Photosensitive resin composition, dry film, cured product and printed wiring board

Abstract

The present invention is a photosensitive resin composition containing a carboxyl group-containing resin, a photopolymerization initiator, titanium oxide, and bentonite, wherein the Y value of the XYZ color system of a cured product of the photosensitive resin composition is 82 or more.

Description

Photosensitive resin composition, dry film, cured product, and printed wiring board

[0001] The present invention relates to a photosensitive resin composition, a dry film, a cured product, and a printed wiring board.

[0002] Printed wiring boards used in electronic devices are substrates on which electronic circuit patterns are wired with copper wires, and various components are mounted. When components are mounted on printed wiring boards with exposed copper wires, there is a risk of the copper wires being broken by external force, or short circuits caused by solder adhering to areas other than the patterned circuit. Therefore, a solder resist layer is formed to protect the patterned circuit and prevent short circuits.

[0003] The solder resist layer is formed, for example, by an alkaline development method using a photosensitive resin composition. The alkaline development method is a method in which the photosensitive resin composition is applied to the entire surface of a substrate, dried to form a coating film, exposed to light to partially cure the dried coating film, and then developed with an alkaline solution to develop the uncured photosensitive resin composition, thereby forming a pattern.

[0004] Solder resist layers of various colors are used depending on the components mounted on the printed wiring board. When mounting light-emitting elements such as light-emitting diodes (LEDs) and electroluminescent elements (ELs), a white solder resist layer with high reflectivity is sometimes used to effectively utilize the light emitted from these elements.

[0005] Highly reflective solder resist layers are often formed from photosensitive resin compositions containing titanium oxide. However, a high content of titanium oxide can result in poor resolution, which is an indicator of ease of pattern formation. For this reason, various attempts have been made to achieve both high resolution and high reflectivity in the cured product (see, for example, Patent Document 1).

[0006] Japanese Patent Application Laid-Open No. 2015-206992

[0007] In recent years, with the trend toward smaller and denser electronic devices, there has been a demand for solder resist layers with higher reflectivity. However, solder resist layers with higher reflectivity have a new problem in that the reflectivity varies depending on the manufacturing conditions.

[0008] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a photosensitive resin composition, a dry film, a cured product, and a printed wiring board that are capable of forming a cured product with little variation in reflectance.

[0009] After extensive research, the inventors discovered that the variation in reflectance is due to the printing condition of the cured coating film. Specifically, after printing a photosensitive resin composition on a substrate, standing the photosensitive resin composition against a rack or the like before drying the composition can cause the printed photosensitive resin composition to flow, resulting in variations in the coating film formation within the substrate, and these variations affect the reflectance. Further research into this phenomenon led to the discovery that adding bentonite to the photosensitive resin composition can control the flowability of the photosensitive resin composition and suppress variations in reflectance.

[0010] That is, the photosensitive resin composition according to the present invention is characterized in that it contains a carboxyl group-containing resin, a photopolymerization initiator, titanium oxide, and bentonite, and that the Y value of the XYZ color system of a cured product of the photosensitive resin composition is 82 or more.

[0011] In another aspect of the present invention, the content of bentonite is preferably 0.1% by mass to 3.0% by mass in terms of solid content relative to the entire photosensitive resin composition.

[0012] In another aspect of the present invention, the content of titanium oxide is preferably 35% by mass to 55% by mass in terms of solid content relative to the entire photosensitive resin composition.

[0013] A dry film according to another aspect of the present invention is characterized by having a resin layer obtained from the above photosensitive resin composition.

[0014] A cured product according to another aspect of the present invention is characterized by being obtained by curing the above-mentioned photosensitive resin composition or the above-mentioned resin layer.

[0015] A printed wiring board according to another aspect of the present invention is characterized by comprising the above-mentioned cured product.

[0016] According to the present invention, it is possible to provide a photosensitive resin composition capable of forming a cured product with little variation in reflectance, a dry film, a cured product, and a printed wiring board.

[0017] The photosensitive resin composition, dry film, cured product, and printed wiring board according to this embodiment will be described below. In this specification, when a numerical range is expressed with "to", it means a range that includes the numerical values ​​(i.e., from ... to ...).

[0018] (Photosensitive Resin Composition) The photosensitive resin composition according to this embodiment contains a carboxyl group-containing resin, a photopolymerization initiator, titanium oxide, and bentonite, and may further contain other components as required.

[0019] <Carboxyl group-containing resin> The carboxyl group-containing resin is a resin having a carboxyl group in the molecule, and various known and commonly used resins can be used, but a carboxyl group-containing resin having no aromatic ring is preferred. As long as the resin contains a carboxyl group without an aromatic ring, either a photosensitive carboxyl group-containing resin having one or more photosensitive unsaturated double bonds itself, or a carboxyl group-containing resin having no photosensitive unsaturated double bond can be used, and is not limited to a specific one.

