JP7806387B2 - printed wiring board - Google Patents

Description

The present invention relates to a printed wiring board, a method for manufacturing the same, and a resin composition and resin sheet used to form an insulating layer of the printed wiring board.

In recent years, there has been an increasing need for substrates that require high-frequency characteristics by using insulating materials with excellent electrical properties, such as modified polyimides or liquid crystal polymers. Laminating modified polyimides or liquid crystal polymers requires high-temperature processing. Therefore, it is common to use a thermosetting resin as a bonding sheet, forming a two-layer structure consisting of the bonding sheet and an insulating material with excellent electrical properties, such as modified polyimides or liquid crystal polymers. Many such bonding sheets have been developed, including the resin composition described in Patent Document 1, for example.

JP 2017-59779 A

In recent years, in order to improve the electrical properties of printed wiring boards, layers of modified polyimides or liquid crystal polymers have been laminated onto inner circuit boards. Laminating such layers in a single layer generally requires processing under high-temperature conditions. Therefore, lamination is often performed using an insulating layer that functions as a bonding sheet. A bonding sheet is an adhesive sheet that is placed between each layer in a multilayer structure to bond the layers together and also functions as an insulating layer to insulate the layers from each other.

When manufacturing printed wiring boards, via holes may be formed in insulating layers and layers such as modified polyimide. The term "via hole" generally refers to a hole that penetrates an insulating layer and a layer such as modified polyimide. One possible method for forming via holes is to use a laser.

The inventors have discovered that laser irradiation generates heat, which can cause interfacial delamination between the insulating layer and the modified polyimide or modified polyimide layer, or further erode the resin surrounding the via hole in the insulating layer, resulting in a step in the cross-sectional shape of the via hole near the interface between the insulating layer and the modified polyimide or modified polyimide layer. Furthermore, a desmear treatment is typically performed after via hole formation, but the degree of surface roughening of each layer differs depending on the components contained in each layer. Therefore, the inventors have discovered that performing the desmear treatment can result in a step in the cross-sectional shape of the via hole near the interface between the insulating layer and the modified polyimide or modified polyimide layer. If this step is large, the reliability of the electrical connection may be compromised.

The present invention aims to provide a printed wiring board in which the step shape of via holes is suppressed; a method for manufacturing the same; and a resin composition and resin sheet used to form the insulating layer of the printed wiring board.

That is, the present invention includes the following.
[1] A printed wiring board comprising, in this order, a resin layer having a first surface, an insulating layer in contact with the first surface of the resin layer and including a cured product of a resin composition, and an inner layer circuit board,
a via hole penetrating the resin layer and the insulating layer in the thickness direction;
The top diameter of the via hole is a (μm),
When the distance from the end of the first surface in the via hole to the end of the contact surface between the first surface and the insulating layer is d (μm),
A printed wiring board that satisfies the relationship: [d/{(1/2)×a}]×100≦5.
[2] The printed wiring board according to [1], wherein the top diameter of the via hole is 50 μm or less.
[3] The printed wiring board according to [1] or [2], wherein the resin composition contains an inorganic filler.
[4] The printed wiring board according to [3], wherein the content of the inorganic filler is 50% by mass or less when the non-volatile components of the resin composition are 100% by mass.
[5] The printed wiring board according to any one of [1] to [4], wherein the linear thermal expansion coefficient of the cured resin composition is 40 ppm or less.
[6] The printed wiring board according to any one of [1] to [5], wherein the resin layer is formed of a thermoplastic resin.
[7] The printed wiring board according to any one of [1] to [6], wherein the resin layer contains either a polyimide resin or a liquid crystal polymer.
[8] A resin composition containing an inorganic filler,
A resin composition for bonding sheets, in which the content of inorganic filler is 50% by mass or less when the non-volatile components in the resin composition are 100% by mass.
[9] A resin sheet comprising a support and a resin composition layer formed on the support using the resin composition according to [8].
[10] (A) A step of forming a resin layer on the surface of the resin composition layer of the resin sheet according to [9] that is not bonded to the support;
(B) a step of laminating a resin sheet having a resin layer formed thereon on an inner layer circuit board and curing the resin composition layer to form an insulating layer;
(C) performing a plasma treatment on the surface of the resin layer to form via holes penetrating the resin layer and the insulating layer;
(D) a step of performing a roughening treatment; and (E) a step of forming a conductor layer on the surface of the resin layer.

The present invention provides a printed wiring board in which the step shape of the via hole is suppressed; a method for manufacturing the same; and a resin composition and resin sheet used to form the insulating layer of the printed wiring board.

FIG. 1 is a cross-sectional view schematically showing a printed wiring board according to one embodiment of the present invention.

The present invention will be described in detail below, showing embodiments and examples. However, the present invention is not limited to the embodiments and examples given below, and can be modified and implemented as desired within the scope of the claims of the present invention and their equivalents.

Before describing the printed wiring board of the present invention and its manufacturing method, we will explain the resin composition used to form the insulating layer of the printed wiring board and the resin sheet used in manufacturing the printed wiring board.

[Resin composition]
The cured product of the resin composition used to form the insulating layer can function as an insulating layer as well as a bonding sheet that bonds an inner layer circuit board and the resin layer. Therefore, the resin composition can be used as a bonding sheet.

The resin composition may be any composition as long as the cured product has sufficient insulating and adhesive properties. Examples of such resin compositions include a composition containing (a) a curable resin. In addition to component (a), the resin composition may also contain (b) an inorganic filler, (c) a curing accelerator, (d) a thermoplastic resin, (e) an elastomer, and (f) other additives, as needed. Each component contained in the resin composition is described in detail below.

<(a) Curable resin>
The resin composition contains (a) a curable resin. Examples of the curable resin include thermosetting resins and photocurable resins, but thermosetting resins that can be used to form insulating layers for printed wiring boards are preferred.

Examples of thermosetting resins include epoxy resins, phenolic resins, naphthol resins, benzoxazine resins, active ester resins, cyanate ester resins, carbodiimide resins, amine resins, and acid anhydride resins. Component (a) may be used singly or in any combination of two or more types in any ratio. Hereinafter, resins that can react with epoxy resins to harden the resin composition, such as phenolic resins, naphthol resins, benzoxazine resins, active ester resins, cyanate ester resins, carbodiimide resins, amine resins, and acid anhydride resins, are collectively referred to as "curing agents." From the perspective of forming an insulating layer, the resin composition preferably contains an epoxy resin and a curing agent as component (a), more preferably an epoxy resin, active ester resin, cyanate ester resin, or phenolic resin, and even more preferably an epoxy resin, cyanate ester resin, or active ester resin.

Examples of epoxy resins for component (a) include bixylenol-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol S-type epoxy resins, bisphenol AF-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol novolac-type epoxy resins, phenol novolac-type epoxy resins, tert-butyl-catechol-type epoxy resins, naphthalene-type epoxy resins, naphthol-type epoxy resins, anthracene-type epoxy resins, glycidylamine-type epoxy resins, glycidyl ester-type epoxy resins, cresol novolac-type epoxy resins, biphenyl-type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexane-type epoxy resins, cyclohexanedimethanol-type epoxy resins, naphthylene ether-type epoxy resins, trimethylol-type epoxy resins, and tetraphenylethane-type epoxy resins. Epoxy resins may be used alone or in combination of two or more types.

The resin composition preferably contains, as component (a), an epoxy resin having two or more epoxy groups per molecule. To significantly achieve the desired effects of the present invention, the proportion of the epoxy resin having two or more epoxy groups per molecule relative to 100% by mass of the non-volatile components of component (a) is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

Epoxy resins include epoxy resins that are liquid at a temperature of 20°C (hereinafter sometimes referred to as "liquid epoxy resins") and epoxy resins that are solid at a temperature of 20°C (hereinafter sometimes referred to as "solid epoxy resins"). The resin composition may contain only liquid epoxy resins or only solid epoxy resins as component (a), but from the perspective of achieving the most pronounced effects of the present invention, it is preferable to contain a combination of liquid epoxy resins and solid epoxy resins.

Preferably, the liquid epoxy resin is one having two or more epoxy groups per molecule.

Preferred liquid epoxy resins are bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AF type epoxy resins, naphthalene type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, phenol novolac type epoxy resins, alicyclic epoxy resins having an ester skeleton, cyclohexane type epoxy resins, cyclohexanedimethanol type epoxy resins, glycidyl amine type epoxy resins, and epoxy resins having a butadiene structure, with cyclohexane type epoxy resins being more preferred.

Specific examples of liquid epoxy resins include DIC's "HP4032," "HP4032D," and "HP4032SS" (naphthalene-type epoxy resins); Mitsubishi Chemical's "828US," "jER828EL," "825," and "Epikote 828EL" (bisphenol A-type epoxy resins); Mitsubishi Chemical's "jER807" and "1750" (bisphenol F-type epoxy resins); Mitsubishi Chemical's "jER152" (phenol novolac-type epoxy resin); and Mitsubishi Chemical's "630" and "630LSD" (glycidylamine-type epoxy resins). ); "ZX1059" (a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "EX-721" (glycidyl ester epoxy resin) manufactured by Nagase ChemteX Corporation; "Celloxide 2021P" (alicyclic epoxy resin with an ester skeleton) manufactured by Daicel Corporation; "PB-3600" (epoxy resin with a butadiene structure) manufactured by Daicel Corporation; and "ZX1658" and "ZX1658GS" (liquid 1,4-glycidylcyclohexane epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd. These may be used alone or in combination of two or more.

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

Preferred solid epoxy resins are bixylenol-type epoxy resins, naphthalene-type epoxy resins, naphthalene-type tetrafunctional epoxy resins, cresol novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, trisphenol-type epoxy resins, naphthol-type epoxy resins, biphenyl-type epoxy resins, naphthylene ether-type epoxy resins, anthracene-type epoxy resins, bisphenol A-type epoxy resins, bisphenol AF-type epoxy resins, and tetraphenylethane-type epoxy resins, with bixylenol-type epoxy resins, naphthalene-type epoxy resins, bisphenol AF-type epoxy resins, and naphthylene ether-type epoxy resins being more preferable.

Specific examples of solid epoxy resins include DIC Corporation's "HP4032H" (naphthalene-type epoxy resin), "HP-4700," "HP-4710" (naphthalene-type tetrafunctional epoxy resin), "N-690" (cresol novolac-type epoxy resin), "N-695" (cresol novolac-type epoxy resin), "HP-7200," "HP-7200HH," "HP-7200H" (dicyclopentadiene-type epoxy resin), "EXA-7311," "EXA-7311-G3," "EXA-7311-G4," "EXA-7311-G4S," and "HP6000" (naphthylene ether-type epoxy resin); and Nippon Kayaku Co., Ltd.'s "EPPN-502H" (trisphenol-type epoxy resin), "NC7000L" (naphthol novolac-type epoxy resin), "NC3000H," and "NC30 00," "NC3000L," and "NC3100" (biphenyl-type epoxy resins); "ESN475V" (naphthalene-type epoxy resin) and "ESN485" (naphthol novolac-type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YX4000H," "YL6121" (biphenyl-type epoxy resin), "YX4000HK" (bixylenol-type epoxy resin), and "YX8800" (anthracene-type epoxy resin) manufactured by Mitsubishi Chemical Corporation; "PG-100" and "CG-500" manufactured by Osaka Gas Chemicals Co., Ltd., and "YL7760" (bisphenol AF-type epoxy resin), "YL7800" (fluorene-type epoxy resin), "jER1010" (solid bisphenol A-type epoxy resin), and "jER1031S" (tetraphenylethane-type epoxy resin) manufactured by Mitsubishi Chemical Corporation. These may be used alone or in combination of two or more.

