Printed wiring boards containing photosensitive resin compositions, photocured forms of photosensitive resin compositions, and photocured films containing photosensitive resin compositions.

Abstract

This invention provides a photosensitive resin composition capable of forming a protective film with excellent insulating reliability, flux resistance, matte appearance, and flexibility. The photosensitive resin composition contains (A) a carboxyl-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound. The aforementioned (B) inorganic filler is talc with a cumulative volume percentage of 50% and a particle size D50 of 0.7 μm to 5.5 μm. The aforementioned (C) photopolymerization initiator contains at least one selected from the group consisting of (C1) α-aminoalkylphenyl ketone photopolymerization initiators and (C2) oxime ester photopolymerization initiators.

Description

Technical Field

[0001] The present invention relates to a photosensitive resin composition suitable as a coating material, for example, an insulating coating material for coating a conductor circuit pattern formed on a printed wiring board having a rigid substrate or a flexible substrate, a photocurable product of the photosensitive resin composition, and a printed wiring board having a photocurable film of the photosensitive resin composition. Prior Art

[0002] A conductor circuit pattern, such as copper foil, is formed on the substrate of a printed wiring board (PCB). Electronic components are mounted on the solder pads of the conductor circuit pattern by soldering. The conductor circuit portion, excluding the solder pads, is covered with an insulating film (solder resist) as a protective film. In particular, for PCBs with flexible substrates, the protective film is required to be flexible. Furthermore, the protective film is sometimes required to have a matte appearance.

[0003] Therefore, a thermosetting / photosensitive resin composition has been proposed (Patent Document 1) containing (A) a thermosetting resin, (B) a resin having an acidic functional group and an unsaturated double bond, (C) a resin having an acidic functional group and no unsaturated double bond, (D) a compound having an unsaturated double bond, (E) a photopolymerization initiator, and (F) an organic filler. Patent Document 1 discloses that the use of (F) an organic filler, particularly organic beads having urethane bonds, imparts flexibility to the protective film that allows it to withstand repeated bending. Furthermore, the use of organic beads can impart a matte appearance to the protective film.

[0004] Meanwhile, the mounting process for electronic components by soldering to solder pads on a conductive circuit pattern involves placing the electronic components on a printed wiring board (PCB) coated with a protective film and then soldering the components to the PCB through a heat treatment in a reflow oven. During this mounting process, solder containing flux may be used. When using solder containing flux, the flux may seep out of the solder and penetrate the protective film through the surface of the insulating film or the openings in the conductive circuit pattern.

[0005] If flux components penetrate the protective film, it may peel off from the printed wiring board or swell, which may cause defects in the insulation film. Therefore, protective films are required to have flux resistance to prevent peeling and swelling of the protective film from the printed wiring board even if flux components seep out of the solder.

[0006] However, the protective film formed from the photosensitive resin composition of Patent Document 1 has low heat resistance due to the organic filler. Therefore, when flux components seep out of the solder during heating in a reflow oven, the flux components can penetrate the protective film, causing the protective film to peel off from the printed wiring board or swell. Therefore, there is room for improvement in flux resistance.

[0007] Furthermore, although the heat resistance of the protective film is improved by adding inorganic fillers to the photosensitive resin composition, flexibility cannot be achieved. Furthermore, reducing the particle size of the inorganic filler to achieve flexibility will result in a problem in that a matte appearance cannot be achieved. [Prior Art Literature] [Patent Document]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2022-017603 Summary of the Invention

[0009] [Problems to be solved by the invention]

[0010] In view of the above, an object of the present invention is to provide a photosensitive resin composition that can form a protective film having insulation reliability, flux resistance, matte appearance, and excellent flexibility. [Methods used to solve the problem]

[0011] The gist of the present invention is as follows. [1] A photosensitive resin composition comprising (A) a carboxyl group-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound. The inorganic filler (B) is talc having a cumulative volume percentage of 50% by volume and a particle size D50 of 0.7 μm or more and 5.5 μm or less, The (C) photopolymerization initiator contains at least one selected from the group consisting of (C1) α-aminoalkylphenone-based photopolymerization initiators and (C2) oxime ester-based photopolymerization initiators. [2] The photosensitive resin composition of [1], wherein the inorganic filler (B) is untreated talc having a cumulative volume percentage of 50% by volume and a particle size D50 of 0.7 μm or more and 5.5 μm or less and not surface-treated with an organic compound. [3] The photosensitive resin composition of [2], wherein the inorganic filler (B) is the untreated talc having a cumulative volume percentage of 50% by volume and a particle size D50 of 1.3 μm or more and 2.3 μm or less. [4] The photosensitive resin composition of [1], wherein the inorganic filler (B) is a surface-treated talc having a particle size D50 of not less than 0.7 μm and not more than 5.5 μm and having been surface-treated with an organic compound, with a cumulative volume percentage of 50% by volume. [5] The photosensitive resin composition of [4], wherein the inorganic filler (B) is the surface-treated talc having a cumulative volume percentage of 50% by volume and a particle size D50 of 2.0 μm or more and 4.0 μm or less. [6] The photosensitive resin composition of [4] or [5], wherein the organic compound is at least one selected from the group consisting of epoxy silane compounds and (meth)acrylic silane compounds. [7] The photosensitive resin composition of [1], wherein the composition contains 8 parts by mass or more and 80 parts by mass or less of the talc described above relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A). [8] The photosensitive resin composition of [1], wherein the composition contains 30 parts by mass or more and 70 parts by mass or less of the talc described above relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A). [9] A photosensitive resin composition as described in [1], which does not contain an organic filler.

[10] A photosensitive resin composition as described in [1], further comprising an organic filler.

[11] A photosensitive resin composition as described in [1], wherein the carboxyl-containing photosensitive resin (A) has a cresol novolac-type epoxy resin skeleton.

[12] A photosensitive resin composition as described in [1], wherein the aforementioned (C1) α-aminoalkylphenone-based photopolymerization initiator contains 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone.

[13] A photosensitive resin composition as described in [1], wherein the aforementioned (C2) oxime ester-based photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropane-2-yl)oxy)-2-methylphenyl)methanone O-acetyl oxime.

