Electrically insulating resin composition, uncured sheet material for interlayer insulation, laminate for circuit board, circuit board, and method for manufacturing circuit board.

Abstract

[Problem] To provide an electrically insulating resin composition, a laminate for a circuit board using the same, and a circuit board, wherein the electrically insulating resin composition provides an electrically insulating hardened material that maintains a low modulus of elasticity over a wide temperature range, exhibits excellent resistance to thermal cycling, and can maintain flexibility and thermal stability over a long period. [Solution] The electrically insulating resin composition of the present invention contains an acid-modified fully hydrogenated styrene-based elastomer, a polymerizable monomer containing reactive double bonds, a thermally conductive inorganic filler, and an organic solvent.

Description

[Technical Field]

[0001] Field of the Invention This invention relates to an electrically insulating resin composition, an uncured sheet for interlayer insulation, a laminate for a circuit board, a circuit board, and a method for manufacturing a circuit board. [Previous Technology]

[0002] Background of the Invention In recent years, electric vehicles have become increasingly popular, and the DC-DC converter that constitutes the charging module is one of the most important components. This component is placed in a harsh environment, subjected to temperature changes caused by the charging and discharging of electricity and the severe influence of the external atmosphere. For this type of component placed in a harsh environment, a metal substrate circuit board is used, which has an electrically insulating layer on a metal substrate such as aluminum or copper with high heat dissipation and conductive circuits disposed thereon.

[0003] Patent Document 1 points out the following problem: if the doping rate of the inorganic filler in the electrical insulating layer of a metal-based circuit board is increased to improve thermal conductivity, the flexibility of the electrical insulating layer decreases and it becomes brittle, and the adhesion of the electrical insulating layer to the metal substrate also decreases. Patent Document 1 further points out that if the doping rate of the inorganic filler is high, solder heat treatment will cause cracks to form on the electrical insulating layer, resulting in a decrease in voltage withstand capability. To address these problems, Patent Document 1 discloses an electrical insulating resin composition for circuit boards using a partially hydrogenated rubber-like polymer compound.

[0004] Patent Document 2 cites a different main reason from that in Patent Document 1 as the main cause of cracks in the electrical insulation layer. Specifically, it points out that the previous electrical insulation layer sometimes had an excessively high elastic modulus, making it prone to cracking when the circuit board is exposed to thermal cycling. Patent Document 1 did not investigate the elastic modulus or thermal cycling resistance of such an electrical insulation layer. Patent Document 2, addressing these problems, discloses an insulating resin composition containing polymers such as phenoxy resins, curing compounds such as epoxy resins, polyether diamine as a curing agent, and inorganic fillers, and having a low storage elastic modulus. However, the hardness of this composition increases significantly at low temperatures, thus requiring further improvement in thermal cycling resistance. Furthermore, this insulating resin composition has a high water absorption rate, showing a tendency for a sharp drop in insulation breakdown voltage upon moisture absorption.

[0005] [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Publication No. 2005-317371 [Patent Document 2] Japanese Patent Application Publication No. 2013-71960 [Summary of the Invention]

[0006] Summary of the Invention [Problem to be Solved by the Invention] The object of the present invention is to provide an electrically insulating resin composition, an uncured sheet for interlayer insulation using the same, a laminate for a circuit board and a circuit board, wherein the electrically insulating resin composition can provide an electrically insulating cured material that has a low modulus of elasticity, excellent resistance to thermal cycling, and can maintain flexibility and thermal stability over a wide temperature range.

[0007] [Means for solving the problem] According to one aspect of the present invention, an electrically insulating resin composition is provided, which contains an acid-modified fully hydrogenated styrene elastomer, a polymerizable monomer containing reactive double bonds, a thermally conductive inorganic filler, and an organic solvent.

[0008] According to another aspect of the present invention, an electrically insulating resin composition as described above is provided, which contains an aromatic hydrocarbon solvent and a low molecular weight alcohol solvent as the organic solvent.

[0009] According to another embodiment of the present invention, an electrically insulating resin composition as described above is provided, which contains the above-described aromatic hydrocarbon solvent and the above-described low molecular weight alcohol solvent in the following blending ratio, namely, the low molecular weight alcohol solvent is 0.1 to 10 parts by mass per 100 parts by mass of the above-described aromatic hydrocarbon solvent.

[0010] According to another embodiment of the present invention, an electrically insulating resin composition as described in any of the above embodiments is provided, wherein the polymerizable monomeric system comprises two or more acrylonitrile, methacrylonitrile, or allyl compounds within one molecule.

[0011] According to another embodiment of the present invention, an electrically insulating resin composition as described in any of the above embodiments is provided, which further contains a cyclic compound having an aromatic ring or an aliphatic ring, having a weight average molecular weight in the range of 300 to 1000, and being solid at room temperature.

[0012] According to another aspect of the present invention, a sheet-like uncured material for interlayer insulation is provided, comprising an electrically insulating resin composition as described in any of the above aspects.

[0013] According to another aspect of the present invention, a multilayer for a circuit board is provided, comprising: an electrically insulating layer formed of a hardened form of an electrically insulating resin composition as described in any of the above aspects; and a metal layer disposed on at least one side of the electrically insulating layer.

[0014] According to another aspect of the present invention, a circuit board laminate as described above is provided, which includes a metal substrate and a metal conductor foil as the metal layer, and is formed by sequentially laminating the metal substrate, the electrical insulating layer and the metal conductor foil.

[0015] According to another aspect of the present invention, a circuit board is provided, which is formed by circuit processing of the circuit board as described above using a multilayer material, and has a circuit pattern formed by circuit processing of the metal conductor foil described above.

[0016] According to another aspect of the present invention, a multilayer for a circuit board is provided, comprising: an electrically insulating layer containing an acid-modified fully hydrogenated styrene-based elastomer and a crosslinked polymeric monomer containing reactive double bonds and a thermally conductive inorganic filler; and a metal layer disposed on at least one side of the electrically insulating layer.

[0017] According to another embodiment of the present invention, a circuit board laminate as described above is provided, wherein the electrically insulating layer further contains a cyclic compound having an aromatic ring or an aliphatic ring, having a weight average molecular weight in the range of 300 to 1000, and being solid at room temperature.

[0018] According to another embodiment of the present invention, a circuit board laminate as described in any of the above embodiments is provided, which includes a metal substrate and a metal conductor foil as the metal layer, and is formed by sequentially laminating the metal substrate, the electrical insulating layer and the metal conductor foil.

[0019] According to another aspect of the present invention, a circuit board is provided, which is formed by circuit processing of the circuit board as described above using a multilayer material, and has a circuit pattern formed by circuit processing of the metal conductor foil described above.