When a liquid epoxy resin and a solid epoxy resin are used in combination as component (a), the ratio by mass (liquid epoxy resin:solid epoxy resin) is preferably 1:0.1 to 1:20, more preferably 1:1 to 1:15, and particularly preferably 1:5 to 1:10. By keeping the ratio of liquid epoxy resin to solid epoxy resin within this range, the desired effects of the present invention can be significantly achieved. Furthermore, when used in the form of a resin sheet, appropriate adhesiveness is typically achieved. Furthermore, when used in the form of a resin sheet, sufficient flexibility is typically achieved, improving handleability. Furthermore, a cured product with sufficient breaking strength can typically be obtained.

The epoxy equivalent of the epoxy resin used as component (a) is preferably 50 g/eq. to 5,000 g/eq., more preferably 50 g/eq. to 3,000 g/eq., even more preferably 80 g/eq. to 2,000 g/eq., and even more preferably 110 g/eq. to 1,000 g/eq. This range ensures that the cured product of the resin composition has sufficient crosslink density. The epoxy equivalent is the mass of the epoxy resin containing one equivalent of epoxy groups. This epoxy equivalent can be measured in accordance with JIS K7236.

From the viewpoint of significantly achieving the desired effects of the present invention, the weight-average molecular weight (Mw) of the epoxy resin as component (a) is preferably 100 to 5,000, more preferably 250 to 3,000, and even more preferably 400 to 1,500. The weight-average molecular weight of the epoxy resin is the weight-average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

From the viewpoint of obtaining a cured product exhibiting good mechanical strength and insulation reliability, the content of the epoxy resin as component (a) is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on 100% by mass of the non-volatile components in the resin composition. From the viewpoint of significantly achieving the desired effects of the present invention, the upper limit of the epoxy resin content is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. In the present invention, the content of each component in the resin composition is the value when the non-volatile components in the resin composition are taken as 100% by mass, unless otherwise specified.

From the viewpoint of achieving the remarkable effects of the present invention, the content of the epoxy resin as component (a) is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on 100% by mass of the resin component in the resin composition. From the viewpoint of achieving the remarkable effects of the present invention, the upper limit of the epoxy resin content is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less. Unless otherwise specified, the resin component refers to the non-volatile components in the resin composition excluding (b) the inorganic filler.

The active ester resin used as component (a) can be a resin having one or more active ester groups per molecule. Among these, preferred active ester resins are those having two or more highly reactive ester groups per molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds. The active ester resin is preferably one obtained by the condensation reaction of a carboxylic acid compound and/or a thiocarboxylic acid compound with a hydroxy compound and/or a thiol compound. In particular, from the perspective of improving heat resistance, active ester resins obtained from a carboxylic acid compound and a hydroxy compound are preferred, and active ester resins obtained from a carboxylic acid compound and a phenol compound and/or a naphthol compound are more preferred.

Examples of carboxylic acid compounds include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid.

Examples of phenol compounds or naphthol compounds include hydroquinone, resorcinol, bisphenol A, bisphenol F, bisphenol S, phenolphthalene, methylated bisphenol A, methylated bisphenol F, methylated bisphenol S, phenol, o-cresol, m-cresol, p-cresol, catechol, α-naphthol, β-naphthol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucin, benzenetriol, dicyclopentadiene-type diphenol compounds, and phenol novolak. Here, "dicyclopentadiene-type diphenol compounds" refer to diphenol compounds obtained by condensing one dicyclopentadiene molecule with two phenol molecules.

Specific preferred examples of active ester resins include active ester resins containing a dicyclopentadiene-type diphenol structure, active ester resins containing a naphthalene structure, active ester resins containing an acetylated phenol novolac, and active ester resins containing a benzoylated phenol novolac. Of these, active ester resins containing a naphthalene structure and active ester resins containing a dicyclopentadiene-type diphenol structure are more preferred. A "dicyclopentadiene-type diphenol structure" refers to a divalent structural unit consisting of phenylene-dicyclopentylene-phenylene.

Commercially available activated ester resins include those containing a dicyclopentadiene-type diphenol structure such as "EXB9451," "EXB9460," "EXB9460S," "HPC-8000-65T," "HPC-8000H-65TM," and "EXB-8000L-65TM" (manufactured by DIC Corporation); and those containing a naphthalene structure such as "EXB9416-70BK," "EXB-8100L-65T," "EXB-8150L-65T," "EXB-8150-65T," "HPC-8150-60T," "HPC-8150-62T," and "HPB-8151-62T" (manufactured by DIC Corporation), and "PC1300-02- 65T" (manufactured by Air Water Inc.); an activated ester resin containing acetylated phenol novolac is "DC808" (manufactured by Mitsubishi Chemical Corporation); an activated ester resin containing benzoated phenol novolac is "YLH1026" (manufactured by Mitsubishi Chemical Corporation); an activated ester resin that is an acetylated phenol novolac is "DC808" (manufactured by Mitsubishi Chemical Corporation); activated ester resins that are benzoated phenol novolac are "YLH1026" (manufactured by Mitsubishi Chemical Corporation), "YLH1030" (manufactured by Mitsubishi Chemical Corporation), and "YLH1048" (manufactured by Mitsubishi Chemical Corporation); and "EXB-8500-65T" (manufactured by DIC Corporation).

To achieve the significant effects of the present invention, the content of the active ester resin as component (a) is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 4% by mass or more, relative to 100% by mass of non-volatile components in the resin composition; it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

From the perspective of achieving significant effects of the present invention, the content of the active ester resin as component (a) is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, based on 100% by mass of the resin component in the resin composition, and is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

As the phenolic resin and naphtholic resin used as component (a), those having a novolac structure are preferred from the viewpoints of heat resistance and water resistance. Furthermore, from the viewpoint of adhesion to the conductor layer, nitrogen-containing phenolic resins are preferred, and triazine skeleton-containing phenolic resins are more preferred.

Specific examples of phenolic resins and naphthol-based resins include "MEH-7700," "MEH-7810," and "MEH-7851" manufactured by Meiwa Kasei Co., Ltd.; "NHN," "CBN," and "GPH" manufactured by Nippon Kayaku Co., Ltd.; "SN170," "SN180," "SN190," "SN475," "SN485," "SN495," "SN-495V," "SN375," and "SN395" manufactured by Nippon Steel Chemical & Material Co., Ltd.; and "TD-2090," "LA-7052," "LA-7054," "LA-1356," "LA-3018-50P," and "EXB-9500" manufactured by DIC Corporation.

To achieve the significant effects of the present invention, the content of the phenolic resin and naphtholic resin as component (a) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to 100% by mass of non-volatile components in the resin composition, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

From the perspective of achieving significant effects of the present invention, the content of the phenolic resin and naphtholic resin as component (a) is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on 100% by mass of the resin components in the resin composition, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

Examples of cyanate ester resins for component (a) 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; multifunctional cyanate resins derived from phenol novolac and cresol novolac; and prepolymers in which these cyanate resins are partially converted to triazine. Specific examples of cyanate ester resins include "PT30," "PT30S," 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 triazinated to form a trimer), all manufactured by Lonza Japan. Cyanate ester resins are preferably used as curing agents when the resin composition does not contain (b) inorganic filler.

Specific examples of benzoxazine-based resins for component (a) include "JBZ-OD100" (benzoxazine ring equivalent weight 218), "JBZ-OP100D" (benzoxazine ring equivalent weight 218), and "ODA-BOZ" (benzoxazine ring equivalent weight 218) manufactured by JFE Chemical Corporation; "P-d" (benzoxazine ring equivalent weight 217) and "F-a" (benzoxazine ring equivalent weight 217) manufactured by Shikoku Chemicals Corporation; and "HFB2006M" (benzoxazine ring equivalent weight 432) manufactured by Showa Highpolymer Co., Ltd.

Specific examples of carbodiimide resins for component (a) include Carbodilite (registered trademark) V-03 (carbodiimide group equivalent weight: 216, V-05 (carbodiimide group equivalent weight: 216), V-07 (carbodiimide group equivalent weight: 200), and V-09 (carbodiimide group equivalent weight: 200), all manufactured by Nisshinbo Chemical Inc.; and Stavaxol (registered trademark) P (carbodiimide group equivalent weight: 302), all manufactured by Rhein Chemie AG.

Amine-based resins as component (a) include resins containing one or more amino groups per molecule, such as aliphatic amines, polyether amines, alicyclic amines, and aromatic amines. Of these, aromatic amines are preferred from the perspective of achieving the desired effects of the present invention. The amine-based resin is preferably a primary amine or secondary amine, with primary amines being more preferred. Specific examples of amine resins include 4,4'-methylenebis(2,6-dimethylaniline), diphenyldiaminosulfone, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, m-phenylenediamine, m-xylylenediamine, diethyltoluenediamine, 4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine, 2,2-bis(3-amino-4-hydroxybenzidine), and 2,2-bis(3-amino-4-hydroxybenzidine). phenyl)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 resins 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.

Examples of acid anhydride resins as component (a) include resins having one or more acid anhydride groups in one molecule. Specific examples of acid anhydride resins 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 styrene-maleic acid resins, which are copolymers of styrene and maleic acid, ethylene glycol bis(anhydrotrimellitate), ethylene glycol bis(anhydrotrimellitate), ethylene glycol bis(anhydrotrimellitate), and ethylene glycol bis(anhydrotrimellitate).

When component (a) contains an epoxy resin and a curing agent, the ratio of the amount of epoxy resin to all curing agents, expressed as the ratio of [total number of epoxy groups in the epoxy resin] to [total number of reactive groups in the curing agent], is preferably in the range of 1:0.01 to 1:5, more preferably 1:0.05 to 1:3, and even more preferably 1:0.1 to 1:2. Here, the "number of epoxy groups in the epoxy resin" refers to the sum of all values obtained by dividing the mass of the non-volatile components of the epoxy resin present in the resin composition by the epoxy equivalent. Furthermore, the "number of active groups in the curing agent" refers to the sum of all values obtained by dividing the mass of the non-volatile components of the curing agent present in the resin composition by the active group equivalent. By maintaining the ratio of epoxy resin to curing agent in component (a) within this range, a cured product with excellent flexibility can be obtained.

To achieve the significant effects of the present invention, the content of the curing agent as component (a) is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to 100% by mass of non-volatile components in the resin composition; it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

From the perspective of achieving significant effects of the present invention, the content of the curing agent as component (a) is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, 20% by mass or more, or 30% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, or 15% by mass or less, based on 100% by mass of the resin component in the resin composition.

