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

Abstract

Provided is a photosensitive resin composition that, while maintaining a low coefficient of thermal expansion (low CTE), has high resolution and excellent embedding properties with respect to a double-sided printed circuit board having fine circuits formed therein. The photosensitive resin composition is characterized by comprising a carboxyl group-containing resin, a photopolymerizable monomer, a photopolymerization initiator, and an inorganic filler, wherein: the melting point or softening point of the photopolymerization initiator is -50°C to 30°C; the inorganic filler is at least one of silica, hydrotalcite, talc, and alumina; and the inorganic filler is a nanofiller.

Description

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

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

[0002] In response to the increasing density of printed wiring boards accompanying the trend toward lighter, thinner, and smaller electronic devices, miniaturization and increased pin counts in semiconductor packages have been put into practical use and mass production has progressed, and recently, semiconductor packages such as BGA (ball grid array) and CSP (chip scale package) using package substrates have been adopted in place of semiconductor packages known as QFP (quad flat package) and SOP (small outline package). In such package substrates, wiring patterns are formed at higher density and closer to each other, so permanent coatings such as solder resists used on package substrates are required to have properties such as heat resistance, high rigidity, and thermal dimensional stability (low coefficient of thermal expansion (low CTE) (i.e., warpage prevention)).

[0003] To impart high reliability to such solder resists for package substrates, a common method is to highly fill the composition with inorganic fillers to improve properties such as rigidity. Among inorganic fillers, silica is widely used to improve the properties of solder resists because it has excellent filling properties and further reduces the coefficient of thermal expansion (CTE) (see Patent Document 1, etc.).

[0004] Curable resin compositions for forming solder resists for package substrates are classified into liquid and dry film types. Dry film-type curable resin compositions (hereinafter simply referred to as "dry films") are increasingly being used due to their advantages, such as smoothness, high film thickness accuracy, and low contamination of the coating. The aforementioned dry films also contain a high amount of inorganic filler in the composition as a method for imparting high reliability to the solder resist for package substrates. Silica, which is used as an inorganic filler, has excellent filling properties and further reduces the coefficient of thermal expansion (CTE), and is therefore widely used to improve the properties of solder resists (see Patent Document 2, etc.).

[0005] JP 2018-165795 A JP 2014-81611 A

[0006] However, if the curable resin composition forming the solder resist for package substrates contains a high inorganic filler depending on the composition, for example, in the case of a dry film type, the melt viscosity of the resin layer formed from the dried coating film of the resin composition increases during formation, reducing the adhesive performance (tackiness), making it more likely to deteriorate the handleability during production and cause lamination problems. Specifically, it has been confirmed that air gets trapped in the boundary between the circuit lines and spaces during lamination onto a printed wiring board on which fine circuits are formed, causing air bubbles (voids) to form in the resin layer of the dry film, leaving room for improvement.

[0007] Furthermore, when forming a coating film on a substrate using the resin composition, a dry coating film is first formed on the substrate by printing and drying in the case of a liquid type, or by laminating in the case of a dry film type. Then, if the resin composition is photosensitive, an exposure step, a development step, and, if necessary, a main curing step using heat or UV light are performed to obtain a patterned cured coating film. However, depending on the composition, for example, if the inorganic filler contained in the resin composition is highly loaded, the resolution is poor and the desired pattern cannot be formed, leaving room for improvement.

[0008] The present invention has been made in consideration of the above points, and provides a photosensitive resin composition that has excellent embeddability into double-sided printed wiring boards on which fine circuits are formed, while maintaining a low coefficient of thermal expansion (CTE), and has high resolution, and also provides a dry film, a cured product, and a printed wiring board made of the photosensitive resin composition.

[0009] The present inventors have conducted extensive research to achieve the above object, and as a result, have discovered a photosensitive resin composition that can address the above-mentioned problems by examining the composition of the photosensitive resin composition. Specifically, the present inventors have discovered a photosensitive resin composition that can address the above-mentioned problems by combining a photopolymerization initiator having a specific melting point or softening point with a specific type of inorganic filler that has a nano-sized average particle size.

[0010] That is, the photosensitive resin composition of the present embodiment contains a carboxyl group-containing resin, a photopolymerizable monomer, a photopolymerization initiator, and an inorganic filler, wherein the melting point or softening point of the photopolymerization initiator is −50 to 30° C., the inorganic filler is at least one of silica, hydrotalcite, talc, and alumina, and the inorganic filler is a nanofiller.

[0011] In the photosensitive resin composition of this embodiment, the viscosity of the photopolymerization initiator at 25° C. may be 0.1 to 300 Pa·s.

[0012] In the photosensitive resin composition of this embodiment, the photopolymerization initiator may be a liquid phosphine oxide-based photopolymerization initiator.

[0013] In the photosensitive resin composition of this embodiment, the photopolymerization initiator may be represented by the following general formula (i).

[0014]

[0015] In the formula, R １ is a linear or branched alkyl group having 1 to 12 carbon atoms, and R ２ represents a cyclohexyl group, a cyclopentyl group, an aryl group, an aryl group substituted with a halogen atom, an alkyl group or an alkoxy group, or a carbonyl group having 1 to 20 carbon atoms.

[0016] In the photosensitive resin composition of this embodiment, the photopolymerization initiator may be represented by the following general formula (ii).

[0017]

[0018] In the photosensitive resin composition of this embodiment, the inorganic filler may be silica.

[0019] In the photosensitive resin composition of this embodiment, the inorganic filler may be spherical.

[0020] In the photosensitive resin composition of this embodiment, the blending amount of the inorganic filler may be 35 to 75 mass % in terms of solid content based on the total amount of the photosensitive resin composition.

[0021] The photosensitive resin composition of the present embodiment may be used for forming a solder resist.

[0022] The dry film of this embodiment is characterized by comprising a first film and a resin layer formed on the first film and consisting of a dried coating film of the above-described photosensitive resin composition.

[0023] The cured product of this embodiment is characterized by being obtained by curing the above-described photosensitive resin composition, or by curing the resin layer of the above-described dry film.

[0024] The printed wiring board of this embodiment is characterized by including the above-described cured product.

[0025] The photosensitive resin composition of the present invention can be obtained with a low coefficient of thermal expansion (CTE), excellent embeddability in double-sided printed wiring boards on which fine circuits are formed, and high resolution. Furthermore, the photosensitive resin composition can be applied to dry films, cured products, and printed wiring boards to obtain good performance.

