Photosensitive resin composition, cured product, printed wiring board, and method for producing printed wiring board

Abstract

To provide a photosensitive resin composition which enables formation of a solder resist that highly achieves both heat resistance and flexibility without impairing conventionally required resolution even if it is made thinner than a conventional film, and has sufficient adhesion to a conductor having a smooth surface.SOLUTION: In a photosensitive resin composition, a carboxyl group-containing resin having a phenol skeleton and a cresol novolac type carboxyl group-containing resin are blended as carboxyl group-containing resins, and a red coloring agent and a blue coloring agent having specific ratios are mixed as coloring agents.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a photosensitive resin composition, particularly to a photosensitive resin composition suitable for use in forming a solder resist. The present invention also relates to a printed wiring board using the photosensitive resin composition and a method for producing the same. [Background technology]

[0002] In recent years, mobile information and communication devices, such as smartphones, have become widespread, and their performance has been rapidly improving. Consumers are demanding that such mobile information and communication devices be made smaller and thinner. To meet this demand, there is a need for higher density and space-saving circuit boards inside the devices. For example, in order to increase the degree of freedom in circuit board layout and effectively utilize the space inside the device, the use of highly flexible and bendable printed wiring boards, so-called flexible printed wiring boards, is expanding, and higher performance is being demanded from flexible printed wiring boards than ever before.

[0003] Incidentally, in printed wiring boards, an insulating film (solder resist layer) made of solder resist is generally used to obtain insulation. In flexible printed wiring boards, in order to achieve the above-mentioned high density and space saving inside the product, there is a demand for thinner insulating films made of solder resist. Therefore, with the expansion of applications of flexible printed wiring boards, there is a demand for solder resists that can exhibit sufficient performance as insulating films for flexible printed wiring boards even when thinned. Specifically, there is a demand for solder resists that have properties such as high flexibility, adhesion, and solder heat resistance in addition to the conventionally required insulation properties and resolution, even when thinned.

[0004] For example, Patent Document 1 proposes a resin composition for forming an insulating film that has properties required for flexible printed wiring boards, such as flexibility, warpage resistance, in addition to fine processability and insulating properties of the insulating film. Also, Patent Document 2 proposes a solder resist composition for forming a solder resist that does not lose properties such as electrical insulation, heat resistance, and adhesion even when the thickness is reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 084714 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-311233 Summary of the Invention [Problem to be solved by the invention]

[0006] Since it is expected that the performance of flexible printed wiring boards will continue to be improved in the future, there is a demand for thinner solder resists to meet this demand, and for solder resists with even higher performance to enable this. The thinner the solder resist, the higher the heat resistance required, and it has been difficult to achieve both heat resistance and flexibility at a high level in thin-film solder resists. Therefore, a continuing technical challenge remains to provide a thin-film solder resist layer that has the high resolution conventionally required and also achieves the contradictory properties of high heat resistance and flexibility, and a resin composition for forming such a thin-film solder resist.

[0007] Furthermore, particularly in the case of flexible printed wiring boards, there are increasing opportunities to use conductors with smooth surfaces such as rolled copper foils, etc. Therefore, it is also a technical challenge to provide a resin composition for forming a thin-film solder resist that has sufficient adhesion to conform to such conductors with smooth surfaces.

[0008] Therefore, an object of the present invention is to provide a photosensitive resin composition that, even when thinner than conventional ones, achieves both high levels of heat resistance and flexibility without impairing the resolution conventionally required and has sufficient adhesion to conductors with smooth surfaces, a cured product thereof, and a printed wiring board comprising the cured product. Another object of the present invention is to provide a method for producing a printed wiring board comprising a highly precise, thin-film solder resist layer that has high heat resistance and flexibility using the photosensitive resin composition. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by providing a photosensitive resin composition containing a carboxyl group-containing resin, a thermosetting resin, a photopolymerization initiator, a photopolymerizable monomer, and a colorant, wherein the carboxyl group-containing resin includes a carboxyl group-containing resin having a phenol skeleton and a cresol novolac-type carboxyl group-containing resin, the colorant includes a red colorant and a blue colorant, and the content ratio of the red colorant to the blue colorant is 1:0.8 to 1:9 by mass, calculated as solid content. The present invention is based on this discovery. Specifically, the gist of the present invention is as follows.

[0010] [1] A photosensitive resin composition containing a carboxyl group-containing resin, a thermosetting resin, a photopolymerization initiator, a photopolymerizable monomer, and a colorant, the carboxyl group-containing resin includes a carboxyl group-containing resin having a phenol skeleton (excluding cresol novolac type carboxyl group-containing resins) and cresol novolac type carboxyl group-containing resins, the colorants include red and blue colorants; and The content ratio of the red colorant and the blue colorant is 1:0.8 to 1:9 by mass in terms of solid content. A photosensitive resin composition comprising: [2] The photosensitive resin composition according to [1], wherein the carboxyl group-containing resin having a phenol skeleton has one or more phenol skeletons selected from the group consisting of bisphenol A type, bisphenol F type, biphenol type, biphenol novolac type, bixylenol type, and biphenyl novolac type. [3] The photosensitive resin composition according to [1] or [2], wherein the photopolymerizable monomer includes a tetrafunctional or higher functional photopolymerizable monomer. [4] The photosensitive resin composition according to any one of [1] to [3], wherein the thermosetting resin contains an epoxy resin. [5] The photosensitive resin composition according to any one of [1] to [4], which is used for forming a solder resist layer. [6] A cured product of the photosensitive resin composition according to any one of [1] to [5]. [7] A printed wiring board comprising the cured product according to [6]. [8] A method for producing a printed wiring board having a solder resist layer, the method comprising the step of exposing and developing the photosensitive resin composition according to any one of [1] to [5] to form a solder resist layer. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a photosensitive resin composition that, even when thinner than conventional ones, achieves both high levels of heat resistance and flexibility without impairing the resolution conventionally required and has sufficient adhesion to conductors with smooth surfaces, a cured product thereof, and a printed wiring board comprising the cured product.Furthermore, it is possible to provide a method for producing a printed wiring board comprising a highly precise, thin-film solder resist layer that has high heat resistance and flexibility using the photosensitive resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Photosensitive resin composition] The photosensitive resin composition of the present invention contains, as essential components, a carboxyl group-containing resin, a thermosetting resin, a photopolymerization initiator, a photopolymerizable monomer, and a colorant. In the photosensitive resin composition of the present invention, the carboxyl group-containing resin includes a carboxyl group-containing resin having a phenol skeleton (excluding cresol novolac carboxyl group-containing resins) and a cresol novolac carboxyl group-containing resin, and the colorant includes a red colorant and a blue colorant in specific content ratios. Hereinafter, in this specification, "carboxyl group-containing resin having a phenol skeleton" refers to a carboxyl group-containing resin having a phenol skeleton, excluding cresol novolac carboxyl group-containing resins, unless otherwise specified. The photosensitive resin composition of the present invention uses a combination of a carboxyl group-containing resin having a phenol skeleton and a cresol novolac-type carboxyl group-containing resin with specific amounts of red and blue colorants. This allows the solder resist layer, which is a cured product of the photosensitive resin composition, to be extremely thin, without impairing the resolution required of conventional solder resist layers. It also provides the solder resist layer with high levels of heat resistance and flexibility, and sufficient adhesion to conductors with smooth surfaces. Therefore, the photosensitive resin composition of the present invention is particularly suitable for forming solder resist layers in the manufacture of printed wiring boards, more specifically, solder resist layers for flexible printed wiring boards. The reason why the combination of a carboxyl group-containing resin having a phenol skeleton and a cresol novolac-type carboxyl group-containing resin with specific amounts of red and blue colorants produces the above-mentioned effects is unclear, but the following explanation can be given. That is, by using a specific content ratio of the red colorant and the blue colorant, i.e., a mass ratio of 1:0.8 to 1:9 in terms of solid content, the photosensitive resin composition can achieve both good sensitivity and reduced excessive exposure, thereby realizing high resolution.On the other hand, by using a carboxyl group-containing resin having a phenol skeleton, which is a linear resin, and a cresol novolac type carboxyl group-containing resin as the carboxyl group-containing resin, it is believed that flexibility and heat resistance are both achieved in the cured product of the photosensitive resin composition, and that distortion with the substrate during thermal curing is suppressed, thereby improving adhesion. Also, by combining a linear carboxyl group-containing resin with a highly functional photopolymerizable monomer, the crosslink density of the cured product of the photosensitive resin composition is increased, resulting in a cured product with particularly excellent flexibility and heat resistance, and particularly suppressing distortion with the substrate during thermal curing. Each component of the photosensitive resin composition will be described in detail below.

