it is bonded to the target member. Therefore, when laminated onto the target member, the first resin composition layer is on the outside (the side facing the external environment), and in the following, the first resin composition layer may simply be referred to as the "outer layer." Furthermore, of the multiple resin composition layers constituting the multilayer resin sheet of the present invention, the layers other than the first resin composition layer are located between the first resin composition layer and the target member after being laminated onto the target member, and in the following, the layers other than the first resin composition layer may be collectively referred to as the "inner layers."

In the multilayer resin sheet of the present invention, the resin composition layers may consist of two or more layers, or even three or more layers. Furthermore, the multilayer resin sheet of the present invention may be formed by creating differences in the content of each component within a substantially single resin sheet. In this case, the portion where the content of each component differs can be interpreted as a layer interface.

The multilayer resin sheet of the present invention is characterized in that, when the etching rate of the cured product of one outermost layer, the first resin composition layer, by desmear treatment is RA, and the etching rate of the cured product of the resin composition layer on the opposite side of the first resin composition layer, by desmear treatment is RD, then RD/RA is 5 or more and less than 100. As a result, even when desmear treatment is performed after peeling off the support, the multilayer resin sheet of the present invention can provide an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes. Furthermore, the multilayer resin sheet of the present invention can provide an insulating layer with little change in film thickness before and after desmear treatment, even when desmear treatment is performed after peeling off the support.

In the present invention, the "etching rate by desmear treatment of the cured resin composition layer" refers to the mass reduction rate (mass %) calculated by the formula: [(M' - M'') / M'] × 100, where M' is the mass of the cured resin composition layer before desmear treatment and M'' is the mass of the cured resin composition layer after desmear treatment. Therefore, the etching rate RA of the cured first resin composition layer by desmear treatment is calculated by the formula: [(MA' - MA'') / MA'] × 100, where MA' is the mass of the cured first resin composition layer before desmear treatment and MA'' is the mass of the cured first resin composition layer after desmear treatment. Furthermore, the etching rate RD of the cured resin composition layer opposite to the first resin composition layer due to desmear treatment can be calculated using the formula: [(MD' - MD'') / MD'] × 100, where MD' is the mass of the cured resin composition layer opposite to the first resin composition layer before desmear treatment, and MD'' is the mass of the cured resin composition layer opposite to the first resin composition layer after desmear treatment. Here, "the outermost resin composition layer opposite to the first resin composition layer" refers to the second resin composition layer in a multilayer resin sheet consisting of two resin composition layers, and the Nth resin composition layer in a multilayer resin sheet consisting of N resin composition layers.

In the present invention, the etching rates RA and RD can be measured according to the method described in the [Measurement of Etching Rate] section below. Specifically, when the target resin composition layer is heat-cured by heating at 100°C for 30 minutes, then at 170°C for 30 minutes, and the resulting cured product is subjected to a desmear treatment in which it is immersed in a swelling solution at 60°C for 10 minutes, an oxidizing agent solution at 80°C for 20 minutes, and a neutralizing solution at 40°C for 10 minutes, the mass of the cured product before the desmear treatment and the mass of the cured product after the desmear treatment are measured and substituted into the above formula to determine the etching rates.

Even when desmearing is performed after peeling off the support, it is important that the etching rate RA is sufficiently smaller than the etching rate RD in order to obtain an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes. The RD/RA ratio is 5 or more, preferably 5.5 or more or 6 or more, more preferably 6.5 or more or 7 or more, and even more preferably 8 or more, 9 or more, 10 or more, 12 or more, 14 or more or 15 or more. In particular, an RD/RA ratio of 10 or more is preferable because it is easier to obtain an insulating layer with exceptionally good surface smoothness.

Even when desmearing is performed after peeling off the support, it is important that the etching rate RD is not too large compared to the etching rate RA, in order to obtain an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes. The RD/RA ratio is less than 100, preferably 98 or less, 96 or less, or 95 or less, more preferably 94 or less, 92 or less, 90 or less, 88 or less, or 86 or less, and even more preferably 85 or less, 84 or less, 82 or less, or 80 or less. In particular, an RD/RA ratio of 85 or less is preferable because it is easier to obtain an insulating layer with particularly good-shaped via holes that show minimal dimensional change in the thickness direction of the insulating layer while effectively reducing smearing.

Even when desmearing is performed after peeling off the support, the surface smoothness is even better, and from the viewpoint of providing an insulating layer with good-shaped via holes and reduced smearing, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing, in addition to the RD/RA ratio being in a specific range, it is preferable that the etching rate RA of the cured product of the first resin composition layer by desmearing is preferably in the range of 1% or less or less, more preferably 0.9% or less, more preferably 0.85% or less or 0.8% or less, even more preferably 0.75% or less, 0.7% or less, 0.65% or less, 0.6% or less or 0.55% or less, even more preferably 0.5% or less, 0.48% or less, 0.46% or less, 0.45% or less, 0.44% or less, 0.42% or less or 0.4% or less, and the lower limit is preferably in the range of 0.05% or more, more preferably 0.06% or more or 0.08% or more, and even more preferably 0.1% or more. Therefore, in a preferred embodiment, the etching rate RA is 0.1% or more and less than 1%.

The etching rate RD of the cured resin composition layer, which is the outermost layer opposite the first resin composition layer, is not limited as long as the RD/RA ratio is within the above-mentioned specific range in relation to the etching rate RA. In particular, since it is easy to obtain an insulating layer with via holes having a particularly good shape (cross-sectional shape) with small dimensional changes in the thickness direction of the insulating layer while suitably reducing smear, the etching rate RD is preferably in the range of 20% or less, more preferably 18% or less, 16% or less or 15% or less, even more preferably 14% or less, 12% or less or 10% or less, even more preferably less than 10%, 9.5% or less or 9% or less, and the lower limit is preferably in the range of 0.5% or more, more preferably 0.6% or more or 0.8% or more, and even more preferably 1% or more, 1.2% or more, 1.4% or more or 1.5% or more.

In the multilayer resin sheet of the present invention, the first resin composition layer, which is one of the outermost layers, yields a cured product with low surface roughness and good surface smoothness when desmeared after curing. In the multilayer resin sheet of the present invention, the arithmetic mean roughness Ra of the cured product of the first resin composition layer after desmearing is less than 50 nm. When the Ra of the cured product of the first resin composition layer after desmearing is less than 50 nm, even if the thickness of the metal film provided as a plating seed layer on it is made thinner, it is easier to suppress plating burn during wiring formation and to form a uniform conductor layer (wiring), which is advantageous from the viewpoint of fine wiring. The Ra of the cured product of the first resin composition layer after desmearing may be even smaller, preferably 45 nm or less, 40 nm or less, or 35 nm or less, more preferably 30 nm or less, 28 nm or less, 26 nm or less, or 25 nm or less. The lower limit of Ra is not particularly limited and may be, for example, 1 nm or more, 2 nm or more, 3 nm or more, etc.

In the present invention, the Ra of the cured product of the first resin composition layer after desmear treatment can be measured according to the method described in the [Measurement of Surface Roughness] section below. Specifically, when the first resin composition layer is heat-cured by heating it at 100°C for 30 minutes, then at 170°C for 30 minutes, and the resulting cured product is subjected to desmear treatment in which it is immersed in a swelling solution at 60°C for 10 minutes, an oxidizing agent solution at 80°C for 20 minutes, and a neutralizing solution at 40°C for 10 minutes, the arithmetic mean roughness Ra of the cured product of the first resin composition layer after desmear treatment is measured to determine the Ra.

In the multilayer resin sheet of the present invention, it is preferable that the layers other than the first resin composition layer contain an inorganic filler, from the viewpoint of obtaining a cured product with a low coefficient of linear thermal expansion and a cured product with a low dielectric loss tangent (and consequently a cured product with low transmission loss when operated in a high-frequency environment). Details of the inorganic filler will be described later.

In the multilayer resin sheet of the present invention, the first resin composition layer may or may not contain an inorganic filler.
In one embodiment, the first resin composition layer contains an inorganic filler, from the viewpoint of obtaining a cured product with a low coefficient of linear thermal expansion and a low dielectric loss tangent. When the first resin composition layer contains an inorganic filler, from the viewpoint of obtaining a cured product with even lower surface roughness and better smoothness after desmear treatment, it is preferable that the inorganic filler contained in the first resin composition layer has a smaller average particle size than the inorganic filler contained in the layers excluding the first resin composition layer. Therefore, in a preferred embodiment, when the average particle size (μm) of the inorganic filler in the first resin composition layer is D1 and the average particle size (μm) of the inorganic filler in the layers excluding the first resin composition layer is D2, D1 < D2. From the viewpoint of enjoying the effects of the present invention even more, D1 and D2 preferably satisfy the relationship D1 ≤ 0.9D2, more preferably D1 ≤ 0.8D2, D1 ≤ 0.7D2, D1 ≤ 0.6D2, D1 ≤ 0.55D2, or D1 ≤ 0.5D2. The method for measuring the average particle size of the inorganic filler will be described later.
In another embodiment, the first resin composition layer may not substantially contain inorganic fillers. For example, when the non-volatile components in the first resin composition layer are considered to be 100% by mass, the inorganic filler content may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, or 0.5% by mass or less. Alternatively, the first resin composition layer may not contain inorganic fillers at all.

Even when desmear treatment is performed after peeling off the support, the surface smoothness is further improved, and from the viewpoint of obtaining an insulating layer with reduced smear and well-shaped via holes, it is preferable that the layers other than the first resin composition layer are thicker than the first resin composition layer in the multilayer resin sheet of the present invention. Therefore, in a preferred embodiment, when the thickness of the multilayer resin sheet (μm) is T and the thickness of the first resin composition layer (μm) is t, t < (T - t). From the viewpoint of enjoying the effects of the present invention even more, the above t and T preferably satisfy the relationship t ≤ 0.2T, more preferably t ≤ 0.15T, t ≤ 0.1T, t ≤ 0.08T, t ≤ 0.06T, or t ≤ 0.05T. Furthermore, even when desmearing is performed after peeling off the support, t and T preferably satisfy the relationship 0.005T ≤ t, 0.01T ≤ t, or 0.02T ≤ t, from the viewpoint of providing an insulating layer with good shape via holes, reduced smearing, and an insulating layer with little change in film thickness before and after desmearing.In the multilayer resin sheet of the present invention, when the thickness (μm) of the outermost resin composition layer opposite to the first resin composition layer is t', it is preferable that t' ≥ 0.1(T-t) in relation to t and T as described above, and more preferably t' ≥ 0.2(T-t), t' ≥ 0.3(T-t), t' ≥ 0.4(T-t), or t' ≥ 0.5(T-t).

The thickness T of the multilayer resin sheet of the present invention has a suitable value that varies depending on the application and may be determined appropriately according to the application. For example, from the viewpoint of thinning printed circuit boards, the thickness T of the multilayer resin sheet is preferably 200 μm or less, more preferably 150 μm or less, 120 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, or 50 μm or less. The lower limit of the thickness T is not particularly limited, but can usually be 5 μm or more, 10 μm or more, etc.

The details of the resin composition layers constituting the multilayer resin sheet of the present invention will be described below. In the following, if it is preferable to apply different compounding components and amounts to the first resin composition layer and other resin composition layers, this will be indicated separately. Unless otherwise indicated, the compounding components and amounts of the first resin composition layer can be applied by substituting "resin composition layer" with "first resin composition layer" as described later, and the compounding components and amounts of the layers excluding the first resin composition layer can be applied by substituting "resin composition layer" with "layers excluding the first resin composition layer" as described later. When the multilayer resin sheet of the present invention is a multilayer resin sheet having a structure in which N layers (where N is an integer of 3 or more) of resin composition layers are laminated, the compounding amounts of the compounding components of the layers excluding the first resin composition layer refer to the amount of each compounding component in the total number of layers excluding the first resin composition layer (number of layers is N-1), and the physical properties of the compounding components of the layers excluding the first resin composition layer refer to the average value of the physical properties of each compounding component in the total number of layers excluding the first resin composition layer (number of layers is N-1).

-Inorganic filler-
In the multilayer resin sheet of the present invention, the resin composition layer may contain an inorganic filler as described above.

Examples of inorganic filler materials include silica, alumina, glass, cordierite, silicon oxide, barium sulfate, barium carbonate, talc, clay, mica powder, zinc oxide, hydrotalcite, boehmite, aluminum silicate, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride, aluminum nitride, manganese nitride, aluminum borate, strontium carbonate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium oxide, zirconium oxide, barium titanate, barium zirconate titanate, barium zirconate, calcium zirconate, zirconium phosphate, and zirconium tungstate phosphate. Among these, silica is particularly preferred. Examples of silica include amorphous silica, fused silica, crystalline silica, synthetic silica, and hollow silica. Spherical silica is also preferred. Inorganic fillers may be used individually or in combination of two or more types.

Examples of commercially available inorganic fillers include "SP60-05" and "SP507-05" from Nippon Steel Chemical & Material Co., Ltd.; "YC100C," "YA050C," "YA050C-MJE," "YA010C," "SC2500SQ," "SO-C4," "SO-C2," and "SO-C1" from Admatex Co., Ltd.; "UFP-30," "DAW-03," and "FB-105FD" from Denka Co., Ltd.; "Silfil NSS-3N," "Silfil NSS-4N," and "Silfil NSS-5N" from Tokuyama Corporation; "Cellspheres" and "MGH-005" from Taiheiyo Cement Corporation; and "Esferique" and "BA-1" from JGC Catalysts & Chemicals Co., Ltd.

The average particle size of the inorganic filler is not particularly limited, but is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, 2 μm or less, 1 μm or less, 0.8 μm or less, or 0.7 μm or less. The lower limit of the average particle size is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.07 μm or more, 0.1 μm or more, or 0.2 μm or more. The average particle size of the inorganic filler can be measured by a laser diffraction/scattering method based on Mie scattering theory. Specifically, the particle size distribution of the inorganic filler can be created on a volume basis using a laser diffraction/scattering particle size distribution analyzer, and the median diameter can be used as the average particle size. A sample can be prepared by weighing 100 mg of inorganic filler and 10 g of methyl ethyl ketone into a vial and dispersing them using ultrasound for 10 minutes. The particle size distribution of the inorganic filler was measured using a laser diffraction particle size distribution analyzer with blue and red light source wavelengths, employing a flow cell method. The average particle size was calculated as the median diameter from the obtained particle size distribution. Examples of laser diffraction particle size distribution analyzers include the "LA-960" manufactured by Horiba, Ltd.

As described above, when the first resin composition layer contains an inorganic filler, it is preferable that D1 < D2, where D1 is the average particle size (μm) of the inorganic filler in the first resin composition layer and D2 is the average particle size (μm) of the inorganic filler in the layers excluding the first resin composition layer. The preferred relationship between D1 and D2 is as described above. In particular, even when desmear treatment is performed after peeling off the support, from the viewpoint of obtaining a cured product with even lower surface roughness and good smoothness after desmear treatment, D1 is preferably 1 μm or less, more preferably 0.8 μm or less, 0.7 μm or less, or 0.6 μm or less, and even more preferably 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, or 0.2 μm or less. The lower limit of D1 is as described above and can be, for example, 0.01 μm or more, 0.02 μm or more, etc.