[0026] [Photosensitive Resin Composition] The photosensitive resin composition of this embodiment contains at least a carboxyl group-containing resin, a photopolymerizable monomer, a photopolymerization initiator having a melting point or softening point within a specific range, and a specific type of inorganic filler having a nano-sized average particle size. It has been discovered that the above-mentioned object can be achieved by combining a photopolymerization initiator having a melting point or softening point within a specific range with a specific type of inorganic filler. The reason for this is not entirely clear, but is presumed to be as follows. That is, depending on the composition of the resin composition, a specific type of inorganic filler, specifically at least one of silica, hydrotalcite, talc, and alumina, has excellent filling properties, resulting in a high filling rate and a low coefficient of thermal expansion (CTE). However, there have been issues with poor embedding and resolution in double-sided printed wiring boards on which fine circuits are formed. Therefore, when a photopolymerization initiator with a melting point or softening point of -50 to 30°C is used, the photopolymerization initiator itself has excellent fluidity, resulting in a large number of components with good fluidity in the composition. This results in excellent fluidity for the entire composition, including the filler, making it possible to embed the composition between fine wiring lines during lamination, one of the processes for forming a structure. Similarly, when a photopolymerization initiator with a melting point or softening point of -50 to 30°C is used, the movement speed of radicals generated during exposure is faster than with other photopolymerization initiators, resulting in a faster photoreaction rate. Meanwhile, the presence of such a photopolymerization initiator improves the fluidity of the coating film in the unexposed areas during development, resulting in excellent developability. In other words, the above two aspects likely facilitate the creation of a clear contrast between the exposed and unexposed areas, thereby enabling excellent resolution. Furthermore, the nano-sized average particle size of the inorganic filler likely creates a synergistic effect with the photopolymerization initiator, making it possible to achieve high resolution. However, this is merely speculation and is not exhaustive. Hereinafter, each component constituting the photosensitive resin composition of the present embodiment will be described. In this specification, when a numerical range is expressed with "to", it means a range that includes the numerical values ​​(i.e., not less than ... and not more than ...).

[0027] [Carboxyl Group-Containing Resin] The carboxyl group-containing resin contained in the photosensitive resin composition of this embodiment is a known resin having a carboxyl group in its molecule. By including a carboxyl group-containing resin in the photosensitive resin composition, alkaline developability can be imparted to the photosensitive resin composition. In particular, a carboxyl group-containing photosensitive resin having an ethylenically unsaturated double bond in its molecule is 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, a compound having multiple ethylenically unsaturated groups in its molecule, i.e., a photopolymerizable monomer, as described below, must be used in combination to make the composition photocurable. Specific examples of the carboxyl group-containing resin include the following compounds (which may be either oligomers or polymers):

[0028] (1) Examples include carboxyl group-containing resins obtained by copolymerizing an unsaturated carboxylic acid such as (meth)acrylic acid with an unsaturated group-containing compound such as styrene, α-methylstyrene, lower alkyl (meth)acrylate, isobutylene, etc.

[0029] (2) Examples include carboxyl group-containing urethane resins obtained by the polyaddition reaction of diisocyanates such as aliphatic diisocyanates, branched aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates with carboxyl group-containing dialcohol compounds such as dimethylolpropionic acid and dimethylolbutanoic acid, and diol compounds such as polycarbonate polyols, polyether polyols, polyester polyols, polyolefin polyols, acrylic polyols, bisphenol A alkylene oxide adduct diols, and compounds having phenolic hydroxyl groups and alcoholic hydroxyl groups.

[0030] (3) Examples include carboxyl group-containing photosensitive urethane resins obtained by polyaddition reaction of diisocyanates with (meth)acrylates of bifunctional epoxy resins such as bisphenol A epoxy resins, hydrogenated bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, bixylenol epoxy resins, and biphenol epoxy resins, or their partially acid anhydride-modified products, carboxyl group-containing dialcohol compounds, and diol compounds.

[0031] (4) An example is a carboxyl group-containing photosensitive urethane resin that is (meth)acrylated at the terminal 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 (2) or (3) described above.

[0032] (5) An example of a carboxyl group-containing photosensitive urethane resin is one in which 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, is added during the synthesis of the resin (2) or (3) above to form a (meth)acrylated terminal.

[0033] (6) A carboxyl group-containing photosensitive resin obtained by reacting a difunctional or more polyfunctional (solid) epoxy resin with (meth)acrylic acid and adding a dibasic acid anhydride to the hydroxyl group present in the side chain is exemplified.

[0034] (7) A carboxyl group-containing photosensitive resin is exemplified by a polyfunctional epoxy resin in which the hydroxyl groups of a bifunctional (solid) epoxy resin are further epoxidized with epichlorohydrin, and then reacted with (meth)acrylic acid to form a polyfunctional epoxy resin, and a dibasic acid anhydride is added to the resulting hydroxyl groups.

[0035] (8) Examples include carboxyl group-containing polyester resins obtained by reacting a dicarboxylic acid such as adipic acid, phthalic acid, or hexahydrophthalic acid with a bifunctional oxetane resin and then adding a dibasic acid anhydride such as phthalic anhydride, tetrahydrophthalic anhydride, or hexahydrophthalic anhydride to the resulting primary hydroxyl groups.

[0036] (9) Examples of carboxyl group-containing photosensitive resins include those obtained by reacting an epoxy compound having multiple epoxy groups in one molecule 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 groups of the resulting reaction product with a polybasic acid anhydride, such as maleic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, or adipic acid.

[0037] (10) 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 is exemplified.

[0038] (11) A carboxyl group-containing photosensitive resin is exemplified by a reaction product 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.

[0039] (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 resins (1) to (11) above is exemplified.

[0040] 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.

[0041] The carboxyl group-containing resins that can be used in this embodiment are not limited to those listed above. The carboxyl group-containing resins listed above may be used alone or in combination. Among the resins listed above, carboxyl group-containing resins synthesized using a compound having a phenolic hydroxyl group as a starting material, such as carboxyl group-containing resins (10) and (11), are preferred because of their excellent HAST (Highly Accelerated Stress Test) resistance and PCT (Pressure Cooker Test) resistance.

[0042] In the photosensitive resin composition of the present embodiment, in consideration of the developability when using a weak alkaline developer such as an aqueous sodium carbonate solution and the drawability of a resist pattern, the acid value of the carboxyl group-containing resin is preferably in the range of 30 to 150 mgKOH / g, and more preferably in the range of 50 to 120 mgKOH / g.

[0043] The weight-average molecular weight of the carboxyl group-containing resin varies depending on the resin skeleton, but is generally in the range of 2,000 to 150,000, preferably 5,000 to 100,000. By using a carboxyl group-containing resin with a weight-average molecular weight of 2,000 or more, resolution and tack-free performance are improved. Furthermore, by using a carboxyl group-containing resin with a weight-average molecular weight of 150,000 or less, developability and storage stability are improved. The weight-average molecular weight is measured by gel permeation chromatography (GPC).

[0044] [Photopolymerizable Monomer] The photopolymerizable monomer contained in the photosensitive resin composition of this embodiment is a monomer having an ethylenically unsaturated double bond. Examples of such photopolymerizable monomers include alkyl(meth)acrylates such as 2-ethylhexyl(meth)acrylate and cyclohexyl(meth)acrylate; hydroxyalkyl(meth)acrylates such as 2-hydroxyethyl(meth)acrylate and 2-hydroxypropyl(meth)acrylate; mono- or di(meth)acrylates of alkylene oxide derivatives such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol; hexanediol, trimethylolpropane, pentaerythritol, ditrimethylolpropane, and dipentaerythritol. and trishydroxyethyl isocyanurate; (meth)acrylates of ethylene oxide or propylene oxide adducts of polyhydric (meth)alcohols such as phenoxyethyl (meth)acrylate and polyethoxydi(meth)acrylate of bisphenol A; (meth)acrylates of glycidyl ethers such as glycerin diglycidyl ether, trimethylolpropane triglycidyl ether and triglycidyl isocyanurate; and melamine (meth)acrylate.

[0045] The photopolymerizable monomer may be blended singly or in combination of two or more types. The blending amount of the photopolymerizable monomer is preferably 0.1 to 40 parts by mass, calculated as solid content, per 100 parts by mass of the carboxyl group-containing resin. When the blending amount is 0.1 part by mass or more, the photocurability is good and pattern formation is easy in alkaline development after irradiation with active energy rays. When the blending amount is 40 parts by mass or less, halation is unlikely to occur and good resolution can be obtained.

