Curable resin composition

Abstract

[Problem] This invention provides a curable resin composition with excellent abrasiveness, chemical resistance, and resistance to incorporation during printing. [Solution] The curable resin composition of this invention comprises (A) epoxy resin, (B) epoxy resin curing agent, and (C) inorganic filler, wherein the aforementioned (C) inorganic filler comprises at least three of (C1) silicon dioxide, (C2) calcium carbonate, and (C3) barium sulfate.

Description

Technical field

[0001] The present invention relates to a hardening resin composition, and a hardening resin composition which can be conveniently used as a filling material for filling holes such as through holes and recesses of the through-holes of printed wiring boards. Prior technology

[0002] With the miniaturization and high functionality of electronic machines, the requirements for the refinement of the pattern of printed patch panels, the reduction of the construction area, and the high density of component construction are increasing. Therefore, a multilayer substrate is commonly used, which forms a double-sided substrate with through-holes (i.e., through-holes) connecting the dissimilar wiring layers to each other electrically.

[0003] In this type of printed wiring board, it is generally in the recesses between the conductor circuits on the surface, or in the through-holes and through-holes where the wiring layer is formed on the inner wall surface. As a thermohardening resin filler, generally, a hardening resin filler comprising an epoxy resin, an epoxy resin hardener, and an inorganic filler as a hardening resin component is used. Furthermore, as a hole-filling processing treatment, the hardened resin filler is filled in the holes of the substrate by means such as screen printing, so that the hardened resin filler is hardened, the remaining hardened material is ground and the substrate is smoothed.

[0004] Incidentally, the heat resistance of printed wiring boards is gradually improving, accompanied by more requirements for hardened resin filling materials to have heat resistance. In addition, the substrate will be exposed to CZ-treated and tin-plated pharmaceutical liquids after hole filling, so electroplating resistance and drug resistance are also required for hardened resin fillers. Furthermore, with the radialization of through-holes and through-holes, the excellence of hardened resin fillers in fillability is increasingly demanded, and it is particularly required that hardened resin fillers are difficult to penetrate into screens during filling (at printing).

[0005] For the various requirements mentioned above as a filler material for hole filling, it is known to resort to the addition of inorganic fillers such as silica and calcium carbonate to improve heat resistance (e.g., Patent Literature 1 et al.). Also, it is known that as an inorganic filler doped calcium carbonate to improve grindability (e.g., Patent Literature 2 and others). Moreover, doping of barium sulfate as an inorganic filler is known to improve drug resistance and penetration (e.g., patent literature 3 , 4 , etc.). [Previous technical literature] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2022-009110 [Patent Document 2] International Publication No. 2016 / 117237 Pamphlet [Patent Document 3] Japanese Patent Application Laid-Open No. 2019-81893 [Patent Document 4] International Publication No. 2021 / 053774 Pamphlet Summary of the Invention

[0007] Although various properties of fillers used for hole filling are required as described above, the various properties are often in a trade-off relationship with each other. Therefore, there is still a desire for hardening resin fillers that can achieve all properties to high standards.

[0008] Therefore, an object of the present invention is to provide a curable resin composition having excellent abrasive properties, as well as excellent chemical resistance and resistance to contamination during printing.

[0009] The inventors of this application have focused on inorganic fillers added to curable resin compositions. By combining a large number of specific inorganic fillers, they have achieved a curable resin composition with excellent polishing properties, chemical resistance, and resistance to contamination during printing. The present invention is based on this knowledge. The gist of the present invention is as follows.

[0010] [1] A curable resin composition, characterized by comprising: (A) Epoxy resin; (B) epoxy resin hardener; and (C) Inorganic fillers, including: The aforementioned (C) inorganic filler includes at least three of (C1) silicon dioxide, (C2) calcium carbonate, and (C3) barium sulfate. [2] In the curable resin composition of [1], when the contents of the silicon dioxide (C1), calcium carbonate (C2), and barium sulfate (C3) relative to the curable resin composition are converted to W C1 (mass %), W C2 (mass %), and W C3 (mass %), respectively, in terms of solid content, the following relationship is satisfied: W C1 ≧ W C2 > W C3, or W C2>W C3≧W C1. [3] The curable resin composition of [1] or [2], wherein the inorganic filler (C) comprises 30 to 80% by mass of the curable resin composition in terms of solid content. [4] In the curable resin composition of any one of [1] to [3], wherein the average particle sizes of the silicon dioxide (C1), calcium carbonate (C2), and barium sulfate (C3) are denoted as RC1 (μm), RC2 (μm), and RC3 (μm), respectively, the following relationship is satisfied: R C1>R C2>R C3, or R C2>R C1>R C3. [5] The curable resin composition of any one of [1] to [4], wherein the epoxy resin (A) comprises at least two of (A1) a bisphenol-type epoxy resin and (A2) an amine-type epoxy resin. [6] A curable resin composition as described in any one of [1] to [5], which is used as a filling material for through holes or recesses in a printed wiring board.

[0011] According to the present invention, by combining three specific inorganic fillers, a curable resin composition having excellent polishing properties, chemical resistance, and resistance to contamination during printing can be realized. Simple diagram description

[0012] FIG. 1a is a schematic diagram illustrating a process for manufacturing a printed wiring board by filling holes with the curable resin composition of the present invention. FIG. 1 b is a schematic diagram illustrating a process for manufacturing a printed wiring board by filling holes with the curable resin composition of the present invention. FIG. 1c is a schematic diagram illustrating a process for manufacturing a printed wiring board by filling holes with the curable resin composition of the present invention. FIG. 1d is a schematic diagram illustrating a process for manufacturing a printed wiring board by filling holes with the curable resin composition of the present invention. FIG. 2a is a schematic cross-sectional view showing one embodiment of a printed wiring board in which holes are filled with the curable resin composition of the present invention. FIG. 2 b is a schematic cross-sectional view showing one embodiment of a printed wiring board in which holes are filled with the curable resin composition of the present invention. Implementation Method

[0013] <Curing Resin Composition> The curable resin composition of the present invention includes (A) an epoxy resin, (B) an epoxy resin hardener, and (C) an inorganic filler as essential components. Each component will be described in detail below.

