JP7662566B2 - Photosensitive resin composition, photocured product of photosensitive resin composition, and printed wiring board having photocured film of photosensitive resin composition - Google Patents

Description

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, a photocured product of the photosensitive resin composition, and a printed wiring board having a photocured film of the photosensitive resin composition.

A conductor circuit pattern such as copper foil is formed on the substrate of the printed wiring board, electronic components are mounted on the soldering lands of the conductor circuit pattern by soldering, and the conductor circuit portion excluding the soldering lands is covered with an insulating film (solder resist film) as a protective film. As the insulating film, a cured film of a photosensitive resin composition containing a carboxyl group-containing photosensitive resin and a photopolymerization initiator may be used. Therefore, the insulating film is required to have adhesion to the substrate of the printed wiring board, resolution, etc.

In response to this, a photosensitive resin composition of the alkali development type has been proposed that contains as essential components (A) a carboxyl group-containing resin, (B) a photopolymerization initiator, (C) a photosensitive monomer, and (D) a pigment, and that contains (B-1) a phosphine oxide-based photoradical polymerization initiator and (B-2) a photocationic polymerization initiator as the photopolymerization initiator (B), and (C-1) a cationic curable monomer as the photosensitive monomer (C) (Patent Document 1). In Patent Document 1, by containing (B-2) a photocationic polymerization initiator and (C-1) a cationic curable monomer, cationic polymerization proceeds after development, resulting in an insulating coating that has excellent adhesion to the substrate.

On the other hand, in the mounting process in which electronic components are mounted on the soldering lands of a conductor circuit pattern by soldering, the electronic components are placed on a printed wiring board on which an insulating coating has been formed, and the electronic components are soldered to the printed wiring board by a heat treatment in a reflow furnace. In the above mounting process, solder containing flux components may be used. When solder containing flux components is used, the flux components may seep out of the solder and permeate into the insulating coating from the surface of the insulating coating or the openings in the conductor circuit pattern.

If flux components penetrate the insulating coating, the insulating coating may peel off from the printed wiring board or blister, causing problems with the insulating coating. Therefore, the insulating coating may be required to have flux resistance that can prevent the insulating coating from peeling off or swelling from the printed wiring board even if flux components seep out from the solder.

However, in the case of the insulating coating formed from the photosensitive resin composition of Patent Document 1, when flux components seep out from the solder, the flux components permeate the insulating coating, which can cause the insulating coating to peel off or swell from the printed wiring board, leaving room for improvement in flux resistance.

JP 2007-017458 A

In view of the above circumstances, the present invention aims to provide a photosensitive resin composition that can form an insulating coating with excellent flux resistance without impairing the basic properties of insulation reliability, coating hardness, developability, and tackiness.

The gist of the configuration of the present invention is as follows.
[1] A composition comprising: (A) a carboxyl group-containing photosensitive resin; (B) a cationic polymerization initiator; (C) a photoradical polymerization initiator; (D) an epoxy compound; and (E) a reactive diluent;
The photosensitive resin composition, wherein the (C) photoradical polymerization initiator contains at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator.
[2] The photosensitive resin composition according to [1], wherein the anion moiety of the cationic polymerization initiator (B) is a phosphorus-based or antimony-based anion moiety.
[3] The photosensitive resin composition according to [1], wherein the anion moiety of the cationic polymerization initiator (B) is phosphorus-based.
[4] The photosensitive resin composition according to any one of [1] to [3], wherein the cationic moiety of the cationic polymerization initiator (B) is an aromatic compound having three or less aromatic rings in one molecule.
[5] The photosensitive resin composition according to any one of [1] to [3], wherein the cationic moiety of the cationic polymerization initiator (B) is an aromatic compound having two or less aromatic rings in one molecule.
[6] The photosensitive resin composition according to any one of [1] to [5], wherein the (C1) α-aminoalkylphenone-based photopolymerization initiator contains 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone.
[7] The photosensitive resin composition according to any one of [1] to [6], wherein the (C2) oxime ester photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime.
[8] The photosensitive resin composition according to any one of [1] to [7], wherein the (D) epoxy compound contains at least one selected from the group consisting of cresol novolac epoxy resins, bisphenol A epoxy resins, biphenyl aralkyl epoxy resins, and triglycidyl isocyanurate.
[9] The photosensitive resin composition according to any one of [1] to [7], wherein the (D) epoxy compound contains at least two kinds selected from the group consisting of cresol novolac type epoxy resins, bisphenol A type epoxy resins, biphenyl aralkyl type epoxy resins, and triglycidyl isocyanurate.
[10] The photosensitive resin composition according to any one of [1] to [7], wherein the epoxy compound (D) contains a cresol novolac type epoxy resin and triglycidyl isocyanurate.
[11] A photocured product of the photosensitive resin composition according to any one of [1] to [10].
[12] A printed wiring board having a photocured film of the photosensitive resin composition according to any one of [1] to [10].

According to an embodiment of the photosensitive resin composition of the present invention, the composition contains (A) a carboxyl group-containing photosensitive resin, (B) a cationic polymerization initiator, (C) a photoradical polymerization initiator, (D) an epoxy compound, and (E) a reactive diluent. The photoradical polymerization initiator (C) contains at least one selected from the group consisting of (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator. This improves the crosslink density of the epoxy compound (D) without impairing the basic properties of insulation reliability, coating hardness, developability, and tackiness, thereby making it possible to obtain a photosensitive resin composition capable of forming an insulating coating with excellent flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the anion portion of the (B) cationic polymerization initiator is phosphorus-based or antimony-based, so that the crosslink density of the (D) epoxy compound is reliably improved and excellent flux resistance can be reliably obtained.

According to an embodiment of the photosensitive resin composition of the present invention, the anion portion of the (B) cationic polymerization initiator is phosphorus-based, which further improves the crosslink density of the (D) epoxy compound, thereby achieving even better coating hardness.