[0020] Specific examples of the carboxyl group-containing resin having no aromatic ring include the compounds (which may be either oligomers or polymers) shown in (1) to (4) below. These may be used alone or in combination of two or more.

[0021] (1) A carboxyl group-containing resin obtained by copolymerizing an unsaturated carboxylic acid and a compound having an unsaturated double bond. (2) A photosensitive carboxyl group-containing resin obtained by reacting a carboxyl group-containing (meth)acrylic copolymer resin with a compound having an oxirane ring and an ethylenically unsaturated group per molecule. (3) A photosensitive carboxyl group-containing resin obtained by reacting an unsaturated monocarboxylic acid with a copolymer of a compound having one epoxy group and one unsaturated double bond per molecule and a compound having one unsaturated double bond per molecule, and then reacting the secondary hydroxyl group produced by this reaction with a saturated or unsaturated polybasic acid anhydride. (4) A photosensitive hydroxyl and carboxyl group-containing resin obtained by reacting a hydroxyl group-containing polymer with a saturated or unsaturated polybasic acid anhydride, and then reacting the carboxylic acid produced by this reaction with a compound having one epoxy group and one unsaturated double bond per molecule.

[0022] Among these, the photosensitive carboxyl group-containing resin (2) above, (a) a carboxyl group-containing (meth)acrylic copolymer resin, and (b) a copolymer resin having a carboxyl group obtained by reacting a compound having an oxirane ring and an ethylenically unsaturated group in one molecule, are preferred.

[0023] The carboxyl group-containing (meth)acrylic copolymer resin (a) is obtained by copolymerizing a (meth)acrylic acid ester with a compound having one unsaturated group and at least one carboxyl group in one molecule. Examples of the (meth)acrylic acid ester constituting the copolymer resin (a) include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, and hexyl (meth)acrylate; hydroxyl group-containing (meth)acrylic acid esters such as 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and caprolactone-modified 2-hydroxyethyl (meth)acrylate; and glycol-modified (meth)acrylates such as methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, isooctyloxydiethylene glycol (meth)acrylate, phenoxytriethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate. These may be used alone or in combination of two or more. Among these, methyl (meth)acrylate and caprolactone-modified 2-hydroxyethyl (meth)acrylate are preferred. In this specification, the term "(meth)acrylate" is a general term that refers to acrylate and methacrylate, and the same applies to other similar expressions.

[0024] Examples of compounds that constitute the copolymer resin (a) and have one unsaturated group and at least one carboxyl group per molecule include acrylic acid; methacrylic acid; modified unsaturated monocarboxylic acids in which the unsaturated group and the carboxylic acid are chain-extended, such as β-carboxyethyl (meth)acrylate, 2-acryloyloxyethyl succinic acid, and 2-acryloyloxyethyl hexahydrophthalic acid; unsaturated monocarboxylic acids having an ester bond due to lactone modification or the like; modified unsaturated monocarboxylic acids having an ether bond; and compounds containing two or more carboxyl groups per molecule, such as maleic acid. These may be used alone or in combination of two or more. Among these, methacrylic acid is preferred.

[0025] The (b) compound having an oxirane ring and an ethylenically unsaturated group in one molecule may be any compound having an ethylenically unsaturated group and an oxirane ring in one molecule, and examples thereof include glycidyl (meth)acrylate, α-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylbutyl (meth)acrylate, and 3,4-epoxycyclohexylmethylaminoacrylate. Of these, 3,4-epoxycyclohexylmethyl (meth)acrylate is preferred. These (b) compounds having an oxirane ring and an ethylenically unsaturated group in one molecule may be used alone or in combination of two or more.

[0026] 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.

[0027] The acid value of the carboxyl group-containing resin is preferably 40 mgKOH / g to 150 mgKOH / g, more preferably 50 mgKOH / g to 130 mgKOH / g. By adjusting the acid value of the carboxyl group-containing resin to 40 mgKOH / g to 150 mgKOH / g, the resolution becomes good.

[0028] The weight-average molecular weight of the carboxyl group-containing resin varies depending on the resin skeleton, but is generally preferably 2,000 to 150,000, and more preferably 5,000 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, resolution and storage stability can be improved.

[0029] The carboxyl group equivalent of the carboxyl group-containing resin is preferably 100 g / eq. to 1,000 g / eq., and more preferably 400 g / eq. to 800 g / eq. Here, "eq." is an abbreviation for "equivalent." By setting the carboxyl group equivalent to 100 g / eq. or more, developability is improved. Furthermore, by setting the carboxyl group equivalent to 1,000 g / eq. or less, crosslink density can be increased, thereby improving the strength of the cured product.

[0030] The content of the carboxyl group-containing resin in the photosensitive resin composition is preferably 20% by mass to 60% by mass, and more preferably 20% by mass to 50% by mass, calculated as solid content. By making the content of the carboxyl group-containing resin 20% by mass or more, the strength of the cured product can be improved. Furthermore, by making the content of the carboxyl group-containing resin 60% by mass or less, the viscosity of the photosensitive resin composition becomes appropriate, and printability is improved.