[14] A photocurable material of the photosensitive resin composition as described in [1].

[15] A printed wiring board having a photocurable film of the photosensitive resin composition as described in [1]. [Effects of the Invention]

[0012] According to an aspect of the photosensitive resin composition of the present invention, the composition comprises (A) a carboxyl group-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound, wherein the inorganic filler (B) is talc having a particle size D50 of 0.7 μm or more and 5.5 μm or less, with a cumulative volume percentage of 50% by volume, and the photopolymerization initiator (C) comprises at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator. Thus, a photosensitive resin composition capable of forming a protective film having excellent insulation reliability, flux resistance, matte appearance, and flexibility can be obtained.

[0013] According to the aspect of the photosensitive resin composition of the present invention, the inorganic filler (B) is composed of 50% by volume of untreated talc having a particle size D50 of 1.3 μm to 2.3 μm without surface treatment with an organic compound, thereby achieving a sufficiently improved balance between flux resistance, matte appearance, and flexibility.

[0014] According to the aspect of the photosensitive resin composition of the present invention, the surface-treated talc having a particle size D50 of 0.7 μm to 5.5 μm and surface-treated with an organic compound and comprising 50% by volume of the inorganic filler (B) can reliably improve insulation reliability, matte appearance, and flexibility.

[0015] According to aspects of the photosensitive resin composition of the present invention, the surface-treated talc having a particle size D50 of 2.0 μm or more and 4.0 μm or less, treated with an organic compound, comprising the inorganic filler (B) at a cumulative volume percentage of 50% by volume, can further reliably improve insulation reliability, matte appearance, and flexibility.

[0016] According to the aspect of the photosensitive resin composition of the present invention, the insulating reliability, matte appearance and flexibility can be further improved by including at least one organic compound selected from the group consisting of epoxy silane compounds and (meth)acrylate silane compounds.

[0017] According to the aspect of the photosensitive resin composition of the present invention, by containing 8 to 80 parts by mass of the talc relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A), flux resistance, matte appearance, and flexibility can be more reliably achieved.

[0018] According to the aspect of the photosensitive resin composition of the present invention, by containing 30 to 70 parts by mass of the talc relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A), the balance between flux resistance, matte appearance, and flexibility can be sufficiently improved.

[0019] According to the aspect of the photosensitive resin composition of the present invention, by not containing organic fillers, the flux resistance can be more reliably improved.

[0020] According to the aspect of the photosensitive resin composition of the present invention, the insulation reliability and flux resistance can be more reliably improved by the aforementioned (A) carboxyl-containing photosensitive resin having a cresol novolac-type epoxy resin skeleton.

[0021] According to aspects of the photosensitive resin composition of the present invention, the inclusion of 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone in the aforementioned (C1) α-aminoalkylphenone-based photopolymerization initiator can contribute to further improvement of flux resistance.

[0022] According to aspects of the photosensitive resin composition of the present invention, the aforementioned (C2) oxime ester-based photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl))methanone O-acetyl oxime, which can help further improve flux resistance. Implementation Method

[0023] Next, the photosensitive resin composition of the present invention is described below. The photosensitive resin composition of the present invention comprises (A) a carboxyl group-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound. The inorganic filler (B) is talc having a particle size D50 of 0.7 μm or greater and 5.5 μm or less, with a cumulative volume percentage of 50% by volume. The photopolymerization initiator (C) comprises at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator. In the photosensitive resin composition of the present invention, talc having a particle size D50 of 0.7 μm or greater and 5.5 μm or less is added as the inorganic filler (B) at a cumulative volume percentage of 50% by volume. In the photosensitive resin composition of the present invention, the inorganic filler (B) comprises talc having a particle size D50 of 0.7 μm to 5.5 μm, with a cumulative volume percentage of 50% by volume. The composition does not contain other inorganic fillers such as barium sulfate, silicon oxide, or mica. The photosensitive resin composition of the present invention can form a protective film that exhibits reliable insulation, excellent flux resistance, a matte appearance, and flexibility.

[0024] <(A) Carboxyl-containing photosensitive resin> The carboxyl-containing photosensitive resin as component (A) serves as the base resin of the photosensitive resin composition. The structure of the carboxyl-containing photosensitive resin is not particularly limited, and examples thereof include resins having one or more photosensitive unsaturated double bonds and free carboxyl groups. Examples of carboxyl-containing photosensitive resins include polybasic acid-modified free radical polymerizable unsaturated monocarboxylic acid-modified epoxy resins having a structure obtained by reacting at least a portion of the epoxy groups of a multifunctional epoxy resin having two or more epoxy groups per molecule with a free radical polymerizable unsaturated monocarboxylic acid to obtain a free radical polymerizable unsaturated monocarboxylic acid-modified epoxy resin, and then reacting the resulting hydroxyl groups with a polybasic acid and / or polybasic acid anhydride.

[0025] Multifunctional epoxy resin The multifunctional epoxy resin forms the backbone of the carboxyl-containing photosensitive resin. The epoxy equivalent weight of the multifunctional epoxy resin is not particularly limited; for example, its upper limit is preferably 3000 g / eq, more preferably 2000 g / eq, even more preferably 1000 g / eq, and particularly preferably 500 g / eq. On the other hand, its lower limit is preferably 100 g / eq, particularly preferably 200 g / eq. The chemical structure of the multifunctional epoxy resin is not particularly limited, and examples thereof include biphenyl aralkyl epoxy resins, phenyl aralkyl epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins, rubber-modified epoxy resins such as silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, cresol novolac-type epoxy resins such as o-cresol novolac-type epoxy resins, bisphenol novolac-type epoxy resins, cycloaliphatic multifunctional epoxy resins, glycidyl ester-type multifunctional epoxy resins, glycidyl amine-type multifunctional epoxy resins, heterocyclic multifunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and multifunctional modified novolac-type epoxy resins. These multifunctional epoxy resins may be used alone or in combination of two or more.

