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

Abstract

[Problem] To provide a photosensitive resin composition capable of efficiently forming a cured product having both excellent dielectric characteristics and resolution in a short time.　[Solution] In this photosensitive resin composition containing a polyphenylene ether resin, a first photopolymerization initiator, a second photopolymerization initiator, and a radical reactive monomer, a weight average molecular weight of the polyphenylene ether resin is adjusted to 250-10,000, the first photopolymerization initiator and the second photopolymerization initiator are made different from each other, and the second photopolymerization initiator is used as a photopolymerization initiator having a 10-hour half-life temperature at 100-200° C.

Description

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

[0001] The present invention relates to a photosensitive resin composition, particularly to a photosensitive resin composition suitable for forming an insulating layer. The present invention also relates to a dry film having a resin layer made of the photosensitive resin composition, a cured product of the photosensitive resin composition or the resin layer of the dry film, and a printed wiring board having the cured product.

[0002] In recent years, with the increasing volume of information processing, there has been a growing need for finer and denser circuit wiring in circuit boards, which are widely used in various electronic devices, in order to reduce the size and improve the functionality of these devices. Furthermore, the spread of high-capacity, high-speed communications, such as fifth-generation (5G) communications systems, and millimeter-wave radar for automotive ADAS (Advanced Driver Assistance Systems), has led to increasingly higher frequencies in electronic device signals. Therefore, the insulating film for the redistribution layer of the latest high-density semiconductor packages is particularly required to meet the demands of high resolution to accommodate the miniaturization associated with higher integration, as well as excellent dielectric properties, such as low dielectric constant and low dielectric loss tangent, to suppress transmission loss in the high-frequency band.

[0003] Incidentally, thermosetting resins or photosensitive resins are generally used as materials for forming insulating films. However, thermosetting resins are advantageous in terms of dielectric properties because the dielectric constant of the cured insulating film can be easily reduced by reducing the polar groups. However, they have problems in that laser processing during via formation is time-consuming and there are limitations in terms of resolution, such as reducing the diameter of vias. On the other hand, photosensitive resins allow vias to be formed in one go in a short time by photolithography, and they are advantageous in terms of resolution. However, they have problems in that the resin component must contain a certain amount of polar groups in order to perform alkaline development, which means there are limitations in terms of dielectric properties.

[0004] In order to solve such problems, for example, Patent Document 1 proposes a technology in which a polyphenylene ether having a specific weight-average molecular weight and synthesized under specific conditions is combined with another polyphenylene ether synthesized under different conditions and blended into a photosensitive resin composition, thereby imparting excellent dielectric properties and development contrast to the insulating film that is the cured product.

[0005] However, there is a growing need for finer and denser circuit wiring, and in response to this, it is expected that there will be a demand for resin compositions that can efficiently form cured products in a short period of time while achieving both better dielectric properties and resolution.

[0006] JP 2023-37449 A

[0007] Under these circumstances, a continuing technical challenge remains to provide a resin composition that can efficiently form a cured product that combines excellent dielectric properties and resolution in a short period of time.

[0008] Therefore, an object of the present invention is to provide a photosensitive resin composition that can efficiently form a cured product in a short time while achieving both excellent dielectric properties and resolution. Another object of the present invention is to provide a dry film having a resin layer made of such a photosensitive resin composition, a cured product of the photosensitive resin composition or the resin layer of the dry film, and a printed wiring board having the cured product.

[0009] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by adjusting the weight-average molecular weight of the polyphenylene ether resin to 250 to 10,000, using an oxime ester-based photopolymerization initiator as the first photopolymerization initiator, and using a photopolymerization initiator having a 10-hour half-life temperature in a temperature range of 100 to 200° C. in a photosensitive resin composition containing a polyphenylene ether resin, a first photopolymerization initiator, a second photopolymerization initiator, and a radical-reactive monomer. That is, the gist of the present invention is as follows.

[0010] [1] A photosensitive resin composition comprising a polyphenylene ether resin, a first photopolymerization initiator, a second photopolymerization initiator, and a radical-reactive monomer, wherein the polyphenylene ether resin has a weight-average molecular weight of 250 to 10,000, the first photopolymerization initiator and the second photopolymerization initiator are different from each other, and the second photopolymerization initiator is a photopolymerization initiator having a 10-hour half-life temperature in a temperature range of 100 to 200°C. [2] The photosensitive resin composition according to [1], further comprising a resin having a weight-average molecular weight of greater than 10,000. [3] The photosensitive resin composition according to [2], wherein the resin having a weight-average molecular weight of greater than 10,000 comprises a resin having a radical-polymerizable group. [4] The photosensitive resin composition according to [3], wherein the resin having a radical-polymerizable group comprises a branched polyphenylene ether. [5] A dry film having a first film and a resin layer formed on at least one surface of the first film, the resin layer being made of the photosensitive resin composition according to any one of [1] to [4]. [6] A cured product obtained by curing the photosensitive resin composition according to any one of [1] to [4] or the resin layer of the dry film according to [5]. [7] A printed wiring board having the cured product according to [6].

[0011] According to the present invention, there is provided a photosensitive resin composition that can efficiently form a cured product having both excellent dielectric properties and resolution in a short time. Furthermore, according to the present invention, there are provided a dry film having a resin layer made of such a photosensitive resin composition, a cured product of the photosensitive resin composition or the resin layer of the dry film, and a printed wiring board having the cured product.

[0012] [Photosensitive Resin Composition] According to one aspect of the present invention, a photosensitive resin composition (hereinafter also referred to as "photosensitive resin composition of the present invention") is provided. The photosensitive resin composition of the present invention can be suitably used for forming an insulating layer in a printed wiring board or the like. In particular, the photosensitive resin composition of the present invention can easily produce a cured product (e.g., an insulating layer) in a short time by irradiating it with light such as ultraviolet light, and therefore can be suitably used for efficiently producing a cured product and a printed wiring board including the cured product.

[0013] The photosensitive resin composition of the present invention contains a polyphenylene ether resin, a first photopolymerization initiator, a second photopolymerization initiator, and a radical-reactive monomer as essential components. Each component of the photosensitive resin composition of the present invention will be described in detail below. Each component may be commercially available or may be appropriately synthesized.

