JP7737077B2 - Substrate with insulating resin layer, laminate using same, and method for manufacturing laminate - Google Patents

Description

The present invention relates to a substrate with an insulating resin layer, a laminate using the same, and a method for manufacturing the laminate.

In recent years, semiconductor packages, which are widely used in electronic devices, communications equipment, personal computers, and other devices, have become increasingly more functional and compact. Furthermore, with this technological development, there is a demand for thinner printed wiring boards and semiconductor element mounting substrates in semiconductor packages.

One method for manufacturing thin printed wiring boards and semiconductor device mounting substrates has been disclosed (see, for example, Patent Document 1), which involves forming a circuit pattern on a laminate of a highly rigid, thick support substrate (carrier substrate) such as stainless steel, on which a layer of copper that can be peeled off in a subsequent process is formed by pattern plating, laminating an insulating layer such as epoxy resin-coated fiberglass, applying heat and pressure, and finally peeling and removing the support substrate to produce a thin printed wiring board. In this way, by laminating the circuit pattern and insulating material on a highly rigid, thick support substrate, and then finally peeling and removing the support substrate, thin printed wiring boards and semiconductor device mounting substrates can be manufactured even using existing manufacturing equipment.

Resin sheets used in these printed wiring boards are also known to be made of multiple layers of resin compositions. One such technology is an insulating resin sheet in which the amount of etching of each layer is controlled to improve the performance of the multilayered film (see, for example, Patent Document 2).

Special Publication No. 59-500341 Japanese Patent Application Laid-Open No. 2017-50561

The sheet described in Patent Document 2 is intended to solve problems with via shaping using laser processing by adjusting the amount of etching for each layer. However, the sheet requires that the total thickness of each layer be 12 μm or more. Therefore, there is a need to develop technology that can achieve even thinner layers (e.g., less than 10 μm) while still satisfying requirements such as insulation and embeddability of patterned conductor layers (hereinafter sometimes simply referred to as "embedding ability").

In order to solve the above-mentioned problems, the present invention aims to provide a substrate with an insulating resin layer that has excellent insulating properties and embeddability, as well as a laminate and a method for manufacturing the laminate using the same.

That is, the present invention is as follows.
<1> A substrate with an insulating resin layer, comprising: a substrate; a first resin layer provided on the substrate, the first resin layer having a thickness reduction of less than 30% when molded for 60 minutes under conditions of 220°C and a pressure of 3.0 MPa; and a second resin layer provided on the first resin layer.
<2> The substrate with an insulating resin layer according to <1>, wherein the second resin layer has a minimum melt viscosity of 100,000 Pa·s or less.
<3> The substrate with an insulating resin layer according to <1> or <2>, wherein the first resin layer has a thickness of less than 10 μm.
<4> The substrate with an insulating resin layer according to any one of <1> to <3>, wherein the second resin layer has a thickness of 2.0 μm or more.
<5> The substrate with an insulating resin layer according to any one of <1> to <4>, wherein a total thickness of the first resin layer and the second resin layer is 3 μm or more and 20 μm or less.
<6> The substrate with an insulating resin layer according to any one of <1> to <5>, wherein the first resin layer contains at least one selected from the group consisting of polyimide, liquid crystal polyester, epoxy resin, cyanate ester compound, maleimide compound, phenolic resin, thermosetting modified polyphenylene ether resin, benzoxazine compound, organic group-modified silicone compound, and compound having a polymerizable unsaturated group.
<7> The substrate with an insulating resin layer according to any one of <1> to <6>, wherein the second resin layer contains at least one selected from the group consisting of an epoxy resin, a cyanate ester compound, a maleimide compound, a phenolic resin, a thermosetting modified polyphenylene ether resin, a benzoxazine compound, an organic group-modified silicone compound, and a compound having a polymerizable unsaturated group.
<8> The substrate with an insulating resin layer according to any one of <1> to <7>, which is used for producing a coreless substrate to be provided in a printed wiring board or a substrate for mounting a semiconductor element.
<9> The substrate with an insulating resin layer according to <8>, wherein the coreless substrate is a three-layer coreless substrate.
<10> A laminate having a build-up layer in which a conductor layer and an insulating layer formed using the substrate with an insulating resin layer according to any one of <1> to <9> are laminated.
<11> The laminate according to <10>, wherein at least one of the insulating layers has a thickness of 1 μm or more and less than 15 μm.
<12> The laminate according to <10> or <11>, wherein the buildup layer has a plurality of the conductor layers and the insulating layers, and the conductor layers are disposed between the insulating layers and on the surface of the outermost layer of the buildup layer.
<13> The laminate according to any one of <10> to <12>, wherein the conductor layers and the insulating layers are alternately stacked in the build-up layer, and the build-up layer has three or four insulating layers.
<14> The laminate according to any one of <10> to <13>, which is a coreless substrate.
<15> A method for producing a laminate, comprising a step of forming an insulating layer on a surface of a conductor layer using the substrate with an insulating resin layer according to any one of <1> to <9>, thereby forming a build-up layer in which the conductor layer and the insulating layer are laminated.
<16> The method for producing a laminate according to <15>, wherein at least one of the insulating layers has a thickness of 1 μm or more and less than 15 μm.
<17> The method for manufacturing a laminate according to <15> or <16>, wherein the buildup layer has a plurality of the conductor layers and the insulating layers, and the conductor layers are disposed between the insulating layers and on the surface of the outermost layer of the buildup layer.
<18> The method for producing a laminate according to any one of <15> to <17>, wherein the insulating layer has three or four layers.
<19> The method for producing a laminate according to any one of <15> to <18>, wherein the laminate is a coreless substrate.

The present invention provides a substrate with an insulating resin layer that has excellent insulating properties and embeddability, as well as a laminate and a method for manufacturing the laminate using the same.

5A and 5B are schematic diagrams for explaining the amount of reduction in thickness of the first resin layer in the present embodiment. FIG. 2 is a schematic diagram illustrating an example of a multilayer coreless substrate according to the present embodiment.

The following describes in detail a mode for carrying out the present invention (hereinafter simply referred to as the "present embodiment"), with reference to the drawings as necessary. However, the present invention is not limited to the present embodiment. Various modifications of the present invention are possible without departing from the spirit of the present invention. In this specification, a laminate is one in which each layer is adhered to one another, but the layers may be peelable from one another as necessary. In the drawings, identical elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, the positional relationships, such as up, down, left, and right, are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown. In this specification, "(meth)acrylic" means "acrylic" and its corresponding "methacrylic," and "(meth)acrylate" means "acrylate" and its corresponding "methacrylate."

In this embodiment, unless otherwise specified, "resin solids" or "resin solids in an insulating resin layer" refers to the resin contained in the insulating resin layer or resin composition and the components that constitute the resin after curing. Furthermore, "100 parts by mass of resin solids" refers to a total of 100 parts by mass of the resin in the insulating resin layer or resin composition and the components that constitute the resin after curing.

[Substrate with insulating resin layer]
The substrate with an insulating resin layer of this embodiment (hereinafter sometimes simply referred to as a "substrate with a resin layer") comprises a substrate, a first resin layer (hereinafter sometimes simply referred to as a "first resin layer") provided on the substrate, and having a thickness loss of less than 30% when molded for 60 minutes under conditions of 220°C and a pressure of 3.0 MPa, and a second resin layer (hereinafter sometimes simply referred to as a "second resin layer") provided on the first resin layer. Hereinafter, the "thickness loss when molded for 60 minutes under conditions of 220°C and a pressure of 3.0 MPa" will be simply referred to as the "thickness loss." Similarly, the first and second resin layers will be collectively referred to as the "resin layers of this embodiment."

The resin-layered substrate of this embodiment includes a first resin layer with a thickness reduction of less than 30% and a second resin layer. The second resin layer typically contains a resin that exhibits fluidity during press processing, and the layer itself exhibits fluidity during press processing. The second resin layer typically embeds a component that forms a laminate together with the resin-layered substrate from the side that contacts the surface of the second resin layer (hereinafter, this layer may be referred to as the "embedded layer"). Examples of such components include a conductor layer, such as a circuit pattern on a substrate. This conductor layer corresponds to the convex portions of the uneven shape formed together with the substrate, and is embedded in the second resin layer. Furthermore, the first resin layer maintains the distance between the substrate and the second resin layer within a predetermined range even after press processing, such as during laminate formation, in order to maintain insulation between the convex portions embedded in the second resin layer and the substrate (hereinafter, this layer may be referred to as the "thickness-retaining layer"). In other words, the first resin layer separates the substrate and the second resin layer even after press processing. Because the second resin layer functions as a buried layer, it is preferable that the second resin layer differ from the first resin layer in at least one of its constituent components and physical properties. While not particularly limited, examples of the different first and second resin layers include those in which the first and second resin layers have different components, those in which the physical properties of these layers are different, and combinations of these. Examples of the different components of the first and second resin layers include those in which the resin types are different, such as using a polyimide for the first resin layer and an epoxy resin for the second resin layer. Examples of the different physical properties include those in which the compounding ratio of the components contained in each layer or the physical properties such as the thickness reduction amount or minimum melt viscosity are different by adjusting the curing state. To adjust the curing state of the first and second resin layers, for example, by changing the coating conditions of each layer, the first resin layer is completely cured and the second resin layer is semi-cured.

The resin layer-attached substrate of this embodiment is useful, for example, as a material for forming an insulating layer on a conductor layer such as a circuit pattern. Examples of such materials include materials for forming insulating layers on printed wiring boards or semiconductor device mounting substrates used in the manufacture of electronic devices, communication devices, personal computers, etc. For example, when producing a printed wiring board or the like, the resin layer-attached substrate of this embodiment is placed on a substrate on which a conductor layer such as a circuit pattern is formed, with the second resin layer in contact with the conductor layer. The first and second resin layers are then heated and pressed to harden, thereby forming an insulating layer on the conductor layer. During this process, the conductor layer such as the circuit pattern is embedded in the second resin layer. Meanwhile, the thickness of the insulating layer present on the conductor layer is maintained within a predetermined range by the first resin layer. Thus, with the resin layer-attached substrate of this embodiment, the first resin layer can function as a thickness-maintaining layer, and the second resin layer can function as an embedding layer. In particular, in the substrate with a resin layer of this embodiment, the thickness of the first resin layer is reduced by less than 30%, so that the thickness of the insulating layer itself can be maintained within a desired range even after pressing. Furthermore, the fluidity of the second resin layer is improved during pressing, allowing a conductor layer such as a circuit pattern to be embedded while suppressing gaps. As a result, the substrate with a resin layer of this embodiment can maintain the thickness of the insulating layer within a desired range, thereby providing excellent insulation in the thickness direction of the insulating layer and allowing a conductor layer to be embedded in the insulating layer while suppressing gaps.

[Base material]
Examples of the substrate include resin films such as polyethylene terephthalate (PET) film, polyimide film, polyamide film, polyester film, polybutylene terephthalate (PBT) film, polypropylene (PP) film, and polyethylene (PE) film, as well as metal foils such as copper foil, aluminum foil, and gold foil. In this embodiment, a substrate with a release layer, such as a resin film with a release layer or a copper foil with a release layer, may be used. The substrate may be peeled from the first resin layer as needed during laminate formation, and when a metal foil such as copper foil is used, it may be patterned and used as a conductor layer. The release layer may also be, for example, a release layer that is provided on a typical substrate with a release layer.