[0026] Among these multifunctional epoxy resins, cresol novolac type epoxy resins are preferred from the viewpoint of more reliably improving insulation reliability and flux resistance. Therefore, the carboxyl group-containing photosensitive resin preferably has a cresol novolac type epoxy resin skeleton.

[0027] Free radical polymerizable unsaturated monocarboxylic acid The carboxyl groups of the radically polymerizable unsaturated monocarboxylic acid react with the epoxy groups of the multifunctional epoxy resin to form ester bonds, introducing photosensitive unsaturated double bonds derived from the radically polymerizable unsaturated monocarboxylic acid into the epoxy resin, thereby imparting photosensitivity to the backbone of the multifunctional epoxy resin. Examples of radically polymerizable unsaturated monocarboxylic acids include acrylic acid, methacrylic acid (acrylic acid and / or methacrylic acid are referred to as "(meth)acrylic acid"), crotonic acid, chamomile acid, angelica acid, and cinnamic acid. Among these, (meth)acrylic acid is preferred based on reactivity, availability, and handling. These radically polymerizable unsaturated monocarboxylic acids can be used alone or in combination of two or more.

[0028] The reaction method of the polyfunctional epoxy resin and the free radical polymerizable unsaturated monocarboxylic acid is not particularly limited. For example, a method of heating the polyfunctional epoxy resin and the free radical polymerizable unsaturated monocarboxylic acid in a suitable solvent (eg, an inert organic solvent) can be used.

[0029] Polybasic acid and / or polybasic acid anhydride The polyacid and / or polyacid anhydride reacts with the hydroxyl groups of the unsaturated monocarboxylated epoxy resin to form ester bonds, introducing free carboxyl groups into the photosensitive resin. The polyacid and / or polyacid anhydride is not particularly limited; either saturated or unsaturated can be used. Examples of polybasic acids include succinic acid, maleic acid, adipic acid, citric acid, phthalic acid, tetrahydrophthalic acid, 3-methyltetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, 3-ethyltetrahydrophthalic acid, 4-ethyltetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, 4-ethylhexahydrophthalic acid, difunctional carboxylic acids such as diglycolic acid, trifunctional carboxylic acids such as trimellitic acid, and tetrafunctional carboxylic acids such as pyromellitic acid. Examples of polybasic acid anhydrides include anhydrides of the above-mentioned polybasic acids. These polybasic acids and polybasic acid anhydrides may be used alone or in combination of two or more.

[0030] The reaction method of the free-radically polymerizable unsaturated monocarboxylic acid-containing epoxy resin and the polyacid and / or polyacid anhydride is not particularly limited. For example, a method of heating the free-radically polymerizable unsaturated monocarboxylic acid-containing epoxy resin and the polyacid and / or polyacid anhydride in a suitable solvent (e.g., an inert organic solvent) can be used.

[0031] Alternatively, a carboxyl-containing photosensitive resin having a chemical structure in which a portion of the carboxyl groups of the polyacid-modified free-radical polymerizable unsaturated monocarboxylic acid epoxy resin is reacted with a compound having one or more free-radical polymerizable unsaturated groups and an epoxy group (e.g., a glycidyl compound) can be used in place of the polyacid-modified free-radical polymerizable unsaturated monocarboxylic acid epoxy resin. Furthermore, the carboxyl-containing photosensitive resin in which the compound having the free-radical polymerizable unsaturated group and the epoxy group are reacted has a chemical structure in which the free-radical polymerizable unsaturated group is introduced into the side chain of the polyacid-modified free-radical polymerizable unsaturated monocarboxylic acid epoxy resin. Therefore, the carboxyl-containing photosensitive resin having a chemical structure in which the compound having the free-radical polymerizable unsaturated group and the epoxy group are reacted has superior photopolymerization reactivity compared to the polyacid-modified free-radical polymerizable unsaturated monocarboxylic acid epoxy resin, and further improves photosensitivity.

[0032] Examples of compounds having a radically polymerizable unsaturated group and an epoxy group include glycidyl acrylate, glycidyl methacrylate (acrylates and / or methacrylates are referred to as "(meth)acrylates"), allyl glycidyl ether, and pentaerythritol tri(meth)acrylate monoglycidyl ether. These compounds having a radically polymerizable unsaturated group and an epoxy group may be used alone or in combination of two or more.

[0033] The reaction method of the polyacid-modified free-radically polymerizable unsaturated monocarboxylic acid-modified epoxy resin and the compound having a free-radically polymerizable unsaturated group and an epoxy group is not particularly limited. For example, a method of heating the free-radically polymerizable unsaturated monocarboxylic acid-modified epoxy resin and the compound having a free-radically polymerizable unsaturated group and an epoxy group in a suitable solvent (e.g., an inert organic solvent) can be used.

[0034] The acid value of the carboxyl group-containing photosensitive resin is not particularly limited. For example, its lower limit is preferably 30 mgKOH / g, more preferably 40 mgKOH / g, from the perspective of reliably imparting alkali developability. On the other hand, its upper limit is preferably 200 mgKOH / g, from the perspective of reliably preventing dissolution of the exposed portion (photocured portion) by an alkaline developer, and is particularly preferably 150 mgKOH / g, from the perspective of more reliably improving insulation reliability.

[0035] The mass average molecular weight of the carboxyl group-containing photosensitive resin is not particularly limited and can be appropriately selected based on the conditions of use as a protective film. For example, its lower limit is preferably 6,000, more preferably 7,000, and particularly preferably 8,000, from the perspective of improving the toughness and tack of the photocured product. On the other hand, its upper limit is preferably 200,000, more preferably 100,000, and particularly preferably 50,000, from the perspective of improving alkali developability. The "mass average molecular weight" referred to above refers to the mass average molecular weight measured at room temperature using gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0036] A carboxyl group-containing photosensitive resin can be prepared using the above-mentioned components in the above-mentioned reaction step. Alternatively, a commercially available carboxyl group-containing photosensitive resin can be used. Examples of commercially available carboxyl group-containing photosensitive resins include "Ripoxy SP-4621," "Ripoxy SP-4785," and "Ripoxy SP-4785L" (all from Showa Denko Co., Ltd.), "ZAR-2000," "ZFR-1122," "ZFR-1887," "FLX-2089," "ZCR-1569H," and "ZCR-1601H" (all from Nippon Kayaku Co., Ltd.), and "Cyclomer P(ACA)Z-250" (from DAICEL Co., Ltd.). These carboxyl group-containing photosensitive resins can be used alone or in combination of two or more.