<(b) Inorganic filler>
The resin composition may contain (b) an inorganic filler. (b) An inorganic compound is used as the inorganic filler material. Examples of inorganic filler materials include silica, alumina, aluminosilicate, glass, cordierite, silicon oxide, barium sulfate, barium carbonate, talc, clay, mica powder, zinc oxide, hydrotalcite, boehmite, 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 titanate zirconate, barium zirconate, calcium zirconate, zirconium phosphate, and zirconium tungstate phosphate. Among these, calcium carbonate and silica are preferred, and silica is particularly preferred. Examples of silica include amorphous silica, fused silica, crystalline silica, synthetic silica, and hollow silica. As the silica, spherical silica is preferred. (b) The inorganic filler may be used alone or in combination of two or more kinds.

Commercially available products of component (b) include, for example, "UFP-30" manufactured by Denka; "SP60-05," "SP507-05," and "SPH516-05" manufactured by Nippon Steel Chemical & Material Co., Ltd.; "YC100C," "YA050C," "YA050C-MJE," and "YA010C" manufactured by Admatechs; "Silfil NSS-3N," "Silfil NSS-4N," and "Silfil NSS-5N" manufactured by Tokuyama Corporation; and "SC2500SQ" manufactured by Admatechs.

The specific surface area of component (b) is preferably 1 m ² /g or more, more preferably 2 m ² /g or more, and particularly preferably 3 m ² /g or more. There is no particular upper limit, but it is preferably 60 m ² /g or less, 50 m ² /g or less, or 40 m ² /g or less. The specific surface area is obtained according to the BET method by adsorbing nitrogen gas onto the surface of a sample using a specific surface area measuring device (Macsorb HM-1210 manufactured by Mountech Co., Ltd.) and calculating the specific surface area using the BET multipoint method.

From the viewpoint of significantly achieving the desired effects of the present invention, the average particle size of component (b) is preferably 0.01 μm or more, more preferably 0.05 μm or more, and particularly preferably 0.1 μm or more, and is preferably 5 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less.

The average particle size of component (b) can be measured using a laser diffraction/scattering method based on Mie scattering theory. Specifically, a volumetric particle size distribution of the inorganic filler is created using a laser diffraction/scattering particle size distribution analyzer, and the median diameter is used as the average particle size. A measurement sample can be prepared by weighing 100 mg of inorganic filler and 10 g of methyl ethyl ketone into a vial and dispersing the mixture ultrasonically for 10 minutes. The volumetric particle size distribution of component (C) is measured using a laser diffraction particle size distribution analyzer with blue and red light source wavelengths using a flow cell system, and the average particle size can be calculated as the median diameter from the particle size distribution obtained. An example of a laser diffraction particle size distribution analyzer is the "LA-960" manufactured by Horiba, Ltd.

From the viewpoint of improving moisture resistance and dispersibility, component (b) is preferably treated with a surface treatment agent. Examples of surface treatment agents include vinylsilane coupling agents, (meth)acrylic coupling agents, fluorine-containing silane coupling agents, aminosilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, alkoxysilanes, organosilazane compounds, and titanate coupling agents. Among these, from the viewpoint of achieving the most pronounced effects of the present invention, vinylsilane coupling agents, (meth)acrylic coupling agents, and aminosilane coupling agents are preferred. Furthermore, one type of surface treatment agent may be used alone, or two or more types may be used in any combination.

Commercially available surface treatment agents include, for example, Shin-Etsu Chemical Co., Ltd.'s "KBM1003" (vinyltriethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM503" (3-methacryloxypropyltriethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM403" (3-glycidoxypropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM803" (3-mercaptopropyltrimethoxysilane), and Shin-Etsu Chemical Co., Ltd.'s "KBE903" (3-aminopropyltriethoxysilane). Examples include Shin-Etsu Chemical Co., Ltd.'s "KBM573" (N-phenyl-3-aminopropyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "SZ-31" (hexamethyldisilazane), Shin-Etsu Chemical Co., Ltd.'s "KBM103" (phenyltrimethoxysilane), Shin-Etsu Chemical Co., Ltd.'s "KBM-4803" (long-chain epoxy-type silane coupling agent), and Shin-Etsu Chemical Co., Ltd.'s "KBM-7103" (3,3,3-trifluoropropyltrimethoxysilane).

The degree of surface treatment with the surface treatment agent preferably falls within a specified range from the perspective of improving the dispersibility of the inorganic filler. Specifically, 100 parts by mass of inorganic filler is preferably surface-treated with 0.2 to 5 parts by mass of surface treatment agent, more preferably 0.2 to 3 parts by mass, and even more preferably 0.3 to 2 parts by mass.

The degree of surface treatment with the surface treatment agent can be evaluated by the amount of carbon per unit surface area of the inorganic filler. From the viewpoint of improving the dispersibility of the inorganic filler, the amount of carbon per unit surface area of the inorganic filler is preferably 0.02 mg/m ² or more, more preferably 0.1 mg/m ² or more, and even more preferably 0.2 mg/m ² or more. On the other hand, from the viewpoint of suppressing an increase in the melt viscosity of the resin varnish and the melt viscosity in the sheet form, it is preferably 1 mg/m ² or less, more preferably 0.8 mg/m ² or less, and even more preferably 0.5 mg/m ² or less.

The amount of carbon per unit surface area of the inorganic filler can be measured after the surface-treated inorganic filler is washed with a solvent (e.g., methyl ethyl ketone (MEK)). Specifically, a sufficient amount of MEK as a solvent is added to the inorganic filler that has been surface-treated with a surface treatment agent, and ultrasonic cleaning is performed at 25°C for 5 minutes. After removing the supernatant and drying the solids, the amount of carbon per unit surface area of the inorganic filler can be measured using a carbon analyzer. A carbon analyzer such as the EMIA-320V manufactured by Horiba, Ltd. can be used.

From the viewpoint of reducing the linear thermal expansion coefficient and suppressing cross-sectional steps in via holes, the content of component (b) is preferably 50% by mass or less, more preferably 48% by mass or less, and even more preferably 45% by mass or less, based on 100% by mass of the non-volatile components in the resin composition; it is preferably 0% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, or 30% by mass or more.

Furthermore, if the non-volatile components in the resin composition are taken as 100% by mass, the amount of resin components is preferably 50% by mass or more, more preferably 52% by mass or more, even more preferably 55% by mass or more, and preferably 100% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and particularly preferably 70% by mass or less.

<(c) Curing Accelerator>
The resin composition may contain (c) a curing accelerator. Examples of the curing accelerator include phosphorus-based curing accelerators, amine-based curing accelerators, imidazole-based curing accelerators, guanidine-based curing accelerators, and metal-based curing accelerators. Amine-based curing accelerators and imidazole-based curing accelerators are preferred, and amine-based curing accelerators are more preferred. The curing accelerators may be used alone or in combination of two or more.

Examples of phosphorus-based curing accelerators include triphenylphosphine, phosphonium borate compounds, tetraphenylphosphonium tetraphenylborate, n-butylphosphonium tetraphenylborate, tetrabutylphosphonium decanoate, (4-methylphenyl)triphenylphosphonium thiocyanate, tetraphenylphosphonium thiocyanate, and butyltriphenylphosphonium thiocyanate, with triphenylphosphine and tetrabutylphosphonium decanoate being preferred.

Examples of amine-based curing accelerators include trialkylamines such as triethylamine and tributylamine, 4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and 1,8-diazabicyclo(5,4,0)-undecene, with 4-dimethylaminopyridine and 1,8-diazabicyclo(5,4,0)-undecene being preferred.

Examples of imidazole curing accelerators include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, 4-Diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, Examples of the imidazole compounds include phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, and 2-phenylimidazoline, as well as adducts of imidazole compounds with epoxy resins. 2-ethyl-4-methylimidazole and 1-benzyl-2-phenylimidazole are preferred.

Commercially available imidazole-based curing accelerators may be used, such as "P200-H50" manufactured by Mitsubishi Chemical Corporation.

Examples of guanidine-based curing accelerators include dicyandiamide, 1-methylguanidine, 1-ethylguanidine, 1-cyclohexylguanidine, 1-phenylguanidine, 1-(o-tolyl)guanidine, dimethylguanidine, diphenylguanidine, trimethylguanidine, tetramethylguanidine, pentamethylguanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene. Examples include 2[4.4.0]dec-5-ene, 1-methylbiguanide, 1-ethylbiguanide, 1-n-butylbiguanide, 1-n-octadecylbiguanide, 1,1-dimethylbiguanide, 1,1-diethylbiguanide, 1-cyclohexylbiguanide, 1-allylbiguanide, 1-phenylbiguanide, and 1-(o-tolyl)biguanide, with dicyandiamide and 1,5,7-triazabicyclo[4.4.0]dec-5-ene being preferred.

Metal-based curing accelerators include, for example, organometallic complexes or organometallic salts of metals such as cobalt, copper, zinc, iron, nickel, manganese, and tin. Specific examples of organometallic complexes include organocobalt complexes such as cobalt(II) acetylacetonate and cobalt(III) acetylacetonate, organocopper complexes such as copper(II) acetylacetonate, organozinc complexes such as zinc(II) acetylacetonate, organoiron complexes such as iron(III) acetylacetonate, organonickel complexes such as nickel(II) acetylacetonate, and organomanganese complexes such as manganese(II) acetylacetonate. Examples of organometallic salts include zinc octoate, tin octoate, zinc naphthenate, cobalt naphthenate, tin stearate, and zinc stearate.

(c) In order to achieve the significant effects of the present invention, the content of the curing accelerator is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and particularly preferably 0.03% by mass or more, based on 100% by mass of the non-volatile components in the resin composition, and is preferably 3% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

(c) In order to achieve the significant effects of the present invention, the content of the curing accelerator is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and particularly preferably 0.03% by mass or more, based on 100% by mass of the resin component in the resin composition, and is preferably 3% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

<(d) Thermoplastic resin>
The resin composition may contain (d) a thermoplastic resin. Examples of (d) thermoplastic resins include phenoxy resins, polyvinyl acetal resins, polyolefin resins, polyimide resins, polyamideimide resins, polyetherimide resins, polysulfone resins, polyethersulfone resins, polyphenylene ether resins, polyetheretherketone resins, and polyester resins, with phenoxy resins being preferred. The thermoplastic resins may be used alone or in combination of two or more.

The polystyrene-equivalent weight-average molecular weight of the (d) thermoplastic resin is preferably 38,000 or more, more preferably 40,000 or more, and even more preferably 42,000 or more. The upper limit is preferably 100,000 or less, more preferably 70,000 or less, and even more preferably 60,000 or less. The polystyrene-equivalent weight-average molecular weight of the (d) thermoplastic resin is measured by gel permeation chromatography (GPC). Specifically, the polystyrene-equivalent weight-average molecular weight of the (d) thermoplastic resin is measured 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 at a column temperature of 40°C, and can be calculated using a standard polystyrene calibration curve.

