JP7601126B2 - Manufacturing method of circuit board and resin sheet with metal foil - Google Patents

Description

The present invention relates to a method for manufacturing a circuit board. It also relates to a resin sheet with metal foil used in the method for manufacturing the circuit board.

Until now, circuit boards such as motherboards for portable electronic devices, system-in-package boards, and chip-scale package boards have been manufactured by building up fiber-reinforced prepreg and copper foil on a core substrate.

Recently, as electronic devices become more functional and thinner, there is a demand for circuit boards to be able to accommodate finer wiring, and the manufacture of circuit boards using resin sheets with metal foil is being considered. This resin sheet with metal foil comprises a metal foil with a supporting substrate, which comprises a metal foil and a supporting substrate, and a resin composition layer bonded to the metal foil of the metal foil with supporting substrate (see, for example, Patent Document 1). It is assumed that the other side of the resin composition layer is provided with a plastic film as a protective film or the like, and prior to laminating the resin sheet with metal foil to a substrate in the manufacture of a circuit board, the plastic film is peeled off to expose the resin composition layer.

JP 2018-172785 A

Metal foil-attached resin sheets do not have a fiber base material like prepregs, so under the heat and pressure conditions used when laminating the base material in the manufacture of circuit boards, resin flow tends to be higher than with prepregs, making it difficult to obtain an insulating layer with a uniform thickness. In order to suppress resin flow, it is possible to increase the molecular weight or amount of resin contained in the resin composition, but this would have an impact on the physical properties of the resulting insulating layer, such as a decrease in crosslink density after thermal curing, which is an issue.

On the other hand, as a method of suppressing resin flow while maintaining the degree of freedom in the design of the resin composition, lamination onto the substrate under low pressure conditions is considered. However, the present inventors have found that laminating a resin sheet with metal foil onto a substrate under low pressure conditions results in a phenomenon in which the insulation resistance between wiring decreases, resulting in a decrease in yield. In particular, in the manufacture of circuit boards in which wiring is formed by a modified semi-additive method using metal foil as a plating seed layer, or a semi-additive method using the exposed surface profile of the insulating layer after removing the metal foil, the inventors have found that the above-mentioned problem of decreased yield tends to become more pronounced when forming wiring with an inter-wiring distance of 35 μm or less.

The objective of the present invention is to provide a new technology that can suppress the decrease in insulation resistance between wiring and achieve good yields, even when forming fine wiring by laminating a resin sheet with metal foil on a substrate under low pressure conditions.

As a result of intensive research, the inventors discovered that the above problems could be solved by a circuit board manufacturing method and a resin sheet with metal foil having the following configuration, and thus completed the present invention.

That is, the present invention includes the following.
[1]
(Y) A method for producing a circuit board, comprising a step of laminating a resin sheet with a metal foil, the resin sheet including a resin composition layer having first and second main surfaces, a metal foil with a supporting substrate bonded to the first main surface of the resin composition layer on the metal foil side, and a plastic film bonded to the second main surface of the resin composition layer, onto a substrate such that the second main surface of the resin composition layer is bonded to the substrate,
A method in which the number of concave or convex parts having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the metal foil-attached resin sheet used in step (Y) on the metal foil-attached metal foil side is 5 or less per ^cm2 .
[2]
The method according to [1], wherein in the step (Y), the resin sheet with the metal foil is laminated on the substrate at a pressure of 1.5 MPa or less.
[3]
(Z) The method according to [1] or [2], further comprising a step of forming wiring by a modified semi-additive method or a semi-additive method.
[4]
The method according to [3], wherein in the step (Z), wiring is formed with a distance between wirings of 35 μm or less.
[5]
The method according to any one of [1] to [4], wherein the number of concave or convex parts having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the plastic film side of the resin sheet with the metal foil is 5 or less per ^cm2 .
[6]
The method according to any one of [1] to [5], wherein the thickness of the metal foil in the metal foil with supporting substrate is 5 μm or less.
[7]
The method according to any one of [1] to [6], wherein the supporting substrate in the metal foil with a supporting substrate is a plastic film or a carrier metal foil.
[8]
The method according to any one of [1] to [7], wherein the resin composition layer contains 40% by mass or more of an inorganic filler when the non-volatile components of the resin composition layer are taken as 100% by mass.
[9]
A resin sheet with a metal foil, comprising: a resin composition layer having first and second main surfaces; a metal foil with a support substrate bonded to the first main surface of the resin composition layer on the metal foil side; and a plastic film bonded to the second main surface of the resin composition layer,
A resin sheet with a metal foil, in which the number of recesses or protrusions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more is 5 or less per ^cm2 on the surface of the resin sheet with a metal foil on the supporting substrate side.
[10]
The resin sheet with a metal foil according to [9], wherein the number of concave or convex parts having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the plastic film side of the resin sheet with the metal foil is 5 or ^less per cm2.

The present invention provides a new technology that can suppress the decrease in insulation resistance between wiring and achieve good yields, even when forming fine wiring by laminating a resin sheet with metal foil on a substrate under low pressure conditions.

FIG. 1 is a schematic end view of a resin sheet with a metal foil. FIG. 2a is a schematic diagram (1) for explaining the method for producing a resin sheet with a metal foil of the present invention. FIG. 2b is a schematic diagram (2) for explaining the method for producing a resin sheet with a metal foil of the present invention.

Below, an embodiment of the present invention will be described with reference to the drawings. Note that each drawing merely shows the shape, size, and arrangement of the components in a schematic manner to the extent that the invention can be understood. The present invention is not limited by the following description, and each component can be modified as appropriate without departing from the gist of the present invention. In the drawings used in the following description, similar components are indicated with the same reference numerals, and duplicated explanations may be omitted. Furthermore, the configuration according to the embodiment of the present invention is not necessarily manufactured or used according to the arrangement of the illustrated example.

[Method of manufacturing circuit board]
The method for producing a circuit board of the present invention (hereinafter also simply referred to as the "method of the present invention") comprises the steps of:
(Y) a step of laminating a resin sheet with a metal foil, the resin sheet including a resin composition layer having first and second main surfaces, a metal foil with a supporting substrate bonded to the first main surface of the resin composition layer on the metal foil side, and a plastic film bonded to the second main surface of the resin composition layer, onto a substrate such that the second main surface of the resin composition layer is bonded to the substrate,
The resin sheet with metal foil used in step (Y) is characterized in that the surface of the resin sheet with metal foil on the side of the supporting substrate on which the metal foil is attached has 5 or less concave or convex portions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more per ^cm2 .

As mentioned above, resin sheets with metal foil do not have a fiber base material like prepregs, so under the heat and pressure conditions when laminating to a base material in the manufacture of circuit boards, resin flow tends to be higher than with prepregs, making it difficult to obtain an insulating layer with a uniform thickness. In order to suppress resin flow, it is possible to increase the molecular weight or amount of resin contained in the resin composition, but this has an impact on the physical properties of the resulting insulating layer, such as a decrease in crosslink density after thermal curing, which is an issue.

On the other hand, as a method of suppressing resin flow while maintaining the degree of freedom in the design of the resin composition, lamination onto the substrate under low pressure conditions is considered. However, the present inventors have found that laminating a resin sheet with metal foil onto a substrate under low pressure conditions results in a phenomenon in which the insulation resistance between wiring decreases, resulting in a decrease in yield. In particular, in the manufacture of circuit boards in which wiring is formed by a modified semi-additive method using metal foil as a plating seed layer, or a semi-additive method using the exposed surface profile of the insulating layer after removing the metal foil, the inventors have found that the above-mentioned problem of decreased yield tends to become more pronounced when forming wiring with an inter-wiring distance of 35 μm or less.

The inventors of the present invention confirmed the state of the circuit wiring of a circuit board in which the insulation resistance between wirings was reduced and the yield was reduced, and confirmed that a conductor was present in a location different from the original circuit formation portion, which was one of the causes of the reduction in the insulation resistance between wirings. When manufacturing a circuit board using a resin sheet with metal foil, as described below, wiring can be formed by a modified semi-additive method in which the metal foil of the sheet is used as a plating seed layer, or a semi-additive method in which the exposed surface profile of the insulating layer after removing the metal foil is used. In the former case, the exposed surface of the metal foil, and in the latter case, the exposed surface of the insulating layer, may have recesses or protrusions with in-plane dimensions of several μm to several hundred μm, and it was also confirmed that the yield is reduced when such recesses or protrusions exist. If a recess exists in the metal foil, when removing the metal foil other than the circuit formation portion in the modified semi-additive method, the metal foil present in the recess is difficult to remove and tends to remain. Even when a recess exists on the exposed surface of the insulating layer, the seed layer formed by electroless plating in the semi-additive method in the recess is difficult to remove and tends to remain. In this way, it is presumed that the conductor remains in areas other than the circuit formation area, which reduces the insulation resistance between the wiring. In circuit boards with wiring with a small distance between the wiring, the influence of such remaining conductors is relatively increased, and it is considered that the problem of reduced yield becomes prominent when forming wiring with a distance between the wiring of 35 μm or less as described above. In addition, the presence of a protrusion causes poor adhesion of the plating resist in the modified semi-additive method and the semi-additive method, which causes the plating conductor to slip into unintended places during electrolytic plating, or the electrolytic plating thickness is insufficient at the protrusion, causing localized insufficient wiring thickness or disconnection, which is an obstacle to achieving the desired wiring design. Among these, the presence of a recess tends to cause a decrease in yield in the manufacture of circuit boards.

The present inventors have found that such recesses and protrusions of the metal foil and insulating layer (resin composition layer) are originally present in the resin sheet with metal foil used in the manufacture of the circuit board. As described above, when the resin sheet with metal foil is laminated to the substrate under low pressure conditions in the manufacture of the circuit board, it is believed that these recesses and protrusions are not sufficiently flattened and remain even at the stage of forming the wiring. In addition, when the cause of the formation of these recesses and protrusions was examined, it was found that they are unintentionally formed in the process of laminating the first resin sheet and the metal foil with the supporting substrate, or the second resin sheet and the plastic film in the manufacture of the resin sheet with metal foil. It is presumed that foreign matter adhering to the surface of the pressure roll used for lamination forms recesses in the metal foil with the supporting substrate or the plastic film as dents during lamination, and when viewed from the metal foil side or the first main surface side of the resin composition layer, this forms recesses (caused by foreign matter adhering to the roll surface that contacts the metal foil with the supporting substrate during lamination) or protrusions (caused by foreign matter adhering to the roll surface that contacts the plastic film during lamination). As described below, the "first resin sheet" used in the manufacture of the resin sheet with metal foil consists of a resin composition layer and a plastic film bonded to the second main surface of the resin composition layer, and the "second resin sheet" consists of a resin composition layer and a metal foil with a supporting substrate bonded to the first main surface of the resin composition layer on the metal foil side.

In contrast, in the process (step (Y)) of laminating a resin sheet with a metal foil and a substrate, the method for producing a circuit board of the present invention uses a resin sheet with a metal foil having 5 or ^less recesses or protrusions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the metal foil with supporting substrate side, even when lamination to the substrate is performed under low pressure conditions, the occurrence of recesses or protrusions on the surface on which the wiring is to be formed is reduced, and a good yield can be achieved. Thus, the present invention can achieve a good yield in the production of circuit boards with fine wiring while maintaining the degree of freedom in designing the resin composition in the resin sheet with a metal foil, and significantly contributes to the fine wiring of circuit boards.