[0013] (Carboxyl group-containing resin) The photosensitive resin composition of the present invention contains, as the carboxyl group-containing resin, a carboxyl group-containing resin having a phenol skeleton and a cresol novolac-type carboxyl group-containing resin. By including these carboxyl group-containing resins in the photosensitive resin composition, alkaline developability can be imparted to the photosensitive resin composition. In particular, photosensitive carboxyl group-containing resins having an ethylenically unsaturated double bond in the molecule are preferred in terms of photocurability and development resistance. The ethylenically unsaturated double bond is preferably derived from acrylic acid, methacrylic acid, or a derivative thereof. When using only a carboxyl group-containing resin without an ethylenically unsaturated double bond, the photosensitive resin composition can be made photocurable by using a compound having multiple ethylenically unsaturated groups in the molecule, i.e., a photopolymerizable monomer, as described below.

[0014] The carboxyl group-containing resin having a phenol skeleton and the cresol novolac type carboxyl group-containing resin can be any carboxyl group-containing resin that has a phenol skeleton or a cresol novolac type skeleton at least in part thereof, without any particular limitation. The carboxyl group-containing resin having a phenol skeleton and the cresol novolac type carboxyl group-containing resin may be used alone or in combination of two or more.

[0015] (Carboxyl group-containing resin with a phenol skeleton) The photosensitive resin composition of the present invention contains a carboxyl group-containing resin having a phenol skeleton as the carboxyl group-containing resin. By including the carboxyl group-containing resin having a phenol skeleton in the photosensitive resin composition, it is possible to impart good flexibility and adhesion to the photosensitive resin composition. Specific examples of the carboxyl group-containing resin having a phenol skeleton include the following compounds (which may be either oligomers or polymers). As mentioned above, in the present invention, the carboxyl group-containing resin having a phenol skeleton does not include cresol novolac-type carboxyl group-containing resins.

[0016] (1) Carboxylic acid-containing photosensitive urethane resins obtained by the polyaddition reaction of diisocyanates with bifunctional epoxy resins having a phenolic skeleton, partially acid anhydride-modified products of reaction products of monocarboxylic acid compounds having ethylenically unsaturated double bonds such as (meth)acrylic acid, carboxyl-containing dialcohol compounds, and diol compounds.

[0017] (2) A photosensitive urethane resin containing a carboxyl group, which is terminally (meth)acrylated by adding a compound having one hydroxyl group and one or more (meth)acryloyl groups in the molecule, such as a hydroxyalkyl (meth)acrylate, during the synthesis of the resin (1).

[0018] (3) A carboxyl group-containing photosensitive urethane resin that is (meth)acrylated at the end by adding a compound having one isocyanate group and one or more (meth)acryloyl groups in the molecule, such as an equimolar reaction product of isophorone diisocyanate and pentaerythritol triacrylate, during the synthesis of the resin in (1).

[0019] (4) A carboxyl group-containing photosensitive resin obtained by reacting an epoxy resin having a phenolic skeleton with (meth)acrylic acid and adding a dibasic acid anhydride to the hydroxyl group present in the side chain.

[0020] (5) A carboxyl group-containing photosensitive resin obtained by reacting a multifunctional epoxy resin in which the hydroxyl groups of a bifunctional epoxy resin having a phenol skeleton are further epoxidized with epichlorohydrin with (meth)acrylic acid, and then adding a dibasic acid anhydride to the resulting hydroxyl groups.

[0021] (6) A carboxyl group-containing photosensitive resin obtained by reacting an epoxy resin having a phenol skeleton with a compound having at least one alcoholic hydroxyl group and one phenolic hydroxyl group in one molecule, such as p-hydroxyphenethyl alcohol, and an unsaturated group-containing monocarboxylic acid, such as (meth)acrylic acid, and then reacting the alcoholic hydroxyl group of the resulting reaction product with a polybasic acid anhydride, such as maleic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, or adipic acid.

[0022] (7) A carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups in one molecule with an alkylene oxide such as ethylene oxide or propylene oxide, reacting the resulting reaction product with an unsaturated group-containing monocarboxylic acid, and then reacting the resulting reaction product with a polybasic acid anhydride.

[0023] (8) A carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups in one molecule with a cyclic carbonate compound such as ethylene carbonate or propylene carbonate, reacting the resulting reaction product with an unsaturated group-containing monocarboxylic acid, and then reacting the resulting reaction product with a polybasic acid anhydride.

[0024] (9) A carboxyl group-containing photosensitive resin obtained by further adding a compound having one epoxy group and one or more (meth)acryloyl groups in one molecule to the resins (1) to (8). In this specification, (meth)acrylate is a general term that refers to acrylate, methacrylate, and mixtures thereof, and the same applies to other similar expressions.

[0025] The carboxyl group-containing resin having a phenol skeleton preferably has one or more phenol skeletons selected from the group consisting of bisphenol A type, bisphenol F type, biphenol type, biphenol novolac type, bixylenol type, and biphenyl novolac type. For example, when the carboxyl group-containing resin having a phenol skeleton has one or more phenol skeletons, the phenol skeleton is preferably selected from each phenol skeleton in the above-mentioned group. Note that when the carboxyl group-containing resin having a phenol skeleton has multiple phenol skeletons, the phenol skeletons may be the same or different from each other.

[0026] The acid value of the carboxyl group-containing resin having a phenol skeleton is preferably 30 to 150 mgKOH / g, more preferably 50 to 120 mgKOH / g. By adjusting the acid value of the carboxyl group-containing resin to 30 mgKOH / g or more, alkaline developability is improved. Furthermore, by adjusting the acid value to 150 mgKOH / g or less, it is possible to easily draw a good resist pattern.

[0027] The weight-average molecular weight of the carboxyl group-containing resin having a phenol skeleton varies depending on the resin skeleton, but is generally preferably 2,000 to 150,000. By making the weight-average molecular weight 2,000 or more, tack-free performance and resolution can be improved. Furthermore, by making the weight-average molecular weight 150,000 or less, developability and storage stability can be improved. A weight-average molecular weight of 5,000 to 100,000 is more preferable.

[0028] The amount of the carboxyl group-containing resin having a phenol skeleton in the photosensitive resin composition is preferably 10 to 40% by mass, more preferably 20 to 35% by mass, calculated as solid content. By adjusting the amount to 10% by mass or more, the coating strength can be improved. Furthermore, by adjusting the amount to 40% by mass or less, the viscosity becomes appropriate and the processability is improved.

