TWI711356B - Dry film and flexible printed wiring board - Google Patents

Abstract

To provide a dry film excellent in folding resistance and the like, and to provide a flexible printed wiring board having the cured product as a protective film, for example, a cover film or a solder resist. It is a dry film with an adhesive surface (a1) for bonding to the object to be protected and a protective surface (b1) on the opposite side of the aforementioned adhesive surface. It is characterized by the ATR method of FT-IR (Fourier Transform Infrared Spectroscopy) (Total reflection method) In the infrared absorption spectrum obtained, the adhesive surface (a1) does not have a peak derived from imine, and the protective surface (b1) has a peak derived from imine, and is an alkali-soluble dry film.

Description

Dry film and flexible printed wiring board

The present invention relates to dry films, and particularly relates to dry films that can be formed from insulating films of flexible printed wiring boards and flexible printed wiring boards.

In recent years, due to the popularization of smart phones and tablet terminals, electronic devices have become smaller and thinner, and circuit boards have become smaller and smaller. Therefore, the use of the flexible printed wiring board that can be foldably stored is expanded, and the flexible printed wiring board is also required to have higher reliability than the current one.

In contrast, as an insulating film for ensuring the insulation reliability of a flexible printed wiring board, a polyimide with excellent mechanical properties such as heat resistance and flexibility as a matrix is widely used in the folded part (bend part). The cover film (for example, Patent Documents 1 and 2 are referenced) and the mounting part (non-bending part) are a mixed process of using a photosensitive resin composition that is excellent in electrical insulation properties and can be finely processed.

That is, a cover film with polyimide having excellent mechanical properties such as heat resistance and flexibility as a substrate is not suitable for fine wiring due to the need for die punching processing. Therefore, in the wafer mounting part where fine wiring is required, it is necessary to use a part of the photolithography processing alkali development type photosensitive Resin composition (solder resist).

In addition, printed wiring boards, particularly flexible printed wiring boards (hereinafter referred to as FPCs) require high flame retardancy, and insulating films, which are one of their main constituent elements, also require excellent flame retardancy. FPCs using polyimide substrates etc. as substrates are thinner than printed wiring boards of glass epoxy substrates. On the other hand, the film thickness of the necessary insulating film is the same for both the printed wiring board and the FPC, so in the case of a thin-film FPC, the burden on the flame retardancy of the insulating film is relatively large. Therefore, in the past, various proposals have been made to make insulating films flame-retardant. For example, it has been proposed to blend a phosphorus-containing compound that can impart flame-retardant properties to the resin composition or an epoxy resin with excellent heat resistance to obtain insulating films. In a curable resin composition. For example, Patent Document 3 discloses that (a) a binder polymer such as an epoxy resin, (b) a halogenated aromatic ring having a bromophenyl group in the molecule, and a (meth)acryloyl group, etc., are polymerizable vinyl A flame-retardant photosensitive resin composition for FPC comprising a photopolymerizable compound having an unsaturated bond, (c) a photopolymerization initiator, (d) a blocked isocyanate compound, and (e) a phosphorus compound having a phosphorus atom in the molecule.

Prior art literature Patent literature

Patent Document 1: JP 62-263692 A

Patent Document 2: Japanese Patent Laid-Open No. 63-110224

Patent Document 3: JP 2007-10794 A

As mentioned above, in the manufacturing step of the flexible printed wiring board, there is a problem that a mixed process of the cover film bonding step and the solder resist forming step has to be used, which is costly and poor in workability.

In contrast to this, although it is considered that the insulating film as a solder resist or the insulating film as a cover film is suitable for both the solder resist and cover film of a flexible printed wiring board, a material that satisfies both requirements has not yet been put into practical use. . In particular, since the durability against folding is one of the most important characteristics in the flexible printed wiring board, it is sought to realize a solder resist and cover film applicable to flexible printed wiring boards and excellent durability against folding material.

In addition, conventional photosensitive resin compositions have been combined with (meth)acrylate monomers in order to adjust the viscosity, improve the physical properties of the cured coating film, and increase the sensitivity. The (meth)acrylate monomer is relatively flammable and impairs the flame retardancy of the photosensitive resin composition. Therefore, in order to compensate, a large amount of flame retardants such as phosphorus-containing compounds must be blended. However, when the photosensitive resin composition is mixed with a flame retardant such as a phosphorous compound, the bending resistance may deteriorate, and the cured coating film may easily crack during the cutting process of the wiring board or the heat shock test. .