[0014] (Polyphenylene ether resin) The photosensitive resin composition of the present invention contains a polyphenylene ether resin. Since the molecular structure of a polyphenylene ether resin is highly symmetric, the inclusion of a polyphenylene ether resin in the photosensitive resin composition can reduce the dielectric constant of a cured product of the photosensitive resin composition. Furthermore, since the polyphenylene ether resin is highly densely stacked due to the interaction between ring structures, and the crosslinking density is high, the inclusion of a polyphenylene ether resin in the photosensitive resin composition can reduce the water absorption rate of a cured product of the photosensitive resin composition, thereby reducing the dielectric constant.

[0015] The polyphenylene ether resin is not particularly limited as long as it contains phenylene ether units as repeating structural units, and any conventionally known resin can be used. Specific examples of polyphenylene ether resins include polymers having structural units represented by the following structural formula in the main chain (preferably, polymers in which the structural units represented by the following structural formula account for 90 mol % or more of all structural units excluding terminal groups). The polyphenylene ether resin may be a homopolymer or a copolymer. Furthermore, the polyphenylene ether resin may be used alone or in combination of two or more types.

[0016] [Wherein, two R a each independently represents a hydrogen atom, a halogen atom, a primary or secondary alkyl group, an aryl group, an aminoalkyl group, a halogenated alkyl group, a hydrocarbonoxy group, or a halogenated hydrocarbonoxy group; beach independently represents a hydrogen atom, a halogen atom, a primary or secondary alkyl group, an aryl group, a halogenated alkyl group, a hydrocarbonoxy group, or a halogenated hydrocarbonoxy group. a cannot both become hydrogen atoms.)

[0017] R a and R b are preferably each independently a hydrogen atom, a primary or secondary alkyl group, or an aryl group. Examples of primary alkyl groups include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-amyl group, an isoamyl group, a 2-methylbutyl group, a 2,3-dimethylbutyl group, a 2-, 3-, or 4-methylpentyl group, or a heptyl group. Examples of secondary alkyl groups include an isopropyl group, a sec-butyl group, or a 1-ethylpropyl group. In particular, R a is preferably a primary or secondary alkyl group having 1 to 4 carbon atoms or a phenyl group. b is preferably a hydrogen atom. Since the polyphenylene ether resin does not have a highly polar substituent, the photosensitive resin composition of the present invention has better dielectric properties (i.e., the photosensitive resin composition of the present invention has a lower dielectric loss tangent).

[0018] Examples of homopolymers of polyphenylene ether resins include polymers of 2,6-dialkylphenylene ether such as poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-diethyl-1,4-phenylene ether), poly(2,6-dipropyl-1,4-phenylene ether), poly(2-ethyl-6-methyl-1,4-phenylene ether), and poly(2-methyl-6-propyl-1,4-phenylene ether). Furthermore, examples of copolymers of polyphenylene ether resins include 2,6-dialkylphenol / 2,3,6-trialkylphenol copolymers such as 2,6-dimethylphenol / 2,3,6-trimethylphenol copolymer, 2,6-dimethylphenol / 2,3,6-triethylphenol copolymer, 2,6-diethylphenol / 2,3,6-trimethylphenol copolymer, and 2,6-dipropylphenol / 2,3,6-trimethylphenol copolymer; graft copolymers obtained by graft polymerizing styrene onto poly(2,6-dimethyl-1,4-phenylene ether); and graft copolymers obtained by graft polymerizing styrene onto 2,6-dimethylphenol / 2,3,6-trimethylphenol copolymer.

[0019] The weight-average molecular weight of the polyphenylene ether resin is 250 to 10,000, and preferably 500 to 8,000. When the photosensitive resin composition of the present invention contains a polyphenylene ether resin having a weight-average molecular weight within the above-mentioned range, after exposure, the unexposed areas dissolve in a developer, but the exposed areas have an increased molecular weight and therefore are less soluble in the developer, thereby achieving a favorable difference in solubility contrast.

[0020] In the present invention, various molecular weights (number average molecular weight, weight average molecular weight) of resin components including polyphenylene ether resin can be measured as polystyrene-equivalent molecular weights by gel permeation chromatography (GPC).

[0021] The polyphenylene ether resin may have a main chain structure that is either a linear structure or a branched structure. Polyphenylene ether resins having a branched structure (hereinafter also referred to as "branched polyphenylene ether") will be described later.

[0022] Examples of commercially available polyphenylene ether resins include Noryl (trademark) SA9000 and Noryl (trademark) SA90 (both manufactured by SHPP Japan LLC).

[0023] The content of the polyphenylene ether resin having a weight-average molecular weight of 250 to 10,000 in the photosensitive resin composition of the present invention is not particularly limited as long as the effects of the present invention are achieved, but is preferably 10 to 80 mass% and more preferably 20 to 70 mass% in terms of solid content relative to the total mass of the photosensitive resin composition. When the content of the polyphenylene ether resin having a weight-average molecular weight of 250 to 10,000 is 10 mass% or more, a cured product that combines good resolution and low dielectric properties can be formed by exposure. On the other hand, when the content of the polyphenylene ether resin having a weight-average molecular weight of 250 to 10,000 is 80 mass% or less, good development resistance can be exhibited during exposure.

