Curable resin composition and cured product, and print wiring board and production method of the same

Abstract

To provide a curable resin composition enabling obtaining a cured product having a low thermal expansion coefficient and excellent in suppression of warpage of a substrate and polishing properties.SOLUTION: A thermal curable resin composition as a curable resin composition containing a solid epoxy resin, an inorganic filler, a curing agent and an organic solvent is such that: the content of the organic solvent is 5 mass% or more and 20 mass% or less based on the total amount of the curable resin composition; the organic solvent includes a first organic solvent having steam pressure at 25°C of 0.01 mmHg or more and 4.00 mmHg or less; the content of the first organic solvent is 30 mass% or more and 100 mass% or less based on the total amount of the organic solvent; and the content of the inorganic filler is 70 mass% or more in terms of solid content based on the total amount of the curable resin composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a curable resin composition, a cured product, a printed wiring board, and a method for producing the same. [Background technology]

[0002] Electronic devices such as smartphones and personal computers use printed wiring boards equipped with electronic elements having various functions. Such printed wiring boards have circuits formed on an insulating substrate to electrically connect the electronic elements. Generally, such circuits are made of copper and have a thickness of, for example, 18 to 35 μm. As electronic devices become smaller, these circuits are being designed to be thinner.

[0003] In order to prevent such circuits from shorting out, it is common practice to apply an insulating material called solder resist ink to the surface of the printed wiring board to form an insulating layer.

[0004] There is also a form in which multiple printed wiring boards are stacked on top of each other, and in this form, an adhesive layer called a prepreg is generally stacked to bond the wiring boards together while maintaining insulation between the boards.

[0005] Printed wiring boards used in communication servers, electric vehicles, and other devices that are subject to high currents or voltages can have circuits with thicknesses exceeding 50 μm. In such cases, the difference in level between the surface of the circuit on the printed wiring board and the surface of the printed wiring board's base material becomes significant, making it difficult to fill the gaps between the circuits when a prepreg layer is laminated on the surface or edges of the circuit. Furthermore, when applying solder resist ink, although it is possible to fill the gaps between the circuits without gaps, it is difficult to achieve a flat surface for the solder resist layer. Another problem is that the difference in thermal expansion between copper and solder resist can lead to cracks in the solder resist.

[0006] Therefore, in order to flatten the surface of the insulating layer, there is a method in which liquid ink is filled between the circuits, and after flattening the board, prepreg is laminated or a solder resist layer is formed.

[0007] Patent Document 1 discloses a thermosetting resin composition containing a polyfunctional cyanate ester resin composition as an essential component, and proposes a method for producing an ultrafine wire printed wiring board in which a thermosetting resin composition layer is formed on a printed wiring board on which an ultrafine wire circuit with a conductor width of 50 μm or less is formed. Patent Document 2 discloses a curable resin composition containing an epoxy acrylate resin, an acrylic monomer, an epoxy resin, a photoinitiator, an epoxy resin curing agent, silica, an antifoaming agent, and a leveling agent, and proposes a production method in which the curable resin composition is applied to a printed wiring board under reduced pressure. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-356202 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-078595 Summary of the Invention [Problem to be solved by the invention]

[0009] However, when these curable resin compositions are used as gap-filling inks for printed wiring boards, there is room for improvement in terms of the thermal expansion coefficient and cracking. If the thermal expansion coefficient of the cured product obtained from the gap-filling ink for printed wiring boards is higher than that of surrounding materials such as wiring and prepregs, the difference in thermal expansion coefficients can cause cracking, delamination, and warping of the board. Therefore, the thermal expansion coefficient of the cured product needs to be matched to that of the surrounding materials.

[0010] Furthermore, if ink is printed on one side of a printed wiring board and cured, the board may warp, making it difficult to print on the back side. On the other hand, if silica is heavily loaded as an inorganic filler to reduce the thermal expansion coefficient, the polishability of the cured product deteriorates. Therefore, achieving both high inorganic filler loading and polishability is a challenge.

[0011] Therefore, an object of the present invention is to provide a curable resin composition that has a low thermal expansion coefficient and can give a cured product that suppresses warping of a substrate and has excellent polishability. Another object of the present invention is to provide a method for producing a printed wiring board, which includes a step of facilitating the polishing of a cured film obtained from the curable resin composition and flattening the surface. [Means for solving the problem]

[0012] As a result of intensive research aimed at achieving the above object, the present inventors have found that the above problem can be solved by adjusting the content of the organic solvent and the content of the inorganic filler in a curable resin composition containing a solid epoxy resin, an inorganic filler, a curing agent, and an organic solvent to fall within specific numerical ranges, and have thus completed the present invention.

[0013] That is, according to the present invention, the following inventions are provided. [1] A curable resin composition comprising a solid epoxy resin, an inorganic filler, a curing agent, and an organic solvent, the content of the organic solvent is 5% by mass or more and 20% by mass or less with respect to the total amount of the curable resin composition, the organic solvent includes a first organic solvent having a vapor pressure at 25°C of 0.01 mmHg or more and 4.00 mmHg or less, the content of the first organic solvent is 30% by mass or more and 100% by mass or less based on the total amount of the organic solvents, A curable resin composition, wherein the content of the inorganic filler is 70 mass % or more, calculated as solid content, based on the total amount of the curable resin composition. [2] The curable resin composition according to [1], further comprising a liquid epoxy resin. [3] The curable resin composition according to [1] or [2], wherein the vapor pressure of the first organic solvent at 25°C is 0.01 mmHg or more and 3.00 mmHg or less. [4] The curable resin composition according to any one of [1] to [3], wherein the first organic solvent is at least one selected from the group consisting of diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether, dipropylene glycol methyl ether acetate, and diethylene glycol monoethyl ether. [5] The curable resin composition according to any one of [1] to [4], which has a viscosity measured at 25°C of 30 dPa·s or more and 500 dPa·s or less. [6] A cured product obtained by curing the curable resin composition according to any one of [1] to [5]. [7] The cured product according to [6], having a thermal expansion coefficient of 25 ppm / °C or less. [8] A printed wiring board comprising a circuit board and the cured product according to [6] or [7] on the circuit board. [9] The printed wiring board according to [8], wherein the thickness of the wiring of the circuit board is 35 μm or more and 500 μm or less.