In step (Y), a resin sheet with metal foil, which includes a resin composition layer having first and second main surfaces, a metal foil with a supporting substrate bonded to the first main surface of the resin composition layer on the metal foil side, and a plastic film bonded to the second main surface of the resin composition layer, is laminated onto a substrate so that the second main surface of the resin composition layer is bonded to the substrate.

The resin composition layer, metal foil with supporting substrate, and plastic film constituting the resin sheet with metal foil used in step (Y) will be described later, including suitable examples thereof, but the method of the present invention is characterized in that the surface of the resin sheet with metal foil used in step (Y) on the side of the metal foil with supporting substrate has 5 or ^less concave or convex portions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more per cm2.

Figure 1 shows a schematic end view of the resin sheet with metal foil used in step (Y). The resin sheet with metal foil 10 includes a resin composition layer 1 having first and second main surfaces, a metal foil 3 with a support substrate bonded to the first main surface (lower main surface in Figure 1) of the resin composition layer on the metal foil 3a side, and a plastic film 2 bonded to the second main surface (upper main surface in Figure 1) of the resin composition layer. The metal foil 3 with a support substrate is composed of the metal foil 3a and the support substrate 3b bonded to the metal foil in a peelable state.

From the viewpoint of achieving a good yield even when lamination to a substrate is performed under low pressure conditions, the number of recesses or protrusions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface (lower surface in FIG. 1 ) of the resin sheet with metal foil used in step (Y) on the side of the metal foil with supporting substrate is 5/cm ² or less, preferably 4.5/cm ² or less, and more preferably 4/cm ² or less. In particular, when the number of the recesses or protrusions is 4/cm ² or less, it is preferable because a good yield can be achieved even when wiring with an inter-wiring distance of 35 μm or less is formed in the manufacture of a circuit board in which wiring is formed by a modified semi-additive method or a semi-additive method. From the viewpoint of achieving a better yield even when fine wiring is formed by the modified semi-additive method or the semi-additive method, it is more preferable that the number of recesses or protrusions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the metal foil-attached resin sheet used in step (Y) on the metal foil-attached metal foil side is 3.5 pcs/cm2 or ^less , and even more preferably 3 pcs/cm2 or ^less , 2.5 pcs/cm2 or ^less , or 2 pcs/cm2 or ^less .

In the present invention, the "maximum diameter" of the surface irregularities of the resin sheet with metal foil refers to the maximum dimension of the irregularities in the planar direction of the surface of the resin sheet with metal foil. If the irregularities are perfect circles when viewed from directly above the surface, this refers to the diameter. If the irregularities are other than perfect circles, this refers to the maximum dimension in the planar direction of the shape. Furthermore, the "maximum height difference" refers to the difference between the maximum height and minimum height of the irregularities in the direction perpendicular to the surface of the resin sheet with metal foil (thickness direction).

In the present invention, the number of recesses or protrusions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the metal foil-attached resin sheet on the side of the metal foil-attached support substrate can be determined by observing the surface under a microscope, analyzing the identified recesses and protrusions with a step gauge, and counting the number of recesses or protrusions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more. A digital microscope may be used as the microscope used for surface observation, and an example of the microscope may be Keyence's "VHX-900." The step gauge used for the unevenness analysis is not particularly limited as long as it can analyze recesses or protrusions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more, but a contact step gauge may be used, and an example of the microscope may be Bruker's "DektakXT" stylus profiling system.

The number of recesses or protrusions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more in the present invention is based on the arithmetic mean value (pieces/cm ² ) of the number of recesses or protrusions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more, determined by randomly selecting 10 areas of 1 cm 2 from within a 15 cm x 15 cm surface of the metal foil-attached resin sheet on the metal foil-attached metal foil side of the supporting substrate, observing and analyzing the selected 10 areas, as described in the section "( ^1-4 ) Observation of surface unevenness" below. By determining the number of surface unevenness as described above, it is possible to accurately determine the success or failure of conditions related to surface unevenness suitable for achieving a good yield, even when lamination to a substrate is performed under low pressure conditions.

The lower limit of the number of recesses or protrusions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the resin sheet with metal foil on the side of the metal foil with supporting substrate is not particularly limited and may be 0 pcs/cm ² .

The upper limit of the maximum diameter of the recesses or protrusions on the surface of the metal foil with support substrate side of the resin sheet with metal foil is, for example, 100,000 μm or less, 10,000 μm or less, 5,000 μm or less, 2,000 μm or less, 1,000 μm or less, and the upper limit of the maximum height difference is, for example, 5 μm or less, 4 μm or less, 3 μm or less.

Even when lamination to the substrate is performed under low pressure conditions, from the viewpoint of achieving a better yield, the number of recesses or protrusions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the plastic film side surface (upper surface in FIG. 1) of the metal foil-attached resin sheet used in step (Y) is preferably 5 pieces/cm ² or less, more preferably 4.5 pieces/cm ² or less, even more preferably 4 pieces/cm ² or less, 3.5 pieces/cm ² or less, or 3 pieces/cm ² or less. The number of the recesses or protrusions on the plastic film side surface may be determined in the same manner as the number of recesses or protrusions on the metal foil-attached surface with the support substrate. The upper limit of the maximum diameter of the recesses or protrusions on the plastic film side surface of the metal foil-attached resin sheet is as described above for the metal foil side surface.

In step (Y), the "substrate" on which the resin sheet with metal foil is laminated mainly refers to a substrate such as a glass epoxy substrate, a metal substrate, a polyester substrate, a polyimide substrate, a BT resin substrate, or a thermosetting polyphenylene ether substrate, or a substrate on one or both sides of which a patterned conductor layer (circuit) is formed. In addition, when manufacturing a circuit board, the inner layer circuit board of an intermediate product on which an insulating layer and/or a conductor layer is to be further formed is also included in the "substrate" of the present invention. When the circuit board is a circuit board with built-in components, a substrate with built-in components may be used.

Prior to step (Y), the plastic film is peeled off from the resin sheet with the metal foil to expose the surface of the resin composition layer (i.e., the second main surface). Then, the resin sheet with the metal foil is laminated onto the substrate so that the second main surface of the resin composition layer is bonded to the substrate.

As mentioned above, the method of the present invention can reduce the occurrence of concave and convex parts on the surface on which the wiring is to be formed, and achieve good yields, even when lamination to the substrate is performed under low pressure conditions to suppress resin flow.

Therefore, in one embodiment, the method of the present invention includes, in step (Y), a step of laminating the resin sheet with the metal foil onto the substrate at a pressure of 1.5 MPa or less. According to the method of the present invention, as described below, even when the pressure during lamination is further reduced, a good yield can be achieved.

In step (Y), lamination of the resin sheet with the metal foil and the substrate is preferably performed under a reduced pressure atmosphere, for example, by vacuum heat pressing or vacuum lamination. Hereinafter, the embodiment in which lamination is performed by vacuum heat pressing is referred to as the "first embodiment," and the embodiment in which lamination is performed by vacuum lamination is referred to as the "second embodiment."

-First embodiment-
In the first embodiment, the circuit board is preferably manufactured using a vacuum hot press device in the following procedure.

First, a laminate structure is prepared in which a resin sheet with metal foil is placed on one or both sides of a substrate so that the resin composition layer and the substrate are bonded, and the laminate structure is set in a vacuum heat press device.

The laminated structure is preferably set in a vacuum heat press device via cushion paper, a metal plate such as a stainless steel plate (SUS plate), a release film, etc. For example, when a resin sheet with metal foil is placed on both sides of a substrate, the laminated structure is set in the vacuum heat press device in the following order: cushion paper/metal plate/release film/laminated structure (i.e., resin sheet with metal foil/substrate/resin sheet with metal foil)/release film/SUS plate/cushion paper. Here, the symbol "/" means that the components shown sandwiching it are arranged so that they are in contact with each other (the same applies in the explanation of the laminated structure in this specification, etc.).

Next, a vacuum heat press process is performed to heat and press the laminated structure under reduced pressure.

The vacuum hot press process can be carried out using a conventional vacuum hot press device that presses the laminated structure from both sides with a heated metal plate such as a stainless steel plate. Commercially available vacuum hot press devices include, for example, the "MNPC-V-750-5-200" manufactured by Meiki Seisakusho Co., Ltd. and the "VH1-1603" manufactured by Kitagawa Seiki Co., Ltd.

The vacuum heat pressing process may be performed only once, or may be repeated two or more times.

In the vacuum hot press process, the bonding pressure (pressing force) is preferably 1.5 MPa or less, as described above, from the viewpoint of suppressing resin flowability and obtaining an insulating layer with a uniform thickness, more preferably 1.4 MPa or less, and even more preferably 1.2 MPa or less or 1 MPa or less. The lower limit is not particularly limited as long as lamination of the resin sheet with metal foil and the substrate can be performed, but it can be, for example, 0.2 MPa or more, 0.3 MPa or more, 0.4 MPa or more, etc.

In the vacuum hot press treatment, the atmospheric pressure, that is, the reduced pressure inside the chamber in which the laminate structure to be treated is stored, is preferably 3×10 ⁻² MPa or less, and more preferably 1×10 ⁻² MPa or less.

In the vacuum hot press treatment, the heating temperature (T) varies depending on the composition of the resin composition layer, but is usually 130°C or higher, and preferably 140°C or higher, 150°C or higher, or 160°C or higher. There is no particular upper limit to the heating temperature (T), but it can usually be 240°C or lower.

From the viewpoint of suppressing cracks, distortion, etc., it is preferable to carry out the vacuum heat pressing process while increasing the temperature stepwise or continuously and/or decreasing the temperature stepwise or continuously. In such a case, it is preferable that the maximum temperature reached satisfies the desired temperature condition described above.

The vacuum hot press treatment may be carried out under heating conditions in which, for example, the temperature is increased from room temperature to the heating temperature (T) at a temperature increase rate S ₁ , the heating temperature (T ₎ is held for a predetermined time, and then the temperature is decreased from the heating temperature (T) to room temperature at a temperature decrease rate S 2. The temperature increase rate S ₁ and the temperature decrease rate S ₂ are usually 0.5°C/min to 30°C/min, preferably 1°C/min to 10°C/min, and more preferably 2°C/min to 8°C/min. The time for holding at the heating temperature (T) may be appropriately determined depending on the composition of the resin composition layer, but is usually 1 minute to 180 minutes, preferably 5 minutes to 150 minutes, and more preferably 10 minutes to 120 minutes.

By the vacuum hot press treatment, the resin composition layer is cured to form an insulating layer. Therefore, when the resin sheet with metal foil is laminated on both sides of the substrate as described above, the resulting laminate has a layer structure of metal foil with supporting substrate (supporting substrate/metal foil)/insulating layer/substrate/insulating layer/metal foil with supporting substrate (metal foil/supporting substrate).

-Second embodiment-
In the second embodiment, the circuit board is preferably manufactured by a method including the following steps (I) and (II) using a vacuum lamination process.
(I) A step of placing a resin sheet with a metal foil obtained by the manufacturing method of the present invention on one or both sides of a substrate so that the resin composition layer and the substrate are bonded, and performing a vacuum lamination process. (II) A step of thermally curing the resin composition layer to form an insulating layer.

In step (I), the resin sheet with metal foil obtained by the manufacturing method of the present invention is placed on one or both sides of the substrate so that the resin composition layer and the substrate are bonded, and then vacuum lamination is performed.

Vacuum lamination can be performed by heat-pressing the resin sheet with metal foil to the substrate from the metal foil side with supporting substrate. Examples of the member for heat-pressing the resin sheet with metal foil to the substrate (hereinafter also referred to as the "heat-pressing member") include a heated metal plate (such as a SUS panel) or a metal roll (SUS roll). Note that it is preferable to press the heat-pressing member through an elastic material such as heat-resistant rubber, rather than directly against the resin sheet with metal foil.