According to an embodiment of the photosensitive resin composition of the present invention, the cationic portion of the cationic polymerization initiator (B) is an aromatic compound having three or less aromatic rings in one molecule, thereby improving the crosslink density of the epoxy compound (D) and reliably achieving excellent flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the cationic portion of the cationic polymerization initiator (B) is an aromatic compound having two or less aromatic rings per molecule, which improves insulation reliability, coating hardness, developability, and tackiness in a well-balanced manner, and further improves the crosslink density of the epoxy compound (D), thereby further improving flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the α-aminoalkylphenone photopolymerization initiator (C1) contains 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone, which, together with the cationic polymerization activity of the cationic polymerization initiator (B), ensures excellent flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the (C2) oxime ester photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime, which, together with the cationic polymerization activity of the (B) cationic polymerization initiator, ensures excellent flux resistance.

According to an embodiment of the photosensitive resin composition of the present invention, the (D) epoxy compound contains at least one selected from the group consisting of cresol novolac epoxy resin, bisphenol A epoxy resin, biphenyl aralkyl epoxy resin, and triglycidyl isocyanurate, so that the crosslink density of the (D) epoxy compound is reliably improved and excellent flux resistance can be reliably obtained.

According to an embodiment of the photosensitive resin composition of the present invention, the (D) epoxy compound contains at least two selected from the group consisting of cresol novolac epoxy resin, bisphenol A epoxy resin, biphenyl aralkyl epoxy resin, and triglycidyl isocyanurate, thereby further improving tackiness.

According to an embodiment of the photosensitive resin composition of the present invention, the (D) epoxy compound contains a cresol novolac type epoxy resin and triglycidyl isocyanurate, which further improves all of the flux resistance, insulation reliability, and coating hardness.

Next, the photosensitive resin composition of the present invention will be described below. The photosensitive resin composition of the present invention contains (A) a carboxyl group-containing photosensitive resin, (B) a cationic polymerization initiator, (C) a photoradical polymerization initiator, (D) an epoxy compound, and (E) a reactive diluent, and the (C) photoradical polymerization initiator contains 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, the (B) cationic polymerization initiator and (C) photoradical polymerization initiator are blended as polymerization initiators. In the photosensitive resin composition of the present invention, the crosslink density of the (D) epoxy compound is improved without impairing the basic properties of insulation reliability, coating hardness, developability, and tackiness, and an insulating coating with excellent flux resistance can be formed.

<(A) Carboxyl Group-Containing Photosensitive Resin>
The carboxyl group-containing photosensitive resin, which is the component (A), is the base resin of the photosensitive resin composition. The structure of the carboxyl group-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 the carboxyl group-containing photosensitive resin include (A1) a polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin (A1 resin) having a structure obtained by reacting at least a part of the epoxy groups of a polyfunctional epoxy resin having two or more epoxy groups in one molecule with a radically polymerizable unsaturated monocarboxylic acid to obtain a radically polymerizable unsaturated monocarboxylated epoxy resin, and then reacting the resulting hydroxyl groups with a polybasic acid and/or a polybasic acid anhydride; (A2) a polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin (A2 resin) having a structure obtained by further introducing a radically polymerizable unsaturated group; and (A3) an acid-modified urethane-modified unsaturated monocarboxylated epoxy resin (A3 resin) having a structure obtained by reacting at least a part of the epoxy groups of a multifunctional epoxy resin having two or more epoxy groups in one molecule with a radically polymerizable unsaturated monocarboxylic acid to obtain an unsaturated monocarboxylated epoxy resin, then subjecting the hydroxyl groups thus produced to an addition reaction with a polyisocyanate compound, and further subjecting the isocyanate groups of the addition-reacted polyisocyanate compound to an addition reaction with a compound having a hydroxyl group and a carboxyl group.

(A1) Polybasic acid modified radically polymerizable unsaturated monocarboxylated epoxy resin Polyfunctional epoxy resin The epoxy equivalent of the polyfunctional epoxy resin is not particularly limited, and for example, the upper limit is preferably 3000 g/eq, more preferably 2000 g/eq, further preferably 1000 g/eq, and particularly preferably 500 g/eq. On the other hand, the lower limit of the epoxy equivalent of the polyfunctional epoxy resin is preferably 100 g/eq, and particularly preferably 200 g/eq. The polyfunctional epoxy resin is not particularly limited, and examples thereof include rubber-modified epoxy resins such as biphenylaralkyl-type epoxy resins, phenylaralkyl-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, and silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, cresol novolac-type epoxy resins such as ortho-cresol novolac-type epoxy resins, bisphenol novolac-type epoxy resins, cyclic aliphatic polyfunctional epoxy resins, glycidyl ester-type polyfunctional epoxy resins, glycidyl amine-type polyfunctional epoxy resins, heterocyclic polyfunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and polyfunctional modified novolac-type epoxy resins. These may be used alone or in combination of two or more.

Radical polymerizable unsaturated monocarboxylic acid The carboxyl group of the radical polymerizable unsaturated monocarboxylic acid reacts with the epoxy group of the polyfunctional epoxy resin to form an ester bond, thereby introducing a photosensitive unsaturated double bond into the epoxy resin, and imparting photosensitivity to the skeleton of the polyfunctional epoxy resin. Examples of radical polymerizable unsaturated monocarboxylic acids include acrylic acid, methacrylic acid (acrylic acid and/or methacrylic acid may be referred to as "(meth)acrylic acid"), crotonic acid, tiglic acid, angelic acid, and cinnamic acid. Among these, (meth)acrylic acid is preferred in terms of reactivity, availability, and handling. These radical polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more.

The method for reacting the polyfunctional epoxy resin with the radically polymerizable unsaturated monocarboxylic acid is not particularly limited, and an example of the method is to heat the polyfunctional epoxy resin and the radically polymerizable unsaturated monocarboxylic acid in an appropriate dispersion medium (e.g., an inert organic solvent).