It is preferable that the inorganic filler is surface-treated with an appropriate surface treatment agent. Surface treatment can improve the moisture resistance and dispersibility of the inorganic filler. Examples of surface treatment agents include silane coupling agents such as vinyl-based silane coupling agents, epoxy-based silane coupling agents, styryl-based silane coupling agents, (meth)acrylic-based silane coupling agents, amino-based silane coupling agents, isocyanurate-based silane coupling agents, ureido-based silane coupling agents, mercapto-based silane coupling agents, isocyanate-based silane coupling agents, and acid anhydride-based silane coupling agents; non-silane coupling-alkoxysilane compounds such as methyltrimethoxysilane and phenyltrimethoxysilane; and silazane compounds. The surface treatment agent may be used alone or in combination of two or more types.

Examples of commercially available surface treatment agents include "KBM403" (3-glycidoxypropyltrimethoxysilane), "KBM803" (3-mercaptopropyltrimethoxysilane), "KBE903" (3-aminopropyltriethoxysilane), "KBM573" (N-phenyl-3-aminopropyltrimethoxysilane), and "SZ-31" (hexamethyldisilazane), all manufactured by Shin-Etsu Chemical Co., Ltd.

From the viewpoint of improving the dispersibility of the inorganic filler, the degree of surface treatment by the surface treatment agent is preferably within a predetermined range. Specifically, it is preferable that 100 parts by mass of the inorganic filler is surface-treated with 0.2 to 5 parts by mass of the surface treatment agent.

The degree of surface treatment by the surface treatment agent can be evaluated by the amount of carbon per unit surface area of the inorganic filler. From the viewpoint of improving the dispersibility of the inorganic filler, the amount of carbon per unit surface area of the inorganic filler is preferably 0.02 mg/ ^m² or more, more preferably 0.1 mg/ ^m² or more, and even more preferably 0.2 mg/ ^m² or more. On the other hand, from the viewpoint of preventing an increase in the melt viscosity of the resin composition and the melt viscosity in sheet form, it is preferably 1.0 mg/ ^m² or less, more preferably 0.8 mg/ ^m² or less, and even more preferably 0.5 mg/ ^m² or less. The amount of carbon per unit surface area of the inorganic filler can be measured after washing the inorganic filler with a solvent (for example, methyl ethyl ketone (MEK)) after surface treatment. Specifically, a sufficient amount of MEK as a solvent is added to the inorganic filler that has been surface-treated with the surface treatment agent, and ultrasonic cleaning is performed at 25°C for 5 minutes. After removing the supernatant and drying the solids, the amount of carbon per unit surface area of the inorganic filler can be measured using a carbon analyzer. A carbon analyzer such as the EMIA-320V manufactured by Horiba, Ltd. can be used.

In the multilayer resin sheet of the present invention, the content of inorganic filler in the resin composition layer may be determined according to the properties required for the multilayer resin sheet. However, from the viewpoint of easily adjusting the above-mentioned RD/RA ratio to a suitable range, and from the viewpoint of realizing a cured product exhibiting an even lower linear thermal expansion coefficient and dielectric loss tangent, when the non-volatile component in the resin composition layer is set to 100% by mass, the content C2 of inorganic filler in the layers excluding the first resin composition layer is preferably 40% by mass or more or 45% by mass or more, more preferably 50% by mass or more, 55% by mass or more or 60% by mass or more, and even more preferably 65% by mass or more, 66% by mass or more, 68% by mass or more, 70% by mass or more, 72% by mass or more or 74% by mass. The upper limit of the content C2 is as described above, but preferably 80% by mass or less, 75% by mass or less or 70% by mass or less.

In one embodiment, the inorganic filler content C1 (mass%) in the first resin composition layer and the inorganic filler content C2 (mass%) in the layers excluding the first resin composition layer satisfy the relationship C1 < C2. When C1 and C2 satisfy the above relationship, it is preferable because it is easy to adjust the RD/RA ratio to a suitable range. The suitable range for C2 is as described above.

As mentioned above, the first resin composition layer does not need to contain inorganic fillers substantially. For example, when the non-volatile components in the first resin composition layer are taken as 100% by mass, the inorganic filler content C1 in the first resin composition layer may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, or 0.5% by mass or less. Alternatively, the first resin composition layer does not need to contain inorganic fillers at all.

-Thermosetting component-
In the multilayer resin sheet of the present invention, the resin composition layer preferably contains a thermosetting resin.

Examples of thermosetting resins include epoxy resins, benzocyclobutene resins, epoxy acrylate resins, urethane acrylate resins, urethane resins, cyanate resins, unsaturated polyester resins, melamine resins, and silicone resins. Thermosetting resins may be used individually or in combination of two or more types.

In particular, even when desmearing is performed after peeling off the support, it is preferable that the thermosetting resin includes an epoxy resin, from the viewpoint of providing an insulating layer with better surface smoothness, reduced smearing, and good-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing.

Examples of epoxy resins include bisphenol-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol novolac-type epoxy resins, phenol novolac-type epoxy resins, tert-butyl-catechol-type epoxy resins, naphthalene-type epoxy resins, naphthol-type epoxy resins, anthracene-type epoxy resins, glycidylamine-type epoxy resins, glycidyl ester-type epoxy resins, cresol novolac-type epoxy resins, biphenyl-type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro-ring-containing epoxy resins, cyclohexane-type epoxy resins, cyclohexanedimethanol-type epoxy resins, naphthylene ether-type epoxy resins, trimethylol-type epoxy resins, and tetraphenylethane-type epoxy resins. Bisphenol-type epoxy resins refer to epoxy resins having a bisphenol structure, and examples include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol S-type epoxy resins, and bisphenol AF-type epoxy resins. Biphenyl-type epoxy resins refer to epoxy resins having a biphenyl structure, where the biphenyl structure may have substituents such as alkyl groups, alkoxy groups, or aryl groups. Therefore, bixylenol-type epoxy resins and biphenylaralkyl-type epoxy resins are also included in biphenyl-type epoxy resins. Epoxy resins may be used individually or in combination of two or more types.

As the epoxy resin, an aromatic epoxy resin is preferred. Here, an aromatic epoxy resin means an epoxy resin that has an aromatic ring in its molecule.

The epoxy resin preferably has two or more epoxy groups per molecule. When the non-volatile components of the epoxy resin are considered to be 100% by mass, the proportion of epoxy resin having two or more epoxy groups per molecule is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

Epoxy resins include liquid epoxy resins at 20°C (hereinafter referred to as "liquid epoxy resins") and solid epoxy resins at 20°C (hereinafter referred to as "solid epoxy resins").

As the liquid epoxy resin, a liquid epoxy resin having two or more epoxy groups in one molecule is preferred.

Preferred liquid epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AF type epoxy resin, naphthalene type epoxy resin, glycidyl ester type epoxy resin, glycidylamine type epoxy resin, phenol novolac type epoxy resin, alicyclic epoxy resins such as alicyclic epoxy resins having an ester skeleton, cyclohexane type epoxy resin, cyclohexanedimethanol type epoxy resin, and epoxy resins having a butadiene structure.

Specific examples of liquid epoxy resins include DIC Corporation's "HP-4032," "HP-4032D," and "HP-4032SS" (naphthalene-type epoxy resin); Mitsubishi Chemical Corporation's "828US," "jER828EL," "825," and "Epicote 828EL" (bisphenol A-type epoxy resin); Mitsubishi Chemical Corporation's "jER807" and "1750" (bisphenol F-type epoxy resin); Mitsubishi Chemical Corporation's "jER152" (phenol novolac-type epoxy resin); and Mitsubishi Chemical Corporation's "630" and "630LSD" (p-aminophenol-type epoxy resin, glycidyl Examples include: luminamine-type epoxy resins; "ZX1059" from Nippon Steel Chemical & Material (a mixture of bisphenol A-type epoxy resin and bisphenol F-type epoxy resin); "EX-721" from Nagase ChemteX (glycidyl ester-type epoxy resin); "Celoxide 2021P" from Daicel Corporation (alicyclic epoxy resin with an ester skeleton); "PB-3600" from Daicel Corporation (epoxy resin with a butadiene structure); and "ZX1658" and "ZX1658GS" from Nippon Steel Chemical & Material (liquid 1,4-glycidylcyclohexane-type epoxy resins).

As the solid epoxy resin, a solid epoxy resin having three or more epoxy groups per molecule is preferred, and an aromatic solid epoxy resin having three or more epoxy groups per molecule is more preferred.

Preferred solid epoxy resins include bixylenol-type epoxy resin, naphthalene-type epoxy resin, naphthalene-type tetrafunctional epoxy resin, cresol novolac-type epoxy resin, dicyclopentadiene-type epoxy resin, trisphenol-type epoxy resin, naphthol-type epoxy resin, biphenyl-type epoxy resin, naphthylene ether-type epoxy resin, anthracene-type epoxy resin, bisphenol A-type epoxy resin, bisphenol AF-type epoxy resin, and tetraphenylethane-type epoxy resin.

Specific examples of solid epoxy resins include DIC's "HP-4032H" (naphthalene-type epoxy resin); DIC's "HP-4700" and "HP-4710" (naphthalene-type tetrafunctional epoxy resins); DIC's "N-690" (cresol novolac-type epoxy resin); DIC's "N-695" (cresol novolac-type epoxy resin); DIC's "HP-7200HH", "HP-7200H", and "HP-7200" (dicyclopentadie). (Naphthylene ether type epoxy resin); DIC Corporation's "EXA-7311", "EXA-7311-G3", "EXA-7311-G4", "EXA-7311-G4S", "HP6000" (naphthylene ether type epoxy resin); Nippon Kayaku Co., Ltd.'s "EPPN-502H" (trisphenol type epoxy resin); Nippon Kayaku Co., Ltd.'s "NC-7000-L" (naphthol novolac type epoxy resin); Nippon Kayaku Co., Ltd.'s "NC-3000-H", "NC-3000", "NC-300 "0-L", "NC-3100" (biphenyl-type epoxy resin); "ESN475V" (naphthol-type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "ESN485" (naphthol novolac-type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YX4000H", "YX4000", "YL6121" (biphenyl-type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "YX4000HK" (bixylenol-type epoxy resin) manufactured by Mitsubishi Chemical Corporation; manufactured by Mitsubishi Chemical Corporation Examples include "YX8800" (anthracene-type epoxy resin); "PG-100" and "CG-500" from Osaka Gas Chemical Co., Ltd.; "YL7760" (bisphenol AF-type epoxy resin) from Mitsubishi Chemical Corporation; "YL7800" (fluorene-type epoxy resin) from Mitsubishi Chemical Corporation; "jER1010" (solid bisphenol A-type epoxy resin) from Mitsubishi Chemical Corporation; and "jER1031S" (tetraphenylethane-type epoxy resin) from Mitsubishi Chemical Corporation.

In the multilayer resin sheet of the present invention, the resin composition layer may contain only a liquid epoxy resin, only a solid epoxy resin, or a combination of a liquid epoxy resin and a solid epoxy resin. From the viewpoint of easily adjusting the above RD/RA ratio to a suitable range, it is preferable that the resin composition layer contains a solid epoxy resin. When a liquid epoxy resin and a solid epoxy resin are used in combination, their mass ratio (liquid epoxy resin: solid epoxy resin) is preferably 1:0.5 to 1:50, more preferably 1:1 to 1:30, and even more preferably 1:2 to 1:20. From the viewpoint of easily adjusting the above RD/RA ratio to a suitable range, it is preferable that the mass ratio X1 of solid epoxy resin/liquid epoxy resin in the first resin composition layer is higher than the mass ratio X2 of solid epoxy resin/liquid epoxy resin in the layers other than the first resin composition layer. For example, the difference between mass ratio X1 and mass ratio X2 (X1-X2) can be 1 or more, 2 or more, 3 or more, 4 or more, or 5 or more. The upper limit of this difference (X1-X2) is usually 20 or less, 15 or less, 14 or less, 12 or less, etc.

The epoxy equivalent of the epoxy resin is preferably 50 g/eq. to 5000 g/eq., more preferably 50 g/eq. to 3000 g/eq., even more preferably 80 g/eq. to 2000 g/eq., and even more preferably 110 g/eq. to 1000 g/eq. The epoxy equivalent is the mass of the epoxy resin containing one equivalent of epoxy groups. This epoxy equivalent can be measured according to JIS K7236.

The weight-average molecular weight (Mw) of the epoxy resin is preferably 100 to 5000, more preferably 250 to 3000, and even more preferably 400 to 1500. The Mw of the epoxy resin can be measured as a polystyrene equivalent by gel permeation chromatography (GPC).

From the viewpoint of easily adjusting the above RD/RA ratio to a suitable range, providing an insulating layer with better surface smoothness, reduced smearing, and well-shaped via holes, the content of thermosetting resin in the resin composition layer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 12% by mass or more, 14% by mass or more, or 15% by mass or more, when the total resin component in the resin composition layer is considered to be 100% by mass. The upper limit of this content is not particularly limited and may be determined according to the properties required of the resin composition, but for example, it may be 60% by mass or less, 50% by mass or less, 45% by mass or less, or 40% by mass or less.

In the present invention, the term "resin component" in reference to the resin composition layer refers to the solid components (non-volatile components) constituting the resin composition layer, excluding the inorganic filler described later.

In the multilayer resin sheet of the present invention, the resin composition layer may contain, in addition to the thermosetting resin and inorganic filler, one or more selected from a curing agent, a thermoplastic resin, a radical polymerizable resin, and a curing accelerator.

- Hardener -
In the multilayer resin sheet of the present invention, the resin composition layer preferably contains a curing agent. The curing agent typically has the function of curing the resin composition layer by reacting with the thermosetting resin.

Examples of curing agents include active ester-based curing agents, phenol-based curing agents, naphthol-based curing agents, acid anhydride-based curing agents, cyanate ester-based curing agents, carbodiimide-based curing agents, and amine-based curing agents. The curing agent may be used alone or in combination of two or more types.

In particular, even when desmear treatment is performed after peeling off the support, the curing agent preferably contains one or more selected from the group consisting of active ester curing agents, phenolic curing agents, and naphthol curing agents, from the viewpoint of obtaining an insulating layer with better surface smoothness, reduced smearing, and well-shaped via holes, and from the viewpoint of obtaining an insulating layer with better surface smoothness, reduced smearing, and well-shaped via holes, it is preferable to include an active ester curing agent, as it makes it easier to adjust the RD/RA ratio to a suitable range, and is preferable to include an active ester curing agent. Therefore, in one embodiment, the curing agent contains one or more selected from the group consisting of active ester curing agents, phenolic curing agents, and naphthol curing agents, and more preferably includes an active ester curing agent.

As the active ester curing agent, compounds having one or more active ester groups in one molecule can be used. Among these, compounds having two or more highly reactive ester groups in one molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, are preferred as active ester curing agents. The active ester curing agent is preferably obtained by a condensation reaction between a carboxylic acid compound and/or a thiocarboxylic acid compound and a hydroxy compound and/or a thiol compound. In particular, from the viewpoint of improving heat resistance, active ester curing agents derived from carboxylic acid compounds are preferred, active ester curing agents obtained from a carboxylic acid compound and a hydroxy compound are more preferred, and active ester curing agents obtained from a carboxylic acid compound and an aromatic hydroxy compound are even more preferred.

As the carboxylic acid compound, either aromatic carboxylic acid compounds or aliphatic carboxylic acids may be used. Examples include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid.