[0046] [Photopolymerization initiator] The photopolymerization initiator contained in the photosensitive resin composition of this embodiment has a melting point or softening point of -50 to 30°C. A melting point or softening point of -50 to 30°C results in excellent fluidity of the photopolymerization initiator itself. Depending on the type of photopolymerization initiator, there are molecules for which a single melting point cannot be identified. Therefore, the softening point is also defined as the temperature at which the fluidity changes from a solid phase to a liquid phase.

[0047] When the melting point or softening point is in the range of −50 to 30° C., the viscosity when preparing the photosensitive resin composition becomes appropriate even when the inclusion of an inorganic filler is taken into consideration, resulting in improved fluidity. It is more preferably −50 to 15° C., and even more preferably −50 to 0° C.

[0048] Furthermore, from the viewpoint of the fluidity of the photopolymerization initiator itself, the viscosity of the photopolymerization initiator at 25° C. is preferably 0.1 to 300 Pa s. The upper limit of the viscosity of the photopolymerization initiator is preferably 300 Pa s or less, more preferably 100 Pa s or less, and even more preferably 10 Pa s or less.

[0049] As the photopolymerization initiator contained in the photosensitive resin composition of the present embodiment, any photopolymerization initiator generally known in the art can be used as long as it has a melting point or softening point of −50 to 30° C. Among these, a liquid phosphine oxide-based photopolymerization initiator can be preferably used.

[0050] The melting point or softening point is measured using a TA Instruments Modulated DSC (Q2000) differential scanning calorimeter. In this device, the temperature of the heat bath is raised while oscillating at a constant amplitude and frequency, and the sample is heated while exhibiting a phase shift from the temperature of the heat bath. Based on the phase shift, the sample is separated into components that follow the temperature modulation and those that do not, and the melting point or softening point is determined from the portion that follows the temperature modulation.

[0051] The liquid phosphine oxide photopolymerization initiator is represented by the following general formula (i): １ is a linear or branched alkyl group having 1 to 12 carbon atoms, and R ２represents a cyclohexyl group, a cyclopentyl group, an aryl group, an aryl group substituted with a halogen atom, an alkyl group or an alkoxy group, or a carbonyl group having 1 to 20 carbon atoms.

[0052]

[0053] Specific examples of the photopolymerization initiator contained in the photosensitive resin composition of this embodiment include the following substances (1) and (2). Among these, (1) "ethyl-2,4,6-trimethylbenzoylphenylphosphinate" is preferred because of its superior embeddability.

[0054] (1) Ethyl 2,4,6-trimethylbenzoylphenylphosphinate (see general formula (ii) below)

[0055]

[0056] (2) In the following general formula (iii), a, b, and c are all integers of 1 to 20. Preferably, they are all integers of 1 to 10.

[0057]

[0058] "Liquid" means that the sample is in a liquid state at room temperature. Room temperature refers to 10 to 40°C, and "liquid at room temperature" refers to a state in which, when a sample is placed in a test tube with an inner diameter of 30 mm to a height of 55 mm and the test tube is held horizontally, the sample passes through the part 85 mm from the bottom within 90 seconds at a temperature in the range of 10 to 40°C. Specific examples of phosphine oxide photopolymerization initiators that are liquid at room temperature include ethyl 2,4,6-trimethylbenzoylphenylphosphinate ((2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide).

[0059] Furthermore, liquid phosphine oxide-based photopolymerization initiators include not only compounds that are liquid at room temperature, but also phosphine oxide-based polymerization initiators that are liquid at room temperature as a mixture of a compound that is solid at room temperature and another compound that is liquid at room temperature. Specifically, a photopolymerization initiator liquefied by mixing ethyl 2,4,6-trimethylbenzoylphenylphosphinate, which is liquid at room temperature, with a phosphine oxide-based photopolymerization initiator that is solid at room temperature, such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide or bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, is used. The preferred mixture ratio is 70 to 98 mass% of the phosphine oxide-based photopolymerization initiator that is liquid at room temperature and 2 to 30 mass% of the phosphine oxide-based polymerization initiator that is solid at room temperature.

[0060] The amount of the photopolymerization initiator (particularly a liquid phosphine oxide-based photopolymerization initiator) is preferably 5 to 30 parts by mass, more preferably 7 to 20 parts by mass, per 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the amount of the phosphine oxide-based photopolymerization initiator is 5 parts by mass or more, sufficient curing is likely to occur, and coating properties such as chemical resistance can be obtained. Furthermore, when the amount is 30 parts by mass or less, the curability of a thick film is improved.

[0061] Furthermore, the photopolymerization initiator contained in the photosensitive resin composition of the present embodiment can be used in combination with one having a melting point or softening point other than −50 to 30° C., as long as the properties are not impaired. For example, bisacylphosphine oxides such as 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-(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, 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylphosphinic acid methyl ester, 2-methylbenzoyldiphenylphosphine oxide, 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichloro ... monoacylphosphine oxides such as pivaloylbenzoyldiphenylphosphine oxide, pivaloylphenylphosphinic acid isopropyl ester, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide; hydroxyacetophenones such as ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, 1-hydroxycyclohexyl 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; 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- Acetophenones such as dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-(dimethylamino)-2-[(4-methylphenyl)methyl)-1-[4-(4-morpholinyl)phenyl]-1-butanone and N,N-dimethylaminoacetophenone; thioxanthones such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone; an Anthraquinones such as anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone, and 2-aminoanthraquinone; ketals such as acetophenone dimethyl ketal and benzyl 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-( oxime esters such as 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime); titanocenes such as 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;Phenyl disulfide 2-nitrofluorene, butyroin, anisoin ethyl ether, azobisisobutyronitrile, tetramethylthiuram disulfide, etc.;

[0062] A photoinitiator aid or sensitizer may be used in combination with the aforementioned 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. In particular, it is preferable to use thioxanthone compounds such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone. The inclusion of a thioxanthone compound can improve deep curing properties. While these compounds may be used as photopolymerization initiators, it is preferable to use them in combination with a photopolymerization initiator. Furthermore, one type of photoinitiator aid or sensitizer may be used alone, or two or more types may be used in combination.

[0063] [Inorganic Filler] The inorganic filler contained in the photosensitive resin composition of this embodiment is at least one of silica, hydrotalcite, talc, and alumina. Compared to other fillers, such inorganic fillers are excellent in reducing the thermal expansion of the cured resin layer and improving its mechanical properties due to their high rigidity and low thermal expansion coefficient. Among these, silica is preferred because of its excellent filling properties, low dielectric constant, low thermal expansion coefficient, and excellent compatibility with dispersants.

[0064] Furthermore, the inorganic filler is preferably spherical in shape, but is not necessarily limited to a perfect sphere. Suitable inorganic fillers have, for example, a sphericity of 0.8 or more as measured below. However, the present invention is not limited to this. Sphericity is measured as follows. First, a photograph of the spherical inorganic filler is taken with a scanning electron microscope (SEM). The sphericity is calculated from the area and perimeter of the particle observed on the photograph, as follows: (sphericity) = {4π × (area) ÷ (perimeter)^2}. Specifically, an image processing device is used, and the average value measured for 100 particles is adopted.