[0024] (First Photopolymerization Initiator) In the photosensitive resin composition of the present invention, the first photopolymerization initiator containing the first photopolymerization initiator is not particularly limited as long as it is a photopolymerization initiator different from the second photopolymerization initiator described later, and examples thereof include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, N,N-diphenyl ether ... α-Aminoacetophenone-based photopolymerization initiators such as methylaminoacetophenone: hydroxyacetophenone-based photopolymerization initiators such as 1-hydroxycyclohexylphenyl 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;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 Acylphosphine oxide photopolymerization initiators such as benzoin, benzil, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, and benzoin n-butyl ether; benzoin alkyl ether photopolymerization initiators; benzophenone, p-methylbenzoylphenyl phosphine oxide ... Benzophenone-based photopolymerization initiators such as benzophenone, Michler's ketone, methylbenzophenone, 4,4'-dichlorobenzophenone, and 4,4'-bisdiethylaminobenzophenone; acetophenone-based photopolymerization initiators such as acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone;Thioxanthone-based photopolymerization initiators such as thioxanthone, 2-ethylthioxanthone, 2-isopropylthioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone; anthraquinone-based photopolymerization initiators such as anthraquinone, chloroanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone, and 2-aminoanthraquinone; ketal-based photopolymerization initiators such as acetophenone dimethyl ketal and benzyl dimethyl ketal; benzoate ester-based photopolymerization initiators such as ethyl-4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate, and p-dimethylbenzoic acid ethyl ester. Photopolymerization initiators include oxime ester-based photopolymerization initiators such as 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(o-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, and 1-(o-acetyloxime); titanocene-based photopolymerization initiators 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, and tetramethylthiuram disulfide. The first photopolymerization initiator may be used alone or in combination of two or more.

[0025] The first photopolymerization initiator preferably includes an oxime ester-based photopolymerization initiator or an acylphosphine oxide-based photopolymerization initiator. Commercially available oxime ester-based photopolymerization initiators include, for example, Irgacure OXE02 (ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(o-acetyloxime)) (manufactured by BASF Japan Ltd.). Commercially available acylphosphine oxide-based photopolymerization initiators include, for example, Omnirad TPO-L (2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester) (manufactured by IGM Resins B.V.).

[0026] The content of the first photopolymerization initiator in the photosensitive resin composition of the present invention is not particularly limited as long as the effects of the present invention are achieved, but is preferably 0.1 to 15 mass %, more preferably 1 to 10%, in terms of solid content, relative to the total mass of the photosensitive resin composition. By having the content of the first photopolymerization initiator be 0.1 mass % or more and 15 mass % or less, the reactivity of the photopolymerizable component contained in the photosensitive resin composition can be made better.

[0027] (Second Photopolymerization Initiator) The photosensitive resin composition of the present invention contains a second photopolymerization initiator. The second photopolymerization initiator is a photopolymerization initiator having a 10-hour half-life temperature in a temperature range of 100 to 200°C, preferably in a temperature range of 120 to 180°C. The photopolymerization initiator having a 10-hour half-life temperature in a temperature range of 100 to 200°C is not particularly limited as long as the effects of the present invention are achieved, but preferably contains a peroxide structure (-O-O-). One type of second photopolymerization initiator may be used alone, or two or more types may be used in combination.

[0028] Examples of photopolymerization initiators having a 10-hour half-life temperature in the temperature range of 100 to 200°C include 3,3,4,4-tetra(t-butylperoxycarbonyl)benzophenone and 2-(1-t-butylperoxy-1-methylethyl)-9H-thioxanthen-9-one.

[0029] The content of the second photopolymerization initiator in the photosensitive resin composition of the present invention is not particularly limited as long as the effects of the present invention are achieved, but is preferably 1 to 10 mass% in terms of solid content relative to the total mass of the photosensitive resin composition. By having the content of the second photopolymerization initiator be 1 mass% or more and 10 mass% or less, the reactivity of the photopolymerizable component contained in the photosensitive resin composition can be made better.

[0030] A photoinitiator co-agent or sensitizer may be used in combination with the first and second photopolymerization initiators described above. Examples of the photoinitiator co-agent 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. One type of photoinitiator co-agent and one type of sensitizer may be used alone, or two or more types may be used in combination.

[0031] As described above, the photosensitive resin composition of the present invention can impart excellent dielectric properties and resolution to the cured product of the photosensitive resin composition by using a combination of different first and second photopolymerization initiators. The reason why the combination of different first and second photopolymerization initiators can impart excellent dielectric properties and resolution to the cured product of the photosensitive resin composition is unclear, but the following is theorized. Generally, to achieve high resolution (e.g., to achieve a small diameter opening), it is necessary to expose the composition until development resistance is achieved and suppress reactions around the exposed area due to halation (if the absorbance of the photosensitive resin composition is low and the amount of light reaching the bottom is excessive, halation may occur). Therefore, in order to achieve development resistance with a small amount of light, it is necessary to use a photopolymerization initiator that promotes curing by exposure in combination with a component that adjusts the light penetration to the bottom of the photosensitive resin composition so that it is appropriate. However, if components that adjust the light transmission to the bottom of the photosensitive resin composition are added that do not contribute to the curing reaction (e.g., UV absorbers or excessive amounts of photopolymerization initiators), they may become unreacted and adversely affect the physical properties of the resulting cured product. Furthermore, the amount of photopolymerization initiator used is limited because excessive use can result in unreacted portions due to exposure. Therefore, combining a radical polymerization initiator that has both photosensitivity and thermal decomposition properties, such as a photopolymerization initiator (i.e., a second photopolymerization initiator) with a first photopolymerization initiator different from the second photopolymerization initiator, is believed to be able to effectively resolve the trade-off described above. Furthermore, using a photopolymerization initiator that generates radicals upon heating can improve curing reactivity during post-cure and also contribute to a low dielectric constant of the cured product. As a result, it is believed that the cured product can achieve both excellent dielectric properties and high resolution.

[0032] (Radical Reactive Monomer) The photosensitive resin composition of the present invention contains a radically reactive monomer. In this specification, "radical reactive" includes a monomer having a radically polymerizable group. Any conventionally known radically reactive monomer can be used. Furthermore, the radically polymerizable group is preferably one having an unsaturated carbon bond, and examples thereof include a vinyl group, an allyl group, a maleimide group, an acrylic group, a methacrylic group, and a styryl group. When the photosensitive resin composition of the present invention contains a radically reactive monomer, the concentration of the radically polymerizable group in the photosensitive resin composition increases, improving the crosslinking density and, as a result, making it easier to achieve development contrast during exposure.