Examples of aromatic hydroxy compounds include (i) polyaddition products of unsaturated aliphatic cyclic compounds containing two double bonds in one molecule and phenols, (ii) various bisphenol compounds, (iii) aromatic polyols in which two or more hydroxyl groups are bonded to a carbon atom on an aromatic ring, and (iv) aromatic monools in which one hydroxyl group is bonded to a carbon atom on an aromatic ring. Examples of polyaddition products of unsaturated aliphatic cyclic compounds and phenols include polyaddition products of unsaturated aliphatic cyclic compounds such as dicyclopentadiene, tetrahydroindene, norbornadiene, limonene, and vinylcyclohexene with phenols that may have substituents (e.g., phenol, cresol, xylenol, ethylphenol, propylphenol, vinylphenol, allylphenol, phenylphenol, benzylphenol, halophenol, etc.), and specifically, for example, dicyclopentadiene-phenol polyadditions. Examples of bisphenol compounds include bisphenol A, bisphenol F, bisphenol AF, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C, and bisphenol M. Examples of aromatic polyols, in which two or more hydroxyl groups are bonded to a carbon atom on an aromatic ring, include hydroquinone, resorcinol, catechol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucin, benzenetriol, and phenol novolac. Examples of aromatic monools, in which one hydroxyl group is bonded to a carbon atom on an aromatic ring, include phenol, cresol, xylenol, ethylphenol, propylphenol, vinylphenol, allylphenol, phenylphenol, benzylphenol, halophenol, naphthol, methylnaphthol, dimethylnaphthol, ethylnaphthol, propylnaphthol, vinylnaphthol, allylnaphthol, phenylnaphthol, benzylnaphthol, and halonaphthol.

Suitable examples of active ester-based curing agents include active ester compounds containing a dicyclopentadiene-type diphenol structure, active ester compounds containing a naphthalene structure, active ester compounds containing an acetylated phenol novolac, and active ester compounds containing a benzoylated phenol novolac. Among these, active ester compounds containing a naphthalene structure and active ester compounds containing a dicyclopentadiene-type diphenol structure are more preferred. "Dicyclopentadiene-type diphenol structure" refers to a divalent structural unit consisting of phenylene-dicyclopentalene-phenylene.

Commercially available active ester curing agents include, as active ester resins containing a dicyclopentadiene-type diphenol structure, "EXB-9451", "EXB-9460", "EXB-9460S", "HPC-8000-65T", "HPC-8000H-65TM", and "HPC-8000L-65TM" (manufactured by DIC Corporation); and as active ester resins containing a naphthalene structure, "EXB-8100L-65T", "EXB-8150-60T", "EXB-8150-62T", "EXB-9416-70BK", "HPC-8150-60T", and "HPC-8150-62T". Examples include "HP-B-8151-62T" and "HP-C-8151-62T" (manufactured by DIC Corporation); "EXB9401" (manufactured by DIC Corporation) as a phosphorus-containing active ester resin; "DC808" (manufactured by Mitsubishi Chemical Corporation) as an active ester resin that is an acetylated phenol novolac; "YLH1026," "YLH1030," and "YLH1048" (manufactured by Mitsubishi Chemical Corporation) as active ester resins that are benzoylated phenol novolacs; and "PC1300-02-65MA" (manufactured by Air Water Corporation) as an active ester resin containing a styryl group and a naphthalene structure.

From the viewpoint of heat resistance and water resistance, phenolic and naphthol-based curing agents are preferred if they have a novolac structure. Furthermore, from the viewpoint of adhesion to the conductive layer, nitrogen-containing phenolic and nitrogen-containing naphthol-based curing agents are preferred, and triazine skeleton-containing phenolic and triazine skeleton-containing naphthol-based curing agents are more preferred.

Specific examples of phenol-based and naphthol-based curing agents include, for example, "MEH-7700," "MEH-7810," "MEH-7851," and "MEH-8000H" from Meiwa Kasei Co., Ltd.; "NHN," "CBN," and "GPH" from Nippon Kayaku Co., Ltd.; and "SN-170," "SN-180," "SN-190," "SN-475," "SN-485," "SN-495," "SN-495V," and "SN-37" from Nippon Steel Chemical & Material Co., Ltd. Examples include "5", "SN-395", "TD-2090", "TD-2090-60M", "LA-7052", "LA-7054", "LA-1356", "LA-3018", "LA-3018-50P", "EXB-9500", "HPC-9500", "KA-1160", "KA-1163", "KA-1165" from DIC Corporation, and "GDP-6115L", "GDP-6115H", "ELPC75" from Gun-ei Chemical Co., Ltd.

Examples of acid anhydride-based curing agents include curing agents having one or more acid anhydride groups in one molecule. Specific examples of acid anhydride-based curing agents include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, dodecenyl succinic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexen-1,2-dicarboxylic acid anhydride, trimellitic anhydride, pyromellitic anhydride, and bensophenone tetracarboxylic acid di Examples of acid anhydrides include anhydrides, biphenyltetracarboxylic acid dianhydride, naphthalenetetracarboxylic acid dianhydride, oxydiphthalic acid dianhydride, 3,3'-4,4'-diphenylsulfontetracarboxylic acid dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-C]furan-1,3-dione, ethylene glycol bis(anhydrotrimellitate), and polymer-type acid anhydrides such as styrene-maleic acid resin copolymerized with styrene and maleic acid. A commercially available acid anhydride-based curing agent is "MH-700" manufactured by Shin Nippon Rika Co., Ltd.

Examples of cyanate ester curing agents include bifunctional cyanate resins such as bisphenol A dicyanate, polyphenol cyanate, oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanatephenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene, bis(4-cyanatephenyl) thioether, and bis(4-cyanatephenyl) ether; polyfunctional cyanate resins derived from phenol novolacs and cresol novolacs; and prepolymers in which these cyanate resins are partially triazined. Specific examples of cyanate ester curing agents include "PT30" and "PT60" (phenol novolac type polyfunctional cyanate ester resins) manufactured by arxada, "ULL-950S" (polyfunctional cyanate ester resin), "BA230", and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate is triazined to form trimers).

Specific examples of carbodiimide-based curing agents include Carbodilite® V-03 (carbodiimide group equivalent: 216 g/eq.), V-05 (carbodiimide group equivalent: 262 g/eq.), V-07 (carbodiimide group equivalent: 200 g/eq.); V-09 (carbodiimide group equivalent: 200 g/eq.) manufactured by Nisshinbo Chemical Co., Ltd.; and Stavaxol® P (carbodiimide group equivalent: 302 g/eq.) manufactured by Lanxess.

Examples of amine-based curing agents include curing agents having one or more amino groups in one molecule, such as aliphatic amines, polyetheramines, alicyclic amines, and aromatic amines. Specific examples of amine-based curing agents include 4,4'-methylenebis(2,6-dimethylaniline), diphenyldiaminosulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, m-phenylenediamine, m-xylylenediamine, diethyltoluenediamine, 4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, and 2,2-bis(3-amino-4-hydroxy Examples include bis(4-aminophenyl)propane, 3,3-dimethyl-5,5-diethyl-4,4-diphenylmethanediamine, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis(4-(4-aminophenoxy)phenyl)sulfone, bis(4-(3-aminophenoxy)phenyl)sulfone, etc. Amine-based curing agents may be commercially available products, such as "KAYABOND C-200S", "KAYABOND C-100", "Kayahard A-A", "Kayahard A-B", and "Kayahard A-S" from Nippon Kayaku Co., Ltd., and "Epicure W" from Mitsubishi Chemical Corporation.

Even when desmear treatment is performed after peeling off the support, the content of the curing agent in the resin composition is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, 35% by mass or more, or 40% by mass or more, when the resin component in the resin composition is considered to be 100% by mass. The upper limit of the content is not particularly limited and may be determined according to the properties required of the resin composition, but for example, it may be 80% by mass or less, 75% by mass or less, or 70% by mass or less.

As mentioned above, it is preferable that the curing agent contains an active ester-based curing agent, from the viewpoint of easily adjusting the RD/RA ratio to a suitable range, providing even better surface smoothness, and resulting in an insulating layer with well-shaped via holes and reduced smearing. In the multilayer resin sheet of the present invention, when the resin composition layer contains an active ester-based curing agent as the curing agent, the content of the active ester-based curing agent in the curing agent is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, 75% by mass or more, or 80% by mass or more, when the non-volatile components of the curing agent are considered to be 100% by mass, from the viewpoint of enjoying the effects of the present invention and obtaining a cured product exhibiting particularly excellent dielectric properties. The upper limit of the content of the active ester-based curing agent in the curing agent is not particularly limited and may be 100% by mass, but may be, for example, 95% by mass or less, 90% by mass or less.

In the multilayer resin sheet of the present invention, when the resin composition layer contains an active ester-based curing agent as a curing agent, the mass ratio of the active ester-based curing agent to the thermosetting resin (active ester-based curing agent/thermosetting resin) is preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.8 or more, 1 or more, 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, or 1.5 or more, from the viewpoint of enjoying the effects of the present invention and exhibiting particularly excellent dielectric properties. The upper limit of the mass ratio (active ester-based curing agent/thermosetting resin) may be, for example, 5 or less, 4.5 or less, 4 or less, etc. In particular, from the viewpoint of making it easier to adjust the etching rate RA to a suitable range, and consequently the RD/RA ratio to a suitable range, the mass ratio (active ester-based curing agent/thermosetting resin) in the first resin composition layer is preferably 1 or more, more preferably 1.2 or more or 1.4 or more, even more preferably 1.5 or more, 1 . It is 6 or higher, 1.8 or higher, or 2 or higher.

-Thermoplastic resin-
In the multilayer resin sheet of the present invention, the resin composition layer may include a thermoplastic resin.

Examples of thermoplastic resins include phenoxy resin, polyimide resin, polyvinyl acetal resin, acrylic resin, polyolefin resin, polybutadiene resin, polyamide-imide resin, polysulfone resin, polyethersulfone resin, polyphenylene ether resin, polyetherimide resin, polycarbonate resin, polyetheretherketone resin, and polyester resin. Among these, resins selected from phenoxy resin, polyimide resin, acrylic resin, polyphenylene ether resin, and polycarbonate resin are preferred. Thermoplastic resins may be used individually or in combination of two or more types.

--Phenoxy resin--
Examples of phenoxy resins include phenoxy resins having one or more skeletons selected from the group consisting of bisphenol A skeleton, bisphenol F skeleton, bisphenol S skeleton, bisphenolacetophenone skeleton, novolac skeleton, biphenyl skeleton, fluorene skeleton, dicyclopentadiene skeleton, norbornene skeleton, naphthalene skeleton, anthracene skeleton, adamantane skeleton, terpene skeleton, and trimethylcyclohexane skeleton. The ends of the phenoxy resin may be any functional group such as a phenolic hydroxyl group or an epoxy group. Phenoxy resins may be used alone or in combination of two or more types. Specific examples of phenoxy resins include "1256" and "4250" (both phenoxy resins containing a bisphenol A skeleton), "YX8100" (phenoxy resin containing a bisphenol S skeleton), and "YX6954" (phenoxy resin containing a bisphenol acetophenone skeleton), all manufactured by Mitsubishi Chemical Corporation; "FX280" and "FX293," all manufactured by Nippon Steel Chemical & Material Co., Ltd.; and "YX7200B35,""YX7500BH30,""YX6954BH30,""YX7553,""YX7553BH30,""YL7769BH30,""YL6794,""YL7213,""YL7290," and "YL7482," all manufactured by Mitsubishi Chemical Corporation.

--Polyimide resin--
Polyimide resins can be resins having an imide structure. Polyimide resins can generally be obtained by imidation reactions between diamine compounds and acid anhydrides, or between diisocyanate compounds and acid anhydrides. Specific examples of polyimide resins include, for example, linear polyimides obtained by reacting a bifunctional hydroxyl-terminated polybutadiene, a diisocyanate compound, and a tetrabasic acid anhydride (polyimide described in Japanese Patent Publication No. 2006-37083), and modified polyimides containing a polysiloxane skeleton (polyimides described in Japanese Patent Publication No. 2002-12667 and Japanese Patent Publication No. 2000-319386, etc.). Commercially available polyimide resins may also be used, for example, "Ricacoat SN20" and "Ricacoat PN20" manufactured by Shin Nippon Rika Co., Ltd.

Examples of particularly suitable polyimide resins are shown below. In one preferred embodiment, the polyimide resin contains structural units represented by the following formula (1) (hereinafter also referred to as "structural unit (1)"). The number of structural units (1) contained in one molecule of polyimide resin is one or more, and is not particularly limited, but can be 100 or less, 50 or less, or 30 or less.

[In formula (1),
_R1 is a tetravalent group represented by the following formula (1-1):
_R2 is a divalent group represented by the following formula (1-2).

(In formula (1-1),
Ar ₁₁ , Ar ₁₂ , Ar ₁₃ , and Ar ₁₄ each independently represent an aromatic ring which may have substituents.
_L11 , _L12 , and _L13 each independently represent a divalent linking group.
nc1 represents a non-negative integer.

(In formula (1-2),
Ar ₂₁ , Ar ₂₂ , Ar ₂₃ , and Ar ₂₄ each independently represent an aromatic ring which may have substituents.
_L21 , _L22 , and _L23 each independently represent a divalent linking group.
nc2 represents an integer greater than or equal to 1.

In formula (1-1), the aromatic ring represented by Ar ₁₁ , Ar ₁₂ , Ar ₁₃ , and Ar ₁₄ (hereinafter also referred to as "aromatic ring C") is preferably an aromatic ring having 6 to 100 carbon atoms, more preferably 6 to 50 carbon atoms, and even more preferably an aromatic carbocyclic ring having 6 to 100 carbon atoms, and even more preferably 6 to 50 carbon atoms. In a preferred embodiment, in formula (1-1), Ar ₁₁ , Ar ₁₂ , Ar ₁₃ , and Ar ₁₄ are each independently aromatic carbocyclic rings having 6 to 14 carbon atoms, which may have substituents. Here, the term "aromatic ring" in this specification means a ring that obeys Hückel's rule, in which the number of electrons in the π-electron system on the ring is 4n+2 (where n is a natural number), and includes monocyclic aromatic rings and fused aromatic rings formed by the fusion of two or more monocyclic aromatic rings. The aromatic ring may be a carbocyclic ring or a heterocyclic ring. Examples of aromatic rings include monocyclic aromatic rings such as benzene rings, furan rings, thiophene rings, pyrrole rings, pyrazole rings, oxazole rings, isoxazole rings, thiazole rings, imidazole rings, pyridine rings, pyridazine rings, pyrimidine rings, and pyrazine rings; condensed rings formed by the fusion of two or more monocyclic aromatic rings such as naphthalene rings, anthracene rings, benzofuran rings, isobenzofuran rings, indole rings, isoindole rings, benzothiophene rings, benzimidazole rings, indazole rings, benzoxazole rings, benzoisoxazole rings, benzothiazole rings, quinoline rings, isoquinoline rings, quinoxaline rings, acridine rings, quinazoline rings, sinnoline rings, and phthalazine rings; and condensed rings formed by the fusion of one or more monocyclic aromatic rings with one or more monocyclic non-aromatic rings, such as indan rings, fluorene rings, and tetraline rings. Of these, aromatic carbon rings having 6 to 14 carbon atoms are preferred, and benzene rings are more preferred.

