WO2025205453A1 - Photosensitive resin composition, dry film, cured product, and printed circuit board - Google Patents

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

The present invention relates to a photosensitive resin composition. It also relates to a dry film, a cured product, and a printed wiring board that use the photosensitive resin composition.

In response to the increasing density of printed wiring boards that accompany the lighter, thinner, and smaller size of electronic devices, smaller semiconductor packages with more pins have been put into practical use and mass production has progressed. Recently, semiconductor packages known as QFPs (quad flat packages) and SOPs (small outline packages) have been replaced by semiconductor packages such as BGAs (ball grid arrays) and CSPs (chip scale packages) that use package substrates. Because wiring patterns on such package substrates are formed more densely and closely together, permanent coatings such as solder resists used on package substrates must have properties such as heat resistance, high rigidity, and thermal dimensional stability (low coefficient of thermal expansion (CTE) (i.e., warpage prevention)).

A common method of imparting high reliability to solder resists for packaging substrates is to add a high amount of inorganic filler to the composition, thereby improving properties such as rigidity. Among inorganic fillers, silica is widely used to improve solder resist properties because of its excellent filling properties, which further lowers the coefficient of thermal expansion (CTE) (see Patent Document 1, etc.).

In addition, curable resin compositions used to form solder resist for package substrates are classified into liquid and dry film types. Dry film-type curable resin compositions (hereinafter simply referred to as "dry film") are increasingly being used due to their advantages, such as smoothness, high film thickness accuracy, and low contamination of the coating. Even in the aforementioned dry film, inorganic fillers are highly loaded into the composition as a method of imparting high reliability to solder resist for package substrates. Silica, which is used as an inorganic filler, has excellent loading properties and further reduces the coefficient of thermal expansion (CTE), and is therefore widely used to improve the properties of solder resist (see Patent Document 2, etc.).

Japanese Patent Application Laid-Open No. 2018-165795 JP 2014-81611 A

However, if the curable resin composition used to form the solder resist for package substrates contains a high inorganic filler content, for example, in the case of a dry film type, the melt viscosity of the resin layer formed from the dried coating of the resin composition increases during formation, reducing its adhesive performance (tackiness), making it more likely to be difficult to handle during manufacturing and causing lamination problems. Specifically, it has been confirmed that air gets trapped at the boundaries between the circuit lines and spaces when laminating onto a printed wiring board with fine circuits, creating air bubbles (voids) in the resin layer of the dry film, leaving room for improvement.

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 process, a development process, and, if necessary, a main curing process using heat or UV light are performed to obtain a patterned cured coating film. However, if the resin composition contains a high amount of inorganic filler, for example, the resolution is poor and the desired pattern cannot be formed, leaving room for improvement.

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

As a result of extensive research to achieve the above objective, the inventors have discovered a photosensitive resin composition that can address the above-mentioned issues by examining the composition of the photosensitive resin composition. Specifically, they have discovered a photosensitive resin composition that can address the above-mentioned issues by combining a photopolymerization initiator with a specific melting point or softening point with a specific type of inorganic filler that has a nano-sized average particle size.

In other words, the photosensitive resin composition of this 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.

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.

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

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

In the formula, ^R1 represents a linear or branched alkyl group having 1 to 12 carbon atoms, and ^R2 represents a cyclohexyl group, a cyclopentyl group, an aryl group, a halogen atom, an aryl group substituted with an alkyl group or an alkoxy group, or a carbonyl group having 1 to 20 carbon atoms.

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

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

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

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

The photosensitive resin composition of this embodiment may also be used to form a solder resist.

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

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

The printed wiring board of this embodiment is characterized by comprising the above-mentioned cured product.

The photosensitive resin composition of the present invention can be obtained as a photosensitive resin composition that has excellent embeddability in double-sided printed wiring boards on which fine circuits are formed, while maintaining a low coefficient of thermal expansion (CTE), and that also has high resolution. Furthermore, this photosensitive resin composition can be applied to dry films, cured products, and printed wiring boards to achieve good performance.