[0033] Examples of radical reactive monomers include (meth)acrylic acid and esters thereof, such as (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, (meth)acrylamide derivatives, such as (meth)acrylamide and isopropylacrylamide, vinyl monomers, such as vinyl chloride, vinylidene chloride, vinyl acetate, methyl vinyl ether, styrene, divinylbenzene, and (meth)acrylonitrile, compounds having an unsaturated double bond, such as isoprene, polyfunctional monomers, such as pentaerythritol tri(meth)acrylate, and (meth)acryloylmorpholine. One type of radical reactive monomer may be used alone, or two or more types may be used in combination.

[0034] As the radical reactive monomer, a monomer having two or more vinyl groups in the molecule is preferably used. Examples of monomers having two or more vinyl groups in the molecule include triallyl isocyanurate, triallyl cyanurate, diallyl phthalate, and diallyl isophthalate. When the radical reactive monomer has two or more vinyl groups, three-dimensional crosslinking is formed in the cured product of the photosensitive resin composition of the present invention, thereby improving its mechanical properties. Furthermore, as the radical reactive monomer, a monomer having a triazine ring in the molecule is preferably used. That is, as the radical reactive monomer, a monomer having a triazine ring and two or more vinyl groups in the molecule is particularly preferably used. When the photosensitive resin composition of the present invention contains a highly reactive radical reactive monomer, particularly a monomer having two or more vinyl groups in the molecule and a triazine ring, the dielectric properties of the photosensitive resin composition of the present invention can be improved when photosensitive.

[0035] Examples of commercially available radical reactive monomers include L-DAIC (manufactured by Shikoku Chemical Industry Co., Ltd.) and TAIC (trademark) (triallyl isocyanurate, manufactured by Mitsubishi Chemical Corporation).

[0036] The content of the radical-reactive monomer in the photosensitive resin composition of the present invention is not particularly limited as long as the effects of the present invention are achieved, but is preferably 5 to 50 mass %, more preferably 10 to 40 mass %, calculated as solid content, relative to the total mass of the photosensitive resin composition. When the content of the radical-reactive monomer is 5 mass % or more, the crosslink density in the photosensitive resin composition described above is sufficiently improved, resulting in excellent development contrast during exposure. On the other hand, when the content of the radical-reactive monomer is 50 mass % or less, the photosensitive resin composition can be cured without impairing the effect of reducing the dielectric constant.

[0037] (Resin having a weight-average molecular weight of more than 10,000) The photosensitive resin composition of the present invention may further contain a resin having a weight-average molecular weight of more than 10,000. When the photosensitive resin composition of the present invention contains a resin having a weight-average molecular weight of more than 10,000, residual stress generated by exposure to light can be alleviated, and as a result, the occurrence of cracks in the cured product can be suppressed.

[0038] Any of the conventionally known resins having a weight-average molecular weight of more than 10,000 can be used, including, for example, polyphenylene ether resins and other resins having a weight-average molecular weight of more than 10,000. The resin having a weight-average molecular weight of more than 10,000 preferably includes a resin having a radically polymerizable group, and more preferably includes a polyphenylene ether resin having a weight-average molecular weight of more than 10,000. Examples of the radically polymerizable group include the radically polymerizable groups described above for the radically reactive monomer. Resins having a weight-average molecular weight of more than 10,000 may be used alone or in combination of two or more.

[0039] As the polyphenylene ether resin having a weight average molecular weight of more than 10,000, the same polyphenylene ether resins as those described above except for the weight average molecular weight of more than 10,000 can be used, but it is preferable to use a branched polyphenylene ether.

[0040] Branched polyphenylene ether is a polyphenylene ether resin synthesized from raw material phenols, including phenols having hydrogen atoms at the ortho and para positions. Because such phenols have hydrogen atoms at the ortho positions, ether bonds can be formed not only at the ipso and para positions but also at the ortho position when oxidatively polymerized with phenols. Therefore, polyphenylene ether resins synthesized using such phenols as raw material phenols can form branched structures. Such branched polyphenylene ethers have excellent solubility in solvents and excellent compatibility and reactivity with each component in a photosensitive resin composition.

[0041] Examples of branched polyphenylene ethers include the polyphenylene ether resins disclosed in WO 2020 / 017570.

[0042] The branched polyphenylene ether may be obtained by either of the following methods: (Method 1) a method of synthesizing a polyphenylene ether resin using, as a raw material phenol, a phenol containing a functional group having an unsaturated carbon bond; or (Method 2) a method of synthesizing a polyphenylene ether resin using, as a raw material phenol, a phenol not containing a functional group having an unsaturated carbon bond, and modifying the obtained polyphenylene ether resin to introduce a functional group having an unsaturated carbon bond into the polyphenylene ether resin.

[0043] The branched polyphenylene ether may be a mixture of two or more polyphenylene ether resins made from different types of raw material phenols.

[0044] The amount of functional groups having unsaturated carbon bonds in the branched polyphenylene ether is not particularly limited as long as the effects of the present invention are achieved, and is preferably within a range that does not significantly change the electrical properties of the polyphenylene ether structure and that allows for the formation of an effective crosslinked structure. Specifically, the amount of functional groups having unsaturated carbon bonds, as a molar ratio relative to all monomers constituting the branched polyphenylene ether, is preferably 3% or more, more preferably 6% or more, and is also preferably 50% or less, more preferably 25% or less. When the amount of functional groups having unsaturated carbon bonds in the polyphenylene ether resin is within the above-mentioned range, the amount of unreacted unsaturated carbon bonds can be reduced when the resin composition layer is cured, improving the crosslink density and the dielectric properties.

[0045] Furthermore, the higher the degree of branching of the branched polyphenylene ether, the more complex the entanglement of the molecular chains becomes, resulting in a stronger coating film of the resin composition layer. Furthermore, when the degree of branching of the branched polyphenylene ether is high, the interaction between the ring structures in the polyphenylene ether resin in the photosensitive resin composition before curing is alleviated, increasing the degree of freedom of the molecular chain of the polyphenylene ether resin. This increases the reactivity of the polyphenylene ether resin and improves the reaction rate. As a result, effects such as a lower dielectric constant of the resin composition and a stronger coating film are expected.