[0029] (Cresol novolac type carboxyl group-containing resin) The photosensitive resin composition of the present invention contains a cresol novolac carboxyl group-containing resin as a carboxyl group-containing resin. By including the cresol novolac carboxyl group-containing resin in the photosensitive resin composition, it is possible to impart good heat resistance to the photosensitive resin composition. Specific examples of the cresol novolac carboxyl group-containing resin include the following compounds (which may be either oligomers or polymers):

[0030] (10) A carboxyl group-containing photosensitive resin obtained by reacting a cresol novolac epoxy resin with (meth)acrylic acid and adding a dibasic acid anhydride to the hydroxyl group present in the side chain.

[0031] (11) A carboxyl group-containing photosensitive resin obtained by reacting a cresol novolac epoxy resin with a compound having at least one alcoholic hydroxyl group and one phenolic hydroxyl group in one molecule, such as p-hydroxyphenethyl alcohol, and an unsaturated group-containing monocarboxylic acid, such as (meth)acrylic acid, and then reacting the alcoholic hydroxyl group of the resulting reaction product with a polybasic acid anhydride, such as maleic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, or adipic acid.

[0032] (12) A carboxyl group-containing photosensitive resin obtained by adding a compound having one epoxy group and one or more (meth)acryloyl groups in one molecule to the resin of (10) or (11).

[0033] The acid value and weight average molecular weight of the cresol novolac type carboxyl group-containing resin can be the same as those described above for the carboxyl group-containing resin having a phenol skeleton.

[0034] The amount of the cresol novolac carboxyl group-containing resin in the photosensitive resin composition is preferably 10 to 40 mass %, more preferably 20 to 30 mass %, calculated as solid content. By adjusting the amount to 10 mass % or more, the coating strength can be improved. On the other hand, by adjusting the amount to 40 mass % or less, the viscosity becomes appropriate and the processability is improved.

[0035] The photosensitive resin composition may contain a carboxyl group-containing resin other than the above-mentioned carboxyl group-containing resin having a phenol skeleton and the cresol novolac-type carboxyl group-containing resin (hereinafter also referred to as "other carboxyl group-containing resin"), provided that the effects of the present invention are not impaired. As the other carboxyl group-containing resin, various conventionally known resins having a carboxyl group in the molecule can be used.

[0036] (thermosetting resin) The photosensitive resin composition of the present invention contains a thermosetting resin. By including a thermosetting resin in the photosensitive resin composition, it is expected that the heat resistance of the photosensitive resin composition will be improved. Any known thermosetting resin can be used. For example, known thermosetting resins such as amino resins such as melamine resins, benzoguanamine resins, melamine derivatives, and benzoguanamine derivatives, isocyanate compounds, blocked isocyanate compounds, cyclocarbonate compounds, epoxy compounds, oxetane compounds, episulfide resins, bismaleimides, and carbodiimide resins can be used. Among these, particularly preferred are thermosetting resins having multiple cyclic ether groups or cyclic thioether groups (hereinafter abbreviated as cyclic (thio)ether groups) in the molecule.

[0037] The thermosetting resin having multiple cyclic (thio)ether groups in the molecule is a compound having multiple 3-, 4-, or 5-membered cyclic (thio)ether groups in the molecule, and examples thereof include a compound having multiple epoxy groups in the molecule, i.e., a polyfunctional epoxy compound; a compound having multiple oxetanyl groups in the molecule, i.e., a polyfunctional oxetane compound; and a compound having multiple thioether groups in the molecule, i.e., an episulfide resin.

[0038] Examples of polyfunctional epoxy compounds include biphenyl-type epoxy resins (epoxy resins containing a biphenyl skeleton); epoxidized vegetable oil; bisphenol A-type epoxy resins; hydroquinone-type epoxy resins; bisphenol-type epoxy resins; thioether-type epoxy resins; brominated epoxy resins; novolac-type epoxy resins; biphenol novolac-type epoxy resins; hydrogenated bisphenol A-type epoxy resins; glycidylamine-type epoxy resins; hydantoin-type epoxy resins; alicyclic epoxy resins; trihydroxyphenylmethane-type epoxy resins; bixylenol-type or biphenol-type epoxy resins; Examples of epoxy resins include, but are not limited to, mixtures thereof; bisphenol S type epoxy resins; bisphenol A novolac type epoxy resins; tetraphenylolethane type epoxy resins; heterocyclic epoxy resins; diglycidyl phthalate resins; tetraglycidyl xylenoylethane resins; naphthalene group-containing epoxy resins; epoxy resins having a dicyclopentadiene skeleton; glycidyl methacrylate copolymer epoxy resins; cyclohexylmaleimide and glycidyl methacrylate copolymer epoxy resins; epoxy-modified polybutadiene rubber derivatives; and CTBN-modified epoxy resins.

[0039] Examples of polyfunctional oxetane compounds include bis[(3-methyl-3-oxetanylmethoxy)methyl]ether, bis[(3-ethyl-3-oxetanylmethoxy)methyl]ether, 1,4-bis[(3-methyl-3-oxetanylmethoxy)methyl]benzene, 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl]benzene, (3-methyl-3-oxetanyl)methyl acrylate, and (3-ethyl-3-oxetanyl)methyl acrylate. Examples of suitable oxetane compounds include polyfunctional oxetanes such as acrylate, (3-methyl-3-oxetanyl)methyl methacrylate, (3-ethyl-3-oxetanyl)methyl methacrylate, and their oligomers or copolymers, as well as ethers of oxetane alcohols with novolak resins, poly(p-hydroxystyrene), cardo-type bisphenols, calixarenes, calixresorcinarenes, or hydroxyl group-containing resins such as silsesquioxane. Other examples include copolymers of unsaturated monomers having an oxetane ring and alkyl (meth)acrylates.

[0040] Examples of compounds with multiple cyclic thioether groups in the molecule include bisphenol A episulfide resins. Using a similar synthesis method, episulfide resins can also be produced in which the oxygen atoms in the epoxy groups of novolac epoxy resins are replaced with sulfur atoms.

[0041] Examples of amino resins such as melamine derivatives and benzoguanamine derivatives include methylolmelamine compounds, methylolbenzoguanamine compounds, methylolglycoluril compounds, and methylolurea compounds.

[0042] The isocyanate compound may be a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, naphthalene-1,5-diisocyanate, o-xylylene diisocyanate, m-xylylene diisocyanate, and 2,4-tolylene dimer; aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, trimethylhexamethylene diisocyanate, 4,4-methylenebis(cyclohexyl isocyanate), and isophorone diisocyanate; alicyclic polyisocyanates such as bicycloheptane triisocyanate; and adducts, biuret compounds, and isocyanurates of the above-mentioned isocyanate compounds.

[0043] The blocked isocyanate compound can be an addition reaction product of an isocyanate compound and an isocyanate blocking agent. Examples of isocyanate compounds that can react with an isocyanate blocking agent include the polyisocyanate compounds described above. Examples of the isocyanate blocking agent include phenol-based blocking agents, lactam-based blocking agents, active methylene-based blocking agents, alcohol-based blocking agents, oxime-based blocking agents, mercaptan-based blocking agents, acid amide-based blocking agents, imide-based blocking agents, amine-based blocking agents, imidazole-based blocking agents, and imine-based blocking agents.

[0044] The amount of the thermosetting resin to be added is preferably such that the number of functional groups in the thermosetting resin to react with the equivalent of the carboxyl groups contained in the carboxyl group-containing resin is 0.6 to 2.5 equivalents, more preferably 0.8 to 2.0 equivalents.