[10] A step of applying the curable resin composition according to any one of [1] to [5] onto a circuit board; semi-curing the curable resin composition to form a semi-cured film; polishing the semi-cured film A method for manufacturing a printed wiring board, comprising:

[11] The method for manufacturing a printed wiring board according to

[10] , wherein the thickness of the wiring on the circuit board is 35 μm or more and 500 μm or less. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a curable resin composition that has a low thermal expansion coefficient and that can give a cured product that suppresses warpage of a substrate and has excellent polishability. In particular, the curable resin composition of the present invention has excellent polishability when cured, particularly at low temperatures. Therefore, the curable resin composition of the present invention can be suitably used as a gap-filling ink for printed wiring boards. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Curable resin composition] The curable resin composition of the present invention contains at least a solid epoxy resin, an inorganic filler, a curing agent, and an organic solvent, and may further contain a liquid epoxy resin and other components.

[0016] Each component constituting the curable resin composition of the present invention will be described below. In this specification, "solid" means a solid state at 40°C. Furthermore, "liquid" means a liquid state or semi-liquid state (paste state) that has fluidity at 40°C.

[0017] (solid epoxy resin) As the solid epoxy resin, any known and commonly used compound having one or more epoxy groups that is in a solid state at 40°C can be used without particular limitation. Examples include bifunctional epoxy compounds having two epoxy groups in the molecule and polyfunctional epoxy compounds having three or more epoxy groups in the molecule. A hydrogenated solid bifunctional epoxy compound may also be used. These solid epoxy resins may be used alone or in combination of two or more.

[0018] Examples of commercially available solid epoxy resins include naphthalene-type epoxy resins such as HP-4700 (trade name, naphthalene-type epoxy resin) manufactured by DIC Corporation, EXA4700 (trade name, tetrafunctional naphthalene-type epoxy resin) manufactured by DIC Corporation, and NC-7000 (trade name, naphthalene skeleton-containing multifunctional solid epoxy resin) manufactured by Nippon Kayaku Co., Ltd.; epoxidized products of condensation products of phenols and aromatic aldehydes having a phenolic hydroxyl group (trisphenol-type epoxy resins) such as EPPN-502H (trade name, trisphenol epoxy resin) manufactured by Nippon Kayaku Co., Ltd.; dicyclopentadiene-type epoxy resins such as Epiclon HP-7200H (trade name, dicyclopentadiene skeleton-containing multifunctional solid epoxy resin) manufactured by DIC Corporation, and XD-1000 (trade name) manufactured by Nippon Kayaku Co., Ltd. Examples of suitable epoxy resins include ethylenediamine aralkyl epoxy resins; biphenyl aralkyl epoxy resins such as NC-3000H (trade name, biphenyl skeleton-containing polyfunctional solid epoxy resin) manufactured by Nippon Kayaku Co., Ltd.; biphenyl / phenol novolac epoxy resins such as NC-3000L (trade name) manufactured by Nippon Kayaku Co., Ltd.; novolac epoxy resins such as Epiclon N660 and Epiclon N690 manufactured by DIC Corporation and EOCN-104S (all trade names) manufactured by Nippon Kayaku Co., Ltd.; biphenyl epoxy resins such as YX4000 (trade name) manufactured by Mitsubishi Chemical Corporation; phosphorus-containing epoxy resins such as TX0712 (trade name) manufactured by Nippon Steel Chemical & Material Co., Ltd.; and tris(2,3-epoxypropyl) isocyanurates such as TEPIC (trade name) manufactured by Nissan Chemical Industries, Ltd.

[0019] The content of the solid epoxy resin is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 18% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less, based on the total amount of the curable resin composition. When the content of the solid epoxy resin is within the above range, a tack-free semi-cured film is formed, and the polishability is good.

[0020] The content of the solid epoxy resin is preferably 1% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 18% by mass or less, and even more preferably 10% by mass or more and 15% by mass or less, calculated as solid content, relative to the entire curable resin composition. When the content of the solid epoxy resin is within the above range, a high amount of inorganic filler can be added, and the thermal expansion coefficient can be reduced.

[0021] (liquid epoxy resin) The liquid epoxy resin may be any known or commonly used compound having one or more epoxy groups that is in a liquid state with fluidity at 40°C, but compounds having two or more epoxy groups are preferred. Examples include monoepoxy compounds such as butyl glycidyl ether, phenyl glycidyl ether, and glycidyl (meth)acrylate, bisphenol A epoxy resins, bisphenol S epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, alicyclic epoxy resins, trimethylolpropane polyglycidyl ether, phenyl-1,3-diglycidyl ether, biphenyl-4,4'-diglycidyl ether, 1,6-hexanediol diglycidyl ether, diglycidyl ether of ethylene glycol or propylene glycol, sorbitol polyglycidyl ether, tris(2,3-epoxypropyl)isocyanurate, and triglycidyl tris(2-hydroxyethyl)isocyanurate, all of which have two or more epoxy groups per molecule. These can be used alone or in combination of two or more types depending on the required properties. Among these, from the viewpoint of making the effects of the present invention more pronounced, bisphenol A type epoxy resins and hydrogenated products thereof, bisphenol F type epoxy resins and hydrogenated products thereof, alicyclic epoxy resins, phenol novolac type epoxy resins, glycidylamine type epoxy resins, etc. can be preferably used, and known and commonly used liquid epoxy resins such as bisphenol A type epoxy resins and hydrogenated products thereof, bisphenol F type epoxy resins and hydrogenated products thereof can be particularly preferably used. These liquid epoxy resins can be used alone or in combination of two or more types.