[0014] [Epoxy resin] The curable resin composition of the present invention includes an epoxy resin (A) as a curable component. Any epoxy resin (A) can be used without limitation as long as it has one or more epoxy groups per molecule. Examples include compounds (monofunctional epoxy compounds) such as butyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and glycidyl (meth)acrylate; difunctional epoxy compounds such as neopentyl glycol diglycidyl ether and 1,6-hexanediol diglycidyl ether; and trifunctional epoxy compounds such as polyglycerol triglycidyl ether, sorbitol polyglycidyl ether, and pentaerythritol polyglycidyl ether. Of these, those having two or more epoxy groups per molecule are preferred.

[0015] Examples of epoxy resins having two or more epoxy groups in one molecule include bisphenol-A epoxy resins, hydrogenated bisphenol-A epoxy resins, bisphenol-F epoxy resins, hydrogenated bisphenol-F epoxy resins, bisphenol-S epoxy resins, and modified bisphenol-F epoxy resins modified to have a trifunctional or higher functionality by reacting epichlorohydrin with bisphenol-F epoxy resins; biphenol-type epoxy resins, tetramethylbiphenol-type epoxy resins, and other biphenol-type epoxy resins; and phenol novolac-type epoxy resins. Epoxy resins, cresol novolac epoxy resins, bisphenol A novolac epoxy resins, alkylphenol novolac epoxy resins, naphthyl ether epoxy resins, naphthol novolac epoxy resins and other novolac epoxy resins; fluorinated epoxy resins such as bisphenol AF epoxy resins and perfluoroalkyl epoxy resins; diaminodiphenylmethane epoxy resins, diaminodiphenylsulfonium glycidylamine epoxy resins, meta-xylene diamine epoxy resins, 1,3-bis(aminomethyl)cyclohexane epoxy resins Epoxy resin, triglycidyl para-aminophenol type epoxy resin, tetraglycidyl diaminodiphenylmethane type epoxy resin, triglycidyl para-aminophenol type epoxy resin, isocyanurate type epoxy resin, aniline type epoxy resin, hydantoin type epoxy resin, aminophenol type epoxy resin, aminocresol type epoxy resin and other amino epoxy resins; naphthalene type epoxy resin, dihydroxynaphthalene type epoxy resin, polyhydroxy bis-naphthaldehyde type epoxy resin, naphthol type epoxy resin, binaphthol type epoxy resin; by polyhydroxy Epoxy resins having a naphthalene skeleton (epoxy resins containing a naphthalene skeleton), such as naphthalene-type epoxy resins obtained by the condensation reaction of naphthalene and aldehydes; epoxy resins containing a condensed ring skeleton, such as bicyclopentadiene-type epoxy resins; trisphenol-type epoxy resins; anthracene-type epoxy resins; alicyclic epoxy resins; chain aliphatic epoxy resins; phosphorus-containing epoxy resins; anthracene-type epoxy resins; norbornene-type epoxy resins; adamantane-type epoxy resins; fluorene-type epoxy resins; alkylphenol-type epoxy resins, etc. These epoxy resins may be used alone or in combination of two or more.

[0016] Among the aforementioned epoxy resins, the present invention preferably uses (A1) a bisphenol-type epoxy resin, (A2) an amine-type epoxy resin, and (A3) a novolac-type epoxy resin. Combining two or more of these epoxy resins is more preferred. For example, combining (A1) a bisphenol-type epoxy resin and (A2) an amine-type epoxy resin can reduce the viscosity of the resin composition, making it easier to adjust the material selection and blending ratio of the inorganic filler.

[0017] When the epoxy resin (A) comprises two epoxy resins (A1) and (A2), the bisphenol-type epoxy resin (A1) is preferably contained in an amount of 10 to 80 parts by mass, more preferably 20 to 70 parts by mass, based on 100 parts by mass of the total solids content of the epoxy resin (A). Furthermore, the amine-type epoxy resin (A2) is preferably contained in an amount of 10 to 50 parts by mass, more preferably 20 to 40 parts by mass, based on 100 parts by mass of the total solids content of the epoxy resin (A).

[0018] Furthermore, when the epoxy resin (A) comprises three epoxy resins (A1) to (A3), the bisphenol-type epoxy resin (A1) is preferably included in an amount of 10 to 90 parts by mass, more preferably 20 to 80 parts by mass, based on 100 parts by mass of the total solids content of the epoxy resin (A). Furthermore, the amine-type epoxy resin (A2) is preferably included in an amount of 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, based on 100 parts by mass of the total solids content of the epoxy resin (A). Furthermore, the novolac-type epoxy resin (A3) is preferably included in an amount of 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, based on 100 parts by mass of the total solids content of the epoxy resin (A).

[0019] The total solid content of the epoxy resin is preferably contained in an amount of 5 to 70 parts by mass, more preferably 10 to 60 parts by mass, relative to the total fixed components of the curable resin composition.