[0037] <(B) Inorganic filler> The inorganic filler (B) is talc having a particle size D50 (hereinafter simply referred to as "D50") of 0.7 μm to 5.5 μm, with a cumulative volume percentage of 50% by volume. In the photosensitive resin composition of the present invention, the inorganic filler (B) is composed of talc particles having a D50 of 0.7 μm to 5.5 μm and does not contain other inorganic fillers such as barium sulfate, silica, and mica. By using talc having a D50 of 0.7 μm to 5.5 μm as the inorganic filler (B), a photosensitive resin composition can be obtained that forms a protective film having excellent insulation reliability, flux resistance, matte appearance, and flexibility.

[0038] Examples of talc include untreated talc that has not been surface-treated with an organic compound (hereinafter simply referred to as "untreated talc") and surface-treated talc that has been surface-treated with an organic compound (hereinafter simply referred to as "surface-treated talc").

[0039] As long as D50 is between 0.7 μm and 5.5 μm, the particle size and particle size distribution of the talc are not particularly limited, regardless of whether it is untreated or surface-treated. For untreated talc, the lower limit of D50 is preferably 0.9 μm, more preferably 1.1 μm, even more preferably 1.3 μm, and particularly preferably 1.5 μm, to further improve flux resistance and matte appearance. On the other hand, the upper limit of D50 is preferably 5.0 μm, more preferably 4.0 μm, even more preferably 2.3 μm, and particularly preferably 2.1 μm, to further improve flexibility. As described above, by setting the D50 of untreated talc within the preferred upper and lower limits, flux resistance, matte appearance, and flexibility can be well-balanced.

[0040] Surface-treated talc can reliably improve insulation reliability, matte appearance, and flexibility. For surface-treated talc, the lower limit of D50 is preferably 1.0 μm, more preferably 1.5 μm, and particularly preferably 2.0 μm, to further reliably improve insulation reliability, matte appearance, and flexibility. On the other hand, the upper limit of D50 is preferably 5.0 μm, and particularly preferably 4.0 μm, to further improve flexibility.

[0041] Examples of organic compounds used for surface treatment of talc include silane compounds. Examples of silane compounds include epoxy-functional silane compounds, (meth)acrylic silane compounds, and phenyl silane compounds. Among these, (meth)silane compounds are preferred, and acrylic silane compounds are particularly preferred, from the perspective of further improving flux resistance.

[0042] The amount of talc with a D50 of 0.7 μm or more and 5.5 μm or less is not particularly limited, but its lower limit is preferably 8 parts by mass relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A) (solid content, the same below) to more reliably achieve flux resistance and a matte appearance, more preferably 30 parts by mass to further improve flux resistance and a matte appearance, and particularly preferably 35 parts by mass. On the other hand, the upper limit of the talc content with a D50 of 0.7 μm or more and 5.5 μm or less is preferably 80 parts by mass relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A) to more reliably achieve flexibility, more preferably 70 parts by mass to further improve flexibility, and particularly preferably 60 parts by mass. As described above, by including talc having a D50 of 0.7 μm to 5.5 μm in a range of 8 to 80 parts by mass per 100 parts by mass of the carboxyl group-containing photosensitive resin (A), flux resistance, matte appearance, and flexibility can be more reliably achieved. By including talc having a D50 of 0.7 to 5.0 μm in a range of 30 to 70 parts by mass per 100 parts by mass of the carboxyl group-containing photosensitive resin (A), flux resistance, matte appearance, and flexibility can be improved in a well-balanced manner.

[0043] <(C) Photopolymerization Initiator> By adding the photopolymerization initiator (C), the curability of the cured coating can be improved and the penetration of flux components into the protective film can be suppressed, thereby forming a protective film with excellent flux resistance.

[0044] The photosensitive resin composition of the present invention contains, as a photopolymerization initiator, at least one selected from the group consisting of (C1) α-aminoalkylphenone-based photopolymerization initiators and (C2) oxime ester-based photopolymerization initiators.

[0045] Examples of the α-aminoalkylphenone-based photopolymerization initiator as the component (C1) include compounds represented by the following general formula (1). (R in formula (1) represents hydrogen or an alkyl group with 1 to 5 carbon atoms.) Among these, 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanol (R in formula (1) represents a methyl group) is preferred as the α-aminoalkylphenone-based photopolymerization initiator, from the perspective of helping to reliably improve the curability of the protective film and further improve the flux resistance. These α-aminoalkylphenone-based photopolymerization initiators may be used alone or in combination of two or more.

[0046] Examples of the oxime ester photopolymerization initiator as component (C2) include (9-ethyl-6-nitro-9H-carbazole-3-yl)(4-((1-methoxypropane-2-yl)oxy)-2-methylphenyl)ethanone O-acetyl oxime, 1,2-octanedione, 1-[4-(phenylthio)-2-(O-benzoyl oxime)], 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole] Examples of the following include (9-ethyl-6-nitro-9H-carbazol-3-yl)-1-(O-acetyl oxime), 2-(acetyloxyiminomethyl)thioxanthen-9-one, 1,8-octanedione, 1,8-bis[9-ethyl-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyl oxime), 1,8-octanedione, 1,8-bis[9-(2-ethylhexyl)-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyl oxime). Among these, (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropane-2-yl)oxy)-2-methylphenyl)ethanone O-acetyl oxime is preferred because it reliably improves the hardening properties of the cured coating and contributes to further improvement in flux resistance. These oxime ester photopolymerization initiators may be used alone or in combination of two or more.