In addition, from the viewpoint of workability improvement, it is pursued to form such an insulating film in a form of a dry film that is suitable for continuous steps and does not require solvent drying.

Therefore, the object of the present invention is to provide a dry film excellent in folding resistance, and to provide a flexible printed wiring board having the cured product as a protective film, such as a cover film or a solder resist.

More specifically, the object of the present invention is to provide a dry film that satisfies the required performance as an insulating film of a flexible printed wiring board and can form a structure suitable for the one-time forming process of the folded part and the mounting part. The cured product serves as a protective film, for example, a flexible printed wiring board of a cover film or a solder resist.

In addition, the object of the present invention is to provide a dry film that can form a photosensitive structure with excellent flame retardancy and folding resistance of the cured product, and to provide a cured product having the cured product as a protective film, such as a cover film or a solder resist. Flexible printed wiring board.

For the purpose of one-time formation of the folded part and the mounting part by alkali development, even if alkali-soluble groups are introduced into the polyimide used in the conventional cover film, development residues are generated due to poor developability, making it difficult to develop in a short time. In addition, since the softening point of polyimide is too high, there is a problem with the lamination when it is made into a dry film.

As a result of diligent review, the inventors found that a dry film having an adhesive surface for bonding with the object to be protected and a protective surface located on the opposite side of the adhesive surface has heat resistance and folding resistance due to the protective surface. The imide structure with excellent performance and flame retardancy can meet the required properties as an insulating film. Since the adhesiveness is the priority on the adhesive side, a dry film without the imide structure can be made to solve the above-mentioned problems. invention.

In addition, the inventors of the present invention have a dry film having an adhesive surface for bonding to the object to be protected and a protective surface on the opposite side of the adhesive surface Among them, the results of the review for the purpose of having both flame retardancy and folding resistance showed that when both the protective surface and the adhesive surface do not contain flame retardants, the folding resistance can be obtained but the flame resistance cannot be obtained, and protection When the flame retardant is provided on the surface side, flame retardancy can be obtained, but the folding resistance is insufficient. Therefore, it is possible to solve the above-mentioned problems by forming a dry film of the assembled flame retardant only on the protective surface side without the flame retardant and to complete the present invention.

That is, the first dry film of the present invention is a dry film having an adhesive surface (a1) for bonding with the object to be protected and a protective surface (b1) on the opposite side of the adhesive surface, and is characterized by the ATR method (total reflection method) In the infrared absorption spectrum obtained by FT-IR (Fourier Transform Infrared Spectrophotometer), the bonding surface (a1) does not have a peak derived from imidine, and the protective surface (b1) has a peak derived from imidine, and It is alkali-soluble.

In the first dry film of the present invention, in the infrared absorption spectrum, the adhesive surface (a1) preferably has a peak derived from acrylic acid.

In the first dry film of the present invention, in the infrared absorption spectrum, the adhesive surface (a1) preferably has a peak derived from the flame retardant, and the protective surface (b1) does not have a peak derived from the flame retardant.

In addition, the first dry film of the present invention has an adhesive layer (A1) having the adhesive surface (a1) and a protective layer (B1) having the protective surface (b1), and the adhesive layer (A1) is made of an alkali-developing resin Preferably, the protective layer (B1) is composed of a resin composition containing an alkali-soluble resin having an amide ring or a skeleton of an amide precursor.

In addition, the second dry film of the present invention has an adhesive surface (a2) for bonding to the object to be protected and a protective layer located on the opposite side of the adhesive surface. The photosensitive dry film on the surface (b2) is characterized by the infrared absorption spectrum obtained by the FT-IR (Fourier transform infrared spectrophotometer) of the ATR method (total reflection method). As for the peak of the agent, the protective surface (b2) does not have a peak derived from the flame retardant.

In the second dry film of the present invention, in the infrared absorption spectrum, the adhesive surface (a2) preferably has a peak derived from acrylic acid.

In the second dry film of the present invention, in the infrared absorption spectrum, it is preferable that the adhesive surface (a2) does not have a peak derived from amide and the protective surface (b2) has a peak derived from amide.