Polybasic acid and/or polybasic acid anhydride The polybasic acid and/or polybasic acid anhydride undergoes an addition reaction with the hydroxyl group of the unsaturated monocarboxylated epoxy resin, thereby introducing a free carboxyl group into the photosensitive resin. The polybasic acid and/or polybasic acid anhydride is not particularly limited, and either saturated or unsaturated may 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, and other tetrahydrophthalic acids, hexahydrophthalic acid, 3-methylhexahydrophthalic acid, 4-methylhexahydrophthalic acid, 3-ethylhexahydrophthalic acid, 4-ethylhexahydrophthalic acid, and other hexahydrophthalic acids, 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 the anhydrides of the polybasic acids described above. These polybasic acids and polybasic acid anhydrides may be used alone or in combination of two or more.

The method for reacting the radically polymerizable unsaturated monocarboxylated epoxy resin with the polybasic acid and/or polybasic acid anhydride is not particularly limited, and examples thereof include a method in which the radically polymerizable unsaturated monocarboxylated epoxy resin and the polybasic acid and/or polybasic acid anhydride are heated in a suitable dispersion medium (e.g., an inert organic solvent).

(A2) Polybasic acid modified radical polymerizable unsaturated monocarboxylated epoxy resin further introduced with radical polymerizable unsaturated group Also, if necessary, a carboxyl group-containing photosensitive resin having a chemical structure in which a compound having one or more radical polymerizable unsaturated groups and an epoxy group (e.g., a glycidyl compound) is further reacted with a part of the carboxyl group of the polybasic acid modified radical polymerizable unsaturated monocarboxylated epoxy resin may be used. The carboxyl group-containing photosensitive resin further reacted with a compound having a radical polymerizable unsaturated group and an epoxy group has a chemical structure in which a radical polymerizable unsaturated group is further introduced into the side chain of the polybasic acid modified radical polymerizable unsaturated monocarboxylated epoxy resin. Therefore, the carboxyl group-containing photosensitive resin having a chemical structure in which a compound having a radical polymerizable unsaturated group and an epoxy group is reacted has better photopolymerization reactivity and further improved photosensitive properties than the polybasic acid modified radical polymerizable unsaturated monocarboxylated epoxy resin.

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

(A3) Acid-modified urethane-modified unsaturated monocarboxylated epoxy resin Polyfunctional epoxy resin As the polyfunctional epoxy resin, there is no particular limitation, but like the (A1) polybasic acid-modified radically polymerizable unsaturated monocarboxylated epoxy resin, examples thereof include rubber-modified epoxy resins such as biphenylaralkyl-type epoxy resins, phenylaralkyl-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, and silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, cresol novolac-type epoxy resins such as ortho-cresol novolac-type, bisphenol novolac-type epoxy resins, cyclic aliphatic polyfunctional epoxy resins, glycidyl ester-type polyfunctional epoxy resins, glycidyl amine-type polyfunctional epoxy resins, heterocyclic polyfunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and polyfunctional modified novolac-type epoxy resins. These may be used alone or in combination of two or more.

Radical polymerizable unsaturated monocarboxylic acid Radical polymerizable unsaturated monocarboxylic acid is not particularly limited, but like (A1) polybasic acid modified radical polymerizable unsaturated monocarboxylic acid epoxy resin, for example, (meth)acrylic acid, crotonic acid, tiglic acid, angelic acid, cinnamic acid, etc. can be mentioned. Among these, (meth)acrylic acid is preferred from the viewpoint of reactivity, availability, and handling. These radical polymerizable unsaturated monocarboxylic acids may be used alone or in combination of two or more kinds.

Polyisocyanate Compound The polyisocyanate compound is not particularly limited, and examples thereof include diisocyanates such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), methylene diisocyanate (MDI), methylene biscyclohexyl isocyanate, trimethylhexamethyl diisocyanate, hexane diisocyanate, hexamethylamine diisocyanate, toluene diisocyanate, 1,2-diphenylethane diisocyanate, 1,3-diphenylpropane diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethyl diisocyanate, etc. These polyisocyanate compounds may be used alone or in combination of two or more kinds.

Compounds Having a Hydroxyl Group and a Carboxyl Group The compounds having a hydroxyl group and a carboxyl group are not particularly limited, and examples thereof include dialkanolalkanoic acids such as dimethylolalkanoic acids such as dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolpentanoic acid, dimethylolheptanoic acid, etc. These compounds may be used alone or in combination of two or more.

The above-mentioned A1 resin, A2 resin, and A3 resin may be used alone or in combination of two or more types.

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

The mass average molecular weight of the carboxyl group-containing photosensitive resin is not particularly limited and can be appropriately selected depending on the conditions of use, etc. For example, the lower limit is preferably 6,000, more preferably 7,000, and particularly preferably 8,000, from the viewpoint of contributing to improving the toughness and tackiness of the photocured product. On the other hand, the upper limit of the mass average molecular weight of the carboxyl group-containing photosensitive resin is preferably 200,000, more preferably 100,000, and particularly preferably 50,000, from the viewpoint of contributing to improving alkaline developability. The above "mass average molecular weight" means the mass average molecular weight measured at room temperature using gel permeation chromatography (GPC) and calculated in terms of polystyrene.

The carboxyl group-containing photosensitive resin may be prepared by the above reaction process using the above components, or a commercially available carboxyl group-containing photosensitive resin may be used. Examples of commercially available carboxyl group-containing photosensitive resins include "Lipoxy SP-4621" and "Lipoxy SP-4785L" (both from Showa Denko K.K.), "ZAR-2000", "ZFR-1122", "ZFR-1887", "FLX-2089", "ZCR-1569H", and "ZCR-1601H" (both from Nippon Kayaku Co., Ltd.), and "Cyclomer P (ACA) Z-250" (Daicel Corporation).

<(B) Cationic Polymerization Initiator>
By adding the cationic polymerization initiator, which is component (B), the activity of cationic polymerization is improved, and as a result, the crosslink density of the epoxy compound (D) is improved. In combination with the radical polymerization activity of the photoradical polymerization initiator (C) described below, this inhibits the penetration of flux components into the insulating coating, and an insulating coating with excellent flux resistance can be formed.