Examples of phenoxy resins include phenoxy resins having one or more skeletons selected from the group consisting of bisphenol A, bisphenol F, bisphenol S, bisphenolacetophenone, novolac, biphenyl, fluorene, dicyclopentadiene, norbornene, naphthalene, anthracene, adamantane, terpene, and trimethylcyclohexane. The terminals of the phenoxy resins may be any functional group, such as a phenolic hydroxyl group or an epoxy group. Phenoxy resins may be used alone or in combination. 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 bisphenolacetophenone skeleton) manufactured by Mitsubishi Chemical Corporation. Other examples include "FX280" and "FX293" manufactured by Nippon Steel Chemical & Material Co., Ltd., and "YX7800BH30," "YX8000BH30," "YL7500BH30," "YX6954BH30," "YX7553," "YX7553BH30," "YL7769BH30," "YL6794," "YL7213," "YL7290," and "YL7482" manufactured by Mitsubishi Chemical Corporation.

Examples of polyvinyl acetal resins include polyvinyl formal resin and polyvinyl butyral resin, with polyvinyl butyral resin being preferred. Specific examples of polyvinyl acetal resins include 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 No. 2006-37083), and polysiloxane skeleton-containing polyimides (polyimides described in JP-A Nos. 2002-12667 and 2000-319386, etc.).

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

A specific example of a polyethersulfone resin is "PES5003P" manufactured by Sumitomo Chemical Co., Ltd. A specific example of a polyphenylene ether resin is "OPE-2St 1200," an oligophenylene ether styrene resin manufactured by Mitsubishi Gas Chemical Co., Inc. A specific example of a polyetheretherketone resin is "Sumiploy K" manufactured by Sumitomo Chemical Co., Ltd. A specific example of a 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 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 elastomers such as polypropylene and ethylene-propylene block copolymer.

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

Of these, phenoxy resin and polyvinyl acetal resin are preferred as the (d) thermoplastic resin. Therefore, in a preferred embodiment, the thermoplastic resin includes one or more resins selected from the group consisting of phenoxy resin and polyvinyl acetal resin. Of these, phenoxy resin is preferred as the thermoplastic resin, and phenoxy resin with a weight-average molecular weight of 40,000 or more is particularly preferred.

From the perspective of achieving significant effects of the present invention, the content of (d) 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, based on 100% by mass of non-volatile components in the resin composition. The upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

(d) In order to achieve the significant effects of the present invention, the content of the thermoplastic resin, based on 100% by mass of the resin component in the resin composition, is preferably 1% by mass or more, more preferably 30.5% by mass or more, even more preferably 1% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less.

<(e) Elastomer>
The resin composition may contain (e) an elastomer. The elastomer as component (e) is a flexible resin, preferably a resin having rubber elasticity or a resin that exhibits rubber elasticity by polymerizing with another component. Examples of rubber elasticity include resins that exhibit an elastic modulus of 1 GPa or less when a tensile test is performed in accordance with Japanese Industrial Standards (JIS K7161) at a temperature of 25°C and a humidity of 40% RH.

In one embodiment, the (e) elastomer is preferably a resin having, within its molecule, one or more structures selected from a polybutadiene structure, a polysiloxane structure, a poly(meth)acrylate structure, a polyalkylene structure, a polyalkyleneoxy structure, a polyisoprene structure, a polyisobutylene structure, a polycarbonate structure, and a polystyrene structure. "(Meth)acrylate" refers to methacrylate and acrylate.

In another embodiment, the (e) elastomer is preferably one or more types selected from resins having a glass transition temperature (Tg) of 25°C or less and resins that are liquid at 25°C or less. The glass transition temperature of resins having a glass transition temperature (Tg) of 25°C or less is preferably 20°C or less, more preferably 15°C or less. The lower limit of the glass transition temperature is not particularly limited, but can usually be -15°C or higher. Furthermore, resins that are liquid at 25°C are preferably resins that are liquid at 20°C or less, more preferably resins that are liquid at 15°C or less. The glass transition temperature can be measured by DSC (differential scanning calorimetry).

(e) Elastomer is typically an amorphous resin component that can be dissolved in an organic solvent. One type of (e) elastomer may be used alone, or two or more types may be used in combination in any ratio.

(e) Examples of elastomers include resins containing a polybutadiene structure. The polybutadiene structure may be contained in the main chain or in a side chain. The polybutadiene structure may be partially or entirely hydrogenated. Resins containing a polybutadiene structure are sometimes referred to as "polybutadiene resins." Specific examples of polybutadiene resins include "Ricon 130MA8," "Ricon 130MA13," "Ricon 130MA20," "Ricon 131MA5," "Ricon 131MA10," "Ricon 131MA17," "Ricon 131MA20," and "Ricon 184MA6" (acid anhydride group-containing polybutadienes) manufactured by Cray Valley Corporation; "GQ-1000" (hydroxyl- and carboxyl-group-introduced polybutadiene), "G-1000," "G-2000," and "G-3000" (polybutadiene having hydroxyl groups at both ends), "GI-1000," "GI-2000," and "GI-3000" (hydrogenated polybutadiene having hydroxyl groups at both ends) manufactured by Nippon Soda Co., Ltd.; and "FCA-061L" (hydrogenated polybutadiene skeleton epoxy resin) manufactured by Nagase ChemteX Corporation. Specific examples of polybutadiene resins include hydroxyl-terminated polybutadiene, linear polyimides made from diisocyanate compounds and tetrabasic acid anhydrides (polyimides described in JP 2006-37083 A and WO 2008/153208 A), and phenolic hydroxyl group-containing butadienes. The content of the butadiene structure in the polyimide resin is preferably 60% to 95% by mass, more preferably 75% to 85% by mass. Details of the polyimide resin can be found in JP 2006-37083 A and WO 2008/153208 A, the contents of which are incorporated herein by reference.

(e) Examples of elastomers include resins containing a poly(meth)acrylate structure. Resins containing a poly(meth)acrylate structure are sometimes called "poly(meth)acrylic resins." Specific examples of poly(meth)acrylic resins include Teisan Resin manufactured by Nagase ChemteX Corporation, and ME-2000, W-116.3, W-197C, KG-25, and KG-3000 manufactured by Negami Chemical Industrial Co., Ltd.

(e) Examples of elastomers include resins containing a polycarbonate structure. Resins containing a polycarbonate structure are sometimes referred to as "polycarbonate resins." Specific examples of polycarbonate resins include "T6002" and "T6001" (polycarbonate diols) manufactured by Asahi Kasei Chemicals Corporation, and "C-1090," "C-2090," and "C-3090" (polycarbonate diols) manufactured by Kuraray Co., Ltd. Linear polyimides made from hydroxyl-terminated polycarbonates, diisocyanate compounds, and tetrabasic acid anhydrides can also be used. The carbonate structure content of the polyimide resin is preferably 60% to 95% by mass, more preferably 75% to 85% by mass. For details of the polyimide resin, please refer to the description in International Publication No. WO 2016/129541, the contents of which are incorporated herein by reference.

(e) Examples of elastomers include resins containing a polysiloxane structure. Resins containing a polysiloxane structure are sometimes referred to as "siloxane resins." Specific examples of siloxane resins include "SMP-2006," "SMP-2003PGMEA," and "SMP-5005PGMEA" manufactured by Shin-Etsu Silicones Co., Ltd., and linear polyimides made from amine-terminated polysiloxanes and tetrabasic acid anhydrides (see, for example, International Publication No. 2010/053185, Japanese Patent Application Laid-Open No. 2002-12667, and Japanese Patent Application Laid-Open No. 2000-319386).

(e) Examples of elastomers include resins containing a polyalkylene structure or a polyalkyleneoxy structure. Resins containing a polyalkylene structure are sometimes referred to as "alkylene resins." Resins containing a polyalkyleneoxy structure are sometimes referred to as "alkyleneoxy resins." The polyalkyleneoxy structure is preferably a polyalkyleneoxy structure having 2 to 15 carbon atoms, more preferably a polyalkyleneoxy structure having 3 to 10 carbon atoms, and particularly preferably a polyalkyleneoxy structure having 5 to 6 carbon atoms. Specific examples of alkylene resins and alkyleneoxy resins include "PTXG-1000" and "PTXG-1800" manufactured by Asahi Kasei Fibers Corporation.

(e) Examples of elastomers include resins containing a polyisoprene structure. Resins containing a polyisoprene structure are sometimes called "isoprene resins." Specific examples of isoprene resins include "KL-610" and "KL613" manufactured by Kuraray Co., Ltd.

(e) Examples of elastomers include resins containing a polyisobutylene structure. Resins containing a polyisobutylene structure are sometimes called "isobutylene resins." Specific examples of isobutylene resins include Kaneka Corporation's "SIBSTAR-073T" (styrene-isobutylene-styrene triblock copolymer) and "SIBSTAR-042D" (styrene-isobutylene diblock copolymer).

(e) Examples of elastomers include resins containing a polystyrene structure. Resins containing a polystyrene structure are sometimes referred to as "styrene resins." Examples of styrene resins include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS), styrene-butadiene-butylene-styrene block copolymers (SBBS), styrene-butadiene diblock copolymers, hydrogenated styrene-butadiene block copolymers, hydrogenated styrene-isoprene block copolymers, and hydrogenated styrene-butadiene random copolymers. Specific examples of styrene resins include hydrogenated styrene-based thermoplastic elastomers "H1041," "Tuftec H1043," "Tuftec P2000," and "Tuftec MP10" (manufactured by Asahi Kasei Corporation); epoxidized styrene-butadiene thermoplastic elastomers "Epofriend AT501" and "CT310" (manufactured by Daicel Corporation); hydroxyl group-modified styrene-based elastomer "Septon HG252" (manufactured by Kuraray Co., Ltd.); carboxyl group-modified styrene-based elastomer "Tuftec N503M," amino group-modified styrene-based elastomer "Tuftec N501," acid anhydride group-modified styrene-based elastomer "Tuftec M1913" (manufactured by Asahi Kasei Chemicals Corporation); unmodified styrene-based elastomer "Septon S8104" (manufactured by Kuraray Co., Ltd.); and styrene-ethylene/butylene-styrene block copolymer "FG1924" (manufactured by Kraton).

(e) The number average molecular weight (Mn) of the elastomer is preferably 1,000 or more, more preferably 1,500 or more, even more preferably 3,000 or more, and particularly preferably 5,000 or more, and is preferably 1,000,000 or less, more preferably 900,000 or less. The number average molecular weight (Mn) can be measured in polystyrene equivalent terms using GPC (gel permeation chromatography).

(e) In order to achieve the significant effects of the present invention, the content of the elastomer is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of non-volatile components in the resin composition, and is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less.

(e) In order to achieve the significant effects of the present invention, the content of the elastomer, when the resin component in the resin composition is taken as 100% by mass, is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

<(f) Other Additives>
In addition to the above-mentioned components, the resin composition may further contain other additives as optional components. Examples of such additives include flame retardants; organic fillers; organometallic compounds such as organocopper compounds, organozinc compounds, and organocobalt compounds; thickeners; antifoaming agents; leveling agents; adhesion promoters; and colorants. These additives may be used alone or in combination of two or more in any ratio. The content of each additive can be appropriately determined by a person skilled in the art.