The second dry film of the present invention has an adhesive layer (A2) with the aforementioned adhesive surface (a2) and a protective layer (B2) with the aforementioned protective surface (b2), the adhesive layer (A2) contains a flame retardant, the aforementioned protective layer (B2) It is better not to contain flame retardant. In the second dry film of the present invention, the adhesive layer (A2) is composed of an alkali-developable resin composition, and the protective layer (B2) is composed of an alkali-soluble skeleton having an amide ring or a precursor of amide The resin composition of the resin is preferable.

In the dry film of the present invention, it is preferable that the aforementioned crest derived from the imine is the crest observed in the range of 1785 to 1765 cm ^-1 . In the dry film of the present invention, the aforementioned wave peak derived from acrylic acid is preferably the wave peak observed in the range of 1420 to 1400 cm ^-1 .

In the dry film of the present invention, the peaks derived from the flame retardant in the infrared absorption spectrum of the adhesive surface (a) are between 3630~3605cm ^-1 , 3535~3510cm ^-1 , 3450~3425cm ^-1 , 3380~3355cm ^-1 It is better to observe the crest in any range.

The dry film of the present invention can preferably be patterned by light irradiation. The dry film of the present invention can be applied to at least any one of the bent portion and the non-bent portion of a flexible printed wiring board, and specifically can be used in at least any of the cover film, solder resist and interlayer insulating material of the flexible printed wiring board. 1 purpose.

In addition, the dry film of the present invention is preferably formed by supporting or protecting at least one side of the adhesive surface and the protective surface with a film.

Furthermore, the flexible printed wiring board of the present invention is characterized by laminating the above-mentioned dry film of the present invention on a flexible printed wiring substrate, and patterning by light irradiation, and forming the pattern at a time with a developer. Into the insulating film. In addition, in the present invention, "pattern" refers to a pattern-like cured product, that is, an insulating film.

According to the present invention, a dry film and a flexible printed wiring board having excellent folding resistance can be realized.

a1‧‧‧Next

b1‧‧‧Protection surface

A1‧‧‧Next layer

B1‧‧‧Protection layer

a2‧‧‧Next

b2‧‧‧Protection surface

A2‧‧‧Next layer

B2‧‧‧Protection layer

1.‧‧Flexible printed wiring board

2‧‧‧Conductor circuit

3‧‧‧Resin layer

4‧‧‧Resin layer

5‧‧‧Mask

[Fig. 1] A schematic diagram of an example of the first dry film of the present invention.

[Fig. 2] A schematic diagram of an example of the second dry film of the present invention.

[Fig. 3] A step diagram schematically showing an example of the manufacturing method of the flexible printed wiring board of the present invention.

[Fig. 4] A schematic diagram showing the steps of another example of the manufacturing method of the flexible printed wiring board of the present invention.

[Figure 5] Adhesive surfaces (a1) of the dry films of Examples 1-1, 1-2 and Comparative Example 1-2 obtained by FT-IR of the ATR method and the protective surfaces of the dry films of Comparative Example 1-2 ( b1) Infrared absorption spectrum.

[Figure 6] Infrared rays of the protective surface (b1) of the dry film of Example 1-1 and Comparative Example 1-1 and the adhesive surface (a1) of the dry film of Comparative Example 1-1 obtained by FT-IR of the ATR method Absorption spectrum.

[Fig. 7] The infrared absorption spectrum of the protective surface (b1) of the dry film of Example 1-2 obtained by FT-IR of the ATR method.

[Fig. 8] Adhesive surface (a2) of the dry film of Example 2-1, Comparative Examples 2-1 to 2-2 obtained by FT-IR of the ATR method, and the protective surface (a2) of the dry film of Comparative Example 2-2 b2) Infrared absorption spectrum.

[Fig. 9] An infrared absorption spectrum of the protective surface (b2) of the dry film of Comparative Example 2-1 obtained by FT-IR of the ATR method.

[Fig. 10] The infrared absorption spectrum of the protective surface (b2) of the dry film of Example 2-1 and Comparative Example 2-3 obtained by FT-IR of the ATR method.

[Fig. 11] An infrared absorption spectrum of the adhesive surface (a2) of the dry film of Comparative Example 2-3 obtained by FT-IR of the ATR method.

The best form of invention

Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings.

