Dry film, cured product, and printed wiring board

Abstract

To provide a dry film capable of exhibiting excellent hiding power and high resolution while enabling formation of a cured product having a uniform shape, and also to provide a cured product and a printed wiring board.SOLUTION: A dry film comprises a first film and a resin layer containing a curable resin composition formed on the first film, wherein the resin layer includes a first layer on the first film side and a second layer formed on the first layer, the thickness of the first layer being greater than that of the second layer, the visible light transmittance of the first layer being higher than that of the second layer, and the average value of visible light transmittance when the thickness of the second layer is 10 μm being 50% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dry film, a cured product, and a printed wiring board. [Background technology]

[0002] Printed wiring boards used in electronic devices are substrates on which electronic circuit patterns are printed using copper wires, and various components are mounted on the printed wiring boards by soldering or other methods.

[0003] When mounting components on a printed wiring board with exposed copper wires, there is a possibility that the copper wires may break due to external force, or that short circuits may occur due to solder adhering to areas other than the circuit pattern. Therefore, a solder resist layer is formed to protect the circuit pattern and prevent short circuits.

[0004] The solder resist layer is formed as the outermost layer of a printed wiring board, and therefore, the solder resist layer is sometimes required to not only protect the circuit but also to provide high visual concealment of the circuit from the viewpoint of enhancing the design.

[0005] A solder resist layer with high hiding power is produced from a curable resin composition containing a large amount of colorant or a dark colorant. However, colorants, particularly black colorants, have high light absorption properties, which can lead to resolution problems such as poor photocuring during resist pattern formation, making it impossible to obtain the desired resist pattern.

[0006] Furthermore, a dry film is used as one of the means for forming a solder resist layer (see, for example, Patent Document 1). The above-mentioned solder resist layer can be formed on a printed wiring board by laminating a resin layer of the dry film onto a substrate having a circuit pattern, and then performing patterning and curing treatment.

[0007] Among printed wiring boards, those on which flat package ICs such as QFPs (Quad Flat Packages) and SOPs (Small Outline Packages) are mounted require the formation of solder resist barriers (hereinafter referred to as "solder resist dams") between electrodes to prevent solder bridging between pads during reflow soldering. In order to form a solder resist using a dry film on a substrate with an uneven structure such as a pad, it is desirable for the resin layer to have a relatively low melt viscosity from the viewpoints of embedding properties and flatness (see, for example, Patent Document 2).

[0008] On the other hand, when a resin layer suitable for such dry films is formed in two layers, distortion in the film thickness of the upper and lower layers occurs on substrates with uneven structures, and this distortion has been found to cause unevenness in the shape of the cured product. In particular, when a resin layer is formed in two layers with different transmittances, it has been found that the problem of variation in resolution due to this distortion in film thickness occurs significantly. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 1995-015119 [Patent Document 2] International Publication No. 2017 / 122460 Brochure Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a dry film, a cured product, and a printed wiring board that have good hiding power and resolution and are capable of forming a cured product of a uniform shape. [Means for solving the problem]

[0011] That is, the dry film according to the present invention has the following features: A dry film having a first film and a resin layer containing a curable resin composition formed on the first film, the resin layer has a first layer on the first film side and a second layer formed on the first layer, The thickness of the first layer is greater than the thickness of the second layer, The visible light transmittance of the first layer is higher than the visible light transmittance of the second layer; The second layer is characterized in that the average visible light transmittance of the second layer is 50% or less when the thickness of the second layer is 10 μm.

[0012] In an embodiment of the present invention, the curable resin composition preferably contains a carboxyl group-containing resin, a photopolymerization initiator, and a colorant.

[0013] In another embodiment of the present invention, the ultraviolet absorption coefficient of the second layer is preferably higher than the ultraviolet absorption coefficient of the first layer, and the ultraviolet absorption coefficient of the second layer is preferably 0.08 or more.

[0014] In addition, in an embodiment of the present invention, it is preferable that at least one of the amount and type of photopolymerization initiator contained in the curable resin composition forming the first layer is different from at least one of the amount and type of photopolymerization initiator contained in the curable resin composition forming the second layer.

[0015] In addition, in an aspect of the present invention, it is preferable that the content of the photopolymerization initiator in the curable resin composition forming the first layer is less than the content of the photopolymerization initiator in the curable resin composition forming the second layer.

[0016] A cured product according to another aspect of the present invention is characterized by being obtained by curing the resin layer of the above-mentioned dry film.

[0017] A printed wiring board according to another aspect of the present invention is characterized by comprising the above-mentioned cured product. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a dry film, a cured product, and a printed wiring board that have good hiding power and resolution and are capable of forming a cured product with a uniform shape. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view of an example of a dry film according to this embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of a structure in which the dry film according to this embodiment is disposed on a substrate. [Figure 3] FIG. 3 is a schematic cross-sectional view of a structure in the example. [Figure 4] FIG. 4 is a schematic cross-sectional view of a structure used in the evaluation of resolution in the examples. [Figure 5] FIG. 5 is a schematic cross-sectional view of a structure used in evaluation of shape uniformity in an example. DETAILED DESCRIPTION OF THE INVENTION

[0020] The dry film, the cured product, and the printed wiring board according to this embodiment will be described below.

[0021] (dry film) The dry film according to this embodiment includes a first film and a resin layer, and may further include other components as required.

[0022] <First Film> The first film serves to support the resin layer of the dry film, and is coated with a curable resin composition when the resin layer is formed. In the present invention, the term "first film" refers to a film that is adhered to at least the resin layer of the dry film when the base material such as a substrate and the resin layer of the dry film are bonded together. The first film may be peeled off from the resin layer after the step of bonding the first film to the base material described below. In this embodiment, it is preferable to peel off from the resin layer in a step after exposure.

[0023] 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.

[0024] Moreover, from the viewpoint of improving mechanical strength, the film made of a thermoplastic resin is preferably a film stretched in a uniaxial or biaxial direction.

[0025] When a thermoplastic resin film is used as the first film, a film having a specific surface configuration may be used by adding a filler to the resin when forming the film (kneading treatment), by matte coating (coating treatment), by subjecting the film surface to a blasting treatment such as sandblasting, or by hairline processing or chemical etching, etc.

[0026] The thickness of the first film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0027] <Resin layer> The resin layer is formed on the first film and contains a curable resin composition. Here, the resin layer is formed by applying and drying the curable resin composition.

[0028] The resin layer has a first layer on the first film side and a second layer formed on the first layer.