The substrate in this embodiment is not particularly limited, but is preferably a metal foil, and more preferably a copper foil. The copper foil may be a copper foil or copper film used in ordinary printed wiring boards. Specific examples of copper foil include electrolytic copper foil, rolled copper foil, and copper alloy film. The copper foil or copper film may be subjected to a known surface treatment, such as a matte treatment, a corona treatment, a nickel treatment, or a cobalt treatment. As the copper foil in this embodiment, commercially available products can be used, and examples of commercially available products that can be used include "GHY5" (trade name, 12 μm thick copper foil) manufactured by JX Nippon Mining & Metals Corporation, "3EC-VLP" (trade name, 12 μm thick copper foil), "3EC-III" (trade name, 12 μm thick copper foil), and "3EC-M2S-VLP" (trade name, 12 μm thick copper foil) manufactured by Mitsui Mining & Smelting Co., Ltd., "GTS-MP" (trade name, 12 μm thick copper foil) manufactured by Furukawa Electric Co., Ltd., and "JXUT-I" (trade name, 1.5 μm thick copper foil) manufactured by JX Nippon Mining & Metals Corporation.

The arithmetic mean roughness (Ra) of the copper foil surface is typically preferably 0.05 μm or more and 2 μm or less, and more preferably 0.08 μm or more and 1.7 μm or less, in order to improve the adhesion strength between the copper foil and the resin layer of this embodiment and prevent layer delamination during long-term use. The arithmetic mean roughness (Ra) is particularly preferably 0.2 μm or more and 1.6 μm or less, in order to achieve better adhesion between the copper foil and the resin layer of this embodiment. In this embodiment, a substrate with an insulating resin layer comprising copper foil having an arithmetic mean roughness within the above range can be suitably used in the manufacture of printed wiring boards and semiconductor device mounting substrates with high-density fine wiring. The arithmetic mean roughness can be measured using a commercially available shape measuring microscope (a laser microscope, for example, Keyence Corporation's "VK-X210" (product name)).

The thickness of the substrate in this embodiment is not particularly limited as long as the effects of this embodiment are achieved. For example, from the viewpoint of improving handleability and reducing costs, a thickness of 5 μm to 200 μm is preferred, 10 μm to 150 μm is more preferred, and 15 μm to 80 μm is even more preferred. Furthermore, when a metal foil such as copper foil is used as the substrate, taking into account the roughening treatment of the surface of the metal foil, the thickness is preferably 1 μm to 18 μm. Furthermore, from the viewpoint of being able to suitably obtain thin printed wiring boards and semiconductor element mounting substrates, a thickness of 2 μm to 15 μm is more preferred.

[First Resin Layer]
In this embodiment, the first resin layer has a thickness reduction of less than 30% when molded for 60 minutes under conditions of 220° C. and a pressure of 3.0 MPa.

First, the thickness reduction amount of the first resin layer in this embodiment will be explained using FIG. 1. FIG. 1 is a schematic diagram for explaining the thickness reduction amount of the first resin layer in this embodiment. As shown in FIG. 1A, the substrate 10 with a resin layer comprises a substrate 12, a first resin layer 14A, and a second resin layer 16A laminated in this order. Similarly, as shown in FIG. 1A, the inner circuit board 20 comprises a substrate 22 and multiple conductor layers 24 disposed on the substrate 22, with the conductor layers 24 forming a circuit having a pattern shape. Furthermore, in the substrate 10 with a resin layer, the second resin layer 16A is disposed so as to contact the surface of the inner circuit board 20 on which the conductor layers 24 are disposed, and then the substrate 10 is heated and pressed (pressed). After this pressing, a laminate 30 is formed, as shown in FIG. 1B. The laminate 30 includes an insulating layer 32 formed of a first resin layer 14B and a second resin layer 16B that are formed by curing the first resin layer 14A and the second resin layer 16A, respectively.

Here, the "thickness reduction amount when molded for 60 minutes under conditions of 220 ° C and 3.0 MPa" for the first resin layer is a numerical value indicating the reduction in the thickness of the first resin layer after molding, expressed as a percentage, relative to the thickness of the first resin layer before molding. This thickness reduction amount is calculated from the thickness X of the first resin layer 14A before press processing and the thickness Y of the first resin layer 14B after molding (press processing) for 60 minutes under conditions of 220 ° C and 3.0 MPa. For example, first, the thickness of the first resin layer (thickness X in FIG. 1) is measured from the cross section of the resin layer-attached substrate 10 using a scanning electron microscope (SEM). Next, the laminate 30 is polished to expose a cross section parallel to the lamination to form a sample, and the thickness of the first resin layer (thickness Y in FIG. 1) is measured for the obtained sample using a scanning electron microscope (SEM). After the measurement, the thickness reduction amount can be evaluated by comparing the thickness X of the first resin layer 14A before pressing with the thickness Y of the first resin layer 14B of the laminate 30 after pressing. Specifically, the thickness reduction amount (TΔ) of the first resin layer can be calculated using the following formula (1) from the thickness X of the first resin layer in a base material with a resin layer, for example, in the form of a resin sheet, and the thickness Y of the first resin layer in a laminate, for example, in the form of a copper-clad laminate.
Thickness reduction amount (%) = (X-Y)/X×100 (1)
However, a resin layer made of the same material as the first resin layer 14A may be sandwiched between flat sheets that do not deform under the pressure conditions described below, and then molded (pressed) for 60 minutes under the pressure conditions described above. The thickness reduction amount may then be calculated in the same manner from the thickness of the resin layer before and after the molding (press processing) and the thickness reduction amount may be used as the thickness reduction amount of the first resin layer.

The thickness reduction of the first resin layer is less than 30% from the viewpoint of ensuring insulation. If the thickness reduction of the first resin layer is 30% or more, the thickness of the first resin layer will be reduced too much under press processing conditions, such as molding for 60 minutes under conditions of 220°C and a pressure of 3.0 MPa, and the insulation properties of the insulating layer will be reduced. From the viewpoint of ensuring insulation, the thickness reduction of the first resin layer is preferably less than 28%, preferably 25% or less, preferably less than 20%, more preferably less than 10%, and particularly preferably 0%. Note that there is no particular limit to this thickness reduction, and it may be 0%. The thickness reduction of the first resin layer can be adjusted to the desired value by appropriately selecting the type of thermosetting resin contained therein, controlling the degree of curing of the resin, or adding an inorganic filler.

The thickness of the first resin layer is not particularly limited, but from the perspective of achieving even thinner layers, it is preferably less than 10 μm. Considering the need to ensure even more reliable insulation, the thickness of the first resin layer is more preferably greater than 0.7 μm and less than 9.0 μm, even more preferably 1.0 μm or more and less than 9.0 μm, even more preferably 2.0 μm or more and less than 9.0 μm, even more preferably 2.5 μm or more and less than 9.0 μm, and particularly preferably 3.0 μm or more and less than 9.0 μm. The upper limit of the thickness of the first resin layer may be 7.0 μm, 5.0 μm, or 3.0 μm. The first resin layer may be in a semi-cured state (B-Stage) or a fully cured state (C-Stage).

The minimum melt viscosity of the first resin layer is not particularly limited, as its contribution to solving the problems of the present invention is small. However, from the perspective of improving thickness reduction and insulation properties, the minimum melt viscosity is preferably 10,000 Pa·s or greater, more preferably 100,000 Pa·s to 50,000,000 Pa·s, and particularly preferably 300,000 Pa·s to 50,000,000 Pa·s. In this specification, "minimum melt viscosity" refers to the lowest viscosity measured using a rheometer (viscoelasticity measuring device) under the following conditions: starting temperature 80°C, ending temperature 180°C, heating rate 3°C/min, frequency 10 pts/s, and strain 0.1%. The minimum melt viscosity of the first resin layer can be adjusted to the desired value by appropriately selecting the type of thermosetting resin contained therein, controlling the degree of curing of the resin, or adding an inorganic filler.

From the viewpoint of further improving the manufacturability of the substrate with an insulating resin layer, the elongation percentage of the first resin layer is preferably 1% or more but less than 50%, more preferably 1% or more but less than 40%, and even more preferably 2% or more but less than 30%. In this specification, "elongation percentage" is calculated using a measurement method in accordance with JIS K7113-1.

In this embodiment, the first resin layer can be formed by known methods such as coating using a varnish, which is a solution of a resin composition containing a thermosetting resin. The thermosetting resin is not particularly limited as long as it satisfies the condition that the thickness reduction is less than 30%, and any desired thermosetting resin can be used depending on the desired physical properties. Furthermore, the resin composition may contain inorganic fillers and other additives, as described below, as necessary.

(thermosetting resin)
As described above, the thermosetting resin used in the first resin layer is not particularly limited, but examples thereof include polyimide, liquid crystal polyester, epoxy resin, cyanate ester compound, maleimide compound, phenolic resin, thermosetting modified polyphenylene ether resin, benzoxazine compound, organic group-modified silicone compound, and compound having a polymerizable unsaturated group. These thermosetting resins may be used alone or in combination of two or more.

Among these thermosetting resins, it is preferable for the first resin layer to contain at least one of polyimide and liquid crystal polyester, in order to more reliably keep the thickness reduction to less than 30%. Furthermore, in order to obtain an insulating resin layer with even better peel strength, it is more preferable for the first resin layer to contain at least one of epoxy resin and phenol resin in addition to at least one of polyimide and liquid crystal polyester, and it is even more preferable for the first resin layer to further contain a bismaleimide compound.

-Polyimide-
As the polyimide, commercially available products can be appropriately selected and used. For example, a block copolymer polyimide can be used. Examples of such block copolymer polyimides include the block copolymer polyimides described in International Publication WO 2010-073952. More specifically, the block copolymer polyimide can be a copolymer polyimide having a structure in which Structure A, in which an imide oligomer composed of a first structural unit is bonded to the end of an imide oligomer composed of a second structural unit, and Structure B, in which an imide oligomer composed of the first structural unit is bonded to the end of an imide oligomer composed of the second structural unit, are alternately repeated. Here, the second structural unit is different from the first structural unit.

These block copolymer polyimides can be synthesized by a step-growth polymerization reaction in which a tetracarboxylic dianhydride and a diamine are reacted in a polar solvent to obtain an imide oligomer, and then a tetracarboxylic dianhydride and another diamine, or a different tetracarboxylic dianhydride and a diamine, are added to perform imidization. As an imide oligomer composed of the first structural unit, for example, an imide oligomer having a weight-average molecular weight of approximately 5,000 to 30,000 is preferred. Examples of tetracarboxylic dianhydrides include 3,4,3',4'-biphenyltetracarboxylic dianhydride. Examples of diamines include 1,3-bis(3-aminophenoxy)benzene and 2,2-bis{4-(4-aminophenoxy)phenyl}propane. These may be used alone or in combination.