(Dry film)

The first dry film of the present invention is a dry film having an adhesive surface (a1) for bonding to a protected object and a protective surface (b1) on the opposite side of the adhesive surface, and is characterized by the ATR method (total reflection method) In the infrared absorption spectrum obtained by FT-IR (Fourier Transform Infrared Spectrophotometer), the bonding surface (a1) does not have a peak derived from imidine, and the protective surface (b1) has a peak derived from imidine, and It is the alkali solubility point. Although polyimide has excellent folding resistance but high softening point, the dry film containing polyimide is the one with poor lamination, but the detailed mechanism is not clear. The dry film of the present invention not only does not contain imine on the adjoining side The laminate is improved, and the adhesive side does not contain imine, and the folding resistance is also excellent.

In the first dry film of the present invention, in the infrared absorption spectrum, it is preferable that the adhesive surface (a1) has a peak derived from acrylic that is matched to improve developability and photoreactivity. By containing the (meth)acrylate monomer on the adhesive surface side, the photocurability is improved and it becomes easy to form a high-definition pattern.

Furthermore, in the first dry film of the present invention, in the infrared absorption spectrum, the adhesive surface (a1) has a peak derived from the flame retardant, and the protective surface (b1) preferably does not have a peak derived from the flame retardant. When the flame retardant is contained on the adhesive surface side but not on the protective surface side, the flexibility and flame retardancy of the cured coating film are improved.

In the first dry film of the present invention, the infrared absorption spectroscopy of the ATR method of FT-IR can be used to determine the aforementioned peak derived from imine, but there is no particular limitation, and a conventional method can be used.

The second dry film of the present invention is used for attaching objects The photosensitive dry film of the adhesive surface (a2) and the protective surface (b2) located on the opposite side of the adhesive surface, characterized by FT-IR (Fourier Transform Infrared Spectroscopy) obtained by the ATR method (total reflection method) In the infrared absorption spectrum of, the adhesive surface (a2) has a peak derived from the flame retardant, and the protective surface (b2) does not have a peak derived from the flame retardant.

In the second dry film of the present invention, it is preferable that the protective surface (b2) has a peak derived from imine in the infrared absorption spectrum. Since the protective surface contains an imide structure, a flame-retardant, tough and non-cracking coating film can be formed, and the required performance as an insulating film of a flexible printed wiring board is also improved.

In addition, in the second dry film of the present invention, it is preferable that, in the infrared absorption spectrum, the adhesive surface (a2) has a peak derived from acrylic that is matched to improve developability and photoreactivity. By containing the (meth)acrylate monomer on the adhesive surface side, the photocurability is improved and it becomes easy to form a high-definition pattern. On the other hand, the aforementioned protective surface (b2) may or may not have a peak derived from acrylic acid. However, because the (meth)acrylate monomer is flammable, the aforementioned protective surface (b2) does not have The crest from acrylic is better.

In the second dry film of the present invention, the above-mentioned peak derived from the flame retardant can be determined by infrared absorption spectrometry by the ATR method of FT-IR, but there is no particular limitation, and a conventional method can be used.

The dry film of the present invention, the peak from (PEI), although appearing in ^{1785 ~ 1765cm -1, 1735 ~ 1705cm} -1, 1400, the range of ~ 1360cm ^-1 740 ~ 720cm ^-1's, but in 1785 ~ 1765cm ^- The crest of ^{1 is} the easiest to observe. Although the acid peak from appearing in the range ^{1650 ~ 1610cm -1, 1420 ~ 1400cm} -1, 825 ~ 795cm -1 , the peak but to 1420 ~ 1400cm ^-1 most easily observed. The aforementioned wave peak from the flame retardant is the wave peak from the conventional flame retardant, and there is no particular limitation, for example, the ranges of 3630~3605cm ^-1 , 3535~3510cm ^-1 , 3450~3425cm ^-1 , 3380~3355cm ^-1 A peculiar wave crest was observed.

The first dry film of the present invention, such as shown in FIG. 1, can be formed by laminating the adhesive layer (A1) with the aforementioned adhesive surface (a1) and the protective layer (B1) with the aforementioned protective surface (b1) . The second dry film of the present invention, as shown in FIG. 2, can be formed by laminating the aforementioned adhesive layer (A2) with the adhesive surface (a2) and the aforementioned protective layer (B2) with the protective surface (b2) . In addition, when the thickness of the dry film is thin or the interface between layers is blurred, it is difficult to determine the appearance of the adhesive layer and the protective layer. However, the layer can be distinguished by analyzing the adhesive surface and protective surface of the dry film by FT-IR of the ATR method. Combination structure.