[0029] The first layer and the second layer of the dry film according to the embodiment have the following relationship. The thickness of the first layer is greater than the thickness of the second layer The visible light transmittance of the first layer is higher than that of the second layer The phrase "high visible light transmittance" is synonymous with "light color of the cured product." In a dry film, the boundary between the first and second layers may be clear or unclear.

[0030] The dry film according to this embodiment will now be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view of the dry film according to this embodiment. In Fig. 1, a resin layer 13 is disposed on a first film 14. When the resin layer 13 is cured, it becomes a cured product. The resin layer 13 has a first layer 11 and a second layer 12. The thickness T1 of the first layer is greater than the thickness T2 of the second layer, and the visible light transmittance of the first layer is higher than the visible light transmittance of the second layer. Because the visible light transmittance of the first layer is higher than that of the second layer, the first layer is lighter in color than the second layer, and as shown in Figure 1, the resin layer on the first film side (lower side) is lighter in color than the resin layer on the opposite side (upper side) from the first film. When the dry film according to this embodiment is disposed on a substrate, it is disposed so that the second layer 12 is in contact with the substrate 4, as shown in FIG.

[0031] The thickness of the first layer is not particularly limited as long as it is thicker than the thickness of the second layer, and can be appropriately selected depending on the purpose, and is preferably, for example, 3 μm to 80 μm. The thickness of the second layer is not particularly limited as long as it is thinner than the thickness of the first layer, and can be appropriately selected depending on the purpose. For example, the thickness is preferably 1 μm to 20 μm, and more preferably 4 μm to 15 μm. By making the thickness of the first layer greater than the thickness of the second layer, a cured product with a uniform shape can be formed.

[0032] The visible light transmittance of the first layer is not particularly limited as long as it is higher than that of the second layer, and can be appropriately selected depending on the purpose, but is preferably 50% to 80%, more preferably 40% to 70%. When the visible light transmittance of the first layer is higher than that of the second layer, good resolution is achieved. The visible light transmittance of the first layer is a value measured on the first layer alone when the thickness of the first layer is set to 10 μm.

[0033] The visible light transmittance of the second layer is 50% or less, preferably 5% to 50%, and more preferably 10% to 40%. When the visible light transmittance of the second layer is within this range, the resolution and hiding power are improved. The visible light transmittance of the second layer is a value measured on the second layer alone when the thickness of the second layer is set to 10 μm.

[0034] The visible light transmittance of the resin layer is defined as the average value of the transmittance in the range of 360 nm to 830 nm. The specific measurement method was as follows: the curable resin composition was applied to a glass plate with a thickness of 1 mm so that the dry coating would be 10 μm, dried at 80°C for 20 minutes, and the entire surface was exposed to the optimum exposure amount using an exposure device equipped with a high-pressure mercury short arc lamp. After that, the film was developed with a 1 wt% sodium carbonate aqueous solution at 30°C for 60 seconds under conditions of a spray pressure of 0.2 MPa, and then the film was placed in a UV conveyor oven for an accumulated exposure amount of 1,000 mJ / cm. 2 After irradiating with ultraviolet light under the conditions, the composition is cured by heating at 150°C for 60 minutes, and the resulting cured product is used. The baseline of the formed cured product is measured in the wavelength range of 300 nm to 850 nm using an ultraviolet-visible spectrophotometer and an integrating sphere device (UV / VIS / NIR spectrometer V-570, manufactured by JASCO Corporation). The transmittance of the cured product from the measured baseline in the wavelength range of 360 nm to 830 nm is measured. During the measurement, the scanning speed is 400 nm / min and the scanning interval is 1 nm. The average value of the measurements obtained in the range of 360 nm to 830 nm is taken as the visible light transmittance of the measured cured product of the curable resin composition.

[0035] The ultraviolet absorption coefficient of the second layer is preferably higher than that of the first layer. When the ultraviolet absorption coefficients of the first layer and the second layer satisfy this relationship, both resolution and hiding power can be achieved. The ultraviolet absorption coefficient of the first layer is not particularly limited as long as it is lower than the ultraviolet absorption coefficient of the second layer, and can be appropriately selected depending on the purpose. It is preferably 0.01 to 0.07, more preferably 0.02 to 0.06. The ultraviolet absorption coefficient of the second layer is preferably 0.08 or more, and more preferably 0.08 to 0.5.

[0036] The ultraviolet absorption coefficient can be measured, for example, by the following method. The curable resin composition is applied to a 1 mm thick glass plate so that the resin layer has four thickness levels after drying (13 μm, 18 μm, 23 μm, and 28 μm), and dried for 20 minutes at 80° C. The absorbance of each resin layer at a wavelength of 365 nm is measured using an ultraviolet-visible-near infrared spectrophotometer. The thickness of the resin layer is plotted on the X axis and the absorbance on the Y axis, and the ultraviolet absorption coefficient is calculated from the slope of the plot according to the Lambert-Beer law.

[0037] The resin layer may have a layer other than the first and second layers. The thickness, visible light transmittance, and ultraviolet light absorption coefficient of the layer are not particularly limited as long as they do not impair the effects of the dry film according to this embodiment, and can be appropriately selected depending on the purpose.

[0038] <<Curable resin composition>> The curable resin composition is not particularly limited as long as it has the property of being cured, and can be appropriately selected depending on the purpose. However, it preferably contains a carboxyl group-containing resin, a thermosetting component, a photopolymerization initiator, and a colorant, and further contains other components as necessary.

[0039] <<<Carboxyl group-containing resin>>> The carboxyl group-containing resin is a resin having a carboxyl group in the molecule, and various conventionally known resins can be used. By including a carboxyl group-containing resin in a curable resin composition, the curable resin composition can be provided with developability (alkali developability). In particular, a carboxyl group-containing photosensitive resin having an ethylenically unsaturated double bond in the 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 only a carboxyl group-containing resin having no ethylenically unsaturated double bond is used, in order to make the composition photocurable, it is necessary to use in combination a compound having multiple ethylenically unsaturated groups in the molecule, i.e., a photopolymerizable monomer, which will be described later.

[0040] Specific examples of the carboxyl group-containing resin include the following compounds (which may be either oligomers or polymers): These may be used alone or in combination of two or more.

[0041] (1) Carboxyl group-containing resins obtained by copolymerizing unsaturated carboxylic acids such as (meth)acrylic acid with unsaturated group-containing compounds such as styrene, α-methylstyrene, lower alkyl (meth)acrylates, and isobutylene.