[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 ...).

[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, the photosensitive resin composition can be imparted with alkaline developability. 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):

(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, or isobutylene.

(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.

(3) Examples include carboxyl group-containing photosensitive urethane resins obtained by the polyaddition reaction of diisocyanates with (meth)acrylates or partially acid anhydride-modified products thereof 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, as well as carboxyl group-containing dialcohol compounds and diol compounds.

(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 described above in (2) or (3).

(5) An example is a carboxyl group-containing photosensitive urethane resin that has been (meth)acrylated at the end by adding a compound having one isocyanate group and one or more (meth)acryloyl groups in the molecule, such as an equimolar reaction product of isophorone diisocyanate and pentaerythritol triacrylate, during the synthesis of the resin described above in (2) or (3).

(6) An example is 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 groups present in the side chains.

(7) An example is a carboxyl group-containing photosensitive resin obtained by reacting a polyfunctional epoxy resin in which the hydroxyl groups of a bifunctional (solid) epoxy resin have been further epoxidized with epichlorohydrin with (meth)acrylic acid, and then adding a dibasic acid anhydride to the resulting hydroxyl groups.

(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.

(9) An example of a carboxyl group-containing photosensitive resin is obtained by reacting an epoxy compound having multiple epoxy groups per molecule with a compound having at least one alcoholic hydroxyl group and one phenolic hydroxyl group per 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.

(10) An example is 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.

(11) An example is a carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups per 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.

(12) An example is 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.

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.

The carboxyl group-containing resins that can be used in this embodiment are not limited to those listed above. Furthermore, the carboxyl group-containing resins listed above may be used alone, or multiple types may be mixed together. Among the resins listed above, carboxyl group-containing resins synthesized using compounds having phenolic hydroxyl groups as starting materials, 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.

In the photosensitive resin composition of this embodiment, taking into consideration the developability and resist pattern drawability when using a weak alkaline developer such as an aqueous sodium carbonate solution, 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.

The weight-average molecular weight of carboxyl group-containing resins varies depending on the resin skeleton, but is generally in the range of 2,000 to 150,000, with 5,000 to 100,000 being preferable. Using a carboxyl group-containing resin with a weight-average molecular weight of 2,000 or more improves resolution and tack-free performance. Using a carboxyl group-containing resin with a weight-average molecular weight of 150,000 or less improves developability and storage stability. Weight-average molecular weight is measured by gel permeation chromatography (GPC).

[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.

The photopolymerizable monomer may be blended alone or in combination of two or more types. The blend amount of the photopolymerizable monomer, converted to solid content, is preferably 0.1 to 40 parts by mass per 100 parts by mass of the carboxyl group-containing resin. When the blend amount is 0.1 part by mass or more, the photocuring properties are good and pattern formation is easy in alkaline development after irradiation with active energy rays. When the blend amount is 40 parts by mass or less, halation is less likely to occur and good resolution can be obtained.

[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 ensures that the photopolymerization initiator itself has excellent fluidity. Depending on the type of photopolymerization initiator, there are molecules for which a single melting point cannot be identified. For this reason, the softening point is also defined as the temperature at which the fluidity changes from a solid phase to a liquid phase.

If the melting point or softening point is in the range of -50 to 30°C, the viscosity when preparing the photosensitive resin composition will be appropriate even when taking into account the inclusion of inorganic fillers, resulting in improved fluidity. A range of -50 to 15°C is more preferable, and -50 to 0°C is even more preferable.

Furthermore, from the perspective 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.

The photopolymerization initiator contained in the photosensitive resin composition of this embodiment can be any commonly known photopolymerization initiator as long as it has a melting point or softening point of -50 to 30°C, but among these, liquid phosphine oxide-based photopolymerization initiators are preferably used.