[0046] In the present invention, the branched structure (degree of branching) of the branched polyphenylene ether can be confirmed according to the following analytical procedure.

[0047] (Analysis Procedure) A chloroform solution of branched polyphenylene ether is prepared to concentrations of 0.1 mg / mL, 0.15 mg / mL, 0.2 mg / mL, and 0.25 mg / mL. A graph showing the correlation between refractive index difference and concentration is created while the solution is being pumped at 0.5 mL / min, and the refractive index increment dn / dc is calculated from the slope. Next, the absolute molecular weight is measured under the following instrument operating conditions. Using the chromatograms from the RI detector and the MALS detector as reference, a regression line is determined by the least squares method from a logarithmic plot (conformation plot) of absolute molecular weight versus radius of gyration, and its slope is calculated.

[0048] (Measurement conditions) Device name: HLC-8320GPC (manufactured by Tosoh Corporation) Mobile phase: chloroform Column: TSKgel (registered trademark) guard column H ＨＲ -H+TSKgel (registered trademark) GMH ＨＲ -H (2 tubes) + TSKgel (registered trademark) G2500H ＨＲ(All manufactured by Tosoh Corporation) Flow rate: 0.6 mL / min Detector: Multi-angle static light scattering (MALS) detector DAWN (registered trademark) HELEOS (registered trademark) + RI detector Optilab (registered trademark) rEX (wavelength 254 nm) (All manufactured by WYATT TECHNOLOGY) Sample concentration: 0.5 mg / mL Sample solvent: Same as mobile phase. Dissolve 5 mg of sample in 10 mL of mobile phase Injection volume: 200 μL Filter: 0.45 μm STD reagent: Standard polystyrene, molecular weight 37,900 STD concentration: 1.5 mg / mL STD solvent: Same as mobile phase. Dissolve 15 mg of sample in 10 mL of mobile phase Analysis time: 100 minutes

[0049] For resins with the same absolute molecular weight, the higher the degree of branching of the polymer chain, the smaller the distance from the center of gravity to each segment (radius of gyration). Therefore, the slope calculated from the logarithmic plot of the absolute molecular weight and radius of gyration obtained by GPC-MALS described above indicates the degree of branching of the branched polyphenylene ether, with a smaller slope indicating a higher degree of branching. In other words, the smaller the slope calculated from the above conformation plot, the more branches the branched polyphenylene ether has, and the greater the slope, the less branches the branched polyphenylene ether has.

[0050] In the branched polyphenylene ether, the gradient is preferably less than 0.6, more preferably 0.50 or less, and even more preferably 0.40 or less. When the gradient is within the above range, the branched polyphenylene ether is considered to have sufficient branching. The lower limit of the gradient is not particularly limited, but can be, for example, 0.05 or more, or 0.20 or more.

[0051] Examples of other resins include known and commonly used resins such as isocyanate compounds, blocked isocyanate compounds, amino resins, maleimide compounds, bismaleimide compounds, benzoxazine resins, carbodiimide resins, cyclocarbonate compounds, epoxy resins, oxetane compounds, episulfide resins, phenoxy resins, phenolic resins, polyvinyl acetal resins, polyamide resins, polyamideimide resins, butadiene resins, and various copolymers.

[0052] The weight average molecular weight of the resin having a weight average molecular weight of more than 10,000 is preferably 15,000 to 100,000, more preferably 20,000 to 80,000.

[0053] When the photosensitive resin composition of the present invention contains a resin having a weight-average molecular weight of more than 10,000, the content thereof is not particularly limited as long as the effects of the present invention are achieved, but is preferably 2 to 25 mass% and more preferably 3 to 20 mass% in terms of solid content relative to the total mass of the photosensitive resin composition. By ensuring that the content of the resin having a weight-average molecular weight of more than 10,000 is 2 mass% or more, the effect of alleviating residual stress generated by exposure can be expected. On the other hand, by ensuring that the content of the resin having a weight-average molecular weight of more than 10,000 is 25 mass% or less, the effect of simultaneously alleviating residual stress generated by exposure and improving solubility in a developer can be expected.

[0054] (Inorganic Filler) The photosensitive resin composition of the present invention may further contain an inorganic filler. Known inorganic fillers can be used as the inorganic filler, and barium sulfate, spherical silica, hydrotalcite, and talc are preferably used. The inorganic fillers may be used alone or in combination of two or more. By including an inorganic filler in the photosensitive resin composition, the physical strength of the photosensitive resin composition and its cured product can be increased.

[0055] As the inorganic filler, spherical silica is particularly preferably used. Any spherical silica that can be used as a filler for electronic materials can be used. The shape of the spherical silica is not limited to a perfect sphere, as long as it is spherical. Suitable spherical silica includes, for example, one having a sphericity of 0.8 or more as measured as follows.

[0056] The sphericity of spherical silica is measured as follows: First, a photograph of the spherical silica is taken with a scanning electron microscope (SEM), and from the area and perimeter of the particle observed on the photograph, (sphericity) = {4π × (area) ÷ (perimeter)} ２Specifically, an average value obtained by measuring 100 particles using an image processing device can be used.

[0057] The average particle size of the spherical silica is not particularly limited as long as the effects of the present invention are achieved, but is preferably 0.01 to 10 μm, more preferably 0.05 to 5 μm, and even more preferably 0.3 to 1 μm. The average particle size of the spherical silica 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 the laser diffraction method is the Microtrac MT3300EXII manufactured by Microtrac-Bell Corporation. The maximum particle size (D100) and particle size (D10) can also be measured in the same manner using the above device. Furthermore, the average particle size of the spherical silica contained in the photosensitive resin composition of the present invention refers to the value measured as described above for spherical silica before preparing (pre-stirring, kneading) the photosensitive resin composition that forms the insulating layer.

[0058] An example of commercially available spherical silica is Admanano YA050C-HHL (manufactured by Admatechs Co., Ltd.).

[0059] The inorganic filler may be surface-treated. Examples of the surface treatment include surface treatment with a coupling agent and surface treatment without introducing an organic group, such as alumina treatment. The surface treatment method for the inorganic filler is not particularly limited, and any known or commonly used method may be used. The surface of the inorganic filler can be treated with a surface treatment agent having a curable reactive group, for example, a coupling agent having a curable reactive group as an organic group.