[0031] <Photopolymerization initiator> The photopolymerization initiator is contained in order to cure the photosensitive resin composition. The photopolymerization initiator is not particularly limited as long as it is one that is used in ordinary photosensitive resin compositions, and can be appropriately selected depending on the purpose, and any known photopolymerization initiator can be used. One type of photopolymerization initiator may be used alone, or two or more types may be used in combination.

[0032] Examples of the 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, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. bisacylphosphine oxides such as bis-(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide and 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 monoacylphosphine oxides such as phenyl(2,4,6-trimethylbenzoyl)phosphinate, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, 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, 2-hydroxy- Hydroxyacetophenones such as 2-methyl-1-phenylpropan-1-one; benzoins such as benzoin, benzil, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, and benzoin n-butyl ether; benzoin alkyl ethers; benzophenones such as benzophenone, p-methylbenzophenone, Michler's ketone, methylbenzophenone, 4,4'-dichlorobenzophenone, and 4,4'-bisdiethylaminobenzophenone;Acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl)-1-[4-(4-morpholinyl)phenyl]-1-butanone acetophenones such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2,4-diisopropylthioxanthone; anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone, Anthraquinones such as 2-aminoanthraquinone; ketals such as acetophenone dimethyl ketal and benzil dimethyl ketal; benzoic acid esters such as ethyl 4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate and p-dimethylbenzoic acid ethyl ester; 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyl oxime esters such as bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium and titanocenes such as bis(cyclopentadienyl)-bis[2,6-difluoro-3-(2-(1-pyr-1-yl)ethyl)phenyl]titanium; phenyl disulfide 2-nitrofluorene, butyroin, anisoin ethyl ether, azobisisobutyronitrile, tetramethylthiuram disulfide, and the like.

[0033] The content of the photopolymerization initiator excluding the oxime ester-based photopolymerization initiator is preferably 0.01 to 30 parts by mass, and more preferably 0.1 to 20 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. By setting the content of the photopolymerization initiator excluding the oxime ester-based photopolymerization initiator to 0.01 parts by mass or more, the photocurability of the photosensitive resin composition is improved, the coating film is less likely to peel, and coating properties such as chemical resistance are also improved. Furthermore, by setting the content of the photopolymerization initiator excluding the oxime ester-based photopolymerization initiator to 30 parts by mass or less, light absorption at the surface of the solder resist coating film is improved, and deep curing properties are less likely to decrease. The content of the oxime ester-based photopolymerization initiator is preferably 0.01 to 5 parts by mass, and more preferably 0.1 to 3.9 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. By setting the content of the oxime ester photopolymerization initiator to 0.01 parts by mass or more, the photocurability of the photosensitive resin composition is improved, and the film properties such as heat resistance, chemical resistance, etc. are also improved. Furthermore, by setting the content of the oxime ester photopolymerization initiator to 5 parts by mass or less, light absorption at the surface of the solder resist coating film is improved, and deep curing properties are less likely to decrease.

[0034] <Titanium Oxide> Titanium oxide is contained to adjust the Y value in the XYZ color system of the cured product of the photosensitive resin composition. Known and commonly used titanium oxide particles that can be used as inorganic fillers or white pigments can be used. Titanium oxide may have a rutile, anatase, or ramsdellite structure. These may be used alone or in combination of two or more. Titanium oxide may be surface-treated or untreated, but titanium oxide that has been surface-treated with an inorganic substance is preferred in terms of preventing color changes after reflow. Examples of inorganic substances include Al, Si, and Zr. Titanium oxide that has not been surface-treated with an organic substance is preferred.

[0035] The volume average particle diameter of titanium oxide is not particularly limited and can be appropriately selected depending on the purpose, and may be, for example, 0.01 μm to 10 μm. The volume average particle diameter of titanium oxide can be measured by laser diffraction. Note that the volume average particle diameter of titanium oxide may be adjusted. The volume average particle diameter can be adjusted, for example, by pre-dispersing the titanium oxide using a bead mill or jet mill.

[0036] The content of titanium oxide is preferably 35% by mass to 55% by mass, more preferably 40% by mass to 55% by mass, even more preferably 40% by mass to 50% by mass, and particularly preferably 40% by mass to 45% by mass, calculated as solid content, relative to the entire photosensitive resin composition. By adjusting the content of titanium oxide to 35% by mass to 55% by mass, the Y value of the XYZ color system of the cured product of the photosensitive resin composition can be increased.

[0037] <Bentonite> Bentonite (also called "Orben") is contained to prevent variations in reflectance of a cured product of the photosensitive resin composition. There are no particular restrictions on the bentonite as long as it is usable in photosensitive resin compositions, and it can be appropriately selected depending on the purpose.