[0020] According to another aspect of the present invention, a method for manufacturing a circuit board is provided, which is a method for manufacturing a circuit board comprising a metal substrate, an electrically insulating layer and a circuit pattern in sequence, and includes the following steps: preparing the metal substrate and the metal conductor foil; selecting one of the metal substrate and the metal conductor foil, and coating one side thereon with an electrically insulating resin composition as described in any of the above aspects to form an uncured electrically insulating layer; forming a laminate composed of the metal substrate, the uncured electrically insulating layer and the metal conductor foil by depositing the other of the metal substrate and the metal conductor foil onto the uncured electrically insulating layer; hot-pressing the laminate; and forming the circuit pattern by processing the metal conductor foil.

[0021] According to another aspect of the present invention, a method for manufacturing a circuit board is provided, which is a method for manufacturing a circuit board having a metal substrate, an electrical insulating layer and a circuit pattern in sequence, and includes the following steps: forming a laminate having the metal substrate, an uncured sheet of interlayer insulation as described above and a metal conductor foil in sequence; hot-pressing the laminate; and forming the circuit pattern by processing the metal conductor foil.

[0022] [Effects of the Invention] According to the present invention, an electrically insulating resin composition, an uncured sheet for interlayer insulation using the same, a laminate for a circuit board, and a circuit board are provided. The electrically insulating resin composition can provide an electrically insulating cured material that has a low modulus of elasticity, excellent resistance to thermal cycling, and can maintain flexibility and thermal stability over a wide temperature range.

Implementation Method

[0024] Embodiments of the present invention will be described below. [Electrically Insulating Resin Composition] The electrically insulating resin composition of the first embodiment of the present invention contains an acid-modified fully hydrogenated styrene-based elastomer, a polymerizable monomer containing reactive double bonds, a thermally conductive inorganic filler, and an organic solvent. As a preferred embodiment, the electrically insulating resin composition of this embodiment further contains a cyclic compound having an aromatic ring or an aliphatic ring, a weight average molecular weight of 300 to 1000, and being a solid at room temperature. Hereinafter, the components contained in the electrically insulating resin composition of this embodiment will be described.

[0025] <Acid-Modified Fully Hydrogenated Styrene Elastomer> The electrically insulating resin composition of this embodiment contains an acid-modified fully hydrogenated styrene elastomer. Through the researchers' intensive study, it was discovered that when using partially hydrogenated styrene elastomers, the unhydrogenated double bonds remaining from the styrene elastomer increase the storage elastic modulus of the electrically insulating layer, resulting in decreased flexibility and becoming a major cause of reduced resistance to thermal cycling. It is also known that even with a higher hydrogenation rate in the partially hydrogenated styrene elastomer, where only a few double bonds remain, this phenomenon still exists. Furthermore, according to further intensive research, it was found that even replacing the partially hydrogenated styrene elastomer with a fully hydrogenated styrene elastomer does not eliminate the above-mentioned problem. However, by further acid-modifying the fully hydrogenated styrene elastomer, an electrically insulating cured material with a lower storage elastic modulus over a wider temperature range and improved resistance to thermal cycling can be obtained. This cured material can maintain good flexibility over a long period.

[0026] Furthermore, regarding fully hydrogenated styrene elastomers, although they do not contain double bonds themselves, they can be used in combination with polymerizable monomers that contain reactive double bonds, for example, by crosslinking via free radical polymerization. Also, fully hydrogenated styrene elastomers do not contain unsaturated bonds in their structure, which also contributes to their long-term thermal stability.

[0027] The styrene-based elastomer constituting the acid-modified fully hydrogenated styrene-based elastomer may contain structural units other than those derived from styrene-based compounds. Examples of structural units other than those derived from styrene-based compounds that may be contained in the styrene-based elastomer include, for example, structural units derived from butadiene and structural units derived from isoprene. Preferred styrene-based elastomers include styrene-butadiene-styrene block elastomers and styrene-isoprene-styrene block elastomers.

[0028] When the acid-modified fully hydrogenated styrene-based elastomer is a styrene-butadiene-based elastomer, the structural units derived from butadiene in the elastomer are completely hydrogenated. Furthermore, when the acid-modified fully hydrogenated styrene-based elastomer is a styrene-isoprene-based elastomer, the structural units derived from isoprene in the elastomer are completely hydrogenated. Here, complete hydrogenation (being completely hydrogenated) means a hydrogenation rate of 100%, which can be determined by, for example, iodine value determination (see examples).

[0029] When the styrene-based elastomer is a copolymer, the content of structural units from the styrene-based compound is in the range of 10 to 40% by mass in one example and in the range of 20 to 30% by mass in another example. More specifically, when the styrene-based elastomer is a styrene-butadiene-based elastomer or a styrene-isoprene-based elastomer, the mass ratio of styrene to butadiene (isoprene) is, in one example, 10:90 to 40:60, and in another example, 20:80 to 30:70.

[0030] The miscibility of fully hydrogenated styrene elastomers modified by acid with thermally conductive inorganic fillers is improved, thus suppressing the increase in hardness at low temperatures (in dynamic viscoelasticity, this is an increase in the storage elastic modulus), which helps improve resistance to thermal cycling. In unmodified fully hydrogenated styrene elastomers, hardness increases easily at low temperatures, resulting in poor resistance to thermal cycling. Furthermore, the effect of acid modification in suppressing the increase in hardness at low temperatures in the cured material is only achieved with fully hydrogenated styrene elastomers; the same effect cannot be obtained even with acid modification of partially hydrogenated styrene elastomers. That is, in partially hydrogenated styrene elastomers, double bonds remain within the molecule, which cross-link due to acid modification, causing the hardness to increase over a wider temperature range (in dynamic viscoelasticity, this is an increase in the storage elastic modulus). Additionally, acid modification of fully hydrogenated styrene elastomers also helps improve the adhesion of the cured material to metal layers such as copper or aluminum.

[0031] Examples of acid-modified fully hydrogenated styrene elastomers include those obtained by adding acrylic acid, methacrylic acid, or other aliphatic unsaturated monocarboxylic acids, or maleic acid, fumaric acid, or their anhydrides to a fully hydrogenated styrene elastomer. In one embodiment of the present invention, among these, it is preferable to be an acid-modified product obtained by adding an unsaturated dicarboxylic acid or its anhydride, and more preferably a maleic anhydride-modified fully hydrogenated styrene elastomer.

[0032] Furthermore, the acid-modified fully hydrogenated styrene elastomer is a hydrophobic compound. Therefore, the electrically insulating resin composition of this embodiment can have low water absorption and low dielectric properties, thereby suppressing the rapid drop in insulation breakdown voltage caused by moisture absorption.

[0033] In this embodiment, the acid-modified fully hydrogenated styrene-based elastomer may be, for example, an acid-modified fully hydrogenated styrene-butadiene-styrene block elastomer or an acid-modified fully hydrogenated styrene-isoprene-styrene block elastomer, or a maleic anhydride-modified fully hydrogenated styrene-butadiene-styrene block elastomer or a maleic anhydride-modified fully hydrogenated styrene-isoprene-styrene block elastomer, or a maleic anhydride-modified fully hydrogenated styrene-butadiene-styrene block elastomer.