[0060] The surface treatment is preferably a surface treatment using a coupling agent. 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 such 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. One type of coupling agent may be used alone, or two or more types may be used in combination.

[0061] The content of the inorganic filler in the photosensitive resin composition is not particularly limited as long as the effects of the present invention are achieved, but it can be, for example, 10 to 60 mass % in terms of solid content relative to the total mass of the photosensitive resin composition. When the content of the inorganic filler is within the above range, an excessive increase in viscosity of the photosensitive resin composition can be suppressed, good coatability and moldability can be maintained, and the cured product of the photosensitive resin composition can have sufficient strength.

[0062] (Organic Solvent) The photosensitive resin composition may contain an organic solvent for the purpose of adjusting the viscosity during preparation thereof or when the photosensitive resin composition is applied to a substrate or film to form a resin layer. 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 anisole, cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, diethylene glycol monomethyl ether acetate, and tripropylene glycol monomethyl ether; esters such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha, and solvent naphtha. The organic solvents may be used alone or in combination of two or more.

[0063] The organic solvent can be evaporated and dried using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, or the like (a method in which a dryer equipped with a heat source of an air heating type using steam is used, and hot air in the dryer is brought into countercurrent contact with the substrate, or a method in which hot air is blown onto the substrate from a nozzle).

[0064] (Other Components) The photosensitive resin composition may further contain, as necessary, components such as a photoinitiator aid, a cyanate compound, a mercapto compound, a urethanization catalyst, a thixotropic agent, an adhesion promoter, a block copolymer, a chain transfer agent, a polymerization inhibitor, a copper inhibitor, an antioxidant, a rust inhibitor, a thickener such as organic bentonite or montmorillonite, at least one of a silicone-based, fluorine-based, or polymer-based antifoaming agent and a leveling agent, a silane coupling agent such as an imidazole-based, thiazole-based, or triazole-based phosphinate, a phosphorus compound such as a phosphazene compound, or the like. These may be known components in the field of electronic materials.

[0065] The photosensitive resin composition of the present invention may be used in a liquid form or may be used in the form of a dry film as described below. When used in a liquid form, the photosensitive resin composition may be a one-component type or a two-component or more-component type.

[0066] [Dry Film] According to another aspect of the present invention, a dry film (hereinafter also referred to as the "dry film of the present invention") is provided, comprising a first film and a resin layer formed on the first film and made of the photosensitive resin composition of the present invention. The first film in the dry film of the present invention refers to a film that is at least adhered to the resin layer when the dry film is integrally molded by laminating the resin layer formed on the dry film to a substrate or other base material by heating or the like so that the resin layer side made of the photosensitive resin composition contacts the dry film. The first film may be peeled from the resin layer in a post-lamination step. In particular, for the dry film of the present invention, peeling from the resin layer in a post-exposure step is preferred. To form the dry film, the photosensitive resin composition of the present invention is diluted with an organic solvent such as those described above to adjust the viscosity to an appropriate level, and then coated to a uniform thickness on the first film using a comma coater, blade coater, lip coater, rod coater, squeeze coater, reverse coater, transfer roll coater, gravure coater, spray coater, or the like. The film is typically dried at a temperature of 50 to 130°C for 1 to 30 minutes to obtain a film. There is no particular restriction on the thickness of the coating film, but it is generally selected appropriately within the range of 1 to 150 μm, preferably 5 to 60 μm, in terms of the thickness after drying.

[0067] The first film can be any known film without particular limitation, and examples of suitable films include polyester films such as polyethylene terephthalate and polyethylene naphthalate, and films made of thermoplastic resins such as polyimide films, polyamideimide films, polypropylene films, and polystyrene films. Among these, polyester films are preferred from the viewpoints of heat resistance, mechanical strength, ease of handling, etc. A laminate of these films can also be used as the first film.

[0068] Moreover, from the viewpoint of improving mechanical strength, the thermoplastic resin film as described above is preferably a film that has been oriented in a uniaxial or biaxial direction.

[0069] The thickness of the first film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0070] After forming a resin layer of the photosensitive resin composition of the present invention 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 dust from adhering to the surface of the resin layer. The second film refers to a film that is peeled from the resin layer before lamination when the dry film is laminated by heating or the like so that the resin layer side of the dry film is in contact with a base material such as a substrate to form an integral mold. Examples of the peelable second film that can be used include polyethylene film, polytetrafluoroethylene film, polypropylene film, and surface-treated paper, as long as the adhesive strength between the resin layer and the second film is smaller than the adhesive strength between the resin layer and the first film when the second film is peeled off.

[0071] The thickness of the second film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0072] In the dry film of the present invention, the photosensitive resin composition of the present invention may be applied to the second film described above and dried to form a resin layer, and the first film may be laminated on the surface of the resin layer. That is, when producing the dry film of the present invention, either the first film or the second film may be used as the film to which the photosensitive resin composition of the present invention is applied.

[0073] [Cured Product] According to another aspect of the present invention, there is provided a cured product (hereinafter also referred to as "cured product of the present invention") obtained by curing the photosensitive resin composition of the present invention or the resin layer of the dry film of the present invention. The cured product of the present invention has excellent dielectric properties and high resolution.

[0074] [Printed Wiring Board] According to another aspect of the present invention, a printed wiring board (hereinafter also referred to as the "printed wiring board of the present invention") comprising the cured product of the present invention described above is provided. That is, the printed wiring board of the present invention has a cured product obtained from the photosensitive resin composition of the present invention or the resin layer of the dry film of the present invention. A method for producing the printed wiring board of the present invention includes, for example, adjusting the viscosity of the photosensitive resin composition of the present invention to a level suitable for the coating method using an organic solvent as described above, applying it to a substrate by a method such as dip coating, flow coating, roll coating, bar coating, screen printing, or curtain coating, and then evaporating and drying (pre-drying) the organic solvent contained in the composition at a temperature of 60 to 100°C to form a tack-free resin layer. In the case of a dry film, the resin layer is formed on the substrate by laminating it onto the substrate using a laminator or the like so that the resin layer contacts the substrate.