In formula (1-1), when Ar ₁₁ , Ar ₁₂ , Ar ₁₃ , and Ar ₁₄ represent substituted aromatic rings, the number of substituents is not limited. Such substituents (hereinafter also referred to as "substituents S") can be said to be halogen atoms, alkyl groups, cycloalkyl groups, alkoxy groups, cycloalkyloxy groups, aryl groups, aryloxy groups, arylalkyl groups, arylalkoxy groups, monovalent heterocyclic groups, alkylidene groups, amino groups, silyl groups, acyl groups, acyloxy groups, carboxyl groups, sulfo groups, cyano groups, nitro groups, hydroxyl groups, mercapto groups, and oxo groups.

In formula (1-1), the divalent linking groups represented by _L11 , _L12 , and _L13 are preferably divalent groups consisting of one or more skeletal atoms selected from carbon atoms, oxygen atoms, nitrogen atoms, sulfur atoms, and silicon atoms (for example, 1 to 3000, 1 to 1000, 1 to 100, and 1 to 50 atoms). Examples of divalent linking groups include _-SO₂- , -CO-, -COO-, -O-, -S-, -O- _{C₆H₄ -O-} (where _-C₆H₄- represents a phenylene group), -O- _C₆H₄ -C( _CH₃ ) _₂ - _C₆H₄ -O-, -COO-(CH₂) _q -OCO- (where _q represents an integer from 1 to 20), _-COO - _H₂C -HC(-O-C(=O) _-CH₃ ) _{-CH₂ - OCO-} , alkylene group, alkenylene group, alkynylene group, arylene group, heteroarylene group, -C(=O)-, -C(=O)-O-, ^-NR₀- (where R ⁰ represents a hydrogen atom, and an alkyl group having 1 to 3 carbon atoms. Examples include -C(=O) ^-NR0- . The number of carbon atoms in the alkylene group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 5 or 1 to 4. The number of carbon atoms in the alkenylene group is preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 5. The number of carbon atoms in the arylene group is preferably 6 to 20, more preferably 6 to 10, and the number of carbon atoms in the heteroarylene group is preferably 2 to 20, more preferably 3 to 10, 4 to 10 or 5 to 10. The alkyl group, alkylene group, alkenylene group, alkylylene group, arylene group, and heteroarylene group described above may further have substituents. Examples of such substituents include the substituent S mentioned above. The divalent linking groups represented by _L11 , _L12 and _L13 preferably do not contain aromatic rings. In one embodiment, the divalent linking group represented by L ₁₁ and the divalent linking group represented by L ₁₃ are the same, and the divalent linking group represented by L ₁₁ and the divalent linking group represented by L ₁₂ are different. In a preferred embodiment, in formula (1-1), L ₁₁ and L ₁₃ are -O- and L ₁₂ is an optionally substituted alkylene group. In a more preferred embodiment, in formula (1-1), Ar ₁₁ , Ar ₁₂ , Ar ₁₃ and Ar ₁₄ are each independently optionally substituted aromatic carbon rings having 6 to 14 carbon atoms, and L ₁₁ and L ₁₃ are -O- and L ₁₂ is an optionally substituted alkylene group. In an even more preferred embodiment, in formula (1-1), L ₁₁ and L ₁₃ are -O- and L ₁₂ is a dimethylmethylene group.

In formula (1-2), examples of aromatic rings represented by Ar ₂₁ , Ar ₂₂ , Ar ₂₃ , and Ar ₂₄ , and the substituents that the aromatic rings may have, are the same as those for aromatic ring C and substituent S, respectively. Therefore, in one preferred embodiment, in formula (1-2), Ar ₂₁ , Ar ₂₂ , Ar ₂₃ , and Ar ₂₄ are each independently aromatic carbon rings having 6 to 14 carbon atoms, which may have substituents. Furthermore, in one preferred embodiment, in formula (1-2), L ₂₁ and L ₂₃ are -O- and L ₂₂ is an optionally substituted alkylene group; in one more preferred embodiment, in formula (1-2), Ar ₂₁ , Ar ₂₂ , Ar ₂₃ and Ar ₂₄ are each independently optionally substituted aromatic carbon rings having 6 to 14 carbon atoms, and L ₂₁ and L ₂₃ are -O- and L ₂₂ is an optionally substituted alkylene group. In yet another preferred embodiment, in formula (1-2), L ₂₁ and L ₂₃ are -O- and L ₂₂ is a dimethylmethylene group.

In one particularly preferred embodiment, in formula (1-1), Ar ₁₁ , Ar ₁₂ , Ar ₁₃ , and Ar ₁₄ are each independently an aromatic carbon ring having 6 to 14 carbon atoms, which may have substituents, and in formula (1-2), Ar ₂₁ , Ar ₂₂ , Ar ₂₃ , and Ar ₂₄ are each independently an aromatic carbon ring having 6 to 14 carbon atoms, which may have substituents. In another particularly preferred embodiment, in formula (1-1), L ₁₁ and L ₁₃ are -O- and L ₁₂ is an alkylene group, which may have substituents, and in formula (1-2), L ₂₁ and L ₂₃ are -O- and L ₂₂ is an alkylene group, which may have substituents.

In formula (1-1), nc1 preferably represents an integer of 1 or more. The upper limit of the integer represented by nc1 is not particularly limited, but it could be, for example, 50, 40, 30, or 20.

In equation (1-2), nc2 preferably represents an integer of 2 or more. The upper limit of the integer represented by nc2 is not particularly limited, but it could be, for example, 60, 50, 40, or 30.

The structural unit (1) can be obtained, for example, by a known method for producing polyimide resins, typically by polymerizing a monomer composition containing a tetracarboxylic dianhydride and a diamine compound to imidize it, or by polymerizing a monomer composition containing a tetracarboxylic dianhydride and a diisocyanate compound to imidize it. It is permissible for the polyimide resin to partially contain polyamic acid structures that may be formed during the imidization process.

Structural unit (1) may be obtained, for example, by reacting 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (a compound represented by formula (I) below; hereinafter also referred to as "BPADA") with 4,4'-[1,4-phenylenebis[(1-methylethylidene)-4,1-phenyleneoxy]]bisbenzeneamine (a compound represented by formula (II) below; hereinafter also referred to as "BPPAN"). That is, _R1 in structural unit (1) is a skeleton derived from BPADA, and _R2 is a skeleton derived from BPPAN.

Furthermore, the polyimide resin may also contain structural units represented by the following formula (2) (hereinafter also referred to as "structural unit (2)"). Therefore, in one embodiment, the polyimide resin further contains structural units represented by the following formula (2). The number of structural units (2) contained in one molecule of polyimide resin is 0 or more and is not particularly limited, but can be 100 or less, 50 or less, or 30 or less.

(In formula (2),
R ₃ represents a tetravalent aliphatic group which may have a substituent or a tetravalent aromatic group which may have a substituent.
_R4 represents a divalent aliphatic group or a divalent aromatic group, which may have a substituent. However, if _R3 is the same as _R1 , _R4 is different from _R2 , and if _R4 is the same as _R2 , _R3 is different from _R1 .

In formula (2), the tetravalent aliphatic group represented by _R3 is a tetravalent group comprising at least carbon atoms, and preferably consisting of one or more skeleton atoms selected from carbon atoms, oxygen atoms, nitrogen atoms, sulfur atoms, and silicon atoms (for example, 1 to 3000, 1 to 1000, 1 to 100, or 1 to 50 atoms). In formula (2), the tetravalent aliphatic group represented by _R3 is more preferably a tetravalent aliphatic group having 1 to 100 carbon atoms, and even more preferably 1 to 50 carbon atoms. In formula (2), when _R3 represents a tetravalent aliphatic group having a substituent, the examples of the substituent are the same as the examples of substituent S.

In formula (2), the tetravalent aromatic group represented by _R3 is preferably a tetravalent aromatic group having 6 to 100 carbon atoms, more preferably 6 to 50 carbon atoms. The aromatic group includes at least an aromatic ring. Examples of aromatic rings included in the aromatic group are the same as the examples of aromatic rings represented by _Ar11 , _Ar12 , _Ar13 , and _Ar14 in formula (1-1). In formula (2), when _R3 represents a tetravalent aromatic group having a substituent, examples of the substituent are the same as the examples of substituent S.

The tetravalent aromatic group represented by _R3 can be a group obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride having an aromatic group that may have substituents. Specific examples of tetracarboxylic dianhydrides having an aromatic group that may have substituents include BPADA, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride.

In formula (2), the divalent aliphatic group represented by _R4 is a divalent group comprising at least carbon atoms, and preferably consisting of one or more skeleton atoms selected from carbon atoms, oxygen atoms, nitrogen atoms, sulfur atoms, and silicon atoms (for example, 1 to 3000, 1 to 1000, 1 to 100, and 1 to 50). In formula (2), the divalent aliphatic group represented by _R4 is more preferably a divalent aliphatic group having 1 to 100 carbon atoms, and even more preferably 1 to 50 carbon atoms. In formula (2), when _R4 represents a substituted divalent aliphatic group, examples of the substituent are the same as examples of substituent S, for example, an alkyl group having 1 to 6 carbon atoms. Therefore, in one embodiment, _R4 is a divalent aliphatic group which may have substituents, and one of the substituents is an alkyl group having 1 to 6 carbon atoms. In another embodiment, _R4 is a divalent aliphatic group which may have substituents, and is a divalent group obtained by removing two amino groups from isophoronediamine.

When R ₄ represents a divalent aliphatic group which may have substituents, it may be a group obtained by removing two amino groups from a diamine compound having a linear aliphatic group which may have substituents, selected from 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, and 1,12-dodecanediamine.

When R ₄ represents a divalent aliphatic group which may have substituents, it may be a group obtained by removing two amino groups from a diamine compound having a branched aliphatic group which may have substituents, selected from 1,2-diaminopropane, 1,2-diamino-2-methylpropane, 1,3-diamino-2-methylpropane, 1,3-diamino-2,2-dimethylpropane, 1,3-diaminopentane, and 1,5-diamino-2-methylpentane.

When R ₄ represents a divalent aliphatic group which may have substituents, it may be a group obtained by removing two amino groups from a diamine compound having an aliphatic group which may have substituents, selected from 5-amino-1,3,3-trimethylcyclohexanemethylamine (isophoronediamine), 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-cyclohexanebis(methylamine), 1,3-cyclohexanebis(methylamine), ^4,4' -diaminodicyclohexylmethane, bis(4-amino-3-methylcyclohexyl)methane, 3(4),8(9)-bis(aminomethyl)tricyclo[5.2.1.0 2,6]decane, 2,5(6)-bis(aminomethyl)bicyclo[2.2.1]heptane, 1,3-diaminoadamantane, 3,3'-diamino-1,1'-biadamantyl, and 1,6-diaminoadamantane. These diamine compounds are characterized by the presence of alicyclic carbon rings in their aliphatic groups.

In formula (2), the divalent aromatic group represented by R ₄ is preferably a divalent aromatic group having 6 to 100 carbon atoms, more preferably 6 to 50 carbon atoms. The aromatic group includes at least an aromatic ring. Examples of aromatic rings included in the aromatic group are the same as those of aromatic ring C. In formula (2), when R ₄ represents a divalent aromatic group having a substituent, examples of the substituent are the same as those of substituent S.

If R ₄ represents a divalent aromatic group which may have substituents, it may be a group obtained by removing two amino groups from a diamine compound having an aromatic group which may have substituents, selected from 4,4'-diaminodiphenyl ether, 1,4-phenylenediamine, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

However, if _R3 is the same as _R1 , _R4 is different from _R2 , and if _R4 is the same as _R2 , _R3 is different from _R1 . In one embodiment, _R3 is the same as _R1 .

The structural unit (2) described above can be obtained, for example, by a known method for producing polyimide resins. Structural unit (2) can be obtained, for example, by reacting BPADA with isophorone diamine. That is, in such structural unit (2), _R3 is a skeleton derived from BPADA, and _R4 is a skeleton derived from isophorone diamine. When _R3 is the same as _R1 , _R3 and _R1 are skeletons derived from BPADA.

The terminal structure of the polyimide resin is not particularly limited. For example, the terminal structure of the polyimide resin may be an acid anhydride group, a carboxyl group, or an amino group derived from its raw material compound (e.g., an acid such as BPADA, or an amine compound such as BPPAN). If the raw material compound further contains maleic anhydride, the terminal structure of the polyimide resin may be a maleimide group.

The glass transition temperature Tg (°C) of polyimide resin is preferably 140°C or higher, more preferably 145°C or higher, and even more preferably 150°C or higher, 160°C or higher, or 170°C or higher. There is no particular upper limit, but it can be 300°C or lower. The glass transition temperature Tg (°C) of polyimide resin can be measured by thermomechanical analysis (TMA).

The content of structural unit (1) in the polyimide resin is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, 30% by mass or more, or 40% by mass or more. The upper limit of this content can be, for example, 98% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less. Here, the content of structural unit (1) (mass percentage) can be calculated from the proportion of the amount (parts by mass) of each material used in the synthesis of the polyimide resin. Alternatively, the molecular weight of the polyimide resin and the formula weight of structural unit (1) may be specified, and the content of structural unit (1) may be calculated as the ratio of the formula weight of structural unit (1) to the molecular weight. When the polyimide resin is a polymer, it is preferable that the content of structural unit (1) estimated from the degree of polymerization falls within the above range.

If the polyimide resin is a resin that further contains structural unit (2), the content of said structural unit (2) may be 0% by mass (i.e., no structural unit (2)), and there is no upper limit as long as it does not hinder the effects of the present invention. The content of structural unit (2) in the polyimide resin can be, for example, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, or 30% by mass or more, 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less. Here, the content of structural unit (2) is calculated in the same way as the content of structural unit (1).

The weight-average molecular weight (Mw) of the polyimide resin is 1,000 or more, preferably 1,000 to 10,000, and more preferably 1,000 to 5,000. The weight-average molecular weight of the resin can be measured as a polystyrene equivalent by gel permeation chromatography (GPC).

--Polyvinyl acetal resin--
Examples of polyvinyl acetal resins include polyvinyl formal resin and polyvinyl butyral resin, with polyvinyl butyral resin being preferred. Specific examples of polyvinyl acetal resins include, for example, the S-Rec BH series, BX series (e.g., BX-5Z), KS series (e.g., KS-1), BL series, and BM series manufactured by Sekisui Chemical Co., Ltd.

--Acrylic resin--
Acrylic resin refers to a polymer obtained by polymerizing monomer components, including (meth)acrylic acid ester monomers. In addition to (meth)acrylic acid ester monomers, the monomer components constituting acrylic resin may also include (meth)acrylamide monomers, styrene monomers, functional group-containing monomers, etc., as copolymer components. Specific examples of acrylic resin include "ARUFON UP-1000", "ARUFON UP-1010", "ARUFON UP-1020", "ARUFON UP-1021", "ARUFON UP-1061", "ARUFON UP-1080", "ARUFON UP-1110", "ARUFON UP-1170", "ARUFON UP-1190", "ARUFON UP-1500", "ARUFON UH-2000", "ARUFON UH-2041", "ARUFON UH-2190", "ARUFON UHE-2012", "ARUFON UC-3510", and "ARUFON" manufactured by Toagosei Co., Ltd. Examples include "UG-4010,""ARUFONUS-6100," and "ARUFON US-6170." These may be used individually or in combination of two or more types.

--Polyolefin resin--
Examples of polyolefin resins include ethylene-based copolymer resins such as low-density polyethylene, ultra-low-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-methyl acrylate copolymer; and polyolefin-based elastomers such as polypropylene and ethylene-propylene block copolymer.