[0034] According to one example, the melt index of the acid-modified fully hydrogenated styrene elastomer can be in the range of 2.5 to 25 g / 10 min at 210°C and 2.16 kgf, and according to another example, it can be in the range of 3 to 7 g / 10 min. Furthermore, from the viewpoint of adhesion to the metal layer, the acid value of the acid-modified fully hydrogenated styrene elastomer can be in the range of 2 to 10.

[0035] Acid-modified fully hydrogenated styrene elastomers can also be used in commercially available products. Examples of commercially available products include Tuftec (registered trademark) M1911, M1913, and M1943 manufactured by Asahi Kasei Corporation, and Kraton (registered trademark) FG1901G manufactured by Kraton Polymer Japan Co., Ltd.

[0036] The weight average molecular weight of acid-modified fully hydrogenated styrene elastomers, in GPC (gel permeation chromatography) analysis using polystyrene conversion, can be in the range of 20,000 to 500,000 in one example and in the range of 50,000 to 350,000 in another example.

[0037] The blending rate of acid-modified fully hydrogenated styrene elastomer in the electrically insulating resin composition is based on the total mass of organic components excluding organic solvents and thermally conductive inorganic fillers, and is in the range of 30 to 85% by mass in one example and 40 to 75% by mass in another example. These ranges are preferred from the viewpoint of storage modulus of elasticity and coefficient of thermal expansion. Furthermore, in order to further impart flexibility to the acid-modified fully hydrogenated styrene elastomer, hydrophobic polymers such as butyl rubber, ethylene-propylene rubber, and unmodified fully hydrogenated styrene elastomers may be added, or in order to improve adhesion to inorganic fillers, epoxy-containing polymers such as ethylene-acrylate-maleic anhydride copolymers (styrene-glycidyl methacrylate copolymers, etc.) may be added.

[0038] <Polymerizable Monomer> As a polymerizable monomer, a polymerizable monomer having a reactive double bond is used. The polymerizable monomer is a compound having one or more reactive double bonds in its molecule, and is a compound that can be hardened by free radical polymerization or thermal polymerization. For example, compounds with highly reactive double bonds such as vinyl, allyl, methyl allyl, acrylamide, or methacrylamide at the end, or monomers with unsaturated groups (reactive double bonds) such as maleimide or bismaleimide, can be used.

[0039] Specific examples of such polymerizable monomers include vinylbenzene, divinylbenzene, bisphenol A epoxy acrylate, methyl methacrylate, isopropyl acrylate, tricyclodecane dimethacrylate, triallyl isocyanurate, ethoxyisocyanurate triacrylate, diallyl phthalate, and diphenylmethane bismaleimide. Furthermore, unsaturated polyesters obtained from difunctional carboxylic acids such as maleic anhydride or phthalic acid and low-molecular-weight diols such as ethylene glycol can also be used.

[0040] The polymerizable monomer, in one form, is preferably a compound containing two or more acrylonitrile, methacrylonitrile, or allyl groups within one molecule. Furthermore, the polymerizable monomer, in another form, is preferably a compound containing a cyclic structure within one molecule. Specifically, in the specific examples disclosed above, examples include compounds containing aromatic rings, or cyclic aliphatic compounds obtained by hydrogenating the aromatic ring, or cyclic aliphatic compounds or heterocyclic compounds such as isocyanurate, tricyclodecane dimethacrylate, triallyl isocyanurate, and ethoxyisocyanurate triacrylate. By using a monomer containing a cyclic structure, compatibility and heat resistance can be further improved. According to one example, the molecular weight of the polymerizable monomer is preferably in the range of 50 to 500.

[0041] The blending rate of the polymerizable monomer having reactive double bonds in the electrically insulating resin composition is based on the total mass of the organic components excluding organic solvents and thermally conductive inorganic fillers, and is in the range of 5.1 to 60.1% by mass in one example and in the range of 15.1 to 50.1% by mass in another example.

[0042] <Cyclic Compound> In a preferred form, the electrically insulating resin composition contains a cyclic compound having an aromatic or aliphatic ring in its molecule. Here, "aromatic ring" includes heteroaromatic rings. By adding a cyclic compound with good compatibility with acid-modified fully hydrogenated styrene-based elastomers and polymerizable monomers, it acts as a compatibilizer, resulting in a cured product with a structure in which the three components are uniformly polymerized. Therefore, the cured product exhibits less hardness variation over a wide temperature range from high to low. Furthermore, the voltage withstand properties of the cured product after thermal degradation are further improved. This is presumably because the cured product is less prone to heat loss at high temperatures, thus suppressing the formation of micropores in the electrical insulation layer caused by volatiles due to solder heat treatment.

[0043] Specific examples of the cyclic skeleton contained in the cyclic compound include benzofuran, indene, rosin, cyclopentane, cyclopentene, cyclohexane, cyclohexene, tricyclodecane, and norethene. Among these, cyclic compounds having aliphatic rings such as rosin, cyclopentane, cyclopentene, cyclohexane, cyclohexene, tricyclodecane, and norethene have better compatibility with aromatic cyclic compounds and can further improve the heat resistance of the cured material, thus they are preferred.

[0044] As a cyclic compound, a polymer of a polymeric monomer having an aromatic ring or an aliphatic ring, or a copolymer of a polymeric monomer having an aromatic ring or an aliphatic unsaturated compound and an aliphatic unsaturated compound, or a hydride thereof, may be used.

[0045] Specific examples of cyclic compounds include (1) polymers of 5-ethylidene-2-northene or dicyclopentadiene as cyclic aliphatic compounds, or copolymers of styrene or vinyltoluene as aromatic vinyl compounds with 1,4-hexadiene, isobutylene or 1,3-pentadiene as aliphatic unsaturated compounds, (2) condensation polymers of rosin derivatives or their esterifications, (3) cyclic dimer acids or modified compounds, (4) copolymers of benzofuran indene resin, etc., wherein compounds of (1) and (2) or their hydrides are preferred.

[0046] By incorporating unsaturated bonds or tertiary carbons into the cyclic compound molecule, the compatibility and uniformity of the electrical insulating resin composition can be further improved.

[0047] In GPC analysis using polystyrene, the weight-average molecular weight of the cyclic compound is in the range of 300 to 1000. By using cyclic compounds with a molecular weight that is between the molecular weight of acid-modified fully hydrogenated styrene-based elastomers and the molecular weight of polymerizable monomers, the compatibility of electrically insulating resin compositions can be further improved.

[0048] Furthermore, the cyclic compound is solid at room temperature (25°C). If the cyclic compound is solid at room temperature, the adhesion of the dried, uncured portion of the electrical insulating resin composition can be suppressed. When manufacturing circuit boards using sheet-like uncured interlayer insulation composed of this dried, uncured material, it will not be sticky, thus improving workability. Furthermore, the cyclic compound is generally hydrophobic. Therefore, it can be used together with acid-modified fully hydrogenated styrene-based elastomers to help the electrical insulating resin composition of this embodiment have low water absorption and low dielectric properties, thereby suppressing the rapid drop in insulation breakdown voltage caused by moisture absorption.