In the vacuum lamination process, the heating temperature is preferably in the range of 60°C to 160°C, more preferably 80°C to 140°C. From the viewpoint of suppressing resin flowability and obtaining an insulating layer with a uniform thickness, the pressure bonding is preferably 1.5 MPa or less, more preferably 1.4 MPa or less, and even more preferably 1.2 MPa or less or 1 MPa or less, as described above, and the lower limit is not particularly limited as long as lamination of the resin sheet with metal foil and the substrate can be performed, but may be, for example, 0.1 MPa or more, 0.2 MPa or more, 0.3 MPa or more, etc. The pressure bonding time is preferably in the range of 20 seconds to 400 seconds, more preferably 30 seconds to 300 seconds. The vacuum lamination process is preferably performed under reduced pressure conditions of 26.7 hPa or less.

The vacuum lamination process can be carried out using a commercially available vacuum laminator. Examples of commercially available vacuum laminators include a two-stage build-up laminator manufactured by Nikko Materials Co., Ltd., a vacuum pressure laminator manufactured by Meiki Seisakusho Co., Ltd., and a vacuum applicator manufactured by Nichigo-Morton Co., Ltd.

After the vacuum lamination process, the laminated resin sheet with metal foil may be smoothed under normal pressure (atmospheric pressure), for example by pressing a heat-pressure bonding member from the metal foil side with the support substrate. The heat-pressure bonding conditions for the smoothing process may be the same as the heat-pressure bonding conditions for the vacuum lamination process described above. The smoothing process may be performed using a commercially available laminator. Note that lamination and smoothing may be performed consecutively using the commercially available vacuum laminator described above.

In step (II), the resin composition layer is thermally cured to form an insulating layer.

The conditions for thermal curing are not particularly limited, and the conditions normally used for forming insulating layers for circuit boards may be used.

For example, the thermal curing conditions for the resin composition layer may vary depending on the composition of the resin composition layer, but the curing temperature may be in the range of 120°C to 240°C (preferably in the range of 150°C to 210°C, more preferably in the range of 170°C to 190°C), and the curing time may be in the range of 5 minutes to 90 minutes (preferably in the range of 10 minutes to 75 minutes, more preferably in the range of 15 minutes to 60 minutes).

Before the resin composition layer is thermally cured, the resin composition layer may be preheated at a temperature lower than the curing temperature. For example, prior to thermally curing the resin composition layer, the resin composition layer may be preheated for 5 minutes or more (preferably 5 minutes to 150 minutes, more preferably 15 minutes to 120 minutes) at a temperature of 50°C or more and less than 120°C (preferably 60°C or more and 110°C or less, more preferably 70°C or more and 100°C or less).

In step (II), the resin composition layer is cured to form an insulating layer. Therefore, when a resin sheet with metal foil is laminated on both sides of a substrate, the resulting laminate has a layer structure of metal foil with supporting substrate (supporting substrate/metal foil)/insulating layer/substrate/insulating layer/metal foil with supporting substrate (metal foil/supporting substrate).

Regardless of whether the first or second embodiment is used, a process of drilling holes, a process of performing a desmear process, and a process of forming wiring may be further performed.

In the drilling process, via holes or the like can be formed in the insulating layer. This process may be carried out by known procedures using, for example, a drill, a laser, plasma, or the like, depending on the composition of the resin composition layer used to form the insulating layer.

The inside of the via holes formed during the drilling process generally contains resin residue (smear) from the insulating layer. Since such smears can cause poor electrical connections between layers, a process to remove the smear (desmear process) is carried out.

The procedure and conditions of the desmear treatment are not particularly limited, and known procedures and conditions that are normally used in the manufacture of circuit boards can be adopted. For example, the desmear treatment can be performed by carrying out a swelling treatment using a swelling liquid, an oxidation treatment using an oxidizing agent solution, and a neutralization treatment using a neutralizing liquid in this order. Examples of the swelling liquid include "Swelling Dip Securigans P" and "Swelling Dip Securigans SBU" manufactured by Atotech Japan. The swelling treatment is preferably performed by immersing the laminate with the via holes formed in the swelling liquid heated to 60°C to 80°C for 5 to 10 minutes. The oxidizing agent solution is preferably an alkaline permanganate solution, such as a solution in which potassium permanganate or sodium permanganate is dissolved in an aqueous solution of sodium hydroxide. The oxidation treatment using the oxidizing agent solution is preferably performed by immersing the laminate after the swelling treatment in an oxidizing agent solution heated to 60°C to 80°C for 10 to 30 minutes. Commercially available alkaline permanganate aqueous solutions include, for example, "Concentrate Compact CP" and "Dosing Solution Securiganth P" manufactured by Atotech Japan. The neutralization treatment using a neutralizing solution is preferably carried out by immersing the laminated plate after oxidation treatment in a neutralizing solution at 30°C to 50°C for 3 to 10 minutes. The neutralizing solution is preferably an acidic aqueous solution, and a commercially available product is, for example, "Reduction Solution Securiganth P" manufactured by Atotech Japan.

Next, wiring is formed on the surface of the insulating layer. As described above, according to the method of the present invention, a good yield can be achieved even when forming wiring with a small distance between the wirings by using the modified semi-additive method that uses the metal foil as a plating seed layer, or the semi-additive method that uses the exposed surface profile of the insulating layer after removing the metal foil.

Thus, in one embodiment, the method for producing a circuit board of the present invention includes the steps of:
(Z) A step of forming wiring by a modified semi-additive method or a semi-additive method is included.

Prior to step (Z), the supporting substrate (i.e., the supporting substrate derived from the metal foil with supporting substrate) is removed from the laminate. As described below, the supporting substrate is joined to the metal foil in a peelable state, and therefore can be easily peeled off and removed. In this way, the metal foil can be exposed. For example, when a resin sheet with metal foil is laminated on both sides of the substrate as described above, a laminate having a layer structure of metal foil/insulating layer/substrate/insulating layer/metal foil can be obtained by peeling off the supporting substrate.

- Wiring formation using modified semi-additive method -
In the modified semi-additive method (MSAP), non-circuit forming portions of a metal foil are protected by a plating resist, and a metal such as copper is thickly applied to the circuit forming portion by electrolytic plating, and then the plating resist is removed, and the metal foil other than the circuit forming portion is removed by etching to form a circuit. The circuit formation by the modified semi-additive method may be carried out according to a known procedure. For example, the circuit formation by the modified semi-additive method can be carried out by a method including: i) providing a plating resist on the surface of the metal foil; ii) exposing and developing the plating resist to form a wiring pattern; iii) electroplating through the plating resist; iv) removing the plating resist; and v) etching and removing the metal foil other than the circuit forming portion. In addition, when the metal foil derived from the resin sheet with the metal foil is thick, the entire surface of the metal foil may be thinned by etching or the like before the above i) so that the metal foil has a desired thickness (usually 5 μm or less, 4 μm or less, or 3 μm or less).

- Wiring formation using semi-additive method -
In the semi-additive process (SAP), the metal foil is removed by etching or the like to expose the insulating layer. At this time, the exposed surface of the insulating layer has a profile derived from the metal foil. Then, a circuit is formed on the exposed surface of the insulating layer by plating or the like. The circuit formation by the semi-additive process may be carried out according to a known procedure, except that the conventional roughening treatment of the insulating layer surface may be omitted by utilizing the exposed surface profile of the insulating layer. For example, the circuit formation by the semi-additive process may be carried out by a method including: i) forming a seed layer by electroless plating on the exposed surface of the insulating layer; ii) providing a plating resist on the seed layer; iii) exposing and developing the plating resist to form a wiring pattern; iv) electroplating through the plating resist; v) removing the plating resist; and vi) etching and removing the seed layer other than the circuit formation portion. Depending on the degree of the exposed surface profile of the insulating layer after removing the metal foil, the insulating layer surface may be roughened prior to the above i).

As described above, according to the method of the present invention, the occurrence of concaves and convexities on the wiring formation surface (metal foil surface in the modified semi-additive method, insulating layer surface in the semi-additive method) can be reduced, and good yields can be achieved. As a result, good yields can be achieved even when wiring with a small wiring distance is formed. For example, in step (Z), wiring with a wiring distance of 35 μm or less can be formed with good yields, and even wiring with a small wiring distance of 30 μm or less or 25 μm or less can be formed with good yields. In particular, when forming wiring with a wiring distance of 25 μm or less, the conventional circuit board manufacturing method shows a significant decrease in yield, whereas the method of the present invention can form wiring with a smaller wiring distance while achieving good yields. According to the method of the present invention, it is possible to form wiring with a small wiring distance of, for example, 20 μm or less, 15 μm or less, 14 μm or less, 12 μm or less, or 10 μm or less with good yields. The lower limit of the distance between the wirings is preferably 5 μm or more or 6 μm or more from the viewpoint of achieving good yield.

[Resin sheet with metal foil]
As described above, the method for producing a circuit board of the present invention is characterized in that the resin sheet with metal foil used in ^step (Y) has 5 or less concave or convex parts with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on its surface on the metal foil-attached metal foil-attached substrate side, and this makes it possible to suppress a decrease in the insulation resistance value between wiring and achieve a good yield even when the resin sheet with metal foil is laminated on the substrate under low pressure conditions to form fine wiring. The present invention also provides such a resin sheet with metal foil.

The resin sheet with metal foil of the present invention is a resin sheet with metal foil comprising a resin composition layer having first and second main surfaces, a metal foil with a supporting substrate bonded to the first main surface of the resin composition layer on the metal foil side, and a plastic film bonded to the second main surface of the resin composition layer, and is characterized in that the surface of the resin sheet with metal foil on the side of the supporting substrate on the metal foil side has 5 or ^less concave or convex portions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more per cm2.

Here, the layer structure of the resin sheet with metal foil of the present invention is as described above with reference to FIG. 1, and the preferred range of the number of the projections and recesses on the surface of the resin sheet with metal foil on the metal foil side with the supporting substrate and the number of projections and recesses on the surface of the plastic film side, as well as the method of determining the number of projections and recesses, are as described above in the section [Method of manufacturing a circuit board].

The "resin composition layer," "plastic film," and "metal foil with supporting substrate" that constitute the resin sheet with metal foil of the present invention are described below.

<Resin composition layer>
The resin composition used in the resin composition layer is not particularly limited as long as the cured product exhibits sufficient insulation properties, and any known resin composition used in the formation of insulating layers for circuit boards may be used.

As mentioned above, resin sheets with metal foils do not have a fiber base material like prepregs, so under the heating and pressurizing conditions when laminating them to a base material in the manufacture of circuit boards, the resin flow is higher than that of prepregs, and as a result, it tends to be difficult to obtain an insulating layer with a uniform thickness. In order to suppress the resin flow, it is possible to increase the molecular weight or amount of the resin contained in the resin composition, but this has an impact on the physical properties of the resulting insulating layer, such as a decrease in crosslink density after thermal curing, which is an issue. On the other hand, laminating the resin sheet with metal foils to a base material under low pressure conditions is a method of suppressing the resin flow while maintaining the freedom of design of the resin composition, but when the resin sheet with metal foils is laminated to a base material under low pressure conditions, the insulation resistance between the wiring decreases, resulting in a phenomenon of a decrease in yield.