[0020] Furthermore, considering the film-forming properties of the curable resin composition, namely, its printability and other coating properties, the epoxy resin used in the present invention is preferably in liquid form rather than in solid form. In particular, the viscosity of the epoxy resin is preferably 50 Pa·s or less, more preferably 20 Pa·s or less, and even more preferably 5 Pa·s or less. The viscosity herein refers to the viscosity measured at 25±1°C, 5.0 rpm, and for 30 seconds using a cone-plate viscometer (Toki Sangyo Co., Ltd., TV-33H, rotor 3°×R9.7 or rotor 1°34'×R24) in accordance with JIS K8803:2011, "Viscosity Measurement Method Using a Cone-Plate Viscometer." [(B) Epoxy resin hardener]

[0021] As the epoxy resin hardener (B), any agent that accelerates the curing reaction of the epoxy resin can be used without limitation. Examples include amines, imidazoles, polyfunctional phenols, acid anhydrides, isocyanates, and polymers containing these functional groups. Various agents can be used as needed. Examples of amines include dicyandiamide and diaminodiphenylmethane. Examples of imidazoles include alkyl-substituted imidazoles and benzimidazole. Furthermore, the imidazole compound may be an imidazole latent hardener such as an imidazole adduct. Examples of polyfunctional phenols include hydroquinone, resorcinol, bisphenol A, and its halogen compounds, as well as condensates of these with aldehydes such as novolacs and resols. Examples of acid anhydrides include phthalic anhydride, hexahydrophthalic anhydride, methyl naphthalic anhydride, and benzophenonetetracarboxylic acid. Examples of isocyanates include toluene diisocyanate and isophorone diisocyanate. These isocyanates may also be masked with phenols or the like. These hardeners may be used alone or in combination of two or more.

[0022] Among the above-mentioned curing agents, amines or imidazoles are convenient from the perspectives of adhesion to the conductive or insulating portion, storage stability, and heat resistance. Preferred are adducts of aliphatic polyamines such as alkylenediamines having 2 to 6 carbon atoms, polyalkylene polyamines having 2 to 6 carbon atoms, and aromatic ring-containing aliphatic polyamines having 8 to 15 carbon atoms, adducts of alicyclic polyamines such as isophoronediamine and 1,3-bis(aminomethyl)cyclohexane, or mixtures containing the above adducts of aliphatic polyamines and alicyclic polyamines as the main component.

[0023] The aforementioned addition compounds of aliphatic polyamines are preferably those obtained by reacting an aromatic glycidyl ether (particularly phenyl glycidyl ether or cresyl glycidyl ether) or an alkyl glycidyl ether with the aforementioned aliphatic polyamines. Furthermore, the aforementioned addition compounds of alicyclic polyamines are preferably those obtained by reacting n-butyl glycidyl ether, bisphenol A diglycidyl ether, or the like with the aforementioned alicyclic polyamines.

[0024] Examples of the aliphatic polyamine include alkylene diamines having 2 to 6 carbon atoms, such as ethylenediamine and propylenediamine; polyalkylene polyamines having 2 to 6 carbon atoms, such as diethylenetriamine and triethylenetriamine; and aromatic ring-containing aliphatic polyamines having 8 to 15 carbon atoms, such as xylene diamine. Examples of commercially available modified aliphatic polyamines include Fujicure FXE-1000, Fujicure FXR-1020, Fujicure FXR-1030, Fujicure FXR-1080, and Fujicure FXR-1090M2 (manufactured by T&K Toka Co., Ltd.), Ancamine 2089K, Sunmide P-117, Sunmide X-4150, Ancamine 2422, Serwet R, Sunmide TX-3000, and Sunmide A-100 (manufactured by Evonik Japan Co., Ltd.).

[0025] Examples of the alicyclic polyamine include isophoronediamine, 1,3-bis(aminomethyl)cyclohexane, bis(4-aminocyclohexyl)methane, norbornenediamine, 1,2-diaminocyclohexane, and laromin. Examples of commercially available modified alicyclic polyamines include ANCAMINE 1618, ANCAMINE 2074, ANCAMINE 2596, ANCAMINE 2199, SUNMIDE IM-544, SUNMIDE 1-544, ANCAMINE 2075, ANCAMINE 2280, ANCAMINE 1934, and ANCAMINE 2228 (manufactured by Evonik Japan Co., Ltd.), Daitocurar F-5197, Daitocurar B-1616 (manufactured by Daito Sangyo Co., Ltd.), Fujicure FXD-821, and Fujicure 4233 (manufactured by T&K TOKA Co., Ltd.), jERCURE 113 (manufactured by Mitsubishi Chemical Corporation), and Laromin C-260 (manufactured by BASF Japan Co., Ltd.). Moreover, as a polyamine type hardening agent, EH-5015S (made by ADEKA Corporation) etc. are mentioned.

[0026] Imidazoles include, for example, reaction products of epoxy resins and imidazoles. Examples include 2-methylimidazole, 4-methyl-2-ethylimidazole, 2-phenylimidazole, 4-methyl-2-phenylimidazole, 1-diphenylethylenedione-2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-undecylimidazole. Commercially available imidazole compounds include imidazoles such as 2E4MZ, C11Z, C17Z, and 2PZ; azine compounds of imidazoles such as 2MZ-A and 2E4MZ-A; isocyanurates of imidazoles such as 2MZ-OK and 2PZ-OK; and hydroxymethyl imidazoles such as 2PHZ and 2P4MHZ (all manufactured by Shikoku Chemicals Co., Ltd.). Examples of commercially available imidazole latent hardeners include Cure Duct P-0505 (manufactured by Shikoku Chemicals Co., Ltd.).

[0027] The amount of the hardener blended, based on 100 parts by mass of the total solids content of the epoxy resin (A), is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, and even more preferably 5 to 20 parts by mass. In particular, a blending amount of 5 parts by mass or greater of the epoxy resin hardener (B) is preferred because the preliminary curing rate of the resin composition generally does not slow, and the composition deep within the pores is sufficiently cured, thereby preventing the formation of cracks. Furthermore, a blending amount of 50 parts by mass or less of the epoxy resin hardener (B) is preferred because storage stability is improved, the preliminary curing rate of the resin composition generally does not increase excessively, and voids are less likely to remain in the cured product. [(C) Inorganic fillers]