--Polybutadiene resin--
Examples of polybutadiene resins include hydrogenated polybutadiene skeleton-containing resins, hydroxyl group-containing polybutadiene resins, phenolic hydroxyl group-containing polybutadiene resins, carboxyl group-containing polybutadiene resins, acid anhydride group-containing polybutadiene resins, epoxy group-containing polybutadiene resins, isocyanate group-containing polybutadiene resins, urethane group-containing polybutadiene resins, and polyphenylene ether-polybutadiene resins.

--Polyamide-imide resin--
Specific examples of polyamide-imide resins include "Viromax HR11NN" and "Viromax HR16NN" manufactured by Toyobo Co., Ltd. Other specific examples of polyamide-imide resins include modified polyamide-imides such as "KS9100" and "KS9300" (polysiloxane skeleton-containing polyamide-imide) manufactured by Resonaq Corporation.

--Polyethersulfone resin--
Specific examples of polyethersulfone resins include "PES5003P" manufactured by Sumitomo Chemical Co., Ltd.

--Polysulfone resin--
Specific examples of polysulfone resins include Solvay Advanced Polymers' polysulfones "P1700" and "P3500".

--Polyphenylene ether resin--
Specific examples of polyphenylene ether resins include "Noryl® SA90" manufactured by SABIC. Specific examples of polyetherimide resins include "Ultem" manufactured by GE.

--Polycarbonate resin--
Examples of polycarbonate resins include hydroxyl group-containing carbonate resins, phenolic hydroxyl group-containing carbonate resins, carboxyl group-containing carbonate resins, acid anhydride group-containing carbonate resins, isocyanate group-containing carbonate resins, and urethane group-containing carbonate resins. Specific examples of polycarbonate resins include "FPC0220" from Mitsubishi Gas Chemical Co., Ltd., "T6002" and "T6001" (polycarbonate diols) from Asahi Kasei Corporation, and "C-1090,""C-2090," and "C-3090" (polycarbonate diols) from Kuraray Co., Ltd. Specific examples of polyether ether ketone resins include "Sumiproi K" from Sumitomo Chemical Co., Ltd. Examples of polyester resins include polyethylene terephthalate resin.

The weight-average molecular weight of the thermoplastic resin is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, 15,000 or more, or 20,000 or more, preferably 200,000 or less, more preferably 150,000 or less, or 100,000 or less, and even more preferably 80,000 or less, or 60,000 or less. The weight-average molecular weight of the thermoplastic resin can be measured as a polystyrene equivalent value by gel permeation chromatography (GPC).

In the multilayer resin sheet of the present invention, when the resin composition layer contains a thermoplastic resin, the content of the thermoplastic resin in the resin composition layer is preferably 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, from the viewpoint of easily adjusting the above RD/RA ratio to a suitable range, providing even better surface smoothness, and resulting in an insulating layer with well-shaped via holes and reduced smearing. The upper limit of the thermoplastic resin content is not particularly limited, but is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less or 5% by mass or less.

- Radical polymerizable resin -
In the multilayer resin sheet of the present invention, the resin composition layer may contain a radical polymerizable resin.

The type of radical polymerizable resin is not particularly limited, as long as it has one or more (preferably two or more) radical polymerizable unsaturated groups per molecule. Examples of radical polymerizable resins include resins having one or more radical polymerizable unsaturated groups selected from maleimide groups, vinyl groups, allyl groups, styryl groups, vinylphenyl groups, acryloyl groups, methacryloyl groups, fumaroyl groups, and maleoil groups. In particular, from the viewpoint of providing an insulating layer with better surface smoothness, reduced smearing, and well-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing, it is preferable that the radical polymerizable resin contains one or more selected from maleimide resin, (meth)acrylic resin, and styryl resin.

The type of maleimide resin is not particularly limited, as long as it has one or more (preferably two or more) maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrole-1-yl groups) per molecule. Examples of maleimide resins include (1) "BMI-3000J", "BMI-5000", "BMI-1400", "BMI-1500", "BMI-1700", and "BMI-689" (all from Designer Molecules). Examples include: (1) Maleimide resins containing an aliphatic skeleton (preferably an aliphatic skeleton with 36 carbon atoms derived from dimeramine) such as "SLK6895-T90" (manufactured by Shin-Etsu Chemical Co., Ltd.); (2) Maleimide resins containing an indan skeleton as described in the Japan Institute of Invention and Innovation, Technical Report No. 2020-500211; and (3) Maleimide resins containing an aromatic ring skeleton directly bonded to the nitrogen atom of the maleimide group, such as "MIR-3000-70MT" (manufactured by Nippon Kayaku Co., Ltd.), "BMI-4000" (manufactured by Yamato Kasei Co., Ltd.), and "BMI-80" (manufactured by Kei-I Kasei Co., Ltd.).

The type of (meth)acrylic resin is not particularly limited as long as it has one or more (preferably two or more) (meth)acryloyl groups in one molecule, and may be a monomer or oligomer. Here, the term "(meth)acryloyl group" is a general term for acryloyl groups and methacryloyl groups. Examples of methacrylic resins include (meth)acrylate monomers, as well as (meth)acrylic resins such as "A-DOG" (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.), "DCP-A" (manufactured by Kyoeisha Chemical Co., Ltd.), "NPDGA", "FM-400", "R-687", "THE-330", "PET-30", and "DPHA" (all manufactured by Nippon Kayaku Co., Ltd.).

The type of styryl resin is not particularly limited as long as it has one or more (preferably two or more) styryl groups or vinylphenyl groups in one molecule, and may be a monomer or oligomer. Examples of styryl resins include styrene monomer, as well as styryl resins such as "OPE-2St," "OPE-2St 1200," and "OPE-2St 2200" (all manufactured by Mitsubishi Gas Chemical Company).

In the multilayer resin sheet of the present invention, when the resin composition layer contains a radical polymerizable resin, the content of the radical polymerizable resin in the resin composition layer is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, 6% by mass or more, 8% by mass or more, or 10% by mass or more, when the resin components in the resin composition are considered as 100% by mass, and may be increased to, for example, 12% by mass or more, 14% by mass or more, or 15% by mass or more. The upper limit of the content is not particularly limited and may be determined according to the properties required of the resin composition, but for example, it may be 60% by mass or less, 50% by mass or less, or 40% by mass or less.

From the viewpoint of providing an insulating layer with better surface smoothness, reduced smearing, and well-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing, it is preferable that the first resin composition layer among the resin composition layers constituting the multilayer resin sheet of the present invention contains a radical polymerizable resin. Therefore, in a preferred embodiment, the first resin composition layer contains a radical polymerizable resin.

- Curing accelerator -
In the multilayer resin sheet of the present invention, the resin composition layer may contain a curing accelerator. By including a curing accelerator, the curing time and curing temperature can be efficiently adjusted.

Examples of curing accelerators include organophosphine compounds such as "TPP," "TPP-K," "TPP-S," and "TPTP-S" (manufactured by Hokko Chemical Industry Co., Ltd.); imidazole compounds such as "Curesol 2MZ," "2P4MZ," "2E4MZ," "Cl1Z," "Cl1Z-CN," "Cl1Z-CNS," "Cl1Z-A," "2MZ-OK," "2MA-OK," and "2PHZ" (manufactured by Shikoku Chemicals Co., Ltd.); amine adduct compounds such as Novacure (manufactured by Asahi Kasei Corporation) and Fujicure (manufactured by Fuji Chemical Industries Co., Ltd.); amine compounds such as 1,8-diazabicyclo[5,4,0]undecene-7,4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and 4-dimethylaminopyridine; and organometallic complexes or organometallic salts such as cobalt, copper, zinc, iron, nickel, manganese, and tin.

In the multilayer resin sheet of the present invention, when the resin composition layer contains a curing accelerator, the content of the curing accelerator in the resin composition layer is preferably 12% by mass or less, more preferably 10% by mass or less, 8% by mass or less, 6% by mass or less, or 5% by mass or less, when the resin component in the resin composition is considered to be 100% by mass, from the viewpoint of easily adjusting the above RD/RA ratio to a suitable range, and the lower limit can be 0.001% by mass or more, 0.01% by mass or more, 0.05% by mass or more, etc.

From the viewpoint of providing an insulating layer with better surface smoothness, reduced smearing, and well-shaped via holes, and further from the viewpoint of providing an insulating layer with little change in film thickness before and after desmearing, it is preferable that the content A1 (mass%) of the curing accelerator relative to 100% by mass of the resin component in the first resin composition layer and the content A2 (mass%) of the curing accelerator relative to 100% by mass of the resin component in the layers other than the first resin composition layer satisfy the relationship A1 > A2. The difference between A1 and A2 (A1 - A2) is preferably 1% by mass or more, more preferably 2% by mass or more, 3% by mass or more, or 4% by mass or more.

-Optional additives-
In the multilayer resin sheet of the present invention, the resin composition layer may further contain any additives. Examples of such additives include: organic fillers such as rubber particles; radical polymerization initiators such as peroxide-based radical polymerization initiators and azo-based radical polymerization initiators; organometallic compounds such as organocopper compounds, organozinc compounds, and organocalt compounds; colorants such as phthalocyanine blue, phthalocyanine green, iodine green, diazo yellow, crystal violet, titanium dioxide, and carbon black; polymerization inhibitors such as hydroquinone, catechol, pyrogallol, and phenothiazine; leveling agents such as silicone-based leveling agents and acrylic polymer-based leveling agents; thickeners such as bentonite and montmorillonite; defoaming agents such as silicone-based defoaming agents, acrylic-based defoaming agents, fluorine-based defoaming agents, and vinyl resin-based defoaming agents; ultraviolet absorbers such as benzotriazole-based ultraviolet absorbers; adhesion improvers such as urea silane; and triazole-based adhesion fertilizers. Adhesion-enhancing agents such as tetrazole-based adhesion enhancers and triazine-based adhesion enhancers; antioxidants such as hindered phenol-based antioxidants; fluorescent whitening agents such as stilbene derivatives; surfactants such as fluorine-based surfactants and silicone-based surfactants; flame retardants such as phosphorus-based flame retardants (e.g., phosphate ester compounds, phosphazene compounds, phosphinic acid compounds, red phosphorus), nitrogen-based flame retardants (e.g., melamine sulfate), halogen-based flame retardants, and inorganic flame retardants (e.g., antimony trioxide); dispersants such as phosphate ester-based dispersants, polyoxyalkylene-based dispersants, acetylene-based dispersants, silicone-based dispersants, anionic dispersants, and cationic dispersants; and stabilizers such as borate-based stabilizers, titanate-based stabilizers, aluminate-based stabilizers, zirconate-based stabilizers, isocyanate-based stabilizers, carboxylic acid-based stabilizers, and carboxylic acid anhydride-based stabilizers. The content of such additives may be determined according to the properties required of the multilayer resin sheet.

- Manufacturing method for multilayer resin sheets -
The method for manufacturing the multilayer resin sheet of the present invention is not particularly limited as long as it can realize a structure in which two or more layers of resin composition are laminated together, and methods known to those skilled in the art may be used. For example, (i) an extrusion molding method in which a resin composition is melted and kneaded using an extruder, extruded, and then formed into a film using a T-die or circular die, etc., (ii) a casting molding method in which a resin composition is dissolved or dispersed in a solvent and then cast into a film, and (iii) other conventionally known film molding methods. Among these, the extrusion molding method or the casting molding method is preferred because it can accommodate thinning. The multilayer resin sheet of the present invention includes two or more layers of resin composition that are laminated together. Methods for forming a multilayer resin sheet by laminating two or more resin composition layers together include, for example, (1) a method of forming a multilayer resin sheet by simultaneously or sequentially forming resin composition layers during coating or extrusion, (2) a method of forming a multilayer resin sheet by bonding two or more separately prepared resin composition layers together using a hot roll laminator or the like, (3) a method of forming a resin sheet having a multilayer structure in substantially one resin sheet by creating differences in the content of each component in the resin sheet during casting molding, and (4) other conventionally known methods for forming multilayer resin sheets.

Below is a preferred example of a method for manufacturing a multilayer resin sheet comprising two resin composition layers, namely a first resin composition layer and a second resin composition layer.

In one embodiment, the method for manufacturing a multilayer resin sheet is as follows:
(A1) A step of preparing a resin sheet with a support, which includes a support and a first resin composition layer bonded to the support; and (B1) A step of applying a second resin composition onto the first resin composition layer and drying the coating film to provide a second resin composition layer (hereinafter, such an embodiment of lamination by coating will also be referred to as the "first embodiment").

In step (A1), a resin sheet with a support is prepared, which includes a support and a first resin composition layer bonded to the support. The support will be described later in the section on [Multilayer Resin Sheet with Support].

A resin sheet with a support can be manufactured, for example, by coating a first resin composition onto a support and drying the coating film to form a first resin composition layer. More specifically, it can be manufactured by preparing a resin varnish by dissolving the first resin composition in an organic solvent, coating this resin varnish onto a support using a die coater or the like, and drying the coating film.

Examples of organic solvents include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ether solvents such as tetrahydropyran, tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, dibutyl ether, and diphenyl ether; alcohol solvents such as methanol, ethanol, propanol, butanol, and ethylene glycol; and 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl diglycol acetate, γ-butyrolactone, and methyl methoxypropionate. Examples include ether ester solvents such as methyl lactate, ethyl lactate, and methyl 2-hydroxyisobutyrate; ether alcohol solvents such as 2-methoxypropanol, 2-methoxyethanol, 2-ethoxyethanol, propylene glycol monomethyl ether, and diethylene glycol monobutyl ether (butyl carbitol); amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; sulfoxide solvents such as dimethyl sulfoxide; nitrile solvents such as acetonitrile and propionitrile; aliphatic hydrocarbon solvents such as hexane, cyclopentane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, and trimethylbenzene. Organic solvents may be used individually or in combination of two or more.

The coating film may be dried by known drying methods such as heating or hot air blowing. Although it varies depending on the boiling point of the organic solvent in the resin varnish, for example, when using a resin varnish containing 30% to 60% by mass of an organic solvent, the first resin composition layer can be formed on the support by drying at 80°C to 180°C for 2 to 10 minutes.

In step (B1), a second resin composition is applied onto the first resin composition layer, and the applied film is dried to form the second resin composition layer. This forms a support-mounted multilayer resin sheet, in which a multilayer resin sheet is formed on the support.

The application of the second resin composition and the drying of the coated film may be carried out in the same manner as the application of the first resin composition and the drying of the coated film in step (A1). From the viewpoint of easily adjusting the above RD/RA ratio to a suitable range, when the drying temperature (°C) of the coated film in step (A1) is T1 and the drying temperature (°C) of the coated film in step (A2) is T2, it is preferable that the relationship T1 > T2, more preferably T1 ≥ (T2 + 20), and even more preferably T1 ≥ (T2 + 40) or T1 ≥ (T2 + 50) is satisfied.

A multilayer resin sheet with a support may further include a protective film similar to that of the support on the side of the multilayer resin sheet that is not bonded to the support (i.e., the side opposite to the support). If a protective film is provided, the multilayer resin sheet with a support can be used by peeling off the protective film when laminating it onto the component to be laminated.

In another embodiment, the method for manufacturing a multilayer resin sheet is as follows:
(A2a) A step of preparing a resin sheet with a first support, which includes a first support and a first resin composition layer bonded to the first support.
(A2b) A step of preparing a resin sheet with a second support, which includes a second support and a second resin composition layer bonded to the second support; and (B2) A step of laminating the first resin sheet with a first support and the second resin sheet with a second support such that the first resin composition layer and the second resin composition layer are bonded together (hereinafter, such an embodiment of lamination is also referred to as the "second embodiment").