[0038] The content of bentonite is preferably 0.1 to 3.0 mass%, more preferably 0.2 to 2.7 mass%, and even more preferably 1.1 to 2.6 mass%, converted into solid content based on the total mass of the photosensitive resin composition. By setting the content of bentonite to 0.1 to 3.0 mass%, variations in the reflectance of the cured product of the photosensitive resin composition can be prevented.

[0039] <Other Components> The other components are not particularly limited as long as they are those typically used in photosensitive resin compositions and can be selected appropriately depending on the purpose. Examples include photopolymerizable monomers, epoxy resins, curing catalysts, photoinitiator assistants, cyanate compounds, elastomers, mercapto compounds, urethanization catalysts, thixotropic agents, adhesion promoters, block copolymers, chain transfer agents, polymerization inhibitors, copper inhibitors, antioxidants, rust inhibitors, 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. Furthermore, thickeners such as montmorillonite can also be used to the extent that they do not impair the properties. These may be used alone or in combination of two or more.

[0040] <<Photopolymerizable Monomer>> The photopolymerizable monomer is contained to promote photocuring of the photosensitive resin composition. Examples of the photopolymerizable monomer include a (meth)acrylate monomer having a (meth)acryloyl group in the molecule.

[0041] Examples of the (meth)acrylate monomer include polyfunctional allyl compounds such as triallyl isocyanurate, diallyl phthalate, and diallyl isophthalate; alkylene polyol poly(meth)acrylates such as ethylene glycol di(meth)acrylate, butanediol di(meth)acrylates, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; acrylates; polyoxyalkylene glycol poly(meth)acrylates such as diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, ethoxylated trimethylolpropane triacrylate, and propoxylated trimethylolpropane tri(meth)acrylate; poly(meth)acrylates such as hydroxypivalic acid neopentyl glycol ester di(meth)acrylate; and isocyanurate-type poly(meth)acrylates such as tris[(meth)acryloxyethyl]isocyanurate. These may be used alone or in combination of two or more.

[0042] The content of the photopolymerizable monomer is preferably 5 to 100 parts by mass, and more preferably 5 to 75 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. By setting the content of the photopolymerizable monomer to 5 to 100 parts by mass relative to 100 parts by mass of the carboxyl group-containing resin, photocurability and resolution are improved.

[0043] <<Epoxy Resin>> The epoxy resin, also referred to as a thermosetting component, is contained in order to cure the photosensitive resin composition. There are no particular limitations on the epoxy resin as long as it is one that is commonly used in photosensitive resin compositions and can be appropriately selected depending on the purpose. However, a polyfunctional epoxy resin having two or more epoxy groups in one molecule is preferred. Examples of polyfunctional epoxy resins include epoxidized vegetable oil, bisphenol A type epoxy resin, hydroquinone type epoxy resin, bisphenol type epoxy resin, biphenyl type epoxy resin, thioether type epoxy resin, brominated epoxy resin, novolac type epoxy resin, biphenol novolac type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol A type epoxy resin, glycidylamine type epoxy resin, hydantoin type epoxy resin, alicyclic epoxy resin, trihydroxyphenylmethane type epoxy resin, bixylenol type or biphenol type epoxy resin, and the like. epoxy resins or mixtures thereof; bisphenol S type epoxy resins, bisphenol A novolac type epoxy resins, tetraphenylolethane type epoxy resins, heterocyclic epoxy resins, diglycidyl phthalate resins, tetraglycidylxylenoylethane 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, CTBN-modified epoxy resins, etc. These may be used alone or in combination of two or more.

[0044] <<Curing Catalyst>> The curing catalyst is a compound that has the property of being cured by heat. Examples of the curing catalyst include imidazole derivatives such as imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole; dicyandiamide, benzyldimethylamine, 4-(dimethylamino)-N,N-dimethylbenzylamine, 4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine. hydrazine compounds such as adipic acid dihydrazide and sebacic acid dihydrazide; phosphorus compounds such as triphenylphosphine; and S-triazine derivatives such as guanamine, acetoguanamine, benzoguanamine, melamine, 2,4-diamino-6-methacryloyloxyethyl-S-triazine, 2-vinyl-2,4-diamino-S-triazine, 2-vinyl-4,6-diamino-S-triazine·isocyanuric acid adduct, and 2,4-diamino-6-methacryloyloxyethyl-S-triazine·isocyanuric acid adduct.

[0045] The content of other components is not particularly limited as long as it does not impair the effects of the present invention, and can be appropriately selected depending on the purpose.

[0046] The Y value of the XYZ color system of the cured product of the photosensitive resin composition according to this embodiment is 82 or more. This means that the Y value when the color of the cured product is assigned to the XYZ color system is 82 or more. A Y value of 82 or more can be said to be a highly reflective cured product. The Y value can be measured using a spectrophotometer (for example, CM-2600d, manufactured by Konica Minolta, Inc.). The Y value here is determined by applying a coating so that the film thickness after drying is 20 μm, drying at 80° C. for 30 minutes, and then exposing the coating to 600 mJ / cm using an exposure device (HMW-680GW, manufactured by Oak Manufacturing Co., Ltd.) equipped with a metal halide lamp. ２The values ​​were measured on a coating film that was a cured product obtained by exposing the entire surface to an exposure amount of 100 ppm, developing with a 1 wt % aqueous sodium carbonate solution at 30°C at a spray pressure of 0.2 MPa for 60 seconds, and then fully curing at 150°C for 60 minutes.