[0047] The amount of at least one photopolymerization initiator selected from the group consisting of α-aminoalkylphenone-based photopolymerization initiators and oxime ester-based photopolymerization initiators is not particularly limited. However, the lower limit is preferably 0.50 parts by mass, more preferably 1.0 parts by mass, and particularly preferably 1.5 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A), from the perspective of reliably improving the curability of the cured coating film and reliably achieving excellent flux resistance. On the other hand, the upper limit of the amount of at least one photopolymerization initiator selected from the group consisting of α-aminoalkylphenone-based photopolymerization initiators and oxime ester-based photopolymerization initiators is preferably 8.0 parts by mass, more preferably 6.0 parts by mass, and particularly preferably 4.0 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A), from the perspective of preventing a decrease in developability and halation.

[0048] <(D) Reactive Diluent> The reactive diluent of component (D) can be, for example, a photopolymerizable monomer, a compound having at least one, and preferably two or more, polymerizable double bonds per molecule. The reactive diluent enhances the photocuring of the photosensitive resin composition, helping to impart sufficient strength, heat resistance, acid resistance, and alkali resistance to the cured coating film of the photosensitive resin composition.

[0049] Examples of the reactive diluent include monomers of monofunctional or polyfunctional (meth)acrylate compounds such as monofunctional (meth)acrylate compounds, bifunctional (meth)acrylate compounds, trifunctional (meth)acrylate compounds, and tetrafunctional or higher functional (meth)acrylate compounds. Examples of the (meth)acrylate monomer include monofunctional (meth)acrylate compounds such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, diethylene glycol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate; 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, dicyclopentyl di(meth)acrylate, and ethylene oxide-modified di(meth)acrylate. Bifunctional (meth)acrylate compounds such as acrylate, allylated cyclohexyl di(meth)acrylate, and isocyanuric acid di(meth)acrylate; trifunctional (meth)acrylate compounds such as trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate; and tetrafunctional or higher-functional (meth)acrylate compounds such as di-trimethylolpropane tetra(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate. These compounds may be used alone or in combination of two or more.

[0050] The amount of the reactive diluent to be added is not particularly limited, but is preferably 5.0 parts by mass to 70 parts by mass, particularly preferably 15 parts by mass to 40 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A).

[0051] <(E) Epoxy Compound> The epoxy compound (E) is used to increase the crosslink density of the cured photosensitive resin composition, imparting sufficient hardness to the cured product. The increased crosslink density of the epoxy compound helps inhibit the penetration of flux components into the protective film, resulting in a protective film with excellent flux resistance.

[0052] Examples of epoxy compounds include epoxy resins. Examples of epoxy resins include the same multifunctional epoxy resins as those used in the preparation of the carboxyl-containing photosensitive resins. Specific examples include biphenyl aralkyl epoxy resins, phenyl aralkyl epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, dicyclopentadiene epoxy resins, rubber-modified epoxy resins such as silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, o-cresol novolac-type epoxy resins, bisphenol novolac-type epoxy resins, cycloaliphatic multifunctional epoxy resins, glycidyl ester-type multifunctional epoxy resins, glycidyl amine-type multifunctional epoxy resins, heterocyclic multifunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and multifunctional modified novolac-type epoxy resins. Examples of epoxy compounds other than epoxy resins include triglycidyl isocyanurate. These epoxy compounds may be used alone or in combination of two or more. The epoxy compound may be the same type of multifunctional epoxy resin used to prepare the carboxyl group-containing photosensitive resin.

[0053] The amount of the epoxy compound to be added is not particularly limited, but is preferably 5.0 parts by mass to 60 parts by mass, particularly preferably 10 parts by mass to 40 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A).

[0054] The photosensitive resin composition of the present invention, by incorporating talc (B) with a D50 of 0.7 μm to 5.5 μm, as an inorganic filler, can form a protective film with an excellent matte appearance and flexibility. Therefore, it is not necessary to contain an organic filler. The absence of an organic filler further reliably improves flux resistance. Alternatively, an organic filler may be further included as an optional component as needed. While flux resistance is slightly reduced compared to compositions without an organic filler, the inclusion of an organic filler improves flexibility.

[0055] Examples of organic fillers include urethane resins (polymers of isocyanates and polyols), acrylic resins, polyethylene, copolymers of styrene and butadiene such as styrene-polybutadiene rubber, and polymers of silicone resins such as silicone rubber. These organic fillers can be used alone or in combination of two or more. The shape of the organic filler is not particularly limited, but particles are preferred.

[0056] The average particle size of the particulate organic filler is not particularly limited, but its lower limit is preferably 0.1 μm, particularly preferably 0.5 μm, from the perspective of improving the matte appearance. On the other hand, the upper limit of the average particle size of the particulate organic filler is preferably 20 μm, particularly preferably 10 μm, from the perspective of imparting excellent flexibility.

[0057] The upper limit of the amount of the organic filler to be blended is preferably 20 parts by mass, and particularly preferably 15 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A), from the perspective of achieving flux resistance. On the other hand, the lower limit of the amount of the organic filler to be blended is preferably 1.0 part by mass, and particularly preferably 5.0 parts by mass, relative to 100 parts by mass of the carboxyl group-containing photosensitive resin (A), from the perspective of further improving flexibility.

[0058] In the photosensitive resin composition of the present invention, in addition to the above-mentioned components (A) to (E), other photopolymerization initiators other than the (C1) α-aminoalkylphenone-based photopolymerization initiator and the (C2) oxime ester-based photopolymerization initiator may be further formulated as optional components as needed. Examples of other photopolymerization initiators include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, and the like; acetophenones such as acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and 2,2-diethoxy-2-phenylacetophenone; benzophenones such as benzophenone, p-phenylbenzophenone, 4,4'-diethylbenzophenone, and dichlorobenzophenone; anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, and 2-aminoanthraquinone; and 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2, Thioxanthones such as 4-dimethylthioxanthone and 2,4-diethylthioxanthone; benzyl dimethyl ketal, acetophenone dimethyl ketal, ethyl p-dimethylaminobenzoate, 2,4,6-trimethylbenzyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzyl)phenylphosphine oxide, bis(2,6-dimethoxybenzyl)-2,4,4-trimethylpentylphosphine oxide, (2,4,6-trimethylbenzyl)ethoxyphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, and 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone. These other photopolymerization initiators may be used alone or in combination of two or more.