To measure the melting point or softening point, a TA Instruments Modulated DSC (Q2000) differential scanning calorimetry analyzer is used. With this device, the temperature of the heat bath is raised while oscillating at a constant amplitude and frequency, and the sample is heated while experiencing a phase shift from the temperature of the heat bath. The phase shift allows the sample to be separated into components that follow the temperature modulation and those that do not, and the melting point or softening point is determined from the part that follows the temperature modulation.

The liquid phosphine oxide photopolymerization initiator is represented by the following general formula (i): In the formula, ^R1 is a linear or branched alkyl group having 1 to 12 carbon atoms, and ^R2 is a cyclohexyl group, a cyclopentyl group, an aryl group, a halogen atom, an aryl group substituted with an alkyl group or an alkoxy group, or a carbonyl group having 1 to 20 carbon atoms.

Specific examples of photopolymerization initiators contained in the photosensitive resin composition of this embodiment include substances (1) and (2) below. Among these, (1) "ethyl-2,4,6-trimethylbenzoylphenylphosphinate" is preferred due to its superior embeddability.

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

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

Liquid means that the sample is liquid 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 at a temperature range of 10 to 40°C, the sample passes through the part 85 mm from the bottom within 90 seconds. Specifically, ethyl-2,4,6-trimethylbenzoylphenylphosphinate ((2,4,6-trimethylbenzoyl)ethoxyphenylphosphine oxide) is a suitable example of such a phosphine oxide photopolymerization initiator that is liquid at room temperature.

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 is used that is 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. The preferred mixture ratio is 70 to 98% by mass of the phosphine oxide-based photopolymerization initiator that is liquid at room temperature and 2 to 30% by mass of the phosphine oxide-based polymerization initiator that is solid at room temperature.

The amount of photopolymerization initiator (especially a liquid phosphine oxide-based photopolymerization initiator) blended is preferably 5 to 30 parts by mass, and more preferably 7 to 20 parts by mass, per 100 parts by mass of the carboxyl group-containing resin, converted into solids. When the blended amount of the aforementioned 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 blended amount is 30 parts by mass or less, the curing properties of thick films are improved.

Furthermore, the photopolymerization initiator contained in the photosensitive resin composition of this 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, 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 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, and pivaloylphenylphosphinic acid isopropyl ester monoacylphosphine oxides such as 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]- Acetophenones such as 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; anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone anthraquinones such as quinone and 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); 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.

A photoinitiator co-agent or sensitizer may be used in combination with the aforementioned photopolymerization initiator. Examples of photoinitiator co-agents or sensitizers include benzoin compounds, anthraquinone compounds, thioxanthone compounds, ketal compounds, benzophenone compounds, tertiary amine compounds, and xanthone compounds. Thioxanthone compounds, such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 4-isopropylthioxanthone, are particularly preferred. The inclusion of a thioxanthone compound can improve deep curing properties. While these compounds may be used as photopolymerization initiators, it is preferable to use them in combination with a photopolymerization initiator. One type of photoinitiator or sensitizer may be used alone, or two or more types may be used in combination.

[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.

Furthermore, the inorganic filler is preferably spherical in shape, but is not necessarily limited to a perfect sphere. Suitable inorganic fillers have a sphericity of 0.8 or more, as measured below. However, this is not limiting. 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 in the photograph, using the formula (sphericity) = {4π × (area) ÷ (perimeter)^2}. Specifically, an image processing device is used, and the average value measured for 100 particles is used.

There are no particular restrictions on the method for producing spherical inorganic fillers, and known methods can be used. For example, they can be produced by burning silicon powder using the VMC (Vaporized Metal Combustion) method. The VMC method involves creating a chemical flame using a burner in an oxygen-containing atmosphere, adding metal powder that will form part of the desired oxide particles into this chemical flame in an amount sufficient to form a dust cloud, and causing a deflagration to occur, resulting in the production of oxide particles.

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.

In the embodiment, the nanofiller has an average particle size (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 size of the nanofiller refers to the particle size at 50% cumulative volume obtained using a dynamic light scattering particle size distribution measurement method. The average particle size of the filler refers to the value measured as described above for the filler before preparing (stirring, kneading) the curable resin composition.