In contrast, according to the resin sheet with metal foil of the present invention, in which the surface on the metal foil side with a supporting substrate has 5 or ^fewer concave or convex parts with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more, a good yield can be achieved even when lamination to the substrate is performed under low pressure conditions to suppress resin flow, and therefore, it is possible to advantageously maintain the freedom in designing the resin composition (layer) used in the resin sheet with metal foil.

For example, the resin composition constituting the resin composition layer may be a resin composition that contains (a) a curable resin and, if necessary, further contains one or more selected from the group consisting of (b) a curing agent, (c) an inorganic filler, (d) a thermoplastic resin, and (e) a curing accelerator. Each component that may be contained in the resin composition is described below.

-(a) Curing resin-
As the curable resin, a conventionally known curable resin used in forming an insulating layer of a circuit board may be used. From the viewpoint of being able to provide a cured product exhibiting both good insulation and heat resistance, The curable resin is preferably at least one selected from the group consisting of thermosetting resins and radically polymerizable resins.

As the thermosetting resin and radically polymerizable resin, known resins used in forming insulating layers of circuit boards may be used. Below, the thermosetting resins and radically polymerizable resins that can be used as the curable resin are described.

Examples of thermosetting resins include epoxy resins, polyarylene ether resins, benzocyclobutene resins, epoxy acrylate resins, urethane acrylate resins, urethane resins, cyanate resins, melamine resins, and silicone resins. The thermosetting resins may be used alone or in combination of two or more. Among them, it is preferable that the curable resin contains an epoxy resin, from the viewpoint of being able to produce a cured product that exhibits both good insulating properties and good heat resistance.

The type of epoxy resin is not particularly limited as long as it has one or more (preferably two or more) epoxy groups in one molecule. Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol AF type epoxy resins, phenol novolac type epoxy resins, tert-butyl-catechol type epoxy resins, naphthol type epoxy resins, naphthalene type epoxy resins, naphthylene ether type epoxy resins, glycidylamine type epoxy resins, glycidyl ester type epoxy resins, cresol novolac type epoxy resins, biphenyl type epoxy resins, phenol aralkyl type epoxy resins, biphenyl aralkyl type epoxy resins, fluorene skeleton type epoxy resins, dicyclopentadiene type epoxy resins, anthracene type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexane dimethanol type epoxy resins, trimethylol type epoxy resins, halogenated epoxy resins, etc. According to the present invention, it is possible to realize a resin sheet with metal foil that provides good yields in the manufacture of circuit boards, regardless of the type of epoxy resin.

Epoxy resins can be classified into epoxy resins that are liquid at a temperature of 20°C (hereinafter referred to as "liquid epoxy resins") and epoxy resins that are solid at a temperature of 20°C (hereinafter referred to as "solid epoxy resins"). The resin composition used in the present invention may contain only liquid epoxy resins as the curable resin, may contain only solid epoxy resins, or may contain a combination of liquid and solid epoxy resins. When a combination of liquid and solid epoxy resins is contained, the blending ratio (liquid:solid) may be in the range of 20:1 to 1:20 by mass (preferably 10:1 to 1:10, more preferably 3:1 to 1:3).

The epoxy group equivalent of the epoxy resin is preferably 50 g/eq. to 2000 g/eq., more preferably 60 g/eq. to 1000 g/eq., and even more preferably 80 g/eq. to 500 g/eq. The epoxy group equivalent is the mass of the epoxy resin containing one equivalent of epoxy groups, and can be measured according to JIS K7236.

The weight average molecular weight (Mw) of the epoxy resin is preferably 100 to 5,000, more preferably 250 to 3,000, and even more preferably 400 to 1,500. The Mw of the epoxy resin can be measured as a polystyrene-equivalent value by gel permeation chromatography (GPC).

The type of radically polymerizable resin is not particularly limited as long as it has one or more (preferably two or more) radically polymerizable unsaturated groups in one molecule. Examples of radically polymerizable resins include resins having one or more radically polymerizable unsaturated groups selected from maleimide groups, vinyl groups, allyl groups, styryl groups, vinylphenyl groups, acryloyl groups, methacryloyl groups, fumaroyl groups, and maleoyl groups. In particular, from the viewpoint of being able to produce a cured product that exhibits both good insulating properties and good heat resistance, it is preferable that the curable resin contains one or more selected from maleimide resins, (meth)acrylic resins, and styryl resins.

There is no particular limitation on the type of maleimide resin, so long as it has one or more (preferably two or more) maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl groups) in one molecule. Examples of maleimide resins include "BMI-3000J", "BMI-5000", "BMI-1400", "BMI-1500", "BMI-1700", and "BMI-689" (all manufactured by Designer Molecules, Inc.). Maleimide resins containing an aliphatic skeleton (preferably an aliphatic skeleton containing a cyclic structure having 10 or more carbon atoms, more preferably an aliphatic skeleton having 36 carbon atoms derived from dimer diamine), such as "MIR-3000-70MT" (manufactured by Nippon Kayaku Co., Ltd.), "BMI-4000", "BMI-1000" (manufactured by Daiwa Kasei Co., Ltd.), and "BMI-80" (manufactured by Keiai Kasei Co., Ltd.); maleimide resins containing an indane skeleton, as described in the Technical Journal of the Japan Institute of Invention and Innovation, No. 2020-500211; maleimide resins containing an aromatic ring skeleton directly bonded to the nitrogen atom of the maleimide group, such as "MIR-3000-70MT" (manufactured by Nippon Kayaku Co., Ltd.), "BMI-4000", "BMI-1000" (manufactured by Daiwa Kasei Co., Ltd.), and "BMI-80" (manufactured by Keiai Kasei Co., Ltd.).

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

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

The resin composition used in the present invention may contain only a thermosetting resin as the curable resin, may contain only a radically polymerizable resin, or may contain a combination of a thermosetting resin and a radically polymerizable resin.

From the viewpoint of producing a cured product exhibiting both good insulation and good heat resistance, the content of the curable resin in the resin composition is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 12% by mass or more, 14% by mass or more, or 15% by mass or more, when the resin component in the resin composition is 100% by mass. The upper limit of the content is not particularly limited and may be determined according to the properties required of the resin composition, and may be 100% by mass, but may also be, for example, 90% by mass or less, 80% by mass or less, 75% by mass or less, or 70% by mass or less. In the present invention, the "resin component" of the resin composition refers to the non-volatile components constituting the resin composition, excluding the inorganic filler described later.

--(b) Hardener--
The resin composition used in the present invention may further contain a curing agent. The curing agent is not particularly limited as long as it has the function of curing the curable resin, and examples thereof include phenol-based curing agents, naphthol-based curing agents, active ester-based curing agents, acid anhydride-based curing agents, benzoxazine-based curing agents, cyanate ester-based curing agents, carbodiimide-based curing agents, and amine-based curing agents. The curing agent may be used alone or in combination of two or more.

As the phenol-based hardener and naphthol-based hardener, from the viewpoint of heat resistance and water resistance, a phenol-based hardener having a novolac structure or a naphthol-based hardener having a novolac structure is preferred. Furthermore, from the viewpoint of achieving an insulating layer having good adhesion strength (peel strength) with the conductor layer, a nitrogen-containing phenol-based hardener or a nitrogen-containing naphthol-based hardener is preferred, and a triazine skeleton-containing phenol-based hardener or a triazine skeleton-containing naphthol-based hardener is more preferred. Among them, from the viewpoint of highly satisfying heat resistance, water resistance, and adhesion strength with the conductor layer, a triazine skeleton-containing phenol novolac resin is preferred.

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

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

The carboxylic acid compound may be either an aromatic carboxylic acid compound or an aliphatic carboxylic acid, such as benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, or pyromellitic acid.

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

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

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

Examples of acid anhydride curing agents include curing agents having one or more acid anhydride groups in one molecule. Specific examples of acid anhydride curing agents include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, dodecenyl succinic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, trimellitic anhydride, pyromellitic anhydride, and benzophenonetetracarboxylic dianhydride. Examples of acid anhydrides include polymeric acid anhydrides such as biphenyltetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, oxydiphthalic dianhydride, 3,3'-4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-C]furan-1,3-dione, ethylene glycol bis(anhydrotrimellitate), and styrene-maleic acid resins in which styrene and maleic acid are copolymerized. Examples of commercially available acid anhydride-based hardeners include "MH-700" manufactured by New Japan Chemical Co., Ltd.

Specific examples of benzoxazine-based curing agents include "JBZ-OD100" (benzoxazine ring equivalent: 218), "JBZ-OP100D" (benzoxazine ring equivalent: 218), and "ODA-BOZ" (benzoxazine ring equivalent: 218) manufactured by JFE Chemical Corporation; "P-d" (benzoxazine ring equivalent: 217) and "F-a" (benzoxazine ring equivalent: 217) manufactured by Shikoku Kasei Corporation; and "HFB2006M" (benzoxazine ring equivalent: 432) manufactured by Showa Polymer Co., Ltd.

Examples of cyanate ester curing agents include bifunctional cyanate resins such as bisphenol A dicyanate, polyphenol cyanate, oligo(3-methylene-1,5-phenylene cyanate), 4,4'-methylenebis(2,6-dimethylphenyl cyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, 2,2-bis(4-cyanate)phenylpropane, 1,1-bis(4-cyanate phenylmethane), bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanate phenyl-1-(methylethylidene))benzene, bis(4-cyanate phenyl)thioether, and bis(4-cyanate phenyl)ether; polyfunctional cyanate resins derived from phenol novolac and cresol novolac; and prepolymers in which these cyanate resins have been partially converted to triazine. Specific examples of cyanate ester-based hardeners include Lonza Japan's "PT30" and "PT60" (phenol novolac-type multifunctional cyanate ester resins), "ULL-950S" (multifunctional cyanate ester resin), "BA230" and "BA230S75" (prepolymers in which part or all of bisphenol A dicyanate has been converted to triazine and formed into a trimer).

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

Amine-based curing agents include curing agents having one or more amino groups in one molecule, such as aliphatic amines, polyether amines, alicyclic amines, and aromatic amines. Specific examples of amine-based curing agents include 4,4'-methylenebis(2,6-dimethylaniline), diphenyldiaminosulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, m-phenylenediamine, m-xylylenediamine, diethyltoluenediamine, 4,4'-diaminodiphenylether, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, 2,2-bis(3-amino-4-hydroxyphenyl)-2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, and 2,2-bis(3-amino-4-hydroxyphenyl)-2,2'-dimethyl-4,4'-diaminobiphenyl. bis(4-aminophenyl)propane, 3,3-dimethyl-5,5-diethyl-4,4-diphenylmethanediamine, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis(4-(4-aminophenoxy)phenyl)sulfone, bis(4-(3-aminophenoxy)phenyl)sulfone, and the like. Commercially available amine-based curing agents may be used, such as "KAYABOND C-200S", "KAYABOND C-100", "KAYAHARD A-A", "KAYAHARD A-B", and "KAYAHARD A-S" manufactured by Nippon Kayaku Co., Ltd., and "Epicure W" manufactured by Mitsubishi Chemical Corporation.

From the viewpoint of achieving a better yield in the manufacture of circuit boards, it is preferable that the curing agent contains an active ester-based curing agent. When the non-volatile components in the curing agent are taken as 100% by mass, the content of the active ester-based curing agent is preferably 30% by mass or more, more preferably 50% by mass or more or 60% by mass or more.

When the resin composition contains a curing agent, the content of the curing agent is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, assuming that the resin component in the resin composition is 100% by mass. The upper limit of the content of the curing agent is preferably 60% by mass or less, more preferably 50% by mass or less, or 40% by mass or less.