[0042] (2) Carboxylic acid-containing urethane resins obtained by the polyaddition reaction of diisocyanates such as aliphatic diisocyanates, branched aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates with carboxyl-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.

[0043] (3) Carboxylic acid group-containing photosensitive urethane resins obtained by the polyaddition reaction of diisocyanates with 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, and monocarboxylic acid compounds having ethylenically unsaturated double bonds such as (meth)acrylic acid, partially acid anhydride-modified products thereof, carboxyl group-containing dialcohol compounds, and diol compounds.

[0044] (4) 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 hydroxyalkyl (meth)acrylate, during the synthesis of the resin (2) or (3).

[0045] (5) A carboxyl group-containing photosensitive urethane resin that is (meth)acrylated at the end by adding a compound having one isocyanate group and one or more (meth)acryloyl groups in the molecule, such as an equimolar reaction product of isophorone diisocyanate and pentaerythritol triacrylate, during the synthesis of the resin (2) or (3).

[0046] (6) A carboxyl group-containing photosensitive resin obtained by reacting a difunctional or more polyfunctional (solid) epoxy resin with (meth)acrylic acid and adding a dibasic acid anhydride to the hydroxyl group present in the side chain.

[0047] (7) A carboxyl group-containing photosensitive resin in which the hydroxyl groups of a bifunctional (solid) epoxy resin are further epoxidized with epichlorohydrin to form a multifunctional epoxy resin, which is then reacted with (meth)acrylic acid, and a dibasic acid anhydride is added to the resulting hydroxyl groups.

[0048] (8) 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.

[0049] (9) A carboxyl group-containing photosensitive resin obtained by reacting an epoxy compound having multiple epoxy groups in one molecule with a compound having at least one alcoholic hydroxyl group and one phenolic hydroxyl group in one molecule, such as p-hydroxyphenethyl alcohol, and an unsaturated group-containing monocarboxylic acid, such as (meth)acrylic acid, and then reacting the alcoholic hydroxyl groups of the resulting reaction product with a polybasic acid anhydride, such as maleic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, or adipic acid.

[0050] (10) A carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups in one molecule with an alkylene oxide such as ethylene oxide or propylene oxide, reacting the resulting reaction product with an unsaturated group-containing monocarboxylic acid, and then reacting the resulting reaction product with a polybasic acid anhydride.

[0051] (11) A carboxyl group-containing photosensitive resin obtained by reacting a compound having multiple phenolic hydroxyl groups in one molecule with a cyclic carbonate compound such as ethylene carbonate or propylene carbonate, reacting the resulting reaction product with an unsaturated group-containing monocarboxylic acid, and then reacting the resulting reaction product with a polybasic acid anhydride.

[0052] (12) A carboxyl group-containing photosensitive resin obtained by adding a compound having one epoxy group and one or more (meth)acryloyl groups in one molecule to the resins (1) to (11).

[0053] In this specification, (meth)acrylate is a general term for acrylate, methacrylate and mixtures thereof, and the same applies to other similar expressions.

[0054] The acid value of the carboxyl group-containing resin is preferably 40 mgKOH / g to 150 mgKOH / g, more preferably 50 mgKOH / g to 130 mgKOH / g. By adjusting the acid value of the carboxyl group-containing resin to 40 mgKOH / g or more, alkaline developability is improved. Furthermore, by adjusting the acid value to 150 mgKOH / g or less, resolution can be improved.

[0055] The weight-average molecular weight of the carboxyl group-containing resin varies depending on the resin skeleton, but is generally preferably 2,000 to 150,000, and more preferably 5,000 to 100,000. By ensuring that the weight-average molecular weight is 2,000 or more, tack-free performance and resolution can be improved. Furthermore, by ensuring that the weight-average molecular weight is 150,000 or less, developability and storage stability can be improved. The weight-average molecular weight (Mw) can be determined by gel permeation chromatography (GPC) using a standard polystyrene equivalent.

[0056] The content of the carboxyl group-containing resin in the curable resin composition is preferably 20% by mass to 60% by mass, more preferably 30% by mass to 50% by mass, calculated as solid content. By setting the content to 20% by mass or more, the strength of the cured product can be improved. Furthermore, by setting the content to 60% by mass or less, the viscosity becomes appropriate and printability is improved.

[0057] <<<Thermosetting component>>> The thermosetting component is not particularly limited as long as it is cured by heating, and can be appropriately selected depending on the purpose. Examples of the thermosetting component include known and commonly used components such as isocyanate compounds, blocked isocyanate compounds, amino resins, maleimide compounds, benzoxazine resins, carbodiimide resins, cyclocarbonate compounds, epoxy compounds, oxetane compounds, and episulfide resins. These may be used alone or in combination of two or more. Among these, epoxy resins are preferred.

[0058] Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, hydrogenated bisphenol A type epoxy resins, brominated bisphenol A type epoxy resins, bisphenol S type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, dicyclopentadiene type epoxy resins, and triphenylmethane type epoxy resins.

[0059] When the curable resin composition contains the carboxyl group-containing resin, the content of the epoxy resin is preferably 0.3 to 2.5 equivalents, more preferably 0.5 to 2.0 equivalents, of epoxy groups per equivalent of carboxyl groups in the carboxyl group-containing resin, calculated on a solids basis. By adjusting the amount of epoxy groups to 0.3 equivalents or more, no carboxyl groups remain in the cured product, improving heat resistance, alkali resistance, electrical insulation, and the like. By adjusting the amount to 2.5 equivalents or less, no thermosetting component remains in the cured product, improving the strength of the cured product.

[0060] <<<Photopolymerization initiator>>> The photopolymerization initiator is contained to adjust the visible light transmittance of the dry film, which can improve the resolution and hiding power. The photopolymerization initiator is not particularly limited as long as it is one that is commonly used in curable resin compositions, and can be appropriately selected depending on the purpose, and any known photopolymerization initiator can be used. One photopolymerization initiator may be used alone, or two or more photopolymerization initiators may be used in combination.

[0061] The photopolymerization initiator may be, for example, one or more photopolymerization initiators selected from the group consisting of oxime ester-based photopolymerization initiators having an oxime ester group, alkylphenone-based photopolymerization initiators, α-aminoacetophenone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, and titanocene-based photopolymerization initiators. Among these, it is preferable to use one or more photopolymerization initiators selected from the group consisting of α-aminoacetophenone-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, oxime ester-based photopolymerization initiators, and titanocene-based photopolymerization initiators, and it is more preferable to use an oxime ester-based photopolymerization initiator. Of the two resin layers, it is even more preferable for the second layer to contain an oxime ester-based photopolymerization initiator or a titanocene-based photopolymerization initiator.