[0028] The curable resin composition of the present invention includes at least three of (C1) silica, (C2) calcium carbonate, and (C3) barium sulfate as essential components as (C) inorganic fillers. By incorporating these three inorganic fillers into the curable resin composition, the present invention achieves a curable resin composition that has a low CTE, excellent polishability, and excellent chemical resistance and resistance to contamination during printing. While it is known that inorganic fillers such as silica, calcium carbonate, and barium sulfate can be used to improve properties such as heat resistance, filling properties, and chemical resistance, the properties of each inorganic filler are trade-offs. For example, while silica is known to contribute to heat resistance and chemical resistance, increasing the amount of silica added degrades filling properties and polishability. Therefore, attempts have been made to improve polishability while simultaneously enhancing heat resistance and chemical resistance by using silica and calcium carbonate together. Furthermore, it is known that the addition of calcium sulfate can improve plating resistance. However, it was unexpected that combining the three inorganic fillers described above could yield a curable resin composition with excellent abrasiveness, chemical resistance, and resistance to contamination during printing. Furthermore, as noted later, by adjusting the blending ratio and particle size of the three inorganic fillers within an appropriate range, abrasiveness, chemical resistance, and resistance to contamination during printing are further enhanced. Furthermore, the plate release properties of the curable resin composition during application are improved, resulting in reduced ink concavity on the through-hole surface when the curable resin composition is filled into the through-hole.

[0029] The silicon dioxide may be either amorphous or crystalline, or a mixture thereof. Amorphous (fused) silicon dioxide is particularly preferred. Furthermore, the calcium carbonate may be either natural heavy calcium carbonate or synthetic precipitated calcium carbonate.

[0030] In the present invention, by adjusting the blending amounts of the three inorganic fillers described above, it is possible to further enhance polishability, chemical resistance, and resistance to penetration during printing. Specifically, when the contents of (C1) silicon dioxide, (C2) calcium carbonate, and (C3) barium sulfate relative to the curable resin composition are expressed as W C1 (mass %), W C2 (mass %), and W C3 (mass %), respectively, calculated on a solids basis, the inorganic fillers are preferably blended to satisfy the following relationship: W C1 ≧ W C2 > W C3, or W C2>W C3≧W C1.

[0031] More specifically, when satisfying the relationship W C1 ≧ W C2 > W C3, the blending amounts of the inorganic fillers are preferably 10-60% by mass, more preferably 20-50% by mass. Furthermore, W C2 is preferably 1-30% by mass, more preferably 5-20% by mass. Furthermore, W C3 is preferably 1-20% by mass, more preferably 2-10% by mass. More specifically, when satisfying the relationship WC2>WC3≧WC1, the blending amounts of the inorganic fillers are preferably 1-20% by mass, more preferably 5-10% by mass. Furthermore, WC2 is preferably 10-60% by mass, more preferably 20-50% by mass. Furthermore, WC3 is preferably 1-30% by mass, more preferably 5-20% by mass.

[0032] The blending ratio of the total (C) inorganic filler is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, based on the solid content of the curable resin composition.

[0033] (C) The shape of the inorganic filler is not particularly limited, and examples thereof include spherical, needle-like, plate-like, scaly, hollow, irregular, hexagonal, cubic, and flake-like. From the perspective of high incorporation of the inorganic filler, a spherical shape is preferred.

[0034] Furthermore, in the present invention, by maintaining a predetermined relationship between the sizes of the three inorganic fillers, low CTE, abrasiveness, chemical resistance, and resistance to penetration during printing can be further enhanced. Specifically, the average particle sizes of (C1) silicon dioxide, (C2) calcium carbonate, and (C3) barium sulfate, expressed as RC1 (μm), RC2 (μm), and RC3 (μm), respectively, relative to the solids content of the curable resin composition, preferably satisfy the following relationship: R C1>R C2>R C3, or R C2>R C1>R C3. The average particle size refers not only to the primary particle size but also to the average particle size (d50) of secondary particles (agglomerates). This is the volume-based d50 value measured by laser diffraction. Examples of random particle size distribution analyzers used in laser diffraction include the Microtrac MT3300EXII manufactured by Nikkiso Co., Ltd. Furthermore, the average particle size of the inorganic filler refers to the value measured as described above on the powder before preparing (preliminary stirring and kneading) the curable resin composition.

[0035] More specifically, the average particle size (R C1) of silicon dioxide (C1) is preferably 1-50 μm, more preferably 3-10 μm. Furthermore, the average particle size (R C2) of calcium carbonate (C2) is preferably 0.5-20 μm, more preferably 1-10 μm. Furthermore, the average particle size (R C3) of barium sulfate (C3) is preferably 0.05-0.5 μm, more preferably 0.1-0.3 μm. When the three inorganic fillers of silicon dioxide, calcium carbonate, and barium sulfate are blended to satisfy the aforementioned relationship, the barium sulfate can enter between the silicon dioxide and calcium carbonate due to the specific size range of the three inorganic fillers, thereby improving the filling capacity.

[0036] The curable resin composition of the present invention may contain compounds other than the three aforementioned inorganic fillers (C), and may further contain non-metallic fillers such as silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, titanium oxide, mica, talc, and organic bentonite, and metal fillers such as copper, gold, silver, palladium, silicon, alloys, and ferrites. [Other ingredients]

[0037] The curable resin composition of the present invention may contain, as a curing component, a curable resin other than the aforementioned epoxy resin. Examples of the curable resin include isocyanate compounds, blocked isocyanate compounds, amino resins, carbodiimide resins, cyclocarbonate compounds, oxetane compounds, episulfide resins, urea resins, melamine resins and other triazine ring-containing resins, unsaturated polyester resins, maleimide resins such as bismaleimide compounds, polyurethane resins, diallyl phthalate resins, benzophenone resins, polyimide resins, polyamidoimide resins, benzocyclobutene resins, novolac-type cyanate resins, bisphenol A-type cyanate resins, bisphenol E-type cyanate resins, tetramethylbisphenol F-type cyanate resins and other bisphenol-type cyanate resins, silicone resins, and other commonly used cyanate resins. These resins may be used alone or in combination of two or more.