Furthermore, inorganic fillers other than nanofillers may be used in combination with the inorganic filler, provided that the properties are not impaired. The average particle size of the inorganic filler other than nanofillers is preferably 100 to 1,000 nm, and 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. Furthermore, 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.

By using two types of inorganic filler with different average particle sizes, the inorganic filler with a smaller average particle size fills the gaps between the inorganic filler with a relatively larger average particle size. This results in a photosensitive resin composition with a high inorganic filler content and a low resin content, i.e., a high ratio of inorganic filler mass to the total mass.

There are no particular restrictions on whether the inorganic filler is surface-treated. In the photosensitive resin composition of this embodiment, it is preferable that the inorganic filler be highly filled, in which 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 surface-treated inorganic filler suppresses aggregation.

The surface treatment method for inorganic fillers is not particularly limited, and known methods can be used. Surface treatment of inorganic fillers 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. It is preferable that the silane coupling agent is immobilized on the silica surface in advance by adsorption or reaction. The amount of coupling agent used per 100 parts by mass of inorganic filler is preferably 0.5 to 10 parts by mass. Note that the reactive functional groups derived from the coupling agent applied to the inorganic filler are not included in compounds having photocurable reactive groups or thermosetting functional groups.

Examples of photocurable reactive groups include ethylenically unsaturated groups such as vinyl groups, styryl groups, methacrylic groups, and acrylic groups. Of these, at least one of vinyl groups and (meth)acrylic groups is preferred.

Examples of thermosetting reactive groups include hydroxyl groups, carboxyl groups, isocyanate groups, amino groups, imino groups, epoxy groups, oxetanyl groups, mercapto groups, methoxymethyl groups, methoxyethyl groups, ethoxymethyl groups, ethoxyethyl groups, and oxazoline groups. Of these, at least one of amino groups and epoxy groups is preferred.

The surface-treated inorganic filler may be contained in the photosensitive resin composition in a surface-treated state, or the inorganic filler may be surface-treated in the composition by blending an untreated inorganic filler and a surface treatment agent separately. However, blending an inorganic filler that has already been surface-treated is preferred. When surface-treating the filler in advance, it is preferable to blend a pre-dispersion in which the inorganic filler has been pre-dispersed in a solvent and a curable component. It is more preferable to pre-disperse the surface-treated inorganic filler in a solvent and blend this pre-dispersion into the composition, or to sufficiently surface-treat the untreated inorganic filler when pre-dispersing it in a solvent, and then blend this pre-dispersion into the composition.

Depending on the manner in which the photosensitive resin composition is used, the inorganic filler may be blended with the carboxyl group-containing resin, etc. in powder or solid form, or may be mixed with a solvent and dispersant to form a slurry and then blended with the carboxyl group-containing resin, etc.

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

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.

[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.

There are no particular restrictions on the type of blue colorant, and any known blue colorant can be used, including pigments, dyes, and pigments. However, from the perspective of reducing environmental impact and impact on the human body, types that do not contain halogen atoms are preferred. Blue colorants include phthalocyanine and anthraquinone types. Pigment types 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 types 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. Blue colorants can be used alone or in combination of two or more types.

The amount of blue colorant blended is 0.3 to 2.5 mass%, preferably 0.3 to 2.0 mass%, calculated as solids content based on the total amount of the photosensitive resin composition. When the amount of blue colorant blended is 0.3 mass% or more, excellent halation suppression effects are achieved. When the amount blended is 2.5 mass% or less, the blueness becomes appropriate, and resolution tends to improve.