[0059] The photosensitive resin composition of the present invention can be further mixed with other optional components as needed, such as colorants, additives, defoaming agents, flame retardants, non-reactive diluents, etc.

[0060] Pigments and pigments used as colorants are not particularly limited. Depending on the desired color, any colorant, such as white, black, blue, green, yellow, violet, orange, or red, can be used. Furthermore, the inclusion of a colorant can impart concealing properties to the protective film. Examples of colorants include inorganic colorants such as titanium dioxide for white colorants, acetylene black and carbon black for black colorants, organic colorants such as phthalocyanine green for green colorants, phthalocyanine blue and direct blue for blue colorants, and diketopyrrolopyrrole colorants such as cromophthalocyanine orange for orange colorants. These colorants can be used alone or in combination of two or more.

[0061] Examples of additives include mercaptobenzoxazole and its derivatives, dicyandiamide (DICY) and its derivatives, melamine and its derivatives, boron trifluoride-amine complexes, organic acid hydrazides, diaminomaleic acid dinitrile (DAMN) and its derivatives, guanamine and its derivatives, amine imide (AI), polyamide and other latent hardeners, and aliphatic dimethyl urea and other thermal hardening catalysts.

[0062] Examples of the defoaming agent include silicone polymers, hydrocarbon polymers, and acrylic polymers.

[0063] The flame retardant is used to impart flame retardancy to the cured coating of the photosensitive resin composition. Examples of the flame retardant include phosphorus-based flame retardants, preferably organic phosphate-based flame retardants. Examples of phosphorus flame retardants include halogen-containing phosphates such as tris(chloroethyl)phosphate, tris(2,3-dichloropropyl)phosphate, tris(2-chloropropyl)phosphate, tris(2,3-bromopropyl)phosphate, tris(bromochloropropyl)phosphate, 2,3-dibromopropyl-2,3-chloropropyl phosphate, tris(tribromophenyl)phosphate, tris(dibromophenyl)phosphate, and tris(tribromoneopentyl)phosphate; non-halogen-containing aliphatic phosphates such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, and tributoxyethyl phosphate; triphenyl phosphate, cresyldiphenyl phosphate, dicresylphenyl phosphate, tricresyl phosphate, tri-xylyl phosphate, dicresyldiphenyl phosphate, tri(isopropylphenyl)phosphate, isopropylphenyldiphenyl phosphate, diisopropylphenylphenyl phosphate, tris(trimethylphenyl)phosphate, tris(triethylphenyl)phosphate, tris(tributyl)phosphate, trioctyl phosphate, and tributoxyethyl phosphate; Non-halogen aromatic phosphates such as tributylphenyl) phosphate, hydroxyphenyl diphenyl phosphate, and octyl diphenyl phosphate; metal phosphonates such as tris-diethylaluminum phosphonate, trimethylethylaluminum phosphonate, tris-diphenylaluminum phosphonate, zinc bis-diethylphosphonate, zinc bis-methylethylphosphonate, zinc bis-diphenylphosphonate, bis-diethylphosphonyltitanium, tetrakis-diethylphosphonyltitanium, bis-methylethylphosphonyltitanium, tetrakis-methylethylphosphonyltitanium, bis-diphenylphosphonyltitanium, and tetrakis-diphenylphosphonyltitanium; HCA-modified compounds such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (HCA), HCA-acrylate addition reaction products, HCA-epoxy resin addition reaction products, and HCA-hydroquinone addition reaction products; and phosphine oxide compounds such as diphenylvinylphosphine oxide, triphenylphosphine oxide, trialkylphosphine oxide, and tris(hydroxyalkyl)phosphine oxide.

[0064] Non-reactive diluents are used to adjust the viscosity, coating properties, and drying properties of the photosensitive resin composition. Examples of non-reactive diluents include organic solvents that are inert to the various components of the photosensitive resin composition. Examples of such organic solvents include ketones such as methyl ethyl ketone, aromatic hydrocarbons such as benzene, toluene, and xylene, alcohols such as methanol, ethanol, n-propanol, isopropanol, and cyclohexanol, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, petroleum solvents such as petroleum ether and naphtha, cellosols such as cellulose and butyl cellosol, carbitols such as butyl carbitol, ethyl acetate, butyl acetate, cellosol acetate, butyl cellosol acetate, carbitol acetate, butyl carbitol acetate, ethylene glycol acetate, ethylene diglycol acetate, and esters such as diethylene glycol monoethyl ether. These may be used alone or in combination of two or more.

[0065] Furthermore, the photosensitive resin composition of the present invention may also contain an extender pigment such as aluminum hydroxide as a flame retardant.

[0066] Next, the method for producing the photosensitive resin composition of the present invention will be described. The method for producing the photosensitive resin composition of the present invention is not limited to a specific method. For example, the above-mentioned components are blended in specific proportions and then kneaded or mixed at room temperature (e.g., 25°C) using a kneading method such as a three-roll mill, ball mill, sand mill, bead mill, or kneader, or a stirring or mixing method such as a rapid mixer, planetary mixer, or triple mixer. Furthermore, pre-kneading or pre-mixing may be performed as needed before kneading or mixing.

[0067] Next, an example of a method for using the photosensitive resin composition of the present invention will be described. Here, a method for coating the photosensitive resin composition of the present invention on a printed wiring board to form an insulating protective film (such as a solder mask) will be described.

[0068] The photosensitive resin composition obtained as described above is applied to a desired thickness using conventional coating methods such as screen printing, spray coating, bar coating, dispensing, blade coating, knife coating, roller coating, or gravure coating. For example, a printed wiring board (a printed wiring board having a rigid substrate or a flexible substrate) having a circuit pattern formed by etching copper foil is coated. Next, the coated photosensitive resin composition is exposed to active energy rays (e.g., laser light) according to the desired pattern using a direct-drawing device to photoharden the patterned coating. The exposure dose can range from 50 mJ / cm² to 2000 mJ / cm². Next, the coating is developed by removing unexposed areas with a dilute aqueous alkali solution. This development method can be performed by spraying or sprinkling, and the dilute aqueous alkali solution can be, for example, a 0.5-5% by mass sodium carbonate solution. Next, the developed coating is cured (thermal curing treatment) by using a hot air circulation dryer at 130-170°C for 20-80 minutes to form a photocurable film (photocurable material) with the desired pattern on the printed wiring board.