[0049] When the electrically insulating resin composition contains cyclic compounds, the doping rate of the cyclic compounds is based on the total mass of the organic components in the electrically insulating resin composition excluding organic solvents and thermally conductive inorganic fillers, and is in the range of 3 to 50% by mass in one example and in the range of 10 to 30% by mass in another example.

[0050] <Thermoconductive Inorganic Filler> The electrically insulating cured material contains a thermally conductive inorganic filler. By including a thermally conductive inorganic filler in the electrically insulating cured material, its thermal conductivity is improved. Examples of thermally conductive inorganic fillers include, for example, silicon dioxide, alumina, aluminum nitride, boron nitride, silicon carbide, and silicon nitride. The shape, particle size, and particle size distribution of the thermally conductive inorganic filler can be appropriately determined during blending; one type can be used alone, or two or more types can be used in combination. By blending a thermally conductive inorganic filler, the coefficient of thermal expansion of the electrically insulating resin composition decreases, and the storage modulus of elasticity increases. The blending rate of the thermally conductive inorganic filler can be determined by considering, for example, the balance of these factors. The mass percentage of the thermally conductive inorganic filler in the electrically insulating cured material is, in one example, in the range of 40 to 90% by mass, and in another example, in the range of 60 to 85% by mass. If a filler with a low dielectric constant, such as silicon dioxide or boron nitride, is used as the thermally conductive inorganic filler, the organic component of the present invention has hydrophobicity and low dielectric properties, thus the resulting cured insulating material has low dielectric properties. Therefore, it has the advantage of being able to better apply the cured electrically insulating material of this embodiment to 5G-related high-frequency applications such as high-frequency substrates.

[0051] <Organic Solvents> The electrically insulating curing material contains organic solvents. Examples of organic solvents include: aromatic hydrocarbon solvents such as benzene, toluene, and xylene; ester solvents such as ethyl acetate, isopropyl acetate, n-propyl acetate, and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as tetrahydrofuran, dimethyl oxitol, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether; and chlorine solvents such as chloroform, carbon tetrachloride, dichloroethane, trichloroethane, and chlorobenzene. However, while the above-mentioned organic solvents can dissolve acid-modified fully hydrogenated styrene elastomers, their stability in solution is insufficient. That is, although the solution is homogeneous immediately after the acid-modified fully hydrogenated styrene elastomer is dissolved in the above-mentioned organic solvents, it will become viscous over time and eventually gel, making it impossible to coat. Therefore, limitations may arise, such as the need to coat the solution within a specified time after preparation.

[0052] On the other hand, lower alcohol solvents such as methanol, ethanol, propanol, and isopropanol cannot dissolve acid-modified fully hydrogenated styrene elastomers, and therefore cannot be used alone as organic solvents in this embodiment. Surprisingly, through the keen research of the inventors, it has been discovered that by using a mixture of lower alcohol solvents and aromatic hydrocarbon solvents, not only can the lower alcohol solvents be used as organic solvents, but the stability of the solution is also dramatically improved compared to using aromatic hydrocarbon solvents alone. That is, it is known that by using a mixture of aromatic hydrocarbon solvents and lower alcohol solvents as organic solvents in this embodiment, the stability of the solution containing acid-modified fully hydrogenated styrene elastomers is improved, preventing gelation over time, and resulting in excellent drying properties of the coating film. Therefore, a stable operating procedure and good quality can be maintained.

[0053] Thus, the electrically insulating resin composition of this embodiment contains, in one form, an aromatic hydrocarbon solvent and a low-molecular-weight alcohol solvent as organic solvents. In this case, regarding the mixing ratio of the aromatic hydrocarbon solvent and the low-molecular-weight alcohol solvent, for every 100 parts by mass of the aromatic hydrocarbon solvent, according to one example, 0.1 to 50 parts by mass of the low-molecular-weight alcohol solvent is used; according to another example, 0.1 to 30 parts by mass of the low-molecular-weight alcohol solvent is used; according to yet another example, 0.1 to 10 parts by mass of the low-molecular-weight alcohol solvent is used; and according to yet another example, 0.1 to 3 parts by mass of the low-molecular-weight alcohol solvent is used.

[0054] <Other Components> The electrically insulating resin composition of this embodiment can be cured by free radical polymerization or thermal polymerization, or by any reaction method. In the case of curing by free radical polymerization, it is preferable to add a free radical polymerization initiator to the electrically insulating resin composition.

[0055] As a free radical polymerization initiator, examples include, for example, diacyl peroxide, alkyl peroxide, dicarbonate peroxide, carbonate peroxide, peroxy ketal, dialkyl peroxide, hydrogen peroxide, ketone peroxide, peroxybenzoic acid, tert-butyl peroxide, diisopropylbenzene peroxide, and azobisisobutyronitrile, azobis-1-cyclohexanenitrile, etc., which are all organic peroxides.

[0056] When the electrically insulating resin composition contains a free radical polymerization initiator, the content of the free radical polymerization initiator is based on the total mass of organic components other than organic solvents and thermally conductive inorganic fillers, and is in the range of 0.1% to 10% by mass in one example and in the range of 1% to 5% by mass in another example.

[0057] The electrically insulating resin composition of this embodiment may contain a coupling agent. Examples of coupling agents include silane-based coupling agents such as epoxy silane, amino silane, and methacryloyloxysilane, titanate-based coupling agents, and aluminum-based coupling agents. These coupling agents can be used either by adding a product obtained by pre-treating a thermally conductive inorganic filler with a coupling agent to the electrically insulating resin composition, or by directly adding the coupling agent to the electrically insulating resin composition. By using a coupling agent, for example, the adhesion to metal layers such as glass cloth or copper foil is improved.

[0058] The electrically insulating resin composition of this embodiment may contain various additives other than those described above. Examples of such additives include ion adsorbents for inhibiting ion migration, anti-aging agents for resisting oxidative degradation, and flame retardants.

[0059] By uniformly mixing the components described above, the electrically insulating resin composition of the first embodiment of the present invention can be prepared.

[0060] [Uncured sheet material for interlayer insulation] The uncured sheet material for interlayer insulation according to the second embodiment of the present invention is an uncured sheet material comprising the electrically insulating resin composition of the first embodiment described above, used to form an electrically insulating layer in a circuit board.

[0061] In one embodiment, the uncured sheet material for interlayer insulation of this embodiment is a sheet composed of a dried uncured material of the electrically insulating resin composition of the first embodiment. In the manufacture of a circuit board, for example, this sheet, formed on a release film, is transferred onto a metal layer (metal substrate or metal conductor foil) and cured to form an electrically insulating layer. In another embodiment, the uncured sheet material for interlayer insulation of this embodiment is a prepreg obtained by impregnating the electrically insulating resin composition of the first embodiment into a fiber sheet. In the manufacture of a circuit board, for example, the prepreg is laminated onto a metal layer (metal substrate or metal conductor foil) and cured to form an electrically insulating layer.