There are no particular restrictions on the type of yellow colorant, and any known yellow colorant can be used, including pigments, dyes, and coloring matter. From the perspective 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, disazo, condensed azo, benzimidazolone, isoindolinone, and anthraquinone. Specific examples of monoazo yellow colorants include Pigment Yellow 1, 2, 3, 4, 5, 6, 9, 10, 12, 61, 62, 62:1, 65, 73, 74, 75, 97, 100, 104, 105, 111, 116, 167, 168, 169, 182, and 183. Examples of disazo yellow colorants include Pigment Yellow 12, 13, 14, 16, 17, 55, 63, 81, 83, 87, 126, 127, 152, 170, 172, 174, 176, 188, and 198. 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 yellow colorants include Solvent Yellow 163, Pigment Yellow 24, 108, 193, 147, 199, and 202.

The amount of yellow colorant blended 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 yellow colorant blended is 0.1 mass % or more, excellent halation suppression effects are achieved. When the amount blended is 2.0 mass % or less, the yellowness becomes appropriate, and resolution is likely to improve.

The photosensitive resin composition of this embodiment may contain colorants of colors other than the above-mentioned blue and yellow colorants. Such other colorants may be conventionally known colorants such as red and green, and may be any of pigments, dyes, and colorants. Specific examples include colorants assigned a Color Index (C.I.; published by The Society of Dyers and Colorists) number. From the perspective of reducing environmental impact and impact on the human body, colorants that do not contain halogens are preferred.

[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. Examples of known thermosetting components include 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. A thermosetting component having multiple cyclic ether groups or cyclic thioether groups (hereinafter abbreviated as cyclic (thio)ether groups) in the molecule is preferred.

The above-mentioned thermosetting components having multiple cyclic (thio)ether groups in their molecules are compounds having multiple three-, four-, or five-membered cyclic (thio)ether groups in their molecules, and examples include compounds having multiple epoxy groups in their molecules (i.e., multifunctional epoxy compounds), compounds having multiple oxetanyl groups in their molecules (i.e., multifunctional oxetane compounds), and compounds having multiple thioether groups in their molecules (i.e., episulfide resins).

Multifunctional 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, mixtures of 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 can be used alone or in combination of two or more.

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 include polyfunctional oxetanes such as acrylate, (3-methyl-3-oxetanyl)methyl methacrylate, (3-ethyl-3-oxetanyl)methyl methacrylate, and their oligomers or copolymers, as well as ethers of oxetane alcohols with novolak resins, poly(p-hydroxystyrene), cardo-type bisphenols, calixarenes, calixresorcinarenes, or hydroxyl group-containing resins such as silsesquioxane. Other examples include copolymers of unsaturated monomers with oxetane rings and alkyl (meth)acrylates.

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

Amino resins such as melamine derivatives and benzoguanamine derivatives include methylolmelamine compounds, methylolbenzoguanamine compounds, methylolglycoluril compounds, and methylolurea compounds.

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

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 mentioned above. Examples of isocyanate blocking agents 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.

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

[Thermosetting catalyst]
The photosensitive resin composition of this embodiment may contain a thermosetting catalyst, such as 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.

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. One type of heat curing catalyst may be used alone, or two or more types may be used in combination.

The amount of thermosetting catalyst blended 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 thermosetting catalyst blended is 0.1 mass % or more, the catalytic effects such as heat resistance are more pronounced. When the amount blended is 10.0 mass % or less, it is a relatively appropriate amount and it is easy to maintain excellent storage stability.

[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.

[Other added ingredients]
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.

The photosensitive resin composition may be used in the form of a dry film or in liquid form. Furthermore, when used in liquid form, it may be a one-component or two-component or more-component composition.

[Application]
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.

[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 aforementioned organic solvent 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.

The first film can be any known film without limitation, and suitable examples include polyester films such as polyethylene terephthalate and polyethylene naphthalate, and films made of thermoplastic resins such as polyimide film, polyamideimide film, polypropylene film, and polystyrene film. Of these, polyester film is preferred from the standpoints of heat resistance, mechanical strength, and ease of handling. Furthermore, a laminate of multiple films listed above can also be used as the first film.