The method for preparing the resin composition is not particularly limited, and examples include a method in which the ingredients are mixed and dispersed, if necessary, together with a solvent, using a rotary mixer or the like.

The cured product (insulating layer) obtained by curing the resin composition at 190°C for 1.5 hours typically exhibits the characteristic of a low coefficient of linear thermal expansion (CTE). The coefficient of linear thermal expansion is preferably 55 ppm/°C or less, more preferably 50 ppm/°C or less, and even more preferably 40 ppm/°C or less. The coefficient of linear thermal expansion can be measured using a thermomechanical analyzer (TMA, SS6100) manufactured by Seiko Instruments Inc., and in detail can be measured by the method described in the Examples section below.

[Resin sheet]
The resin sheet includes a support and a resin composition layer formed from a resin composition provided on the support. The resin composition is as described above.

From the viewpoint of enabling thinner printed wiring boards and providing a cured product of the resin composition with excellent insulating properties even when the cured product is thin, the thickness of the resin composition layer is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less, 30 μm or less, or 20 μm or less. There is no particular lower limit to the thickness of the resin composition layer, but it can typically be 1 μm or more, 5 μm or more, etc.

Examples of the support include films made of plastic materials, metal foils, and release paper, with films made of plastic materials and metal foils being preferred.

When a film made of a plastic material is used as the support, examples of the plastic material include polyesters such as polyethylene terephthalate (hereinafter sometimes abbreviated as "PET") and polyethylene naphthalate (hereinafter sometimes abbreviated as "PEN"), polycarbonate (hereinafter sometimes abbreviated as "PC"), acrylics such as polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, polyimide, etc. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, with inexpensive polyethylene terephthalate being particularly preferred.

When a metal foil is used as the support, examples of the metal foil include copper foil and aluminum foil, with copper foil being preferred. The copper foil may be a foil made of the single metal copper, or a foil made of an alloy of copper and another metal (e.g., tin, chromium, silver, magnesium, nickel, zirconium, silicon, titanium, etc.).

The surface of the support that will be bonded to the resin composition layer may be subjected to a matte finish, corona treatment, or antistatic treatment.

The support may also be a support with a release layer, which has a release layer on the surface that bonds with the resin composition layer. Examples of release agents used in the release layer of the support with a release layer include one or more release agents selected from the group consisting of alkyd resins, polyolefin resins, urethane resins, and silicone resins. Commercially available products may be used as the support with a release layer, including PET films with a release layer primarily composed of an alkyd resin-based release agent, such as "SK-1," "AL-5," and "AL-7" manufactured by Lintec Corporation, "Lumirror T60" manufactured by Toray Industries, Inc., "Purex" manufactured by Teijin Limited, and "Uni-Peel" manufactured by Unitika Limited; and "U2-NR1" manufactured by DuPont Films.

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

In one embodiment, the resin sheet may further include other layers as needed. Examples of such other layers include a protective film conforming to the support and provided on the surface of the resin composition layer that is not bonded to the support (i.e., the surface opposite the support). The thickness of the protective film is not particularly limited, but is, for example, 1 μm to 40 μm. By laminating a protective film, it is possible to prevent the adhesion of dust and other particles to the surface of the resin composition layer and prevent scratches.

A resin sheet can be produced, for example, by preparing a resin varnish by dissolving a resin composition in an organic solvent, applying this resin varnish to a support using a die coater or the like, and then drying it to form a resin composition layer.

Examples of organic solvents include ketones such as acetone, methyl ethyl ketone (MEK), and cyclohexanone; acetate esters such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, and carbitol acetate; carbitols such as cellosolve and butyl carbitol; aromatic hydrocarbons such as toluene and xylene; and amide solvents such as dimethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone. These organic solvents may be used alone or in combination.

Drying may be carried out by known methods such as heating or hot air blowing. Drying conditions are not particularly limited, but drying is carried out so that the organic solvent content in the resin composition layer is 10% by mass or less, preferably 5% by mass or less. While this varies depending on the boiling point of the organic solvent in the resin varnish, for example, when using a resin varnish containing 30% to 60% by mass of organic solvent, a resin composition layer can be formed by drying at 50°C to 150°C for 3 to 10 minutes.

The resin sheet can be stored rolled up. If the resin sheet has a protective film, it can be used by peeling off the protective film.

[Printed wiring board and method of manufacturing printed wiring board]
As shown in FIG. 1 , a printed wiring board 1 according to one embodiment of the present invention includes, in this order, an inner circuit board 2, an insulating layer 3 containing a cured product of the resin composition described above, and a resin layer 4. The resin layer 4 has a first surface 4a facing the insulating layer 3 and a second surface 4b facing the insulating layer 3. Since the insulating layer 3 is in contact with the first surface 4a of the resin layer 4, there is typically no other layer between the resin layer 4 and the insulating layer 3. As shown in FIG. 1 , a conductor layer 5 may typically be provided on the second surface 4b of the resin layer 4. The insulating layer 3 and the resin layer 4 each have a via hole 6 formed therein, penetrating the insulating layer 3 and the resin layer 4 in the thickness direction. The via hole 6 is typically used for electrical connection between the conductor layer 5 and a metal layer (not shown), such as wiring, provided on the inner circuit board 2. For example, a conductor layer 5 (not shown) is formed not only on the second surface 4 b of the resin layer 4 but also in the via holes 6 , thereby achieving electrical continuity between the conductor layer 5 and the metal layer of the inner circuit board 2 .

A step may form within the via hole 6 at the position of the first surface 4a of the resin layer 4. Such a step may be formed, for example, by the following mechanism. Typically, after the via hole 6 is formed, a desmear process is performed to remove smears within the via hole 6. In the desmear process, an oxidizer solution is generally brought into contact with the insulating layer 3 and the resin layer 4. In this desmear process, contact with the oxidizer solution causes the resin components contained in the insulating layer 3 and the resin layer 4 to fall off and dissolve, resulting in the roughening of the surface of each layer. At this time, the degree to which the surface roughening of each layer progresses may vary depending on the components contained in each layer. Therefore, a step may form at the position of the first surface 4a of the resin layer 4.

When such a step is formed, a distance d may be formed between the end 41 of the first surface 4a within the via hole 6 and the end 42 of the contact surface between the first surface 4a and the insulating layer 3. Here, unless otherwise specified, "end 41 of the first surface 4a within the via hole 6" refers to the end of the first surface 4a that is closer to the center of the via hole 6. Also, unless otherwise specified, "end 42 of the contact surface between the first surface 4a and the insulating layer 3" refers to the end of the contact surface between the first surface 4a and the insulating layer 3 that is closer to the center of the via hole 6. Also, hereinafter, the distance d may be referred to as the "step distance" d.

When via holes 6 are formed by laser irradiation, heat generated by the laser irradiation can cause interfacial delamination between the resin layer 4 and the insulating layer 3. Furthermore, heat from laser irradiation can deteriorate the resin around the via holes 6 in the insulating layer 3. When interfacial delamination and resin deterioration occur, the insulating layer 3 is significantly eroded during desmearing, which can result in an increase in the step distance d. When the step distance d increases in this way, there are areas where the conductor layer 5 is not formed when it is formed within the via holes 6, which can result in less reliable electrical connections.

In the printed wiring board 1 of the present invention, the step distance d can be reduced by adjusting the components in the resin composition, and more preferably by forming the via holes 6 by plasma treatment. Specifically, the top diameter a (μm) of the via holes 6 and the step distance d (μm) within the via holes 6 are
[d/{(1/2)×a}]×100≦5
Here, unless otherwise specified, the top diameter a of the via hole 6 refers to the diameter of the opening of the via hole 6 on the side opposite to the inner layer circuit board 2. This prevents the occurrence of areas where the conductor layer 5 is not formed when forming the conductor layer 5 inside the via hole 6, thereby improving the reliability of the electrical connection.

The value of [d/{(1/2) x a}] x 100 is usually 5 or less, preferably 4.5 or less, and more preferably 4 or less. It can also be preferably 0 or more, and more preferably 0.5 or more. [d/{(1/2) x a}] x 100 can be measured as described in the Examples below.

The printed wiring board of the present invention can generally reduce unevenness at the bottom and sidewall of the via hole where the inorganic filler is excavated. As a result, it is possible to make the thickness of the conductor layer formed in the via hole uniform, thereby improving the reliability of the electrical connection. When the resin composition of the present invention contains an inorganic filler, the inorganic filler has a small average particle size, and the content thereof is 50% by mass or less when the non-volatile components of the resin composition are taken as 100% by mass, thereby reducing unevenness.

From the perspective of thinning the printed wiring board, the thickness of the insulating layer is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, 30 μm or less, or 20 μm or less, and is preferably 1 μm or more, more preferably 5 μm or more.

From the perspective of thinning the printed wiring board, the thickness of the resin layer is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, 30 μm or less, or 20 μm or less, and is preferably 1 μm or more, more preferably 5 μm or more.

From the perspective of thinning the printed wiring board, the total thickness of the insulating layer and resin layer is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, 60 μm or less, or 40 μm or less, and is preferably 2 μm or more, more preferably 6 μm or more, and even more preferably 10 μm or more.

When the thickness of the resin layer is b and the thickness of the insulating layer is c, from the perspective of thinning the printed wiring board, b/c is preferably 0.5 or more, more preferably 1 or more, and even more preferably 1.5 or more, and is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less.

The method for producing a printed wiring board of the present invention comprises:
(A) forming a resin layer on the surface of the resin composition layer of the resin sheet that is not bonded to the support;
(B) a step of laminating a resin sheet having a resin layer formed thereon on an inner layer circuit board and curing the resin composition layer to form an insulating layer;
(C) performing a plasma treatment on the surface of the resin layer to form via holes;
(D) a step of performing a roughening treatment; and (E) a step of forming a conductor layer on the surface of the resin layer.

The insulating layer used in the printed wiring board of the present invention functions not only as an insulating layer that insulates each layer, but also as a bonding sheet that bonds the inner layer circuit board and the resin layer.

The method for manufacturing a printed wiring board is preferably carried out in the order of steps (A), (B), (C), (D), and (E). Each step in the method for manufacturing a printed wiring board is described below.

<Process (A)>
In step (A), a resin layer is formed on the surface of the resin composition layer of the resin sheet that is not bonded to the support (i.e., the surface opposite to the support). Specifically, a film-like resin layer is laminated on the surface of the resin composition layer that is not bonded to the support, thereby forming a resin layer on the resin composition layer. The lamination of the resin composition layer and the resin layer may be performed under the same conditions as those for laminating the inner layer circuit board and the resin composition layer, which will be described later. Alternatively, a resin varnish may be prepared by dissolving the material for the resin layer in an organic solvent, and the resin varnish may be applied to the resin composition layer using a die coater or the like, and then dried to form a resin layer. The organic solvent is as described above.

The resin layer may be formed from a thermoplastic resin. Examples of materials for the resin layer include polyimide, liquid crystal polymer, polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polyether ether ketone, polybenzimidazole, aramid, polyamideimide, and polyetherimide. Of these, the resin layer is preferably made from either a polyimide resin or a liquid crystal polymer.