[0045] (Photopolymerizable monomer) The photosensitive resin composition of the present invention contains a photopolymerizable monomer. The photopolymerizable monomer is a monomer having an ethylenically unsaturated double bond. Examples of such photopolymerizable monomers include commonly known polyester (meth)acrylates, polyether (meth)acrylates, urethane (meth)acrylates, carbonate (meth)acrylates, and epoxy (meth)acrylates. Specific examples include alkyl acrylates such as 2-ethylhexyl acrylate and cyclohexyl acrylate; hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate; mono- or diacrylates of alkylene oxide derivatives such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol; acrylamides such as N,N-dimethylacrylamide, N-methylolacrylamide, and N,N-dimethylaminopropylacrylamide; aminoalkyl acrylates such as N,N-dimethylaminoethyl acrylate and N,N-dimethylaminopropyl acrylate; hexanediol, trimethylolpropane, pentaerythritol, ditrimethylolpropane, dipentaerythritol, and trishydroxyethyl isocyanurate. Examples of suitable photopolymerizable monomers include polyhydric alcohols, polyhydric acrylates such as polyhydric alcohols or their alkylene oxide adducts or ε-caprolactone adducts; phenols, such as phenoxy acrylate and bisphenol A diacrylate, and their alkylene oxide adducts; acrylates of glycidyl ethers, such as glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, and triglycidyl isocyanurate; and, in addition to the above, acrylates and melamine acrylates obtained by directly or via diisocyanate urethane acrylate of polyols, such as polyether polyols, polycarbonate diols, hydroxyl-terminated polybutadienes, and polyester polyols, and at least one of the methacrylates corresponding to the above acrylates. Such photopolymerizable monomers can also be used as reactive diluents.

[0046] The photopolymerizable monomer preferably includes a tetrafunctional or higher functional photopolymerizable monomer. In the present invention, a tetrafunctional or higher functional photopolymerizable monomer refers to a photopolymerizable monomer having four or more ethylenically unsaturated double bonds in one molecule. More preferably, a hexafunctional or higher functional photopolymerizable monomer is used. Examples of tetrafunctional or higher photopolymerizable monomers include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, polyepoxy tetra(meth)acrylate, polyester tetra(meth)acrylate, penta(meth)acrylates such as dipentaerythritol penta(meth)acrylate and tripentaerythritol penta(meth)acrylate, hexa(meth)acrylates such as dipentaerythritol hexa(meth)acrylate and tripentaerythritol hexa(meth)acrylate, hepta(meth)acrylates such as tripentaerythritol hepta(meth)acrylate, octa(meth)acrylates such as tripentaerythritol octa(meth)acrylate, tetrafunctional or higher polyurethane poly(meth)acrylates, tetrafunctional or higher polyepoxy poly(meth)acrylates, and tetrafunctional or higher polyester poly(meth)acrylates. Further examples include modified products of these tetrafunctional or higher (meth)acrylate monomers, such as polyalkylene oxide-modified adducts, polycaprolactone-modified adducts, and polycarbonate-modified adducts; tetrafunctional or higher polyurethane poly(meth)acrylates; tetrafunctional or higher polyepoxy poly(meth)acrylates; and tetrafunctional or higher polyester poly(meth)acrylates. These tetrafunctional or higher photopolymerizable monomers may be used alone or in combination of two or more. By including a tetrafunctional or higher photopolymerizable monomer, the crosslink density during photopolymerization of the photosensitive resin composition is increased, thereby improving the heat resistance of the photosensitive resin composition.

[0047] The content of the photopolymerizable monomer is preferably 10 to 100 parts by mass, calculated as solid content, relative to 100 parts by mass of the carboxyl group-containing resin. When the content of the photopolymerizable monomer is 10 parts by mass or more, the photocurability is good, and pattern formation is easy in alkaline development after irradiation with active energy rays. On the other hand, when the content of the photopolymerizable monomer is 100 parts by mass or less, halation is less likely to occur and good resolution can be obtained. Furthermore, when a photopolymerizable monomer with 4 or more functionalities is used, from the viewpoint of the photocurability and resolution as described above, the content thereof is preferably 20 to 50 parts by mass, calculated as solid content, relative to 100 parts by mass of the carboxyl group-containing resin.

[0048] Photopolymerizable monomers are effective, particularly when a non-photosensitive carboxyl group-containing resin that does not have an ethylenically unsaturated double bond is used, because a photopolymerizable monomer must be used in combination to make the composition photocurable.

[0049] (Photopolymerization initiator) The photosensitive resin composition of the present invention contains a photopolymerization initiator. Any known photopolymerization initiator can be used. Examples of types of photopolymerization initiators include α-aminoacetophenone-based photopolymerization initiators, hydroxyacetophenone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzoin alkyl ether-based photopolymerization initiators, benzophenone-based photopolymerization initiators, acetophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, anthraquinone-based photopolymerization initiators, ketal-based photopolymerization initiators, benzoic acid ester-based photopolymerization initiators, oxime ester-based photopolymerization initiators, titanocene-based photopolymerization initiators, and alkylphenone-based photopolymerization initiators. Among these, acylphosphine oxide-based photopolymerization initiators, oxime ester-based photopolymerization initiators, and titanocene-based photopolymerization initiators are preferred, and oxime ester-based photopolymerization initiators are more preferred.

[0050] Examples of the α-aminoacetophenone-based photopolymerization initiator include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and N,N-dimethylaminoacetophenone.

[0051] Examples of hydroxyacetophenone-based photopolymerization initiators include 1-hydroxy-cyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one, and 2-hydroxy-2-methyl-1-phenylpropan-1-one.

[0052] Examples of the acylphosphine oxide photopolymerization initiator include bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, bis-(2,6-dimethoxybenzoyl)phenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bis Examples of the photopolymerization initiator include -(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylphosphinic acid methyl ester, 2-methylbenzoyldiphenylphosphine oxide, pivaloylphenylphosphinic acid isopropyl ester, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide. An example of a commercially available acylphosphine oxide photopolymerization initiator is Omnirad 819 manufactured by IGM Resins.

[0053] Examples of the benzoin-based photopolymerization initiator include benzoin, benzil, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, and benzoin n-butyl ether.

[0054] Examples of the benzophenone-based photopolymerization initiator include benzophenone, p-methylbenzophenone, Michler's ketone, methylbenzophenone, 4,4'-dichlorobenzophenone, and 4,4'-bisdiethylaminobenzophenone.

[0055] Examples of acetophenone-based photopolymerization initiators include acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino 1-propanone.

[0056] Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone.

[0057] Examples of the anthraquinone-based photopolymerization initiator include anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone, and 2-aminoanthraquinone.

[0058] Examples of the ketal-based photopolymerization initiator include acetophenone dimethyl ketal and benzyl dimethyl ketal.

[0059] Examples of the benzoic acid ester photopolymerization initiator include ethyl-4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate, and p-dimethylbenzoic acid ethyl ester.

[0060] Examples of oxime ester photopolymerization initiators include 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime), etc. Commercially available oxime photopolymerization initiators include TOE-04-A3 manufactured by Nippon Chemical Industry Co., Ltd., Irgacure OXE01 and OXE02 manufactured by BASF Japan Ltd., N-1919, ADEKA Arcles NCI-831 and NCI-831E manufactured by ADEKA Corporation, and TR-PBG-304 manufactured by Changzhou Power Electronic New Materials Co., Ltd.

[0061] Examples of titanocene photopolymerization initiators include bis(2,4-cyclopentadienyl)bis[2,6-difluoro-3-(1-pyrryl)phenyl]titanium(IV), bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium, and bis(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1-pyr-1-yl)ethyl)phenyl]titanium. Commercially available titanocene photopolymerization initiators include JMT-784 manufactured by Yueyang Kimoutain Sci-tech Co., Ltd. and GR-FMT manufactured by Hubei Gurun Technology Co., Ltd.

[0062] Examples of alkylphenone photopolymerization initiators include 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropanone, 2-methyl-1-[4-(methoxythio)phenyl]-2-morpholinopropan-1-one, and 2-benzyl-2-(dimethylamino)-4'-morpholinobutyrophenone.