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

After a resin layer consisting of a dried coating of the photosensitive resin composition of this embodiment has been formed on the first film, it is preferable to further laminate a peelable second film on the surface of the resin layer to prevent contamination of the surface of the resin layer (preventing adhesion of dust, dirt, etc.). Examples of peelable second films that can be used include polyethylene film, polytetrafluoroethylene film, polypropylene film, and surface-treated paper.

When peeling off the second film, the adhesive strength between the resin layer and the second film should be smaller than the adhesive strength between the resin layer and the first film. The thickness of the second film is, for example, 10 to 150 μm.

When using a dry film to create a cured coating on a printed wiring board, the second film is peeled off from the dry film, and the exposed resin layer of the dry film is placed on a substrate with a circuit formed on it, and the two are bonded together using a laminator or similar. In this way, a resin layer is formed on the substrate with a circuit formed on it. The formed resin layer is then exposed to light, developed, and heat-cured to form a cured coating. The second film can be peeled off either before or after exposure.

[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.

[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 manufacturing 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.

The above-mentioned substrates include printed wiring boards with circuits already formed 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, wafers, etc.

A vacuum laminator or similar device is preferably used to bond the dry film to the substrate, and the process is carried out under pressure and heat. By using a vacuum laminator, even if the circuit board surface is uneven when a circuit is formed on it, the dry film adheres tightly to the circuit board, preventing the inclusion of air bubbles. It also improves the ability to fill recesses on the board surface. Pressure conditions of approximately 0.1 to 2.0 MPa are preferred, and heating conditions of 40 to 120°C are preferred.

After applying the photosensitive resin composition of this embodiment, volatilization drying is carried out using a hot air circulation drying oven, IR oven, hot plate, convection oven, etc. (a method in which hot air is countercurrently contacted inside a dryer equipped with a heat source that uses steam for air heating, or a method in which hot air is blown onto the support from a nozzle). Drying conditions include, for example, 40 to 130°C and 1 to 30 minutes.

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

Furthermore, the cured product can be irradiated with active energy rays and then heat-cured (e.g., 100 to 220°C, 10 to 60 minutes), or heat-cured and then irradiated with active energy rays (e.g., 1000 mJ/ ^cm2 ), or heat-cured alone to form a final finish curing (main curing), thereby forming a cured film with excellent properties such as adhesion and hardness.

The exposure device used for the above-mentioned active energy ray irradiation may be a device equipped with a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a mercury short arc lamp, or the like, and 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 be used. The lamp or laser light source of the direct imaging device emits light having 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 1000 mJ/cm ² , and preferably 20 to 800 mJ/cm ² .

The above-mentioned development methods include dipping, showering, spraying, and brushing, and the developer used is an alkaline aqueous solution of potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, amines, etc.

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

The following provides a more detailed explanation using examples and comparative examples, but the present invention is not limited to these examples and comparative examples. Note that "parts" and "%" below are all by mass unless otherwise specified.

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

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. While maintaining the temperature below 40°C, 228 parts of 25% aqueous sodium hydroxide solution was added, and the reaction was carried out at 50°C for 10 hours. After the reaction was complete, the reaction liquid was cooled to 40°C, and while maintaining the temperature below 40°C, 37.5% aqueous phosphoric acid solution was added to neutralize the solution to pH 4. The reaction liquid was then 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 water, solvent, etc. were removed under reduced pressure at a temperature below 50°C, yielding a polymethylol compound.

The resulting 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 resulting methanol solution of the polymethylol compound was dried at room temperature in a vacuum dryer. The solids content at this time was 55.2%. 500 parts of the resulting methanol solution of the polymethylol compound and 440 parts of 2,6-xylenol were dissolved uniformly at 50°C. After uniform dissolution, the methanol was removed under reduced pressure at a temperature below 50°C, and 8 parts of oxalic acid were 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.