[0062] [Laminated body for circuit board and circuit board] The laminated body for manufacturing a circuit board according to the third embodiment of the present invention is a laminated body having an electrically insulating layer composed of a hardened material of an electrically insulating resin composition of the first embodiment described above, and a metal layer located on at least one side of the electrically insulating layer.

[0063] Examples of circuit board laminates according to this embodiment include: a circuit board laminate with at least two layers formed by depositing an electrically insulating layer on a metal conductor foil; a circuit board laminate with at least three layers formed by sequentially depositing a metal conductor foil, an electrically insulating layer, and a metal conductor foil; and a circuit board laminate with at least three layers formed by sequentially depositing a metal substrate, an electrically insulating layer, and a metal conductor foil. Here, the metal conductor foil is a metal layer used to form circuit patterns through circuit processing. Among these, the circuit board laminate with a two-layer structure of metal conductor foil and an electrically insulating layer, and the circuit laminate system with a three-layer structure of metal conductor foil, an electrically insulating layer, and a metal conductor foil are used as common printed wiring board materials for inner layer circuits of single-sided circuit boards, double-sided circuit boards, and multilayer circuit boards. Furthermore, the circuit board laminate system with a three-layer structure of metal substrate, an electrically insulating layer, and a metal conductor foil is used in the manufacture of metal substrate circuit boards.

[0064] Among these circuit board laminates, the electrically insulating resin composition of the first embodiment is particularly suitable as the electrically insulating layer of the circuit board laminate used in the manufacture of a metal substrate circuit board. Hereinafter, the metal substrate circuit board laminate will be described in detail with reference to the drawings.

[0065] FIG1 is a partial cross-sectional view schematically showing an example of a circuit board laminate according to the third embodiment of the present invention. The circuit board laminate 10 shown in FIG1 is a metal substrate circuit board laminate, which sequentially includes a metal substrate 11, an electrically insulating layer 12 and a metal conductor foil 13.

[0066] The metal substrate 11 is made of, for example, a single metal or an alloy. Materials for the metal substrate 11 may include, for example, aluminum, iron, copper, aluminum alloys, copper alloys, or stainless steel. The metal substrate 11 may also further contain non-metals such as carbon. For example, the metal substrate 11 may also contain aluminum composited with carbon. Furthermore, the metal substrate 11 may have a single-layer structure or a multi-layer structure.

[0067] The metal substrate 11 has high thermal conductivity. Typically, the metal substrate 11 has a thermal conductivity of 60 W·m⁻¹·K⁻¹ or higher.

[0068] The metal substrate 11 may or may not be flexible. The thickness of the metal substrate 11 is in the range of 0.1 to 5 mm in one example and in the range of 0.5 to 3 mm in another example.

[0069] The electrical insulating layer 12 is composed of a cured form of the electrical insulating resin composition of the first embodiment. As described above, although the acid-modified fully hydrogenated styrene elastomer does not contain double bonds, in a system using a polymerizable monomer containing reactive double bonds, a cross-linked polymer is formed in the electrical insulating layer 12 by, for example, a free radical polymerization reaction. The components contained in the electrical insulating layer 12, or the mixing ratio of these components, can be described using the description of the electrical insulating resin composition of the first embodiment.

[0070] The thickness of the electrical insulation layer 12 is in the range of 10 to 300 μm in one example and in the range of 50 to 150 μm in another example.

[0071] The metal conductor foil 13 is made of, for example, a single metal or an alloy. For example, copper or aluminum can be used as the material for the metal conductor foil 13. The thickness of the metal conductor foil 13 is in the range of 5 to 500 μm in one example and in the range of 35 to 300 μm in another example.

[0072] The circuit board laminate (metal substrate circuit board laminate) 10 can be manufactured by known methods. For example, the circuit board laminate 10 can be manufactured by the following steps: by coating an electrically insulating resin composition of the first embodiment onto one side of a metal substrate 11 and drying it to obtain an uncured electrically insulating layer; then by depositing a metal conductor foil 13 on the uncured electrically insulating layer to form a laminate formed by sequentially depositing the metal substrate 11, the uncured electrically insulating layer and the metal conductor foil 13; then by hot pressing the laminate to harden the uncured electrically insulating layer to form an electrically insulating layer 12.

[0073] Alternatively, the circuit board laminate 10 can be manufactured by the following steps: by coating one side of the metal conductor foil 13 with the electrically insulating resin composition of the first embodiment and drying it to obtain an uncured electrically insulating layer; then by depositing the metal substrate 11 on the uncured electrically insulating layer to form a laminate formed by sequentially depositing the metal substrate 11, the uncured electrically insulating layer and the metal conductor foil 13; then by hot pressing the laminate to harden the uncured electrically insulating layer to form an electrically insulating layer 12.

[0074] Alternatively, the uncured sheet material for interlayer insulation of the second embodiment can also be used to manufacture the circuit board laminate 10. That is, the circuit board laminate 10 can be manufactured by the following steps: preparing an adhesive sheet (transfer sheet) on which the uncured sheet material for interlayer insulation of the second embodiment is formed on a release film; then, depositing the adhesive sheet on the surface of one of the metal substrate 11 and the metal conductor foil 13 with the uncured sheet material facing the surface; then peeling off the release film and transferring the uncured sheet material for interlayer insulation onto the surface; then, by depositing the other of the metal substrate 11 and the metal conductor foil 13 on the uncured sheet material for interlayer insulation, a laminate containing the metal substrate 11, the uncured sheet material for interlayer insulation, and the metal conductor foil 13 in sequence is formed; then, by hot pressing the laminate, the uncured sheet material for interlayer insulation is cured to form an electrical insulating layer 12.

[0075] The circuit board of the fourth embodiment of the present invention includes a circuit pattern formed by circuit processing of the metal conductor foil of the circuit board laminate of the third embodiment. This patterning can be obtained, for example, by forming a mask pattern on the metal conductor foil 13 and removing the exposed portion of the metal conductor foil 13 by etching. The circuit board (metal substrate circuit board) of this embodiment can be obtained, for example, by performing the above-described patterning on the metal conductor foil 13 of the circuit board laminate 10, and performing cutting and hole-making processes as needed.

[0076] [Example] The following describes the experiments conducted in accordance with the present invention. <Preparation of styrene-butadiene elastomer> Using a tank reactor equipped with a stirrer and a jacket, batch polymerization of unhydrogenated styrene-butadiene elastomer was first carried out by the following method. First, as monomers, a cyclohexane solution containing 20 parts by mass of styrene (concentration 20 by mass%) and a cyclohexane solution containing 80 parts by mass of butadiene (concentration 20 by mass%) were prepared.

[0077] 1 L of cyclohexane was added to the reactor described above. Butyllithium (BuLi) and N,N,N',N'-tetramethylethylenediamine were added to the reactor. The butyllithium (BuLi) was 0.115 parts by mass relative to 100 parts by mass of all monomers (total of styrene and butadiene) prepared above, and the N,N,N',N'-tetramethylethylenediamine was 0.30 mol relative to 1 mol of BuLi.