[0038] Furthermore, the curable resin composition of the present invention may also contain a silane coupling agent. The addition of the silane coupling agent can improve the adhesion between the inorganic filler and the epoxy resin and suppress cracking in the cured product.

[0039] Examples of silane coupling agents include epoxy silane, vinyl silane, imidazole silane, mercapto silane, methacryloxy silane, amino silane, styryl silane, isocyanate silane, sulfide silane, and urea silane. Silane coupling agents can also be incorporated by using inorganic fillers that have been surface-treated with a silane coupling agent.

[0040] When the curable resin composition of the present invention contains a silane coupling agent, the blending ratio of the silane coupling agent is preferably 0.05 to 2.5 parts by mass per 100 parts by mass of the inorganic filler, from the viewpoint of achieving both adhesion between the (C) inorganic filler and the (A) epoxy resin and defoaming properties.

[0041] The curable resin composition of the present invention may also contain other thiazolium compounds having a thiazolium ring, obtained by reacting a phenolic compound, formalin, and a primary amine, as needed. The inclusion of the thiazolium compound facilitates roughening of the cured product using, for example, a potassium permanganate aqueous solution during electroless plating after the curable resin composition, which has been filled into the holes of a printed circuit board, has been cured, thereby enhancing the peel strength from the plated layer.

[0042] Furthermore, conventional colorants such as phthalocyanine blue, phthalocyanine green, disazo yellow, titanium oxide, carbon black, and naphthalene black used in conventional screen printing resist inks may also be added.

[0043] Conventional thermal polymerization inhibitors such as hydroquinone, hydroquinone monomethyl ether, tertiary butylcatechol, pyrogallol, and phenothioate may be added to enhance storage stability. Conventional thickeners and thixotropic agents such as clay, kaolin, organobentonite, and microcrystalline kaolinite may also be added to adjust viscosity. Furthermore, conventional additives such as silicone-based, fluorine-based, and polymer-based defoamers, leveling agents, and adhesion-imparting agents such as imidazole-based, thiazole-based, and triazole-based agents may be incorporated. Organobentonite is particularly preferred because it creates a protruding state that facilitates polishing and removal of protruding portions from the pore surface, resulting in excellent polishing properties. Conventional colorants such as phthalocyanine blue, phthalocyanine green, iodine green, disazo yellow, crystal violet, titanium oxide, carbon black, and naphthalene black may also be incorporated.

[0044] When the curable resin composition of the present invention primarily comprises a liquid epoxy resin as the epoxy resin (A), a diluent solvent is not necessarily required. However, a diluent solvent may be added to adjust the viscosity of the curable resin composition to the extent that voids are not generated.

[0045] Examples of the diluent solvent include ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as methyl celulose, butyl celulose, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and triethylene glycol monoethyl ether; esters such as ethyl acetate, butyl acetate, and acetates of the above glycol ethers; alcohols such as ethanol, propanol, ethylene glycol, and propylene glycol; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, naphtha, hydrogenated naphtha, and solvent naphtha. [Applications of Curable Resin Compositions]

[0046] The curable resin composition of the present invention can be used generally in a wide range of applications, but is preferably used to form a cured film for printed wiring boards, more preferably to form a permanent protective film, and even more preferably to be used as a solder resist, interlayer insulating layer, coverlay, or hole filling filler. Among these applications, it is particularly preferably used as a hole filling filler, specifically as a hole filling filler for through-holes such as through-holes and recesses in printed wiring boards.

[0047] When the curable resin composition is used as a filler for hole filling, the filler can be applied to, for example, through-holes or bottomed recesses in multilayer printed circuit boards using conventional patterning methods such as screen printing, roll coating, die coating, and vacuum printing. The inner diameter of the hole or recess filled with the curable resin composition is not particularly limited, but for package substrates such as IC substrates, server substrates, and automotive substrates, it is preferably 0.05 to 0.8 mm, and the depth is 0.4 to 10 mm. In this case, it is preferably completely filled until the curable resin composition slightly protrudes from the hole or recess.

[0048] Therefore, the viscosity of the curable resin composition of the present invention at 25±1°C is preferably in the range of 100 to 1000 dPa·s, more preferably 200 to 800 dPa·s, and particularly preferably 200 to 600 dPa·s. This range facilitates filling of pores, and effectively fills recessed portions and through-holes without causing voids. The viscosity herein refers to the viscosity measurement method performed in accordance with JIS K8803:2011-10, Cone-Plate Viscometer, using a cone-plate viscometer (TV-33H, manufactured by Toki Sangyo Co., Ltd., rotor 3° x R 9.7), at 25°C, a rotor speed of 5 rpm, and 30 seconds.

[0049] By heating a multilayer printed circuit board with holes or recesses filled with a curable resin composition at, for example, 80-160°C for approximately 30-180 minutes, the curable resin composition is cured to form a cured product. To facilitate removal of unwanted portions of the cured product protruding from the substrate surface after hole filling by physical polishing, the curing of the curable resin composition can be performed in two stages. Specifically, the curable resin composition can be preliminarily cured at a lower temperature before undergoing the final curing (complete curing). Preliminary curing conditions are preferably heating at 80-110°C for approximately 30-180 minutes. The preliminarily cured product has a lower hardness, making it easier to remove unwanted portions protruding from the substrate surface by physical polishing, resulting in a flat surface. The final curing is then performed by heating. Preliminary curing conditions are preferably heating at 130-180°C for approximately 30-180 minutes.

[0050] Curing, both during preliminary curing and final curing, can be performed using a hot air circulation drying oven, IR oven, hot plate, or convection oven (using a heat source utilizing steam to heat the air, allowing the hot air within the dryer to countercurrently contact the object being cured, or blowing the hot air through a nozzle onto the object being cured). Hot air circulation drying ovens are particularly preferred. Due to their low expansion properties, the cured object exhibits minimal expansion and contraction, resulting in a final cured object with excellent dimensional stability, low hygroscopicity, adhesion, and electrical insulation. Furthermore, the hardness of the preliminary cured object can be controlled by varying the heating time and temperature during preliminary curing.