[0065] The method for producing the spherical inorganic filler is not particularly limited, and known methods can be used. For example, it can be produced by burning silicon powder using the VMC (Vaporized Metal Combustion) method. The VMC method is a method in which a chemical flame is formed using a burner in an oxygen-containing atmosphere, and a metal powder that constitutes part of the target oxide particles is introduced into this chemical flame in an amount sufficient to form a dust cloud, causing a deflagration to occur and obtaining oxide particles.

[0066] Incidentally, examples of commercially available spherical inorganic fillers include spherical silica, such as ADMAFINE SO-C2 and SO-E2 manufactured by Admatechs Co., Ltd., SFP-20M and SFP-30M manufactured by Denka Co., Ltd., Admanano manufactured by Admatechs Co., Ltd., UFP-30 manufactured by Denka Co., Ltd., the Seahoster series manufactured by Nippon Shokubai Co., Ltd., the Sciqas series manufactured by Sakai Chemical Industry Co., Ltd., and SG-SO100 manufactured by Kyoritsu Material Co., Ltd.

[0067] The nanofiller in the embodiment has an average particle diameter (D50) of less than 100 nm, preferably 5 nm or more and 90 nm or less, and more preferably 10 nm or more and 80 nm or less. The average particle diameter of the nanofiller refers to the particle diameter at 50% cumulative volume obtained using a dynamic light scattering particle size distribution measurement method. The average particle diameter of the filler refers to the value measured as described above for the filler before preparing (stirring, kneading) the curable resin composition.

[0068] Furthermore, inorganic fillers other than nanofillers may be used in combination with the inorganic filler as long as the properties are not impaired. The average particle size of the inorganic filler other than nanofillers is preferably 100 to 1,000 nm, more preferably 300 to 900 nm. The average particle size of the inorganic filler refers to the average particle size (D50) including not only the particle size of primary particles but also the particle size of secondary particles (aggregates), and is the D50 value measured by laser diffraction. An example of a measuring device using laser diffraction is the Microtrac MT3300EXII manufactured by Microtrac-Bell Corporation. The average particle size of the inorganic filler contained in the photosensitive resin composition of this embodiment refers to the value measured as described above for the inorganic filler before preparing (pre-stirring, kneading) the photosensitive resin composition.

[0069] By using two types of inorganic fillers with different average particle sizes as the inorganic filler, the inorganic filler with a smaller average particle size fills the gaps between the inorganic fillers with a relatively larger average particle size, thereby making it possible to obtain a photosensitive resin composition with a high inorganic filler content and a low resin content, i.e., a high ratio of the inorganic filler mass to the total mass.

[0070] There is no particular limitation on whether the inorganic filler is surface-treated. In the photosensitive resin composition of this embodiment, the inorganic filler is preferably highly filled, and in such a case, the resin content is relatively low. For this reason, it is preferable to perform a surface treatment on the inorganic filler to improve dispersibility. The use of a surface-treated inorganic filler suppresses aggregation.

[0071] The surface treatment method for the inorganic filler is not particularly limited, and known methods can be used. Surface treatment of the inorganic filler with a surface treatment agent having a curable reactive group, such as a coupling agent having a curable reactive group as an organic group, is preferred. Examples of coupling agents that can be used include silane-based, titanate-based, aluminate-based, and zircoaluminate-based coupling agents. Among these, silane-based coupling agents are preferred. Examples of silane-based coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, N-(2-aminomethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-anilinopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane. These may be used alone or in combination. The silane coupling agent is preferably immobilized on the surface of the silica in advance by adsorption or reaction. The amount of the coupling agent to be used per 100 parts by mass of the inorganic filler is preferably 0.5 to 10 parts by mass. Note that the reactive functional group derived from the coupling agent applied to the inorganic filler is not included in the compound having a photocurable reactive group or a thermosetting functional group.

[0072] Examples of the photocurable reactive group include ethylenically unsaturated groups such as vinyl, styryl, methacryl, and acrylic groups, among which at least one of vinyl and (meth)acrylic groups is preferred.

[0073] Examples of the thermosetting reactive group include a hydroxyl group, a carboxyl group, an isocyanate group, an amino group, an imino group, an epoxy group, an oxetanyl group, a mercapto group, a methoxymethyl group, a methoxyethyl group, an ethoxymethyl group, an ethoxyethyl group, an oxazoline group, etc. Among these, at least one of an amino group and an epoxy group is preferred.

[0074] The surface-treated inorganic filler may be contained in the photosensitive resin composition in a surface-treated state, or the surface-untreated inorganic filler and the surface treatment agent may be blended separately to surface-treat the inorganic filler in the composition. However, blending an inorganic filler that has been surface-treated in advance is preferred. When surface-treating in advance, it is preferred to blend a pre-dispersion in which the inorganic filler is pre-dispersed in a solvent and a curable component. The surface-treated inorganic filler is pre-dispersed in a solvent, and this pre-dispersion is blended into the composition. Alternatively, it is more preferred to pre-disperse the surface-untreated inorganic filler in a solvent, subject it to sufficient surface treatment, and then blend this pre-dispersion into the composition.

[0075] Depending on the mode of use of the photosensitive resin composition, the inorganic filler may be blended in a powder or solid state with the carboxyl group-containing resin or the like, or may be mixed with a solvent and a dispersant to form a slurry and then blended with the carboxyl group-containing resin or the like.

[0076] The amount of inorganic filler is preferably 35 to 75 mass %, more preferably 40 to 65 mass %, and even more preferably 40 to 55 mass %, calculated as solid content based on the total amount of the photosensitive resin composition. When the amount of inorganic filler is 35 mass % or more, the cured product has high strength and high rigidity. Furthermore, the coefficient of thermal expansion (CTE) is reduced. When the amount of inorganic filler is 75 mass % or less, the amount of inorganic filler is appropriate, and excellent resolution is also achieved.

[0077] Furthermore, the inorganic filler contained in the photosensitive resin composition of this embodiment can be an inorganic filler other than silica, hydrotalcite, talc, or alumina, as long as the properties are not impaired. Examples include barium sulfate, Neuburg silica, aluminum hydroxide, clay, magnesium carbonate, calcium carbonate, natural mica, synthetic mica, barium titanate, iron oxide, non-fibrous glass, mineral wool, aluminum silicate, calcium silicate, and zinc oxide. One type of inorganic filler may be used alone, or two or more types may be used in combination.

[0078] [Colorant] The photosensitive resin composition of the present embodiment may further contain a colorant, such as at least one of a blue colorant and a yellow colorant.

[0079] The type of blue colorant is not particularly limited, and known blue colorants can be used, including pigments, dyes, and coloring matters. However, from the viewpoint of reducing environmental impact and impact on the human body, types that do not contain halogen atoms are preferred. Blue colorants include phthalocyanine-based and anthraquinone-based colorants. Pigment-based colorants include compounds classified as pigments, specifically, the following: Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, and 60. Dye-based colorants include Solvent Blue 35, 63, 68, 70, 83, 87, 94, 97, 122, 136, 67, and 70. In addition to the above, metal-substituted or unsubstituted phthalocyanine compounds can also be used. One type of blue colorant may be used alone, or two or more types may be used in combination.