[0078] Next, half of the cyclohexane solution containing styrene prepared above was added over a period of 10 minutes, followed by further polymerization for 10 minutes. The polymerization temperature was adjusted to 60°C. Next, the entire amount of the cyclohexane solution containing butadiene prepared above was added over a period of 60 minutes, followed by further polymerization for 10 minutes. The polymerization temperature was adjusted to 60°C. Then, the remaining cyclohexane solution containing styrene was added over a period of 10 minutes, followed by further polymerization for 10 minutes. The polymerization temperature was adjusted to 60°C. This yielded an unhydrogenated styrene-butadiene elastomer.

[0079] Subsequently, the obtained unhydrogenated styrene-butadiene elastomer was subjected to a hydrogenation reaction in the presence of a titanium catalyst and a trimethylaluminum catalyst at a hydrogen pressure of 0.7 MPa and a temperature of 70°C to adjust the hydrogenation rate. This yielded a fully hydrogenated (100% hydrogenation rate) styrene-butadiene elastomer and a partially hydrogenated styrene-butadiene elastomer. Of these, a portion of the fully hydrogenated styrene-butadiene elastomer was used in Comparative Example 3 as unmodified fully hydrogenated styrene-butadiene elastomer D (refer to Table 2).

[0080] Subsequently, maleic anhydride was added to the obtained fully hydrogenated or partially hydrogenated styrene-butadiene elastomers using peroxide. This yielded acid-modified fully hydrogenated styrene-butadiene elastomer A and acid-modified partially hydrogenated styrene-butadiene elastomer B. Furthermore, for the partially hydrogenated styrene-butadiene elastomer, in addition to acid modification, epoxy modification was also performed using a peracetic acid method to obtain epoxy-modified partially hydrogenated styrene-butadiene elastomer C. The characteristic values ​​of each obtained styrene-butadiene elastomer are shown in Table 1.

[0081] [Table 1]

[0082] Notes on Table 1: • (Note 1) Iodine value is determined according to agricultural and forestry standards by the conventional redox titration using Wijs Reagent. • (Note 2) Hydrogenation rate is the value calculated based on the measured iodine value (a) of the unhydrogenated product and the measured iodine value (b) of the fully or partially hydrogenated product using the following formula: Hydrogenation rate (%) = (a - b) ÷ a × 100 • (Note 3) MFR (Melting Flow Rate) is expressed in accordance with ISO 1133 as the number of grams in 10 minutes at 210°C and 2.16 kgf. • (Note 4) St represents the abbreviation for styrene, and Bd represents the abbreviation for butadiene.

[0083] <Preparation of Electrically Insulating Resin Compositions> The components used in the preparation of the electrically insulating resin composition are shown. • Styrene-based elastomers: Styrene-butadiene elastomers A to D as shown in Table 1 • Polymerizable monomers: Tricyclodecanediethanol dimethacrylate • Cyclic compounds: Dicyclopentadiene-based polymers (petroleum resins with a weight average molecular weight of 380, iodine value of 177–194, and softening point of 135–150°C) • Free radical polymerization initiator: 1,3-bis(tributylperoxyisopropyl)benzene • Thermally conductive inorganic filler: Alumina particles with an average particle size (d50) of 12 μm • Coupling agent: γ-methacryloxypropyltrimethoxysilane • Organic solvents: Toluene, ethanol

[0084] (Example 1) 60 parts by mass of styrene-butadiene elastomer A (acid-modified fully hydrogenated) and 30.1 parts by mass of polymerizable monomer were dissolved in 257.5 parts by mass of toluene. Then, 5.4 parts by mass of free radical polymerization initiator and 4.5 parts by mass of coupling agent were added and the mixture was kneaded. 508 parts by mass of thermally conductive inorganic filler were added, and the mixture was stirred for 5 minutes using a centrifugal defoaming mixer to obtain electrically insulating resin composition 1 (slurry).

[0085] (Example 2) Except that 257.5 parts by mass of toluene is changed to a mixture of 257.5 parts by mass of toluene and 0.8 parts by mass of ethanol, an electrically insulating resin composition 2 (slurry) is obtained by the same method as in Example 1.

[0086] (Example 3) Except that 257.5 parts by mass of toluene is changed to a mixture of 257.5 parts by mass of toluene and 1.5 parts by mass of ethanol, an electrically insulating resin composition 3 (slurry) is obtained by the same method as in Example 1.

[0087] (Example 4) 60 parts by mass of styrene-butadiene elastomer A (acid-modified fully hydrogenated compound), 12.4 parts by mass of polymerizable monomer, and 17.7 parts by mass of cyclic compound were dissolved in 257.5 parts by mass of toluene. Then, 5.4 parts by mass of free radical polymerization initiator and 4.5 parts by mass of coupling agent were added and the mixture was kneaded. 508 parts by mass of thermally conductive inorganic filler were added, and the mixture was stirred for 5 minutes using a centrifugal defoaming mixer to obtain electrically insulating resin composition 4 (slurry).

[0088] (Example 5) Except that 257.5 parts by mass of toluene is changed to a mixture of 257.5 parts by mass of toluene and 0.8 parts by mass of ethanol, an electrically insulating resin composition 5 (slurry) is obtained by the same method as in Example 4.

[0089] (Example 6) Except that 257.5 parts by mass of toluene is changed to a mixture of 257.5 parts by mass of toluene and 1.5 parts by mass of ethanol, an electrically insulating resin composition 6 (slurry) is obtained by the same method as in Example 4.

[0090] (Comparative Example 1) Except for changing styrene-butadiene elastomer A (acid-modified fully hydrogenated) to styrene-butadiene elastomer B (acid-modified partially hydrogenated), an electrically insulating resin composition R1 (slurry) was obtained by the same method as in Example 4.

[0091] (Comparative Example 2) Except for changing styrene-butadiene elastomer A (acid-modified fully hydrogenated) to styrene-butadiene elastomer C (epoxy-modified partially hydrogenated), an electrically insulating resin composition R2 (slurry) was obtained by the same method as in Example 4.

[0092] (Comparative Example 3) Except for changing styrene-butadiene elastomer A (acid-modified fully hydrogenated) to styrene-butadiene elastomer D (unmodified fully hydrogenated), an electrically insulating resin composition R3 (slurry) was obtained by the same method as in Example 4.

[0093] (Comparative Example 4) A commercially available epoxy resin composition was used as the electrically insulating resin composition R4.

[0094] <Coating Stability> The stability of each electrically insulating resin composition (slurry) obtained above as a coating solution was evaluated by confirming its state after being stored at room temperature (approximately 25°C) for 1 hour and after being stored for 12 hours. The results are shown in Table 2 below. A: No gelling after 12 hours, coating properties are not a problem. B: No gelling after 1 hour, coating properties are not a problem, but gelling occurred after 12 hours, becoming gelatinous. C: Gelatinization occurred within 1 hour, becoming gelatinous.

[0095] <Manufacturing of a laminate for a circuit board> A laminate for a circuit board comprising an electrically insulating layer using each of the electrically insulating resin compositions (slurries) obtained above. Among them, as shown in Table 2, the electrically insulating resin compositions of Examples 1 and 4, which have a coating stability evaluation of B, are those that have been used for about 1 hour after the preparation of the slurry.