[0051] After curing the curable resin composition in the above manner, the surface of the printed circuit board is flattened by removing unnecessary portions of the cured product protruding from the surface using conventional physical polishing methods. The wiring layer on the surface is then patterned into a predetermined pattern to form a predetermined circuit pattern. Alternatively, if desired, the surface of the cured product can be roughened using a potassium permanganate aqueous solution, followed by electroless plating or other methods to form a wiring layer on the cured product.

[0052] As one embodiment of the present invention, an embodiment of a printed wiring board including a multilayer printed wiring board in which a curable resin composition is used as a filler for filling through holes or recessed portions will be described with reference to the drawings.

[0053] First, a method for filling holes, such as through-holes, on a typical printed circuit board using the curable resin composition of the present invention will be described with reference to the accompanying drawings. Figures 1a to 1d are schematic diagrams illustrating the steps for filling through-holes (vias) on a printed circuit board using a curable resin composition. First, a printed circuit board 1 (Figure 1a) having a through-hole 5a with a plated inner wall surface is prepared. The printed wiring board 1 shown in Figure 1a can be preferably used by forming a through-hole using a drill or the like on the surface of an insulating layer 10 having a wiring layer 50 provided thereon. Electroless or electrolytic plating is then applied to the inner wall of the through-hole 5a and the surface of the wiring layer.

[0054] Next, the through-hole 5a is filled with a curable resin composition. Examples of filling methods include placing a mask with openings in the through-hole portion on the printed circuit board and applying the curable resin composition through the mask using a printing method or other methods, or filling the through-hole with the curable resin composition using a dot printing method or other methods. The curable resin composition filled by heating the printed circuit board 1 is then pre-cured (Figure 1b). Pre-curing generally refers to a state where the epoxy resin reaction rate reaches 80% to 97%. Pre-curing is preferably performed by pre-curing the curable resin composition at a relatively low temperature, followed by a secondary pre-curing at a higher temperature than the primary curing temperature. This pre-curing allows for easy removal of unwanted portions of the pre-cured material 6 protruding from the surface of the printed wiring board 1 by physical polishing, as described later, resulting in a flat surface. Furthermore, the hardness of the pre-cured material 6 can be adjusted by varying the heating time and temperature during the pre-curing.

[0055] Next, the unnecessary portion of the pre-hardened material 6 protruding from the surface of the through hole 5a is removed by grinding and then flattened (FIG. 1c). Grinding can be suitably performed by a belt grinder or polishing.

[0056] Next, the surface of the printed circuit board 1 is pre-treated by polishing or roughening as needed to form the outer insulating layer 7 (Figure 1d). This pre-treatment forms a roughened surface with an excellent anchoring effect on the surface of the wiring layer 50, thereby achieving excellent adhesion to the outer insulating layer 7. Depending on the subsequent treatment, the outer insulating layer 7 can be a solder mask (not shown), an insulating resin layer (not shown), or a protective mask (not shown), etc., and can be formed by coating various conventional thermosetting resin compositions or curable resin compositions such as photocurable and thermosetting resin compositions, or by laminating dry films or prepreg sheets. If a fine pattern is to be formed on the outer insulating layer 7, it is preferably to use photocurable and thermosetting resin compositions or such dry films.

[0057] Afterwards, the printed circuit board 1 is heated and fully cured (finally cured) to form the outer insulating layer 7. Furthermore, when a light-curing or thermosetting resin composition is used to form the outer insulating layer 7, it is dried (temporarily cured) and exposed to light in a conventional manner before fully curing. Furthermore, when a double-sided substrate as shown in FIG. 1(a) is used as the printed circuit board 1, a multilayer printed circuit board can be formed by alternately forming the wiring layer 50 and the insulating layer 10 using a more conventional method, and forming through-holes 5a as needed.

[0058] Figures 2a and 2b are schematic cross-sectional views showing an example of a partial manufacturing process for a printed circuit board according to the present invention. First, a printed circuit board 2 is prepared in which copper foil 8 is laminated on both sides of a substrate 9. Electroless plating and electroplating are performed on the surface of the substrate 9 to impart thickness, and a plated film (not shown) may also be formed on the surface of the substrate 9. Copper plating is preferably used as the electroless plating and electroplating. Subsequently, a hole is drilled using a drill bit or the like to form a through hole 5b as shown in Figure 2a. As the substrate 9, a glass epoxy substrate, a resin substrate such as a polyimide substrate, a bismaleimide-triazine resin substrate, or a fluororesin substrate, or a copper foil substrate of these resin substrates, a ceramic substrate, or a metal substrate can be used.

[0059] The curable resin composition of the present invention is filled into the through-hole 5b formed in the printed circuit board 2. Specifically, a mask (not shown) with an opening corresponding to the diameter of the through-hole 5b is placed on the printed circuit board 2. The through-hole 5b can be easily filled by applying the mask by printing or dotting. Next, the curable resin composition is cured by heating or other methods to form a preliminary cured product 6. Similarly to the above, the unnecessary portion of the preliminary cured product 6 protruding from the through-hole 5b is polished to remove and flatten the surface (Figure 2b). Polishing can be performed using a belt sander or polishing.

[0060] A plating film (not shown) can be further formed on the surface of the printed circuit board 2 where the through-holes 5b are being filled. An etching resist is then formed, and the non-resist-formed areas are etched. The etching resist can then be stripped off to form a wiring layer (not shown). [Example]

[0061] Next, examples are given to further illustrate the present invention, but the present invention is not limited to these examples. In addition, the following "parts" and "%" are based on mass unless otherwise specified. <Preparation of Curable Resin Composition>

[0062] The various components shown in Table 1 below were blended in the proportions (parts by mass) shown in each table and mixed in a blender to prepare the curable resin compositions of Examples 1 to 7 and Comparative Examples 1 to 3.