[0080] The blending amount of the blue colorant is 0.3 to 2.5 mass %, preferably 0.3 to 2.0 mass %, calculated as solid content based on the total amount of the photosensitive resin composition. When the blending amount of the blue colorant is 0.3 mass % or more, the halation suppression effect is excellent. When the blending amount is 2.5 mass % or less, the blueness becomes appropriate and resolution tends to be improved.

[0081] The type of yellow colorant is not particularly limited, and known yellow colorants may be used, and may be any of pigments, dyes, and coloring matters. From the viewpoint of reducing environmental impact and impact on the human body, types that do not contain halogen atoms are preferred. Examples of yellow colorants include monoazo-based, disazo-based, condensed azo-based, benzimidazolone-based, isoindolinone-based, and anthraquinone-based. Specific examples of monoazo-based 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. Examples of condensed azo yellow colorants include Pigment Yellow 93, 94, 95, 128, 155, 166, and 180. Examples of benzimidazolone yellow colorants include Pigment Yellow 120, 151, 154, 156, 175, and 181. Examples of isoindolinone yellow colorants include Pigment Yellow 110, 109, 139, 179, and 185. Examples of anthraquinone-based yellow colorants include Solvent Yellow 163, Pigment Yellow 24, 108, 193, 147, 199, and 202.

[0082] The amount of the yellow colorant is 0.1 to 2.0 mass %, preferably 0.2 to 1.5 mass %, calculated as solid content based on the total amount of the photosensitive resin composition. When the amount of the yellow colorant is 0.1 mass % or more, the halation suppression effect is excellent. When the amount is 2.0 mass % or less, the yellowness becomes appropriate, and resolution is likely to be improved.

[0083] The photosensitive resin composition of this embodiment may contain colorants of colors other than the blue colorant and yellow colorant described above. As the other colorants, known and commonly used colorants such as red and green can be used, and any of pigments, dyes, and coloring matters can be used. Specific examples include colorants assigned a Color Index (C.I.; published by The Society of Dyers and Colorists) number. From the viewpoint of reducing environmental impact and impact on the human body, halogen-free colorants are preferred.

[0084] [Thermosetting Component] The photosensitive resin composition of this embodiment may contain a thermosetting component. Addition of the thermosetting component is expected to improve the heat resistance of the composition. The thermosetting component may be used alone or in combination of two or more. Known resins and compounds are used as the thermosetting component. For example, known thermosetting components 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 are used. Preferably, the thermosetting component has multiple cyclic ether groups or cyclic thioether groups (hereinafter abbreviated as cyclic (thio)ether groups) in the molecule.

[0085] The thermosetting component having a plurality of cyclic (thio)ether groups in the molecule is a compound having a plurality of three-, four-, or five-membered cyclic (thio)ether groups in the molecule, and examples thereof include a compound having a plurality of epoxy groups in the molecule, i.e., a polyfunctional epoxy compound, a compound having a plurality of oxetanyl groups in the molecule, i.e., a polyfunctional oxetane compound, and a compound having a plurality of thioether groups in the molecule, i.e., an episulfide resin.

[0086] Examples of polyfunctional epoxy compounds include epoxidized vegetable oils; 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; bisphenol F 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, or any of these. Examples of epoxy resins include, but are not limited to, a mixture of these epoxy resins; 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. These epoxy resins may be used alone or in combination of two or more.

[0087] 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 oligomers or copolymers thereof, 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)acrylate.

[0088] Examples of compounds having multiple cyclic thioether groups in the molecule include bisphenol A episulfide resins, etc. Also included are episulfide resins in which the oxygen atoms of the epoxy groups of novolac epoxy resins are replaced with sulfur atoms using a similar synthesis method.

[0089] Examples of amino resins such as melamine derivatives and benzoguanamine derivatives include methylolmelamine compounds, methylolbenzoguanamine compounds, methylolglycoluril compounds, and methylolurea compounds.

[0090] The isocyanate compound may be a polyisocyanate compound, such as 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.

[0091] 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.

[0092] The amount of the thermosetting component to be added is preferably such that the number of functional groups in the thermosetting component to react with 1 mol of carboxyl groups contained in the carboxyl group-containing resin is 0.5 to 2.5 mol, more preferably 0.8 to 2.0 mol.

[0093] [Thermosetting Catalyst] The photosensitive resin composition of this embodiment may contain a thermosetting catalyst. Examples of the thermosetting 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; amine compounds such as 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; and phosphorus compounds such as triphenylphosphine. Furthermore, commercially available thermosetting catalysts include, for example, 2MZ-A, 2MZ-OK, 2PHZ, 2P4BHZ, and 2P4MHZ (all of which are trade names for imidazole-based compounds) manufactured by Shikoku Chemicals Corporation, and U-CAT 3513N (a trade name for a dimethylamine-based compound), DBU, DBN, and U-CAT SA 102 (all of which are bicyclic amidine compounds and salts thereof) manufactured by San-Apro Co., Ltd. However, the present invention is not limited to these, and any other suitable thermosetting catalyst may be used as long as it is an epoxy resin or oxetane compound thermosetting catalyst, or a thermosetting catalyst that promotes the reaction of at least one of an epoxy group and an oxetanyl group with a carboxyl group, and these catalysts may be used alone or in combination of two or more.

[0094] Furthermore, 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 can also be used, and these compounds that also function as adhesion promoters are preferably used in combination with a heat curing catalyst. The heat curing catalyst may be used alone or in combination of two or more types.

[0095] The amount of the thermosetting catalyst is 0.1 to 10.0 mass %, preferably 0.3 to 3.0 mass %, calculated as solid content based on the total amount of the photosensitive resin composition. When the amount of the thermosetting catalyst is 0.1 mass % or more, the catalytic effects such as heat resistance are more effectively exhibited. When the amount is 10.0 mass % or less, it is a relatively appropriate amount and it is easy to maintain excellent storage stability.

[0096] [Organic Solvent] The photosensitive resin composition of the present embodiment contains an organic solvent for the purposes of adjusting the viscosity when preparing the composition and 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. These organic solvents may be used alone or in combination of two or more.

[0097] [Other Additive Components] The photosensitive resin composition of the present embodiment 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.

[0098] The photosensitive resin composition may be used in the form of a dry film or in the form of a liquid. When used in the form of a liquid, the photosensitive resin composition may be one-component or two or more-component.

[0099] [Uses] The photosensitive resin composition of this embodiment is useful for forming a pattern layer as a permanent coating on a printed wiring board, such as a solder resist, a coverlay, or an interlayer insulating layer, and is particularly useful for forming a solder resist (for solder resist formation). Furthermore, the photosensitive resin composition of this embodiment forms a cured product that has excellent film strength even when thin, and is therefore suitable for forming a pattern layer on a printed wiring board that requires thinness, such as a package substrate (a printed wiring board used for a semiconductor package). Furthermore, the cured product obtained from the photosensitive resin composition of this embodiment has a high elastic modulus and a low CTE, and is therefore suitable for forming a pattern layer on a package substrate that is thin in total thickness and lacks rigidity.

[0100] [Dry Film] The photosensitive resin composition of this embodiment is in the form of a dry film comprising a first film and a resin layer formed on the first film as a dried coating of the photosensitive resin composition. To form the dry film, the photosensitive resin composition of this embodiment is diluted with the organic solvent described above to adjust the viscosity to an appropriate level. The photosensitive resin composition is then applied 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 dried at a temperature of 50 to 130°C for 1 to 30 minutes to form a film. The thickness of the applied film is not particularly limited, and the dried film thickness is in the range of 1 to 150 μm, preferably 10 to 60 μm.