[0022] Examples of commercially available liquid epoxy resins include jER828, jER834, and jER872 (all trade names) manufactured by Mitsubishi Chemical Corporation; YD-127, YD-128, and YD-134 manufactured by Nippon Steel Chemical & Material Co., Ltd.; Araldite GY240, Araldite GY250, Araldite GY260, Araldite GY261, Araldite GY266, and Araldite GY2600 (all trade names) manufactured by Huntsman Japan Co., Ltd.; and DI Bisphenol A epoxy resins such as Epicron 840, Epicron 850, Epicron 860, Epicron 900-IM, Epicron EXA-4816, and Epicron EXA-4822 (all trade names) manufactured by C Corporation, and ELA-134 (trade name) manufactured by Sumitomo Chemical Co., Ltd.; hydrogenated bisphenol A epoxy resins such as ST-3000 (trade name) manufactured by Nippon Steel Chemical & Material Co., Ltd.; Epicron 830, Epicron 830-S, and Epicron 830-S manufactured by DIC Corporation. Examples of suitable epoxy resins include bisphenol F epoxy resins such as Piclon 835 and JER807 (both trade names) manufactured by Mitsubishi Chemical Corporation; hydrogenated bisphenol F epoxy resins such as YDF-170 and YDF-175 (both trade names) manufactured by Nippon Steel Chemical & Material Co., Ltd.; bisphenol A / bisphenol F epoxy resins such as ZX-1059 (trade name) manufactured by Nippon Steel Chemical & Material Co., Ltd.; alicyclic epoxy resins such as CELLOXIDE 2021 manufactured by Daicel Corporation and Araldite CY175 and CY179 (both trade names) manufactured by Asahi Kasei Epoxy Corporation; naphthalene epoxy resins such as Epiclon HP-4032 (trade name) manufactured by DIC Corporation; phenol novolac epoxy resins such as JER152 manufactured by Mitsubishi Chemical Corporation and Epiclon N-730 and N-740 (both trade names) manufactured by DIC Corporation; and glycidyl amine epoxy resins such as JER604 (trade name) manufactured by Mitsubishi Chemical Corporation.

[0023] When the curable resin composition contains a liquid epoxy resin, the content of the liquid epoxy resin is preferably 5 parts by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 40 parts by mass or less, and even more preferably 5 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the total of the solid epoxy resin and the liquid epoxy resin. When the content of the liquid epoxy resin is within the above numerical range, the coating film after drying is tack-free and has excellent flexibility, resulting in good polishability.

[0024] (inorganic filler) The inorganic filler relieves stress due to cure shrinkage, adjusts the thermal expansion coefficient, and increases the physical strength of the cured product. Known inorganic fillers used in general resin compositions can be used as the inorganic filler. Examples of inorganic fillers that can be used include non-metallic fillers and metallic fillers. Specific examples of non-metallic fillers include silica, barium sulfate, calcium carbonate, silicon nitride, aluminum nitride, boron nitride, alumina, magnesium oxide, aluminum hydroxide, magnesium hydroxide, titanium oxide, mica, talc, and organic bentonite. Specific examples of metallic fillers include copper, gold, silver, palladium, and silicone. Furthermore, a magnetic filler can also be used as the inorganic filler. Examples of the magnetic filler that can be used include non-conductive magnetic fillers and conductive magnetic fillers. Specific examples of non-conductive magnetic fillers include spinel ferrites, hexagonal ferrites, and garnet ferrites, while examples of conductive magnetic fillers include pure iron powder, Fe alloys, Ni alloys, and amorphous alloys. These inorganic fillers can be used alone or in combination of two or more.

[0025] Among these inorganic fillers, talc, silica, barium sulfate, and aluminum oxide, which have excellent low moisture absorption and low thermal expansion, are preferably used, with silica and talc being particularly preferred. Examples of silica include amorphous silica, non-crystalline silica, crystalline silica, synthetic silica, and hollow silica. Mixtures of these may also be used. Amorphous (fused) silica is particularly preferred. While there are no particular limitations on the talc, the smaller its average particle size, the better. It is preferably 15 μm or less, more preferably 5 μm or less, and even more preferably 2 μm or less. Examples of talc with a particle size of 15 μm or less include Fuji Talc Kogyo Co., Ltd. (trade names: "LMP100" and "LMP200"), and Matsumura Sangyo Co., Ltd. (trade name: "Hi Filler #5000PJ"), with "LMP100" being particularly preferred. Such talc may also be surface-treated to improve adhesion to resins. Such talc is commercially available, sold by Nippon Talc Co., Ltd., Fuji Talc Kogyo Co., Ltd., and other companies.

[0026] 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 flaky shapes. However, spherical shapes are preferred from the viewpoint of enabling a high content of inorganic filler.

[0027] The content of the inorganic filler, calculated as solid content, is 70% by mass or more and 95% by mass or less, preferably 75% by mass or more and 90% by mass or less, and more preferably 80% by mass or more and 90% by mass or less, based on the total amount of the curable resin composition. When the content of the inorganic filler is within the above range, the polishability and the thermal expansion coefficient are good.

[0028] (hardening agent) As the curing agent, well-known conventional curing agents for curing epoxy resins can be used. Examples of curing agents include amines, imidazoles, phenols, acid anhydrides, isocyanates, imidazole latent curing agents such as imidazole adducts, and polymers containing these functional groups. A plurality of these may be used as needed. Examples of acid anhydrides include phthalic anhydride, hexahydrophthalic anhydride, methylnadic anhydride, and benzophenone tetracarboxylic acid. Examples of isocyanates include tolylene diisocyanate and isophorone diisocyanate. These isocyanates may be masked with phenols or the like. These curing agents may be used alone or in combination.