The surface of the resin layer may be subjected to corona treatment, plasma treatment, or UV treatment. Using such a resin layer can increase the adhesion between the resin layer and the insulating layer. The conditions for the corona treatment, plasma treatment, or UV treatment may be determined appropriately depending on the material of the resin layer, etc.

In addition, in step (A), a laminate plate having a resin layer and a metal foil such as copper foil laminated thereon may be laminated onto the resin composition layer so that the resin layer faces the side of the resin composition layer that is not bonded to the support, thereby forming a resin layer on the resin composition layer. In this case, the metal foil is removed by etching after step (A) is completed and before step (B) is started, or after step (B) is completed.

Commercially available resin layers may be used, such as "Vecstar-FCCL:CTF-25" manufactured by Kuraray Co., Ltd. and polyimide copper-clad laminate (ESPANEX: MC12-25-00HRM, manufactured by Nippon Steel Chemical Co., Ltd.).

The printed wiring board of the present invention typically exhibits excellent lamination between resin composition layers. This makes it possible to uniformly form the thickness of the conductor layer formed in the via hole, improving the reliability of electrical connection. Specifically, lamination is achieved by forming a resin layer on the surface of the resin sheet where the resin composition layer is not bonded to the support. When the resin sheet with the resin layer formed thereon is cut to an appropriate size, lifting is usually not observed around the cut edges due to insufficient adhesion between the resin layer and the resin composition layer. Lamination can be measured using the method described in the examples below.

<Process (B)>
In step (B), a resin sheet having a resin layer formed thereon is laminated on an inner layer circuit board, and the resin composition layer is cured to form an insulating layer. In step (B), an insulating layer is usually formed on a main surface of the inner layer circuit board. The main surface of the inner layer circuit board refers to the surface of the inner layer circuit board on which the insulating layer is provided.

Performing step (B) may include the step (B-1) of preparing an inner layer circuit board. The inner layer circuit board typically comprises a support substrate and a metal layer provided on the surface of the support substrate. The metal layer is exposed on the main surface of the inner layer circuit board.

Examples of materials for the support substrate include glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates. Materials for the metal layer include copper foil, copper foil with a carrier, and the materials for the conductor layer described below, with copper foil being preferred.

In step (B), for example, a resin composition layer of a resin sheet on which a resin layer has been formed is laminated on the main surface of the inner layer circuit board, and the resin composition layer is thermally cured to form an insulating layer.

The inner layer circuit board and the resin sheet can be laminated, for example, by peeling off the support and then heat-pressing the resin sheet to the inner layer circuit board from the resin layer side. Typically, this lamination is performed so that the inner layer circuit board and the resin composition layer are bonded together. Examples of the member used to heat-press the resin sheet to the inner layer circuit board (hereinafter also referred to as the "heat-pressing member") include a heated metal plate (such as a stainless steel panel) or a metal roll (such as a stainless steel roll). It is preferable to press the heat-pressing member not directly onto the resin sheet, but rather via an elastic material such as heat-resistant rubber, so that the resin sheet can adequately conform to the surface irregularities of the inner layer circuit board.

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

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

After lamination, the laminated resin sheets may be smoothed under normal pressure (atmospheric pressure), for example, by pressing a thermocompression member from the resin layer side. The pressing conditions for the smoothing process may be the same as the thermocompression conditions for lamination described above. The smoothing process may be performed using a commercially available laminator. Note that lamination and smoothing may also be performed consecutively using the commercially available vacuum laminator described above.

After laminating the resin sheet onto the inner layer circuit board, the resin composition layer is heat-cured to form an insulating layer. The heat-curing conditions for the resin composition layer are not particularly limited, and conditions typically used for forming insulating layers for printed wiring boards may be used.

For example, although the thermal curing conditions for the resin composition layer vary depending on the type of resin composition, the curing temperature is preferably 120°C to 240°C, more preferably 150°C to 220°C, and even more preferably 170°C to 210°C. The curing time is preferably 5 to 120 minutes, more preferably 10 to 100 minutes, and even more preferably 15 to 100 minutes.

Before thermally curing the resin composition layer, 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 at a temperature of 50°C or higher but lower than 120°C (preferably 60°C or higher but lower than 115°C, more preferably 70°C or higher but lower than 110°C) for 5 minutes or more (preferably 5 to 150 minutes, more preferably 15 to 120 minutes, and even more preferably 15 to 100 minutes).

Instead of forming an insulating layer using a resin sheet, a resin composition may be applied directly to the main surface of the inner layer circuit board, followed by forming a resin layer, and then the resin composition may be thermally cured to form the insulating layer. The conditions for forming the insulating layer in this case are the same as those for forming an insulating layer using a resin sheet. The resin composition to be applied is as described above. The resin layer is formed by laminating it on the resin composition, and the resin layer and lamination conditions are as described above.

After step (B) is completed and before step (C) is performed, a step of forming a plasma treatment mask on the insulating layer may be performed to effectively form via holes in the insulating layer. The mask forming step may include, for example, (B-2) a step of laminating a dry film on the resin layer, and (B-3) a step of exposing and developing the dry film using a photomask to obtain a patterned dry film.

In step (B-2), a dry film is laminated onto the resin layer formed on the main surface of the inner layer circuit board. The lamination conditions for the resin layer and dry film can be the same as the lamination conditions for the inner layer circuit board and resin sheet.

The dry film used in step (B-2) may be any film that can be used to obtain a patterned dry film through exposure and development, and preferably one that is resistant to the plasma treatment in step (C). Furthermore, a photosensitive dry film made from a photoresist composition may be used as the dry film. Examples of such dry films that can be used include dry films made from resins such as novolac resins and acrylic resins.

From the viewpoint of improving the processability of via holes, the thickness of the dry film is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more, and is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less.

In step (B-3), exposure is performed by irradiating the dry film with active energy rays through a photomask having a predetermined pattern. The details of exposure typically involve irradiating the surface of the dry film with active energy rays through a photomask, photocuring the exposed portions of the dry film. Examples of active energy rays include ultraviolet light, visible light, electron beams, and X-rays, with ultraviolet light being preferred. The dose and duration of ultraviolet light exposure can be appropriately set depending on the dry film. Examples of exposure methods include contact exposure, in which a mask pattern is placed in close contact with the dry film for exposure, and non-contact exposure, in which parallel light is used for exposure without the mask pattern being placed in close contact with the dry film.

After exposure, development is performed to remove either the exposed or unexposed portions of the dry film (usually the unexposed portions), forming a patterned dry film as a mask. Development can be performed using either wet or dry development. Examples of development methods include dipping, puddling, spraying, brushing, and scraping.

In step (C) described below, plasma treatment is performed using the patterned dry film as a mask to form via holes.

<Step (C)>
Step (C) is a step of performing plasma treatment on the surface of the resin layer to form via holes in the resin layer and the insulating layer. Since the insulating layer contains a cured product of the resin composition of the present invention, even when via holes are formed by plasma treatment, the step distance d from the end of the first surface in the via hole to the end of the laminated surface between the first surface and the insulating layer can be reduced, resulting in improved reliability of electrical connection. Furthermore, unlike sandblasting, plasma treatment can smoothly form via holes even when the resin layer is formed of a flexible material such as a thermoplastic resin.

Plasma treatment involves treating the surface of the resin layer with plasma generated by introducing gas into a plasma generator, thereby forming via holes in the resin layer and insulating layer. There are no particular limitations on the method for generating plasma, and examples include microwave plasma, which generates plasma using microwaves; high-frequency plasma, which uses high-frequency waves; atmospheric pressure plasma, which is generated under atmospheric pressure; and atmospheric pressure plasma, which is generated in a vacuum. Atmospheric pressure plasma, which is generated in a vacuum, is preferred.

Furthermore, the plasma used in step (C) is preferably RF plasma excited by high frequency waves.

The gas to be converted into plasma can be a gas that etches only the cured resin component in the insulating layer and removes the inorganic filler. Such gases are preferably _CF4 , Ar, _O2 , _N2 , or a combination thereof, more preferably a mixed gas containing _O2 and _CF4 , Ar, and _N2 , and even more preferably a mixed gas of _CF4 and _O2 .

The irradiation time for plasma treatment is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 3 minutes or more, since the insulating layer contains a resin composition with excellent plasma processability. There is no particular upper limit, but 60 minutes or less is preferred, 30 minutes or less is more preferred, and 20 minutes or less is even more preferred.

In the present invention, via holes are formed by plasma treatment, so the top diameter a of the via hole can be made small. The top diameter a is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less, or 20 μm or less. There is no particular lower limit, but it can be 1 μm or more, for example.

<Step (D)>
Step (D) is a step of roughening the surfaces of the resin layer and the insulating layer. Specifically, it is a step of removing foreign matter, such as resin components and inorganic fillers contained in the insulating layer and the resin layer that have fallen off in step (C), from the via holes using a treatment liquid. Foreign matter may be present on the surfaces of the resin layer and the insulating layer after step (C). This foreign matter may include, for example, inorganic fillers excavated by plasma treatment or resin components of the resin layer. This foreign matter may cause a decrease in the adhesive strength of the conductor layer. Therefore, step (D) is performed to remove these foreign matter. More specifically, step (D) is a step of contacting the resin layer surface with a treatment liquid after step (C) to remove the foreign matter. Step (D) may be performed once or multiple times.

The procedures and conditions for step (D) are not particularly limited, and known procedures and conditions commonly used in forming insulating layers for printed wiring boards can be employed. For example, the insulating layer can be roughened by performing a swelling treatment with a swelling liquid, a roughening treatment with an oxidizing agent, and a neutralization treatment with a neutralizing liquid, in that order. The swelling liquid used for the roughening treatment is not particularly limited, but examples include alkaline solutions and surfactant solutions. Alkaline solutions are preferred, and sodium hydroxide solutions and potassium hydroxide solutions are more preferred. Commercially available swelling liquids include "Swelling Dip Securigans P," "Swelling Dip Securigans SBU," and "Swelling Dip Securigant P," both manufactured by Atotech Japan. The swelling treatment with a swelling liquid is not particularly limited, but can be performed by immersing the insulating layer in a swelling liquid at 30°C to 90°C for 1 to 20 minutes. From the viewpoint of suppressing swelling of the resin of the insulating layer to an appropriate level, it is preferable to immerse the insulating layer in a swelling solution at 40°C to 80°C for 5 to 15 minutes. The oxidizing agent used in the roughening treatment is not particularly limited, but examples thereof include alkaline permanganate solutions prepared by dissolving potassium permanganate or sodium permanganate in an aqueous solution of sodium hydroxide. Roughening treatment using an oxidizing agent such as an alkaline permanganate solution is preferably carried out by immersing the insulating layer in an oxidizing agent solution heated to 60°C to 100°C for 10 to 30 minutes. Furthermore, the concentration of permanganate in the alkaline permanganate solution is preferably 5% by mass to 10% by mass. Commercially available oxidizing agents include alkaline permanganate solutions such as "Concentrate Compact CP" and "Dosing Solution Securigance P" manufactured by Atotech Japan. Furthermore, the neutralizing solution used in the roughening treatment is preferably an acidic aqueous solution, and a commercially available product such as "Reduction Solution Securigant P" manufactured by Atotech Japan is one example. Treatment with a neutralizing solution can be carried out by immersing the surface that has been roughened with an oxidizing agent in a neutralizing solution at 30°C to 80°C for 1 to 30 minutes. From the standpoint of workability, etc., a method in which the object that has been roughened with an oxidizing agent is immersed in a neutralizing solution at 40°C to 70°C for 5 to 20 minutes is preferred.