[0063] In addition, *1 to *10 in Table 1 represent the following components. *1: Bisphenol-type epoxy resin (NIPPON STEEL Chemical & Material Co., Ltd., ZX-1059) *2: Phenol novolac type epoxy resin (Dow Chemical Co., DEN 431) *3: Amine-type epoxy resin (manufactured by ADEKA Co., EP-3950S) *4: Imidazole hardener (manufactured by Shikoku Kasei Holdings Co., 2P4MHZ) *5: Novolac-type phenolic resin (manufactured by MEIWAKASEI., LTD., HF-1M) *6: Imidazole hardener (manufactured by Shikoku Kasei Holdings Co., 2MZA-PW) *7: Silicon dioxide (Denka Company Limited, FB7SDC, average particle size 6.0 μm) *8: Silicon dioxide (ADMATECHS COMPANY LIMITED, SO-C2, average particle size 0.5 μm) *9: Calcium carbonate (Bihoku Powder Industry Co., Ltd., SOFTON 1500, average particle size 1.5 μm) *10: Calcium carbonate (Maruo Calcium Co., Ltd., SUPER SS, average particle size 2.2 μm) *11: Calcium carbonate (Maruo Calcium Co., Ltd., CALTEX 5S, average particle size 0.6 μm) *12: Barium sulfate (SAKAI CHEMICAL INDUSTRY CO., LTD., B-33, average particle size 0.3 μm) *13: Barium sulfate (SAKAI CHEMICAL INDUSTRY CO., LTD., B-200, average particle size 0.3 μm) <Evaluation of penetration resistance during printing>

[0064] The permeation resistance of each of the curable resin compositions of Examples and Comparative Examples was evaluated as follows.

[0065] The curable resin compositions of each Example and Comparative Example were screen-printed onto one side of a glass epoxy substrate (FR-4 substrate: 150 mm x 290 mm x 1.6 mm thick, with a conductive layer formed by plating, a through-hole diameter of 0.15 mm (after plating), and a pitch of 1 mm). Using a semi-automatic printer (SERIA CORPORATION), the curable resin compositions were applied to the through-holes using the following printing conditions. After filling, the substrate was placed on a substrate rack and heated in a hot air circulation drying oven at 110°C for 60 minutes, followed by heating at 150°C for 60 minutes to cure the curable resin composition. Evaluation substrates were then prepared. (Printing conditions) Scraper: Scraper thickness 20mm, flat scraper (hardness 70°) Screen printing plate: PET200mesh bias plate, 800μm aperture (dot pattern), emulsion thickness 20μm Printing pressure: 50kg Scraper speed: 10mm / s Scraper angle: 95° (inclination 5°)

[0066] The printed surface (squeegee contact side) of the evaluation substrate prepared as described above was observed at 50-100x magnification using an optical microscope (VHX-6000, manufactured by Keynes Corporation). The ink diameter in the through-holes was measured. The ink diameter (800 μm) was subtracted from the measured ink diameter to calculate how many μm larger the ink diameter was than the screen printing plate's aperture diameter. Based on the calculated results, the penetration resistance was evaluated according to the following criteria. ◎: less than 50μm ○: 50 or more but less than 150 μm △: 150μm or more and less than 300μm × :300μm or more The evaluation results are shown in Table 1 below. <Ink Notch Evaluation>

[0067] The through-hole surfaces and cross-sections on the printed side (squeegee contact side) of the evaluation substrate used in the "Printing Penetration Resistance Evaluation" section above were observed using an optical microscope (VHX-6000, manufactured by Keynes Co., Ltd.). Observe 100 random through-hole locations and count any ink depressions. Ink depressions were evaluated using the following criteria. Ink depression refers to the phenomenon where the surface of the cured material filling the through-hole is sunken below the copper surface of the through-hole. ○: No depression △: 1~10 places ╳: More than 10 places The evaluation results are shown in Table 1 below. <Grinding Performance Evaluation>

[0068] The polishing properties of the curable compositions of Examples and Comparative Examples were evaluated as follows.

[0069] Each curable resin composition was screen-printed onto a 250mm x 280mm copper-clad substrate, resulting in a solid coating area of ​​95mm x 145mm. The cured ink film thickness reached 40-50μm. The curable resin composition was then heated in a hot air circulation drying oven at 150°C for 60 minutes to cure, forming a cured film. The thickness of the cured film formed as described above was measured using a film thickness meter (Kett Electric Laboratory Co. Ltd., LZ-990) and this was designated as the initial film thickness. Next, the surface of the cured film was polished once using a two-axis polishing machine equivalent to High Cut Buff #320. The thickness of the cured film after polishing was measured in the same manner as above and designated as the post-polishing film thickness. The post-polishing cured film ratio was calculated from the measured results using the following formula. Resin film thickness ratio after polishing (%) = film thickness after polishing / initial film thickness × 100 The polishing properties were evaluated based on the obtained resin film thickness ratio after polishing according to the following criteria. ○: less than 60% △: greater than 60% and less than 75% ╳: greater than 75% The evaluation results are shown in Table 1 below. <Chemical Resistance Evaluation>

[0070] The chemical resistance of the curable resin composition of each Example and Comparative Example was evaluated. The evaluation was performed as follows.

[0071] The printed surface of the evaluation substrate used for the above-mentioned printing penetration evaluation was polished. The areas where the polished resin protruded from the substrate surface were then plated using a commercial electroless tin plating bath at a tin thickness of 1 ± 0.2 μm. After tin plating, 100 random locations around the through-holes were observed using an optical microscope to identify any defective through-holes that showed whitening of the curing resin or areas where the plating had not adhered. Chemical resistance was evaluated according to the following criteria. ◎:0 places ○: 1 place △: 2~5 places ╳: 6 or more The evaluation results are shown in Table 1 below.