The adhesive layer (A1) with the aforementioned adhesive surface (a1) and the protective layer (B1) with the aforementioned protective surface (b1) of the first dry film of the present invention will be described in detail below.

(Protection layer (B1))

The protective layer (B1) can be formed using a resin composition containing an alkali-soluble resin having an amide ring or a skeleton of an amide precursor. For example, a carboxyl group-containing resin or a carboxyl group-containing photosensitive resin containing an amide ring or a amide precursor skeleton, a compound having an ethylenically unsaturated bond, a photopolymerization initiator, and a photocuring property of a thermoreactive compound can be used Thermosetting resin composition.

(Alkali-soluble resin with amide ring or skeleton of amide precursor)

The aforementioned alkali-soluble resin having an amide ring or an amide precursor skeleton has one or more alkali soluble groups among a phenolic hydroxyl group or a carboxyl group, and an amide ring or an amide precursor skeleton. A conventional method can be used to introduce the amide ring or the amide precursor skeleton into the alkali-soluble resin. For example, a resin obtained by reacting a carboxylic anhydride component with an amine component and/or an isocyanate component. The imidization can be carried out by thermal imidization or chemical imidization, or they can be used in combination.

Here, as the carboxylic anhydride component, for example, tetracarboxylic acid anhydride or tricarboxylic acid anhydride, etc., but not limited to these acid anhydrides, is a compound having an acid anhydride group and a carboxyl group that react with an amino group or an isocyanate group, including derivatives thereof use. Moreover, these carboxylic anhydride components can be used individually or in combination.

Although the amine component can use diamines such as aliphatic diamines or aromatic diamines, polyvalent amines such as aliphatic polyether amines, diamines with carboxylic acids, diamines with phenolic hydroxyl groups, etc., but it is not limited to these And other amines. In addition, these amine components can be used alone or in combination.

As the isocyanate component, diisocyanates such as aromatic diisocyanates and their isomers or polymers, aliphatic diisocyanates, alicyclic diisocyanates and their isomers, or other widely used diisocyanates can be used, But it is not limited to these isocyanates. Moreover, these isocyanate components can be used individually or in combination.

The alkali-soluble resin having an amide ring or a skeleton of an amide precursor described above may have an amide bond. This can be isocyanate and carboxyl Amine bond obtained by acid reaction, or obtained by other reactions. Furthermore, it may have a bond constituted by other addition and condensation.

In the synthesis of such an alkali-soluble resin having an alkali-soluble group and an amide ring or an amide precursor skeleton, a conventionally used organic solvent can be used. The organic solvent does not react with the raw materials carboxylic anhydrides, amines, and isocyanates, and there is no problem in dissolving these raw materials. In particular, the structure is not limited. In particular, from the viewpoint of the high solubility of raw materials, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethylsulfide, γ -Aprotic solvents such as butyrolactone are preferred.

The alkali-soluble resin described above with one or more alkali-soluble groups among phenolic hydroxyl groups or carboxyl groups and an amide ring or amide precursor skeleton, in order to correspond to the photolithography step, its acid value is 20~ 200mgKOH/g is better, more preferably 60~150mgKOH/g. When the acid value is 20 mgKOH/g or more, the solubility to alkalis increases and the developability becomes better. Furthermore, the degree of crosslinking with the thermosetting component after light irradiation becomes high, and sufficient image development contrast can be obtained. In addition, when the acid value is 200 mgKOH/g or less, the so-called thermal fog in the PEB (POST EXPOSURE BAKE) step after light irradiation described later can be suppressed, and the process width can be increased.

In addition, the molecular weight of the alkali-soluble resin considers developability and cured coating film properties, and the mass average molecular weight is preferably 1,000 to 100,000, and more preferably 2,000 to 50,000. When the molecular weight is above 1,000, sufficient development resistance and hardened physical properties can be obtained after exposure to PEB. In addition, when the molecular weight is 100,000 or less, alkali solubility increases and developability improves.