Examples of cationic polymerization initiators include those in which the anion portion is composed of a phosphorus-based compound such as PF ₆ ^- , an antimony-based compound such as SbF ₆ ^- , or a boron-based compound such as BF ₄ ^- or [BX ₄ ] ^- (X represents a functional group in which two or more hydrogen atoms of a phenyl group are substituted with fluorine atoms or trifluoromethyl groups), and the cationic portion is composed of an aromatic sulfonium, aromatic iodonium, aromatic diazonium, aromatic ammonium, thioxanthonium, or the like.

As the anion portion of the cationic polymerization initiator, phosphorus-based and antimony-based are preferred because they reliably improve the crosslink density of the epoxy compound (D) and reliably provide excellent flux resistance, and phosphorus-based initiators are particularly preferred because they further improve the crosslink density of the epoxy compound (D) and provide even better coating hardness.

As the cationic portion of the cationic polymerization initiator, aromatic sulfonium, aromatic iodonium, aromatic diazonium, and aromatic ammonium, which are compounds having an aromatic ring, are preferred, and aromatic sulfonium is particularly preferred because it can reliably obtain flux resistance. In addition, as the compound having an aromatic ring, which is the cationic portion of the cationic polymerization initiator, an aromatic compound having 3 or less aromatic rings in one molecule is preferred because it can improve the crosslink density of the (D) epoxy compound and reliably obtain excellent flux resistance, and an aromatic compound having 2 or less aromatic rings in one molecule is particularly preferred because it can improve insulation reliability, coating hardness, developability, and tackiness in a well-balanced manner, and the crosslink density of the (D) epoxy compound is further improved, thereby further improving flux resistance.

Examples of aromatic sulfonium salts include benzyl(4-hydroxyphenyl)methylsulfonium hexafluorophosphate, benzyl(4-hydroxyphenyl)methylsulfonium hexafluoroantimonate, dimethyl-p-acetoxyphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluoroantimonate, dimethyl-p-acetoxyphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium tetrafluoroborate, benzyl(4-acetoxyphenyl)methylsulfonium hexafluorophosphate, benzyl(4-acetoxyphenyl)methylsulfonium hexafluoroantimonate, dimethyl-4-hydroxyphenylsulfonium hexafluoroantimonate, dimethyl-4-hydroxyphenylsulfonium hexafluorophosphate, diphenyl-4-(phenylthio)phenylsulfonium hexafluorophosphate, diphenyl-4-(phenylthio)phenylsulfonium hexafluoroantimonate, diphenyl-4-(phenylthio)phenylsulfonium Examples include tetrafluoroborate.

Examples of aromatic iodonium salts include diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, diphenyliodonium tetrafluoroborate, and 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate.

Examples of aromatic diazonium salts include phenyldiazonium hexafluorophosphate, phenyldiazonium hexafluoroantimonate, and phenyldiazonium tetrafluoroborate.

Examples of aromatic ammonium salts include 1-benzyl-2-cyanopyridinium hexafluorophosphate, 1-benzyl-2-cyanopyridinium hexafluoroantimonate, and 1-benzyl-2-cyanopyridinium tetrafluoroborate.

Examples of cationic polymerization initiators on the market include "San-Aid SI-60L", "San-Aid SI-80L", "San-Aid SI-100L", "San-Aid SI-110L", "San-Aid SI-150L", "San-Aid SI-180L", "San-Aid SI-80", "San-Aid SI-100", "San-Aid SI-110", "San-Aid SI-145", "San-Aid SI-150", "San-Aid SI-160", "San-Aid SI-180", "San-Aid SI-300", and "San-Aid SI-360" (all from Sanshin Chemical Industry Co., Ltd.), "Adeka Optomer SP-150", "Adeka Optomer SP-170", and "Adeka Optomer SP-172" (all from ADEKA Corporation).

These cationic polymerization initiators may be used alone or in combination of two or more.

The amount of cationic polymerization initiator is not particularly limited, but 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 carboxyl group-containing photosensitive resin (A), from the viewpoint of reliably improving the crosslink density of the epoxy compound (D) and reliably obtaining excellent flux resistance. On the other hand, the upper limit of the amount of cationic polymerization initiator is preferably 10 parts by mass, more preferably 8.0 parts by mass, and particularly preferably 6.0 parts by mass, relative to 100 parts by mass of carboxyl group-containing photosensitive resin (A), from the viewpoint of preventing a decrease in developability.

<(C) Photoradical Polymerization Initiator>
The incorporation of the photoradical polymerization initiator, which is component (C), in combination with the cationic polymerization activity of the cationic polymerization initiator improves the hardening property of the insulating coating, suppressing the penetration of flux components into the insulating coating, and enabling the formation of an insulating coating with excellent flux resistance.

The photosensitive resin composition of the present invention contains at least one photoradical polymerization initiator selected from the group consisting of (C1) α-aminoalkylphenone-based photopolymerization initiators and (C2) oxime ester-based photopolymerization initiators.

（式（１）中におけるＲは、水素または炭素数１～５個のアルキル基を表す）で表される化合物を挙げることができる。これらのうち、絶縁被膜の硬化性が確実に向上して優れた耐フラックス性を確実に得ることができる点から、α－アミノアルキルフェノン系光重合開始剤として、１－(４－モルホリノフェニル)－２－(ジメチルアミノ)－２－(４－メチルベンジル）－１－ブタノン（式（１）中におけるＲがメチル基）が好ましい。これらのα－アミノアルキルフェノン系光重合開始剤は、単独で使用してもよく、２種以上を併用してもよい。 The α-aminoalkylphenone-based photopolymerization initiator, which is the component (C1), is, for example, a compound represented by the following general formula (1):

(in formula (1), R represents hydrogen or an alkyl group having 1 to 5 carbon atoms). Of these, 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone (in formula (1), R represents a methyl group) is preferred as the α-aminoalkylphenone photopolymerization initiator, since it reliably improves the curing properties of the insulating coating and reliably provides excellent flux resistance. These α-aminoalkylphenone photopolymerization initiators may be used alone, or two or more of them may be used in combination.