[0029] Among the above-mentioned curing agents, amines and imidazoles are preferably used from the viewpoints of adhesion between the insulating parts and conductor wiring circuits of electronic components such as printed wiring boards, storage stability, and heat resistance. Preferred are adduct compounds of aliphatic polyamines such as alkylenediamines having 2 to 6 carbon atoms, polyalkylenepolyamines having 2 to 6 carbon atoms, and aromatic ring-containing aliphatic polyamines having 8 to 15 carbon atoms, or adduct compounds of alicyclic polyamines such as isophoronediamine and 1,3-bis(aminomethyl)cyclohexane, or mixtures of the above-mentioned adduct compounds of aliphatic polyamines and the above-mentioned adduct compounds of alicyclic polyamines.

[0030] The adduct compounds of the aliphatic polyamines are preferably those obtained by addition reaction of the aliphatic polyamines with aryl glycidyl ethers (particularly phenyl glycidyl ether or tolyl glycidyl ether) or alkyl glycidyl ethers, and the adduct compounds of the alicyclic polyamines are preferably those obtained by addition reaction of the alicyclic polyamines with n-butyl glycidyl ether, bisphenol A diglycidyl ether, or the like.

[0031] Examples of aliphatic polyamines include alkylenediamines having 2 to 6 carbon atoms, such as ethylenediamine and propylenediamine, polyalkylenepolyamines 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 xylylenediamine. Examples of commercially available modified aliphatic polyamines include FXE-1000 or FXR-1020, Fujicure FXR-1030, Fujicure FXR-1080, and FXR-1090M2 (all trade names, manufactured by Fuji Chemical Industry Co., Ltd.), Ancamine 2089K, Sanmaid P-117, Sanmaid X-4150, Ancamine 2422, Surwet R, Sanmaid TX-3000, and Sanmaid A-100 (all trade names, manufactured by Air Products Japan Co., Ltd.).

[0032] Examples of alicyclic polyamines include isophoronediamine, 1,3-bis(aminomethyl)cyclohexane, bis(4-aminocyclohexyl)methane, norbornenediamine, 1,2-diaminocyclohexane, and laromine. Commercially available modified alicyclic polyamines include, for example, Ancamine 1618, Ancamine 2074, Ancamine 2596, Ancamine 2199, Sanmaid IM-544, Sanmaid I-544, Ancamine 2075, Ancamine 2280, Ancamine 1934, and Ancamine 2228 (all trade names, manufactured by Air Products Japan Co., Ltd.), Daitoclar F-5197 and Daitoclar B-1616 (all trade names, manufactured by Daito Sangyo Co., Ltd.), Fujicure FXD-821 and Fujicure 4233 (all trade names, manufactured by Fuji Chemical Industry Co., Ltd.), jER Cure 113 (trade name, manufactured by Mitsubishi Chemical Corporation), and Laromin C-260 (trade name, manufactured by BASF Japan Co., Ltd.). Other examples of polyamine curing agents include EH-5015S (trade name, manufactured by ADEKA Corporation).

[0033] Imidazoles include, for example, reaction products of epoxy resins and imidazole, etc. Examples include 2-methylimidazole, 4-methyl-2-ethylimidazole, 2-phenylimidazole, 4-methyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-undecylimidazole. Commercially available imidazoles include imidazoles such as 2E4MZ, C11Z, C17Z, and 2PZ (all trade names, reaction products of epoxy resin and imidazole), 2MZ-A, 2E4MZ-A, and 2MZA-PW (all trade names, imidazole azine compounds), 2MZ-OK and 2PZ-OK (all trade names, imidazole isocyanurate salts), 2PHZ, and 2P4MHZ (all trade names, imidazole hydroxymethyl derivatives) (all manufactured by Shikoku Chemical Industry Co., Ltd.). Commercially available imidazole-type latent curing agents include, for example, Curesol P-0505 (trade name, manufactured by Shikoku Chemical Industry Co., Ltd.). Furthermore, preferred curing agents used in combination with imidazoles are modified aliphatic polyamines, polyamine-type curing agents, and imidazole-type latent curing agents.

[0034] Examples of the phenolic curing agent that can be used include conventionally known phenolic novolac resins, alkylphenol novolac resins, bisphenol A novolac resins, dicyclopentadiene-type phenolic resins, Xylok-type phenolic resins, terpene-modified phenolic resins, cresol / naphthol resins, polyvinylphenols, phenol / naphthol resins, α-naphthol skeleton-containing phenolic resins, triazine skeleton-containing cresol novolac resins, biphenylaralkyl-type phenolic resins, and Xylok-type phenolic novolac resins. Examples of commercially available phenolic resins include HF-1M, HF-4M (all trade names: phenolic novolac resins), MEH-7800 (trade name: Xylok-type phenolic novolac resin), and MEH-7851 (trade name: biphenylaralkyl-type novolac resin) (all manufactured by Meiwa Kasei Co., Ltd.).

[0035] Among the above-mentioned curing agents, from the viewpoint of storage stability of the curable resin composition, at least two or more of the above-mentioned curing agents may be contained, and one of them may be an imidazole.Furthermore, from the viewpoint of suppressing cracking and delamination, it is preferable to contain at least one of polyamine and indazole latent curing agent.Furthermore, when an imidazole is contained, it is preferable to contain two or more imidazoles.

[0036] The content of the curing agent, calculated as solid content, is preferably 20 parts by mass or more and 100 parts by mass or less, more preferably 25 parts by mass or more and 50 parts by mass or less, and even more preferably 25 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass in total of the solid epoxy resin and the liquid epoxy resin.