Examples of polar solvents include polar solvents that dissolve polyimides, such as N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, sulfolane, and tetramethylurea. It is also possible to use a mixture of ketone and ether solvents. Examples of ketone solvents include methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl-n-hexyl ketone, diethyl ketone, diisopropyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, acetylacetone, diacetone alcohol, and cyclohexene-n-one. Examples of ether solvents include dipropyl ether, diisopropyl ether, dibutyl ether, tetrahydrofuran, tetrahydropyran, ethyl isoamyl alcohol, ethyl-t-butyl ether, ethyl benzyl ether, diethylene glycol dimethyl ether, cresyl methyl ether, anisole, and phenetole. These polar solvents may be used alone or in combination of two or more.

A preferred method for removing the water produced during imidization is to add a solvent that forms an azeotrope with water, such as toluene or xylene, to the reaction system and remove the water from the system. Furthermore, to accelerate the reaction, an amine catalyst, such as pyridine, or a two-component catalyst consisting of a base such as pyridine and a cyclic ester such as γ-valerolactone can be used. The imidization reaction temperature is preferably 120°C or higher and 200°C or lower. By finally distilling off the solvent that forms an azeotrope with water, such as toluene or xylene, and the catalyst, such as pyridine, from the system, a polar solvent solution containing only the block copolymer polyimide can be obtained.

The block copolymer polyimide preferably has a structural unit represented by the following formula (A) and a structural unit represented by the following formula (B): where m and n in the formula are positive numbers that fall within the range of the preferred weight-average molecular weight described below.

The tetracarboxylic dianhydride used in the synthesis of block copolymerized polyimides is preferably 3,4,3',4'-biphenyltetracarboxylic dianhydride. The diamines used in the synthesis of block copolymerized polyimides are preferably 1,3-bis(3-aminophenoxy)benzene and 2,2-bis{4-(4-aminophenoxy)phenyl}propane. Furthermore, to control the molecular weight of the blocks of each structural unit, for example, in the first-stage reaction, the molar ratio of tetracarboxylic dianhydride to diamine may be shifted to a higher ratio, thereby leaving an acid anhydride or amine skeleton at the terminal, and in the second-stage reaction, the molar ratio of tetracarboxylic dianhydride to another diamine or another tetracarboxylic dianhydride to diamine may be shifted to the opposite ratio from the first-stage reaction. This makes it possible to obtain block copolymerized polyimides with the desired molecular weight.

Although not particularly limited, the weight-average molecular weight (Mw) of the above-mentioned block copolymer polyimide is preferably 50,000 or more and 300,000 or less, and more preferably 80,000 or more and 200,000 or less. A weight-average molecular weight of 50,000 or more can more effectively prevent the first resin layer from becoming brittle. A weight-average molecular weight of 300,000 or less can more effectively prevent coating difficulties due to increased solution viscosity. In this specification, the weight-average molecular weight is measured by GPC (gel permeation chromatography) using NMP as a solvent and converted into polystyrene.

To control the final molecular weight, it is also possible to synthesize the product by shifting the molar ratio of tetracarboxylic dianhydride to diamine so that one is more abundant than the other. When the block copolymer polyimide has the structural unit represented by formula (A) and the structural unit represented by formula (B), the molar ratio of each structural unit is preferably (structural unit represented by formula (A)):(structural unit represented by formula (B)) = 1:9 to 3:1, and more preferably (structural unit represented by formula (A)):(structural unit represented by formula (B)) = 1:3 to 3:1. When the molar ratio of these structural units is within the above range, deterioration in adhesive strength and solder heat resistance can be more effectively suppressed.

The polyimide used in this embodiment may be, for example, a solvent-soluble polyimide synthesized by the manufacturing method described in JP 2005-15629 A. Specifically, the solvent-soluble polyimide is obtained by polycondensing an aliphatic tetracarboxylic acid dianhydride represented by the following formula (C), and one or more aliphatic tetracarboxylic acids represented by the following formula (D) and derivatives of the aliphatic tetracarboxylic acids (hereinafter collectively referred to as "aliphatic tetracarboxylic acids") with one or more diamines in a solvent in the presence of a tertiary amine:

In formula (C), R is a tetravalent aliphatic hydrocarbon group having 4 to 16 carbon atoms.

In formula (D), R is a tetravalent aliphatic hydrocarbon group having 4 to 16 carbon atoms, and Y ₁ to Y ₄ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 8 carbon atoms.

In this method for producing solvent-soluble polyimides, approximately equimolar amounts of aliphatic tetracarboxylic acids and diamines are heated in a solvent in the presence of a tertiary amine to undergo polycondensation. Furthermore, the molar ratio of aliphatic tetracarboxylic acids to diamines is preferably 100 mol% of one to 95 mol% or more and 105 mol% or less of the other.

In the production of typical polyimides, tetracarboxylic dianhydrides are typically used as the tetracarboxylic acids. However, in the above-mentioned method for producing solvent-soluble polyimides, practical polyimides can be produced using not only aliphatic tetracarboxylic dianhydrides, but also non-anhydride aliphatic tetracarboxylic acids and derivatives such as esters of aliphatic tetracarboxylic acids and alcohols. Using aliphatic tetracarboxylic acids directly is advantageous in terms of production equipment and costs.

Examples of aliphatic tetracarboxylic acid dianhydrides represented by formula (C) include 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,4,5-cyclopentanetetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride. Examples of aliphatic tetracarboxylic acids and derivatives thereof represented by formula (D) include 1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,4,5-cyclopentanetetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid, as well as alcohol esters thereof. These may be used alone or in combination of two or more. Of these, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride and 1,2,4,5-cyclohexanetetracarboxylic acid are preferred.

In the above-mentioned method for producing solvent-soluble polyimide, other tetracarboxylic acids and their derivatives can be mixed and used as long as the solvent solubility is not impaired. Examples of such tetracarboxylic acids and their derivatives include pyromellitic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,3,3',4'-biphenyltetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, 2,2-bis(2,3-dicarboxyphenyl)propane, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane, bis(3,4-dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl)sulfone, and bis(3,4-dicarboxyphenyl)sulfone. Examples of other tetracarboxylic acids and derivatives thereof include bis(2,3-dicarboxyphenyl)ether, bis(2,3-dicarboxyphenyl)ether, 3,3',4,4'-benzophenonetetracarboxylic acid, 2,2',3,3'-benzophenonetetracarboxylic acid, 4,4-(p-phenylenedioxy)diphthalic acid, 4,4-(m-phenylenedioxy)diphthalic acid, ethylenetetracarboxylic acid, 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid, 1,1-bis(2,3-dicarboxyphenyl)ethane, and bis(2,3-dicarboxyphenyl)methane, bis(3,4-dicarboxyphenyl)methane, and derivatives thereof. The proportion of these other tetracarboxylic acids and derivatives thereof in the reaction substrate is preferably less than 50 mol % based on 100 mol % of all tetracarboxylic acids and derivatives thereof in the reaction substrate.

As diamines, aromatic diamines having 6 to 28 carbon atoms and aliphatic diamines having 2 to 28 carbon atoms are preferred. Examples of diamines include p-phenylenediamine, m-phenylenediamine, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-ditrifluoromethylbiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2, Examples of the diamines include aromatic diamines such as 2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(3-aminophenoxy)phenyl]sulfone, and 9,9-bis(4-aminophenyl)fluorene; aliphatic diamines such as ethylenediamine, hexamethylenediamine, polyethylene glycol bis(3-aminopropyl)ether, polypropylene glycol bis(3-aminopropyl)ether, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 4,4'-diaminodicyclohexylmethane, 3(4),8(9)-bis(aminomethyl)-tricyclo[5.2.1.02,6]decane, metaxylylenediamine, paraxylylenediamine, isophoronediamine, and norbornanediamine; and siloxanediamines. These may be used alone or in combination of two or more. Among these diamines, aromatic diamines such as 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-ditrifluoromethylbiphenyl, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane are preferred. Among aliphatic diamines, 4,4'-diaminodicyclohexylmethane and 3(4),8(9)-bis(aminomethyl)-tricyclo[5.2.1.02,6]decane are preferred.

In the above-mentioned method for producing solvent-soluble polyimide, it is preferable to use 0.001 moles or more and 1.0 moles or less of tertiary amine per mole of aliphatic tetracarboxylic acid, and it is more preferable to use 0.01 moles or more and 0.2 moles or less.

Tertiary amines include, for example, trimethylamine, triethylamine, tripropylamine, tributylamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, triethylenediamine, N-methylpyrrolidine, N-ethylpyrrolidine, N-methylpiperidine, N-ethylpiperidine, imidazole, pyridine, quinoline, and isoquinoline. Of these tertiary amines, triethylamine is particularly preferred.

Solvents used in the above-mentioned method for producing solvent-soluble polyimide include, for example, γ-butyrolactone, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, hexamethylphosphoramide, tetramethylene sulfone, p-chlorophenol, m-cresol, and 2-chloro-4-hydroxytoluene. These may be used alone or in combination of two or more. Of these, γ-butyrolactone, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone are preferred, with γ-butyrolactone and N,N-dimethylacetamide being more preferred. A poor solvent for polyimide can also be used in combination to the extent that the polymer does not precipitate. Examples of poor solvents include hexane, heptane, benzene, toluene, xylene, chlorobenzene, and o-dichlorobenzene. The amount of the solvent used is preferably such that the total mass of the aliphatic tetracarboxylic acids and the diamine is 1% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 45% by mass or less, based on the mass of the entire reaction solution.

The method for adding the aliphatic tetracarboxylic acids and diamine is not particularly limited, and examples include adding both components at once, or gradually adding one of the components in solid or solution form to a solution containing the other component (it does not have to be completely dissolved). Adding both components at once is particularly advantageous in terms of productivity, as it shortens the addition time.

In order to maximize its catalytic effect, the tertiary amine is preferably added before the target temperature is reached. It is particularly preferable to add the tertiary amine at the same time as the solvent, aliphatic tetracarboxylic acids, and diamine.

The method for adding the solvent is not particularly limited. Examples include a method in which the solvent is added to the reaction vessel in advance; a method in which the solvent is added to the reaction vessel containing either or both of the aliphatic tetracarboxylic acids and the diamine; and a method in which either the aliphatic tetracarboxylic acids and the diamine are dissolved in the solvent before adding it to the reaction vessel. These methods can be used alone or in combination of two or more. Furthermore, the above-mentioned solvents can be added, depending on the purpose, to the solvent-soluble polyimide solution during the reaction, while it remains in the reaction vessel after the reaction, or after it is removed from the reaction vessel after the reaction.

In this embodiment, when the first resin layer contains polyimide, its content is not particularly limited, but from the viewpoint of improving heat resistance and curing properties, it is preferably 10 parts by mass or more and 90 parts by mass or less, and more preferably 30 parts by mass or more and 80 parts by mass or less, per 100 parts by mass of resin solids in the first resin layer.

- Liquid crystal polyester -
Liquid crystal polyester is an aromatic polyester that exhibits liquid crystallinity when melted. Known liquid crystal polyesters can be appropriately selected and used. Known liquid crystal polyesters include, for example, aromatic polyesters described in JP-A-2001-11296. Specific examples of liquid crystal polyesters include aromatic polyesters containing 90 mol % or more of a structural unit represented by the following formula (E) (hereinafter simply referred to as "structural unit (E)").