As the oxime ester photopolymerization initiator of component (C2), for example, (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime, 1,2-octanedione, 1-[4-(phenylthio)-2-(O-benzoyloxime)], ethanone 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), 2-(acetyloxyiminomethyl)thioxanthen-9-one, 1,8-octanedione, 1,8-bis[9-ethyl-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime), 1,8-octanedione, 1,8-bis[9-(2-ethylhexyl)-6-nitro-9H-carbazol-3-yl]-, 1,8-bis(O-acetyloxime), and the like can be mentioned. Of these, (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime is preferred because it reliably improves the curing properties of the insulating coating and reliably provides excellent flux resistance. These oxime ester photopolymerization initiators may be used alone or in combination of two or more types.

The amount of at least one photoradical polymerization initiator selected from the group consisting of α-aminoalkylphenone-based photopolymerization initiators and oxime ester-based photopolymerization initiators is not particularly limited, but 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 (A) carboxyl group-containing photosensitive resin, from the viewpoint of reliably improving the curing property of the insulating coating and reliably obtaining excellent flux resistance. On the other hand, the upper limit of the amount of at least one photoradical polymerization initiator selected from the group consisting of α-aminoalkylphenone-based photopolymerization initiators and oxime ester-based photopolymerization initiators relative to 100 parts by mass of (A) carboxyl group-containing photosensitive resin, from the viewpoint of preventing a decrease in developability and halation, is preferably 8.0 parts by mass, more preferably 6.0 parts by mass, and particularly preferably 4.0 parts by mass.

<(D) Epoxy Compound>
The epoxy compound (D) is used to increase the crosslink density of the photocured product of the photosensitive resin composition to impart sufficient hardness to the photocured product. The increased crosslink density of the epoxy compound contributes to the formation of an insulating coating with excellent flux resistance by suppressing the penetration of flux components into the insulating coating.

Epoxy compounds include, for example, epoxy resins. Epoxy resins include, for example, the same epoxy resins as the polyfunctional epoxy resins that can be used to prepare the carboxyl group-containing photosensitive resins described above. Specific examples include rubber-modified epoxy resins such as biphenylaralkyl-type epoxy resins, phenylaralkyl-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, and silicone-modified epoxy resins, ε-caprolactone-modified epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, cresol novolac-type epoxy resins such as ortho-cresol novolac-type epoxy resins, bisphenol novolac-type epoxy resins, cyclic aliphatic polyfunctional epoxy resins, glycidyl ester-type polyfunctional epoxy resins, glycidyl amine-type polyfunctional epoxy resins, heterocyclic polyfunctional epoxy resins, bisphenol-modified novolac-type epoxy resins, and polyfunctional modified novolac-type epoxy resins. In addition, examples of epoxy compounds other than epoxy resins include, for example, triglycidyl isocyanurate. These epoxy compounds may be used alone or in combination of two or more.

Among these epoxy compounds, it is preferable to contain at least one selected from the group consisting of cresol novolac epoxy resin, bisphenol A epoxy resin, biphenyl aralkyl epoxy resin, and triglycidyl isocyanurate, because the crosslink density of the epoxy compound is reliably improved and excellent flux resistance can be reliably obtained. It is more preferable to contain at least two selected from the group consisting of cresol novolac epoxy resin, bisphenol A epoxy resin, biphenyl aralkyl epoxy resin, and triglycidyl isocyanurate, because tackiness is further improved. It is particularly preferable to contain cresol novolac epoxy resin and triglycidyl isocyanurate, because all of flux resistance, insulation reliability, and coating hardness are further improved.

The amount of the epoxy compound is not particularly limited, but the lower limit is preferably 5.0 parts by mass, more preferably 10 parts by mass, and particularly preferably 15 parts by mass, per 100 parts by mass of the carboxyl group-containing photosensitive resin (A) in order to obtain an insulating coating with sufficient hardness after photocuring of the photosensitive resin composition. On the other hand, the upper limit of the amount of the epoxy compound is preferably 50 parts by mass, more preferably 40 parts by mass, and particularly preferably 30 parts by mass, per 100 parts by mass of the carboxyl group-containing photosensitive resin (A) in order to prevent a decrease in developability.

<(E) Reactive Diluent>
The reactive diluent, which is the component (E), is, for example, a photopolymerizable monomer, and is a compound having at least one polymerizable double bond per molecule, preferably two or more polymerizable double bonds per molecule. The reactive diluent reinforces the photocuring of the photosensitive resin composition, and contributes to imparting sufficient strength, heat resistance, acid resistance, alkali resistance, etc. to the cured coating film of the photosensitive resin composition.

Examples of reactive diluents 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 (meth)acrylate compounds. Examples of the (meth)acrylate monomer include monofunctional (meth)acrylate compounds such as 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, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, ethylene oxide modified phosphate di(meth)acrylate, and allylated cyclohexyl acrylate. Examples of the acrylates include bifunctional (meth)acrylate compounds such as xyl di(meth)acrylate and isocyanurate 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(acryloxyethyl)isocyanurate; and tetrafunctional or higher (meth)acrylate compounds such as ditrimethylolpropane tetra(meth)acrylate, propionic acid-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and caprolactone-modified dipentaerythritol hexa(meth)acrylate. These may be used alone or in combination of two or more.

The amount of reactive diluent is not particularly limited, but is preferably 5.0 parts by weight or more and 70 parts by weight or less, and particularly preferably 15 parts by weight or more and 40 parts by weight or less, per 100 parts by weight of (A) carboxyl group-containing photosensitive resin.