[0069] Furthermore, instead of the above-mentioned exposure process of directly irradiating the desired pattern with active energy rays using a direct drawing device, after coating the photosensitive resin composition, a negative film (photomask) having a pattern that makes the area outside the circuit pattern transparent is adhered to the negative film and irradiated with active energy rays (e.g., ultraviolet rays with a wavelength of 300 to 400 nm) to photoharden the coating film. [Example]

[0070] Examples 1-12, Comparative Examples 1-5 The components listed in Table 1 below were mixed in the proportions shown in Table 1 and mixed at room temperature using a three-roller mixer to prepare the photosensitive resin compositions used in Examples 1-12 and Comparative Examples 1-5. The prepared photosensitive resin compositions were then applied to substrates as follows to produce test specimens. The amounts of each component listed in Table 1 are expressed in parts by mass unless otherwise specified. Blanks in Table 1 indicate that no amount was mixed.

[0071] Details of the components in Table 1 are as follows. (A) Carboxyl-containing photosensitive resin ･Lipoxy SP-4785: Polyacid-modified unsaturated monocarboxylic acid epoxy resin with a glycidyl methacrylate-modified cresol novolac structure, solids (resin content) 65% by mass, Showa Denko Co., Ltd. ･ZCR-1601H: Polyacid-modified unsaturated monocarboxylic acid epoxy resin with a bisphenol novolac structure, solids (resin content) 65% by mass, Nippon Kayaku Co., Ltd. ･ZFR-1887: Polyacid-modified unsaturated monocarboxylic acid epoxy resin, solid content (resin content) 65% by mass, Nippon Kayaku Co., Ltd.

[0072] (B) Inorganic fillers ･FG-20: Untreated talc, D50: 2.0μm, Japan Talc Co., Ltd. ･FG-15: Untreated talc, D50: 1.5μm, Japan Talc Co., Ltd. SG-95: Untreated talc, D50: 2.1μm, Japan Talc Co., Ltd. SG-2000: Untreated talc, D50: 0.9μm, Japan Talc Co., Ltd. ･FH-105: Untreated talc, D50 5.0μm, Fuji Talc Industrial Co., Ltd. ･FG-20 epoxy silane 3% surface treated talc: Surface treated with epoxy functional silane compound to a concentration of 3% by mass, D50 2.5μm, Japan Talc Co., Ltd. ･FG-20 5% Acrylic Silane Surface Treatment: Surface-treated talc with 5% acrylic silane compound, D50: 3.0μm, Japan Talc Co., Ltd.

[0073] (C) Photopolymerization initiator ･Omnirad379:IGM Resins BV

[0074] (D) Reactive diluent ･KAYARAD DPCA-20: Nippon Kayaku Co., Ltd.

[0075] (E) Epoxy compounds ･YX-4000: Biphenyl type epoxy resin, Mitsubishi Chemical Corporation ･N-695: Cresol novolac epoxy resin, DIC Corporation

[0076] Colorants ･Carbon black:Toyo Ink Manufacturing Co., Ltd. additive ･DICY-7: Mitsubishi Chemical Corporation ･U-CAT 3513N:SAN-APRO Co., Ltd. ･Melamine: Nissan Chemical Industries, Ltd. defoaming agent ･AC-2300C: Shin-Etsu Chemical Co., Ltd. flame retardants ･Exolit OP-935: Aluminum tris-diethylphosphonate, Clariant Japan Co., Ltd. ･Aluminum hydroxide Non-reactive diluent ･EDGAC: Sanyo Chemicals Co., Ltd.

[0077] Inorganic fillers other than talc ･B-30: Barium sulfate, D50 0.1~0.2μm, Sakai Chemical Industry Co., Ltd. ･SO-C2: Silicon oxide, D50: 0.5μm, Admatechs Co., Ltd. MIN-U-SIL 5Micron: D50 is 5μm, Ar Brown Co., Ltd. organic fillers Urethane beads: D50 is 3.5μm, Dainichi Seika Co., Ltd.

[0078] Test body preparation steps As follows, the photosensitive resin compositions of the examples and comparative examples prepared as described above were coated on a substrate to produce a test body having a cured coating film on the substrate. Substrate: 2-layer FCCL (Flexible Copper Laminate) (Cu foil: 12.5μm thick, polyimide film thickness: 25μm) Surface treatment: soft etching Coating method: screen printing Pre-drying: oven, 80℃, 20 minutes Dry film thickness (20±3μm) Exposure: 100 mJ / cm² on the coating, exposure device: Orbotech direct drawing (DI) exposure device "Nuvogo1000R" (light source: laser) Post-hardening (heat hardening treatment): oven at 150°C for 60 minutes

[0079] Evaluation Project (1) Flux resistance A frame with polyimide tape (150μm thick) was placed on the opening pattern of the hard coating on the Cu foil. The inside of the frame was filled with rosin flux and covered with a lid. Reflow was performed in a reflow oven (TNP-538EM, manufactured by Tamura Manufacturing Co., Ltd.) at a preheat temperature of 150°C to 180°C for 80 seconds and a peak temperature of 240°C for 40 seconds. After reflow, the lid was removed and the condition of the hard coating was visually observed and evaluated as follows. A rating of △ or higher was considered acceptable. ◎: There is no peeling or swelling of the hardened coating, and there are no abnormalities on the surface of the hardened coating. ○: There is no peeling or swelling of the hardened coating, but there are traces of penetration on the surface of the hardened coating. △: There is some peeling and swelling in the cured coating. ×: The cured coating film exhibits significant peeling and swelling.

[0080] (2) Gloss value (matt appearance) The 60-degree specular reflectance (%) of the hardened coating surface of the test specimen was measured using a VG-2000 gloss meter (Nippon Denshoku Industries Co., Ltd.). A gloss value of 30% or less was considered matte and passed.