[0075] Substrates constituting the printed wiring board of the present invention include printed wiring boards and flexible printed wiring boards on which circuits have been formed in advance using copper or the like, as well as copper-clad laminates for high-frequency circuits made of materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / non-woven cloth epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, fluororesin / polyethylene / polyphenylene ether, polyphenylene oxide / cyanate, etc., and include copper-clad laminates of all grades (FR-4, etc.), as well as metal substrates, polyimide films, polyethylene terephthalate films, polyethylene naphthalate (PEN) films, glass substrates, ceramic substrates, wafer plates, etc.

[0076] The dry film resin layer is preferably bonded to the substrate under pressure and heat using a vacuum laminator or the like. By using such a vacuum laminator, when a circuit-formed substrate is used, the dry film adheres tightly to the circuit board even if the circuit board surface is uneven, preventing the inclusion of air bubbles and improving the ability to fill recesses in the substrate surface. The pressure condition is preferably about 0.1 to 2.0 MPa, and the heating condition is preferably 40 to 120°C.

[0077] The volatilization drying carried out after the photosensitive resin composition of the present invention is applied to a substrate can be carried out using a hot air circulation drying oven, an IR oven, a hot plate, a convection oven, or the like (a method in which hot air in a dryer equipped with a heat source of an air heating type using steam is brought into countercurrent contact with the substrate, or a method in which hot air is blown onto the substrate from a nozzle).

[0078] After forming a resin layer on a substrate, the resin layer is selectively exposed to active energy rays through a photomask with a predetermined pattern, and the unexposed areas are developed with an organic solvent to form a patterned cured product. In the case of a dry film, after exposure, the first film is peeled off from the dry film and development is carried out, thereby forming a patterned cured product on the substrate. Note that, 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, a cured product with excellent properties such as adhesion and hardness can be formed by irradiating the cured product with active energy rays and then heat-curing (e.g., 100 to 250°C), or by irradiating active energy rays after heat-curing, or by heat-curing alone to perform final finish curing (main curing).

[0079] The exposure device used for the active energy ray irradiation may be any 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 may have a maximum wavelength in the range of 350 to 450 nm. The exposure dose for image formation varies depending on factors such as the film thickness, but is generally 10 to 1,000 mJ / cm. ２ , preferably 20 to 800 mJ / cm ２ The range may be:

[0080] The developing method may be a dipping method, a shower method, a spray method, a brush method, or the like, and a wide variety of organic solvents may be used as the developer, such as ester-based solvents, ketone-based solvents, alcohol-based solvents, amide-based solvents, ether-based solvents, and hydrocarbon-based solvents.

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, the numerical values ​​for each component mean parts by mass unless otherwise specified.

[0082] (Synthesis of Branched Polyphenylene Ether: Resin with a Weight-Average Molecular Weight of More than 10,000) Prior to the preparation of the photosensitive resin composition, branched polyphenylene ether, one of its components, was synthesized according to the following procedure. 19.8 g of 2,6-dimethylphenol and 2.42 g of 2-allylphenol were mixed in a 500 mL separable flask, and 261 g of toluene was added to dissolve the resulting mixture. Furthermore, 0.18 mass% of di-μ-hydroxo-bis[(N,N,N',N'-tetramethylethylenediamine)copper(II)] chloride (Cu / TMEDA) and 0.16 mass% of tetramethylethylenediamine (TMEDA) were added and reacted. While blowing dry air into the reaction solution at a flow rate of 75 mL / min, the mixture was stirred at a stirring rate of 200 rpm using a four-blade paddle impeller and heated to 40°C for a predetermined time to obtain a reaction solution containing polyphenylene ether. Next, heating of the resulting reaction solution was stopped, and further blowing of dry air was stopped. Then, the reaction solution was filtered to remove di-μ-hydroxo-bis[(N,N,N',N'-tetramethylethylenediamine)copper(II)] chloride (Cu / TMEDA), and a mixture of 1200 mL of methanol, 4.0 mL of concentrated hydrochloric acid, and 27.0 mL of water was added to cause reprecipitation. The precipitate was collected by filtration under reduced pressure, washed with methanol, and dried at 80°C for 24 hours to obtain a branched polyphenylene ether. The resulting branched polyphenylene ether had a number-average molecular weight of 13,000, a weight-average molecular weight of 45,000, and a slope calculated from a conformation plot of 0.31. The number average molecular weight and weight average molecular weight of the branched polyphenylene ether were measured as polystyrene-equivalent molecular weights by gel permeation chromatography (GPC) using a high-speed GPC apparatus (HLC-8320GPC, manufactured by Tosoh Corporation) as a measuring apparatus, chloroform as an eluent, and an RI detector as a detector.

[0083] [Preparation of Photosensitive Resin Compositions] The components shown in Tables 1 and 2 below were mixed in the amounts (solid content amounts) shown in the tables and mixed with a stirrer to prepare the photosensitive resin compositions of Examples 1 to 16 and Comparative Examples 1 to 4. Details of each component in Tables 1 and 2 are as follows: Polyphenylene ether resin: Noryl™ SA9000 (weight average molecular weight: 1,700, manufactured by SHPP Japan LLC) First photopolymerization initiator 1: Irgacure OXE02 (ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(o-acetyloxime)) (manufactured by BASF Japan Ltd.) First photopolymerization initiator 2: Omnirad TPO-L (manufactured by IGM Resins B.V.) Second photopolymerization initiator: 2-(1-t-butylperoxy-1-methylethyl)-9H-thioxanthen-9-one (manufactured by NOF Corporation) Radical reactive monomer 1: L-DAIC (manufactured by Shikoku Chemicals Corporation) Radical reactive monomer 2: TAIC™ (triallyl isocyanurate, manufactured by Mitsubishi Chemical Corporation) Resin 1 having a weight-average molecular weight of more than 10,000: branched polyphenylene ether synthesized according to the procedure described above (weight-average molecular weight: 45,000) Resin 2 having a weight-average molecular weight of more than 10,000: LBR-305 (butadiene homopolymer, weight-average molecular weight: 26,000, manufactured by Kuraray Co., Ltd.) Inorganic filler: spherical silica slurry Admanano YA050C-HHL (solid content 40% by mass, manufactured by Admatechs Co., Ltd.) Heat curing catalyst: Perbutyl (registered trademark) P40 (manufactured by NOF Corporation)