[0062] Commercially available oxime ester photopolymerization initiators include Irgacure OXE01 and Irgacure OXE02 (both manufactured by BASF Japan Ltd.), N-1919, and NCI-831 (manufactured by ADEKA Corporation). Photopolymerization initiators having two oxime ester groups in the molecule can also be used, and specific examples include oxime ester compounds having a carbazole structure represented by the following general formula:

[0063] [ka] (wherein X represents a hydrogen atom, an alkyl group having 1 to 17 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a phenyl group, a phenyl group (substituted with an alkyl group having 1 to 17 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an amino group, an alkylamino group having an alkyl group of 1 to 8 carbon atoms, or a dialkylamino group), or a naphthyl group (substituted with an alkyl group having 1 to 17 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, an amino group, an alkylamino group having an alkyl group of 1 to 8 carbon atoms, or a dialkylamino group), and Y and Z each represent a hydrogen atom, an alkyl group having 1 to 17 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a halogen group, a phenyl group, a phenyl group (substituted with an alkyl group having 1 to 17 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, Ar represents a bond, an alkylene having 1 to 10 carbon atoms, vinylene, phenylene, biphenylene, pyridylene, naphthylene, thiophene, anthrylene, thienylene, furylene, 2,5-pyrrole-diyl, 4,4'-stilbene-diyl, or 4,2'-stilbene-diyl, and n is an integer of 0 or 1.

[0064] Further, examples of the carbazole oxime ester compound include compounds that can be represented by the following general formula:

[0065] [ka] (In the formula, R1 represents an alkyl group having 1 to 4 carbon atoms, or a phenyl group which may be substituted with a nitro group, a halogen atom, or an alkyl group having 1 to 4 carbon atoms. R2 represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a phenyl group which may be substituted with an alkyl group or alkoxy group having 1 to 4 carbon atoms. R3 may be linked via an oxygen atom or a sulfur atom and represents an alkyl group having 1 to 20 carbon atoms which may be substituted with a phenyl group, or a benzyl group which may be substituted with an alkoxy group having 1 to 4 carbon atoms. R4 represents a nitro group or an acyl group represented by XC(=O)-. X represents an aryl group which may be substituted with an alkyl group having 1 to 4 carbon atoms, a thienyl group, a morpholino group, a thiophenyl group, or a structure represented by the following formula:

[0066] [ka]

[0067] Examples of titanocene photopolymerization initiators include bis(cyclopentadienyl)-diphenyl-titanium, bis(cyclopentadienyl)-dichloro-titanium, bis(cyclopentadienyl)-bis(2,3,4,5,6-pentafluorophenyl)titanium, and bis(cyclopentadienyl)-bis(2,6-difluoro-3-(pyrrol-1-yl)phenyl)titanium. These may be synthesized as appropriate, or commercially available products may be used. Examples of commercially available products include JMT-784 (manufactured by Yueyang Kimoutain Sci-tech Co. Ltd.).

[0068] Examples of alkylphenone photopolymerization initiators include α-hydroxyalkylphenone types, such as Omnirad 184, Darocure 1173, Irgacure 2959, and Omnirad 127 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one) (all manufactured by IGM Resins).

[0069] Examples of α-aminoacetophenone-based photopolymerization initiators include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and N,N-dimethylaminoacetophenone. Commercially available products include Omnirad 907, Omnirad 369, and Omnirad 379 (all manufactured by IGM Resins).

[0070] Examples of acylphosphine oxide photopolymerization initiators include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, etc. Commercially available products include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and Omnirad 819 (all manufactured by IGM Resins).

[0071] The amount of the photopolymerization initiator, excluding oxime ester-based photopolymerization initiators, is preferably 0.01 to 30 parts by mass, calculated as solid content, per 100 parts by mass of the carboxyl group-containing resin. When the amount is 0.01 part by mass or more, the photocurability of the curable resin composition is good, the cured product is less likely to peel, and properties such as chemical resistance are also good. On the other hand, when the amount is 30 parts by mass or less, light absorption at the surface of the resin layer is good, and deep curing is less likely to decrease. A more preferred amount is 0.1 to 20 parts by mass. The amount of the oxime ester photopolymerization initiator is preferably 0.01 to 5 parts by mass, calculated as solid content, per 100 parts by mass of the carboxyl group-containing resin. When the amount is 0.01 part by mass or more, the photocurability of the curable resin composition is good, and properties such as heat resistance and chemical resistance are also good. On the other hand, when the amount is 5 parts by mass or less, light absorption at the surface of the resin layer is good, and deep curing is less likely to decrease. A more preferred amount is 0.1 to 3.9 parts by mass.

[0072] The type and content of the photopolymerization initiator preferably satisfy the following conditions. At least one of the amount and type of photopolymerization initiator contained in the curable resin composition that forms the first layer and at least one of the amount and type of photopolymerization initiator contained in the curable resin composition that forms the second layer may be the same, but are preferably different. Furthermore, the content of the photopolymerization initiator in the curable resin composition forming the first layer is more preferably lower than the content of the photopolymerization initiator in the curable resin composition forming the second layer. By setting the type and content of the photopolymerization initiator within the above conditions, it is possible to improve the deep curability, and a curable resin composition with good resolution can be obtained.

[0073] <<<Coloring agent>>> The colorant is contained in order to adjust the visible light transmittance of the dry film, which can improve the resolution and hiding power. The colorant is not particularly limited as long as it is one that is used in ordinary curable resin compositions and can be appropriately selected depending on the purpose. Conventional and well-known colorants such as black, red, blue, green, yellow, and white can be used, and any of pigments, dyes, and coloring matters can be used. Regarding the black color, only a black colorant may be used, or a colorant other than black may be mixed to produce the black color.