[0047] <Method for Producing Photosensitive Resin Composition> The method for producing the photosensitive resin composition is not particularly limited, and the photosensitive resin composition can be produced by, for example, blending the above-described components in a predetermined ratio and then kneading or mixing them at room temperature using a kneading means such as a triple roll mill, a ball mill, a bead mill, or a sand mill, or a stirring means such as a super mixer or a planetary mixer. Furthermore, prior to the kneading or mixing, pre-kneading or pre-mixing may be performed as necessary.

[0048] (Dry film) The dry film according to this embodiment is formed by laminating a resin layer and a first film, and if necessary, a second film, which is another component, may be formed on the surface of the resin layer opposite to the surface in contact with the first film.

[0049] <Resin Layer> The resin layer is formed by applying the photosensitive resin composition according to this embodiment to the first film described below and drying the applied layer. The thickness of the resin layer is not particularly limited and can be appropriately selected depending on the purpose.

[0050] <Other Components> The other components are not particularly limited and can be appropriately selected depending on the purpose. For example, a second film can be mentioned.

[0051] <<First Film>> The first film has a role of supporting the resin layer of the dry film, and is coated with a curable resin composition when forming the resin layer. In the present invention, the first film refers to a film that is adhered to the resin layer in the step of laminating the substrate and the resin layer side of the dry film. The first film may be peeled from the resin layer after the step of laminating it on the substrate described below. In this embodiment, it is preferable to peel it from the resin layer in a step after exposure.

[0052] 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.

[0053] Moreover, from the viewpoint of improving mechanical strength, the film made of a thermoplastic resin is preferably a film stretched in a uniaxial or biaxial direction.

[0054] When a thermoplastic resin film is used as the first film, a film having a specific surface configuration may be used by adding a filler to the resin when forming the film (kneading treatment), by matte coating (coating treatment), by subjecting the film surface to a blasting treatment such as sandblasting, or by hairline processing or chemical etching, etc.

[0055] The thickness of the first film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0056] <<Second Film>> The second film is a film that is laminated on the side of the resin layer opposite to the first film side for the purpose of preventing dust from adhering to the surface of the resin layer, etc. Specifically, the second film is a film that is peeled off from the resin layer immediately before the dry film is bonded to a base material such as a substrate.

[0057] The second film may be, for example, a polyethylene film, a polytetrafluoroethylene film, a polypropylene film, or surface-treated paper. The adhesive strength of the second film to the resin layer may be smaller than the adhesive strength between the resin layer and the first film. Since the adhesive strength of the second film is smaller than that of the first film, the second film can be peeled off without moving the first film.

[0058] The thickness of the second film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0059] <Method for Producing Dry Film> A dry film is obtained by diluting a photosensitive resin composition with an organic solvent to adjust the viscosity to an appropriate level, applying the diluted composition to a first film, and drying the diluted composition. Coating methods include a dry comma coater, blade coater, lip coater, rod coater, squeeze coater, reverse coater, transfer roll coater, gravure coater, spray coater, and applicator. The drying temperature is preferably 50°C to 130°C. The drying time is preferably 1 minute to 30 minutes. There are no particular restrictions on the film thickness when applied, but it is generally selected appropriately so that the film thickness after drying is in the range of 1 μm to 150 μm, preferably 5 μm to 60 μm.

[0060] (Cured Product) The cured product according to the embodiment is obtained by curing the above-mentioned photosensitive resin composition or the resin layer of the above-mentioned dry film. The size and shape of the cured product are not particularly limited as long as they are the size and shape of a typical solder resist, and can be appropriately selected depending on the purpose.

[0061] The cured product can be obtained, for example, by forming a resin layer from the photosensitive resin composition, forming a pattern, developing the pattern, and then performing main curing.

[0062] The resin layer is formed, for example, by a method of forming a tack-free resin layer or a method of laminating a dry film.

[0063] The tack-free resin layer can be formed by adjusting the viscosity of the photosensitive resin composition using an organic solvent to a level suitable for the coating method, applying the composition to a substrate in a film thickness of 10 μm to 40 μm after drying, and then volatilizing and drying the organic solvent contained in the photosensitive resin composition.

[0064] Examples of the substrate include printed wiring boards and flexible printed wiring boards on which circuits have been formed in advance using copper or the like, copper-clad laminates made of 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, and polyphenylene oxide / cyanate, metal substrates, polyimide films, polyethylene terephthalate films, polyethylene naphthalate (PEN) films, glass substrates, ceramic substrates, and wafer plates.

[0065] Examples of methods for applying the composition to a substrate include dip coating, flow coating, roll coating, bar coating, screen printing, and curtain coating.