[0063] Among these photopolymerization initiators, it is preferable to use an oxime ester-based photopolymerization initiator. By using a highly sensitive photopolymerization initiator such as an oxime ester-based photopolymerization initiator, even a small amount can efficiently proceed with the polymerization of the carboxyl group-containing resin and the photosensitive monomer, thereby reducing unreacted components after the photosensitive resin composition is exposed to light and cured. The photopolymerization initiator may be used alone or in combination of two or more.

[0064] The content of the photopolymerization initiator, in terms of solid content, is preferably 1 to 20 parts by mass relative to 100 parts by mass of the carboxyl group-containing resin, in the case of photopolymerization initiators other than oxime ester-based photopolymerization initiators. When the content is 1 part by mass or more, the photocurability of the photosensitive resin composition is good, the coating is less likely to peel, and coating properties such as chemical resistance are also good. On the other hand, when the content is 20 parts by mass or less, the effect of reducing outgassing is obtained, and further, light absorption at the surface of the solder resist coating film is good, and deep curing properties are not likely to decrease. A more preferred content is 2 to 10 parts by mass. Furthermore, in the case of an oxime ester-based photopolymerization initiator, the content of the photopolymerization initiator is preferably 0.1 to 0.8 parts by mass relative to 100 parts by mass of the carboxyl group-containing resin, in terms of solid content. When the content is 0.1 part by mass or more, the photocurability of the photosensitive resin composition is good, and coating properties such as heat resistance and chemical resistance are also good. On the other hand, when the content is 0.8 parts by mass or less, the light absorption of the solder resist coating film is good, and deep curing properties are not likely to decrease. More preferably, it is 0.4 to 0.7 parts by mass.

[0065] A photoinitiator aid or sensitizer may be used in combination with the above-described photopolymerization initiator. Examples of the photoinitiator aid or sensitizer include benzoin compounds, anthraquinone compounds, thioxanthone compounds, ketal compounds, benzophenone compounds, tertiary amine compounds, and xanthone compounds. Thioxanthone compounds, such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone, are particularly preferred. The inclusion of a thioxanthone compound can improve the deep curing properties of the photosensitive resin composition. While these compounds may be used as photopolymerization initiators, they are preferably used in combination with a photopolymerization initiator. The photoinitiator aid and sensitizer may each be used alone or in combination of two or more.

[0066] These photopolymerization initiators, photoinitiator assistants, and sensitizers absorb specific wavelengths, which can reduce sensitivity in some cases and function as ultraviolet absorbers. However, they are not used solely for the purpose of improving the sensitivity of the photosensitive resin composition. They can absorb light of specific wavelengths as needed to increase the photoreactivity of the surface, change the line shape and openings of the resist to vertical, tapered, or reverse tapered, and improve the accuracy of the line width and opening diameter.

[0067] (coloring agent) The photosensitive resin composition of the present invention contains a red colorant and a blue colorant. As the red colorant and the blue colorant, for example, the following colorants can be used.

[0068] Red colorants include monoazos, disazos, azolakes, benzimidazolone, perylene, diketopyrrolopyrrole, condensed azos, anthraquinones, and quinacridones, and specific examples thereof include those having the following Color Index (CI; published by The Society of Dyers and Colourists) numbers:

[0069] Examples of monoazo red colorants include Pigment Red 1, 2, 3, 4, 5, 6, 8, 9, 12, 14, 15, 16, 17, 21, 22, 23, 31, 32, 112, 114, 146, 147, 151, 170, 184, 187, 188, 193, 210, 245, 253, 258, 266, 267, 268, and 269. Examples of disazo red colorants include Pigment Red 37, 38, and 41. Examples of monoazo lake-based red colorants include Pigment Red 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 50:1, 52:1, 52:2, 53:1, 53:2, 57:1, 58:4, 63:1, 63:2, 64:1, and 68. Examples of benzimidazolone-based red colorants include Pigment Red 171, 175, 176, 185, and 208. Examples of perylene-based red colorants include Solvent Red 135, 179, Pigment Red 123, 149, 166, 178, 179, 190, 194, and 224. Examples of diketopyrrolopyrrole red colorants include Pigment Red 254, 255, 264, 270, and 272. Examples of condensed azo red colorants include Pigment Red 220, 144, 166, 214, 220, 221, and 242. Examples of anthraquinone red colorants include Pigment Red 168, 177, and 216, Solvent Red 52, 149, 150, and 207. Examples of quinacridone red colorants include Pigment Red 122, 202, 206, 207, and 209.

[0070] The content of the red colorant is not particularly limited, but is preferably 0.5 to 2.5 parts by mass, more preferably 1 to 2.3 parts by mass, and even more preferably 1.5 to 2.2 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content.

[0071] Blue colorants include phthalocyanine and anthraquinone types, and pigment types include compounds classified as pigments, such as Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, and 60. Dye types include Solvent Blue 35, 63, 67, 68, 70, 83, 87, 94, 97, 122, and 136. In addition to the above, metal-substituted or unsubstituted phthalocyanine compounds can also be used.

[0072] The content of the blue colorant is not particularly limited, but is preferably 0.5 to 7 parts by mass, more preferably 1 to 5 parts by mass, and even more preferably 1.5 to 3 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content.

[0073] In the photosensitive resin composition, the content ratio of the red colorant to the blue colorant is, in terms of solid content, 1:0.8 to 1:9 by mass, preferably 1:0.85 to 1:5, and more preferably 1:0.9 to 1:3. By including the red colorant and the blue colorant in such a ratio in the photosensitive resin composition, it is possible to reduce excessive exposure while maintaining the sensitivity of the photosensitive resin composition to exposure, and as a result, it is possible to achieve high resolution when the photosensitive resin composition is exposed and cured.

[0074] Furthermore, when a solder resist layer is formed using a photosensitive resin composition, if the photosensitive resin composition contains a large amount of filler, the filler does not disperse sufficiently in the photosensitive resin composition, resulting in surface defects such as unevenness in the solder resist layer. This problem tends to occur particularly noticeably in thin solder resist layers having a thickness of, for example, 10 μm or less. On the other hand, since filler has the effect of reducing the light transmittance of the solder resist layer, a low filler content in the photosensitive resin composition is likely to result in development residues due to excessive exposure of the photosensitive resin composition. As described above, by setting the content ratio of the red colorant and the blue colorant within a specific range, the photosensitive resin composition of the present invention can reduce excessive exposure without containing a large amount of filler, thereby solving the problem of surface defects in the solder resist layer and achieving high resolution. Therefore, the photosensitive resin composition of the present invention can be suitably used not only for forming solder resist layers of normal thickness but also for forming thin solder resist layers.

[0075] The photosensitive resin composition may contain a black colorant in addition to the red and blue colorants described above. Examples of black colorants that can be used include carbon black and Pigment Black 1, 6, 7, 8, 9, 10, 11, 12, 13, 18, 20, 25, 26, 28, 29, 30, 31, and 32.

[0076] The content of the black colorant is not particularly limited, but is preferably 0.01 to 0.1 parts by mass, more preferably 0.02 to 0.08 parts by mass, and even more preferably 0.04 to 0.06 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content.

[0077] As the coloring agent, in addition to the coloring agents of the above colors, known coloring agents such as green, yellow, purple, orange, brown, and white can be used.