-(c) Inorganic filler-
The resin composition used in the present invention may further contain an inorganic filler. By including an inorganic filler, it is possible to realize an insulating layer having a low linear thermal expansion coefficient and a low dielectric loss tangent.

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

Commercially available inorganic fillers include, for example, "UFP-30" manufactured by Denka Chemical Industry Co., Ltd.; "SP60-05" and "SP507-05" manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YC100C", "YA050C", "YA050C-MJE", and "YA010C" manufactured by Admatechs Co., Ltd.; "UFP-30" manufactured by Denka Co., Ltd.; "Silfil NSS-3N", "Silfil NSS-4N", and "Silfil NSS-5N" manufactured by Tokuyama Corporation; "SC2500SQ", "SO-C4", "SO-C2", and "SO-C1" manufactured by Admatechs Co., Ltd.; "DAW-03" and "FB-105FD" manufactured by Denka Co., Ltd.; "Cellfiers" and "MGH-005" manufactured by Taiheiyo Cement Corporation; "Sferique" and "BA-1" manufactured by JGC Catalysts and Chemicals Co., Ltd., and the like.

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

The specific surface area of the inorganic filler is not particularly limited, but is preferably 0.1 m ² /g or more, more preferably 0.5 m ² /g or more, and even more preferably 1 m ² /g or more, 3 m ² /g or more, or 5 m ² /g or more. The upper limit of the specific surface area is not particularly limited, but is preferably 100 m ² /g or less, more preferably 80 m ² /g or less, and even more preferably 60 m ² /g or less, 50 m ² /g or less, or 40 m ² /g or less. The specific surface area of the inorganic filler is obtained by adsorbing nitrogen gas to the sample surface using a specific surface area measuring device (Macsorb HM-1210 manufactured by Mountech Co., Ltd.) according to the BET method, and calculating the specific surface area using the BET multipoint method.

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

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

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

When the resin composition contains an inorganic filler, the content of the inorganic filler in the resin composition is, for example, 40% by mass or more, preferably 50% by mass or more, 60% by mass or more, 65% by mass or more, or 70% by mass or more, assuming that the non-volatile components in the resin composition are 100% by mass, from the viewpoint of easily realizing a resin composition that provides even better dielectric properties. The upper limit of the content of the inorganic filler is not particularly limited, but may be, for example, 90% by mass or less, 85% by mass or less, etc.

-(d) Thermoplastic resin-
The resin composition used in the present invention may further contain a thermoplastic resin. Examples of the thermoplastic resin include a phenoxy resin, a polyvinyl acetal resin, a polyolefin resin, a polystyrene resin, a polyimide resin, a polyamide-imide resin, and a polyether-imide resin. Examples of the thermoplastic resin include polysulfone resin, polyethersulfone resin, polyphenylene ether resin, polyetheretherketone resin, and polyester resin. The thermoplastic resin may be used alone or in combination of two or more. good.

The polystyrene-equivalent weight average molecular weight of the thermoplastic resin is preferably 8,000 or more, more preferably 10,000 or more, even more preferably 20,000 or more or 30,000 or more. The upper limit is preferably 100,000 or less, more preferably 70,000 or less, even more preferably 60,000 or less. The polystyrene-equivalent Mw of the thermoplastic resin is measured by the GPC method. Specifically, the polystyrene-equivalent Mw of the thermoplastic resin is measured at a column temperature of 40°C using a Shimadzu Corporation LC-9A/RID-6A measuring device, a Showa Denko Corporation Shodex K-800P/K-804L/K-804L column, and chloroform or the like as the mobile phase, and can be calculated using the calibration curve of standard polystyrene.

Examples of phenoxy resins include phenoxy resins having one or more skeletons selected from the group consisting of bisphenol A skeleton, bisphenol F skeleton, bisphenol S skeleton, bisphenolacetophenone skeleton, novolac skeleton, biphenyl skeleton, fluorene skeleton, dicyclopentadiene skeleton, norbornene skeleton, naphthalene skeleton, anthracene skeleton, adamantane skeleton, terpene skeleton, and trimethylcyclohexane skeleton. The terminal of the phenoxy resin may be any functional group such as a phenolic hydroxyl group or an epoxy group. The phenoxy resin may be used alone or in combination of two or more types. Specific examples of phenoxy resins include "1256" and "4250" (both phenoxy resins containing a bisphenol A skeleton), "YX8100" (phenoxy resin containing a bisphenol S skeleton), and "YX6954" (phenoxy resin containing a bisphenol acetophenone skeleton) manufactured by Mitsubishi Chemical Corporation. Other examples include "FX280" and "FX293" manufactured by Nippon Steel Chemical & Material Co., Ltd., and "YL7800BH40", "YL7500BH30", "YX6954BH30", "YX7553", "YX7553BH30", "YL7769BH30", "YL6794", "YL7213", "YL7290", and "YL7482" manufactured by Mitsubishi Chemical Corporation.

Examples of polyvinyl acetal resins include polyvinyl formal resins and polyvinyl butyral resins, with polyvinyl butyral resins being preferred. Specific examples of polyvinyl acetal resins include Denka Butyral 4000-2, Denka Butyral 5000-A, Denka Butyral 6000-C, and Denka Butyral 6000-EP, manufactured by Denki Kagaku Kogyo Co., Ltd., and the S-LEC BH series, BX series (e.g. BX-5Z), KS series (e.g. KS-1), BL series, and BM series, manufactured by Sekisui Chemical Co., Ltd.

Specific examples of polyimide resins include "Rikacoat SN20" and "Rikacoat PN20" manufactured by New Japan Chemical Co., Ltd. Specific examples of polyimide resins also include modified polyimides such as linear polyimides obtained by reacting bifunctional hydroxyl-terminated polybutadiene, a diisocyanate compound, and a tetrabasic acid anhydride (polyimides described in JP-A-2006-37083), and polysiloxane skeleton-containing polyimides (polyimides described in JP-A-2002-12667 and JP-A-2000-319386, etc.).

Specific examples of polyamide-imide resins include "Viromax HR11NN" and "Viromax HR16NN" manufactured by Toyobo Co., Ltd. Specific examples of polyamide-imide resins include modified polyamide-imides such as "KS9100" and "KS9300" (polyamide-imide containing a polysiloxane skeleton) manufactured by Hitachi Chemical Co., Ltd.

A specific example of polyethersulfone resin is "PES5003P" manufactured by Sumitomo Chemical Co., Ltd. A specific example of polyphenylene ether resin is "OPE-2St 1200" oligophenylene ether styrene resin manufactured by Mitsubishi Gas Chemical Co., Ltd. A specific example of polyetheretherketone resin is "Sumiploy K" manufactured by Sumitomo Chemical Co., Ltd. A specific example of polyetherimide resin is "Ultem" manufactured by GE Corporation.

Specific examples of polysulfone resins include polysulfones "P1700" and "P3500" manufactured by Solvay Advanced Polymers.

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

Examples of polystyrene resins include homopolymers of styrene, copolymers of styrene and diene compounds (butadiene, isoprene, etc.), and hydrogenated products thereof.

Examples of polyester resins include polyethylene terephthalate resin, polyethylene naphthalate resin, polybutylene terephthalate resin, polybutylene naphthalate resin, polytrimethylene terephthalate resin, polytrimethylene naphthalate resin, polycyclohexane dimethyl terephthalate resin, etc.

When the resin composition contains a thermoplastic resin, the content of the thermoplastic resin is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, assuming that the resin components in the resin composition are 100% by mass. The upper limit is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

-(e) Curing accelerator-
The resin composition used in the present invention may further contain a curing accelerator. Examples of the curing accelerator include amine-based curing accelerators, imidazole-based curing accelerators, guanidine-based curing accelerators, metal-based curing accelerators, and peroxide-based curing accelerators. The curing accelerator may be used alone or in combination of two or more.

When the resin composition contains a curing accelerator, the content of the curing accelerator in the resin composition may be determined according to the properties required of the resin composition, but when the resin component in the resin composition is taken as 100% by mass, it is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less, and the lower limit may be 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, etc.

The resin composition used in the present invention may further contain other additives. Examples of such additives include organic fillers such as rubber particles; photocationic polymerization initiators and photoacid generators such as sulfonium salts, iodonium salts, and nonionics; photosensitizers such as naphthoquinone diazide compounds; radical polymerization initiators such as peroxide radical polymerization initiators and azo radical polymerization initiators; organometallic compounds such as organocopper compounds, organozinc compounds, and organocobalt compounds; colorants such as phthalocyanine blue, phthalocyanine green, iodine green, diazo yellow, crystal violet, titanium oxide, and carbon black; polymerization inhibitors such as hydroquinone, catechol, pyrogallol, and phenothiazine; leveling agents such as silicone leveling agents and acrylic polymer leveling agents; thickeners such as bentone and montmorillonite; defoamers such as silicone defoamers, acrylic defoamers, fluorine defoamers, and vinyl resin defoamers; ultraviolet absorbers such as benzotriazole ultraviolet absorbers. surfactants such as fluorine-based surfactants and silicone-based surfactants; flame retardants such as phosphorus-based flame retardants (e.g., phosphate ester compounds, phosphazene compounds, phosphinic acid compounds, red phosphorus), nitrogen-based flame retardants (e.g., melamine sulfate), halogen-based flame retardants, and inorganic flame retardants (e.g., antimony trioxide); dispersants such as phosphate ester-based dispersants, polyoxyalkylene-based dispersants, acetylene-based dispersants, silicone-based dispersants, anionic dispersants, and cationic dispersants; stabilizers such as borate-based stabilizers, titanate-based stabilizers, aluminate-based stabilizers, zirconate-based stabilizers, isocyanate-based stabilizers, carboxylic acid-based stabilizers, and carboxylic acid anhydride-based stabilizers. The amount of such additives may be determined according to the properties required for the resin composition.

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

The resin composition can be prepared by appropriately mixing the necessary components among the above components, and kneading or mixing them as necessary using a kneading means such as a triple roll mill, ball mill, bead mill, or sand mill, or a stirring means such as a super mixer or planetary mixer.

The resin composition layer used in the present invention can be formed, for example, by preparing a resin varnish by dissolving the liquid resin composition in an organic solvent or by applying the resin varnish directly to a plastic film using a die coater or the like when forming a "first resin sheet" described below, or by applying the resin varnish to a metal foil of a metal foil with a support substrate when forming a "second resin sheet" described below, and then drying the applied resin varnish.

The organic solvent may be the same as the organic solvent described as a component of the resin composition. The organic solvent may be used alone or in combination of two or more kinds.

Drying may be performed by known methods such as heating or blowing hot air. There are no particular limitations on the drying conditions, but drying is performed so that the content of organic solvent in the resin composition layer is 10% by mass or less, preferably 5% by mass or less. Although it varies depending on the boiling point of the organic solvent in the resin composition or resin varnish, for example, when using a resin composition or resin varnish containing 30% by mass to 60% by mass of organic solvent, the resin composition layer can be formed by drying at 50°C to 150°C for 3 to 10 minutes.

From the viewpoint of reducing the height of the circuit board, the thickness of the resin composition layer is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less, or 20 μm or less. The lower limit of the thickness of the resin composition layer is not particularly limited, but can usually be 1 μm or more, 5 μm or more, etc.

<Plastic film>
In the resin sheet with metal foil of the present invention, the second main surface of the resin composition layer is bonded to a plastic film (see Figure 1; in the resin sheet 10 with metal foil, the second main surface of the resin composition layer 1 (the upper main surface in Figure 1) is bonded to a plastic film 2).