[0066] The volatilization drying can be carried out using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, etc. (a method in which hot air in a dryer equipped with a heat source of an air heating method using steam is brought into countercurrent contact with the substrate, or a method in which hot air is blown onto the substrate from a nozzle). The volatilization drying temperature is preferably 60°C to 100°C. The volatilization drying time is preferably 15 to 90 minutes.

[0067] The dry film can be attached by attaching the resin layer of the dry film to the substrate and then peeling off the first film. The substrate and the first film can be those described above.

[0068] The dry film is preferably bonded to the substrate under pressure and heat using a vacuum laminator or the like. This is because the resin layer of the dry film adheres tightly to the circuit board, even if the circuit board has an uneven surface, preventing the inclusion of air bubbles and improving the filling of recesses in the substrate surface. The pressure is preferably about 0.1 MPa to 2.0 MPa. The heating temperature is preferably 40°C to 120°C.

[0069] The pattern formation can be performed by a method using a photomask or a method using a direct imaging device. In the case of a dry film, after exposure, the first film is peeled off from the dry film and development is performed. Alternatively, the first film may be peeled off from the dry film before exposure, and the exposed resin layer may be exposed and developed, as long as the properties are not impaired.

[0070] The method using a photomask is a method of selectively exposing to active energy rays through a photomask having a predetermined pattern formed thereon. The exposure device used for the active energy ray irradiation is preferably an apparatus having a light source that irradiates ultraviolet rays in the range of 350 nm to 450 nm. Examples of the light source include a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, and a mercury short arc lamp.

[0071] An example of a method using a direct imaging device is a method using a laser direct imaging device, which is a method of drawing an image directly with a laser using CAD data from a computer.

[0072] The laser light source of the direct imaging device may have a maximum wavelength in the range of 350 nm to 450 nm. The exposure dose varies depending on the thickness of the cured product, but is generally 10 mJ / cm ２ ~1,000mJ / cm ２ is preferred, and 20 mJ / cm ２ ~800 mJ / cm ２ is more preferred.

[0073] Development can be carried out by applying a developer to the unexposed areas, dissolving the photosensitive resin composition in the unexposed areas and the developer, and then removing the resulting solution.

[0074] Examples of the developer include aqueous alkali solutions of potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, amines, etc. Among these, sodium carbonate is preferred. The concentration of the developer is preferably 0.3% by mass to 3% by mass.

[0075] Examples of the method for applying the developer include dipping, showering, spraying, and brushing.

[0076] The main curing can be carried out by irradiating the developed cured product with active energy rays and then heat curing, or by irradiating the cured product with active energy rays after heat curing, or by heat curing alone. The heating temperature is preferably 100°C to 220°C. There are no particular restrictions on the heating time, and it can be appropriately selected depending on the purpose.

[0077] (Printed Wiring Board) A printed wiring board according to one embodiment of the present invention has the above-described cured product. There are no particular limitations on the size or type of the printed wiring board, and they can be appropriately selected depending on the purpose.

[0078] Next, tests conducted by the present inventors will be described, but the present invention is not limited to these.

[0079] <Synthesis Example 1 of Carboxyl Group-Containing Resin> 325.0 parts by mass of dipropylene glycol monomethyl ether as a solvent was heated to 110°C in a flask equipped with a thermometer, a stirrer, a dropping funnel, and a once-through condenser, and a mixture of 174.0 parts by mass of methacrylic acid, 174.0 parts by mass of ε-caprolactone-modified methacrylic acid (weight average molecular weight 314), 77.0 parts by mass of methyl methacrylate, 222.0 parts by mass of dipropylene glycol monomethyl ether, and 12.0 parts by mass of t-butylperoxy 2-ethylhexanoate (Perbutyl O, manufactured by NOF Corporation) as a polymerization catalyst was added dropwise over 3 hours, and the mixture was further stirred at 110°C for 3 hours to deactivate the polymerization catalyst, thereby obtaining a resin solution. After cooling the resulting resin solution, 289.0 parts by mass of an epoxy resin (Cyclomer M100, manufactured by Daicel Corporation), 3.0 parts by mass of triphenylphosphine, and 1.3 parts by mass of hydroquinone monomethyl ether were added, and the mixture was heated to 100°C and stirred to carry out ring-opening addition polymerization of the epoxy groups, yielding a carboxyl group-containing resin. The resulting carboxyl group-containing resin had a nonvolatile content of 45.5% by mass and an acid value of 79.8 mgKOH / g of the solid matter.

[0080] (Examples 1 to 7, Comparative Examples 1 to 3) <Preparation of Photosensitive Resin Compositions> Photosensitive resin compositions were prepared by blending the materials in the proportions shown in Table 1, premixing them in a mixer, and then kneading them in a three-roll mill. The units in the table are parts by mass.