<Step (E)>
Step (E) is a step of forming a conductor layer on the surface of the resin layer. In this step, a conductor layer is also typically formed in the via hole. Therefore, the conductor layer may also be formed on the surface of the insulating layer exposed in the via hole. The conductor material used for the conductor layer is not particularly limited. In a preferred embodiment, the conductor layer contains one or more metals selected from the group consisting of gold, platinum, palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel, titanium, tungsten, iron, tin, and indium. The conductor layer may be a single metal layer or an alloy layer. Examples of alloy layers include layers formed from alloys of two or more metals selected from the above group (e.g., nickel-chromium alloys, copper-nickel alloys, and copper-titanium alloys). Among these, from the viewpoints of versatility in forming the conductor layer, cost, ease of patterning, etc., a single metal layer of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or an alloy layer of a nickel-chromium alloy, a copper-nickel alloy, or a copper-titanium alloy is preferred, a single metal layer of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or an alloy layer of a nickel-chromium alloy is more preferred, and a single metal layer of copper is even more preferred.

The conductor layer may have a single-layer structure, or a multi-layer structure consisting of two or more single-metal or alloy layers made of different types of metals or alloys. If the conductor layer has a multi-layer structure, the layer in contact with the cured body is preferably a single-metal layer of chromium, zinc, or titanium, or an alloy layer of nickel-chromium alloy.

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

In a preferred embodiment of step (E), the conductor layer is formed by sputtering. When forming the conductor layer by sputtering, typically, a conductor seed layer is first formed on the surface of the resin layer by sputtering, and then a conductor sputtered layer is formed on the conductor seed layer by sputtering. Before forming the conductor seed layer by sputtering, the surface of the resin layer may be cleaned by reverse sputtering. Various gases can be used for the reverse sputtering, with Ar, O ₂ , and N ₂ being preferred. When the seed layer is made of Cu or a Cu alloy, Ar or O ₂ or an Ar/O ₂ mixed gas is preferred. When the seed layer is made of Ti, Ar or N ₂ or an Ar/N ₂ mixed gas is preferred. When the seed layer is made of Cr or a Cr alloy (such as nichrome), Ar or O ₂ or an Ar/O ₂ mixed gas is preferred. Sputtering can be performed using various sputtering devices, such as magnetron sputtering and mirror tron sputtering. Metals for forming the conductor seed layer include Cr, Ni, Ti, and nichrome. Cr and Ti are particularly preferred. The thickness of the conductor seed layer is usually preferably 5 nm or more, more preferably 10 nm or more, and is preferably 1000 nm or less, more preferably 500 nm or less. Examples of metals that form the conductor sputtered layer include Cu, Pt, Au, and Pd. Cu is particularly preferred. The thickness of the conductor sputtered layer is usually preferably 50 nm or more, more preferably 100 nm or more, and is preferably 3000 nm or less, more preferably 1000 nm or less.

After forming a conductor layer by sputtering, a copper plating layer may be formed on the conductor layer by electrolytic copper plating. The thickness of the copper plating layer is typically preferably 5 μm or more, more preferably 8 μm or more, and is preferably formed to be 75 μm or less, more preferably 35 μm or less. Conventional methods such as subtractive and semi-additive methods can be used to form the circuit.

[Semiconductor device]
The semiconductor device of the present invention includes a printed wiring board, and can be manufactured using a printed wiring board obtained by the manufacturing method of the present invention.

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

The semiconductor device of the present invention can be manufactured by mounting a component (semiconductor chip) on a conductive point on a printed wiring board. A "conductive point" is a "point on a printed wiring board that transmits electrical signals," and the location can be either on the surface or embedded. Furthermore, there are no particular restrictions on the semiconductor chip, as long as it is an electrical circuit element made of semiconductor material.

The method for mounting semiconductor chips when manufacturing semiconductor devices is not particularly limited as long as the semiconductor chip functions effectively, but specific examples include wire bonding mounting, flip-chip mounting, bumpless build-up layer (BBUL) mounting, anisotropic conductive film (ACF) mounting, and non-conductive film (NCF) mounting. Here, a "bumpless build-up layer (BBUL) mounting method" refers to a mounting method in which a semiconductor chip is directly embedded in a recess in a printed wiring board and connected to the wiring on the printed wiring board.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples. In the following explanation, "parts" and "%" representing amounts mean "parts by mass" and "% by mass", respectively, unless otherwise specified. Furthermore, the operations described below were carried out in an environment of room temperature and normal pressure, unless otherwise specified.

<Inorganic filler used>
Inorganic filler 1: 100 parts of spherical silica (Denka's "UFP-30", average particle size 0.078 μm, specific surface area 30.7 m ² /g) surface-treated with 2 parts of N-phenyl-3-aminopropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., KBM573).
Inorganic filler 2: 100 parts of spherical silica ("SC2500SQ" manufactured by Admatechs, average particle size 0.63 μm, specific surface area 11.2 m ² /g) surface-treated with 1 part of N-phenyl-3-aminopropyltrimethoxysilane (KBM573 manufactured by Shin-Etsu Chemical Co., Ltd.).

<Preparation of Resin Composition 1>
6 parts of bixylenol type epoxy resin ("YX4000HK" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight: approximately 185), 5 parts of naphthalene type epoxy resin ("ESN475V" manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., epoxy equivalent weight: approximately 332), 15 parts of bisphenol AF type epoxy resin ("YL7760" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight: approximately 238), 2 parts of naphthylene ether type epoxy resin ("HP6000L" manufactured by DIC Corporation, epoxy equivalent weight: approximately 213), 2 parts of cyclohexane type epoxy resin ("ZX1" manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight: approximately 213), Two parts of phenoxy resin ("YL7500BH30" manufactured by Mitsubishi Chemical Corporation, a 1:1 solution of cyclohexanone:methyl ethyl ketone (MEK) with a solids content of 30% by mass, Mw=44,000), and five parts of hydrogenated styrene-based thermoplastic elastomer ("P2000" manufactured by Asahi Kasei Corporation, styrene/ethylene-butylene-butadiene ratio=67/33) were heated and dissolved with stirring in a mixed solvent of 20 parts of solvent naphtha, 10 parts of cyclohexanone, and 10 parts of toluene. After cooling to room temperature, 4 parts of a triazine skeleton-containing cresol novolac curing agent ("LA-3018-50P" manufactured by DIC Corporation, hydroxyl group equivalent of approximately 151, 2-methoxypropanol solution with a solids content of 50%), 6 parts of an active ester curing agent ("HP-B-8151-62T" manufactured by DIC Corporation, active group equivalent of 238, toluene solution with a solids content of 62%), 30 parts of inorganic filler 1, and 0.05 parts of an amine curing accelerator (4-dimethylaminopyridine (DMAP)) were mixed therein and dispersed uniformly using a high-speed rotary mixer. The mixture was then filtered using a cartridge filter ("SHP020" manufactured by ROKITECHNO Corporation) to prepare Resin Composition 1.

<Preparation of Resin Composition 2>
Resin composition 2 was prepared in the same manner as in the preparation of resin composition 1, except that the amount of inorganic filler 1 was changed from 30 parts to 60 parts.

<Preparation of Resin Composition 3>
In the preparation of Resin Composition 1, 30 parts of Inorganic Filler 1 was changed to 60 parts of Inorganic Filler 2. Resin Composition 3 was prepared in the same manner as in the preparation of Resin Composition 1 except for the above-mentioned changes.

The following table shows the components and their blending amounts used in preparing Resin Compositions 1 to 3. The abbreviations in the table are as follows:
YX4000HK: bixylenol type epoxy resin, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight: approximately 185 g/eq.
ESN475V: naphthalene-type epoxy resin, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., epoxy equivalent: approximately 332 g/eq.
YL7760: Bisphenol AF type epoxy resin, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight: about 238 g/eq.
HP6000L: naphthylene ether type epoxy resin, manufactured by DIC Corporation, epoxy equivalent weight: approximately 213 g/eq.
ZX1658GS: cyclohexane type epoxy resin, manufactured by Mitsubishi Chemical Corporation, epoxy equivalent weight: approximately 135 g/eq.
BS230S: cyanate-based curing agent, manufactured by Lonza Japan, cyanate equivalent 232 g/eq.
LA-3018-50P: Triazine skeleton-containing cresol novolac curing agent, manufactured by DIC Corporation, hydroxyl group equivalent of approximately 151 g/eq., 50% solids solution in 2-methoxypropanol; HPB-8151-62T: DIC Corporation, active group equivalent of 238 g/eq., 62% solids solution in toluene; YX7500BH30: Phenoxy resin, manufactured by Mitsubishi Chemical Corporation, 30% solids solution in 1:1 cyclohexanone:methyl ethyl ketone (MEK), Mw=44,000
P2000: manufactured by Asahi Kasei Corporation, hydrogenated styrene-based thermoplastic elastomer (styrene/ethylene-butylene-butadiene ratio = 67/33)
DMAP: Amine curing accelerator, 4-dimethylaminopyridine. Curing agent content: The content of the curing agent when the resin component in the resin composition is 100% by mass. Active ester curing agent content: The content of the active ester curing agent when the resin component in the resin composition is 100% by mass. Inorganic filler content: The content of the inorganic filler when the non-volatile components in the resin composition are 100% by mass.

<Preparation of resin sheet>
A PET film ("Lumirror R80" manufactured by Toray Industries, Inc., thickness 38 μm, softening point 130°C, "release PET") that had been release-treated with an alkyd resin-based release agent ("AL-5" manufactured by Lintec Corporation) was prepared as a support. Resin compositions 1 to 4 were each uniformly applied to the release agent on the support using a die coater so that the thickness of the resin composition layer after drying would be 15 μm, and the resulting film was dried at 70°C to 95°C for 2 minutes to obtain a resin composition layer on the release PET. Next, a roughened surface of a polypropylene film ("Alphan MA-411" manufactured by Oji F-Tex Co., Ltd., thickness 15 μm) was laminated as a protective film on the side of the resin sheet not bonded to the support so as to be bonded to the resin composition layer. This yielded a resin sheet consisting, in this order, of the release PET (support), the resin composition layer, and the protective film.

<Measurement of Thickness of Resin Composition Layer, etc.>
The thickness was measured using a contact type film thickness meter (MCD-25MJ, manufactured by Mitutoyo Corporation).

<Preparation of evaluation substrate>
(1) Preparation of Silicon Wafer A silicon wafer (copper thickness: 1 μm, substrate thickness: 0.8 mm, size: 8 inches) having a copper layer laminated on one side was prepared as a substrate, and placed in an oven at 130° C. and dried for 30 minutes.