In addition to the above-mentioned components (A) to (E), the photosensitive resin composition of the present invention may further contain, as an optional component, other photoradical polymerization initiators other than α-aminoalkylphenone-based photopolymerization initiators and oxime ester-based photopolymerization initiators, if necessary. Other photoradical polymerization initiators include, for example, benzoin-based initiators such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, and benzoin isobutyl ether; acetophenone-based initiators such as acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and 2,2-diethoxy-2-phenylacetophenone; benzophenone-based initiators such as benzophenone, p-phenylbenzophenone, 4,4'-diethylaminobenzophenone, and dichlorobenzophenone; anthraquinone-based initiators such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tertiarybutylanthraquinone, and 2-aminoanthraquinone; 2-methylthioxanthone, 2-ethylthioxanthone, 2-chloroanthraquinone, and the like. Thioxanthone-based compounds such as oxanthone, 2,4-dimethylthioxanthone, and 2,4-diethylthioxanthone; benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ethyl ester, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, (2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, and 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone can be mentioned. These other photoradical polymerization initiators may be used alone or in combination of two or more kinds.

The photosensitive resin composition of the present invention may further contain other optional components, such as inorganic fillers, colorants, additives, defoamers, flame retardants, non-reactive diluents, etc., as necessary.

Examples of inorganic fillers include aluminum hydroxide, barium sulfate, mica, talc, and silica.

The colorant is not particularly limited to pigments, dyes, etc., and any colorant can be used depending on the desired color, such as white colorant, black colorant, blue colorant, green colorant, yellow colorant, purple colorant, orange colorant, red colorant, etc. Colorants include, for example, inorganic colorants such as titanium dioxide as a white colorant, acetylene black as a black colorant, carbon black, etc., phthalocyanine-based colorants such as phthalocyanine green as a green colorant, phthalocyanine blue as a blue colorant, lyonol blue as a blue colorant, and diketopyrrolopyrrole-based colorants such as chromophthalic orange as an orange colorant. These colorants may be used alone or in combination of two or more kinds.

Additives include, for example, mercaptobenzoxazal and its derivatives, dicyandiamide (DICY) and its derivatives, melamine and its derivatives, boron trifluoride-amine complex, organic acid hydrazide, diaminomaleonitrile (DAMN) and its derivatives, guanamine and its derivatives, aminimide (AI), latent curing agents such as polyamines, and heat curing catalysts such as aliphatic dimethylurea.

Examples of antifoaming agents include silicone-based polymers, hydrocarbon-based polymers, and acrylic-based polymers.

The flame retardant is intended to impart flame retardancy to the insulating coating of the photosensitive resin composition. Examples of the flame retardant include phosphorus-based flame retardants, and organic phosphate-based flame retardants are preferred. Examples of phosphorus-based flame retardants include halogen-containing phosphate esters 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-chloropropylphosphate, tris(tribromophenyl)phosphate, tris(dibromophenyl)phosphate, and tris(tribromoneopentyl)phosphate; trimethyl phosphate, triethyl phosphate, etc. non-halogenated aliphatic phosphate esters such as tributyl phosphate, trioctyl phosphate, and tributoxyethyl phosphate; triphenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, tricresyl phosphate, trixylenyl phosphate, xylenyl diphenyl phosphate, tris(isopropylphenyl)phosphate, isopropylphenyl diphenyl phosphate, diisopropylphenyl phenyl phosphate, tris(trimethylphenyl)phosphate, and tris(t-butylphenyl)phosphate. non-halogen-based aromatic phosphate esters such as hydroxyphenyl diphenyl phosphate and octyl diphenyl phosphate; aluminum trisdiethylphosphinate, aluminum trismethylethylphosphinate, aluminum trisdiphenylphosphinate, zinc bisdiethylphosphinate, zinc bismethylethylphosphinate, zinc bisdiphenylphosphinate, titanyl bisdiethylphosphinate, titanium tetrakisdiethylphosphinate, titanyl bismethylethylphosphinate, titanium tetrakismethylethylphosphinate, bisdiphenylphosphinic acid These include metal salts of phosphinic acid such as titanyl and titanium tetrakisdiphenylphosphinate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (hereinafter referred to as HCA), HCA-modified compounds such as the addition reaction product of HCA and acrylic ester, the addition reaction product of HCA and epoxy resin, and the addition reaction product of HCA and hydroquinone, and phosphine oxide compounds such as diphenylvinylphosphine oxide, triphenylphosphine oxide, trialkylphosphine oxide, and tris(hydroxyalkyl)phosphine oxide.

The non-reactive diluent is a component for adjusting the viscosity, coatability, and drying property of the photosensitive resin composition. Examples of the non-reactive diluent include organic solvents that are inactive to the components blended in the photosensitive resin composition. Examples of the organic solvent 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 petroleum naphtha, cellosolves such as cellosolve and butyl cellosolve, carbitols such as carbitol and butyl carbitol, esters such as ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, ethylene glycol acetate, and diethylene glycol monoethyl ether acetate. These may be used alone or in combination of two or more.

The method for producing the photosensitive resin composition of the present invention is not limited to a specific method, and can be, for example, produced by mixing the above-mentioned components in a predetermined ratio and then kneading or mixing the mixed components at room temperature (e.g., 25°C) using a kneading means such as a triple roll mill, ball mill, sand mill, bead mill, or kneader, or a stirring or mixing means such as a super mixer, planetary mixer, or trimix. In addition, prior to the kneading or mixing, pre-kneading or pre-mixing may be performed as necessary.

Next, an example of a method for using the photosensitive resin composition of the present invention will be described. Here, a method for forming an insulating film (e.g., a solder resist film, etc.) by applying the photosensitive resin composition of the present invention to a printed wiring board will be described.

The photosensitive resin composition of the present invention obtained as described above is applied to a desired thickness on a printed wiring board having a circuit pattern formed by etching a copper foil, for example, by using a known coating method such as screen printing, a spray coater, a bar coater, an applicator, a blade coater, a knife coater, a roll coater, or a gravure coater. Next, an exposure process is performed in which active energy rays (for example, laser light) are directly irradiated onto the applied photosensitive resin composition in a desired pattern using a direct imaging device, and the coating film is photocured in the pattern. Examples of the exposure amount include 50 mJ/cm ² to 2000 mJ/cm ^2. Next, the coating film is developed by removing the non-exposed area with a dilute alkaline aqueous solution. Examples of the development method include a spray method and a shower method, and examples of the dilute alkaline aqueous solution include a 0.5 to 5 mass % sodium carbonate aqueous solution. Next, the developed coating film is thermally cured by performing a post-cure (thermal curing treatment) for 20 to 80 minutes in a hot air circulation dryer or the like at 130 to 170°C, thereby forming a photocured film (photocured product) having a desired pattern on the printed wiring board.