[0078] Yellow colorants include monoazo, disazo, condensed azo, benzimidazolone, isoindolinone, and anthraquinone colorants. For example, anthraquinone yellow colorants include Solvent Yellow 163, Pigment Yellow 24, 108, 193, 147, 199, and 202. Isoindolinone yellow colorants include Pigment Yellow 110, 109, 139, 179, and 185. Condensed azo yellow colorants include Pigment Yellow 93, 94, 95, 128, 155, 166, and 180. Benzimidazolone yellow colorants include Pigment Yellow 120, 151, 154, 156, 175, and 181. Examples of monoazo yellow colorants include Pigment Yellow 1, 2, 3, 4, 5, 6, 9, 10, 12, 61, 62, 62:1, 65, 73, 74, 75, 97, 100, 104, 105, 111, 116, 167, 168, 169, 182, and 183. Examples of disazo yellow colorants include Pigment Yellow 12, 13, 14, 16, 17, 55, 63, 81, 83, 87, 126, 127, 152, 170, 172, 174, 176, 188, and 198.

[0079] Examples of purple, orange, brown, and white colorants include Pigment Violet 19, 23, 29, 32, 36, 38, and 42, Solvent Violet 13 and 36, CI Pigment Orange 1, 5, 13, 14, 16, 17, 24, 34, 36, 38, 40, 43, 46, 49, 51, 61, 63, 64, 71, and 73, Pigment Brown 23 and 25, and titanium oxide, respectively.

[0080] The colorants of each color may be used alone or in combination of two or more thereof. Two or more colorants of different colors may be used in combination as long as the effects of the present invention are not impaired.

[0081] The colorant may be any of pigments, dyes, and coloring matters, but it is preferable that the colorant does not contain halogen in view of reducing the environmental load and the effect on the human body.

[0082] (organic solvent) The photosensitive resin composition of the present invention may contain an organic solvent for the purpose of adjusting the viscosity when preparing the composition or when applying it to a substrate or film. Examples of the organic solvent include ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene; glycol ethers such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, diethylene glycol monomethyl ether acetate, and tripropylene glycol monomethyl ether; esters such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha, and solvent naphtha. The organic solvents may be used alone or in combination of two or more.

[0083] The organic solvent can be evaporated and dried using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, etc. (a method using an oven equipped with a heat source for air heating using steam, in which hot air in the dryer is brought into countercurrent contact, or a method in which hot air is blown onto the support from a nozzle).

[0084] (filler) The photosensitive resin composition of the present invention may contain a filler as needed to increase the physical strength of the coating film. Known inorganic or organic fillers can be used as such fillers, with barium sulfate, spherical silica, hydrotalcite, and talc being particularly preferred. Furthermore, to achieve flame retardancy, metal oxides and metal hydroxides such as aluminum hydroxide can also be used as extender pigment fillers.

[0085] The filler content, calculated as solid content, is preferably 300% by mass or less relative to the total mass of the photosensitive resin composition. If the filler content exceeds 300% by mass, the viscosity of the photosensitive resin composition increases, resulting in poor application and moldability and brittleness of the cured product. A more preferred range is 5 to 300% by mass. When the photosensitive resin composition of the present invention is used to form a solder resist layer (thin film solder resist layer) having a thickness of, for example, 10 μm or less, the inclusion of a filler in the photosensitive resin composition can easily cause problems such as surface defects in the formed solder resist layer. Therefore, when the photosensitive resin composition of the present invention is used to form such a thin film solder resist layer, the filler content is preferably smaller than that of a photosensitive resin composition used to form a conventional solder resist layer, from the viewpoint of suppressing surface defects in the thin film solder resist layer. Specifically, the filler content of the photosensitive resin composition in this case, calculated as solid content, is preferably 30% by mass or less, more preferably 20% by mass or less, relative to the total mass of the photosensitive resin composition.

[0086] (Other added ingredients) In addition to the above-mentioned components, the photosensitive resin composition of the present invention may further contain, as necessary, components such as cyanate compounds, elastomers, mercapto compounds, urethanization catalysts, thixotropic agents, adhesion promoters, block copolymers, chain transfer agents, polymerization inhibitors, copper inhibitors, antioxidants, rust inhibitors, thickeners such as organic bentonite and montmorillonite, at least one of silicone-based, fluorine-based, and polymer-based antifoaming agents and leveling agents, imidazole-based, thiazole-based, and triazole-based silane coupling agents, and flame retardants such as phosphinates, phosphate ester derivatives, and phosphorus compounds such as phosphazene compounds. These may be known in the field of electronic materials.

[0087] The photosensitive resin composition of the present invention may be used in the form of a dry film or in a liquid form. When used in a liquid form, it may be one-component or two or more-component.

[0088] [Dry film] When the photosensitive resin composition of the present invention is used in the form of a dry film, the photosensitive resin composition is applied to a first film and dried to form a resin layer.

[0089] A dry film is a laminate having a structure in which a first film, a resin layer, and an optional peelable second film are laminated in this order. The resin layer is a layer formed by applying a photosensitive resin composition to the first film or the second film and drying it. A dry film is obtained by forming a resin layer on the first film, and then laminating a second film thereon, or by forming a resin layer on the second film and laminating the resulting laminate on the first film.

[0090] When forming a dry film, the photosensitive resin composition is diluted appropriately with an organic solvent to adjust the viscosity to an appropriate level, and then coated to a uniform thickness on the first film using a comma coater, blade coater, lip coater, rod coater, squeeze coater, reverse coater, transfer roll coater, gravure coater, spray coater, or the like, and typically dried at a temperature of 50 to 130° C. for 1 to 30 minutes to obtain a film. There are no particular restrictions on the thickness of the coated film, but it is generally selected appropriately in the range of 3 to 100 μm in terms of the film thickness after drying.

[0091] The first film can be any known film without particular limitation, and examples of suitable films include polyester films such as polyethylene terephthalate and polyethylene naphthalate, and films made of thermoplastic resins such as polyimide films, polyamideimide films, polypropylene films, and polystyrene films. Among these, polyester films are preferred from the viewpoints of heat resistance, mechanical strength, ease of handling, etc. A laminate of these films can also be used as the first film.

[0092] The second film may be, for example, a polyethylene film, a polytetrafluoroethylene film, a polypropylene film, or surface-treated paper, as long as the adhesive strength between the resin layer and the second film is smaller than the adhesive strength between the resin layer and the first film when the second film is peeled off.

[0093] [Cured product] The cured product of the present invention is obtained by curing the above-mentioned photosensitive resin composition of the present invention or the resin layer of the dry film of the present invention, and even when made thinner than conventional products, it achieves a high level of both heat resistance and flexibility without impairing the resolution conventionally required, and has sufficient adhesion to conductors with smooth surfaces. The cured product of the present invention is, for example, a thin solder resist layer having a thickness of 3 to 100 μm, preferably 3 to 13 μm, and more preferably 3 to 10 μm.

[0094] [Printed wiring board] The printed wiring board of the present invention has a cured product obtained from the resin layer of the photosensitive resin composition or dry film of the present invention described above. In the method for producing a printed wiring board of the present invention, for example, the photosensitive resin composition of the present invention is adjusted to a viscosity suitable for the coating method using an organic solvent and applied to a substrate by a method such as dip coating, flow coating, roll coating, bar coating, screen printing, or curtain coating. The organic solvent contained in the composition is then evaporated and dried (pre-dried) at a temperature of 60 to 100°C to form a tack-free resin layer. When a thin-film solder resist layer is formed as the resin layer, the photosensitive resin composition of the present invention is applied to the substrate by the above-mentioned methods, preferably by roll coating, bar coating, or screen printing. When a dry film is used, the resin layer is formed on the substrate by laminating it to the substrate using a laminator or the like so that the resin layer contacts the substrate, and then peeling off the first film.