In the second embodiment, steps (A2a) and (A2b) may be carried out in the same manner as step (A1) in the first embodiment. Here, from the viewpoint of easily adjusting the RD/RA ratio to a suitable range, if the drying temperature (°C) of the coating film in step (A2a) is Ta and the drying temperature (°C) of the coating film in step (A2b) is Tb, it is preferable that the relationship Ta > Tb, more preferably Ta ≥ (Tb + 20), and even more preferably Ta ≥ (Tb + 40) or Ta ≥ (Tb + 50) is satisfied.

In step (B2), the first support-equipped resin sheet and the second support-equipped resin sheet are laminated so that the first resin composition layer and the second resin composition layer are joined together. This forms a multilayer resin sheet between the first support and the second support. The second support can function as a protective film in the first embodiment. The support-equipped multilayer resin sheet manufactured in the second embodiment can be used when laminating it onto a target member by peeling off the second support (protective film).

Regarding the lamination in step (B2), the lamination temperature is preferably in the range of 60°C to 160°C, more preferably in the range of 80°C to 140°C, the lamination pressure is preferably in the range of 0.098 MPa to 1.77 MPa, more preferably in the range of 0.29 MPa to 1.47 MPa, and the lamination time is preferably in the range of 20 seconds to 400 seconds, more preferably in the range of 30 seconds to 300 seconds. Lamination may preferably be carried out under reduced pressure conditions of 26.7 hPa or less.

Lamination can be performed using a commercially available vacuum laminator. Examples of commercially available vacuum laminators include vacuum pressure laminators manufactured by Meiki Seisakusho Co., Ltd., vacuum applicators manufactured by Nikko Materials Co., Ltd., and batch-type vacuum pressure laminators.

The multilayer resin sheet of the present invention can provide an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes, even when desmearing is performed after peeling off the support. The multilayer resin sheet of the present invention can also provide an insulating layer with little change in film thickness before and after desmearing. Therefore, the multilayer resin sheet of the present invention can be suitably used as a multilayer resin sheet for forming an insulating layer of a printed circuit board (multilayer resin sheet for insulating layer of printed circuit board), and more suitably used as a multilayer resin sheet for forming an interlayer insulating layer of a printed circuit board (multilayer resin sheet for interlayer insulating layer of printed circuit board). The multilayer resin sheet of the present invention can also be suitably used when the printed circuit board is a circuit board with embedded components. The resin composition of the present invention can also be suitably used as a multilayer resin sheet for forming an insulating layer in which a conductor layer (including a rewiring layer) is formed in contact (multilayer resin sheet for insulating layer for forming a conductor layer).

[Multilayer resin sheet with support]
The present invention also provides a support-mounted multilayer resin sheet, in which the multilayer resin sheet of the present invention is provided on a support.

The multilayer resin sheet with a support of the present invention is
The multilayer resin sheet of the present invention,
The multilayer resin sheet includes a support that is bonded to a first resin composition layer.

The multilayer resin sheet of the present invention is as described in the [Multilayer Resin Sheet] section above. In the multilayer resin sheet with a support of the present invention, the first resin composition layer of the multilayer resin sheet of the present invention is bonded to the support.

Examples of support materials include thermoplastic resin films, metal foils, and release paper, with thermoplastic resin films and metal foils being preferred. Therefore, in one preferred embodiment, the support material is a thermoplastic resin film or a metal foil.

When using a thermoplastic resin film as a support, examples of thermoplastic resins include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylics such as polycarbonate (PC) and polymethyl methacrylate (PMMA), cyclic polyolefins, triacetylcellulose (TAC), polyether sulfide (PES), polyether ketones, and polyimides. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, and inexpensive polyethylene terephthalate is particularly preferred.

When using metal foil as a support, examples of metal foil include copper foil and aluminum foil, with copper foil being preferred. As for copper foil, foil made of single-metal copper may be used, or foil made of an alloy of copper with another metal (for example, tin, chromium, silver, magnesium, nickel, zirconium, silicon, titanium, etc.) may be used.

The support may have a matte finish, corona treatment, or antistatic treatment applied to the surface that joins with the first resin composition layer. Alternatively, a support with a release layer, having a release layer on the surface that joins with the first resin composition layer, may be used. Examples of release agents used in the release layer of the support with a release layer include one or more release agents selected from the group consisting of alkyd resins, polyolefin resins, urethane resins, and silicone resins. Commercially available support with a release layer may be used; examples include PET films having a release layer mainly composed of an alkyd resin-based release agent, such as "SK-1," "AL-5," and "AL-7" from Lintec Corporation, "Lumirror T60" from Toray Industries, Inc., "Purex" from Teijin Corporation, and "Unipeel" from Unitika Corporation.

The thickness of the support is not particularly limited, but is preferably in the range of 5 μm to 75 μm, and more preferably in the range of 10 μm to 60 μm. When using a support with a release layer, it is preferable that the overall thickness of the support with the release layer be within the above range.

In one embodiment, the multilayer resin sheet with a support may further include any additional layer as needed. Such an additional layer may be, for example, a protective film provided on the side of the multilayer resin sheet that is not bonded to the support (i.e., the side opposite to the support). The thickness of the protective film is not particularly limited, but is, for example, 1 μm to 40 μm. By laminating the protective film, the adhesion of dust and other debris to the surface of the multilayer resin sheet, as well as scratches, can be suppressed.

The method for manufacturing a multilayer resin sheet with a support is as described in the "Multilayer Resin Sheet" section above.

A multilayer resin sheet with a support can be stored by being rolled up. If the resin sheet with a support has a protective film, it can be used by peeling off the protective film. Here, when the adhesive strength between the support and the multilayer resin sheet (specifically the first resin composition layer) is S1, and the adhesive strength between the protective film and the multilayer resin sheet (specifically the outermost layer opposite to the first resin composition layer) is S2, the relationship S1 > S2 is satisfied. As a result, the protective film can be peeled off from the multilayer resin sheet before the support, the surface of the multilayer resin sheet opposite to the first resin composition layer can be exposed, and consequently, the multilayer resin sheet can be laminated and used so that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the member to be laminated.

The multilayer resin sheet with support of the present invention can be suitably used to form an insulating layer of a printed circuit board (for insulating layers of printed circuit boards), and more suitably used to form an interlayer insulating layer of a printed circuit board (for interlayer insulating layers of printed circuit boards). The sheet-like laminated material of the present invention can also be suitably used as a resin composition for forming an insulating layer (for insulating layers for forming conductive layers) in which a conductive layer (including a rewiring layer) is formed in contact therewith.

[Printed circuit board]
The printed circuit board of the present invention includes an insulating layer made of a cured product of the multilayer resin sheet of the present invention.

Printed wiring boards can be manufactured, for example, using the multilayer resin sheet of the present invention by a method including the following steps (I) to (IV).
(I) Laminating the multilayer resin sheet of the present invention onto an inner layer substrate such that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the inner layer substrate; (II) Curing (e.g., by heat curing) the multilayer resin sheet to form an insulating layer; (III) Forming via holes in the insulating layer with a laser and performing desmear treatment; (IV) Forming a metal film on the surface of the insulating layer after desmear treatment.

-Step (I)-
In step (I), the multilayer resin sheet of the present invention is laminated on the inner layer substrate such that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the inner layer substrate.

The "internal layer substrate" used in process (I) is a material that serves as the substrate for a printed circuit board, and examples include glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, thermosetting polyphenylene ether substrates, etc. The substrate may also have a conductive layer on one or both sides, and this conductive layer may be patterned. An internal layer substrate with conductive layers (circuits) formed on one or both sides is sometimes called an "internal layer circuit board." Furthermore, intermediate products on which an insulating layer and/or conductive layer is to be formed during the manufacturing of a printed circuit board are also included in the definition of "internal layer substrate" in this invention. If the printed circuit board is a component-embedded circuit board, an internal layer substrate with embedded components may be used.

The lamination of the inner layer substrate and the multilayer resin sheet can be performed, for example, by using the multilayer resin sheet with support of the present invention and heat-pressing the multilayer resin sheet onto the inner layer substrate from the support side. Examples of the heat-pressing member used to heat-press the multilayer resin sheet onto the inner layer substrate (hereinafter also referred to as the "heat-pressing member") include a heated metal plate (such as a SUS end plate) or a metal roll (such as a SUS roll). The heat-pressing member may be pressed directly onto the multilayer resin sheet with support, or it may be pressed via an elastic material such as heat-resistant rubber to ensure that the resin sheet adequately conforms to the surface irregularities of the inner layer substrate.

The lamination of the inner layer substrate and the multilayer resin sheet may be carried out by a vacuum lamination method. In the vacuum lamination method, the heat-pressure temperature is preferably in the range of 60°C to 160°C, more preferably in the range of 80°C to 140°C, the heat-pressure pressure is preferably in the range of 0.098 MPa to 1.77 MPa, more preferably in the range of 0.29 MPa to 1.47 MPa, and the heat-pressure time is preferably in the range of 20 seconds to 400 seconds, more preferably in the range of 30 seconds to 300 seconds. Lamination may preferably be carried out under reduced pressure conditions of 26.7 hPa or less.

Lamination can be performed using a commercially available vacuum laminator. Examples of commercially available vacuum laminators include vacuum pressure laminators manufactured by Meiki Seisakusho Co., Ltd., vacuum applicators manufactured by Nikko Materials Co., Ltd., and batch-type vacuum pressure laminators.

After lamination, the laminated multilayer resin sheet may be smoothed by pressing a heat-sealing member from the support side under normal pressure (atmospheric pressure). The pressing conditions for the smoothing process can be the same as the heat-sealing conditions for lamination. The smoothing process can be performed using a commercially available laminator. Lamination and smoothing may be performed continuously using the commercially available vacuum laminator mentioned above.

The support may be removed between steps (I) and (II), or after step (II). If a metal foil is used as the support, the conductive layer may be formed using the metal foil without removing the support.

-Step (II)-
In step (II), the multilayer resin sheet is cured (e.g., by thermal curing) to form an insulating layer made of the cured multilayer resin sheet.

The curing conditions for the multilayer resin sheet are not particularly limited, and conditions commonly used when forming the insulating layer of a printed circuit board may be used.

For example, the thermosetting conditions for a multilayer resin sheet vary depending on the composition of the resin composition layers, but in one embodiment, the curing temperature is preferably 120°C to 250°C, more preferably 150°C to 240°C, and even more preferably 170°C to 230°C. The curing time can be preferably 5 minutes to 240 minutes, more preferably 10 minutes to 150 minutes, and even more preferably 15 minutes to 120 minutes.

Before heat-curing the multilayer resin sheet, it may be preheated at a temperature lower than the curing temperature. For example, prior to heat-curing the multilayer resin sheet, it may be preheated at a temperature of 50°C to 120°C, preferably 60°C to 115°C, more preferably 70°C to 110°C for 5 minutes or more, preferably 5 minutes to 150 minutes, more preferably 15 minutes to 120 minutes, and even more preferably 15 minutes to 100 minutes.

-Step (III)-
In process (III), via holes are formed in the insulating layer using a laser, and then desmear treatment is performed.

For example, a _CO2 laser, UV-YAG laser, or excimer laser may be used as the laser light source for forming via holes in the insulating layer. Among these, a _CO2 laser is preferred from the viewpoint of enjoying the effects of the present invention to the fullest extent. Therefore, in one embodiment, via holes are formed in the insulating layer using a _CO2 laser.

The dimensions and shape of the via holes may be determined as appropriate according to the design of the printed circuit board. For example, the shape of the via holes is not particularly limited, but is generally circular (approximately circular). The top diameter of the via holes is preferably 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less, and the lower limit may be, for example, 3 μm or more, 5 μm or more, 10 μm or more, etc. Here, the top diameter of the via hole refers to the diameter of the opening of the via hole on the insulating layer surface (the insulating layer surface derived from the first resin composition layer).

By using the multilayer resin sheet of the present invention, it is possible to form via holes with a good cross-sectional shape that exhibits little dimensional change in the thickness direction of the insulating layer. In one embodiment, when the cross-section of a via hole is observed, if R1 is the maximum via diameter (μm) in the insulating layer portion derived from the first resin composition layer, and R2 is the maximum via diameter (μm) in the insulating layer portion derived from layers other than the first resin composition layer, then the relationship R1 ≥ R2 is satisfied. In a preferred embodiment, R1 and R2 satisfy the relationship R1 ≥ R2, as well as the relationship (R1 - R2) ≤ 0.1R1.

After forming via holes in the insulating layer with a laser, a desmear treatment is performed. This removes resin residue (smear) from within the via holes. The procedure and conditions for the desmear treatment are not particularly limited, and known procedures and conditions commonly used when forming the insulating layer of a printed circuit board can be adopted. For example, the desmear treatment can be performed by carrying out swelling treatment with a swelling solution, desmear (roughening) treatment with an oxidizing agent solution, and neutralization treatment with a neutralizing solution in this order.

The swelling solution used for desmear treatment is not particularly limited, but examples include alkaline solutions and surfactant solutions, and is preferably an alkaline solution, with sodium hydroxide solution and potassium hydroxide solution being more preferred. Examples of commercially available swelling solutions include "Swelling Dip Securigant P" and "Swelling Dip Securigant SBU" manufactured by Atotec Japan. The swelling treatment with the swelling solution is not particularly limited, but can be carried out, for example, by immersing the insulating layer in a swelling solution at 30°C to 90°C for 1 to 20 minutes. From the viewpoint of suppressing the swelling of the resin of the insulating layer to an appropriate level, it is preferable to immerse the insulating layer in a swelling solution at 40°C to 80°C for 5 to 15 minutes.

The oxidizing agent solution used for desmearing is not particularly limited, but examples include an alkaline permanganate solution obtained by dissolving potassium permanganate or sodium permanganate in an aqueous solution of sodium hydroxide. The roughening treatment with an oxidizing agent solution such as an alkaline permanganate solution is preferably carried out by immersing the insulating layer in the oxidizing agent solution heated to 60°C to 100°C for 10 to 30 minutes. Furthermore, the concentration of permanganate in the alkaline permanganate solution is preferably 5% to 10% by mass. Examples of commercially available oxidizing agents include alkaline permanganate solutions such as "Concentrate Compact CP" and "Dosing Solution Securigans P" manufactured by Atotec Japan.

Furthermore, an acidic aqueous solution is preferred as the neutralizing solution used in desmear treatment. A commercially available example is "Reduction Securigant P" manufactured by Attec Japan. Neutralization treatment with a neutralizing solution can be performed by immersing the treated surface, which has been roughened with an oxidizing agent, in a neutralizing solution at 30°C to 80°C for 5 to 30 minutes. From the viewpoint of workability, it is preferable to immerse the object that has been roughened with an oxidizing agent in a neutralizing solution at 40°C to 70°C for 5 to 20 minutes.

Here, when desmearing is performed after peeling off the support, the desmearing process also serves as a roughening treatment for the exposed surface of the insulating layer. As mentioned above, the multilayer resin sheet of the present invention is advantageous because, even when desmearing is performed after peeling off the support, it is possible to obtain an insulating layer with good surface smoothness, reduced smearing, and well-shaped via holes. Therefore, in one embodiment, desmearing is performed after peeling off the support. In a preferred embodiment, step (III) is the step of forming via holes in the insulating layer with a laser, peeling off the support, and then performing desmearing.