From the standpoint of availability, for example, polyoxybenzoate, which is essentially a homopolymer of structural unit (E), can be used as an aromatic polyester containing the structural unit (E). Known methods can be used to manufacture such aromatic polyesters. Note that aromatic polyesters containing the structural unit (E) are often poorly soluble or insoluble in common solvents, and because they are poorly soluble or infusible, they do not exhibit liquid crystallinity. Therefore, aromatic polyesters containing the structural unit (E) are preferably used as powders. The powders are obtained by pulverizing aromatic polyester resins or fibers, and the average particle size is typically between 0.1 μm and 100 μm, preferably between 0.5 μm and 15 μm.

Although not particularly limited, the weight average molecular weight of the liquid crystal polyester is typically 1,000 or more and 100,000 or less, and preferably 10,000 or more and 50,000 or less.

As the liquid crystal polyester, commercially available products can be selected appropriately and used, for example, "Econol E101-F" (trade name) manufactured by Sumitomo Chemical Co., Ltd. can be used.

In this embodiment, when the first resin layer contains liquid crystal polyester, its content is not particularly limited, but from the viewpoint of improving heat resistance and curability, it is preferably 10 parts by mass or more and 90 parts by mass or less per 100 parts by mass of the resin solid content in the first resin layer, and more preferably 30 parts by mass or more and 80 parts by mass or less.

-Epoxy resin-
The epoxy resin is not particularly limited as long as it has two or more epoxy groups in one molecule, and any conventionally known epoxy resin can be used. The epoxy equivalent of the epoxy resin is preferably 250 g/eq or more and 850 g/eq or less, more preferably 250 g/eq or more and 450 g/eq or less, in order to improve adhesiveness and flexibility. The epoxy equivalent can be measured by a conventional method.

Examples of epoxy resins include polyoxynaphthylene-type epoxy resins, biphenyl aralkyl-type epoxy resins, naphthalene tetrafunctional-type epoxy resins, xylene-type epoxy resins, naphthol aralkyl-type epoxy resins, naphthalene aralkyl-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol A novolac-type epoxy resins, trifunctional phenol-type epoxy resins, tetrafunctional phenol-type epoxy resins, naphthalene-type epoxy resins, biphenyl-type epoxy resins, aralkyl novolac-type epoxy resins, alicyclic epoxy resins, polyol-type epoxy resins, glycidyl amine-type epoxy resins, glycidyl ester-type epoxy resins, compounds in which the double bonds of diene compounds such as butadiene have been epoxidized, and compounds obtained by reacting hydroxyl-containing silicone resins with epichlorohydrin. Among these, from the viewpoints of plating copper adhesion and flame retardancy in particular, the epoxy resin is preferably a polyoxynaphthylene-type epoxy resin, a biphenyl aralkyl-type epoxy resin, a naphthalene tetrafunctional-type epoxy resin, a xylene-type epoxy resin, a naphthol aralkyl-type epoxy resin, or a naphthalene aralkyl-type epoxy resin. These epoxy resins can be used alone or in combination of two or more.

In this embodiment, if the first resin layer contains an epoxy resin, its content is not particularly limited, but from the standpoint of improving heat resistance and curing properties, it is preferably 1 part by mass or more and 60 parts by mass or less, and more preferably 1 part by mass or more and 30 parts by mass or less, per 100 parts by mass of resin solids in the first resin layer.

- Cyanate ester compounds -
Cyanate ester compounds have excellent properties such as chemical resistance and adhesiveness, and their excellent chemical resistance makes it possible to form a uniformly roughened surface, making them suitable for use as a component of the resin layer in this embodiment.

Examples of cyanate ester compounds include α-naphthol aralkyl cyanate ester compounds represented by the following formula (F), novolac cyanate ester compounds represented by the following formula (G), biphenyl aralkyl cyanate ester compounds represented by the following formula (H), 1,3-dicyanatobenzene, 1,4-dicyanatobenzene, 1,3,5-tricyanatobenzene, bis(3,5-dimethyl-4-cyanatophenyl)methane, 1,3-dicyanatonaphthalene, 1,4-dicyanatonaphthalene, and 1,6-dicyanatonaphthalene. , 1,8-dicyanatonaphthalene, 2,6-dicyanatonaphthalene, 2,7-dicyanatonaphthalene, 1,3,6-tricyanatonaphthalene, 4,4'-dicyanatobiphenyl, bis(4-cyanatophenyl)methane, bis(4-cyanatophenyl)propane, bis(4-cyanatophenyl)ether, bis(4-cyanatophenyl)thioether, bis(4-cyanatophenyl)sulfone, 2,2'-bis(4-cyanatophenyl)propane, and bis(3,5-dimethyl-4-cyanatophenyl)methane. These cyanate ester compounds may be used alone or in combination of two or more.

Of these, α-naphthol aralkyl cyanate ester compounds represented by formula (F), novolac cyanate ester compounds represented by formula (G), and biphenyl aralkyl cyanate ester compounds represented by formula (H) are preferred because they have excellent flame retardancy, high curability, and a low thermal expansion coefficient of the cured product.

In formula (F), ^R1 represents a hydrogen atom or a methyl group, and ⁿ¹ represents an integer of 1 or more. ⁿ¹ is preferably an integer of 1 to 50.

In formula (G), ^R2 represents a hydrogen atom or a methyl group, and ⁿ² represents an integer of 1 or greater. ⁿ² is preferably an integer of 1 to 50.

In formula (H), ^R3 represents a hydrogen atom or a methyl group, and ⁿ³ represents an integer of 1 or more. ⁿ³ is preferably an integer of 1 to 50.

In this embodiment, when the first resin layer contains a cyanate ester compound, its content is not particularly limited, but from the viewpoint of improving heat resistance and adhesion to the copper foil, it is preferably 1 part by mass or more and 60 parts by mass or less, and more preferably 1 part by mass or more and 30 parts by mass or less, per 100 parts by mass of the resin solid content in the first resin layer.

-Maleimide compound-
The maleimide compound can improve the moisture absorption and heat resistance of the insulating resin layer, and is therefore preferably used as a component of the resin layer in this embodiment. The maleimide compound is not particularly limited as long as it has two or more maleimide groups in one molecule, and any conventionally known maleimide compound can be used.

Examples of maleimide compounds include bismaleimide compounds such as bis(4-maleimidophenyl)methane, 2,2-bis{4-(4-maleimidophenoxy)-phenyl}propane, bis(3,5-dimethyl-4-maleimidophenyl)methane, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane, and bis(3,5-diethyl-4-maleimidophenyl)methane; as well as polyphenylmethane maleimide. The resin composition solution can also be blended in the form of a prepolymer of these maleimide compounds, or a prepolymer of a maleimide compound and an amine compound. These maleimide compounds can be used alone or in combination of two or more.

Of these, bismaleimide compounds are preferred in terms of improving heat resistance, and bis(3-ethyl-5-methyl-4-maleimidophenyl)methane is more preferred.

In this embodiment, when the first resin layer contains a maleimide compound, its content is not particularly limited, but from the viewpoint of improving heat resistance and adhesion to copper foil, it is preferably 5 parts by mass or more and 75 parts by mass or less, and more preferably 5 parts by mass or more and 45 parts by mass or less, per 100 parts by mass of the resin solids in the first resin layer.

-Phenol resin-
The phenolic resin is not particularly limited as long as it has two or more phenolic hydroxyl groups in one molecule, and any conventionally known phenolic resin can be used. Examples of phenolic resins include phenol novolac resins, alkylphenol volac resins, bisphenol A novolac resins, dicyclopentadiene-type phenolic resins, Xylok-type phenolic resins, terpene-modified phenolic resins, polyvinylphenols, aralkyl-type phenolic resins, and biphenylaralkyl-type phenolic resins, which are compounds in which two or more hydrogen atoms bonded to an aromatic ring in one molecule are substituted with hydroxyl groups. These phenolic resins can be used alone or in combination of two or more.

-Thermosetting modified polyphenylene ether resin-
The thermosetting modified polyphenylene ether resin is a resin obtained by blending a thermoplastic polyphenylene ether resin and an epoxy resin, dissolving the blend in a solvent such as toluene, and adding 2-ethyl-4-methylimidazole as a catalyst to crosslink the blend. The thermosetting modified polyphenylene ether resin can be used alone or in a suitable mixture of two or more types.

-Benzoxazine compounds-
The benzoxazine compound is not particularly limited as long as it has an oxazine ring as a basic skeleton. In the present embodiment, the benzoxazine compound also includes compounds having a polycyclic oxazine skeleton, such as naphthoxazine compounds. The benzoxazine compounds can be used alone or in appropriate mixtures of two or more.

-Organic group modified silicone compound-
The organic group-modified silicone compound is not particularly limited, and specific examples include di(methylamino)polydimethylsiloxane, di(ethylamino)polydimethylsiloxane, di(propylamino)polydimethylsiloxane, di(epoxypropyl)polydimethylsiloxane, and di(epoxybutyl)polydimethylsiloxane. These organic group-modified silicone compounds can be used alone or in appropriate mixtures of two or more.

- Compound having a polymerizable unsaturated group -
Compounds having a polymerizable unsaturated group are not particularly limited as long as they are not limited to those mentioned above, and include vinyl compounds such as ethylene, propylene, styrene, divinylbenzene, and divinylbiphenyl; (meth)acrylates of monohydric or polyhydric alcohols such as methyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, polypropylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; epoxy (meth)acrylates such as bisphenol A epoxy (meth)acrylate and bisphenol F epoxy (meth)acrylate; and benzocyclobutene resins. These compounds having a polymerizable unsaturated group can be used alone or in combination. The term "(meth)acrylate" encompasses both methacrylate and acrylate.

[Second Resin Layer]
In this embodiment, as described above, the second resin layer is typically a layer containing a resin that has fluidity during press processing, and the layer itself also has fluidity during press processing. The second resin layer is typically a layer in which a component that forms a laminate together with the resin layer-attached substrate is embedded from the side that contacts the surface of the second resin layer. Examples of the component include a (conductor layer) such as a circuit pattern provided on a substrate, and the conductor layer corresponds to the convex portion of the uneven shape formed together with the substrate and is embedded in the second resin layer.

From the viewpoint of improving the embeddability of the conductor layer, the minimum melt viscosity of the second resin layer is preferably 100,000 Pa·s or less, more preferably 10 to 80,000 Pa·s, and even more preferably 30 to 60,000 Pa·s. From the same viewpoint, the minimum melt viscosity of the second resin layer is preferably lower than the minimum melt viscosity of the first resin layer, more preferably 10,000 Pa·s or more lower, even more preferably 20,000 Pa·s or more lower, and particularly preferably 40,000 Pa·s or more lower. The minimum melt viscosity of the second resin layer may be less than 50,000,000 Pa·s, 49,950,000 Pa·s or less, or 49,900,000 Pa·s or less. The minimum melt viscosity of the second resin layer can be adjusted to a desired value by appropriately selecting the type of thermosetting resin contained therein, controlling the degree of hardening of the resin, or adding an inorganic filler.