[0037] (organic solvent) The curable resin composition of the present invention contains an organic solvent to improve printability and polishability after semi-curing. The organic solvent used in the present invention includes a first organic solvent having a vapor pressure of 0.01 mmHg or more and 4.00 mmHg or less at 25°C. Hereinafter, an organic solvent having a vapor pressure of 0.01 mmHg or more and 4.00 mmHg or less will also be referred to as the "first organic solvent." The vapor pressure of the first organic solvent at 25°C is preferably 0.01 mmHg or more and 3.00 mmHg or less, more preferably 0.01 mmHg or more and 2.00 mmHg or less, and even more preferably 0.01 mmHg or more and 1.50 mmHg or less. If the vapor pressure of the organic solvent is within the above numerical range, solvent volatilization is suppressed, resulting in good printability, and warping is also suppressed, resulting in good polishability. A known vapor pressure measurement method may be used to measure the vapor pressure of the organic solvent. Examples of known vapor pressure measurement methods include the static method, the ebulliometric method, and the gas flow method (gas flow method). The Antoine equation may also be used to calculate the vapor pressure of an organic solvent at 25°C from the vapor pressure values at other temperatures. For organic solvents that are available through transfer or other means, the vapor pressure may be the value provided by the supplier.

[0038] As the organic solvent, diethylene glycol monoethyl ether acetate (0.148 mmHg at 25°C), dipropylene glycol methyl ether (0.48 mmHg at 25°C), dipropylene glycol methyl ether acetate (0.239 mmHg at 25°C), and diethylene glycol monoethyl ether (0.143 mmHg at 25°C) can be particularly used. These organic solvents may be used alone or in combination of two or more. The vapor pressures in this specification are based on values provided by the suppliers.

[0039] The content of the organic solvent is 5% by mass or more and 20% by mass or less, preferably 7% by mass or more and 18% by mass or less, and more preferably 9% by mass or more and 16% by mass or less, based on the total amount of the curable resin composition. When the content of the organic solvent is within the above range, printability and suppression of warping after semi-curing are improved.

[0040] The curable resin composition of the present invention may further contain an organic solvent having a vapor pressure of less than 0.01 mmHg or more than 4.00 mmHg for the purpose of preparing the composition, adjusting the viscosity during application, etc. As the organic solvent having a vapor pressure of less than 0.01 mmHg or more than 4.00 mmHg, any known or commonly used organic solvent other than those mentioned above can be used. Hereinafter, the organic solvent having a vapor pressure of less than 0.01 mmHg or more than 4.00 mmHg will also be referred to as the "second organic solvent."

[0041] The organic solvents described above may be used alone or in combination of two or more. In an embodiment in which two or more organic solvents are used in combination, it is preferable to use the first organic solvents in combination. Even in an embodiment in which the first organic solvent and the second organic solvent are used in combination, it is sufficient as long as the ratio of the first organic solvent is a certain value or more (for example, preferably 30 mass% or more, preferably 60 mass% or more, more preferably 80 mass% or more, and even more preferably 90 mass% or more, based on the total organic solvents). When the organic solvents in the above combination are used, the solvents are appropriately volatilized, resulting in good printability and polishability of the semi-cured film.

[0042] (Other added ingredients) The curable resin composition of the present invention may further contain other components, as needed, such as antioxidants, antifoaming agents, leveling agents, cyanate compounds, elastomers, mercapto compounds, thixotropic agents, adhesion promoters, chain transfer agents, polymerization inhibitors, copper inhibitors, rust inhibitors, thickeners, and flame retardants. These may be any of those known in the field of electronic materials.

[0043] The curable resin composition of the present invention may also contain a silane coupling agent. By incorporating a silane coupling agent, it is possible to improve the adhesion between the inorganic filler and the epoxy resin and suppress the occurrence of cracks in the cured product.

[0044] Examples of silane coupling agents include epoxy silane, vinyl silane, imidazole silane, mercapto silane, methacryloxy silane, amino silane, styryl silane, isocyanate silane, sulfide silane, ureido silane, etc. The silane coupling agent may be compounded by using an inorganic filler that has been surface-treated in advance with the silane coupling agent.

[0045] 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 inorganic filler and the epoxy resin and defoaming properties.

[0046] [viscosity] The viscosity in the present invention, as measured under the following conditions, is preferably 30 dPa·s or more and 500 dPa·s or less, more preferably 50 dPa·s or more and 400 dPa·s or less, and even more preferably 80 dPa·s or more and 200 dPa·s or less. If the viscosity is within the above range, good printability will be achieved.

[0047] The viscosity of the curable resin composition of the present invention is measured as follows. That is, the viscosity was measured at 25°C and 5 rpm using a cone-plate rotational viscometer (cone and plate type) (manufactured by Toki Sangyo Co., Ltd., TVE-33H, rotor 3° × R9.7) in accordance with JIS-Z8803:2011, Section 10, "Method for measuring viscosity using a cone-plate rotational viscometer," and the 30-second value was defined as the viscosity.

[0048] [Preparation method] The curable resin composition of the present invention can be prepared by weighing and blending the components, pre-mixing them with a mixer, and then dispersing and kneading the components in a kneader.

[0049] Examples of the kneading machine include a bead mill, a ball mill, a sand mill, a three-roll mill, and a two-roll mill. Among these, it is preferable to use a bead mill in order to improve dispersibility. Dispersion conditions such as the type and particle size of the beads of the bead mill can be appropriately set depending on the target viscosity.

[0050] [Application] The curable resin composition of the present invention can be preferably used as an ink for filling differences in height in printed wiring boards, and can also be suitably used for permanently filling holes in printed wiring boards, such as via holes.

[0051] [Cured product] The cured product of the present invention is obtained by curing the curable resin composition of the present invention. The production conditions, such as curing conditions, will be described later. The cured product of the present invention can be suitably used for electronic parts such as printed wiring boards.

[0052] [Coefficient of thermal expansion] The thermal expansion coefficient of the cured product in the present invention, as measured under the following conditions, is preferably 25 ppm / ° C. or less, more preferably 20 ppm / ° C. or less, and even more preferably 17 ppm / ° C. or less. If the thermal expansion coefficient is within the above range, cracking, delamination, and warpage of the substrate are suppressed.