[0096] (Example 101) The electrically insulating resin composition 1 obtained in Example 1 was coated onto a silicone-treated polyethylene terephthalate (PET) film and dried at 110°C for 10 minutes to obtain an adhesive sheet having a sheet-like uncured material. An aluminum substrate with a thickness of 1 mm was prepared, and the adhesive sheet was deposited on the aluminum substrate with the sheet-like uncured material side facing the aluminum substrate. The PET film was then peeled off, thereby transferring the sheet-like uncured material onto the aluminum substrate. Subsequently, a copper foil with a thickness of 70 μm was deposited on the sheet-like uncured material, and a hot press was used to heat and pressurize it at a temperature of 190°C and a pressure of 5 MPa for 50 minutes to produce a circuit board laminate 101 composed of an aluminum substrate (1 mm thickness), an electrically insulating layer (100 μm thickness), and a copper foil (70 μm thickness).

[0097] (Example 102) Except that an electrically insulating resin composition 2 is used instead of an electrically insulating resin composition 1, a circuit board laminate 102 is manufactured by the same method as in Example 101.

[0098] (Example 103) Except that an electrically insulating resin composition 3 is used instead of an electrically insulating resin composition 1, a circuit board laminate 103 is manufactured by the same method as in Example 101.

[0099] (Example 104) Except that an electrically insulating resin composition 4 is used instead of an electrically insulating resin composition 1, a circuit board laminate 104 is manufactured by the same method as in Example 101.

[0100] (Example 105) Except that an electrically insulating resin composition 5 is used instead of an electrically insulating resin composition 1, a circuit board laminate 105 is manufactured by the same method as in Example 101.

[0101] (Example 106) Except that an electrically insulating resin composition 3 is used instead of an electrically insulating resin composition 1, a circuit board laminate 106 is manufactured by the same method as in Example 101.

[0102] (Comparative Example 101) Except that an electrically insulating resin composition R1 is used instead of an electrically insulating resin composition 1, a circuit board laminate R101 is manufactured by the same method as in Example 101.

[0103] (Comparative Example 102) Except that an electrically insulating resin composition R2 is used instead of an electrically insulating resin composition 1, a circuit board laminate R102 is manufactured by the same method as in Example 101.

[0104] (Comparative Example 103) Except that an electrically insulating resin composition R3 is used instead of an electrically insulating resin composition 1, a circuit board laminate R103 is manufactured by the same method as in Example 101.

[0105] (Comparative Example 104) Except that an electrically insulating resin composition R4 is used instead of an electrically insulating resin composition 1, a circuit board laminate R104 is manufactured by the same method as in Example 101.

[0106] <Evaluation> The multilayer circuit boards obtained above were evaluated using the following evaluation method. The results are shown in Table 3. <Withstand Voltage> The multilayer circuit boards were cut to specified dimensions, and copper foil was etched to obtain samples with circular electrode patterns of ϕ20mm. Two samples were prepared for each multilayer circuit board. One sample was immersed in insulating oil, and an AC voltage was applied between the copper foil and the aluminum substrate at room temperature. The applied voltage was increased, and the lowest voltage at which insulation failure occurred was set as the withstand voltage of state A. Another sample was subjected to solder heat treatment by floating it in a solder bath at 260°C for 1 minute. An AC voltage was applied in the same manner as above, and the insulation failure voltage value was measured. This insulation failure voltage value was set as the withstand voltage after solder heat treatment (withstand voltage after hot soldering).

[0107] The withstand voltage performance is evaluated based on the measured values ​​of the withstand voltage after hot soldering. Furthermore, the withstand voltage for state A is investigated in the following discussion: A: The withstand voltage after hot soldering is 4kV or higher. B: The withstand voltage after hot soldering is less than 4kV.

[0108] <Peel Strength> A sample with a narrow pattern of 10 mm width and 60 mm length was obtained by cutting the circuit board into a multilayer material to a specified size and etching the copper foil. Two samples were made for each circuit board multilayer material. One sample was held by one end of the copper foil pattern and peeled at a speed of 50 mm / min with the aluminum substrate perpendicular to the copper foil. The force at this time was set as the peel strength (N / cm) of state A. Another sample was subjected to solder heat treatment by floating it in a solder bath at 260°C for 1 minute. The peel strength was then measured in the same manner as above. The measured value was set as the peel strength after solder heat treatment (post-soldering peel strength).

[0109] The peel strength is evaluated based on the measured value of the peel strength after hot soldering. Furthermore, the peel strength of condition A will be discussed again in the following discussion. A: Peel strength after hot soldering is 10 N / cm or higher. B: Peel strength after hot soldering is less than 10 N / cm.

[0110] <Storage Modulus of Elasticity> The electrical insulating layer was removed by etching copper foil and aluminum substrate from the circuit board laminate using a ferric chloride solution. This was then cut to specified dimensions, resulting in a sample consisting only of an electrical insulating layer measuring 50 mm in length, 3 mm in width, and 0.1 mm in thickness. The storage modulus of elasticity E' (MPa) of the sample was measured using a dynamic viscoelasticity measuring device (RAS G2 manufactured by TA Instruments) at a frequency of 1 Hz and a heating rate of 2 °C / min, in tensile mode, within the range of -50 °C to 250 °C. The storage modulus of elasticity E' at -40 °C, 20 °C, and 125 °C is shown in Table 3.

[0111] <Cold and Hot Cycling Test> A 3216 chip resistor (3.2mm x 1.6mm) was mounted on a circuit board multilayer using Sn-3.0Ag-0.5Cu solder (M705-GRN360-K2-V manufactured by Senju Metals). After measuring the initial chip resistance, it was placed in an environmental testing machine and repeatedly subjected to cold and hot cycling at -40℃ (15 minutes) and 125℃ (15 minutes) as one cycle. After 500, 1000, 1500, 2000, 2500, and 3000 cycles, the chip was removed and its resistance was measured. A resistance value that increased by more than 3% compared to the initial resistance value was considered a fault. The number of cycles before the fault occurred is recorded in Table 3.

[0112] <Thermal Conductivity> Prepare a copper foil with a thickness of 18 μm and an adhesive sheet with sheet-like uncured material as described in the examples above. Lay the adhesive sheet onto the copper foil with the sheet-like uncured material facing the copper foil, and peel off the PET film. Repeat the above steps three times to transfer the sheet-like uncured material into three layers onto the copper foil. Then, lay a copper foil with a thickness of 18 μm, different from the copper foil mentioned above, onto the sheet-like uncured material to obtain a laminate consisting of two copper foils sandwiching three layers of sheet-like uncured material. Mount the laminate on a hot press and hot press it at a temperature of 190°C and a pressure of 5 MPa for 50 minutes to obtain a composite molded body (copper foil (thickness 18 μm) / insulation layer (thickness 0.3 mm) / copper foil (thickness 18 μm)) with an insulating layer thickness of 0.3 mm.