[0074] Examples of black colorants include carbon black, zirconium nitride, and Pigment Black 1, 6, 7, 8, 9, 10, 11, 12, 13, 18, 20, 25, 26, 28, 29, 30, 31, and 32. Red colorants include monoazo-based, disazo-based, azo-lake-based, benzimidazolone-based, perylene-based, diketopyrrolopyrrole-based, condensed azo-based, anthraquinone-based, and quinacridone-based. Blue colorants include phthalocyanine and anthraquinone compounds, and pigment compounds can be used. In addition to these, metal-substituted or unsubstituted phthalocyanine compounds can also be used. Green colorants include phthalocyanine-based, anthraquinone-based, and perylene-based compounds, and metal-substituted or unsubstituted phthalocyanine compounds can also be used. Yellow colorants include monoazo-based, disazo-based, condensed azo-based, benzimidazolone-based, isoindolinone-based, and anthraquinone-based colorants. Examples of white colorants include rutile or anatase titanium oxide, etc. In addition, purple, orange, brown, and other colorants may be added to adjust the color tone.

[0075] The content of the colorant is not particularly limited and can be appropriately selected depending on the purpose, but the content of the colorant in the first layer and the second layer is preferably as follows. The content of the colorant in the first layer is preferably 0 to 30 parts by mass, and more preferably 0 to 20 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the content of the colorant falls within this range, good resolution is achieved. The content of the colorant in the second layer is preferably 0.5 to 100 parts by mass, and more preferably 1 to 80 parts by mass, relative to 100 parts by mass of the carboxyl group-containing resin, calculated as solid content. When the content of the colorant falls within this range, good hiding power is achieved.

[0076] <<<Other ingredients>>> The other components are not particularly limited as long as they are those used in ordinary curable resin compositions and can be appropriately selected depending on the purpose, and examples thereof include photopolymerizable monomers, fillers, other additives, etc. These may be used alone or in combination of two or more.

[0077] The photopolymerizable monomer is a monomer having an ethylenically unsaturated double bond, and examples of such photopolymerizable monomers include commonly known polyester (meth)acrylates, polyether (meth)acrylates, urethane (meth)acrylates, carbonate (meth)acrylates, and epoxy (meth)acrylates. Specifically, alkyl acrylates such as 2-ethylhexyl acrylate and cyclohexyl acrylate; hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate; mono- or diacrylates of alkylene oxide derivatives such as ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol; acrylamides such as N,N-dimethylacrylamide, N-methylolacrylamide, and N,N-dimethylaminopropylacrylamide; aminoalkyl acrylates such as N,N-dimethylaminoethyl acrylate and N,N-dimethylaminopropyl acrylate; hexanediol, trimethylolpropane, pentaerythritol, ditrimethylolpropane, dipentaerythritol, trishydroxyethyl Examples of suitable acrylates include polyhydric acrylates derived from polyhydric alcohols such as isocyanurate or their alkylene oxide adducts or ε-caprolactone adducts; polyhydric acrylates such as phenols such as phenoxy acrylate and bisphenol A diacrylate or their alkylene oxide adducts; acrylates derived from glycidyl ethers such as glycerin diglycidyl ether, trimethylolpropane triglycidyl ether, and triglycidyl isocyanurate; and, without limitation, acrylates and melamine acrylates obtained by directly acridating polyols such as polyether polyols, polycarbonate diols, hydroxyl-terminated polybutadienes, and polyester polyols or by urethane acrylate via diisocyanates, as well as methacrylates corresponding to the above acrylates. These may be used alone or in combination of two or more. The photopolymerizable monomer can also be used as a reactive diluent.

[0078] The content of the photopolymerizable monomer is preferably 5 to 100 parts by mass, calculated as solid content, relative to 100 parts by mass of the carboxyl group-containing resin. When the content is 5 parts by mass or more, the photocurability is good and pattern formation is easy in alkaline development after irradiation with active energy rays. On the other hand, when the content is 100 parts by mass or less, halation is less likely to occur and good resolution can be obtained.

[0079] As the filler, known inorganic or organic fillers can be used, but barium sulfate, silica and talc are particularly preferred. The content of the filler is not particularly limited and can be appropriately selected depending on the purpose.

[0080] <<Other additives>> The curable resin composition of the present invention may further contain, as necessary, components such as a photoinitiator aid, a cyanate compound, an elastomer, 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, a flame retardant such as a phosphorus compound such as a phosphinate, a phosphate ester derivative, or a phosphazene compound, or an organic solvent. These may be compounds known in the field of electronic materials.

[0081] <Method for producing curable resin composition> The method for producing the curable resin composition is not particularly limited, and the composition can be produced, for example, by blending the above components in a predetermined ratio and then kneading or mixing them at room temperature using a kneading means such as a triple roll mill, a ball mill, a bead mill, or a sand mill, or a stirring means such as a super mixer or a planetary mixer. Furthermore, prior to the kneading or mixing, pre-kneading or pre-mixing may be performed as necessary.

[0082] <Other materials> The other members are not particularly limited as long as they are those used in ordinary dry films and can be appropriately selected depending on the purpose, and examples thereof include a second film.

[0083] <<Second Film>> The second film is a film laminated on the surface of the resin layer for the purpose of preventing dust from adhering to the surface of the resin layer, etc. Specifically, when bonding a base material such as a substrate to the resin layer of the dry film, the second film is a film that is peeled off from the resin layer before the step of bonding the dry film to the base material, which will be described later.

[0084] The second film may be, for example, a polyethylene film, a polytetrafluoroethylene film, a polypropylene film, or surface-treated paper. The adhesive strength of the second film to the resin layer may be smaller than the adhesive strength between the resin layer and the first film. Since the adhesive strength of the second film is smaller than that of the first film, the second film can be peeled off without moving the first film.

[0085] The thickness of the second film is not particularly limited, but can be, for example, 10 μm to 150 μm.

[0086] <Dry film manufacturing method> The dry film can be obtained by diluting the curable resin composition with an organic solvent to adjust the viscosity to an appropriate level, applying the dilution to a uniform thickness onto the first film using a comma coater, blade coater, lip coater, rod coater, squeeze coater, reverse coater, transfer roll coater, gravure coater, spray coater, applicator, or the like, and drying the resulting mixture at a temperature of 50°C to 130°C for 1 minute to 30 minutes to form a resin layer. There are no particular restrictions on the thickness of the applied curable resin composition, but the thickness of the resin layer after drying is generally selected appropriately within the range of 1 μm to 150 μm, preferably 5 μm to 60 μm.

[0087] When the resin layer is produced from layers containing two types of curable resin compositions with different compositions, the two layers may be produced simultaneously or one layer at a time. Simultaneous production of two layers means that the respective curable resin compositions are simultaneously applied to the first film and the layer on the first film side. Producing one layer at a time means, for example, applying a curable resin composition to form one layer to a first film, drying the composition to form one layer, and then applying a curable resin composition to form the other layer to the formed layer, followed by drying the composition to produce the film. Alternatively, two different types of curable resin compositions may be applied to different first films in layers, and the resulting resin layers may be dried and then bonded together using a laminator or the like to produce the laminate.