[0081] (3) Softness The specimens with the hardened coating formed on them were bent using a mandrel test. The occurrence of cracks in the hardened coating was observed visually and under a ×200 optical microscope to evaluate whether cracks had occurred. A score of △ or above was considered acceptable. ◎: No cracks occurred after bending 10 times with a diameter of 2 mm. ○: No cracks occurred after bending once at φ2mm, but cracks occurred after bending 10 times. △: Cracks occurred when the steel was bent once at φ2mm, but no cracks occurred when it was bent once at φ3mm. ×: Cracks occurred when bending once with a diameter of 3 mm.

[0082] (4) Insulation reliability Following the above test specimen preparation procedures, a comb-shaped electrode (line / space = 30μm / 30μm) was used instead of a two-layer FCCL substrate to produce a test specimen. Using a HAST device, insulation resistance was measured at 110°C and 85% RH for 24 hours with a DC32V supply. The evaluation criteria were as follows: a score of △ or higher was considered acceptable. ◎: Insulation resistance value is 1.0×10 9Ω or more. ○: The insulation resistance value is 1.0×10 8Ω or more and less than 1.0×10 9Ω. △: The insulation resistance value is 1.0×10 7Ω or more and less than 1.0×10 8Ω. ×: The insulation resistance value is less than 1.0×10 7Ω.

[0083] The evaluation results are shown in Table 1 below.

[0084]

[0085] As shown in Table 1, Examples 1 to 12 in which the inorganic filler is talc with a D50 of 0.7 μm or more and 5.5 μm or less can form a protective film having insulation reliability, flux resistance, matte appearance, and excellent flexibility.

[0086] In particular, Examples 1, 4, and 5, in which the inorganic filler was talc with a D50 of 1.3 μm to 2.3 μm, showed well-balanced improvements in flux resistance, matte appearance, and flexibility compared to Examples 6 and 7, in which the inorganic filler was talc with a D50 of 0.9 μm and 5.0 μm, respectively. Furthermore, Example 1, in which approximately 50 parts by mass of talc with a D50 of 0.7 μm to 5.5 μm was added to 100 parts by mass of the carboxyl group-containing photosensitive resin, further improved flux resistance and matte appearance compared to Example 2, in which approximately 20 parts by mass of talc with a D50 of 0.7 μm to 5.5 μm was added. Furthermore, Example 1, in which the carboxyl group-containing photosensitive resin had a cresol novolac-type epoxy resin backbone, showed even greater improvements in insulation reliability and flux resistance compared to Examples 8 and 9, in which the carboxyl group-containing photosensitive resin did not have a cresol novolac-type epoxy resin backbone.

[0087] Example 3, which further incorporates urethane beads as an organic filler, exhibits slightly lower flux resistance compared to Example 1, but further improves flexibility. Furthermore, Examples 10 and 11, which utilize surface-treated talc, demonstrate improved insulation reliability, matte appearance, and flexibility. In particular, Example 11, which utilizes surface-treated talc treated with an acrylic silane compound, exhibits excellent flux resistance. Furthermore, Example 12, which utilizes surface-treated talc and further incorporates urethane beads as an organic filler, exhibits improved flux resistance, matte appearance, and insulation reliability, while also improving flexibility.

[0088] On the other hand, Comparative Example 1, in which the inorganic filler was barium sulfate with a D50 of 0.1-0.2 μm, failed to achieve flexibility and a matte appearance. Comparative Example 2, in which the inorganic filler was silicon oxide with a D50 of 0.5 μm, failed to achieve a matte appearance. Comparative Example 3, in which the inorganic filler was silicon oxide instead of talc, even though its D50 was 5 μm, failed to achieve flexibility and insulation reliability. Comparative Example 4, in which urethane beads were blended with an organic filler instead of an inorganic filler, even though its D50 was 3.5 μm, failed to achieve flux resistance and insulation reliability. Comparative Example 5, in which neither inorganic nor organic fillers were blended, failed to achieve a matte appearance. [Industrial Applicability]

[0089] The photosensitive resin composition of the present invention can form a protective film with excellent insulation reliability, flux resistance, matte appearance, and flexibility, and therefore has high utilization value in the field of insulating protective films provided on printed wiring boards using flexible substrates.

Claims

1. A photosensitive resin composition comprising (A) a carboxyl-containing photosensitive resin, (B) an inorganic filler, (C) a photopolymerization initiator, (D) a reactive diluent, and (E) an epoxy compound, wherein the aforementioned (A) carboxyl-containing photosensitive resin is a polyacid-modified unsaturated monocarboxylate epoxy resin having a glycidyl methacrylate-modified cresol phenolic varnish structure; the aforementioned (B) inorganic filler is untreated talc with a particle size D50 of 1.3 μm to 2.0 μm and a cumulative volume percentage of 50% of untreated talc with a particle size D50 of 2.0 μm to 4.0 μm and a cumulative volume percentage of 50% of surface- ...

2. The photosensitive resin composition of claim 1, wherein the aforementioned organic compound is selected from at least one of the group consisting of epoxy silane compounds and (meth)acrylate silane compounds.

3. The photosensitive resin composition of claim 1, wherein, relative to 100 parts by mass of the carboxyl-containing photosensitive resin of claim (A), it contains 8 to 80 parts by mass of the aforementioned talc.

4. The photosensitive resin composition of claim 1, wherein, relative to 100 parts by mass of the carboxyl-containing photosensitive resin of claim (A), it contains 30 to 70 parts by mass of the aforementioned talc.

5. The photosensitive resin composition of claim 1, which does not contain organic fillers.

6. The photosensitive resin composition of claim 1, further comprising organic filler.

7. The photosensitive resin composition of claim 1, wherein the aforementioned (C1)α-aminoalkylphenyl ketone photopolymerization initiator contains 1-(4-morpholinylphenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone.

8. The photosensitive resin composition of claim 1, wherein the aforementioned (C2) oxime ester photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazole-3-yl)(4-((1-methoxypropane-2-yl)oxy)-2-methylphenyl) ketone O-acetylgoxime.

9. A photocurable form of the photosensitive resin composition as claimed in claim 1.

10. A printed wiring board having a photocurable film of a photosensitive resin composition as claimed in claim 1.