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/alkylene oxide introducing device, and a stirrer. The system was purged with nitrogen while stirring, and then heated to an elevated temperature. 45 parts of ethylene oxide were gradually introduced at 150°C and 8 kg/ ^cm² to cause a reaction. The reaction was continued for approximately 4 hours until the reaction gauge pressure reached 0.0 kg/ ^cm² , and then cooled to room temperature. 3.3 parts of a 36% aqueous hydrochloric acid solution were added to the resulting reaction solution and mixed to neutralize the sodium hydroxide. The resulting neutralized reaction product was diluted with toluene, washed three times with water, and the solvent was removed using an evaporator to obtain an ethylene oxide adduct of novolak resin A with a hydroxyl value of 175 g/eq.

The resulting ethylene oxide adduct of novolak resin A contained an average of 1 mole of ethylene oxide 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 added to a reactor equipped with a stirrer, thermometer, and air inlet tube. The mixture was stirred while blowing in air, heated to 115°C, and allowed to react for an additional 4 hours while the water produced by the reaction was distilled off 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, and the mixture was heated to 110°C. 45 parts of tetrahydrophthalic anhydride was added and reacted for 4 hours. After cooling, the mixture was removed and a carboxyl group-containing resin solution was obtained. The resulting carboxyl group-containing resin had a solids content of 70% and an acid value of the solids of 65 mgKOH/g.

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 triple roll mill to prepare a photosensitive resin composition. The values for each component shown in Table 1 represent the solid content, excluding the solvent.

Details of each component in Table 1 are as follows:
Carboxyl group-containing resin: The carboxyl group-containing resin obtained by the synthesis of the carboxyl group-containing resin described above. The values in the table are the values of the solid content.
Photopolymerizable monomer: dipentaerythritol hexaacrylate (DPHA)
Colorant 1: Firstgen Blue 5380 Phthalocyanine Blue Colorant 2: Yellow S1515/AGR Chromophthal Yellow Photopolymerization initiator 1: Omnirad TPO-L manufactured by IGM Japan LLC
Ethyl 2,4,6-trimethylbenzoylphenylphosphinate Melting point: -12°C
Photopolymerization initiator 2: Omnipol TP manufactured by IGM Japan LLC. Softening point: 10°C. See the following formula for the structure: In the following formula, a, b, and c are all integers of 1 to 20, preferably 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 (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

[Viscosity measurement]
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 is measured using a cone-plate viscometer (TVE-33H, manufactured by Toki Sangyo Co., Ltd.) 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, under conditions of 25°C, 5.0 rpm, and 30 seconds.

The viscosities of the 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: Cannot be measured because it is solid

[Melt point or softening point measurement]
The melting point or softening point was measured using a differential scanning calorimeter, Modulated DSC (Q2000) manufactured by TA Instruments. In this device, the temperature of the heat bath was raised while oscillating at a constant amplitude and frequency, and the sample was heated 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 those that did not, and the melting point or softening point was determined from the portion that followed the temperature modulation.

[Preparation of dry film having photosensitive resin composition]
Using each resin composition obtained as described above, a photosensitive resin composition laminate structure was prepared. 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 a dry film for each Example and Comparative Example consisting of three layers: the first film, the photosensitive resin layer, and the second film.

[Preparation of cured product (cured coating film)]
The second film was peeled off from the dry film prepared above and placed 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 adhere the substrate and the photosensitive resin layer to each other.

Next, using an exposure device equipped with a high-pressure mercury lamp (short arc lamp), the dry film was exposed (exposure amount: 400 to 600 mJ/cm ² ), and then the first film was peeled off from the dry film to expose the photosensitive resin layer. This was then developed for 60 seconds using a 1 mass % Na ₂ CO ₃ aqueous solution at 30°C and a spray pressure of 2 kg/cm ² to form a resin layer with a predetermined resist pattern. The resin layer was then irradiated in a UV conveyor furnace equipped with a high-pressure mercury lamp at an exposure amount of 1000 mJ/cm ² , and then heated at 150°C for 60 minutes to completely cure the resin layer, producing a cured product (cured coating film) for each example and comparative example.