[0088] (cured product) The cured product according to the embodiment is obtained by curing the resin layer of the dry film. The size and shape of the cured product are not particularly limited and can be appropriately selected depending on the purpose.

[0089] The cured product can be produced, for example, by laminating the resin layer onto a substrate using a laminator or the like so that the resin layer is in contact with the substrate, forming a resin layer on the substrate, and then curing the resin layer.

[0090] Substrates include printed wiring boards and flexible printed wiring boards with circuits already formed using copper or other materials, as well as copper-clad laminates for high-frequency circuits made from materials such as paper phenol, paper epoxy, glass cloth epoxy, glass polyimide, glass cloth / non-woven cloth epoxy, glass cloth / paper epoxy, synthetic fiber epoxy, fluororesin, polyethylene, polyphenylene ether, polyphenylene oxide, cyanate, etc., including copper-clad laminates of all grades (FR-4, etc.), as well as metal substrates, polyimide film, polyethylene terephthalate film, polyethylene naphthalate (PEN) film, glass substrates, ceramic substrates, and wafer plates.

[0091] The dry film is preferably bonded to the substrate under pressure and heat using a vacuum laminator or the like. By using such a vacuum laminator, even if a circuit-formed substrate is used, the dry film adheres tightly to the circuit substrate, even if the circuit substrate surface is uneven, preventing the inclusion of air bubbles and improving the filling of 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.

[0092] After laminating a dry film onto a substrate, it is selectively exposed to active energy rays through a photomask with a predetermined pattern formed thereon, and the unexposed areas are developed with a dilute alkaline aqueous solution (e.g., a 0.3 to 3% by weight aqueous solution of sodium carbonate) to form a patterned cured product. In the case of a dry film, after exposure, the first film is peeled off from the dry film and development is carried out, thereby forming a patterned cured product on the substrate. It is also possible to peel off the first film from the dry film before exposure and expose and develop the exposed resin layer, provided that this does not impair the properties. Furthermore, 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 220°C), or by irradiating active energy rays after heat-curing, or by heat-curing alone to form a final finish curing (main curing).

[0093] The exposure device used for the above-mentioned active energy ray irradiation may be a device equipped with a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a mercury short arc lamp, or the like, and capable of irradiating ultraviolet rays in the range of 350 to 450 nm. Furthermore, a direct imaging device (for example, a laser direct imaging device that directly draws an image with a laser based on CAD data from a computer) may also be used. The lamp or laser light source of the direct imaging device may have a maximum wavelength in the range of 350 to 450 nm. The exposure dose for image formation varies depending on the thickness of the cured product, etc., but is generally 10 to 1000 mJ / cm. 2 , preferably 20 to 800 mJ / cm 2 The range may be:

[0094] The developing method may be a dipping method, a shower method, a spray method, a brush method, or the like, and the developing solution may be an aqueous alkali solution such as potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, or an amine.

[0095] (Printed wiring board) A printed wiring board according to one embodiment of the present invention has a cured resin layer of the above-mentioned dry film. The size and type of the printed wiring board are not particularly limited and can be appropriately selected depending on the purpose. [Example]

[0096] Next, tests conducted by the present inventors will be described, but the present invention is not limited to these.

[0097] <Preparation of carboxyl group-containing photosensitive resin> An autoclave equipped with a thermometer, a nitrogen introducing device that also serves as an alkylene oxide introducing device, and a stirrer was charged with 119.4 parts by mass of a novolac cresol resin (Shonor CRG951, manufactured by Aica Kogyo Co., Ltd., OH equivalent: 119.4), 1.19 parts by mass of potassium hydroxide, and 119.4 parts of toluene, and the system was purged with nitrogen while stirring, and then heated to an elevated temperature. Next, 63.8 parts by mass of propylene oxide was slowly added dropwise, and the mixture was heated at 125°C to 132°C and 0 kg / cm 2 ~4.8kg / cm 2 The mixture was reacted at 400°C for 16 hours. After that, it was cooled to room temperature, and 1.56 parts by mass of 89% phosphoric acid was added to the reaction solution and mixed to neutralize the potassium hydroxide, yielding a propylene oxide reaction solution of a novolac cresol resin with a solids content of 62.1% and a hydroxyl value of 182.2 g / eq. This propylene oxide reaction solution had an average of 1.08 moles of propylene oxide added per equivalent of phenolic hydroxyl group. The resulting propylene oxide reaction solution (293.0 parts by mass), acrylic acid (43.2 parts by mass), methanesulfonic acid (11.53 parts by mass), methylhydroquinone (0.18 parts by mass), and toluene (252.9 parts by mass) were placed in a reactor equipped with a stirrer, thermometer, and air inlet tube. Air was blown in at a rate of 10 mL / min, and the mixture was stirred at 110°C for 12 hours. The water produced by the reaction was distilled off as an azeotrope with toluene, resulting in 12.6 parts by mass of water. The mixture was then cooled to room temperature, neutralized with 35.35 parts by mass of 15% aqueous sodium hydroxide, and then washed with water. The toluene was then distilled off using an evaporator, replacing it with 118.1 parts by mass of diethylene glycol monoethyl ether acetate, to obtain a novolac acrylate resin solution. Next, 332.5 parts by mass of the obtained novolac acrylate resin solution and 1.22 parts by mass of triphenylphosphine were charged into a reactor equipped with a stirrer, a thermometer, and an air inlet tube, and air was blown in at a rate of 10 mL / min. While stirring, 60.8 parts by mass of tetrahydrophthalic anhydride was gradually added, and the mixture was reacted at 95°C to 101°C for 6 hours, cooled, and then removed. In this way, a solution of a carboxyl group-containing photosensitive resin (hereinafter abbreviated as carboxyl group-containing photosensitive resin) with a solid content of 65% and an acid value of the solid matter of 87.7 mgKOH / g was obtained.

[0098] (Examples 1 to 7, Comparative Examples 1 to 5) <Preparation of Curable Resin Composition> The materials were blended in the proportions shown in Table 1, premixed in a mixer, and then kneaded in a three-roll mill to prepare curable resin compositions. The values ​​in the table are the contents in a solution containing a solvent. The units in the table are parts by mass.