The thickness of the second resin layer is not particularly limited, but from the viewpoint of improving the embeddability of the conductor layer and further enhancing the insulating properties, it is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. On the other hand, from the viewpoint of further thinning the substrate, the thickness of the second resin layer is preferably 25 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 9.0 μm or less. Considering the viewpoint of further thinning the substrate in addition to the viewpoint of further improving the embeddability and insulating properties of the conductor layer, the thickness of the second resin layer is more preferably 2.0 μm to 20 μm, even more preferably 3.0 μm to 20 μm, even more preferably 4.0 μm to 15 μm, particularly preferably 5.0 μm to 10 μm, and extremely preferably 5.0 μm to 9.0 μm.

From the viewpoint of making the substrate thinner, the total thickness of the first resin layer and the second resin layer is preferably 30 μm or less, more preferably 15 μm or less, even more preferably 20 μm or less, even more preferably 15 μm or less, even more preferably 14 μm or less, particularly preferably less than 12 μm, and extremely preferably 10 μm or less. From the viewpoint of more effectively and reliably achieving the effects of the present invention even with such a thinner substrate, the total thickness is preferably 3.0 μm or more, more preferably 5.0 μm or more, and even more preferably 6.0 μm or more. From the above viewpoints, the total thickness is more preferably 3.0 μm or more and 30 μm or less, even more preferably 3.0 μm or more and 20 μm or less, even more preferably 5.0 μm or more and 20 μm or less, even more preferably 5.0 μm or more and 15 μm or less, particularly preferably 5.0 μm or more and 14 μm or less, even more particularly preferably 5.0 μm or more and less than 12 μm, and extremely preferably 5.0 μm or more and 10 μm or less.

The second resin layer in this embodiment can be formed by known means such as coating using a varnish, which is preferably a solution of a resin composition containing a thermosetting resin. There are no particular limitations on the thermosetting resin, and any desired thermosetting resin can be used depending on the desired physical properties. Furthermore, the resin composition may contain inorganic fillers and other additives, as described below, as needed.

(thermosetting resin)
As described above, the thermosetting resin used in the second resin layer is not particularly limited, but examples thereof include epoxy resins, cyanate ester compounds, maleimide compounds, phenolic resins, thermosetting modified polyphenylene ether resins, benzoxazine compounds, organic group-modified silicone compounds, and compounds having a polymerizable unsaturated group. These thermosetting resins may be the same as those exemplified above for use in the first resin layer. These thermosetting resins may be used alone or in combination of two or more.

Among these thermosetting resins, the second resin layer preferably contains at least one of an epoxy resin and a phenolic resin, and more preferably contains both an epoxy resin and a phenolic resin, in order to obtain an insulating resin layer with even better peel strength. From the same perspective, it is also more preferable for the second resin layer to further contain a bismaleimide compound.

In this embodiment, if the second resin layer contains an epoxy resin, its content is not particularly limited, but from the standpoint of improving heat resistance and curing properties, it is preferably 10 parts by mass or more and 80 parts by mass or less, and more preferably 30 parts by mass or more and 70 parts by mass or less, per 100 parts by mass of resin solids in the second resin layer.

In this embodiment, when the second resin layer contains a cyanate ester compound, its content is not particularly limited, but from the viewpoint of improving heat resistance and adhesion to the copper foil, it is preferably 15 parts by mass or more and 85 parts by mass or less, and more preferably 25 parts by mass or more and 65 parts by mass or less, per 100 parts by mass of the resin solid content in the second resin layer.

In this embodiment, when the second resin layer contains a maleimide compound, its content is not particularly limited, but from the viewpoint of improving heat resistance and adhesion to copper foil, it is preferably 5 parts by mass or more and 75 parts by mass or less, and more preferably 5 parts by mass or more and 45 parts by mass or less, per 100 parts by mass of the resin solid content in the second resin layer.

[Other ingredients]
The first and second resin layers in this embodiment may each contain other components such as a filler, if necessary.

-Filling material-
As the filler, a spherical filler is preferred from the viewpoints of low thermal expansion coefficient, moldability, packing property, and rigidity. The spherical filler is not particularly limited as long as it is a spherical filler used in the insulating layer of a printed wiring board.

Spherical fillers include, for example, silicas such as magnesium hydroxide, magnesium oxide, natural silica, fused silica, amorphous silica, and hollow silica; molybdenum compounds such as molybdenum disulfide, molybdenum oxide, and zinc molybdate; alumina; aluminum nitride; glass; titanium oxide; and zirconium oxide. These spherical fillers may be used alone or in combination of two or more.

As a spherical filler, spherical silica such as spherical fused silica is preferred due to its low thermal expansion. Commercially available spherical fused silica includes SC2050-MB, SC2500-SQ, SC4500-SQ, SO-C2, and SO-C1 (all trade names) manufactured by Admatechs Co., Ltd., and SFP-130MC (trade name) manufactured by Denki Kagaku Kogyo Co., Ltd.

The average particle size of spherical fillers such as spherical silica is not particularly limited, but is preferably 0.01 μm to 5 μm, more preferably 0.05 μm to 3 μm, even more preferably 0.1 μm to 2 μm, and particularly preferably 0.3 μm to 1.5 μm. The average particle size of spherical silica can be measured using a laser diffraction/scattering method based on Mie scattering theory. Specifically, a particle size distribution of spherical silica is created on a volume basis using a laser diffraction/scattering particle size distribution analyzer, and the median diameter is used as the average particle size. A preferred measurement sample is spherical silica dispersed in water using ultrasonic waves. An example of a laser diffraction/scattering particle size distribution analyzer that can be used is the "LA-500" (product name) manufactured by Horiba, Ltd.

In this embodiment, the content of spherical filler is not particularly limited, but in order to improve moldability, it is preferably 50 parts by mass or more and 500 parts by mass or less, and more preferably 100 parts by mass or more and 400 parts by mass or less, per 100 parts by mass of resin solids in each resin layer.

The spherical filler of this embodiment may also be surface-treated with a silane coupling agent or the like. The silane coupling agent may be the silane coupling agent described below.

-Other ingredients-
Each resin layer in this embodiment may contain, as an additional component, a silane coupling agent, for example, for the purpose of improving the moisture absorption and heat resistance of the insulating resin layer according to this embodiment. The silane coupling agent is not particularly limited, as long as it is a silane coupling agent generally used in the surface treatment of inorganic materials. Specific examples of silane coupling agents include aminosilane-based silane coupling agents such as γ-aminopropyltriethoxysilane and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, epoxysilane-based silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, vinylsilane-based silane coupling agents such as γ-methacryloxypropyltrimethoxysilane, cationic silane-based silane coupling agents such as N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, and phenylsilane-based silane coupling agents. These silane coupling agents may be used alone or in combination of two or more.

In this embodiment, the content of the silane coupling agent in each resin layer is not particularly limited, but from the viewpoint of improving moisture absorption and heat resistance, it is preferably 0.05 parts by mass or more and 5 parts by mass or less, and more preferably 0.1 parts by mass or more and 3 parts by mass or less, per 100 parts by mass of spherical filler. When two or more types of silane coupling agents are used in combination, it is preferable that the total amount of these be within the above range.

Each resin layer in this embodiment may contain a wetting and dispersing agent for purposes such as improving the manufacturability of the resin layer in this embodiment. The wetting and dispersing agent is not particularly limited, as long as it is a wetting and dispersing agent generally used in paints, etc. Specific examples of wetting and dispersing agents include Disperbyk (registered trademark)-110, -111, -180, -161, BYK (registered trademark)-W996, -W9010, and -W903, all manufactured by BYK Japan K.K. These wetting and dispersing agents may be used alone or in combination of two or more.

In this embodiment, the content of the wetting and dispersing agent in each resin layer is not particularly limited. However, in order to improve the manufacturability of the resin layer in this embodiment, the content is preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 0.5 parts by mass or more and 3 parts by mass or less, per 100 parts by mass of the spherical filler. When two or more types of wetting and dispersing agents are used in combination, it is preferable that the total amount of these be within the above range.

Each resin layer in this embodiment may contain a curing accelerator for purposes such as adjusting the curing rate. The curing accelerator is not particularly limited and may be, for example, a commonly used curing accelerator used to accelerate the curing of epoxy resins or cyanate ester compounds. Specific examples of curing accelerators include organometallic salts containing metals such as copper, zinc, cobalt, nickel, and manganese, such as zinc octylate, cobalt naphthenate, nickel octylate, and manganese octylate; imidazoles and their derivatives, such as 2-ethyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, and 2,4,5-triphenylimidazole; and tertiary amines, such as triethylamine and tributylamine. These curing accelerators may be used alone or in combination.

In this embodiment, the content of the curing accelerator in each resin layer is not particularly limited. However, in order to obtain a higher glass transition temperature, the content is preferably 0.001 to 5 parts by mass, and more preferably 0.01 to 3 parts by mass, per 100 parts by mass of the resin solids in each resin layer. When two or more types of curing accelerators are used in combination, it is preferable that the total amount of these accelerators be within the above range.

The resin layer in this embodiment may contain various other polymer compounds and/or flame-retardant compounds. There are no particular limitations on the polymer compounds and flame-retardant compounds, as long as they are commonly used.

Polymer compounds include, other than the thermosetting resins mentioned above, various thermoplastic resins, as well as their oligomers and elastomers. Specific examples of polymer compounds include polyimide, polyamide-imide, polystyrene, polyolefin, styrene-butadiene rubber (SBR), isoprene rubber (IR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), polyurethane, polypropylene, (meth)acrylic oligomer, (meth)acrylic polymer, and silicone resin. From the standpoint of compatibility, acrylonitrile-butadiene rubber and styrene-butadiene rubber are preferred.

The flame-retardant compound may be any flame-retardant compound other than the fillers described above, such as phosphorus-containing compounds (e.g., phosphate esters, melamine phosphate, and phosphorus-containing epoxy resins), nitrogen-containing compounds (e.g., melamine and benzoguanamine), oxazine ring-containing compounds, and silicone-based compounds. These polymer compounds and flame-retardant compounds may be used alone or in combination of two or more.

The resin layer in this embodiment may also contain various additives for various purposes. Specific examples of additives include ultraviolet absorbers, antioxidants, photopolymerization initiators, fluorescent brighteners, photosensitizers, dyes, pigments, thickeners, lubricants, antifoaming agents, dispersants, leveling agents, and gloss agents. These additives may be used alone or in combination of two or more.

(Resin composition)
The first and second resin layers in this embodiment can each be formed using a resin composition. Each resin composition is prepared by mixing the above-mentioned thermosetting resin with other components, such as a filler, as needed. The resin composition may also be in the form of a solution in which these components are dissolved in an organic solvent, as needed. Such a resin composition solution can be suitably used as a varnish when preparing the substrate with an insulating resin layer of this embodiment, as described below. The organic solvent is not particularly limited as long as it can suitably dissolve or disperse each component and achieve the effects of the resin layer in this embodiment. Specific examples of organic solvents include alcohols (e.g., methanol, ethanol, and propanol), ketones (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone), amides (e.g., dimethylacetamide and dimethylformamide), and aromatic hydrocarbons (e.g., toluene and xylene). These organic solvents can be used alone or in combination of two or more.

The content of organic solvent in the resin composition solution is not particularly limited and may be determined appropriately so as to achieve the viscosity of the solution that will achieve the desired thickness range for each resin layer. The content may be, for example, 20 to 1,000 parts by weight, 20 to 500 parts by weight, or 30 to 300 parts by weight, per 100 parts by weight of the resin composition solution.