[0081]

[0082] Details of each component in Table 1 are as follows. <Carboxyl Group-Containing Resin> - Synthesis Example 1 of Carboxyl Group-Containing Resin (Note: The values ​​in Table 1 are values ​​of the solid content) <Photopolymerization Initiator> - 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone (Omnirad 907, manufactured by IGM Resins B.V.) <Titanium Oxide> - Titanium Oxide A (rutile-type titanium oxide, surface-treated with Al and Si, not surface-treated with an organic substance, volume average particle size: 0.25 μm, CR-90, manufactured by Ishihara Sangyo Kaisha, Ltd.) - Titanium Oxide B (rutile-type titanium oxide, surface-treated with Al and Zr, not surface-treated with an organic substance, volume average particle size: 0.25 μm, CR-97, manufactured by Ishihara Sangyo Kaisha, Ltd.) <Bentonite> - Organic bentonite (Benton 38, manufactured by Toshin Kasei Co., Ltd.) Urethane as a substitute for bentonite (urea-modified urethane, BYK-425, manufactured by BYK Japan KK) <Other components> Photopolymerizable monomer (dipentaerythritol hexaacrylate) Epoxy resin (jER-828 (bifunctional epoxy resin (bisphenol A type epoxy resin), manufactured by Mitsubishi Chemical Corporation) Antifoaming agent (silicone-based antifoaming agent, KS-66, manufactured by Shin-Etsu Chemical Co., Ltd.) The bentonite content and titanium oxide content in Table 1 are both values ​​calculated as solids relative to the entire photosensitive resin composition.

[0083] The resulting photosensitive resin compositions were evaluated for reflectance (Y value), reflectance variation, change in color after reflow, and developability as follows. The evaluation results are shown in Table 2.

[0084] <Reflectance of the cured product> The photosensitive resin composition obtained was applied to the entire surface of a copper substrate pretreated by buffing by screen printing so that the film thickness after drying would be 20 μm, and the substrate was dried for 30 minutes in a dry circulation type drying oven at 80°C. This drying was carried out while the substrate was placed flat on a rack. Next, the substrate was exposed to 600 mJ / cm using an exposure device (HMW-680GW, manufactured by Oak Manufacturing Co., Ltd.) equipped with a metal halide lamp. ２ and developed for 60 seconds (30°C, 0.2 MPa, 1 wt% Na ２ CO ３ ) and then curing was carried out for 60 minutes at 150°C in a hot air circulation drying oven to prepare a substrate for evaluation. The Y value of the prepared evaluation substrate in the XYZ color system was measured using a spectrophotometer (CM-2600d, manufactured by Konica Minolta, Inc.). A Y value of 82.0 or higher is considered to be good.

[0085] <Variation in reflectance> The obtained photosensitive resin composition was applied to the entire surface of a copper solid substrate (9.5 mm x 15.0 mm) that had been pretreated by buffing by screen printing so that the film thickness after drying would be 20 μm, and the substrate was left standing on a rack (angle: 65°) for 30 minutes. Thereafter, while still standing, the substrate was dried in a hot air circulating drying oven at 80°C for 30 minutes. Next, an exposure device (HMW-680GW, manufactured by Oak Manufacturing Co., Ltd.) equipped with a metal halide lamp was used to expose the substrate to 600 mJ / cm ２ and developed for 60 seconds (30°C, 0.2 MPa, 1 wt% Na ２ CO ３ ) and then curing was carried out for 60 minutes at 150°C in a hot air circulation drying oven to prepare a substrate for evaluation. For the prepared evaluation substrate, the Y value of the XYZ color system was measured at 10 points (randomly) on the substrate using a spectrophotometer (CM-2600d, manufactured by Konica Minolta, Inc.), the standard deviation of the measurement results at 10 points was calculated, and the variation in reflectance was evaluated based on the following evaluation criteria. - Evaluation criteria - ◯: Standard deviation is 0 or more and 1.5 or less △: Standard deviation is more than 1.5 and 1.8 or less ×: Standard deviation is more than 1.8

[0086] <Change in Color After Reflow> The photosensitive resin composition obtained was applied to the entire surface of a copper substrate that had been pretreated by buffing by screen printing so that the film thickness after drying would be 20 μm, and the substrate was dried for 30 minutes in a dry circulation type drying oven at 80°C. This drying was carried out while the substrate was placed flat on a rack. Next, an exposure device (HMW-680GW, manufactured by Oak Manufacturing Co., Ltd.) equipped with a metal halide lamp was used to expose the substrate to 600 mJ / cm ２ and developed for 60 seconds (30°C, 0.2 MPa, 1 wt% Na ２ CO ３ After that, the coating was cured in a hot air circulation drying oven at 150°C for 60 minutes to prepare a substrate for evaluation. ＊ a ＊ b ＊ The L value of the evaluation substrate after the reflow process was measured using a spectrophotometer (CM-2600d, manufactured by Konica Minolta, Inc.). The evaluation substrate was subjected to a reflow process five times using a reflow device (NIS-20-82C, manufactured by Atec Techtron Co., Ltd.) at a maximum temperature of 260°C for 10 seconds. ＊ a ＊ b ＊ The values ​​were measured using a spectrophotometer (CM-2600d, manufactured by Konica Minolta, Inc.). ＊ a ＊ b ＊ The difference between the values ​​was calculated, and the color after reflow was calculated using the following formula, and the change in color after reflow (ΔE after reflow) was measured based on the following evaluation criteria. ＊ ab = [(ΔL ＊ ) ２ + (Δa ＊ ) ２ + (Δb ＊ ) ２ ] １／２ -Evaluation criteria- ◯: ΔE ＊ ab is less than 1.4 △: ΔE ＊ ab is 1.4 or more and less than 1.8 ×: ΔE ＊ ab is 1.8 or more. In Comparative Examples 1 to 3, the evaluation result of the variation in reflectance (Y value) was "x", so no evaluation was performed.