[0099] [Table 1]

[0100] Details of each component other than the carboxyl group-containing photosensitive resin in Table 1 are as follows. Thermosetting component (epoxy resin): EPICLON N-770 (DIC Corporation) Photopolymerization initiator 1: Irgacure OXE02 (BASF Japan Ltd., oxime ester type) Photopolymerization initiator 2: TOE-04-A3 (manufactured by Nippon Chemical Industry Co., Ltd., oxime ester type) Photopolymerization initiator 3: 2,4,6-trimethylbenzoyldiphenylphosphine oxide (acylphosphine oxide type) Photopolymerization initiator 4: Omnirad369 (manufactured by IGM Resins BV, α-aminoacetophenone type) Photopolymerization initiator 5: JMT-784 (Yueyang Kimoutain Sci-tech Co. Ltd., titanocene type) Blue colorant: CI Pigment Blue 15:3 Yellow colorant: CI Pigment yellow 147 Red colorant: CI Pigment red 149 Photopolymerizable monomer: Dipentaerythritol hexaacrylate (manufactured by Nippon Kayaku Co., Ltd.) Filler: Barium sulfate (product name: B-30, manufactured by Sakai Chemical Industry Co., Ltd.) Melamine: (Nissan Chemical Co., Ltd.) Solvent: Propylene glycol monomethyl ether acetate

[0101] <Determining the optimal exposure amount> The optimum exposure dose for the resin layer or dry film in the examples was determined by the following experiment. A copper solid substrate with a copper thickness of 18 μm was pretreated using an etching agent (CZ-8100, manufactured by MEC Co., Ltd.) to prepare a substrate. Next, the obtained curable resin composition was applied onto a substrate so that the thickness after curing would be 10 μm, and dried at 80° C. for 20 minutes to prepare a resin layer. In the case of the dry film, the obtained dry film was laminated using a vacuum laminator so that the second layer (L2) was in contact with the substrate, to produce a structure as shown in FIG. Next, the resin layer or the structure was exposed through a Stouffer 41-step step tablet using an exposure device equipped with a high-pressure mercury short arc lamp. In the structure, the first film was peeled off, and development was performed for 60 seconds with a 1 wt % sodium carbonate aqueous solution at 30°C at a spray pressure of 0.2 MPa. The exposure amount at which the remaining step tablet pattern became 15 was determined as the optimal exposure amount (mJ / cm). 2 ) was decided.

[0102] <Measurement of visible light transmittance> Each of the obtained curable resin compositions was applied to a 1 mm thick glass plate as a substrate using an applicator so that the thickness after curing would be 10 μm, and then dried at 80°C for 20 minutes to produce a resin layer. The obtained resin layer was exposed to an optimal exposure dose using an exposure device equipped with a high-pressure mercury short arc lamp, and then developed with a 1 wt% sodium carbonate aqueous solution at 30°C for 60 seconds at a spray pressure of 0.2 MPa. The resulting resin layer was then subjected to a UV conveyor oven with an integrated exposure dose of 1,000 mJ / cm. 2 After irradiating with ultraviolet light under the conditions above, the samples were cured by heating at 150°C for 60 minutes to obtain a cured product of each curable resin composition. Using a UV-visible spectrophotometer and an integrating sphere device (UV / VIS / NIR spectrometer V-570, manufactured by JASCO Corporation), a baseline was measured in the range of 300 nm to 850 nm using the same glass plate as the glass plate on which the curable resin composition was applied. The transmittance of the cured product of each curable resin composition from the baseline in the wavelength range of 360 nm to 830 nm was measured at a scanning speed of 400 nm / min and a scanning interval of 1 nm, and the average value of the transmittance in this wavelength range was recorded as the visible light transmittance (%) of the cured product of that curable resin composition.

[0103] <Measurement of ultraviolet absorption coefficient> The curable resin composition was applied to a 1 mm thick glass plate so that the resin layer would have four different thicknesses after drying (13 μm, 18 μm, 23 μm, and 28 μm), and then dried at 80°C for 20 minutes. The absorbance of each resin layer at a wavelength of 365 nm was measured using a UV-Visible-Near-Infrared Spectrophotometer (V-570, manufactured by JASCO Corporation). The thickness of the resin layer was plotted on the X axis and the absorbance on the Y axis, and the UV absorption coefficient was calculated from the slope according to the Lambert-Beer law.

[0104] [Table 2]

[0105] <Dry film preparation> Dry films were produced using the obtained curable resin compositions A to H in the combinations shown in Table 3. The curable resin composition for forming the first layer (L1) was applied to a 38 μm thick polyester film (corresponding to the first film) using an applicator so that the thickness after drying would be as shown in Table 3, and then dried at 80° C. for 10 minutes. Thereafter, the curable resin composition for forming the second layer (L2) was applied on the first layer so that the thickness after drying would be as shown in Table 3, and then dried at 80° C. for 10 minutes to prepare a dry film.

[0106] [Table 3]

[0107] The obtained dry films were evaluated for hiding power, resolution, and shape uniformity as follows. The evaluation results are shown in Table 4.

[0108] <Concealment> The substrate used was a printed wiring board with a circuit formed thereon with a copper thickness of 25 μm, a line width of 100 μm, and a line spacing of 100 μm. The printed wiring board was pretreated using an etching agent (CZ-8100, manufactured by MEC Co., Ltd.), and the resulting dry films were bonded together using a vacuum laminator so that the second layer (L2) was in contact with the substrate, producing the structure shown in Figure 3. The structure was formed by laminating the second layer 12 (L2), first layer 11 (L1), and first film 14 in this order on the substrate 4. The resulting structure was exposed to a solder resist pattern at an optimal exposure dose using an exposure device equipped with a high-pressure mercury short arc lamp, and then the first film was peeled off. The structure was developed for 60 seconds using a 1 wt% sodium carbonate aqueous solution at 30°C under a spray pressure of 0.2 MPa, yielding a structure with a pattern formed. The structure with the pattern formed was then heated in a UV conveyor furnace for an integrated exposure dose of 1,000 mJ / cm. 2 After irradiating with ultraviolet light under the conditions above, the coating was cured by heating at 150°C for 60 minutes to obtain an evaluation substrate.