In this embodiment, the arithmetic mean roughness (Ra) of each resin layer surface is preferably 2.0 μm or less, more preferably 0.10 μm to 1.0 μm, and even more preferably 0.15 μm to 0.50 μm. Having the arithmetic mean roughness (Ra) within the above-mentioned range improves the adhesion strength between the substrate (e.g., copper foil) and the first resin layer, or between the resin layers themselves, and more effectively prevents layer delamination during long-term use. Depending on the purpose, each surface of the resin layer may be in contact with the substrate or with something other than the substrate (e.g., another resin layer). However, it is preferable that the arithmetic mean roughness (Ra) of either surface be within the above-mentioned range. The arithmetic mean roughness of the resin layer surface can be measured using a commercially available shape measuring microscope (a laser microscope, for example, the "VK-X210" (product name) manufactured by Keyence Corporation).

(Method for producing substrate with insulating resin layer)
The method for producing a substrate with an insulating resin layer in this embodiment is not particularly limited as long as it includes a step of laminating an insulating resin layer made of the above-mentioned resin composition on a substrate such as copper foil. In the laminating step, for example, first, a solution (varnish) in which the resin composition is dissolved or dispersed in an organic solvent is applied to the surface of the substrate, and the solution is dried under heat and/or reduced pressure to remove the organic solvent and solidify the resin composition, thereby forming a first resin layer. As described above, the first resin layer may be in a semi-cured state or a fully cured state. Then, a solution (varnish) in which another resin composition is dissolved or dispersed in an organic solvent is applied to the surface of the substrate on the first resin layer, and the solution is dried under heat and/or reduced pressure to remove the organic solvent and solidify the resin composition, thereby forming a second resin layer. In this case, the second resin layer is preferably in a B-stage (semi-cured state). In addition, a protective layer such as a plastic film may be provided on the second resin layer. The protective layer is appropriately removed during the production of the laminate described below. The drying conditions are not particularly limited, but are such that the content of the organic solvent in each resin layer is typically 10 parts by mass or less, and preferably 5 parts by mass or less, per 100 parts by mass of each resin layer. The conditions for achieving drying vary depending on the amount of organic solvent in the varnish, but for example, in the case of a varnish containing 30 parts by mass or more and 60 parts by mass or less of organic solvent per 100 parts by mass of varnish, drying can be carried out for about 3 to 10 minutes under heating conditions of 50°C or more and 160°C or less.

The method for applying the resin composition to the substrate is not particularly limited, but known application methods such as bar coater application, air knife application, gravure application, reverse gravure application, microgravure application, micro reverse gravure coater application, die coater application, dip application, spin coat application, and spray application can be used.

<Laminate of this embodiment and manufacturing method thereof>
A laminate using the substrate with an insulating resin layer of this embodiment (hereinafter, sometimes simply referred to as a "laminate") can be used, for example, to produce a coreless substrate to be provided in a printed wiring board or a substrate for mounting semiconductor elements. The coreless substrate may be a coreless substrate for a build-up material. The laminate of this embodiment is, for example, a laminate in which a conductor layer and an insulating layer formed using the substrate with an insulating resin layer of this embodiment are laminated, and may have a build-up layer. At least one of the conductor layer and the insulating layer may be a plurality of layers, and the laminate may be formed by alternately laminating the conductor layer and the insulating layer. Here, for example, when forming an insulating layer by laminating the substrate with an insulating resin layer of this embodiment, the insulating layer can be formed by laminating the second resin layer of the substrate with an insulating resin layer of this embodiment using copper foil as the substrate so that it contacts the substrate on which the conductor layer is formed. Furthermore, when forming an insulating layer using three or more substrates with insulating resin layers, the substrate can be removed as necessary, and each resin layer can be laminated to form the insulating layer. Furthermore, when the substrate in the substrate with an insulating resin layer of this embodiment is copper foil, the copper foil may serve as the conductor layer, or the conductor layer may be formed by laminating another conductor (copper foil, etc.), such as the copper foil of a copper-clad laminate, on the insulating layer.

When the laminate of this embodiment has a build-up layer, for example, the build-up layer has multiple conductor layers and insulating layers, with the conductor layers being arranged between each insulating layer and on the surface of the outermost layer of the build-up layer. In this case, there is no particular limit to the number of insulating layers, but it can be, for example, three or four layers. Furthermore, a coreless substrate can be produced using the laminate of this embodiment. Examples of coreless substrates include coreless substrates with two or more layers, and may be, for example, a three-layer coreless substrate. The configuration of the coreless substrate will be described later.

In the laminate of this embodiment, from the viewpoint of realizing the demand for thinner films, it is preferable that the thickness of at least one insulating layer be 1 μm or more and less than 15 μm. The thickness of the insulating layer varies depending on the various uses of the laminate, but, for example, it is more preferable that it be 1 μm or more and 14 μm or less, and even more preferable that it be 1 μm or more and 12 μm or less. Furthermore, from the same viewpoint, it is particularly preferable that the thicknesses of all insulating layers be within the above numerical range.

In the laminate, the thickness of the layer derived from the first resin layer described above is not particularly limited, but from the perspective of even thinner film thickness, it is preferably less than 10 μm. Considering the need to ensure even more reliable insulation, the thickness of the layer is more preferably 1.0 μm to 9.0 μm, more preferably 2.0 μm to 9.0 μm, even more preferably 2.5 μm to 9.0 μm, and particularly preferably 3.0 μm to 9.0 μm. The upper limit of the layer thickness may be 7.0 μm or 5.0 μm.

In the laminate, the thickness of the layer derived from the second resin layer described above is not particularly limited, but from the perspective of improving the embeddability of the conductor layer and further enhancing the insulating properties, it is preferably 2.0 μm or more, and more preferably 3.0 μm or more. On the other hand, from the perspective of making the substrate thinner, the layer thickness is preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 9.0 μm or less. Considering the perspective of making the substrate thinner in addition to the perspective of further enhancing the embeddability and insulating properties of the conductor layer, the layer thickness is more preferably 2.0 μm to 20 μm or less, even more preferably 3.0 μm to 20 μm or less, even more preferably 4.0 μm to 15 μm or less, particularly preferably 5.0 μm to 10 μm or less, and extremely preferably 5.0 μm to 9.0 μm or less.

[Printed wiring board]
The laminate of this embodiment can be used as a printed wiring board. Here, the printed wiring board can be obtained by using a laminate obtained from the substrate with an insulating resin layer of this embodiment as a build-up material for a metal foil-clad laminate in which the insulating resin layer, called a core substrate, is fully cured. By using the substrate with an insulating resin layer of this embodiment and the laminate obtained therefrom, it is possible to manufacture a thin printed wiring board without using a thick support substrate (carrier substrate), for example. Furthermore, the printed wiring board obtained using the substrate with an insulating resin layer of this embodiment has even better adhesion between layers and productivity (yield rate).

A conductor circuit is formed on the surface of a metal foil-clad laminate using the metal foil of a commonly used metal foil-clad laminate and/or a conductor layer obtained by plating after peeling off the metal foil. The substrate of the metal foil-clad laminate is not particularly limited, but examples include glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates.

In this embodiment, "build-up" means laminating the insulating resin layer of the insulating resin layer-equipped substrate of this embodiment onto the metal foil and/or conductor layer on the surface of the metal foil-clad laminate.

Typically, when an insulating resin layer (resin composition layer) is laminated onto a metal foil-clad laminate using an adhesive film or similar build-up material, the resulting printed wiring board has a cured insulating resin layer, i.e., an insulating layer, on one or both sides. A conductor layer is formed on this insulating layer, but the surface roughness of the insulating layer is low. For this reason, roughening treatments, including desmearing, are typically used to create irregularities in the insulating layer, and then the conductor layer is formed using electroless plating and/or electrolytic plating.

However, when the substrate with an insulating resin layer of this embodiment is laminated to a metal foil-clad laminate as a build-up material, the resulting printed wiring board will have a substrate such as copper foil on one or both sides. Therefore, if the substrate is conductive, such as copper foil, a circuit pattern can be formed directly on the substrate without plating, allowing for the formation of high-density fine wiring. Furthermore, when manufacturing a printed wiring board or a substrate for mounting semiconductor elements, even if plating is performed after etching the substrate, the substrate surface is transferred to the insulating resin layer, improving adhesion between the insulating layer and the plating.

In the manufacture of printed wiring boards, holes such as via holes and/or through holes are drilled as needed to electrically connect each conductor layer. After drilling, a roughening treatment, including a desmearing process, is then performed. If the surface of the printed wiring board is protected by a conductor layer, such as copper foil, that has excellent adhesion to the insulating layer, roughening of the surface of the printed wiring board can be suppressed even when a roughening process is performed.

Drilling is typically performed using a mechanical drill, carbon dioxide laser, UV laser, YAG laser, or the like. If the surface of a printed wiring board is protected by a conductive layer such as copper foil, the energy of these drills or lasers can be increased. Therefore, according to this embodiment, inorganic materials such as glass fibers exposed on the surface of the hole during drilling can be effectively removed. Note that roughening treatment typically consists of a swelling process, a surface roughening and smear dissolution process, and a neutralization process.

In the swelling process, a swelling agent is used to swell the surface of the insulating layer. There are no particular restrictions on the swelling agent, so long as it improves the wettability of the insulating layer surface and swells the insulating layer surface to an extent that promotes oxidative decomposition in the subsequent surface roughening and smear dissolution processes. Examples include alkaline solutions and surfactant solutions.

In the surface roughening and smear dissolution process, an oxidizing agent is used to roughen the surface of the insulating layer and dissolve the smear. Examples of oxidizing agents include alkaline permanganate solutions, with specific examples including aqueous potassium permanganate solutions and aqueous sodium permanganate solutions. This type of oxidizing agent treatment is called wet desmearing, but other known roughening treatments, such as dry desmearing using plasma treatment or UV treatment, mechanical polishing using a buff, or sandblasting, may also be used in combination with wet desmearing.

In the neutralization step, the oxidizing agent used in the previous step is neutralized with a reducing agent. Examples of reducing agents include amine-based reducing agents. Suitable examples include acidic aqueous solutions such as an aqueous solution of hydroxylamine sulfate, an aqueous solution of ethylenediaminetetraacetic acid, and an aqueous solution of nitrilotriacetic acid.

In this embodiment, after providing the via holes and/or through holes, or after desmearing the interior of the via holes and/or through holes, it is preferable to perform metal plating to electrically connect the conductor layers. In this embodiment, even after metal plating, the surface of the conductor layer is transferred to the insulating layer, improving adhesion between the insulating layer and the metal plating.

The metal plating method is not particularly limited, and any metal plating method commonly used in the manufacture of multilayer printed wiring boards can be used as appropriate. The metal plating method and the type of chemicals used for plating are not particularly limited, and any metal plating method and chemicals commonly used in the manufacture of multilayer printed wiring boards can be used as appropriate. The chemicals used for metal plating may be commercially available products. The metal plating method is not particularly limited, and examples include treatment with a degreasing solution, treatment with a soft etching solution, acid cleaning, treatment with a pre-dip solution, treatment with a catalyst solution, treatment with an accelerator solution, treatment with a chemical copper solution, acid cleaning, and immersion in a copper sulfate solution followed by application of an electric current.