[0087] <Developability> The photosensitive resin composition obtained was applied to the entire surface of a copper substrate pretreated by buffing by screen printing so that the film thickness after drying would be 20 μm, and the substrate was dried for 40 minutes in a dry circulation type drying oven at 80°C. This drying was carried out while the substrate was placed flat on a rack. Next, the substrate was exposed to 600 mJ / cm using an exposure device (HMW-680GW, manufactured by Oak Manufacturing Co., Ltd.) equipped with a metal halide lamp. ２ and developed for 60 seconds (30°C, 0.2 MPa, 1 wt% Na ２ CO ３ ), and then curing was carried out for 60 minutes in a hot air circulation drying oven at 150°C to prepare a substrate for evaluation. The evaluation substrate was visually inspected for the presence or absence of powder (development residue) of the cured product of the photosensitive resin composition, and the developability was evaluated based on the following evaluation criteria. -Evaluation criteria- ◯: No development residue △: Development was successful, but some powder remained ×: Development residue Note that for Comparative Examples 1 to 3, the evaluation result for the variation in reflectance (Y value) was "X", so no evaluation was performed.

[0088]

[0089] Examples 1 to 7, which are photosensitive resin compositions containing a carboxyl group-containing resin, a photopolymerization initiator, titanium oxide, and bentonite, and in which the cured product of the photosensitive resin composition had a Y value of 82 or more in the XYZ color system, were evaluated for reflectance variation as "Good" or "Good." On the other hand, Comparative Example 1, which does not contain bentonite, Comparative Example 2, which contains a conventional anti-sagging agent, and Comparative Example 3, in which the cured product of the photosensitive resin composition had a Y value of 79.7 in the XYZ color system, were evaluated for reflectance variation as "Poor." Therefore, a photosensitive resin composition containing a carboxyl group-containing resin, a photopolymerization initiator, titanium oxide, and bentonite, and in which the cured product has a Y value of 82 or more in the XYZ color system, can suppress variation in the reflectance of the cured product.

[0090] Furthermore, Examples 2, 4, 6, and 7, in which the bentonite content was 1.1% by mass to 2.6% by mass, were all evaluated as "good" for the reflectance variation, ΔE after reflow, and developability. In contrast, Example 1, in which the bentonite content was 0.7% by mass, was evaluated as "fair" for the reflectance variation, and Example 5, in which the bentonite content was 2.7% by mass, was evaluated as "fair" for the ΔE after reflow. From these results, it can be said that when the bentonite content is 1.1% by mass to 2.6% by mass, the reflectance variation and discoloration after reflow can be further suppressed.

[0091] Furthermore, Examples 1 to 2 and 4 to 5, in which the titanium oxide content was 45% by mass or less, were evaluated as "good" in terms of developability, whereas Example 3, in which the titanium oxide content was 49% by mass, was evaluated as "fair." From this, it can be said that photosensitive resin compositions in which the titanium oxide content was 45% by mass or less had good developability.

[0092] Although the embodiments for carrying out the present invention have been specifically described above, the present invention is not limited to these and can be modified in various ways without departing from the spirit of the present invention.

Claims

1. A photosensitive resin composition containing a carboxyl group-containing resin, a photopolymerization initiator, titanium oxide, and bentonite, characterized in that the Y value of the XYZ color system of a cured product of the photosensitive resin composition is 82 or more.

2. The photosensitive resin composition according to claim 1, wherein the content of the bentonite is 0.1% by mass to 3.0% by mass in terms of solid content relative to the total amount of the photosensitive resin composition.

3. The photosensitive resin composition according to claim 1 or 2, wherein the content of the titanium oxide is 35% by mass to 55% by mass in terms of solid content relative to the entire photosensitive resin composition.

4. A dry film comprising a first film and a resin layer formed on the first film, the resin layer being a dry coating of the photosensitive resin composition according to claim 1.

5. A cured product obtained by curing the photosensitive resin composition according to claim 1 or 2, or the resin layer of the dry film according to claim 4.

6. A printed wiring board having the cured product according to claim 5.

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