-Process (IV)-
After the desmear treatment in step (III), a metal film is formed on the surface of the insulating layer in step (IV). The formed metal film can be used as a plating seed layer to form wiring.

The thickness of the metal film (plating seed layer) is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less. After forming a conductor layer on the metal film in a desired pattern, any unnecessary portions other than the conductor layer formation area are removed by etching or the like. At this time, the smaller the thickness of the metal film, the easier it is to remove the unnecessary portions of the metal film, and the less erosion of the conductor pattern is minimized when removing the unnecessary portions, which is advantageous for realizing fine wiring.

In this regard, when a thin metal film is formed on the surface of an insulating layer, variations in the thickness of the conductive layer formed on the metal film by electroplating tend to occur, a phenomenon known as "plating burn." This is presumed to be due to the unevenness of the insulating layer surface, which easily leads to uneven thickness of the metal film. More specifically, the electrical resistance of the thin metal film is higher than that of the thick metal film. When a conductive layer is formed on top of this using electroplating, the plating growth is slower in the areas with thin metal films and high electrical resistance compared to other areas, resulting in insufficient formation of the conductive layer and making it difficult to form a uniform conductive layer.

In contrast, by using the present invention in a multilayer resin sheet, it is possible to form an insulating layer with good surface smoothness, and even if the thickness of the metal film is reduced, plating burn can be suppressed. For example, the thickness of the metal film may be reduced to 280 nm or less, 260 nm or less, or 250 nm or less.

The metal film (plating seed layer) includes at least a conductive seed layer. The conductive seed layer is a layer that functions as an electrode in the electroplating method. The conductive material constituting the conductive seed layer is not particularly limited as long as it exhibits sufficient conductivity, but preferred examples include copper, palladium, gold, platinum, silver, aluminum, and their alloys. The metal film may also include a diffusion barrier layer. The diffusion barrier layer is a layer that prevents the conductive material constituting the conductive seed layer from diffusing into the insulating layer and causing dielectric breakdown. The material constituting the diffusion barrier layer is not particularly limited as long as it can suppress or prevent the diffusion of the conductive material constituting the conductive seed layer, but preferred examples include titanium, tungsten, tantalum, and their alloys. When the metal film includes a diffusion barrier layer, the "thickness of the metal film" in this invention refers to the average thickness of the entire metal film, including not only the conductive seed layer but also the diffusion barrier layer.

When the metal film includes a diffusion barrier layer, the thickness of the diffusion barrier layer is not particularly limited as long as it can suppress and prevent the diffusion of the conductive material constituting the conductive seed layer. However, from the viewpoint of contributing to fine wiring, it is preferably 50 nm or less, more preferably 40 nm or less, and even more preferably 30 nm or less. The lower limit of the thickness of the diffusion barrier layer is not particularly limited and can be, for example, 1 nm or more, 3 nm or more, 5 nm or more, etc. In this case, the remainder of the metal film is preferably a conductive seed layer, and the thickness of the conductive seed layer may be determined in relation to the thickness of the diffusion barrier layer so that the overall thickness of the metal film falls within the above preferred range.

The metal film may be formed by dry plating or by wet plating. Examples of dry plating include physical vapor deposition (PVD) methods such as sputtering, ion plating, and vacuum deposition, and chemical vapor deposition (CVD) methods such as thermal CVD and plasma CVD. Examples of wet plating include electroless plating. From the viewpoint of easily forming a thin metal film with a more uniform thickness, sputtering or electroless plating is preferred, and among these, sputtering is particularly preferred from the viewpoint of realizing fine wiring with excellent adhesion strength. Therefore, in one preferred embodiment, the metal film is formed by sputtering in step (IV).

After step (IV), a conductive layer can be formed on the metal film by electroplating. Therefore, in one embodiment, the method for manufacturing a printed circuit board of the present invention includes, as step (V), a step of forming a conductive layer on the metal film by electroplating.

The conductive material used in the conductive layer is not particularly limited. In a preferred embodiment, the conductive layer contains one or more metals selected from the group consisting of gold, platinum, palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel, titanium, tungsten, iron, tin, and indium. The conductive layer may be a single-metal layer or an alloy layer. Examples of alloy layers include layers formed from alloys of two or more metals selected from the above group (e.g., nickel-chromium alloy, copper-nickel alloy, and copper-titanium alloy). Among these, from the viewpoint of versatility in conductive layer formation, cost, and ease of patterning, single-metal layers of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or alloy layers of nickel-chromium alloy, copper-nickel alloy, or copper-titanium alloy are preferred, single-metal layers of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or alloy layers of nickel-chromium alloy are more preferred, and single-metal layers of copper are even more preferred.

The conductive layer may be a single-layer structure, or it may be a multi-layer structure in which two or more single-metal layers or alloy layers made of different types of metals or alloys are laminated. When the conductive layer is a multi-layer structure, the layer in contact with the insulating layer is preferably a single-metal layer of chromium, zinc, or titanium, or an alloy layer of nickel-chromium alloy.

The thickness of the conductor layer depends on the desired printed circuit board design, but is generally 3 μm to 35 μm, preferably 5 μm to 30 μm.

The conductive layer may be formed by a so-called semi-additive method. Specifically, a photoresist (plating resist) is formed on the metal film formed in step (IV), exposing a portion of the metal film corresponding to the desired wiring pattern. Next, a conductive layer is formed on the exposed metal film by electroplating, and then the photoresist is removed. Afterward, unnecessary metal films other than the conductive layer formation area are removed by etching or other means to form a conductive layer (wiring) with the desired wiring pattern.

By using the multilayer resin sheet of the present invention, it is possible to form fine conductor circuits with L/S ratios of, for example, 5/5 μm or less, 4/4 μm or less, 3/3 μm or less, 2/2 μm or less, 1.5/1.5 μm or less, or 1/1 μm or less, while suppressing plating burn.

If necessary, the formation of the insulating layer and conductor layer in steps (I) to (V) may be repeated to form a multilayer wiring board.

[Semiconductor Chip Packages]
A semiconductor chip package can be manufactured using the multilayer resin sheet of the present invention. The present invention also provides such a semiconductor chip package. The semiconductor chip package of the present invention includes an insulating layer (redistribution-forming layer) for forming a redistribution layer, which is made of a cured product of the multilayer resin sheet of the present invention.

A semiconductor chip package can be manufactured, for example, using the multilayer resin sheet of the present invention by a method including the following steps (1) to (6). The multilayer resin sheet of the present invention may be used to form the redistribution layer in step (5). An example of forming a redistribution layer using the multilayer resin sheet is shown below, but the technique for forming a redistribution layer in a semiconductor chip package is well known, and those skilled in the art can manufacture a semiconductor package using the multilayer resin sheet of the present invention in accordance with known techniques.
(1) A step of laminating a temporary fixing film onto the substrate,
(2) A step of temporarily fixing the semiconductor chip onto a temporary fixing film,
(3) A step of forming a sealing layer on a semiconductor chip,
(4) Steps to peel off the substrate and temporary fixing film from the semiconductor chip,
(5) A step of forming a redistribution layer as an insulating layer on the surface from which the substrate and temporary fixing film of the semiconductor chip have been peeled off, and (6) A step of forming a redistribution layer as a conductive layer on the redistribution layer.

-Process (1)-
The material used for the substrate is not particularly limited. Examples of substrates include silicon wafers, glass wafers, glass substrates, metal substrates such as copper, titanium, stainless steel, and cold-rolled steel sheets (SPCC), substrates made by impregnating glass fibers with epoxy resin and heat-curing treatment (e.g., FR-4 substrates), and substrates made of bismaleimidotriazine resin (BT resin).

The temporary fixing film is not limited in material as long as it can be peeled off from the semiconductor chip in step (4) and temporarily fix the semiconductor chip. Commercially available temporary fixing films can be used. Examples of commercially available products include Riva Alpha manufactured by Nitto Denko Corporation.

-Process (2)-
Temporary fixing of semiconductor chips can be performed using known devices such as flip-chip bonders and die bonders. The layout and number of semiconductor chips can be appropriately set according to the shape and size of the temporary fixing film, the number of semiconductor packages to be produced, etc. For example, they can be temporarily fixed in a matrix arrangement with multiple rows and multiple columns.

-Process (3)-
A sealing resin sheet, which has a sealing resin composition layer provided on a support, is laminated onto a semiconductor chip, or a sealing resin composition is applied onto a semiconductor chip and cured (e.g., by thermal curing) to form a sealing layer.

For example, lamination of a semiconductor chip and a sealing resin sheet can be performed by heating and pressing the sealing resin sheet onto the semiconductor chip from the support side. Lamination of the semiconductor chip and the sealing resin sheet may also be carried out by a vacuum lamination method, and the lamination conditions are the same as those described in relation to the manufacturing method of a printed circuit board, and the preferred range is also the same.

After lamination, the sealing resin composition layer is heat-cured to form a sealing layer. The heat-curing conditions are the same as those described in relation to the manufacturing method of printed circuit boards.

The support for the encapsulating resin sheet may be peeled off after the encapsulating resin sheet has been laminated onto the semiconductor chip and heat-cured, or the support may be peeled off before the encapsulating resin sheet has been laminated onto the semiconductor chip.

When applying the sealing resin composition to form a sealing layer, the application conditions are the same as those for forming the resin composition layer described in relation to the method for manufacturing a multilayer resin sheet of the present invention, and the preferred range is also the same.

-Process (4)-
The method for peeling off the substrate and the temporary fixing film can be appropriately changed depending on the material of the temporary fixing film, etc. Examples include a method of peeling off the temporary fixing film by heating and foaming (or expanding) it, and a method of peeling off the temporary fixing film by irradiating it with ultraviolet light from the substrate side to reduce the adhesive strength of the temporary fixing film.

In the method of peeling off a temporary fixing film by heating and foaming (or expanding) it, the heating conditions are usually 100 to 250°C for 1 to 90 seconds or 5 to 15 minutes. In the method of peeling off a temporary fixing film by irradiating it with ultraviolet light from the substrate side to reduce its adhesive strength, the amount of ultraviolet light irradiated is usually 10 mJ/ ^cm² to 1000 mJ/ ^cm² .

-Process (5)-
The material used to form the rewiring layer (insulating layer) is not particularly limited as long as it has insulating properties when the rewiring layer (insulating layer) is formed, and the rewiring layer can be formed using the multilayer resin sheet of the present invention. In step (5), the multilayer resin sheet of the present invention is laminated such that the surface opposite to the first resin composition layer is bonded to the surface of the semiconductor chip from which the substrate and temporary fixing film have been peeled off. The multilayer resin sheet is then cured to form the rewiring layer.

After forming the redistribution layer, via holes may be formed in the redistribution layer to interlayer connect the semiconductor chip and the conductor layer described later. The via holes may be formed by known methods depending on the material of the redistribution layer.

-Process (6)-
The formation of the conductor layer on the rewiring layer may be carried out in the same manner as in step (V) described in relation to the manufacturing method of a printed circuit board. Alternatively, steps (5) and (6) may be repeated to alternately stack the conductor layer (rewiring layer) and the rewiring layer (insulating layer) (build-up).

In manufacturing a semiconductor chip package, the following steps may be further performed: (7) forming a solder resist layer on a conductor layer (redistribution layer), (8) forming bumps, and (9) dicing multiple semiconductor chip packages into individual semiconductor chip packages. These steps may be carried out according to various methods known to those skilled in the art for the manufacture of semiconductor chip packages.

By forming a redistribution layer using the multilayer resin sheet of the present invention, a semiconductor chip package can be realized regardless of whether the semiconductor package is a fan-in type package or a fan-out type package. Furthermore, the multilayer resin sheet of the present invention can be applied to both fan-out type panel-level packages (FO-PLP) and fan-out type wafer-level packages (FO-WLP).

[Semiconductor equipment]
The semiconductor device of the present invention includes a layer made of a cured multilayer resin sheet of the present invention. The semiconductor device of the present invention can be manufactured using the printed circuit board or semiconductor chip package of the present invention.

Examples of semiconductor devices include various types of semiconductor devices used in electrical products (e.g., computers, mobile phones, digital cameras, and televisions) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft).

The present invention will be specifically described below with reference to examples and comparative examples. The present invention is not limited to the following examples.

(thermosetting resin)
(1) Biphenyl-type epoxy resin (NC-3000, manufactured by Nippon Kayaku Co., Ltd.)
(2) Biphenyl-type epoxy resin (NC-3000-H manufactured by Nippon Kayaku Co., Ltd.)
(3) p-aminophenol type epoxy resin (Mitsubishi Chemical Corporation's "630")
(4) Dicyclopentadiene type epoxy resin (DIC Corporation's "HP-7200")

(Hardening agent)
(1) Aminotriazine skeleton cresol novolac resin-containing liquid (DIC Corporation's "LA-3018-50P", containing 50% by mass of non-volatile components and 50% by mass of propylene glycol monoethyl ether)
(2) Triazine skeleton phenol novolac resin-containing liquid (DIC Corporation's "LA-7054", containing 60% by mass of non-volatile components and 40% by mass of methyl ethyl ketone)
(3) Active ester resin-containing liquid (DIC Corporation's "HPC-8000-65T", containing 65% by mass of non-volatile components and 35% by mass of toluene)

(Curing accelerator)
(1) Imidazole compound (2-phenyl-4-methylimidazole, "2P4MZ" manufactured by Shikoku Chemicals Co., Ltd.)

(thermoplastic resin)
(1) Phenoxy resin-containing liquid (YX6954BH30 manufactured by Mitsubishi Chemical Corporation, containing 30% by mass of non-volatile components, 35% by mass of methyl ethyl ketone, and 35% by mass of cyclohexanone)
(2) Polyimide resin 1 (Polyimide resin synthesized in Synthesis Example 1 below, 20% by mass of non-volatile components)

(Radical polymerizable resin)
Maleimide resin 1 (SLK6895-T90, an aliphatic skeleton-containing maleimide resin having a structure represented by the following formula (which may include some unsaturated bonds), 90% by mass of nonvolatile components and 10% by mass of toluene)

(Inorganic filler)
(1) Silica 1 (Spherical silica with an average particle size of 1.0 μm, obtained by surface-treating 100 parts by mass of "SO-C4" manufactured by Admatex Co., Ltd. with 0.4 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.))
(2) Silica 2 (Spherical silica with an average particle size of 0.5 μm, obtained by surface-treating 100 parts by mass of "SO-C2" manufactured by Admatex Co., Ltd. with 0.6 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.))
(3) Silica 3 (Spherical silica with an average particle size of 0.10 μm, obtained by surface-treating 100 parts by mass of "YC100C" manufactured by Admatex Co., Ltd. with 3.0 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.))

(solvent)
(1) Solvent (MEK, methyl ethyl ketone, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

(Synthesis Example 1: Polyimide Resin 1)
A monomer composition was obtained by mixing 49.6 g of 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (hereinafter also referred to as "BPADA"), 50.4 g of 4,4'-[1,4-phenylenebis[(1-methylethylidene)-4,1-phenyleneoxy]]bisbenzeneamine (hereinafter also referred to as "BPPAN"), and 40 g of toluene as a solvent in 400 g of N,N-dimethylacetamide (hereinafter also referred to as "DMAc") as a solvent. The mixture was stirred and reacted at room temperature and atmospheric pressure for 3 hours. This yielded a polyamic acid solution.