[0095] The substrates include printed wiring boards and flexible printed wiring boards with circuits already formed using copper or the like, as well as copper-clad laminates for high-frequency circuits made from materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / non-woven cloth epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, fluororesin, polyethylene, polyphenylene ether, polyphenylene oxide, cyanate, etc., including copper-clad laminates of all grades (FR-4, etc.), as well as metal substrates, polyimide films, polyethylene terephthalate films, polyethylene naphthalate (PEN) films, glass substrates, ceramic substrates, wafer plates, etc.

[0096] The volatilization drying carried out after coating the photosensitive resin composition of the present invention can be carried out using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, or the like (a method in which hot air in a dryer equipped with a heat source of an air heating type using steam is brought into countercurrent contact with the substrate, or a method in which hot air is blown onto the substrate from a nozzle).

[0097] After forming a resin layer on a substrate, it is selectively exposed to active energy rays through a photomask with a predetermined pattern, and the unexposed areas are developed with a dilute alkaline aqueous solution (e.g., a 0.3 to 3% by weight aqueous solution of sodium carbonate) to form a patterned cured product. In the case of a dry film, after exposure, the first film is peeled off from the dry film and development is carried out, thereby forming a patterned cured product on the substrate. It is also possible to peel off the first film from the dry film before exposure and expose and develop the exposed resin layer, provided that this does not impair the properties. Furthermore, the cured product can be irradiated with active energy rays and then heat-cured (e.g., at 100 to 220°C), or irradiated with active energy rays after heat-curing, or heat-cured alone for final finish curing (main curing), to form a cured coating film with excellent properties such as adhesion and hardness.

[0098] The exposure device used for the above-mentioned active energy ray irradiation may be a device equipped with a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a mercury short arc lamp, or the like, and capable of irradiating ultraviolet rays in the range of 350 to 450 nm. Furthermore, a direct imaging device (for example, a laser direct imaging device that directly draws an image with a laser based on CAD data from a computer) may also be used. The lamp or laser light source of the direct imaging device may have a maximum wavelength in the range of 350 to 450 nm. The exposure dose for image formation varies depending on factors such as the film thickness, but is generally 10 to 1,000 mJ / cm. 2 , preferably 20 to 800 mJ / cm 2 In addition, when a thin film solder resist layer is formed using the photosensitive resin composition of the present invention, the exposure dose is preferably 10 to 500 mJ / cm. 2 , more preferably 20 to 300 mJ / cm 2 is.

[0099] The developing method may be a dipping method, a shower method, a spray method, a brush method, or the like, and the developing solution may be an aqueous alkali solution such as potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, or an amine. [Example]

[0100] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are all by mass unless otherwise specified.

[0101] [Synthesis of cresol novolac-type carboxyl group-containing resin solution] To 650 parts of diethylene glycol monoethyl ether acetate, 1070 parts of orthocresol novolac epoxy resin (DIC Corporation, EPICLON N-695, softening point 95 ° C, epoxy equivalent 214, average functionality 7.6) (number of glycidyl groups (total number of aromatic rings): 5.0 mol), 360 parts (5.0 mol) of acrylic acid, and 1.5 parts of hydroquinone were added, heated to 100 ° C, and stirred to dissolve uniformly. Next, 4.3 parts of triphenylphosphine were added, and the mixture was heated to 110 ° C and reacted for 2 hours. After that, 1.6 parts of triphenylphosphine were added, and the mixture was heated to 120 ° C and reacted for another 12 hours. 525 parts of aromatic hydrocarbon (SOLVESSO (trademark) 150, Ando Parachemie Co., Ltd.) and 608 parts (4.0 mol) of tetrahydrophthalic anhydride were added to the resulting reaction solution, and the reaction was carried out at 110 ° C for 4 hours. Furthermore, 142.0 parts (1.0 mol) of glycidyl methacrylate was added to the resulting reaction solution, and the mixture was reacted for 4 hours at 115° C. In this way, a cresol novolac type carboxyl group-containing resin solution having a solid acid value of 77 mgKOH / g and a solid content of 65% was obtained.

[0102] [Preparation of Photosensitive Resin Composition] The components shown in Table 1 below were mixed in the amounts (solid content) shown in the table, pre-mixed with a mixer, and then kneaded with a three-roll mill to prepare the photosensitive resin compositions of Examples 1 to 7 and Comparative Examples 1 to 4. Details of each component in Table 1 are as follows: Carboxyl group-containing resin 1 having a phenol skeleton: Carboxyl group-containing resin having a bisphenol F skeleton (KAYARAD ZFR-1401H, manufactured by Nippon Kayaku Co., Ltd.) Carboxyl group-containing resin 2 having a phenol skeleton: Carboxyl group-containing resin having a bisphenol A skeleton (KAYARAD ZAR-2023H, manufactured by Nippon Kayaku Co., Ltd.) Carboxyl group-containing resin 3 with a phenol skeleton: Photosensitive carboxyl group-containing resin using biphenyl novolac-type multifunctional epoxy (KAYARAD ZCR-1601H, manufactured by Nippon Kayaku Co., Ltd.) Cresol novolac type carboxyl group-containing resin: A solution of the cresol novolac type carboxyl group-containing resin synthesized by the method described above. Thermosetting resin 1: Bisphenol A epoxy resin (jER 834, manufactured by Mitsubishi Chemical Corporation) Thermosetting resin 2: Bisphenol A epoxy resin (jER 828, manufactured by Mitsubishi Chemical Corporation) Thermosetting resin 3: Phenol novolac epoxy resin (EPICRON N-740, manufactured by DIC Corporation) Photopolymerizable monomer 1: Caprolactone-modified dipentaerythritol hexaacrylate (KAYARAD DPCA-60, manufactured by Nippon Kayaku Co., Ltd.) Photopolymerizable monomer 2: dipentaerythritol polyacrylate (NK Ester A-9550, manufactured by Shin-Nakamura Chemical Co., Ltd.) Photopolymerizable monomer 3: trimethylolpropane ethylene oxide modified triacrylate (Aronix (registered trademark) M350, manufactured by Toagosei Co., Ltd.) Photopolymerization initiator: Oxime ester photopolymerization initiator (TOE-04-A3, manufactured by Nippon Chemical Industry Co., Ltd.) Red colorant: Pigment Red 149 Blue colorant: Pigment Blue 15:3 Black colorant: carbon black

[0103] [Preparation of evaluation board] Each photosensitive resin composition of the Examples and Comparative Examples was applied by screen printing to the entire surface of a substrate (150 mm long, 95 mm wide, and with an electrolytic copper foil circuit pattern of 12 μm thick) so that the film thickness after drying and curing would be 10 μm, and the substrate was dried at 75° C. for 30 minutes and allowed to cool to room temperature to prepare evaluation substrates for evaluating resolution, appropriate exposure dose, heat resistance, and flexibility (bending ability). Furthermore, evaluation substrates for evaluating adhesion were prepared in the same manner as above, except that rolled copper foil was used instead of electrolytic copper foil.

[0104] (Resolution evaluation) A Kodak Step Tablet No. 2 was placed on the surface of the photosensitive resin composition coating on each evaluation substrate prepared by the method described above, and the substrate was exposed using a direct imaging exposure device with an exposure dose resulting in 7 steps after exposure, forming a cylindrical pattern with a diameter (φ) of 200 μm. Development was then performed by spraying a developer (a 1% by weight aqueous solution of NaCO at a liquid temperature of 30°C) at a spray pressure of 0.2 MPa for 60 seconds, followed by heating at 150°C for 60 minutes to fully cure the photosensitive resin composition coating. The diameters of the top (opening) and bottom circles of the cylindrical pattern formed on the cured product of the photosensitive resin composition on each substrate were measured, and the resolution of each photosensitive resin composition in the Examples and Comparative Examples was evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0105] ⊚: The top diameter is 200 μm, and the bottom diameter is 95% to 100% of the diameter of the opening, showing extremely good resolution. ○: The top diameter is 200 μm, and the bottom diameter is 85% or more and less than 95% of the diameter of the opening, and the resolution is good. △: The top diameter and bottom diameter are 80 to 90% of 200 μm, and the resolution is acceptable. ×: Halation and undercut occur, resulting in unacceptable resolution.