[Evaluation of CTE]
The cured product (cured coating film) prepared in the "Preparation of Cured Product (Cured Coating Film)" section for 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 preferable that the α1 be 45 ppm or less.

[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 an 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 achieve a surface roughness Ra equivalent to 0.05 μm. For the dry films corresponding to the above-mentioned examples and comparative examples, the second film was peeled off, and then the dry films were laminated onto the etched substrate using the above-mentioned batch vacuum pressure laminator. The lamination conditions were heat lamination at 5 kgf/cm ² , 80°C, 1 minute, and 1 Torr, followed by leveling using a hot plate press at 10 kgf/cm ² , 90°C, and 1 minute. After lamination, 100 locations were checked through the first film to see if air had entered the boundary between the lines and spaces, causing bubbles (voids) to form in the resin layer. The evaluation criteria were as follows:
A: No voids were observed.
B: Voids were observed in one or two places.
C: Three or more voids were observed.

[Resolution evaluation (evaluation of minimum aperture diameter)]
A copper-clad laminate with a thickness of 1.6 mm and a thickness of 35 μm was subjected to copper etching treatment using a CZ-8101B process manufactured by MEC Co., Ltd. to achieve a surface roughness Ra equivalent to 1.0 μm. The laminate structure of each example and comparative example was laminated onto a copper-clad laminate that had been subjected to copper etching treatment under conditions of a vacuum pressure of 3 hPa and a vacuum time of 30 seconds in a first chamber at 90 ° C. using a vacuum laminator CVP-300 manufactured by Nikko Materials Co., Ltd., and then pressed in a second chamber under conditions of a press pressure of 0.5 MPa, a press time of 30 seconds, and a temperature of 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.

Subsequently, the film was developed for 60 seconds using a 1% by _{mass Na2CO3} aqueous solution at 30°C under a spray pressure of 2 kg/ ^cm2 . The film was then irradiated with ultraviolet light in a UV conveyor oven at an integrated exposure dose of 1000 mJ/ ^cm2 , and then heat-cured at 170°C for 60 minutes. The pattern openings of each of the obtained test pieces were observed under a scanning electron microscope (SEM) at 2000x magnification to evaluate the minimum opening diameter. The minimum opening diameter is preferably 35 μm or less.

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

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

[Consideration]
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 even when the amount of inorganic filler is increased, good embeddability and resolution properties are exhibited. 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.

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

Claims (14)

A photosensitive resin composition containing a carboxyl group-containing resin, a photopolymerizable monomer, a photopolymerization initiator, and an inorganic filler,
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;
The inorganic filler is a nanofiller.
A photosensitive resin composition comprising: 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. The photosensitive resin composition according to claim 2, wherein the photopolymerization initiator is a liquid phosphine oxide-based photopolymerization initiator. The photosensitive resin composition according to claim 3 , wherein the photopolymerization initiator is represented by the following general formula (i):

(In the formula, ^R1 represents a linear or branched alkyl group having 1 to 12 carbon atoms, and ^R2 represents a cyclohexyl group, a cyclopentyl group, an aryl group, a halogen atom, an aryl group substituted with an alkyl group or an alkoxy group, or a carbonyl group having 1 to 20 carbon atoms.) The photosensitive resin composition according to claim 4 , wherein the photopolymerization initiator is represented by the following general formula (ii):
The photosensitive resin composition according to claim 1, wherein the inorganic filler is silica. The photosensitive resin composition according to claim 1, wherein the inorganic filler is spherical. 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. The photosensitive resin composition according to claim 1, wherein the photosensitive resin composition is for forming a solder resist. A dry film comprising a first film and a resin layer formed on the first film, the resin layer being a dried coating of the photosensitive resin composition described in any one of claims 1 to 9. A cured product obtained by curing the photosensitive resin composition described in any one of claims 1 to 9. A cured product obtained by curing the resin layer of the dry film described in claim 10. A printed wiring board comprising the cured product according to claim 11. A printed wiring board comprising the cured product according to claim 12.