[0072] [Table 1] composition Example Comparative Example 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 epoxy resin Bisphenol epoxy resin*1 70 70 60 70 70 70 80 70 70 70 70 70 70 70 70 Novolac epoxy resin*2 - - 20 - - - 20 - - - - - - - - Amine type epoxy resin*3 30 30 20 30 30 30 - 30 30 30 30 30 30 30 30 Epoxy resin hardener Imidazole hardener*4 10 10 10 10 10 10 - - 10 10 10 10 10 10 10 Phenol novolac resin*5 - - - - - - 30 30 - - - - - - - Imidazole hardener*6 - - - - - - 4 4 - - - - - - - Inorganic fillers Silicon dioxide*7 80 125 125 - - 125 160 170 30 40 20 125 115 150 - Silicon dioxide*8 - - - 20 125 - - - - - - - - - Calcium carbonate*9 30 30 30 - - 10 30 50 - 20 40 50 - 145 Calcium carbonate*10 - - - 115 30 - - - 115 - - - Calcium carbonate*11 - - - - - - - - - - - 30 - - - Barium sulfate*12 10 10 10 30 - 30 10 15 20 60 60 - - 15 20 Barium sulfate*13 - - - - 10 - - - - 10 - - - Inorganic filler content (mass %) 52 60 60 60 60 60 60 64 60 52 52 60 60 60 60 Evaluate Resistance to penetration during printing ○ ◎ ◎ ○ ○ ◎ ○ ◎ △ ○ ○ ◎ ╳ △ △ Ink notches on the TH surface ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ △ △ ╳ △ △ Abrasiveness ○ ○ ○ ◎ ○ △ ○ ○ ○ △ ○ ○ △ ╳ ◎ Chemical resistance ○ ◎ ◎ ○ ○ ○ ○ ○ ○ ○ ○ ◎ ○ ◎ ╳

[0073] As is apparent from the evaluation results in Table 1, the curable resin compositions containing three inorganic fillers: silicon dioxide, calcium carbonate, and barium sulfate (Examples 1-12) exhibit excellent abrasiveness, chemical resistance, and resistance to contamination during printing. On the other hand, it was found that the curable resin composition containing both silica and calcium carbonate as inorganic fillers (Comparative Example 1), the curable resin composition containing both silica and barium sulfate (Comparative Example 2), and the curable resin composition containing both calcium carbonate and barium sulfate (Comparative Example 3) failed to achieve uniform improvements in abrasiveness, chemical resistance, and penetration resistance during printing.

[0074] Furthermore, it was found that when the contents of the silicon dioxide (C1), calcium carbonate (C2), and barium sulfate (C3) in the curable resin composition, calculated on a solids basis, were WC1 (mass %), WC2 (mass %), and WC3 (mass %), respectively, curable resin compositions satisfying the relationship WC1 ≧ WC2 > WC3 (Examples 1-3, 5-8, and 12) showed significantly improved chemical resistance and resistance to penetration during printing. Furthermore, it was found that curable resin compositions satisfying the relationship WC2 > WC3 ≧ WC1 exhibited even better polishability.

[0075] Furthermore, when the average particle sizes of the aforementioned silicon dioxide (C1), calcium carbonate (C2), and barium sulfate (C3) are denoted as RC1 (μm), RC2 (μm), and RC3 (μm), respectively, a curable resin composition (Example 2) satisfying the relationship RC1>RC2>RC3 is compared with a curable resin composition (Example 12) satisfying the relationship RC2>RC1>RC3. It is found that ink recesses on the through-hole surface are improved, and the plate release properties during application of the curable resin composition are enhanced.

[0076] 1: Printed Circuit Board 2: Printed Circuit Board 5a: Through hole 5b: Through hole 6: Prepare the hardened material 7: Outer insulation layer 8: Copper foil 9:Substrate 10: Insulation layer 50: Wiring layer

Claims

1. A curable resin composition, characterized by comprising: (A) an epoxy resin; (B) an epoxy resin curing agent; and (C) an inorganic filler, wherein, The aforementioned (A) epoxy resin comprises at least two of (A1) bisphenol type epoxy resin and (A2) amine type epoxy resin. Relative to 100 parts by mass of the total solids content of the (A) epoxy resin, the (A1) bisphenol type epoxy resin, converted to solids, comprises 10 to 80 parts by mass, and the (A2) amine type epoxy resin, converted to solids, comprises 10 to 50 parts by mass. The aforementioned (C) inorganic filler comprises at least three of (C1) silicon dioxide, (C2) calcium carbonate, and (C3) barium sulfate. When the contents of the aforementioned (C1) silicon dioxide, (C2) calcium carbonate, and (C3) barium sulfate relative to the aforementioned curing resin composition are converted to solids content as WC1 (mass%), WC2 (mass%), and WC3 (mass%), respectively, the following relationship is satisfied: WC2 > WC3 ≥ WC1.

2. The curable resin composition as claimed in claim 1, wherein the aforementioned (C) inorganic filler comprises 30 to 80% by mass of the aforementioned curable resin composition in terms of solid content.

3. The curable resin composition of claim 1, wherein the average particle sizes of the aforementioned (C1) silicon dioxide, (C2) calcium carbonate and (C3) barium sulfate are respectively RC1 (μm), RC2 (μm) and RC3 (μm), satisfy the following relationship: RC1 > RC2 > RC3 or RC2 > RC1 > RC3.

4. The curable resin composition as claimed in claim 1, wherein, relative to 100 parts by weight of the total solids content of the (A) epoxy resin, the (A1) bisphenol type epoxy resin is included in a proportion of 60 to 80 parts by weight of solids content, and the (A2) amine type epoxy resin is included in a proportion of 20 to 40 parts by weight of solids content.

5. A curable resin composition as claimed in any of claims 1 to 4, used as a filler for through holes or recesses in a printed wiring board.

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