(Thermally reactive compound)

As the heat-reactive compound, a conventionally used compound having a functional group such as a cyclic (thio) ether group that can undergo a curing reaction upon heat can be used. It is particularly suitable to use a bifunctional epoxy resin having two epoxy groups in the molecule, a multifunctional epoxy resin having a plurality of epoxy groups in the molecule, and the like.

(Photopolymerization initiator)

As the photopolymerization initiator, those conventionally used can be used. In particular, when used in the PEB step after light irradiation described later, a photopolymerization initiator that also has a function as a photobase generator is preferable. In addition, in this PEB step, a photopolymerization initiator and a photobase generator can be used in combination.

A photopolymerization initiator that also has a function as a photobase generator. The molecular structure changes due to light irradiation such as ultraviolet rays or visible light, or molecular cleavage produces one or more types of thermal reactivity as described below The compound of the basic substance that is the catalyst of the polymerization reaction of the compound. Examples of basic substances include secondary amines and tertiary amines.

Such photopolymerization initiators that also function as photobase generators include, for example, α-aminoacetophenone compounds, oxime ester compounds, or having an oxyimino group and N-methylated aromatic Compounds with substituents such as amine groups, N-acylated aromatic amine groups, nitrobenzyl carbamate groups, and alkoxybenzyl carbamate groups. Among them, oxime ester compounds and α-aminoacetophenone compounds are preferred, and oxime ester compounds are more preferred. The α-aminoacetophenone compound is particularly preferably one having two or more nitrogen atoms.

α-Aminoacetophenone compound has benzoin ether in the molecule It is sufficient if the bond is exposed to light to cause cracks in the molecule to produce a basic substance (amine) that functions as a hardening catalyst.

As the oxime ester compound, a compound that generates a basic substance upon light irradiation can be used.

Such a photopolymerization initiator can be used singly or in combination of two or more kinds. The blending amount of the photopolymerization initiator in the resin composition is preferably 0.1-40 parts by mass relative to 100 parts by mass of the alkali-soluble resin, more preferably 0.1-30 parts by mass. When it is 0.1 parts by mass or more, a good comparison of development resistance between the light-irradiated part and the unirradiated part can be obtained. In addition, when it is 40 parts by mass or less, the properties of the cured product are improved.

(Next layer (A1))

The subsequent layer (A1) can be formed using an alkali developable resin composition. The aforementioned alkali-developable resin composition can be a resin composition that contains at least one functional group of phenolic hydroxyl and carboxyl groups and can be developed by an alkali solution. A photocurable resin composition or a thermosetting resin composition can be used. Resin composition. Preferably, for example, a resin composition containing a compound having two or more phenolic hydroxyl groups, a carboxyl group-containing resin, and a compound having a phenolic hydroxyl group and a carboxyl group, and conventionally used ones can be used.

Specifically, for example, a photocurable thermosetting resin containing a carboxyl group-containing resin or a carboxyl group-containing photosensitive resin, a compound having an ethylenically unsaturated bond, a photopolymerization initiator, and a thermoreactive compound used as a solder resist composition in the past Composition. In addition, resins containing carboxyl-containing urethane resins, carboxyl-containing resins, photobase generators, and thermosetting components can also be used Lipid composition. Here, as for the carboxyl group-containing resin or the carboxyl group-containing photosensitive resin, the compound having an ethylenically unsaturated bond, the photopolymerization initiator, and the photobase generator, conventionally used compounds can be used, and as the heat-reactive compound, A conventionally used compound having a functional group such as a cyclic (thio) ether group that can undergo a curing reaction by heat is used.

The subsequent layer (A1) preferably contains a (meth)acrylate monomer. As the (meth)acrylate monomer, conventional ones can be used.

The subsequent layer (A1) preferably contains a flame retardant. As the flame retardant, the conventional flame retardant can be used. The conventional flame retardant is the same as the adhesive layer (A2) described later.

The resin composition used in the adhesive layer (A1) and the resin protective layer (B1) described above may be combined with the following components as necessary.

(Polymer resin)

The polymer resin aims at improving the flexibility and dryness to the touch of the obtained cured product, and can be used with conventional users. Examples of such polymer resins include cellulose, polyester, phenoxy resin polymer, polyvinyl acetal, polyvinyl butyral, polyamide, polyamide, etc. Amine-based adhesive polymers, block copolymers, elastomers, etc. The polymer resin may be used alone or in combination of two or more types.