Examples of materials for plastic films include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylics such as polycarbonate (PC) and polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, and polyimide. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, with inexpensive polyethylene terephthalate being particularly preferred.

The plastic film may be subjected to a matte treatment, a corona treatment, or an antistatic treatment on the surface to be bonded to the resin composition layer. In addition, the plastic film may be a plastic film with a release layer having a release layer on the surface to be bonded to the resin composition layer. The release agent used in the release layer of the plastic with a release layer may be, for example, one or more release agents selected from the group consisting of alkyd resins, polyolefin resins, urethane resins, and silicone resins.

The plastic film may be a commercially available product, such as PET film "SK-1", "AL-5", or "AL-7" manufactured by Lintec Corporation, "Lumirror T60" manufactured by Toray Industries, "Purex" manufactured by Teijin Limited, or "Unipeel" manufactured by Unitika Limited.

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

<Metal foil with supporting substrate>
In the resin sheet with metal foil of the present invention, the first main surface of the resin composition layer is bonded to the metal foil side of the metal foil with supporting substrate (see Figure 1; in the resin sheet with metal foil 10, the first main surface of the resin composition layer 1 (the lower main surface in Figure 1) is bonded to the metal foil 3a of the metal foil with supporting substrate 3).

The metal foil with a support substrate includes a metal foil and a support substrate that is bonded to the metal foil in a peelable manner. Referring to FIG. 1, the metal foil with a support substrate 10 includes a metal foil 3a and a support substrate 3b that is bonded to the metal foil in a peelable manner.

In metal foil with a supporting substrate, the material of the supporting substrate is not particularly limited and may be a plastic film or a carrier metal foil.

When the supporting substrate is a plastic film, the material may be the same as that explained in "<Plastic film>" above. When the supporting substrate is a carrier metal foil, examples include aluminum foil, aluminum alloy foil, stainless steel foil, titanium foil, titanium alloy foil, copper foil, copper alloy foil, etc. When a carrier metal foil is used as the supporting substrate, it may be electrolytic metal foil or rolled metal foil, and among these, electrolytic copper foil, electrolytic copper gold foil, rolled copper foil, and rolled copper alloy foil are preferred.

The support substrate is peeled off from the metal foil during the manufacture of the circuit board. From the viewpoint of being able to carry out such peeling smoothly, the support substrate may be a support substrate with a peeling layer having a peeling layer on the surface that is bonded to the metal foil. The peeling layer is not particularly limited as long as it can peel the support substrate from the metal foil, and examples thereof include an alloy layer of an element selected from the group consisting of Cr, Ni, Co, Fe, Mo, Ti, W, and P; an organic coating, and the like.

In the case of metal foil with a supporting substrate, the material of the metal foil is preferably, for example, copper foil or copper alloy foil.

In the metal foil with a support substrate, the thickness of the support substrate is not particularly limited, but is preferably 7 μm or more, more preferably 9 μm or more or 10 μm or more, and the upper limit is preferably 250 μm or less, more preferably 200 μm or less or 150 μm or less. When using a support substrate with a release layer, it is preferable that the overall thickness of the support substrate with a release layer is within the above range.

In the case of metal foil with a supporting substrate, the thickness of the metal foil is preferably 5 μm or less, more preferably 3 μm or less, from the viewpoint of contributing to the formation of fine wiring, and the lower limit is preferably 0.1 μm or more, more preferably 0.5 μm or more or 1 μm or more.

Metal foil with a supporting substrate may be a commercially available product. For example, products including an ultra-thin copper foil and a carrier copper foil bonded to the ultra-thin copper foil in a peelable state include "MT18Ex", "MT18SD-H", "MT18FL", and "MT18GN" manufactured by Mitsui Kinzoku Co., Ltd., and "JXUT-III foil" manufactured by JX Metals Corporation.

The method for producing the resin sheet with metal foil of the present invention is described below.

As described above, the resin sheet with metal foil of the present invention includes a resin composition layer having first and second main surfaces, a metal foil with a support substrate bonded to the first main surface of the resin composition layer on the metal foil side, and a plastic film bonded to the second main surface of the resin composition layer. The resin sheet with metal foil having such a layer structure can be produced by laminating a metal foil with a support substrate to a first resin sheet consisting of a resin composition layer and a plastic film bonded to the second main surface of the resin composition layer so as to be bonded to the first main surface of the resin composition layer on the metal foil side, or by laminating a plastic film to be bonded to the second main surface of the resin composition layer on a second resin sheet consisting of a resin composition layer and a metal foil with a support substrate bonded to the first main surface of the resin composition layer on the metal foil side. The resin sheet with metal foil of the present invention is characterized in that the surface on the side of the metal foil with supporting substrate has 5 or less concave or convex portions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more per ^cm2. This can be achieved by providing a roll for removing foreign matter adhering to the lamination roll that comes into contact with the supporting substrate of the metal foil with supporting substrate when laminating the first resin sheet and the metal foil with supporting substrate, or by subjecting the resin sheet with metal foil to a process for flattening the surface after lamination.

<First Resin Sheet>
In one embodiment, the resin sheet with a metal foil of the present invention is produced by laminating a metal foil with a supporting substrate to a first resin sheet consisting of a resin composition layer and a plastic film bonded to the second main surface of the resin composition layer, so that the metal foil side is bonded to the first main surface of the resin composition layer (see Figure 2a; a first resin sheet 5 and a metal foil with a supporting substrate 3 are laminated so that the resin composition layer and the metal foil are bonded to obtain a resin sheet with a metal foil 10).

Referring to FIG. 1, the first resin sheet 5 is composed of a resin composition layer 1 and a plastic film 2 bonded to the second main surface of the resin composition layer (the upper main surface in FIG. 1). The resin composition layer and the plastic film constituting the first resin sheet are as described above, including preferred examples thereof.

The first resin sheet is formed by providing a resin composition layer on a plastic film. For example, the first resin sheet can be formed by preparing a resin varnish by dissolving the resin composition in a liquid form in its original form or in an organic solvent, applying this to a plastic film using a die coater or the like, and then drying the same. The organic solvent and drying conditions are as described above.

<Second Resin Sheet>
In another embodiment, the resin sheet with metal foil of the present invention is produced by laminating a plastic film to a second resin sheet consisting of a resin composition layer and a metal foil with a supporting substrate bonded to the first main surface of the resin composition layer on the metal foil side, so that the plastic film is bonded to the second main surface of the resin composition layer (see Figure 2b; the second resin sheet 6 and the plastic film 2 are laminated so that the resin composition layer and the plastic film are bonded to each other, thereby obtaining a resin sheet with metal foil 10).

Referring to FIG. 1, the second resin sheet 6 is composed of a resin composition layer 1 and a metal foil 3 with a supporting substrate that is bonded to the first main surface (the lower main surface in FIG. 1) of the resin composition layer, and the metal foil 3a of the metal foil with a supporting substrate is bonded to the resin composition layer. The resin composition layer and the metal foil with a supporting substrate that constitute the second resin sheet are as described above, including preferred examples thereof.

The second resin sheet is formed by providing a resin composition layer on the metal foil of the metal foil with a supporting substrate. For example, the second resin sheet can be formed by preparing a resin varnish by dissolving the resin composition in an organic solvent or by applying the liquid resin composition directly onto the metal foil of the metal foil with a supporting substrate using a die coater or the like, and then drying the same. The organic solvent and drying conditions are as described above.

In one embodiment, the resin sheet with metal foil of the present invention can be manufactured by sandwiching a first resin sheet and a metal foil with a support substrate, or a second resin sheet and a plastic film between a pair of rolls A and B, and pressing at least one of the rolls in the direction of the other roll. In such a lamination process, by providing roll C1 for removing foreign matter adhering to the surface of roll A that contacts the metal foil with a support substrate, it is possible to reduce the occurrence of recesses on the surface of the metal foil with a support substrate, and by providing roll C2 for removing foreign matter adhering to the surface of roll B that contacts the plastic film, it is possible to reduce the occurrence of protrusions on the metal foil with a support substrate.

Figure 2a shows a schematic diagram (1) for explaining a method for obtaining a resin sheet with metal foil by laminating a first resin sheet and a metal foil with a supporting substrate. Hereinafter, the lamination process shown in Figure 2a is also referred to as "process (X-1)."

In the lamination step shown in FIG. 2a, i.e., step (X-1), a metal foil 3 with a supporting substrate is laminated onto a first resin sheet 5 so that the metal foil side is bonded to the resin composition layer of the first resin sheet. Thus, in FIG. 2a, the first resin sheet 5 includes a plastic film on the left side and a resin composition layer on the right side. Also in FIG. 2a, the metal foil 3 with a supporting substrate includes a metal foil on the left side and a supporting substrate on the right side. The first resin sheet 5 and the metal foil 3 with a supporting substrate are laminated to obtain a resin sheet 10 with a metal foil.

Figure 2b shows a schematic diagram (2) for explaining a method for laminating a second resin sheet and a plastic film to obtain a resin sheet with a metal foil. Hereinafter, the lamination process shown in Figure 2b is also referred to as "process (X-2)."

In the lamination step shown in Figure 2b, i.e., step (X-2), a plastic film 2 is laminated onto a second resin sheet 6 so as to be bonded to the resin composition layer of the second resin sheet. Thus, in Figure 2b, the first resin sheet 6 includes a resin composition layer on the left side and a metal foil with a supporting substrate on the right side, with the metal foil of the metal foil with a supporting substrate and the resin composition layer being bonded. The second resin sheet 6 and the plastic film 2 are laminated together to obtain a resin sheet 10 with metal foil.

Note that Figures 2a and 2b show a mode in which the resin sheets or other materials to be laminated are conveyed from top to bottom and laminated by pressure bonding from the left and right directions, but the resin sheets or other materials to be laminated may also be conveyed horizontally and laminated by pressure bonding from the top and bottom directions.

Regardless of whether the above process is (X-1) or (X-2), roll A is provided so as to be in contact with the supporting substrate of the metal foil with a supporting substrate (R _A in FIG. 2a or FIG. 2b), and roll B is provided so as to be in contact with the plastic film (R _B in FIG. 2a or FIG. 2b).

The roll surface lengths of roll A and roll B (dimension in the depth direction of the roll in FIG. 2a or FIG. 2b) may be appropriately determined according to the width (dimension in the direction perpendicular to the conveying direction (TD direction)) of the first resin sheet or the metal foil with the support substrate used in the step (X-1), or according to the width of the second resin sheet or the plastic film used in the step (X-2) so that a resin sheet with a metal foil can be produced by laminating them together. The material of roll A and roll B is not particularly limited as long as each member such as a resin sheet can be laminated together to produce a resin sheet with a metal foil, and any of a rubber roll, a metal roll, and a composite roll consisting of a metal core material and a rubber lining may be used. In addition, rolls made of the same material or different materials may be used as roll A and roll B. The pressure between the roll A and the roll B (pressure applied to the laminated member) is not particularly limited as long as the resin sheet with the metal foil can be produced by laminating each member such as a resin sheet on top of the other, and may be appropriately determined within a range of, for example, 0.1 MPa to 3 MPa, and may preferably be within a range of 0.2 MPa to 2.5 MPa, or 0.3 MPa to 2 MPa. By providing the dust removal rolls C1 and C2 described later, it is possible to reduce the occurrence of concaves or convexities on the metal foil with the support substrate side during lamination, regardless of the pressure applied, and therefore it is possible to produce a resin sheet with the metal foil of the present invention in which the concaves or convexities on the surface of the metal foil with the support substrate side having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more are 5 pieces/cm ² or less. The temperature when laminating by laminating with the roll A and the roll B is not particularly limited as long as the resin sheet with the metal foil can be produced by laminating each member such as a resin sheet on top of the other, and may be room temperature (about 25 ° C.) or may be a heating condition. From the viewpoint of being able to sufficiently adhere each member such as a resin sheet, it is preferable to laminate under heating conditions, and the temperature may be, for example, in the range of 50° C. to 130° C., and preferably in the range of 80° C. to 120° C. The conveying speed (lamination speed) of each member such as a resin sheet when laminated by pressure bonding with roll A and roll B is not particularly limited as long as each member such as a resin sheet can be laminated on top of each other to produce a resin sheet with a metal foil, and may be appropriately determined, for example, in the range of 0.1 m/min to 50 m/min.