[0101] As the first film, any known film can be used without limitation, and for example, films made of thermoplastic resins such as polyester films such as polyethylene terephthalate and polyethylene naphthalate, polyimide films, polyamideimide films, polypropylene films, and polystyrene films are preferably used. Among these, polyester films are preferred from the viewpoints of heat resistance, mechanical strength, handleability, etc. Furthermore, a laminate obtained by laminating a plurality of the films listed above can be used as the first film.

[0102] The thermoplastic resin film used for the first film is preferably a uniaxially or biaxially stretched film from the viewpoint of improving mechanical strength. The thickness of the first film is, for example, 10 to 150 μm.

[0103] After a resin layer consisting of a dried coating film of the photosensitive resin composition of this embodiment is formed on the first film, it is preferable to further laminate a peelable second film on the surface of the resin layer for the purpose of preventing the surface of the resin layer from being soiled (preventing adhesion of dust, dirt, etc.) Examples of the peelable second film that can be used include polyethylene film, polytetrafluoroethylene film, polypropylene film, and surface-treated paper.

[0104] The second film may be designed so that 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. The thickness of the second film is, for example, 10 to 150 μm.

[0105] When a cured coating is produced on a printed wiring board using a dry film, the second film is peeled off from the dry film, and the exposed resin layer of the dry film is placed on a substrate on which a circuit has been formed, and the two are laminated using a laminator or the like. In this way, a resin layer is formed on the substrate on which a circuit has been formed. Next, the formed resin layer is exposed to light, developed, and heat-cured to form a cured coating. The second film may be peeled off either before or after exposure.

[0106] [Cured Product] The cured product of this embodiment can be obtained by curing the photosensitive resin composition of this embodiment or the resin layer of the dry film of this embodiment.

[0107] [Printed Wiring Board] The printed wiring board of this embodiment is a component having a cured product prepared from the photosensitive resin composition of this embodiment or a resin layer of a dry film. When producing the printed wiring board of this embodiment, for example, the photosensitive resin composition of this embodiment is prepared using an organic solvent to a viscosity suitable for the coating method, and then coated onto a substrate by a method such as dip coating, flow coating, roll coating, bar coating, screen printing, or curtain coating, to a film thickness of, for example, 10 to 30 μm after drying. The organic solvent contained in the composition is then evaporated and dried (pre-dried) at a temperature of 60 to 100°C, forming a tack-free resin layer. In the case of a dry film, the resin layer is bonded to the substrate using a laminator or the like so that the resin layer contacts the substrate, and then the first film is peeled off, and the resin layer is formed on the substrate.

[0108] Examples of the substrate include printed wiring boards on which circuits have been formed in advance using copper or the like, flexible printed wiring boards, paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / non-woven cloth epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, copper-clad laminates made from materials such as fluororesin-polyethylene-polyphenylene ether, and polyphenylene oxide-cyanate, metal substrates, polyimide substrates such as polyimide film, polyethylene terephthalate (PET) substrates such as polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, glass substrates, ceramic substrates, and wafers.

[0109] The dry film is preferably bonded to the substrate using a vacuum laminator or the like, under pressure and heat. By using a vacuum laminator, even if the circuit board surface has irregularities, the dry film adheres tightly to the circuit board, preventing the inclusion of air bubbles. Furthermore, the ability to fill recesses on the substrate surface is improved. The pressure is preferably about 0.1 to 2.0 MPa, and the heating temperature is preferably 40 to 120°C.

[0110] The photosensitive resin composition of this embodiment is dried by evaporation after application 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.) Drying conditions include, for example, 40 to 130°C and 1 to 30 minutes.

[0111] After the resin layer is formed on the substrate, it is selectively exposed to active energy rays through a photomask having a predetermined pattern formed thereon, and the unexposed areas are developed with a dilute alkaline aqueous solution (e.g., a 0.3 to 3 mass % sodium carbonate aqueous solution) to form a pattern of the cured product. In the case of a dry film, after exposure, the first film is peeled from the dry film and then developed to form a patterned cured product on the substrate. Note that, as long as the properties are not impaired, the first film may be peeled from the dry film before exposure, and the exposed resin layer may be exposed and developed.

[0112] Furthermore, the cured product is irradiated with active energy rays and then heat-cured (for example, at 100 to 220°C for 10 to 60 minutes), or is heat-cured and then exposed to active energy rays (for example, at 1000 mJ / cm ２ ) or by heat curing alone for final finish curing (main curing), a cured film with excellent properties such as adhesion and hardness is formed.

[0113] The exposure device used for the irradiation of the above-mentioned active energy rays 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 draws an image directly 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 emits light with 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 is.

[0114] Examples of the developing method include a dipping method, a shower method, a spray method, and a brush method, and the developer used is an aqueous alkali solution such as potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, or an amine.

[0115] The photosensitive resin composition used in the dry film and the resin layer of the dry film of this embodiment can be used to form a pattern of a cured film using the above-mentioned developer.

[0116] The present invention will be described in more detail below with reference to examples and comparative examples, but is not limited to these examples and comparative examples. In the following, "parts" and "%" are all by mass unless otherwise specified.

[0117] [Synthesis of Carboxyl Group-Containing Resin] Before preparing the photosensitive resin composition, the carboxyl group-containing resin used in this example was prepared according to the following procedure.

[0118] First, 456 parts of bisphenol A, 228 parts of water, and 649 parts of 37% formalin were placed in a flask equipped with a condenser and a stirrer, and 228 parts of a 25% aqueous sodium hydroxide solution was added while maintaining the temperature at 40°C or below, and the mixture was allowed to react at 50°C for 10 hours. After completion of the reaction, the reaction solution was cooled to 40°C, and while maintaining the temperature at 40°C or below, a 37.5% aqueous phosphoric acid solution was added to neutralize the mixture to pH 4. The reaction solution was allowed to stand, and the aqueous layer was separated. After separating the aqueous layer, 300 parts of methyl isobutyl ketone was added and dissolved uniformly, and the mixture was washed three times with 500 parts of distilled water. The mixture was then reduced pressure at a temperature of 50°C or below, and the water, solvent, etc. were removed to obtain a polymethylol compound.

[0119] The obtained polymethylol compound was dissolved in 550 parts of methanol to obtain 1,230 parts of a methanol solution of the polymethylol compound. A portion of the obtained methanol solution of the polymethylol compound was dried at room temperature in a vacuum dryer. The solid content at this time was 55.2%. 500 parts of the obtained methanol solution of the polymethylol compound and 440 parts of 2,6-xylenol were uniformly dissolved at 50°C. After uniform dissolution, the methanol was removed under reduced pressure at a temperature of 50°C or less, and 8 parts of oxalic acid was added, followed by a reaction at 100°C for 10 hours. After completion of the reaction, the distillate was removed under reduced pressure at 180°C and 50 mmHg to obtain 550 parts of novolak resin A.