[0084]

[0085] [Preparation of Dry Film for Evaluation 1] Each of the photosensitive resin compositions of the Examples and Comparative Examples obtained according to the procedure described above was applied to a first film (polyethylene terephthalate film, film thickness: 50 μm) so that the film thickness after drying would be 25 μm, and the film was dried by heating at 80° C. for 20 minutes to form a resin layer, thereby preparing each dry film for evaluation of dielectric properties.

[0086] [Evaluation of Dielectric Properties] The resin layer of each dry film for evaluating dielectric properties prepared according to the procedure described above was laminated on a copper foil at a temperature of 90°C. This process was repeated twice to form a resin layer with a thickness of 50 µm. Then, a contact exposure machine was used to expose the resin layer to 600 mJ / cm ２ Then, the film was exposed to light using a UV conveyor oven at an integrated exposure dose of 1000 mJ / cm ２ The cured product was then irradiated with ultraviolet light under the conditions of 0.005 or less, and heated at 200°C for 60 minutes to form a cured product. The cured product was then peeled off from the copper foil and dried at 105°C for 60 minutes to obtain a cured product for evaluation. The dielectric dissipation factor of each cured product for evaluation was measured within one hour using an SPDR dielectric resonator and network analyzer manufactured by Agilent Technologies Inc. at 25°C and 10 GHz. The dielectric dissipation factor of the resin layer of each dry film (i.e., the cured product of each photosensitive resin composition) was evaluated according to the following criteria. The evaluation results are shown in Tables 1 and 2. ⊚: The dielectric dissipation factor was 0.005 or less, indicating very excellent dielectric properties. ∘: The dielectric dissipation factor was 0.006 or less, indicating greater than 0.005, indicating sufficiently excellent dielectric properties. ×: The dielectric dissipation factor was greater than 0.006, indicating insufficient dielectric properties.

[0087] [Preparation of Dry Film for Evaluation 2] Each of the photosensitive resin compositions of the Examples and Comparative Examples obtained according to the procedure described above was applied to a first film (polyethylene terephthalate film, film thickness: 50 μm) so that the film thickness after drying would be 10 μm, and the film was dried by heating at 80° C. for 20 minutes to form a resin layer, thereby preparing each dry film for evaluating resolution and crack resistance.

[0088] [Preparation of CZ-treated substrate] A substrate (copper clad laminate, CCL-HL832NX, TYPE A Series, thickness 0.4 mm, manufactured by Mitsubishi Gas Chemical Company, Inc.) was roughened on both surfaces using a roughening agent (MEC Etch Bond Series CZ-8100, manufactured by MEC Co., Ltd.) under conditions such that the etching depth was approximately 1 μm, thereby preparing a CZ-treated substrate.

[0089] [Evaluation of Resolution] The resin layer of each dry film for evaluating resolution and crack resistance, which was prepared according to the procedure described above, was laminated onto a CZ-treated substrate, which was also prepared according to the procedure described above, at a temperature of 90° C. Then, a projection exposure machine was used to expose the resin layer at 100 mJ / cm to form vias with opening diameters of 10 to 30 μm (at 10 μm intervals). ２ The film was exposed under the conditions of and developed for 20 seconds using propylene glycol monomethyl acetate to form vias. The formed vias were observed using an optical microscope (magnification: 2000x), and the resolution of the photosensitive resin composition constituting the resin layer of each dry film was evaluated according to the following criteria. The evaluation results are shown in Tables 1 and 2. ∘: Vias with an opening diameter of 20 μm or less were opened without any development residue. ×: Vias with an opening diameter of 20 μm or less were not opened, or were opened but had development residue.

[0090] [Evaluation of Crack Resistance] Each dry film for evaluation was laminated onto a CZ-treated substrate in the same manner as in the resolution evaluation described above, and then a via was formed. The formed via and the area around the via were observed with an optical microscope (magnification: 2000x), and the crack resistance of the photosensitive resin composition constituting the resin layer of each dry film was evaluated according to the following criteria. The evaluation results are shown in Tables 1 and 2. ⊚: No cracks in either the via or the area around the via. ◯: One crack in the via or the area around the via. ×: Two or more cracks in the via or the area around the via.

[0091] The evaluation results shown in Tables 1 and 2 indicate that the photosensitive resin compositions of Examples 1 to 16 have excellent dielectric properties and can form cured products with high resolution. Furthermore, the cured products formed from the photosensitive resin compositions of Examples 1 to 16 have high crack resistance. On the other hand, the photosensitive resin compositions of Comparative Examples 1 to 4 have poor resolution, which is incompatible with the excellent dielectric properties of the cured products.

Claims

1. A photosensitive resin composition comprising a polyphenylene ether resin, a first photopolymerization initiator, a second photopolymerization initiator, and a radical-reactive monomer, wherein the polyphenylene ether resin has a weight-average molecular weight of 250 to 10,000, the first photopolymerization initiator and the second photopolymerization initiator are different from each other, and the second photopolymerization initiator is a photopolymerization initiator having a 10-hour half-life temperature in the temperature range of 100 to 200°C.

2. The photosensitive resin composition according to claim 1, further comprising a resin having a weight average molecular weight of more than 10,000.

3. The photosensitive resin composition according to claim 2, wherein the resin having a weight average molecular weight of more than 10,000 includes a resin having a radical polymerizable group.

4. The photosensitive resin composition according to claim 3, wherein the resin having a radical polymerizable group comprises a branched polyphenylene ether.

5. A dry film comprising a first film and a resin layer made of the photosensitive resin composition according to claim 1 formed on at least one surface of the first film.

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

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

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