[0106] (Evaluation of proper exposure) A Kodak Step Tablet No. 2 was placed on the coating surface of the photosensitive resin composition on each evaluation substrate prepared by the method described above, and the substrates were exposed to varying amounts of light using a direct imaging exposure device. Development was then performed by spraying a developer (a 1% by weight aqueous solution of Na2CO3 at a liquid temperature of 30°C) at a spray pressure of 0.2 MPa for 60 seconds. The exposure amount at which the remaining coating film of the photosensitive resin composition on each evaluation substrate reached seven levels was defined as the appropriate exposure amount for each photosensitive resin composition. The appropriate exposure amounts for each photosensitive resin composition in the Examples and Comparative Examples were evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0107] ○: The appropriate exposure is 60 mJ / cm 2 More than 120mJ / cm 2 The photosensitive resin composition is cured well with an extremely low exposure dose. △: The correct exposure is 120 mJ / cm 2 More than 200mJ / cm 2 The photosensitive resin composition is cured well with a low exposure dose.

[0108] (Evaluation of heat resistance) The photosensitive resin composition coating surface on each evaluation substrate prepared by the above method was exposed using a direct imaging exposure device at an exposure dose resulting in a post-exposure step number of 7. Next, a developer (a 1% by weight Na2CO3 aqueous solution at a liquid temperature of 30°C) was sprayed at a spray pressure of 0.2 MPa for 60 seconds to develop the coating, and the photosensitive resin composition coating was then fully cured by heating at 150°C for 60 minutes. A rosin-based flux was applied to the cured photosensitive resin composition obtained after the full curing, and each substrate was immersed in a solder bath at 260°C for 5 or 10 seconds. After washing and removing the applied rosin-based flux with denatured alcohol, the cured photosensitive resin composition was inspected for swelling or peeling, and the heat resistance of the cured photosensitive resin composition of each example and comparative example was evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0109] ◯: No swelling or peeling of the cured photosensitive resin composition was observed even after immersion in a solder bath for 10 seconds once. △: After a single immersion in a solder bath for 10 seconds, swelling and peeling of the cured photosensitive resin composition was observed, but after a single immersion for 5 seconds, no swelling or peeling of the cured photosensitive resin composition was observed. ×: After immersion in a solder bath for 5 seconds once, swelling or peeling of the cured photosensitive resin composition was observed.

[0110] (Flexibility assessment) The photosensitive resin composition coating surface on each evaluation substrate prepared by the above-described method was exposed using a direct imaging exposure device at an exposure dose resulting in a post-exposure step number of 7. Next, a developer (a 1% by weight Na2CO3 aqueous solution at a liquid temperature of 30°C) was sprayed at a spray pressure of 0.2 MPa for 60 seconds to develop the coating, and the substrate was further heated at 150°C for 60 minutes to fully cure the photosensitive resin composition coating. Each substrate was then folded 180° along the seam so that the surface bearing the cured photosensitive resin composition was facing outward. The presence or absence of cracks in the cured photosensitive resin composition was confirmed visually and under an optical microscope at 200x magnification. The flexibility (bendability) of the cured photosensitive resin compositions of the Examples and Comparative Examples was evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0111] ◯: No cracks were observed in the cured product of the photosensitive resin composition, and the copper foil surface was not exposed. ×: Cracks were observed in the cured product of the photosensitive resin composition, and the copper foil surface was exposed.

[0112] (Evaluation of Adhesion) The coating surface of the photosensitive resin composition on each evaluation substrate prepared by the above-described method for evaluating adhesion was exposed using a direct imaging exposure device at an exposure dose resulting in a post-exposure step number of 7. Next, a developer (a 1% by weight Na2CO3 aqueous solution at a liquid temperature of 30°C) was sprayed at a spray pressure of 0.2 MPa for 60 seconds to develop the coating, and the substrate was further heated at 150°C for 60 minutes to fully cure the photosensitive resin composition coating. Each substrate was then immersed in 10% hydrochloric acid at 25°C for 10 minutes. After immersion, the substrates were washed with pure water and dried. Then, the substrates were tape-peeled with cellophane tape and visually inspected for peeling of the cured photosensitive resin composition. The adhesion of the cured photosensitive resin composition of each of the Examples and Comparative Examples was evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0113] ◯: After tape peeling, no peeling was observed in the cured product of the photosensitive resin composition. ×: Peeling was observed in the cured product of the photosensitive resin composition after tape peeling.

[0114] [Table 1]

[0115] The evaluation results shown in Table 1 indicate that when the photosensitive resin compositions of each Example were used, a cured product (solder resist layer) could be formed that had good resolution, a high level of both heat resistance and flexibility, and sufficient adhesion to conductors with smooth surfaces. Specifically, a photosensitive resin composition containing a phenolic carboxyl group-containing resin and a cresol novolac carboxyl group-containing resin as the carboxyl group-containing resin, and specific proportions of red and blue colorants as colorants, was shown to be able to form a solder resist layer that had good resolution, a high level of both heat resistance and flexibility, and sufficient adhesion to conductors with smooth surfaces, even when the solder resist layer formed after curing was as thin as 10 μm. On the other hand, when the photosensitive resin compositions of each Comparative Example were used, the resulting solder resist layer either had poor resolution despite a high level of both heat resistance and flexibility, or had good resolution but failed to achieve both heat resistance and flexibility.

Claims

1. A photosensitive resin composition containing a carboxyl group-containing resin, a thermosetting resin, a photopolymerization initiator, a photopolymerizable monomer, and a colorant, the carboxyl group-containing resin includes a carboxyl group-containing resin having a phenol skeleton (excluding cresol novolac carboxyl group-containing resins) and a cresol novolac carboxyl group-containing resin; the content of the carboxyl group-containing resin having a phenol skeleton in the photosensitive resin composition is 20 to 35 mass% in terms of solid content, the content of the cresol novolac carboxyl group-containing resin in the photosensitive resin composition is 10 to 40 mass% in terms of solid content, the colorants include a red colorant and a blue colorant; The red colorant and the blue colorant have a content ratio of 1:0.8 or more and less than 1:1.5 by mass, calculated as solid content, and The content of the black colorant is 0.01 to 0.1 parts by mass, calculated as solid content, per 100 parts by mass of the carboxyl group-containing resin. A photosensitive resin composition comprising:

2. 2. The photosensitive resin composition according to claim 1, wherein the carboxyl group-containing resin having a phenol skeleton has one or more phenol skeletons selected from the group consisting of bisphenol A type, bisphenol F type, biphenol type, biphenol novolac type, bixylenol type, and biphenyl novolac type.

3. The photosensitive resin composition according to claim 1 or 2, wherein the photopolymerizable monomer comprises a tetrafunctional or higher functional photopolymerizable monomer.

4. The photosensitive resin composition according to any one of claims 1 to 3, wherein the thermosetting resin comprises an epoxy resin.

5. The photosensitive resin composition according to any one of claims 1 to 4, which is used for forming a solder resist layer.

6. A cured product of the photosensitive resin composition according to any one of claims 1 to 5.

7. A printed wiring board comprising the cured product according to claim 6.

8. A method for producing a printed wiring board provided with a solder resist layer, the method comprising the step of exposing and developing the photosensitive resin composition according to any one of claims 1 to 5 to form a solder resist layer.

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