[0109] The evaluation substrate was observed from the resin layer side visually and with an optical microscope (digital microscope, magnification 50x, VHX-6000, manufactured by Keyence Corporation) to determine whether the copper circuit could be confirmed, and the hiding power was evaluated based on the following evaluation criteria. -Evaluation criteria- ◎: Wiring pattern is difficult to see even with an optical microscope 〇: The wiring pattern is difficult to see visually, but can be seen with an optical microscope. ×: The wiring pattern can be visually confirmed

[0110] <Resolution> The substrate was a plated copper substrate without a circuit formed on it. The substrate was pretreated with an etching agent (CZ-8100, manufactured by MEC Co., Ltd.), and the resulting dry films were laminated using a vacuum laminator so that the second layer (L2) was in contact with the substrate, producing the structure shown in Figure 3. A negative mask for evaluating resolution, with a solder resist dam width of 100 μm, was placed on the fabricated structure, and the solder resist pattern was exposed to the optimum exposure dose using an exposure device equipped with a high-pressure mercury short arc lamp. After that, the first film was peeled off, and development was carried out for 60 seconds using a 1 wt% aqueous solution of sodium carbonate at 30°C under a spray pressure of 0.2 MPa, obtaining a solder resist pattern. The structure on which the pattern was formed was then exposed in a UV conveyor furnace with an integrated exposure dose of 1,000 mJ / cm. 2 After irradiating with ultraviolet light under the conditions above, the coating was cured by heating at 150°C for 60 minutes to obtain an evaluation substrate.

[0111] For the obtained evaluation boards, the maximum and minimum widths of the cross sections of the formed solder resist layers (solder resist dam widths) were measured (see FIG. 4), and the shapes of the solder resist dams were evaluated based on the following evaluation criteria. If the difference between the maximum and minimum widths of the solder resist dam is large, the solder resist may peel off, causing a short circuit, and therefore the resolution can be said to be poor. -Evaluation criteria- ◎: The difference between the maximum and minimum dam widths is 10 μm or less ○: The difference between the maximum and minimum dam widths is more than 10 μm and 30 μm or less ×: The difference between the maximum and minimum dam widths is more than 30 μm

[0112] <Shape uniformity> The substrate was a circuit board with Cu pads 25 μm thick, 200 μm wide, and 150 μm apart. The substrate was pretreated with an etching agent (CZ-8100, manufactured by MEC Co., Ltd.), and the resulting dry films were bonded together using a vacuum laminator so that the second layer (L2) was in contact with the substrate, producing the structure shown in Figure 3. A negative mask for resolution evaluation was placed on the fabricated structure so that a solder resist dam with a width of 100 μm was formed in the center between the Cu pads, and the solder resist pattern was exposed to the optimum exposure dose using an exposure device equipped with a high-pressure mercury short arc lamp. After that, the first film was peeled off and development was carried out for 60 seconds using a 1 wt% sodium carbonate aqueous solution at 30°C under conditions of a spray pressure of 0.2 MPa, obtaining a solder resist pattern. The structure on which the pattern was formed was then exposed in a UV conveyor furnace with an integrated exposure dose of 1,000 mJ / cm. 2 After irradiating with ultraviolet light under the conditions above, the coating was cured by heating at 150°C for 60 minutes to obtain an evaluation substrate.

[0113] The cross-sectional shapes of 10 solder resist dams formed on the obtained evaluation board were observed. The solder resist dam width was measured on each of the left and right sides, as shown in Figure 5, by measuring the difference between the maximum and minimum widths from the center line indicated by the solid line in Figure 5 (one-side dam width reduction: indicated by the thick line in Figure 5). When comparing the one-side dam width reductions on the left and right sides of the same solder resist dam, dams with a difference of 5 μm or more were deemed to be distorted. The number of distorted dams was counted, and the uniformity of the shape was evaluated based on the following evaluation criteria: -Evaluation criteria- ◎: One or less distorted dam 〇: 2 to 4 distorted dams ×: 5 or more distorted dams

[0114] [Table 4]

[0115] In the dry films of Examples 1 to 7, the thickness of the region opposite the substrate side (first layer) is thicker than the thickness of the region on the substrate side (second layer), the visible light transmittance of the first layer is higher than that of the second layer, and the average visible light transmittance of the second layer is 50% or less. These cured dry films have excellent hiding power and resolution, and can be formed into cured products with uniform shapes. In contrast, the dry film of Comparative Example 1 had a first layer that was thinner than the second layer. The cured product of this dry film received evaluation results of "x" for both resolution and shape uniformity, indicating that a cured product with a uniform shape could not be formed. The dry film of Comparative Example 2 had a visible light transmittance of the first layer that was lower than that of the second layer, and the average visible light transmittance of the second layer exceeded 50%. The cured product of this dry film received evaluation results of "x" for shape uniformity, indicating that a uniform cured product could not be formed. The dry film of Comparative Example 3 had an average visible light transmittance of the second layer that exceeded 50%. The cured product of this dry film received evaluation results of "x" for hiding power. The dry films of Comparative Examples 4 and 5 did not have a two-layer structure, i.e., did not have a first layer and a second layer. The cured products of these dry films received evaluation results of "x" for resolution and hiding power. The cured products of these dry films did not achieve both hiding power and resolution.

[0116] Although the embodiments for carrying out the present invention have been specifically described above, the present invention is not limited to these and can be modified in various ways without departing from the spirit of the present invention.

Claims

1. A dry film having a first film and a resin layer containing a curable resin composition formed on the first film, the resin layer has a first layer on the first film side and a second layer formed on the first layer, the thickness of the first layer is greater than the thickness of the second layer; a visible light transmittance of the first layer is higher than a visible light transmittance of the second layer; A dry film characterized in that the average visible light transmittance of the second layer when the thickness of the second layer is 10 μm is 50% or less.

2. The dry film according to claim 1 , wherein the curable resin composition contains a carboxyl group-containing resin, a photopolymerization initiator, and a colorant.

3. the second layer has a higher ultraviolet absorption coefficient than the first layer; 3. The dry film according to claim 1, wherein the second layer has an ultraviolet absorption coefficient of 0.08 or more.

4. 3. The dry film according to claim 1, wherein at least one of the amount and type of photopolymerization initiator contained in the curable resin composition forming the first layer is different from at least one of the amount and type of photopolymerization initiator contained in the curable resin composition forming the second layer.

5. The dry film according to claim 4, wherein the content of the photopolymerization initiator in the curable resin composition forming the first layer is less than the content of the photopolymerization initiator in the curable resin composition forming the second layer.

6. A cured product obtained by curing the resin layer of the dry film according to claim 1 or 2.

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

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