Furthermore, when a build-up is performed using a substrate with a semi-cured insulating resin layer, a printed wiring board can usually be obtained by subjecting the semi-cured insulating resin layer to a heat treatment or the like to completely cure it. In this embodiment, another substrate with an insulating resin layer may be further laminated on the obtained printed wiring board.

The lamination method using the build-up method is not particularly limited, but a vacuum pressure laminator can be suitably used. In this case, the substrate with the insulating resin layer of this embodiment can be laminated to a metal foil-clad laminate via an elastic material such as rubber. The lamination conditions are not particularly limited as long as they are conditions used in laminating ordinary printed wiring boards, but examples include a temperature of 70°C to 140°C, a contact pressure of 1 kgf/ ^cm2 to 11 kgf/ ^cm2 , and a reduced atmospheric pressure of 20 hPa or less. After lamination, the laminated insulating resin layer may be smoothed by hot pressing with a metal plate. Lamination and smoothing can be performed continuously using a commercially available vacuum pressure laminator. After lamination or smoothing, the insulating resin layer can be completely cured by heating and thermal curing. The thermal curing conditions vary depending on the types of components contained in the resin composition, but typically include a curing temperature of 100°C to 300°C and a pressure of 0. The pressure is from kgf/cm ² to 100 kgf/cm ² (from about 9.8 kPa to about 9.8 MPa), and the curing time is from 30 seconds to 5 hours.

In this embodiment, methods for forming a circuit pattern on the copper foil or conductor layer on one or both sides of the printed wiring board include the semi-additive method, the full-additive method, and the subtractive method. Of these, the semi-additive method is preferred from the perspective of forming fine wiring patterns.

An example of a method for forming a circuit pattern using the semi-additive method is to selectively apply electrolytic plating using a plating resist (pattern plating), then peel off the plating resist and etch the entire surface appropriately to form a wiring pattern. When forming a circuit pattern using the semi-additive method, electroless plating and electrolytic plating are combined, and in this case, it is preferable to dry the surface after both electroless plating and electrolytic plating. There are no particular restrictions on the drying method after electroless plating, but it is preferable to dry the surface at a temperature of 80°C or higher and 180°C or lower for 10 to 120 minutes. There are no particular restrictions on the drying method after electrolytic plating, but it is preferable to dry the surface at a temperature of 130°C or higher and 220°C or lower for 10 to 120 minutes. Copper plating is preferred as the plating method.

The insulating layer formed using the resin-layered substrate of this embodiment has excellent plating adhesion. Here, "plating adhesion" can be evaluated by, for example, using a sample on which a conductor layer (plated copper) with a thickness of 18 μm has been formed, measuring the adhesive strength of the conductor layer three times in accordance with JIS C6481 (5.7. (Peel Strength)) and calculating the average value. For samples that swell due to drying after electrolytic copper plating, evaluation is performed using the unswelled portion. "Plating adhesion" is preferably 0.1 kN/m or more, more preferably 0.2 kN/m or more, and even more preferably 0.3 kN/m or more.

An example of a subtractive method for forming a circuit pattern is a technique in which a conductor layer is selectively removed using an etching resist to form the circuit pattern. Specifically, the circuit pattern is formed as follows: A dry film resist (e.g., RD-1225 (trade name) manufactured by Hitachi Chemical) is laminated onto the entire surface of the copper foil at a temperature of 110±10°C and a pressure of 0.50±0.02 MPa. Next, the surface is exposed to light along the circuit pattern and masked. The dry film resist is then developed using a 1% aqueous sodium carbonate solution, and finally stripped using an amine-based resist stripper. This allows the circuit pattern to be formed on the copper foil.

In this embodiment, an insulating layer and/or a conductor layer can be further laminated on the printed wiring board to obtain a multilayer printed wiring board. The multilayer printed wiring board may have a circuit board as an inner layer. The insulating resin layer in the substrate with an insulating resin layer of this embodiment constitutes one of the insulating layers and conductor layers of the multilayer printed wiring board.

The lamination method is not particularly limited, and methods commonly used in lamination molding of ordinary printed wiring boards can be used. Examples of lamination methods include a multi-stage press, a multi-stage vacuum press, a laminator, a vacuum laminator, and an autoclave molding machine. The temperature during lamination is not particularly limited, but is, for example, 100°C or higher and 300°C or lower. The pressure during lamination is not particularly limited, but is, for example, 0.1 kgf/ ^cm2 or higher and 100 kgf/cm2 or ^lower (approximately 9.8 kPa or higher and approximately 9.8 MPa or lower). The heating time during lamination is not particularly limited, but is, for example, 30 seconds to 5 hours. Furthermore, if necessary, post-curing may be performed at a temperature range of, for example, 150°C or higher and 300°C or lower to adjust the degree of curing.

[Semiconductor element mounting substrate]
As described above, the laminate of this embodiment can be used as a semiconductor device mounting substrate. A semiconductor device mounting substrate can be produced, for example, by laminating the insulating resin layer-equipped substrate of this embodiment on a metal foil-clad laminate, and then masking and patterning a substrate such as copper foil on one side or the surface of the resulting laminate to form a circuit pattern. The masking and patterning can be performed using known masking and patterning methods used in the manufacture of printed wiring boards, and are not particularly limited, but it is preferable to form the circuit pattern by the subtractive method described above. The circuit pattern may be formed on only one side of the laminate, or on both sides.

[Multilayer coreless substrate (multilayer printed wiring board)]
The laminate of this embodiment can be a coreless substrate. An example of a coreless substrate is a multilayer coreless substrate. The multilayer coreless substrate has, for example, a plurality of insulating layers each consisting of a first insulating layer and one or more second insulating layers laminated on one side of the first insulating layer, a first conductor layer disposed between each of the plurality of insulating layers, and a second conductor layer disposed on the surface of the outermost layer of the plurality of insulating layers, wherein the first insulating layer and the second insulating layer each comprise a cured product of the insulating resin layer in the substrate with an insulating resin layer of this embodiment. A specific example of a multilayer coreless substrate will be described with reference to FIG. 2. FIG. 2 is a schematic diagram showing an example of a multilayer coreless substrate of this embodiment. The multilayer coreless substrate 100 shown in Fig. 2 includes a first insulating layer 111 and two second insulating layers 112 stacked on one side of the first insulating layer 111 (toward the bottom surface in the figure), and the first insulating layer 111 and the two second insulating layers 112 are each formed using the insulating resin layer in one of the base materials with an insulating resin layer of this embodiment. The multilayer coreless substrate 100 shown in Fig. 2 also has a plurality of conductor layers, including a first conductor layer 113 disposed between each of the plurality of insulating layers (insulating layers 111 and 112) and a second conductor layer 113 disposed on the outermost layer of the plurality of insulating layers (insulating layers 111 and 112).

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples in any way.

[Example 1]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting and dispersing agent (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with N-methyl-2-pyrrolidone (hereinafter referred to as "NMP") to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish B, which is a solution of the resin composition. The resulting varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer having a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 μm, and the thickness of the second resin layer was 5.4 μm.

[Example 2]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 300 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B (resin composition) was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 µm, and the thickness of the second resin layer was 5.1 µm.

[Example 3]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting and dispersing agent (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidodiphenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 420 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by mass of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan K.K.), 1 part by mass of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan K.K.), 2 parts by mass of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by mass of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, having a first resin layer and a second resin layer in this order from the substrate side. The first resin layer had a thickness of 2.5 μm, and the second resin layer had a thickness of 4.7 μm.

[Example 4]
50 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 50 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting and dispersing agent (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 300 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B (resin composition) was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 µm, and the thickness of the second resin layer was 5.1 µm.

[Example 5]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish B, which is a solution of the resin composition. The resulting varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer having a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 μm, and the thickness of the second resin layer was 8.9 μm.

[Example 6]
Biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd.) 40 parts by mass, 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Kasei Co., Ltd.) 60 parts by mass, spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.) 60 parts by mass, wetting and dispersing agent (product name: BYK-W903, manufactured by BYK-Chemie Co., Ltd.) 0.2 parts by mass of PEG-1000 (manufactured by Mitsui Mining & Smelting Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a solution of resin composition, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then heated and dried at 200°C for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish B, which is a solution of the resin composition. The resulting varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer having a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.7 μm, and the thickness of the second resin layer was 5.4 μm.

[Example 7]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 350 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B (resin composition) was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 µm, and the thickness of the second resin layer was 4.8 µm.

[Example 8]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 30 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 350 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B (resin composition) was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 1.8 µm, and the thickness of the second resin layer was 3.2 µm.
[Example 9]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 30 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 350 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B (resin composition) was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 1.8 µm, and the thickness of the second resin layer was 1.6 µm.

[Example 10]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish B, which is a solution of the resin composition. The resulting varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer having a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 μm, and the thickness of the second resin layer was 23.2 μm.

[Example 11]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish B, which is a solution of the resin composition. The resulting varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer having a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 μm, and the thickness of the second resin layer was 17.9 μm.

[Example 12]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish B, which is a solution of the resin composition. The resulting varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer having a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 μm, and the thickness of the second resin layer was 14.3 μm.

[Example 13]
60 parts by mass of block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute), 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.), 60 parts by mass of spherical silica (product name: SO-C1, average particle size 0.3 μm, manufactured by Admatechs Co., Ltd.), and 0.2 parts by mass of a wetting dispersant (product name: BYK-W903, manufactured by BYK Japan Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 180° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish B, which is a solution of the resin composition. The resulting varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer having a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 μm, and the thickness of the second resin layer was 4.5 μm.

[Comparative Example 1]
Biphenyl aralkyl phenolic resin (product name: KAYAHARD) GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidodiphenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish A, which is a solution of a resin composition. The obtained varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 150° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Biphenyl aralkyl phenolic resin (product name: KAYAHARD) GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidodiphenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 300 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by mass of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan K.K.), 2 parts by mass of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan K.K.), 1 part by mass of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by mass of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition, Varnish B. The resulting Varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then heated and dried at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, having a first resin layer and a second resin layer in this order from the substrate side. The first resin layer had a thickness of about 2.0 μm, and the second resin layer had a thickness of 5.1 μm.

[Comparative Example 2]
Biphenyl aralkyl phenolic resin (product name: KAYAHARD) GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenylaralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalenearalkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidodiphenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, and 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.5 parts by mass were blended and mixed, and then diluted with methyl ethyl ketone to obtain varnish A, which is a solution of a resin composition. The obtained varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then dried by heating at 150° C. for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed on the copper foil.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl group equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidodiphenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 420 parts by mass, styrene butadiene rubber (product name: JSR 40 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.0 µm, and the thickness of the second resin layer was 4.3 µm.

[Comparative Example 3]
60 parts by mass of a block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute) and 40 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then heated and dried at 180°C for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed thereon.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 300 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B (resin composition) was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 2.5 µm, and the thickness of the second resin layer was 5.1 µm.