[0120] 130 parts of the obtained novolak resin A, 2.6 parts of a 50% aqueous sodium hydroxide solution, and 100 parts of toluene / methyl isobutyl ketone (mass ratio = 2 / 1) were charged into an autoclave equipped with a thermometer, a nitrogen introducing device that also serves as an alkylene oxide introducing device, and a stirrer, and the system was purged with nitrogen while stirring. Then, the temperature was raised to 150°C and 8 kg / cm ２ 45 parts of ethylene oxide was gradually introduced and reacted at a reaction gauge pressure of 0.0 kg / cm ２ The reaction mixture was stirred for about 4 hours until the reaction mixture reached a concentration of 100%, and then cooled to room temperature. 3.3 parts of a 36% aqueous solution of hydrochloric acid was added to the reaction mixture and mixed to neutralize the sodium hydroxide. The resulting neutralized reaction product was diluted with toluene, washed with water three times, and the solvent was removed using an evaporator to obtain an ethylene oxide adduct of novolak resin A having a hydroxyl value of 175 g / eq.

[0121] The resulting ethylene oxide adduct of novolak resin A had an average of 1 mole of ethylene oxide added per equivalent of phenolic hydroxyl group. Next, 175 parts of the resulting ethylene oxide adduct of novolak resin A, 50 parts of acrylic acid, 3.0 parts of p-toluenesulfonic acid, 0.1 parts of hydroquinone monomethyl ether, and 130 parts of toluene were charged into a reactor equipped with a stirrer, thermometer, and air inlet tube, and the mixture was stirred while blowing in air. The temperature was raised to 115°C, and the reaction was continued for another 4 hours while distilling off the water produced by the reaction as an azeotrope with toluene. The mixture was then cooled to room temperature. The resulting reaction solution was washed with a 5% aqueous solution of NaCl, and the toluene was removed by distillation under reduced pressure. Diethylene glycol monoethyl ether acetate was then added to obtain an acrylate resin solution with a solids content of 68%. Then, 312 parts of the obtained acrylate resin solution, 0.1 parts of hydroquinone monomethyl ether, and 0.3 parts of triphenylphosphine were placed in a four-neck flask equipped with a stirrer and a reflux condenser, the mixture was heated to 110°C, 45 parts of tetrahydrophthalic anhydride was added, and the mixture was reacted for 4 hours. After cooling, the mixture was taken out and a solution of a carboxyl group-containing resin was obtained. The obtained carboxyl group-containing resin had a solids content of 70% and an acid value of the solids of 65 mgKOH / g.

[0122] The components shown in Table 1 below were mixed in the amounts shown in the table, pre-mixed using a mixer, and then kneaded using a three-roll mill to prepare photosensitive resin compositions. The numerical values ​​for each component shown in Table 1 represent the solid content, excluding the solvent.

[0123] Details of each component in Table 1 are as follows. Carboxyl group-containing resin: A carboxyl group-containing resin obtained by synthesizing the carboxyl group-containing resin described above. The values ​​in the table are values ​​for solids content. Photopolymerizable monomer: Dipentaerythritol hexaacrylate (DPHA) Colorant 1: Fastogen Blue 5380 Phthalocyanine Blue Colorant 2: Yellow S1515 / AGR Chromophthal Yellow Photopolymerization initiator 1: Omnirad TPO-L ethyl-2,4,6-trimethylbenzoylphenylphosphinate manufactured by IGM Japan LLC Melting point: -12°C Photopolymerization initiator 2: Omnipol TP manufactured by IGM Japan LLC Softening point: 10°C (see the formula below for structure). In the formula below, a, b, and c are all integers of 1 to 20, preferably all integers of 1 to 10. Photopolymerization initiator 3: Omnirad 907 manufactured by IGM Japan LLC, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone, melting point: 74°C. Heat curing catalyst 1: melamine. Heat curing catalyst 2: dicyandiamide. Inorganic filler 1: spherical silica (MEK-AC-2140Z manufactured by Nissan Chemical Industries, Ltd.), average particle size (D50): 12 nm. Inorganic filler 2: spherical silica (YA050C manufactured by Admatechs Co., Ltd.), average particle size (D50): 50 nm. Inorganic filler 3: spherical silica (MEK-AC-5140Z manufactured by Nissan Chemical Industries, Ltd.), average particle size (D50): 80 nm. Inorganic filler 4: alumina (NP-ALO-1 manufactured by EM Japan Co., Ltd.), average particle size (D50): 80 nm. Inorganic filler 5: spherical silica. Silica (SFP-30) manufactured by Denka Corporation, average particle size (D50): 550 nm. Inorganic filler 6: barium sulfate (B-30 manufactured by Sakai Chemical Industry Co., Ltd.), average particle size (D50): 300 nm. Inorganic filler 7: talc (Nano Ace D-600 manufactured by Nippon Talc Co., Ltd.), average particle size (D50): 600 nm. Inorganic filler 8: titanium oxide (CR-97 manufactured by Ishihara Sangyo Kaisha, Ltd.), average particle size (D50): 250 nm. Thermosetting component: multifunctional phenol novolac epoxy resin (EPICLON (registered trademark) N-770) manufactured by DIC Corporation. Organic solvent: diethylene glycol monoethyl ether acetate.

[0124]

[0125] [Measurement of Viscosity] The viscosity measurement refers to a viscosity measured in accordance with JIS Z 8803:2011, Section 10, "Method for measuring viscosity using a cone-plate rotational viscometer." Specifically, the viscosity measurement refers to a value measured using a cone-plate viscometer (TVE-33H, manufactured by Toki Sangyo Co., Ltd.) under conditions of 25°C, 5.0 rpm, and 30 seconds, using a 3°×R14 cone rotor for liquid substances with a viscosity of less than 10 Pa s, or a 3°×R9.7 cone rotor for paste-like substances with a viscosity of 10 to 300 Pa s.

[0126] The viscosities of photopolymerization initiators 1, 2, and 3 at 25°C are as follows: Photopolymerization initiator 1: 0.7 Pa·s Photopolymerization initiator 2: 227 Pa·s Photopolymerization initiator 3: Unmeasurable due to being solid

[0127] [Measurement of Melting Point or Softening Point] A differential scanning calorimeter, Modulated DSC (Q2000) manufactured by TA Instruments, was used to measure the melting point or softening point. In this device, the temperature of the heat bath was raised while oscillating at a constant amplitude and frequency, and the sample was raised while exhibiting a phase shift from the temperature of the heat bath. Based on the phase shift, the sample was separated into components that followed the temperature modulation and components that did not, and the melting point or softening point was determined from the portion that followed the temperature modulation.

[0128] [Preparation of Dry Films Having Photosensitive Resin Compositions] Photosensitive resin composition laminate structures were prepared using the resin compositions obtained above. First, each composition of the Examples and Comparative Examples disclosed in Table 1 was applied to a 35 μm-thick polyethylene terephthalate (PET) film (hereinafter referred to as the first film) and dried to prepare a photosensitive resin layer. Next, a 15 μm-thick biaxially oriented polypropylene (OPP) film (hereinafter referred to as the second film) was laminated onto the surface of the photosensitive resin layer to prepare dry films for each Example and Comparative Example consisting of three layers: the first film, the photosensitive resin layer, and the second film.

[0129] [Preparation of cured product (cured coating film)] The second film was peeled off from the dry film prepared above on a low-profile copper foil, and the photosensitive resin layer of the dry film prepared in [Preparation of dry film having photosensitive resin composition] was attached to the copper foil surface side. Subsequently, using a batch-type vacuum pressure laminator (MVLP-500 manufactured by The Japan Steel Works, Ltd.), heat lamination was performed under conditions of pressure: 0.8 MPa, 70°C, 1 minute, and vacuum: 133.3 Pa, to closely bond the substrate and the photosensitive resin layer.