As described above, when producing the resin sheet with metal foil of the present invention, in which the surface on the metal foil side with a supporting substrate has 5 or ^less concave or convex portions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more, it is preferable to provide a roll C1 (hereinafter also referred to as "dust removal roll C1") for removing foreign matter adhering to the surface of roll A that contacts the supporting substrate of the metal foil with a supporting substrate (R _C1 in Figures 2a and 2b ).

As the dust-removing roll C1, a roll having a function of removing foreign matter such as dust adhering to the surface of the roll A can be used, and for example, a roll having an adsorption surface capable of adsorbing foreign matter adhering to the surface of the roll A can be used. Such an adsorption surface is preferably made of a material capable of adsorbing foreign matter adhering to the surface of the roll A and not adhering to the surface of the roll A. For example, a roll having an adsorption surface made of a sticky or non-sticky polymer compound (such as silicon-based rubber or non-silicon-based rubber) that exhibits adsorption properties against foreign matter may be used. The roll surface length of the dust-removing roll C1 may be appropriately determined according to the width of the metal foil with support substrate used. In addition, the diameter of the roll C1 is not particularly limited as long as it can remove foreign matter adhering to the surface of the roll A, and may be appropriately determined. For example, the diameter of the roll C1 may be smaller than the diameter of the roll A with which the roll C1 is in contact. Although FIG. 2a and FIG. 2b show an embodiment in which one roll C1 is provided in contact with the surface of the roll A, two or more rolls C1 may be provided for the roll A. The pressure between roll A and roll C1 is not particularly limited as long as it can remove foreign matter adhering to the surface of roll A, and may be appropriately determined, for example, in the range of 0.01 MPa to 0.1 MPa, and preferably in the range of 0.02 MPa to 0.08 MPa. The dust removal roll C1 may be a commercially available product, such as a polymer rubber dust removal roll manufactured by YanGo (RUS series, HSS series, LPS series, SRR series, etc.) or a dust removal roller manufactured by TEKNEK.

As described above, when producing the resin sheet with a metal foil of the present invention, a roll C2 (hereinafter also referred to as "dust removal roll C2") may be provided to remove foreign matter adhering to the surface of roll B that comes into contact with the plastic film (R _C2 in Figures 2a and 2b).

The dust removal roll C2 may be the same as the dust removal roll C1, including preferred examples thereof. In addition, the pressure between roll B and roll C2 may be the same as the pressure between roll A and roll C1.

When manufacturing the resin sheet with metal foil of the present invention, a roll D1 for removing foreign matter adhering to the surface of the dust removal roll C1 and a roll D2 for removing foreign matter adhering to the surface of the dust removal roll C2 may be provided. The configuration of the rolls D1 and D2 is not particularly limited as long as they have the function of removing foreign matter adhering to the surface of the dust removal roll C1 and C2, but it is preferable that the rolls D1 and D2 have an adhesive layer for adsorbing foreign matter such as dust on the surface. By providing such rolls D1 and D2, it is possible to prevent foreign matter from accumulating on the surface of the dust removal roll C1 and C2 in the lamination process and reducing the adsorption force of the dust removal roll, and it is possible to more reliably remove foreign matter adhering to the surface of the rolls A and B stably for a long time. Such rolls D1 and D2 may be commercially available products, and examples of such rolls include dust transfer adhesive tape rolls, "Gapless TMULT" and "Gapless TMSRR" manufactured by YanGo Co., Ltd., and adhesive rolls manufactured by TEKNEK Co., Ltd.

In addition to/instead of using the above-mentioned dust removal rolls C1 and C2, a first resin sheet and a metal foil with a supporting substrate, or a second resin sheet and a plastic film may be laminated together, and then the surface of the resulting resin sheet with metal foil on the side of the metal foil with supporting substrate may be subjected to a smoothing treatment to produce a resin sheet with metal foil of the present invention having 5 or ^{less recesses or protrusions on the surface on the side of the metal foil with supporting substrate with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more per cm2} .

Such a smoothing process may be carried out under normal pressure (atmospheric pressure), for example, by pressing a smooth pressure-bonding member from the metal foil-bearing substrate side, with no foreign matter adhering to the surface of the resin sheet with the metal foil (or after reducing the amount of foreign matter adhering to the surface). The pressure-bonding conditions for the smoothing process may be the same as the heat-bonding conditions for the vacuum lamination process described in the above section [Method for manufacturing circuit boards].

The resin sheet with metal foil of the present invention has 5 or ^less concaves or convexities with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the metal foil with supporting substrate, and therefore, even when lamination to a substrate is performed under low pressure conditions in the manufacture of a circuit board, the occurrence of concaves or convexities on the surface on which wiring is to be formed is reduced, and a good yield can be achieved. Therefore, the resin sheet with metal foil of the present invention can be suitably used in the manufacture of a circuit board, and can be suitably used in the manufacture of a circuit board including a step of laminating the resin sheet with metal foil to a substrate under low pressure conditions (for example, a pressure of 1.5 MPa or less; suitable pressure conditions are as described above).

The resin sheet with metal foil of the present invention can achieve good yield even when forming wiring with a small distance between the wirings in the manufacture of circuit boards in which wiring is formed by a modified semi-additive method using the metal foil as a plating seed layer, or a semi-additive method using the exposed surface profile of the insulating layer after removing the metal foil. Therefore, the resin sheet with metal foil of the present invention can be suitably used in the manufacture of circuit boards including a process of forming wiring by a modified semi-additive method or a semi-additive method, and can be suitably used in the manufacture of circuit boards in which the distance between the wirings is small (e.g., 35 μm or less, 30 μm or less, 25 μm or less).

The present invention will be specifically explained below with reference to examples. The present invention is not limited to these examples. In the following, "parts" and "%" representing amounts mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[Example 1]
(1) Production of resin sheet with metal foil (1-1) Preparation of resin composition 1 Tetramethylbisphenol type epoxy resin ("YX4000H" manufactured by Mitsubishi Chemical Corporation, epoxy group equivalent 194 g/eq.), 8 parts of biphenylaralkyl type epoxy resin ("NC3000L" manufactured by Nippon Kayaku Co., Ltd., epoxy group equivalent about 271 g/eq.), 10 parts of naphthalene type epoxy resin ("HP6000L" manufactured by DIC Corporation, epoxy group equivalent about 213 g/eq.), 2 parts of bifunctional epoxy resin ("ZX1658GS" manufactured by Nippon Steel Chemical & Material Co., Ltd., epoxy group equivalent about 133 g/eq.), 4 parts of phenol-based hardener having a triazine skeleton and a cresol novolac structure ("LA-3018-50P" manufactured by DIC Corporation, phenol equivalent about 151, 2-methoxypropanol solution with a solid content of 50%) 6 parts of an active ester resin (DIC Corporation "HP-C-8151-62T", phenol equivalent of about 238, toluene solution with solids of 62%), 5 parts of a phenoxy resin (Mitsubishi Chemical Corporation "YL7800BH40", MEK and cyclohexane solution with solids of 40%), and 40 parts of an inorganic filler (Admatechs Corporation "SO-C2", surface treatment amount: 0.6 mass% of amino-based silane coupling agent relative to 100 mass% of inorganic filler) surface-treated with an amino-based silane coupling agent (Shin-Etsu Chemical Co., Ltd. "KBM573", N-phenyl-3-aminopropyltrimethoxysilane), and 1 part of a MEK solution with a solids content of 5% of a curing accelerator (1,4-dimethylaminopyridine) were added to prepare resin composition 1.

(1-2) Preparation of a first resin sheet The resin composition 1 prepared in (1-1) above was uniformly applied to a PET film ("AL5" manufactured by Lintec Corporation, thickness 38 μm) using a die coater so that the thickness after drying would be 18 μm. The film was then dried in an oven to prepare a first resin sheet having a layer structure of a resin composition layer/PET film.

(1-3) Production of resin sheet with metal foil A metal foil with a support substrate ("MT18Ex (2 um)" manufactured by Mitsui Kinzoku Co., Ltd., ultra-thin copper foil thickness 2 μm, carrier copper foil thickness 18 μm) was prepared. Then, using a roll laminator ("VA770" manufactured by Taisei Laminator Co., Ltd.), the above-mentioned metal foil with a support substrate was laminated on the first resin sheet prepared in (1-2) above so as to bond the resin composition layer and the ultra-thin copper foil side. In detail, the first resin sheet and the metal foil with a support substrate were sandwiched between a pair of rolls A and B, and one roll was pressed in the direction of the other roll to laminate (the roll in contact with the support substrate of the metal foil with a support substrate is referred to as roll A, and the roll in contact with the PET film of the first resin sheet is referred to as roll B). At that time, copper powder of 100 μm mesh simulating foreign matter was intentionally attached to the roll surfaces of roll A and roll B in advance, and roll C1 (non-silicon cleaning roll "SRR-370" manufactured by Yango) was provided to remove the foreign matter attached to the surface of roll A and clean it. The lamination conditions were a temperature of 100° C. and a pressure of 0.3 MPa. In this way, a resin sheet with metal foil was produced having a layer structure of plastic film/resin composition layer/metal foil with supporting substrate (metal foil/supporting substrate).

(1-4) Observation of surface irregularities of resin sheet with metal foil The surface of the resin sheet with metal foil on the side of the supporting substrate and the metal foil was observed using a digital microscope (Keyence Corporation's "VHX-900"). In detail, 10 areas of 1 ^cm2 were randomly selected from within a 15 cm x 15 cm area on the surface of the supporting substrate and the metal foil, and observed. The irregularities identified by the observation were then analyzed using a contact step gauge (Bruker's "DektakXT" stylus profiling system), and the number of recesses or protrusions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm was determined. The arithmetic mean value of the number of recesses or protrusions determined for the 10 areas was calculated, and the integer value obtained by rounding off the arithmetic mean value to the first decimal place was used as the number of recesses or protrusions (pieces/ ^cm2 ) on the surface of the resin sheet with metal foil on the side of the supporting substrate and the metal foil. As a result, the number of concave or convex portions having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm was 4/cm ² .

In the same manner as above, the number of recesses or protrusions on the surface of the plastic film side of the obtained resin sheet with metal foil was determined. As a result, the number of recesses or protrusions with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm was 1/ ^cm2 .

(2) Manufacturing of evaluation circuit board (2-1) Lamination of resin sheet with metal foil to substrate The PET film was peeled off from the obtained resin sheet with metal foil to expose the resin composition layer. In addition, a copper-clad laminate (Panasonic Electric Works "R1515A", copper layer thickness 18 μm, substrate thickness 0.8 mm) was prepared as a substrate. Using a batch-type vacuum pressure laminator (Nikko Materials Co., Ltd. two-stage build-up laminator "CVP700"), the resin sheet with metal foil was laminated on both sides of the copper-clad laminate so that the resin composition layer was in contact with the copper-clad laminate. The lamination was performed by reducing the pressure for 30 seconds to 5 hPa or less, and pressing at a temperature of 100 ° C. and a pressure of 1.0 MPa for 30 seconds. Next, a heat press was performed at a temperature of 100 ° C. and a pressure of 0.55 MPa for 60 seconds.