[0053] In the present invention, the thermal expansion coefficient of the cured product is evaluated as follows. That is, the curable resin composition was applied to the shiny side (copper side) of a 20 cm × 20 cm, 18 μm thick GTS-MP foil (manufactured by Furukawa Circuit Foil Co., Ltd.) using an applicator so that the thickness of the applied film before curing was 100 μm or more and 150 μm or less, and after semi-curing at 100°C for 60 minutes, the curable resin composition was cured by heating at 180°C for 60 minutes to obtain a cured product. The obtained cured product was peeled off from the copper foil and cut into a measurement size of 3 mm x 16 mm to prepare a measurement sample. The obtained measurement sample was subjected to TMA measurement using a thermomechanical analyzer (TMA Q400, manufactured by TA Instruments Japan Co., Ltd.). The TMA measurement was performed twice consecutively, with a test load of 5 g and the sample heated from room temperature to 300°C at a heating rate of 10°C / min. The intersection of two tangents with different thermal expansion coefficients in the second measurement was determined as the glass transition temperature T g In addition, the thermal expansion coefficient α in the region below the glass transition temperature was calculated.

[0054] [Printed wiring board] The printed wiring board of the present invention comprises a circuit board and a cured product obtained from the curable resin composition of the present invention.

[0055] Examples of the substrates include glass substrates, printed wiring boards and flexible printed wiring boards with circuits already formed using copper or the like, copper-clad laminates for high-frequency circuits made from materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / non-woven cloth epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, fluororesin / polyethylene / polyphenylene ether, polyphenylene oxide / cyanate, and other materials, including copper-clad laminates of all grades (FR-4, etc.), as well as metal substrates, polyimide films, polyethylene terephthalate films, polyethylene naphthalate (PEN) films, ceramic substrates, wafer plates, etc.

[0056] The thickness of the copper wiring of the printed wiring board of the present invention is preferably 35 μm or more and 500 μm or less, more preferably 50 μm or more and 400 μm or less, and even more preferably 70 μm or more and 300 μm or less.

[0057] [Printed wiring board manufacturing method] In the method for producing a printed wiring board of the present invention, for example, the curable resin composition of the present invention is applied to a substrate by a method such as dip coating, flow coating, roll coating, bar coating, screen printing, or curtain coating, and then the composition is dried (semi-cured) at a temperature of 60 to 150°C for 30 to 90 minutes to evaporate the organic solvent contained in the composition. This allows for the formation of a tack-free resin layer (semi-cured film). The semi-cured film is softer than the cured product after full curing because the organic solvent evaporates but the curing reaction of the curable resin does not progress completely. Therefore, the semi-cured film has better polishability than the cured product after full curing. Therefore, polishing the surface of the semi-cured film after semi-curing makes it easier to obtain a flat surface than polishing the surface of the cured product. After forming the semi-cured film, final curing (full curing) is performed at a temperature of 100 to 300°C for 30 to 90 minutes to form a cured film with excellent properties such as printability and thermal expansion coefficient. Furthermore, a solder resist layer or prepreg layer can be formed on the semi-cured film.

[0058] The volatilization drying (semi-curing) performed after applying the curable resin composition of the present invention to a substrate can be performed using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, etc. (a method in which hot air in a dryer equipped with a heat source of an air heating method using steam is brought into countercurrent contact with the substrate, or a method in which hot air is blown onto the substrate from a nozzle.) Examples of the apparatus include a hot air circulation drying oven such as DF610 manufactured by Yamato Scientific Co., Ltd.

[0059] In the semi-curing step, the resin composition may be subjected to a degassing treatment. A conventionally known method can be used for the degassing treatment. For example, the resin composition may be degassed by adjusting the temperature at a relatively low temperature, such as below room temperature, under reduced pressure or normal pressure. This method can remove air bubbles trapped during printing and suppress the occurrence of voids.

[0060] After the above-mentioned coating and semi-curing steps, the resin composition may be coated on the back surface and semi-cured depending on the shape of the printed wiring board. Since the resin composition of the present invention achieves a low thermal expansion coefficient and suppresses warpage of the board, it can be suitably used even when coating and semi-curing are performed on both sides of the printed wiring board.

[0061] The resulting semi-cured product is then subjected to other treatments as necessary and then polished. Specifically, this is done using a buffing machine with a high-cut buff or the like until the copper surface of the copper circuit is completely exposed. Thereafter, a solder resist layer can be formed and prepreg can be laminated. The formation of the solder resist or the like can be performed after or before the main curing.

[0062] The polished semi-cured product is then subjected to other treatments as necessary before being fully cured. Full curing can be carried out using a hot air circulation drying oven, IR oven, hot plate, convection oven, etc. (a method using a steam-heated air heating system in which hot air is brought into countercurrent contact with the substrate, or a method in which hot air is blown onto the substrate from a nozzle). Examples of equipment include a hot air circulation drying oven such as the DF610 manufactured by Yamato Scientific Co., Ltd.

[0063] After planarizing and fully curing the resin composition, the surface of the cured product may be roughened as needed by using an oxidizing agent such as an aqueous potassium permanganate solution or by CZ treatment (treatment with an organic acid-based etching agent) before forming a solder resist layer or prepreg layer. Surface roughening forms a roughened surface with excellent anchoring effect, thereby improving adhesion between the solder resist layer or prepreg layer and the surface of the cured product.

[0064] Furthermore, after the resin composition has been planarized and fully cured, and after the surface roughening, circuits can be formed by a subtractive method, semi-additive method, or the like. In either method, after electroless plating, electrolytic plating, or both, a heat treatment called annealing may be performed at approximately 80 to 180°C for 10 to 60 minutes to remove metal stress and improve strength. The metal plating used here is not particularly limited and may include copper, tin, solder, nickel, etc., and multiple combinations may also be used. The plating used here can also be substituted with metal sputtering, etc. [Example]

[0065] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples. In the following, "parts" and "%" are all by mass unless otherwise specified.