(2) Lamination of Resin Layer The protective film was peeled off from each prepared resin sheet, and a liquid crystal polymer film (Vecstar-FCCL:CTF-25, manufactured by Kuraray Co., Ltd., thickness 25 μm) was laminated so as to contact the resin composition layer using a batch-type vacuum pressure laminator (Nikko Materials Co., Ltd., one-stage build-up laminator, V160). The lamination was performed by reducing the pressure for 20 seconds to a pressure of 13 hPa or less, setting the temperature of the upper plate to 80 ° C. and the temperature of the lower plate to 60 ° C., and then pressing the sheets together at atmospheric pressure for 20 seconds. This is referred to as resin sheet A laminated with a resin layer.

In Example 3, the liquid crystal polymer film (Vecstar-FCCL:CTF-25, manufactured by Kuraray Co., Ltd.) was replaced with a flexible polyimide copper-clad laminate (ESPANEX:MC12-25-00HRM, manufactured by Nippon Steel Chemical Co., Ltd.), and the polyimide film was laminated so that it was in contact with the resin composition layer.

(3) Lamination of a resin sheet laminated with a resin layer and a silicon wafer The support was peeled off from each resin sheet A laminated with a resin layer, and the resin composition layer was laminated on one side of the wafer using a batch vacuum pressure laminator (Nikko Materials Co., Ltd., two-stage build-up laminator, CVP700) so that the resin composition layer was in contact with the silicon wafer. Lamination was performed by reducing the pressure for 30 seconds to 13 hPa or less, and then pressing at 130 ° C. and a pressure of 0.74 MPa for 45 seconds. Next, a heat press was performed at 120 ° C. and a pressure of 0.5 MPa for 75 seconds.

(4) Thermal curing of resin composition layer The silicon wafer laminated with the resin sheet was placed in an oven at 100°C for 30 minutes, then transferred to an oven at 180°C for 30 minutes to thermally cure the resin composition layer, forming an insulating layer. This resulted in a substrate A having a total thickness of 40 μm, including the insulating layer and resin layer. At this time, the copper in the flexible copper-clad laminate was etched out with iron(III) chloride.

(5) Dry Film Pattern Formation A 20 μm thick dry film (manufactured by Nikko Materials Co., Ltd., "ALPHO 20A263") was bonded to the surface of the resin layer of substrate A. The dry film was laminated using a batch-type vacuum pressure laminator (manufactured by Meiki Seisakusho Co., Ltd., "MVLP-500"), which was depressurized for 30 seconds to a pressure of 13 hPa or less, and then pressurized for 20 seconds at a pressure of 0.1 MPa and a temperature of 70 ° C. Then, a glass mask with a via pattern was placed on the polyethylene terephthalate film, which is the protective layer of the dry film, and UV irradiation was performed using a UV lamp at an irradiation intensity of 150 mJ / cm ² , and patterning was performed to form via holes with a top diameter of 40 μm. After UV irradiation, the substrate was sprayed with a 1% aqueous sodium carbonate solution at 30 ° C. at a spray pressure of 0.15 MPa for 30 seconds.

(6) Plasma Processing In Examples 1 to 3, a vacuum plasma etching device (M120W manufactured by Nissin Co., Ltd.) was used to perform processing for 40 minutes under the conditions of a _CF4 / _O2 mixture ratio of 1:7 (sccm) and a pressure of 120 Pa, forming a via hole with a top diameter of approximately 40 μm in the resin layer of the via-processed substrate, and then the dry film was peeled off to obtain a via evaluation substrate.

(7) UV-YAG laser via processing In Comparative Example 3, a UV-YAG laser processing machine ("LU-2L212/M50L" manufactured by Via Mechanics) was used to irradiate the resin layer of Substrate A with laser light to form multiple via holes with a top diameter of approximately 40 μm. The laser light irradiation conditions were a power of 0.8 W and 50 shots. This substrate was used as a laser evaluation substrate.

The laser evaluation substrate was immersed in a swelling solution (Swelling Dip Securigant P, manufactured by Atotech Japan, an aqueous solution of diethylene glycol monobutyl ether and sodium hydroxide) at 60°C for 5 minutes. Next, it was immersed in a roughening solution (Concentrate Compact P, manufactured by Atotech Japan (aqueous solution of _KMnO4 : 60 g/L, NaOH: 40 g/L)) at 80°C for 15 minutes. Finally, it was immersed in a neutralizing solution (Reduction Showreusin Securigant P, manufactured by Atotech Japan (aqueous solution of sulfuric acid)) at 40°C for 5 minutes. Then, it was dried at 80°C for 30 minutes.

<Observation of via hole cross section>
The via evaluation substrate and laser evaluation substrate were heated at 150°C for 30 minutes, and then a copper layer (200 nm thick) was formed on the resin layer using a sputtering device (Canon Anelva's "E-400S"). Then, a cross-section was observed using a FIB-SEM composite device (SII Nano Technology's "SMI3050SE") to determine [d/{(1/2) × a}] × 100. Evaluation was also performed according to the following criteria.
Good: [d/{(1/2) x a}] x 100 is 5% or less.
×: [d/{(½)×a}]×100 exceeds 5%.

<Observation of via hole walls>
The via evaluation substrate and the laser evaluation substrate were heated at 150°C for 30 minutes, and then a copper layer (200 nm thick) was formed on the insulating layer using a sputtering device (Canon Anelva's "E-400S"). Then, a cross-section was observed using an FIB-SEM composite device (SII Nano Technology's "SMI3050SE") and evaluated according to the following criteria.
◯: A copper layer is formed uniformly and without interruption on the wall surfaces of the via holes formed in the insulating layer and the resin layer.
×: The copper layer was not formed uniformly due to irregularities.

<Evaluation of lamination properties>
The resin sheet A with a resin layer was cut to a size appropriate for laminating onto a silicon wafer, and evaluated according to the following criteria.
◯: No lifting is observed around the cut due to insufficient adhesion of the resin layer and the resin composition layer from the cut portion.
x: Lifting was observed around the cut area due to insufficient adhesion between the resin layer and the resin composition layer.

<Measurement of coefficient of linear thermal expansion (CTE)>
(Preparation of Cured Product for Evaluation)
A glass cloth-based epoxy resin double-sided copper-clad laminate ("R5715ES" manufactured by Matsushita Electric Works, Ltd., thickness 0.7 mm, 255 mm square) was placed on the release agent-untreated surface of a release agent-treated PET film ("501010" manufactured by Lintec Corporation, thickness 38 μm, 240 mm square), and the four sides were fixed with polyimide adhesive tape (width 10 mm) (hereinafter referred to as "fixed PET film").

Resin compositions 1 to 3 were applied using a die coater to a PET film (Toray Industries, Inc., "Lumirror R80," 38 μm thick, softening point 130°C, hereafter referred to as "release PET") that had been release-treated with an alkyd resin-based release agent (Lintec Corporation, "AL-5"), so that the dried resin composition layer would be 40 μm thick. The film was then dried at 80°C to 120°C (average 100°C) for 10 minutes to obtain a resin sheet. Each resin sheet (40 μm thick, 200 mm square) was then centrally laminated using a batch-type vacuum pressure laminator (Nikko Materials Co., Ltd., two-stage build-up laminator, CVP700) so that the resin composition layer was in contact with the release-agent-treated surface of the fixed PET film, obtaining a resin sheet. The lamination process was carried out by reducing the pressure to 13 hPa or less for 30 seconds, and then pressing the pieces together at 100°C and a pressure of 0.74 MPa for 30 seconds.

Next, the release PET was peeled off from the resin sheet with the support, and the sheet was placed in an oven at 190°C and thermally cured for 1.5 hours.

After thermal curing, the polyimide adhesive tape was peeled off, and the cured product was removed from the glass cloth-based epoxy resin double-sided copper-clad laminate. The PET film ("501010" manufactured by Lintec Corporation) was also peeled off, yielding a sheet-like cured product. The resulting cured product is referred to as the "cured product for evaluation."

The cured product for evaluation was cut into test pieces measuring 5 mm wide and 15 mm long, and thermomechanical analysis was performed using a Seiko Instruments Inc. thermomechanical analyzer (TMA, SS6100) using the tensile load method. Specifically, the test pieces were mounted in the thermomechanical analyzer and measured twice consecutively under measurement conditions of a load of 1 g and a heating rate of 5°C/min. The linear thermal expansion coefficient (ppm/°C) in the planar direction over the temperature range of 25°C to 150°C was calculated from the two measurements.

In Comparative Examples 1 and 2, the resin composition layer and resin layer of the resin sheet could not be laminated, so the top diameter of the via holes, etc., could not be observed or measured.

REFERENCE SIGNS LIST 1 printed wiring board 2 inner layer circuit board 3 insulating layer 4 resin layer 4a first surface 4b second surface 41 end of first surface in via hole 42 end of contact surface between first surface and insulating layer 5 conductive layer 6 via hole a top diameter d step distance

Claims (7)

A printed wiring board comprising, in this order, a resin layer having a first surface, an insulating layer in contact with the first surface of the resin layer and including a cured product of a resin composition, and an inner layer circuit board,
the resin layer is formed of a thermoplastic resin,
The resin composition includes a thermosetting resin,
a via hole penetrating the resin layer and the insulating layer in a thickness direction;
The top diameter of the via hole is a (μm),
When the distance from the end of the first surface in the via hole to the end of the contact surface between the first surface and the insulating layer is d (μm),
A printed wiring board that satisfies the relationship: 0.5≦[d/{(1/2)×a}]×100≦5. A printed wiring board comprising, in this order, a resin layer having a first surface, an insulating layer in contact with the first surface of the resin layer and including a cured product of a resin composition, and an inner layer circuit board,
the resin layer is formed of a thermoplastic resin,
The resin composition includes a thermosetting resin,
a via hole penetrating the resin layer and the insulating layer in a thickness direction;
The top diameter of the via hole is a (μm),
When the distance from the end of the first surface in the via hole to the end of the contact surface between the first surface and the insulating layer is d (μm),
The relationship 0.5≦[d/{(½)×a}]×100≦5 is satisfied,
a printed wiring board, wherein, when cut along a plane parallel to the inner layer circuit board, the diameter of the via hole penetrating the insulating layer on the first surface side and the diameter of the via hole on the inner layer circuit board side are larger than the diameter of the via hole penetrating the resin layer on the second surface side and the diameter of the via hole on the first surface side, respectively. The printed wiring board according to claim 1 or 2, wherein the top diameter of the via hole is 50 μm or less. The printed wiring board according to any one of claims 1 to 3, wherein the resin composition contains an inorganic filler. The printed wiring board according to claim 4, wherein the content of the inorganic filler is 50% by mass or less, when the non-volatile components of the resin composition are 100% by mass. The printed wiring board according to any one of claims 1 to 5, wherein the linear thermal expansion coefficient of the cured resin composition is 40 ppm or less. The printed wiring board according to any one of claims 1 to 6, wherein the resin layer contains either a polyimide resin or a liquid crystal polymer.