[Comparative Example 4]
30 parts by mass of a block copolymer polyimide (product name: YN-003N, manufactured by PI Technical Research Institute) and 60 parts by mass of 2,2-bis-{4-(4-maleimidophenoxy)phenyl}propane (product name: BMI-80, manufactured by K.I. Chemical Co., Ltd.) were blended and mixed, and then diluted with NMP to obtain a resin composition solution, Varnish A. The obtained Varnish A was applied to the matte side of a 12 μm thick copper foil (product name: 3EC-M2S-VLP, manufactured by Mitsui Mining & Smelting Co., Ltd.) using a bar coater to obtain a coating film. The coating film was then heated and dried at 180°C for 10 minutes to obtain a resin-coated copper foil having a first resin layer formed thereon.

Next, biphenyl aralkyl phenolic resin (product name: KAYAHARD GPH-103, hydroxyl equivalent: 231 g/eq., manufactured by Nippon Kayaku Co., Ltd.) 36 parts by mass, biphenyl aralkyl type epoxy resin (product name: NC-3000-FH, manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent: 320 g/eq.) 39 parts by mass, naphthalene aralkyl type epoxy resin (product name: HP-9900, epoxy equivalent: 274 g/eq., manufactured by DIC Corporation) 7 parts by mass, bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (product name: BMI-70, manufactured by K.I. Kasei Co., Ltd.) 18 parts by mass, slurry silica (product name: SC2050-MB, average particle size 0.7 μm, manufactured by Admatechs Co., Ltd.) 300 parts by mass, styrene butadiene rubber (product name: JSR 20 parts by weight of wetting and dispersing agent 1 (product name: DISPERBYK-161, manufactured by BYK Japan KK), 1 part by weight of wetting and dispersing agent 2 (product name: DISPERBYK-111, manufactured by BYK Japan KK), 2 parts by weight of silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by weight of 2,4,5-triphenylimidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) were blended and mixed, and then diluted with methyl ethyl ketone to obtain a resin composition solution, Varnish B. The obtained Varnish B (resin composition) was applied to the first resin layer side of the resin-coated copper foil obtained by the above-mentioned method using a bar coater to obtain a coating film. The coating film was then dried by heating at 150°C for 10 minutes to obtain a substrate (resin sheet) with an insulating resin layer, which had a first resin layer and a second resin layer in this order from the substrate side. The thickness of the first resin layer was 4 µm, and the thickness of the second resin layer was 5.1 µm.

<Characteristics>
The properties of the substrate with an insulating resin layer were measured by the following methods.

[Fabrication of inner layer circuit board]
The copper foil surfaces on both sides of a glass cloth-based BT resin double-sided copper-clad laminate (copper foil thickness 12 μm, thickness 0.2 mm, manufactured by Mitsubishi Gas Chemical Company, Inc., product name: CCL-HL832NS) on which an inner layer circuit with a copper residual ratio of 60% was formed were subjected to a roughening treatment with a pretreatment liquid (manufactured by MEC Co., Ltd., product name: CZ8100) to obtain an inner layer circuit board.

[Preparation of metal foil-clad laminate]
The two substrates with insulating resin layers were arranged with the second resin layer surfaces facing the inner layer circuit board, sandwiching the inner layer circuit board, and then laminate molding was performed at a pressure of 3.0 MPa and a temperature of 220°C for 60 minutes to obtain a copper-clad laminate.

[Measurement of thickness reduction (TΔ)]
The copper-clad laminate obtained as described above was polished parallel to the lamination direction to expose the cross section, thereby obtaining a sample. The thickness of the first resin layer of the obtained sample was measured using a scanning electron microscope (SEM), and the thickness reduction was evaluated by comparing it with the thickness of the first resin layer in the insulating resin layer-attached substrate. The thickness reduction (TΔ) of the first resin layer was calculated as described above from the thickness of the first resin layer in the insulating resin layer-attached substrate and the thickness of the first resin layer in the copper-clad laminate. The thickness reduction of the second resin layer was also calculated as described above.

[Formability (embedding) of printed wiring boards]
Copper foils on both sides of the copper-clad laminate were removed by etching to obtain samples. The surfaces of the obtained samples were visually observed to evaluate the presence or absence of voids. Here, voids refer to areas where there are gaps and no resin. If many voids were observed, specifically, if the area occupied by voids in the observation area was 30% or more on average relative to the resin, the sample was evaluated as "C" as it was not moldable. If the presence of voids was confirmed but the number was small, specifically, if the area occupied by voids in the observation area was less than 30% on average relative to the resin, the sample was evaluated as "B" as it was moldable. If no voids were confirmed, the sample was evaluated as "A" as it was well moldable. The results are shown in Table 1.

<Minimum melt viscosity of resin sheet>
The minimum melt viscosity of the second resin layer in the substrate with an insulating resin layer obtained as described above was measured using a rheometer (manufactured by TA Instruments Japan Co., Ltd.) under conditions of a starting temperature of 80°C, an ending temperature of 180°C, a heating rate of 3°C/min, a frequency of 10 pts/s, and a strain of 0.1%. The lower this minimum melt viscosity, the better the flow characteristics (resin flow properties) during laminate production and the more excellent the moldability. The results of the minimum melt viscosity of the second resin layer are shown in Table 1.

<Insulation reliability evaluation>
(Preparation of inner layer circuit board for insulation reliability evaluation)
An inner layer circuit for evaluating insulation reliability was formed by a subtractive method on a glass fabric-based BT resin double-sided copper-clad laminate (copper foil thickness 12 μm, thickness 0.2 mm, manufactured by Mitsubishi Gas Chemical Company, Inc., product name: CCL-HL832NS). The copper foil surfaces on both sides of the laminate were subjected to a roughening treatment with a pretreatment liquid (manufactured by MEC Co., Ltd., product name: CZ8101), to obtain an inner layer circuit board for evaluating insulation reliability.

(Preparation of substrate for evaluation of insulation reliability)
The substrate with an insulating resin layer was placed with the second resin layer surface facing the inner layer circuit board for insulation reliability evaluation, so as to sandwich the inner circuit board, and then laminate molding was performed for 120 minutes at a pressure of 3.0 MPa and a temperature of 220°C to obtain a copper-clad laminate with an insulating layer thickness of 5 µm. An outer layer circuit for insulation reliability evaluation was fabricated from the copper-clad laminate by a subtractive method to obtain a substrate for insulation reliability evaluation.

-Insulation reliability evaluation method-
The above-mentioned insulation reliability evaluation substrate was subjected to moisture absorption treatment under conditions of 85° C. and 60% RH for 168 hours, and then to reflow treatment three times at 260° C. For the insulation reliability evaluation substrate after reflow treatment, the resistance value was measured for 96 hours under HAST conditions (130° C., 85% RH, 5.0 V), and the final resistance value was calculated and evaluated according to the following criteria, together with visual inspection during the measurement.
<Standards>
"A": No short circuit occurs during the measurement, and the final resistance is 1.0 x 10 ⁸ Ω or more.
"B": No short circuit occurs during measurement and the final resistance is less than 1.0 x 10 ⁸ Ω.
"C": There is a short circuit during measurement.
The results are shown in Table 1.

As shown in Table 1, the examples all had excellent insulation reliability and embeddability, with a rating of B or higher. On the other hand, the comparative examples, in which the thickness reduction of the first resin layer exceeded 30%, had a low insulation reliability rating of C. Furthermore, comparative example 2, in which the minimum melt viscosity of the second resin layer was 150,000 Pa·s, had poor embeddability, with a rating of C.

Industrial Applicability

The present invention provides a substrate with an insulating resin layer that is useful for printed wiring boards or substrates for mounting semiconductor elements, as well as a laminate and a method for manufacturing a laminate using the same, and has industrial applicability in these fields.

10...substrate with resin layer, 12...substrate, 14...first resin layer, 16...second resin layer, 20...inner layer circuit board, 22...substrate, 24...conductor layer, 30...laminated body, 100...multilayer coreless substrate, 111, 112...insulating layer, 113...conductor layer.

Claims (19)

A substrate;
a first resin layer provided on the substrate, the first resin layer having a thickness reduction of less than 30% when molded for 60 minutes under conditions of 220°C and a pressure of 3.0 MPa;
a second resin layer provided on the first resin layer;
Equipped with
The substrate with an insulating resin layer, wherein the first resin layer contains polyimide, a bismaleimide compound, and 50 to 500 parts by mass of spherical silica per 100 parts by mass of resin solids. The substrate with an insulating resin layer according to claim 1, wherein the minimum melt viscosity of the second resin layer is 100,000 Pa·s or less. The substrate with an insulating resin layer according to claim 1 or 2, wherein the thickness of the first resin layer is less than 10 μm. The substrate with an insulating resin layer according to any one of claims 1 to 3, wherein the thickness of the second resin layer is 2.0 μm or more. The substrate with an insulating resin layer according to any one of claims 1 to 4, wherein the total thickness of the first resin layer and the second resin layer is 3 μm or more and 20 μm or less. The substrate with an insulating resin layer according to any one of claims 1 to 5, wherein the first resin layer contains at least one selected from the group consisting of liquid crystal polyester, epoxy resin, cyanate ester compound, phenolic resin, thermosetting modified polyphenylene ether resin, benzoxazine compound, organic group-modified silicone compound, and compound having a polymerizable unsaturated group. The substrate with an insulating resin layer according to any one of claims 1 to 6, wherein the second resin layer contains at least one selected from the group consisting of epoxy resins, cyanate ester compounds, maleimide compounds, phenolic resins, thermosetting modified polyphenylene ether resins, benzoxazine compounds, organic group-modified silicone compounds, and compounds having a polymerizable unsaturated group. The substrate with an insulating resin layer according to any one of claims 1 to 7, which is used to produce a coreless substrate to be provided in a printed wiring board or a substrate for mounting semiconductor elements. The substrate with an insulating resin layer according to claim 8, wherein the coreless substrate is a three-layer coreless substrate. A laminate having a build-up layer formed by stacking a conductor layer and an insulating layer formed using the substrate with an insulating resin layer described in any one of claims 1 to 9. The laminate described in claim 10, wherein the thickness of at least one of the insulating layers is 1 μm or more and less than 15 μm. The laminate described in claim 10 or 11, wherein the build-up layer has a plurality of the conductor layers and the insulating layers, and the conductor layers are disposed between each of the insulating layers and on the surface of the outermost layer of the build-up layer. The laminate described in any one of claims 10 to 12, wherein the conductor layers and the insulating layers are alternately stacked in the build-up layer, and the build-up layer has three or four insulating layers. The laminate according to any one of claims 10 to 13, which is a coreless substrate. A method for manufacturing a laminate, comprising the step of forming an insulating layer on the surface of a conductor layer using a substrate with an insulating resin layer according to any one of claims 1 to 9, thereby forming a build-up layer in which the conductor layer and the insulating layer are laminated. The method for manufacturing a laminate described in claim 15, wherein the thickness of at least one of the insulating layers is 1 μm or more and less than 15 μm. The method for manufacturing a laminate described in claim 15 or 16, wherein the build-up layer has a plurality of the conductor layers and the insulating layers, and the conductor layers are arranged between each of the insulating layers and on the surface of the outermost layer of the build-up layer. A method for manufacturing a laminate according to any one of claims 15 to 17, wherein the insulating layers are three or four. The method for producing a laminate according to any one of claims 15 to 18, wherein the laminate is a coreless substrate.