In addition, instead of the exposure treatment in which active energy rays are directly irradiated according to a desired pattern using the direct imaging device described above, an exposure treatment may be performed in which a coating film made tack-free by pre-drying the coating film by heating at a temperature of about 60 to 100°C for about 15 to 60 minutes after application of the photosensitive resin composition of the present invention is adhered to a negative film (photomask) having a pattern in which the circuit pattern lands are made transparent, and active energy rays (e.g., ultraviolet rays with a wavelength of 300 to 400 nm) are irradiated from above to photocure the coating film.

Examples 1 to 19, Comparative Example 1
The components shown in Table 1 below were blended in the ratios shown in Table 1 below and mixed at room temperature using a three-roll mill to prepare photosensitive resin compositions used in Examples 1 to 19 and Comparative Example 1. The prepared photosensitive resin compositions were then applied to substrates as described below to prepare test specimens. The blending amount of each component shown in Table 1 below is shown in parts by mass unless otherwise specified. Note that blank spaces in the blending amounts in Table 1 below mean that no blend was used.

Details of each component in Table 1 below are as follows.
(A) Carboxyl group-containing photosensitive resin Lipoxy SP-4785: polybasic acid-modified unsaturated monocarboxylated epoxy resin having a glycidyl methacrylate-modified cresol novolac structure, solid content (resin content) 65% by mass, diethylene glycol monoethyl ether acetate 35% by mass, Showa Denko K.K. ZCR-1601H: polybasic acid-modified unsaturated monocarboxylated epoxy resin having a bisphenol novolac structure, solid content (resin content) 65% by mass, diethylene glycol monoethyl ether acetate 35% by mass, Nippon Kayaku Co., Ltd. FLX-2089: acid-modified urethane-modified unsaturated monocarboxylated epoxy resin, solid content (resin content) 65% by mass, diethylene glycol monoethyl ether acetate 35% by mass, Nippon Kayaku Co., Ltd.

(B) Cationic polymerization initiator San-Aid SI-110: benzyl (4-hydroxyphenyl) methylsulfonium hexafluorophosphate (number of aromatic rings: 2), Sanshin Chemical Industry Co., Ltd. San-Aid SI-150L: dimethyl-p-acetoxyphenylsulfonium hexafluoroantimonate (number of aromatic rings: 1), Sanshin Chemical Industry Co., Ltd. San-Aid SI-100L: benzyl (4-hydroxyphenyl) methylsulfonium hexafluoroantimonate (number of aromatic rings: 2), Sanshin Chemical Industry Co., Ltd. Adeka Optomer SP170: triphenylsulfonium hexafluoroantimonate (number of aromatic rings: 3), ADEKA Corporation

(C) Photoradical polymerization initiator Omnirad 379: IGM Resins B.V.

(D) Epoxy compounds N-695: cresol novolac type epoxy resin, DIC Corporation TEPIC: triglycidyl isocyanurate, Nissan Chemical Industries, Ltd. NC-3000: biphenyl aralkyl type epoxy resin, Nippon Kayaku Co., Ltd. EPICLON 860: bisphenol A type epoxy resin, DIC Corporation VG3101L: high heat resistant trifunctional epoxy resin, Printec Co., Ltd.

(E) Reactive diluent: KAYARAD DPCA-20: Nippon Kayaku Co., Ltd.

Inorganic filler EF-013: Nippon Light Metal Co., Ltd. Colorant Carbon black: Toyo Ink Mfg. Co., Ltd. Additive DICY-7: Mitsubishi Chemical Corporation U-CAT 3513N: San-Apro Co., Ltd. Melamine: Nissan Chemical Industries, Ltd. Defoamer AC-2300C: Shin-Etsu Chemical Co., Ltd. Flame retardant Exolit OP-935: Clariant Japan Co., Ltd. Non-reactive diluent EDGAC: Sanyo Chemical Products Co., Ltd.

Test Specimen Preparation Step The photosensitive resin compositions of the Examples and Comparative Examples prepared as described above were applied onto a substrate in the manner described below to prepare test specimens having a cured coating film on the substrate.
Substrate: 2-layer FCCL (flexible copper clad laminate) (Cu foil: thickness 12.5 μm, polyimide film thickness: 25 μm)
Surface treatment: Soft etching treatment Coating method: Screen printing Pre-drying: In an oven at 80°C for 20 minutes Dry film thickness (20±5μm)
Exposure: 100 mJ/cm ² on the coating film, exposure device: direct imaging (DI) exposure device "Nuvogo1000R" manufactured by Orbotech (light source: laser)
Development: 1% by weight sodium carbonate aqueous solution, development temperature 30° C., spray pressure 0.2 MPa
Post cure (thermal curing): 150°C in oven for 60 minutes

(1) Flux resistance A frame with a polyimide tape laminated (thickness 150 μm) was placed on the opening pattern of the cured coating on the Cu foil, and the inside of the frame was filled with rosin-based flux. The lid was then placed on the frame, and reflow was performed using a reflow furnace (product name: TNP-538EM, manufactured by Tamura Corporation) under the following conditions: preheat temperature 150-180°C, 80 seconds, peak temperature 240°C, 40 seconds. After reflow, the lid was removed, and the condition of the cured coating was visually observed and rated as follows. A rating of △ or higher was judged to be acceptable.
⊚: The cured coating film is free of peeling or blistering, and the surface of the cured coating film is free of abnormalities.
◯: There is no peeling or blistering of the cured coating film, but there are traces of penetration on the surface of the cured coating film.
△: The cured coating film has some peeling or swelling.
×: The cured coating film exhibits significant peeling or blistering.