Subsequently, the polyamic acid solution was heated, and while maintaining the temperature at approximately 160°C, the condensed water was azeotropically removed with toluene under a nitrogen stream. It was confirmed that a predetermined amount of water had accumulated in the moisture meter and that no further water leakage was observed. After confirmation, the reaction solution was further heated and stirred at 200°C for 1 hour. After that, it was cooled. This yielded a varnish containing 20% by mass of polyimide resin (hereinafter also referred to as "polyimide resin 1") as a non-volatile component.

From the above reaction pathway, it was estimated that polyimide resin 1 contains a structural unit represented by the following formula (C1a). Furthermore, from the above reaction pathway, it was estimated that polyimide resin 1 contains a first skeleton derived from BPADA and a second skeleton derived from BPPAN.

Furthermore, the glass transition temperature Tg (TMA method) of polyimide resin 1 was 210°C. Tg was measured using a Rigaku TMA apparatus at a heating rate of 5°C/min from 25°C to 250°C.

(Example 1)
25 parts by mass of biphenyl-type epoxy resin (NC-3000, manufactured by Nippon Kayaku Co., Ltd.), 2 parts by mass of bisphenol-type epoxy resin (ZX1059, manufactured by Nippon Steel Chemical & Material Co., Ltd.), 7 parts by mass of dicyclopentadiene-type epoxy resin (HP-7200, manufactured by DIC Corporation), 5 parts by mass of aminotriazine skeleton cresol novolac resin-containing solution (LA-3018-50P, manufactured by DIC Corporation) (2.5 parts by mass of non-volatile components), and active ester resin-containing solution (HPC-8000-65T, manufactured by DIC Corporation). 200 parts by mass of (130 parts by mass of non-volatile components), 10 parts by mass of imidazole compound (2P4MZ manufactured by Shikoku Chemicals Co., Ltd.), 10 parts by mass of phenoxy resin-containing liquid (YX6954BH30 manufactured by Mitsubishi Chemical Corporation) (3 parts by mass of non-volatile components), 15 parts by mass of maleimide resin (13.5 parts by mass of non-volatile components), 5 parts by mass of polyimide resin 1 (1 part by mass of non-volatile components), and 125 parts by mass of methyl ethyl ketone (MEK) were mixed and stirred at room temperature until a homogeneous solution was obtained to obtain resin composition varnish A.

Formation of the outer layer (first resin composition layer; the layer that becomes the outer layer after lamination):
To the obtained resin composition varnish A, 130 parts by mass of silica 3 (spherical silica obtained by surface-treating 100 parts by mass of "YC100C" manufactured by Admatex Co., Ltd. with 3.0 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.)) was mixed and stirred at room temperature until a homogeneous solution was obtained to obtain resin composition varnish B.

Using an applicator, the resin composition varnish B obtained was applied to the release surface of a PET film (38 μm thick), and then dried in a gear oven at 170°C for 180 seconds to evaporate the solvent. In this way, a sheet-like molded body A (outer layer; first resin composition layer) with a thickness of 2 μm was obtained on the PET film.

Formation of the inner layer (the layer excluding the first resin composition layer; the layer that becomes the inner layer after lamination): Formation method 1
- Lamination by coating: 20 parts by mass of biphenyl-type epoxy resin (NC-3000, manufactured by Nippon Kayaku Co., Ltd.), 3 parts of bisphenol-type epoxy resin (ZX1059, manufactured by Nippon Steel Chemical & Material Co., Ltd.), 10 parts by mass of dicyclopentadiene-type epoxy resin (HP-7200, manufactured by DIC Corporation), 15 parts by mass of aminotriazine skeleton cresol novolac resin-containing liquid (LA-3018-50P, manufactured by DIC Corporation) (7.5 parts by mass of non-volatile components), active ester resin-containing liquid (DIC 80 parts by mass of "HPC-8000-65T" manufactured by the company (52 parts non-volatile components), 2 parts by mass of imidazole compound ("2P4MZ" manufactured by Shikoku Chemicals Co., Ltd.), 5 parts by mass of phenoxy resin-containing liquid ("YX6954BH30" manufactured by Mitsubishi Chemical Corporation) (1.5 parts by mass non-volatile components), 5 parts by mass of polyimide resin 1 (1 part by mass non-volatile components), and 200 parts by mass of methyl ethyl ketone (MEK) were mixed and stirred at room temperature until a homogeneous solution was obtained to obtain resin composition varnish C.

To the obtained resin composition varnish C, 290 parts by mass of silica 2 (spherical silica obtained by surface-treating 100 parts by mass of "SO-C2" manufactured by Admatex Co., Ltd. with 0.6 parts by mass of a silane coupling agent having an N-phenyl-3-aminopropyl group ("KBM-573" manufactured by Shin-Etsu Chemical Co., Ltd.)) was mixed and stirred at room temperature until a homogeneous solution was obtained to obtain resin composition varnish D.

Next, the obtained resin composition varnish D was applied to the obtained sheet-like molded body A to a total thickness of 40 μm, and then dried in a gear oven at 100°C for 2 minutes to evaporate the solvent. In this way, a sheet-like molded body C (inner layer; layer excluding the first resin composition layer) with a thickness of 38 μm was formed on the sheet-like molded body A, and a multilayer resin sheet B with a thickness of 40 μm was obtained. The multilayer resin sheet B has a layer structure of sheet-like molded body C / sheet-like molded body A / support.

[Fabrication of evaluation boards]
(1) Preparation of inner layer substrate A glass cloth substrate epoxy resin double-sided laminate (copper foil thickness 18 μm, substrate thickness 0.3 mm, size 500 mm x 500 mm, Panasonic "R5715ES") on which the inner layer circuit was formed was etched on both sides to create 25 copper patterns with an L/S ratio of 1 mm/1 mm and a length of 5 cm, thereby obtaining a textured substrate. Subsequently, the copper surface was roughened by etching to 1 μm using MEC "CZ8100".

(2) Lamination of multilayer resin sheet onto inner layer substrate The obtained multilayer resin sheet B was placed on the substrate surface from the sheet-like molded body C side and laminated on both sides of the inner layer circuit board using a batch-type vacuum pressure laminator (Nichigo Morton 2-stage build-up laminator CVP700) so that the sheet-like molded body C was in contact with the inner layer circuit board. Lamination was carried out by reducing the pressure to 13 hPa or less for 30 seconds, and then pressing at 100°C and a pressure of 0.74 MPa for 30 seconds. Next, a hot press was performed at 100°C and a pressure of 0.5 MPa for 60 seconds.

(3) Curing of multilayer resin sheets The multilayer resin sheets with laminated supports were heated at 100°C for 30 minutes, and then at 170°C for 30 minutes to heat-cur the multilayer resin sheets and form an insulating layer. The resulting laminated sample is referred to as "Laminated Sample D".

(4) Formation of via holes A via hole was formed in the insulating layer by drilling holes in the laminated sample D using a _CO2 laser processing machine "LC-2E21B/1C" manufactured by Hitachi Via Mechanics Co., Ltd. The top diameter (diameter) of the via hole on the insulating layer surface was 50 μm. The drilling conditions were a mask diameter of 1.60 mm, a focus offset value of 0.050, a pulse width of 25 μs, an energy of 0.33 mJ/shot (output 0.66 W, frequency 2000 Hz), an aperture of 13, a number of shots of 2, and burst mode.
Next, the support was removed from the via-formed laminated sample D.

(5) Desmear treatment Desmear treatment was performed on the via-formed laminated sample D according to the following procedure.

Swelling treatment:
The via-formed laminated sample D was placed in a 60°C swelling solution (Atotec Japan's "Swelling Dip Securigant P," an aqueous solution of diethylene glycol monobutyl ether and sodium hydroxide) and agitated at a swelling temperature of 60°C for 10 minutes. Afterwards, it was washed with pure water.

Roughening treatment:
The swollen laminated sample was placed in an oxidizing agent solution at 80°C (Atotec Japan's "Concentrate Compact CP," an aqueous solution with approximately 6% potassium permanganate and approximately 4% sodium hydroxide) and agitated at a roughening temperature of 80°C for 20 minutes.

Neutralization treatment:
Subsequently, the sample was washed for 10 minutes with a neutralizing solution at 40°C (Reduction Securigant P, manufactured by Atotech Japan, an aqueous sulfuric acid solution), and then further washed with pure water. The resulting laminated sample is referred to as "Laminated Sample E".

[Measurement of surface roughness]
For layered sample E, the Ra value was determined using a non-contact surface roughness meter (WYKO NT3300, manufactured by B-In Instruments) in VSI mode with a 50x lens, measuring a range of 121 μm × 92 μm. The measured value was obtained by calculating the average of 10 randomly selected points. Surface roughness was judged based on the arithmetic mean roughness (Ra) value according to the following criteria.

Criteria for determining arithmetic mean roughness (Ra):
◎: Arithmetic mean roughness (Ra) is less than 30 nm ○: Arithmetic mean roughness (Ra) is 30 nm or more and less than 50 nm ×: Arithmetic mean roughness (Ra) is 50 nm or more

[Measurement of etching rate]
Using an applicator, the obtained resin composition varnish B was applied to the release surface of a PET film (thickness 38 μm), and then dried in a gear oven at 100°C for 2 minutes to evaporate the solvent. In this way, a sheet-like molded body A' with a thickness of 38 μm was obtained on the PET film. Separately, a sheet-like molded body C' with a thickness of 38 μm was obtained on the PET film in the same manner, except that resin composition varnish D was used.
Next, sheet-like molded bodies A' and C' were heated at 100°C for 30 minutes, and then at 170°C for 30 minutes, respectively, to obtain cured bodies A' and C'.
The masses of the obtained hardened bodies A' and C' were measured, respectively.

Next, the obtained hardened bodies A' and C' were subjected to swelling, roughening, and neutralization treatments in the same manner as described in "(5) Desmear Treatment" above, and then desmear treatment was carried out. Thus, desmeared hardened bodies A'' and C'' were obtained.
The masses of hardened bodies A'' and C'' after desmear treatment were measured.

Using the masses of the obtained cured bodies A', C', A'', and C'', the etching rate RA of the cured material of the first resin composition layer due to desmear treatment and the etching rate RD of the cured material of the outermost resin composition layer opposite the first resin composition layer due to desmear treatment were calculated based on the following formula.

Etching rate RA = 100 × (mass of A' - mass of A'') / mass of A' Etching rate RD = 100 × (mass of C' - mass of C'') / mass of C'

<Evaluation of smear removal ability>
The area around the bottom of the via hole was observed using a scanning electron microscope (SEM), and the maximum smear length from the wall surface of the via hole bottom was measured from the obtained images. Smear removal performance was evaluated according to the following criteria.
Evaluation criteria:
○: Maximum smear length is less than 2 μm ×: Maximum smear length is 2 μm or more

<Evaluation of the cross-sectional shape of a beer hall>
The diameter portion of the via hole was cut out in cross-section using a FIB (Fibrillation Isolation Bomb), observed with a scanning electron microscope (SEM), and the maximum via diameter R1 in the insulating layer portion derived from the first resin composition layer and the maximum via diameter R2 in the insulating layer portion derived from the layers excluding the first resin composition layer were measured from the obtained images. The cross-sectional shape of the via hole was evaluated according to the following criteria.

Evaluation criteria:
○: R1 ≥ R2
X: R1 < R2

<Evaluation of film thickness change before and after desmear treatment>
Cross-sections were taken from laminated sample D (after thermosetting) and laminated sample E (after desmearing) using FIB, and the insulating layer was observed using a scanning electron microscope (SEM). The thickness of the insulating layer portion originating from the first resin composition layer was measured from the obtained images. Based on the difference in thickness between the insulating layer portion originating from the first resin composition layer in laminated sample D and the insulating layer portion originating from the first resin composition layer in laminated sample E, the following criteria were used for evaluation.

Evaluation criteria:
◎: Thickness difference is less than 0.5 μm ○: Thickness difference is 0.5 μm or more, but less than 1.0 μm ×: Thickness difference is 1.0 μm or more

(Example 2)
A sample was prepared and evaluated in the same manner as in Example 1, except that the method for forming the inner layer was changed to the following formation method 2, and the resulting multilayer resin sheet B' was used.

Formation of the inner layer: Formation method 2 - Lamination by lamination Using an applicator, the obtained resin composition varnish D was applied to the release surface of a PET film (thickness 38 μm), and then dried in a gear oven at 100°C for 2 minutes to evaporate the solvent. In this way, a sheet-like molded body C with a thickness of 38 μm was obtained on the PET film.

Sheet-shaped molded body A and sheet-shaped molded body C were laminated together using a vacuum pressure laminator (MVLP-500, manufactured by Meiki Seisakusho Co., Ltd.) at a pressure of 0.4 MPa and a temperature of 100°C for 60 seconds, with their coated surfaces overlapping, to obtain a multilayer resin sheet B'.

(Examples 3-5 and Comparative Examples 1-3)
Samples were prepared and evaluated in the same manner as in Example 1, except that the formulations of the outer and inner layers were changed as shown in Table 1.

Claims (11)

A multilayer resin sheet comprising two or more resin composition layers, each consisting of a first resin composition layer which is the outermost layer and layers other than the first resin composition layer,
When the etching rate of the cured product of the first resin composition layer by desmear treatment is denoted as RA, and the etching rate of the cured product of the outermost resin composition layer on the opposite side of the first resin composition layer by desmear treatment is denoted as RD, then RD/RA is 5 or more and less than 100.
The etching rate RA is 0.1% or more and less than 1%.
The etching rate RD is between 0.5% and 20%.
When the thickness of the multilayer resin sheet (μm) is T and the thickness of the first resin composition layer (μm) is t, then t ≤ 0.2T.
A multilayer resin sheet in which the arithmetic mean roughness Ra of the cured product of the first resin composition layer after desmear treatment is less than 50 nm. The multilayer resin sheet according to claim 1, wherein when D1 is the average particle size (μm) of the inorganic filler in the first resin composition layer and D2 is the average particle size (μm) of the inorganic filler in the layers excluding the first resin composition layer, D1 < D2. The multilayer resin sheet according to claim 1, wherein the content of inorganic filler in the first resin composition layer is 5% by mass or less, when the non-volatile components in the first resin composition layer are taken as 100% by mass. The multilayer resin sheet according to claim 1, wherein the etching rate RA is 0.1% or more and 0.5% or less . A multilayer resin sheet according to claim 1, wherein the RD/RA is 10 or more and less than 100 . The multilayer resin sheet according to claim 1, which is used by laminating it onto a target member such that the surface opposite to the first resin composition layer is bonded to the target member. A multilayer resin sheet according to claim 1, for use as an insulating layer in a printed circuit board. A multilayer resin sheet with a support, comprising a multilayer resin sheet according to any one of claims 1 to 7, and a support bonded to the first resin composition layer of the multilayer resin sheet. A method for manufacturing a printed circuit board, comprising the following steps (I) to (IV).
(I) Laminating a multilayer resin sheet according to any one of claims 1 to 7 onto an inner layer substrate such that the surface of the multilayer resin sheet opposite to the first resin composition layer is bonded to the inner layer substrate; (II) Curing the multilayer resin sheet to form an insulating layer; (III) Forming via holes in the insulating layer with a laser and performing desmear treatment; (IV) Forming a metal film on the surface of the insulating layer after desmear treatment. A printed circuit board comprising an insulating layer made of a cured multilayer resin sheet according to any one of claims 1 to 7. A semiconductor device including the printed circuit board described in claim 10.