(2-2) Heat Curing of Resin Composition Layer The copper-clad laminate having the resin sheet with the metal foil laminated thereon was placed in an oven at 180° C. and heated for 30 minutes to heat cure the resin composition layer and form an insulating layer.

(2-3) Formation of Wiring Next, wiring was formed by the modified semi-additive process (MSAP) according to the following procedure.

(2-3-1) Removal of Support Substrate The carrier copper foil was peeled off from the laminate obtained in (2-2) above to expose the ultra-thin copper foil.

(2-3-2) Formation of plating resist and exposure/development After exposing the ultra-thin copper foil, plating resist (Showa Denko K.K.'s pattern forming dry film "RY5115", thickness 15 μm) was laminated on both sides of the substrate. Next, a 15 cm square glass mask (exposure mask) on which a wiring pattern (details are shown below) was formed was placed on the plating resist, and it was exposed (exposure amount 210 mJ) by a stepper (Ushio Inc.'s projection exposure device "UX-2240"). After that, it was aged at room temperature for 30 minutes, and then a 1 wt % sodium carbonate aqueous solution at 30° C. was sprayed for 30 seconds using a spray-type developer to develop the plating resist (pattern formation).

Glass mask wiring pattern:
A glass mask having 25 comb-tooth patterns (wiring width 20 μm, spacing 20 μm, wiring length 10 mm, 16 lines) in which wiring from the anode and wiring from the cathode face each other was used.

(2-3-3) Electrolytic Plating Next, electrolytic copper plating was carried out using a chemical solution manufactured by Atotech Japan, to form wiring with a wiring height of 10 μm.

(2-3-4) Removal of Plating Resist After electrolytic plating, the substrate was immersed in a resist stripper ("R100S" manufactured by Mitsubishi Gas Chemical Company, Inc.) at 50° C. for 120 seconds while performing ultrasonic treatment, to strip the plating resist.

(2-3-5) Flash Etching Next, the obtained substrate was immersed in a plating seed layer etching agent for the semi-additive process (Melstrip SE-300) at 25° C. to remove unnecessary copper plating layer other than the wiring formation portion, thereby forming comb-tooth wiring. In this way, an evaluation substrate was obtained.

[Example 2]
Except for producing a resin sheet with metal foil having 2 concave or convex portions/ ^cm2 with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm on the surface of the metal foil with supporting substrate side, an evaluation circuit board having comb-tooth wiring was obtained in the same manner as in Example 1. The number of surface concave or convex portions on the metal foil with supporting substrate side was adjusted by changing the amount of attached copper powder of 100 μm mesh simulating foreign matter.

[Example 3]
An evaluation circuit board having comb-tooth wiring was obtained in the same manner as in Example 1, except that wiring was formed by a semi-additive process (SAP) utilizing the exposed surface profile of an insulating layer instead of MSAP, which utilizes an ultra-thin copper foil as a plating seed layer.

In detail, instead of (2-3-1) in Example 1, the following (2-3-1'(1)) and (2-3-1'(2)) were carried out to form a plating seed layer (electroless copper plating layer), but the evaluation circuit board having comb-tooth wiring was obtained in the same manner as in Example 1.

(2-3-1'(1)) Removal of metal foil with supporting substrate After the resin composition layer was thermally cured to form an insulating layer, the carrier copper foil was peeled off to expose the ultra-thin copper foil. The ultra-thin copper foil was then removed by wet etching (aqueous ferric chloride solution) to expose the insulating layer.

(2-3-1'(2)) Electroless Plating A conductor layer was formed on the exposed surface of the insulating layer by carrying out a plating process including the following steps 1 to 6 (copper plating process using a chemical solution manufactured by Atotech Japan).
1. Alkaline cleaning (cleaning the surface of the insulating layer and adjusting the charge)
The plate was washed at 60° C. for 5 minutes using Cleaning Cleaner Security 902 (trade name).
2. Soft etching (cleaning the surface of the insulating layer)
The film was treated with an aqueous solution of sulfuric acid and sodium peroxodisulfate at 30° C. for 1 minute.
3. Pre-dip (adjustment of the charge on the surface of the insulating layer for Pd application)
The film was treated with Pre.Dip Neoganth B (trade name) at room temperature for 1 minute.
4. Adding an activator (adding Pd to the surface of the insulating layer)
The cells were treated with Activator Neoganth 834 (trade name) at 35° C. for 5 minutes.
5. Reduction (reduction of Pd added to the insulating layer)
The mixture was treated with Reducer Neoganth WA (trade name) and Reducer Accelerator 810 mod. (trade name) at 30° C. for 5 minutes.
6. Electroless copper plating process (precipitating Cu on the surface of the insulating layer (Pd surface))
The substrate was treated for 20 minutes at 35° C. using a mixture of Basic Solution Printganth MSK-DK (trade name), Copper solution Printganth MSK (trade name), Stabilizer Printganth MSK-DK (trade name), and Reducer Cu (trade name). The thickness of the electroless copper plating layer formed was 0.8 μm.

[Example 4]
An evaluation circuit board having comb-tooth wiring was obtained in the same manner as in Example 3, except that (1) a resin sheet with metal foil was produced in which the surface on the metal foil side with the supporting substrate had 2 concave or convex portions/ ^cm2 each having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm, and (2) a glass mask having 25 comb-tooth patterns (wiring width 8 μm, wiring distance 8 μm, wiring length 10 mm, 16 lines) was used.

[Example 5]
(1) Instead of (1-1) in Example 1, the following (1-1') was carried out to prepare resin composition 2 and produce a first resin sheet, and (2) a resin sheet with metal foil was produced in which the surface on the metal foil side with a supporting substrate had 2 recesses or protrusions/ ^cm2 with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm. An evaluation circuit board having comb-tooth wiring was obtained in the same manner as in Example 1, except for the above.

(1-1') Preparation of Resin Composition 2 5 parts of maleimide resin ("SLK-6895-M90" manufactured by Shin-Etsu Chemical Co., Ltd., maleimide equivalent 345 g/eq., MEK solution with solid content of 90 wt%), 10 parts of biphenylaralkyl type maleimide resin ("MIR-3000-70MT" manufactured by Nippon Kayaku Co., Ltd., maleimide equivalent 393 g/eq., MEK and toluene solution with solid content of 70 wt%), 5 parts of liquid acrylate resin ("A-DOG" manufactured by Shin-Nakamura Chemical Co., Ltd., vinyl group equivalent of about 163 g/eq.), copolymer elastomer ("P200" manufactured by Asahi Kasei Corporation) Resin composition 2 was prepared by adding 2 parts of a 30 wt % toluene solution of an amino-silane coupling agent ("KBM573" manufactured by Shin-Etsu Chemical Co., Ltd., N-phenyl-3-aminopropyltrimethoxysilane), 40 parts of an inorganic filler ("SO-C2" manufactured by Admatechs Co., Ltd., surface treatment amount: 0.6% by mass of amino-silane coupling agent per 100% by mass of inorganic filler), and 1 part of a toluene solution of 5% solids of a peroxide curing accelerator ("Perhexyne 25B" manufactured by NOF Chemical Corporation).

[Comparative Example 1]
Except for producing a resin sheet with metal foil having 8 concave or convex portions/ ^cm2 with a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm on the surface of the metal foil with supporting substrate, an evaluation circuit board having comb-tooth wiring was obtained in the same manner as in Example 1. The number of surface concave or convex portions on the metal foil with supporting substrate side was adjusted by changing the amount of copper powder of 100 μm mesh simulating foreign matter attached thereto and by omitting roll C1 for removing foreign matter attached to the surface of roll A.

[Comparative Example 2]
(1) A resin sheet with metal foil was produced in which the number of concaves or convexities on the surface of the metal foil with support substrate, each having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm, was 8/ ^cm2 , and (2) a glass mask having 25 comb tooth patterns (wiring width 8 μm, wiring distance 8 μm, wiring length 10 mm, 16 lines) was used. Except for this, an evaluation circuit board with comb tooth wiring was obtained in the same manner as in Example 3. The number of surface irregularities on the metal foil with support substrate side was adjusted by changing the amount of copper powder of 100 μm mesh simulating foreign matter and omitting roll C1 for removing foreign matter attached to the surface of roll A.

<Evaluation of wiring yield>
For the evaluation circuit boards obtained in each Example and Comparative Example, the insulation resistance value of the comb-tooth wiring was measured using a resistance meter ("ECM-100" manufactured by J-RAS). When the ratio of comb-tooth wirings having an insulation resistance value of 1× ¹⁰ Ω or more was 60% or more (i.e., the number of comb-tooth wirings having an insulation resistance value of 1× ¹⁰ Ω or more was 15 or more), it was evaluated as "good", and when it was less than 60%, it was evaluated as "poor".

REFERENCE SIGNS LIST 1 resin composition layer 2 plastic film 3 metal foil with supporting substrate 3a metal foil 3b supporting substrate 5 first resin sheet 6 second resin sheet 10 resin sheet with metal foil R _A roll A
R _B Roll B
R _C1 Roll C1
R _C2 Roll C2

Claims (10)

(Y) A method for producing a circuit board, comprising a step of laminating a resin sheet with a metal foil, the resin sheet including a resin composition layer having first and second main surfaces, a metal foil with a supporting substrate bonded to the first main surface of the resin composition layer on a metal foil side, and a plastic film bonded to the second main surface of the resin composition layer, onto a substrate such that the second main surface of the resin composition layer is bonded to the substrate,
A method in which the number of concave or convex parts having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the metal foil-attached resin sheet used in step (Y) on the metal foil-attached metal foil side is 5 or less per ^cm2 . The method according to claim 1, in which in step (Y), the resin sheet with the metal foil is laminated to the substrate at a pressure of 1.5 MPa or less. The method according to claim 1, further comprising the step of forming wiring by a modified semi-additive method or a semi-additive method. The method according to claim 3, in which in step (Z), wiring is formed with a distance between wirings of 35 μm or less. The method according to claim 1, wherein the number of concave or convex parts having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the plastic film side of the resin sheet with the metal foil is 5 or less per ^cm2 . The method according to claim 1, wherein the thickness of the metal foil with the supporting substrate is 5 μm or less. The method according to claim 1, wherein the support substrate in the metal foil with a support substrate is a plastic film or a carrier metal foil. The method according to claim 1, wherein the resin composition layer contains 40% by mass or more of an inorganic filler when the non-volatile components of the resin composition layer are taken as 100% by mass. A resin sheet with a metal foil, comprising: a resin composition layer having first and second main surfaces; a metal foil with a support substrate bonded to the first main surface of the resin composition layer on the metal foil side; and a plastic film bonded to the second main surface of the resin composition layer,
A resin sheet with a metal foil, in which the number of concave or convex parts having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more is 5 or less per ^cm2 on the surface of the resin sheet with a metal foil on the supporting substrate side. 10. The resin sheet with a metal foil according to claim 9, wherein the number of concave or convex parts having a maximum diameter of 0.8 μm or more and a maximum height difference of 0.7 μm or more on the surface of the resin sheet with the metal foil on the plastic film side is 5 or less per cm ² .

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