[0066] [Examples 1 to 8, Comparative Examples 1 to 5] <Preparation of Curable Resin Composition> The components shown in Table 1 were mixed and stirred, and dispersed in a three-roll mill to obtain curable resin compositions of Examples 1 to 8 and Comparative Examples 1 to 5.

[0067] [Table 1]

[0068] The contents in Table 1 are in parts by mass. Details of each component in Table 1 are as follows: *1: XD-1000, solid epoxy resin, manufactured by Nippon Kayaku Co., Ltd. *2: EPICLON N-870, solid epoxy resin, manufactured by DIC Corporation *3: EOCN-104S, solid epoxy resin, *4: jER828, liquid epoxy resin, manufactured by Mitsubishi Chemical Corporation *5: ZX-1059, liquid epoxy resin, manufactured by Nippon Steel Chemical & Material Co., Ltd. *6:FE920A-SQ, Silica, manufactured by Admatechs Co., Ltd. *7: LMP-100, talc, manufactured by Fuji Talc Industry Co., Ltd. *8: Super #2000, heavy calcium carbonate, manufactured by Maruo Calcium Co., Ltd. *9: HF1M, phenolic hardener, manufactured by Meiwa Kasei Co., Ltd. *10: HF4M, phenolic hardener, manufactured by Meiwa Kasei Co., Ltd. *11: 2E4MZ, imidazole curing agent, manufactured by Shikoku Chemicals Co., Ltd. *12:2MZA-PW, imidazole curing agent, manufactured by Shikoku Chemicals Co., Ltd. *13: Jukisol CA, organic solvent (diethylene glycol monoethyl ether acetate, 0.148 mmHg (25°C)), manufactured by Dow Chemical Company *14: PMA, organic solvent (propylene glycol monomethyl ether acetate, 3.92 mmHg (25°C)) *15: Dowanol DPM, organic solvent (dipropylene glycol methyl ether, 0.48 mmHg (25°C)), manufactured by Dow Chemical Co.

[0069] <Measurement of viscosity of curable resin composition> The viscosity at 25°C was measured for the curable resin compositions of Examples 1 to 8 and Comparative Examples 1 to 5. That is, 0.2 ml of a sample was taken, and the viscosity was measured at 25°C and 5 rpm using a cone-plate rotational viscometer (cone and plate type) (manufactured by Toki Sangyo Co., Ltd., TVE-33H, rotor 3° × R9.7) in accordance with JIS-Z8803:2011, section 10, "Method for measuring viscosity using a cone-plate rotational viscometer" at 30 seconds.

[0070] <Warping after semi-curing> For the curable resin compositions of Examples 1 to 8 and Comparative Examples 1 to 2 and 4 to 5, the curable resin composition was applied to a 100 μm thick surface of a 20 cm × 20 cm GTS-MP foil (manufactured by Furukawa Circuit Foil Co., Ltd., thickness 35 μm) using an applicator. After semi-curing for 60 minutes at 100°C in a hot air circulation drying oven, the copper foil was cut into 5 cm square pieces. The cut copper foil was placed on an FR4 material measuring approximately 250 mm × 280 mm and 1.6 mm thick. After placement, the amount of warping at four corners of the copper foil was measured with a ruler, and the total value was used to compare the warping. A rating of ⊚ or ◯ was considered acceptable. (Evaluation criteria) ◎: Less than 1 mm. ○: 1 mm or more and less than 5 mm. △: 5mm or more and less than 20mm. ×: 20 mm or more. Comparative Example 3 was not evaluated because the viscosity was too high and printing was not possible.

[0071] <Abrasiveness> The curable resin compositions of Examples 1-8 and Comparative Examples 1-2, 4-5 were screen-printed onto a 0.8 mm thick copper plate (FR4 material) measuring approximately 250 mm x 280 mm, with a thickness of 40-50 μm and an area of 120 mm x 120 mm under the following conditions. The curable resin compositions were then semi-cured in a hot air circulating oven at 100°C for 60 minutes. The semi-cured substrates were polished using a hole-filling buffing machine (Ishii Hyoki Co., Ltd., HS4-axis polishing machine) with a nonwoven fabric buff equivalent to #320, a feed speed of 1.0 m / min, and a load current of 2.0 A. The number of passes required to completely expose the copper circuit was compared. A ◎ or ○ was deemed acceptable. (Printing conditions) Squeegee: 9mm thick, flat squeegee (hardness 70°) Screen: PET100 mesh bias screen, emulsion thickness 20 μm Printing pressure: 30kg Squeegee speed: 100mm / sec Squeegee angle: 70° (Evaluation criteria) ◎: Less than 3 passes. ○: 3 or more passes but less than 5 passes. △: 5 or more passes but less than 7 passes. ×: 7 passes or more. Comparative Example 3 was not evaluated because the viscosity was too high and printing was not possible.

[0072] <Fillability> The curable resin compositions of Examples 1-8 and Comparative Examples 1-2 and 4-5 were screen-printed onto a substrate (FR4 material, 1.6 mm thick, 150 mm x 90 mm, manufactured by Henmi Slide Rule Co., Ltd.) with a copper circuit thickness of 105 μm under the following conditions to achieve a film thickness of 40-50 μm on the copper. The printed material was semi-cured for 60 minutes at 100°C in a hot air circulating oven, and then cured for 60 minutes at 180°C. The cross-section of the cured product between the copper circuits (L / S = 400 μm / 400 μm) on the cured substrate was observed at 50-100x magnification with an optical microscope (Keyence Corporation, VHX-6000) to compare the number of voids. A ◎ or ○ was judged as acceptable. (Printing conditions) Squeegee: 9mm thick, flat squeegee (hardness 70°) Screen: PET100 mesh bias screen, emulsion thickness 20 μm Printing pressure: 30kg Squeegee speed: 100mm / sec Squeegee angle: 70° (Evaluation criteria) ◎: 0 (no voids). ○: 1 or more and less than 5 ×: 6 or more. Comparative Example 3 was not evaluated because the viscosity was too high and printing was not possible.