(2) Insulation reliability: A test specimen was prepared using a comb-shaped electrode (line width/space = 30 μm/30 μm) instead of a two-layer FCCL substrate according to the above test specimen preparation process, and the insulation resistance was measured by applying DC 32 V using a HAST device after humidifying the specimen at 110°C and 85% R.H. for 24 hours. The evaluation criteria were as follows, and a rating of △ or higher was determined to be a pass.
⊚: The insulation resistance value is 1.0×10 ⁹ Ω or more.
◯: The insulation resistance value is 1.0×10 ⁸ Ω or more and less than 1.0×10 ⁹ Ω.
Δ: The insulation resistance value is 1.0×10 ⁷ Ω or more and less than 1.0×10 ⁸ Ω.
×: The insulation resistance value is less than 1.0×10 ⁷ Ω.

(3) Coating Hardness The pencil hardness of the cured coating on the copper foil of the two-layer FCCL substrate was evaluated in accordance with the test method of JIS K-5600-5-4.

(4) Developability After development, the test specimens were visually inspected for the presence or absence of residues on the copper foil and polyimide film, and rated according to the following three-level scale. A rating of Δ or higher was deemed to be acceptable.
◯: No residue was found on either the copper foil or the polyimide film.
Δ: No residue was found on the copper foil, but some residue was found on the polyimide film.
×: Residues were observed on both the copper foil and the polyimide film.

(5) Tackiness In the test specimen preparation process, after preliminary drying at 80° C. for 20 minutes, a negative film was brought into contact with the coating film, and the coating was exposed to light. The coating was visually observed for tackiness, and rated on the following three-level scale. A rating of △ or higher was judged to be acceptable.
○: No sticking.
△: Sticking marks remain on the coating film.
×: After the negative film was peeled off, the coating film was found to be stuck to the negative film.

The evaluation results are shown in Table 1 below.

As shown in Table 1 above, in Examples 1 to 19, which used an α-aminoalkylphenone-based photopolymerization initiator and an oxime ester-based photopolymerization initiator as the photoradical polymerization initiator, and further contained a cationic polymerization initiator, an insulating coating was formed that had excellent insulation reliability, coating hardness, developability, and tackiness, as well as excellent flux resistance.

In particular, Example 1, which used a phosphorus-based photoradical polymerization initiator, showed improved coating hardness compared to Examples 5, 9, and 19, which used antimony-based photoradical polymerization initiators. Also, Examples 1 to 18, in which the cationic portion of the cationic polymerization initiator is an aromatic compound with one or two aromatic rings in one molecule, showed well-balanced improvements in insulation reliability, coating hardness, developability, and tackiness, and further improved flux resistance compared to Example 19, in which the cationic portion is an aromatic compound with three aromatic rings.

In addition, Examples 1 to 12, which contain two epoxy compounds selected from the group consisting of cresol novolac epoxy resin, bisphenol A epoxy resin, biphenyl aralkyl epoxy resin, and triglycidyl isocyanurate, have improved tackiness compared to Examples 14 to 17, which contain one epoxy compound selected from the group consisting of cresol novolac epoxy resin, bisphenol A epoxy resin, biphenyl aralkyl epoxy resin, and triglycidyl isocyanurate. In addition, Example 1, which contains cresol novolac epoxy resin and triglycidyl isocyanurate as epoxy compounds, has improved flux resistance, insulation reliability, and coating hardness.

On the other hand, in Comparative Example 1, which did not contain a cationic polymerization initiator, flux resistance could not be achieved.

INDUSTRIAL APPLICABILITY The photosensitive resin composition of the present invention is capable of forming an insulating coating having excellent flux resistance without impairing basic properties such as insulation reliability, coating hardness, developability, and tackiness, and is therefore highly useful in the field of insulating protective films provided on printed wiring boards using flexible or rigid substrates.

Claims (9)

(A) a carboxyl group-containing photosensitive resin, (B) a cationic polymerization initiator, (C) a photoradical polymerization initiator, (D) an epoxy compound, and (E) a reactive diluent;
the (C) photoradical polymerization initiator contains (C1) an α-aminoalkylphenone-based photopolymerization initiator and (C2) an oxime ester-based photopolymerization initiator,
The cationic moiety of the cationic polymerization initiator (B) is an aromatic sulfonium.
The photosensitive resin composition according to claim 1, wherein the epoxy compound (D) contains at least two kinds selected from the group consisting of cresol novolac type epoxy resins, bisphenol A type epoxy resins, biphenyl aralkyl type epoxy resins, and triglycidyl isocyanurate . The photosensitive resin composition according to claim 1, wherein the anion portion of the cationic polymerization initiator (B) is phosphorus-based or antimony-based. The photosensitive resin composition according to claim 1, wherein the anion portion of the cationic polymerization initiator (B) is phosphorus-based. The photosensitive resin composition according to any one of claims 1 to 3, wherein the cationic portion of the cationic polymerization initiator (B) is an aromatic compound having three or less aromatic rings in one molecule. The photosensitive resin composition according to any one of claims 1 to 3, wherein the cationic portion of the cationic polymerization initiator (B) is an aromatic compound having two or less aromatic rings in one molecule. The photosensitive resin composition according to any one of claims 1 to 5, wherein the (C1) α-aminoalkylphenone-based photopolymerization initiator contains 1-(4-morpholinophenyl)-2-(dimethylamino)-2-(4-methylbenzyl)-1-butanone. The photosensitive resin composition according to any one of claims 1 to 6, wherein the (C2) oxime ester photopolymerization initiator contains (9-ethyl-6-nitro-9H-carbazol-3-yl)(4-((1-methoxypropan-2-yl)oxy)-2-methylphenyl)methanone O-acetyloxime. A photocured product of the photosensitive resin composition according to any one of claims 1 to 7 . A printed wiring board having a photocured film of the photosensitive resin composition according to any one of claims 1 to 7 .