[0130] Next, using an exposure device equipped with a high-pressure mercury lamp (short arc lamp), the dry film was exposed to light (exposure amount: 400 to 600 mJ / cm ２ After this, the first film was peeled off from the dry film to expose the photosensitive resin layer. ２ CO ３ Using an aqueous solution, 30°C, spray pressure 2 kg / cm ２ The resist was then developed for 60 seconds under the conditions of 1000 mJ / cm. ２ The resin layer was then heated at 150° C. for 60 minutes to completely cure the resin layer, thereby producing a cured product (cured coating film) for each of the Examples and Comparative Examples.

[0131] [Evaluation of CTE] The cured product (cured coating film) prepared in [Preparation of Cured Product (Cured Coating Film)] corresponding to each Example and Comparative Example was peeled from the copper foil, and a sample of a measurement size (3 mm x 16 mm) was measured for CTE using a TMA-Q400EM manufactured by TA Instruments. The measurement conditions were a test load of 5 g, and the sample was heated from room temperature at a heating rate of 10°C / min, repeated twice, and the linear expansion coefficient α1 below Tg was obtained after the second heating. The obtained α1 was evaluated as CTE. A lower α1 leads to more suppression of stress generation, so it is preferably 45 ppm or less.

[0132] [Embeddability in Fine Pitch L / S (Evaluation of Embeddability)] A double-sided printed wiring board having a copper thickness of 10 μm and a comb-tooth pattern fine circuit with L (line: wiring width) / S (space: spacing width) = 10 μm / 10 μm was pretreated by etching using a CZ process manufactured by MEC Co., Ltd. to a surface roughness Ra equivalent to 0.05 μm. After peeling off the second film from the dry films corresponding to each of the above-prepared examples and comparative examples, the dry films were laminated onto the etched substrate using the above-mentioned batch-type vacuum pressure laminator. The lamination conditions were 5 kgf / cm ２ The laminate was then heated and laminated at 80°C for 1 minute at 1 Torr, and then pressed with a hot plate press at 10 kgf / cm ２ Leveling was carried out under conditions of 1 minute at 90°C. After lamination, 100 points were checked through the first film to see if air had entered the boundaries between the lines and spaces, causing bubbles (voids) in the resin layer. The evaluation criteria were as follows: A: No voids were observed. B: Voids were observed in 1 to 2 places. C: Voids were observed in 3 or more places.

[0133] [Resolution evaluation (minimum opening diameter evaluation)] FR-4 1.6 mm thick copper clad laminate with 35 μm thick copper foil was subjected to copper etching treatment to a surface roughness Ra equivalent to 1.0 μm using CZ-8101B treatment manufactured by MEC Co., Ltd. The laminate structure of each example and comparative example was laminated onto a copper clad laminate that had been copper etched using a vacuum laminator CVP-300 manufactured by Nikko Materials Co., Ltd. in a first chamber at 90 ° C. under conditions of a vacuum pressure of 3 hPa and a vacuum time of 30 seconds, and then pressed in a second chamber under conditions of a press pressure of 0.5 MPa, a press time of 30 seconds, and 70 ° C. Then, using an exposure device equipped with a high-pressure mercury lamp (short arc lamp), exposure was performed through a negative mask having a negative pattern with via opening diameters of 50 μm, 45 μm, 40 μm, 35 μm, 30 μm, and 25 μm. The exposure amount was adjusted using a step tablet (Photec 41 step) so that the gloss sensitivity was level 10. 10 minutes after exposure, the first film was peeled off from each laminate structure to expose the photosensitive resin layer.

[0134] Subsequently, 1 mass % Na ２ CO ３ Using an aqueous solution, spray pressure 2 kg / cm ２ Then, the film was developed in a UV conveyor oven at an integrated exposure dose of 1000 mJ / cm for 60 seconds. ２ After irradiating with ultraviolet light under the conditions of (a) above, the composition was heat-cured at 170°C for 60 minutes. For each of the obtained test pieces, the pattern openings were observed under a scanning electron microscope (SEM) at 2000 magnifications to evaluate the minimum opening diameter. The minimum opening diameter is preferably 35 µm or less.

[0135] The melting point of the photopolymerization initiator 1 was -12°C, the softening point of the photopolymerization initiator 2 was 10°C, and the softening point of the photopolymerization initiator 3 was 74°C.

[0136] The compositions and evaluations of the photosensitive resin compositions of Examples 1 to 6 and Comparative Examples 1 to 5 and their cured products are shown in Tables 1 and 2.

[0137]

[0138]

[0139] [Discussion] The results of each Example and Comparative Example show that there are significant differences in the properties of the photopolymerization initiator. The results of Example 1 and Comparative Example show that when the melting point or softening point of the photopolymerization initiator is within a specific range, the fluidity of the resin composition increases, and good embeddability and resolution properties are exhibited even when the amount of inorganic filler is increased. Furthermore, while a similar tendency is observed in Examples 4 to 6, Examples 1 to 4, which contain ethyl-2,4,6-trimethylbenzoylphenylphosphinate and in which at least one of silica, hydrotalcite, talc, and alumina, each having a nano-sized average particle size, is blended in a specific amount, show better embeddability properties.

[0140] Furthermore, evaluation of various physical properties in the examples showed that the photosensitive resin composition of this embodiment, its dry film, and its cured product were extremely favorable for application to printed wiring boards.

Claims

1. A photosensitive resin composition containing a carboxyl group-containing resin, a photopolymerizable monomer, a photopolymerization initiator, and an inorganic filler, wherein the melting point or softening point of the photopolymerization initiator is -50 to 30°C, the inorganic filler is at least one of silica, hydrotalcite, talc, and alumina, and the inorganic filler is a nanofiller.

2. The photosensitive resin composition according to claim 1, wherein the viscosity of the photopolymerization initiator at 25°C is 0.1 to 300 Pa·s.

3. The photosensitive resin composition according to claim 2, wherein the photopolymerization initiator is a liquid phosphine oxide-based photopolymerization initiator.

4. The photosensitive resin composition according to claim 3, wherein the photopolymerization initiator is represented by the following general formula (i): (In the formula, R １ is a linear or branched alkyl group having 1 to 12 carbon atoms, and R ２ represents a cyclohexyl group, a cyclopentyl group, an aryl group, an aryl group substituted with a halogen atom, an alkyl group or an alkoxy group, or a carbonyl group having 1 to 20 carbon atoms.

5. The photosensitive resin composition according to claim 4, wherein the photopolymerization initiator is represented by the following general formula (ii):

6. The photosensitive resin composition according to claim 1, wherein the inorganic filler is silica.

7. The photosensitive resin composition according to claim 1, wherein the inorganic filler is spherical.

8. The photosensitive resin composition according to claim 1, wherein the amount of the inorganic filler is 35 to 75 mass % in terms of solid content based on the total amount of the photosensitive resin composition.

9. The photosensitive resin composition according to claim 1, wherein the photosensitive resin composition is for forming a solder resist.

10. 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 any one of claims 1 to 9.

11. A cured product obtained by curing the photosensitive resin composition according to any one of claims 1 to 9.

12. A cured product obtained by curing the resin layer of the dry film according to claim 10.

13. A printed wiring board comprising the cured product according to claim 11.

14. A printed wiring board comprising the cured product according to claim 12.

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