[0073] <Thermal expansion coefficient> The curable resin compositions of Examples 1 to 8 and Comparative Examples 1 to 2, 4 to 5 were applied using an applicator to the shiny side (copper side) of a 20 cm × 20 cm, 18 μm thick GTS-MP foil (manufactured by Furukawa Circuit Foil Co., Ltd.) so that the thickness of the applied film before curing was 100 μm or more and 150 μm or less. The composition was semi-cured at 100°C for 60 minutes in a hot air circulation drying oven, and then heated at 180°C for 60 minutes to cure the curable resin composition, yielding a cured product. The obtained cured product was peeled off from the copper foil and cut into a measurement size of 3 mm x 16 mm to prepare a measurement sample. The obtained measurement sample was subjected to TMA measurement using a thermomechanical analyzer (TMA Q400, manufactured by TA Instruments Japan Co., Ltd.). The TMA measurement was performed twice consecutively, with a test load of 5 g and the sample heated from room temperature to 300°C at a heating rate of 10°C / min. The intersection of two tangents with different thermal expansion coefficients in the second measurement was determined as the glass transition temperature T g The thermal expansion coefficient α in the region below the glass transition temperature was also calculated. ⊚ or ○ was judged as passing. (Evaluation criteria) ⊚: Less than 17 ppm / °C. ◯: 17 ppm / °C or more and less than 25 ppm / °C. △: 25 ppm / °C or more and less than 35 ppm / °C. ×: 35 ppm / °C or more. Comparative Example 3 was not evaluated because the viscosity was too high and printing was not possible.

[0074] The results of the above measurements and evaluations are shown in Table 2. [Table 2]

[0075] The results in Table 2 above confirm that the compositions of each Example had a viscosity of 70 dPa·s or more and 200 dPa·s, demonstrating good filling properties. It was also confirmed that the semi-cured products of each Example exhibited reduced warpage and good polishability compared to the comparative examples. Furthermore, it was confirmed that the cured products of each Example exhibited a low coefficient of thermal expansion.

[0076] Comparing the Examples and Comparative Example 1, the solvent content in Comparative Example 1 is over 20%, so more solvent volatilizes than in the Examples, resulting in greater warpage after semi-curing and poorer polishability. Furthermore, it can be seen that the evaporation of a large amount of organic solvent easily generates voids, resulting in poor filling properties. Comparing the Example and Comparative Example 2, the content of inorganic filler in Comparative Example 2 is 65%, which is less than that of the Example, and the thermal expansion coefficient is 28 ppm / °C. It can be seen that a higher thermal expansion coefficient results in greater warpage after semi-curing and poorer polishability. Comparing the working example with Comparative Example 3, it can be seen that the solvent content in Comparative Example 3 is 3%, so the viscosity becomes 2500 dPa·s or more, making printing impossible. Comparing the Examples and Comparative Example 4, Comparative Example 4 does not contain a solvent and contains 51% inorganic filler, so the thermal expansion coefficient is 38 ppm / °C, which is higher than that of the Examples. It can be seen that a higher thermal expansion coefficient results in greater warping after semi-curing and poorer polishability. Comparing the Examples and Comparative Example 5, Comparative Example 5 does not contain a solid epoxy resin, but only a liquid epoxy resin, which results in greater shrinkage during semi-curing and greater warpage after semi-curing. Furthermore, it is clear that the warpage is greater than in the Examples, and the surface becomes more tacky after semi-curing, resulting in poor polishability.

Claims

1. A curable resin composition comprising a solid epoxy resin, an inorganic filler, a curing agent, and an organic solvent, the content of the organic solvent is 5% by mass or more and 20% by mass or less with respect to the total amount of the curable resin composition, the organic solvent includes a first organic solvent having a vapor pressure at 25°C of 0.01 mmHg or more and 4.00 mmHg or less, the content of the first organic solvent is 30% by mass or more and 100% by mass or less based on the total amount of the organic solvents, A curable resin composition, characterized in that the content of the inorganic filler is 70 mass % or more, calculated as solid content, based on the total amount of the curable resin composition.

2. The curable resin composition of claim 1 further comprising a liquid epoxy resin.

3. The curable resin composition according to claim 1, wherein the vapor pressure of the first organic solvent at 25°C is 0.01 mmHg or more and 3.00 mmHg or less.

4. 4. The curable resin composition according to claim 3, wherein the first organic solvent is at least one selected from the group consisting of diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether, dipropylene glycol methyl ether acetate, and diethylene glycol monoethyl ether.

5. The curable resin composition according to claim 1, having a viscosity measured at 25°C of 30 dPa·s or more and 500 dPa·s or less.

6. A cured product obtained by curing the curable resin composition according to any one of claims 1 to 5.

7. The cured product according to claim 6, having a thermal expansion coefficient of 25 ppm / °C or less.

8. A printed wiring board comprising a circuit board and the cured product according to claim 6 on the circuit board.

9. 9. The printed wiring board according to claim 8, wherein the thickness of the copper wiring of the circuit board is 35 μm or more and 500 μm or less.

10. A step of applying the curable resin composition according to any one of claims 1 to 5 onto a circuit board; semi-curing the curable resin composition to form a semi-cured film; polishing the semi-cured film; A method for manufacturing a printed wiring board, comprising:

11. The method for manufacturing a printed wiring board according to claim 10, wherein the thickness of the wiring of the circuit board is 35 μm or more and 500 μm or less.

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