[0113] ・Specific gravity determination of the insulating layer: The copper foil on both sides of the above composite molded body was etched away using ferric chloride solution to obtain a separate insulating layer. The specific gravity ρ (g / cm3) of the test piece obtained by cutting it into a length of 5cm × width of 5cm × thickness of 0.3mm was determined using Archimedes' method.

[0114] ・The specific heat of the insulating layer was measured by taking a sample from the individual insulating layer obtained by removing the copper foil of the above composite molded body by etching, and using a DSC8500 manufactured by PerkinElmer.

[0115] ・Determination of Thermal Conductivity of the Insulating Layer A 10mm × 10mm piece was cut from the above-mentioned composite molded body as a test piece. The thermal diffusivity (α) in the thickness direction of the test piece was measured using a NETZSCH LFA467 HyperFlash desktop xenon lamp flash thermal conductivity analyzer. The measurement was conducted in an atmospheric environment at 25°C. Based on the measured values ​​of thermal diffusivity α, specific heat Cp, and specific gravity ρ, the thermal conductivity was calculated using the following formula: Thermal conductivity [W / m・K]=α[m2 / s]×Cp[J / kg・K]×ρ[g / cm3]

[0116] [Table 2]

[0117] [Table 3]

[0118] <Exploration> Based on Tables 2 and 3, the following is explored, for example. Based on the evaluation results of coating stability, it can be seen that the coating stability of the slurries of the electrically insulating resin compositions of Examples 2, 3, 5, and 6, which contain a small amount of ethanol in toluene, is improved compared to the electrically insulating resin compositions of Examples 1 and 4, which use only toluene as an organic solvent. It can be seen that this phenomenon is unique to the use of acid-modified fully hydrogenated styrene-based elastomers as styrene-based elastomers and is not applicable to Comparative Examples 1 to 3.

[0119] Furthermore, it can be seen that compared with comparative examples 101 to 103, the circuit board laminates of examples 101 to 106 using acid-modified fully hydrogenated styrene elastomers have a lower storage modulus of elasticity from low temperature to high temperature and excellent flexibility, as well as better resistance to thermal cycling.

[0120] Furthermore, based on the comparison between Examples 101 to 103 and Examples 104 to 106, it can be seen that by adding cyclic compounds, the storage modulus of elasticity is lowered and the flexibility is further improved, and the resistance to thermal cycling is also further improved. Moreover, compared to Examples 101 to 103, Examples 104 to 106 suppress the decrease in withstand voltage and peel strength of solder in state A after heat treatment. Therefore, it can be seen that by adding cyclic compounds, thermal stability can be improved. [Simplified Explanation of the Diagram]

[0023] FIG1 is a partial cross-sectional view schematically showing an example of a circuit board laminate according to one embodiment of the present invention.

Claims

1. An electrically insulating resin composition comprising an acid-modified fully hydrogenated styrene elastomer, a polymerizable monomer containing reactive double bonds, a thermally conductive inorganic filler, and an organic solvent; wherein the electrically insulating resin composition comprises an aromatic hydrocarbon solvent and a low-molecular-weight alcohol solvent selected from methanol, ethanol, propanol, and isopropanol as the aforementioned organic solvent.

2. The electrically insulating resin composition of claim 1 contains the aforementioned aromatic hydrocarbon solvent and the aforementioned low molecular weight alcohol solvent in the following blending ratio, namely, for every 100 parts by mass of the aforementioned aromatic hydrocarbon solvent, the aforementioned low molecular weight alcohol solvent is 0.1 to 10 parts by mass.

3. The electrically insulating resin composition of claim 1, wherein the aforementioned polymeric monomer contains two or more acrylonitrile, methacrylonitrile, or allyl groups within one molecule.

4. The electrically insulating resin composition of claim 1 further contains a cyclic compound having an aromatic or aliphatic ring, a weight-average molecular weight in the range of 300 to 1000, and being solid at room temperature.

5. A sheet-like uncured material for interlayer insulation, comprising an electrically insulating resin composition as claimed in any one of claims 1 to 4.

6. A multilayer for a circuit board, comprising: an electrically insulating layer formed of a cured form of an electrically insulating resin composition as described in any one of claims 1 to 4; and a metal layer disposed on at least one side of the aforementioned electrically insulating layer.

7. The circuit board laminate of claim 6, which comprises a metal substrate and a metal conductor foil as the aforementioned metal layer, and is formed by sequentially laminating the aforementioned metal substrate, the aforementioned electrical insulating layer and the aforementioned metal conductor foil.

8. A circuit board formed by processing a multilayer onto a circuit board as described in claim 7, and having a circuit pattern formed by processing the aforementioned metal conductor foil.

9. A multilayer for a circuit board, comprising: an electrically insulating layer containing an acid-modified fully hydrogenated styrene-based elastomer and a crosslinked polymeric monomer containing reactive double bonds, a cyclic compound, and a thermally conductive inorganic filler; and a metal layer disposed on at least one side of the aforementioned electrically insulating layer; wherein the aforementioned cyclic compound is a compound having aliphatic rings, a weight average molecular weight in the range of 300 to 1000, and is a solid at room temperature.

10. The circuit board laminate of claim 9, wherein the aforementioned cyclic compound has one or more aliphatic rings selected from rosin, cyclopentane, cyclopentene, cyclohexane, cyclohexene, tricyclodecane, and norethene.

11. The circuit board laminate of claim 9, comprising a metal substrate and a metal conductor foil as the aforementioned metal layer, and formed by sequentially laminating the aforementioned metal substrate, the aforementioned electrical insulating layer and the aforementioned metal conductor foil.

12. A circuit board formed by processing a multilayer onto a circuit board as claimed in claim 11, and having a circuit pattern formed by processing the aforementioned metal conductor foil.

13. A method for manufacturing a circuit board, comprising a metal substrate, an electrically insulating layer, and a circuit pattern sequentially, and including the following steps: preparing the aforementioned metal substrate and a metal conductor foil; selecting one of the aforementioned metal substrate and the aforementioned metal conductor foil, and coating one side thereon with an electrically insulating resin composition as claimed in any one of claims 1 to 4 to form an uncured electrically insulating layer; forming a laminate composed of the aforementioned metal substrate, the aforementioned uncured electrically insulating layer, and the aforementioned metal conductor foil by depositing the other of the aforementioned metal substrate and the aforementioned metal conductor foil onto the aforementioned uncured electrically insulating layer; hot-pressing the aforementioned laminate; and forming the aforementioned circuit pattern by processing the aforementioned metal conductor foil.

14. A method for manufacturing a circuit board, comprising a metal substrate, an electrical insulating layer and a circuit pattern sequentially, and comprising the following steps: forming a laminate sequentially comprising the aforementioned metal substrate, an uncured sheet of interlayer insulation as claimed in claim 5 and a metal conductor foil; hot-pressing the aforementioned laminate; and forming the aforementioned circuit pattern by processing the aforementioned metal conductor foil.

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