(Inorganic filler)

Inorganic filler can inhibit the hardening shrinkage of the hardened material and improve adhesion It is matched with the characteristics of sex and hardness. As such inorganic fillers, for example, barium sulfate, amorphous silica, fused silica, spherical silica, talc, clay, magnesium carbonate, calcium carbonate, alumina, aluminum hydroxide, nitriding Silicon, aluminum nitride, boron nitride, Neuburg Siliceous Earth, etc.

(Colorant)

The coloring agent can be matched with conventional coloring agents such as red, blue, green, yellow, white, and black, and can be any of pigments, dyes, and pigments.

(Organic solvents)

The organic solvent can be matched to prepare the resin composition or adjust the viscosity of the substrate or carrier film. Examples of such organic solvents include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, and petroleum solvents. Such an organic solvent can be used alone or in a mixture of two or more.

(Compounds with ethylenically unsaturated bonds)

As for the compound having an ethylenically unsaturated bond, conventional monofunctional, bifunctional, and polyfunctional compounds can be used.

(Other ingredients)

If necessary, it can be combined with sulfhydryl compounds, adhesion promoters, antioxidants, ultraviolet absorbers and other ingredients. For this, you can use familiarity User. In addition, it can be used with conventionally used tackifiers such as micronized silica, magnesia, organic bentonite, montmorillonite, silicone-based, fluorine-based, polymer-based defoamers and/or flat Conventional additives such as chemical agents, silane coupling agents, rust inhibitors, etc.

In addition, the protective layer (B1) preferably contains substantially no flame retardant described later from the viewpoint of the flexibility of the cured coating film.

In the dry film of the present invention, the adhesive layer (A1) is preferably thicker than the protective layer (B1) from the viewpoint of followability to copper circuits.

The following describes the aforementioned adhesive layer (A2) with the adhesive surface (a2) and the aforementioned protective layer (B2) with the protective surface (b2) of the second dry film of the present invention.

(Protection layer (B2))

The protective layer (B2) is a composition that does not substantially contain a flame retardant, and is not particularly limited. For example, it is possible to use alkali-soluble resins, compounds having ethylenically unsaturated bonds, and photopolymerization agents that have been conventionally used as solder resist compositions. A photocurable thermosetting resin composition of an initiator and a thermoreactive compound. In this specification, "substantially free" means that the constituent components are not actively matched, but it does not exclude that a small amount is contained within a range that does not impair the effects of the present invention. For example, in the resin composition, it is preferably 5% by mass or less, more preferably 3% by mass or less.

As the alkali-soluble resin, conventionally used ones can be used, for example, an alkali-soluble resin that contains one or more functional groups of a phenolic hydroxyl group or a carboxyl group and can be developed in an alkali solution. Among them, a compound having two or more phenolic hydroxyl groups, a carboxyl group-containing resin, and a compound having a phenolic hydroxyl group and a carboxyl group are good.

As mentioned above, for the alkali-soluble resin, conventionally used ones can be used, but it is preferable to use alkali-soluble resins having better properties such as bending resistance and heat resistance having an amide ring or a skeleton of an amide precursor.

(Alkali-soluble resin with amide ring or skeleton of amide precursor)

The aforementioned alkali-soluble resin having an amide ring or a skeleton of an amide precursor is the same as the above-mentioned protective layer (B1).

(Compounds with ethylenically unsaturated bonds)

Regarding the compound having an ethylenically unsaturated bond, the same as the protective layer (B1) described above, and conventional monofunctional, bifunctional, and multifunctional compounds can be used.

(Thermally reactive compound)

The thermally reactive compound is the same as the above-mentioned protective layer (B1).

(Photopolymerization initiator)

The photopolymerization initiator is the same as the above protective layer (B1).

(Next layer (A2))

The subsequent layer (A2) can be formed using an alkali-developing resin composition. The aforementioned alkali-developable resin composition may be a composition containing a resin that contains at least one functional group of a phenolic hydroxyl group and a carboxyl group and can be developed in an alkali solution. A photocurable resin composition or a thermosetting resin can be used. Composition. Better For example, a resin composition containing a compound having two or more phenolic hydroxyl groups, a carboxyl group-containing resin, and a compound having a phenolic hydroxyl group and a carboxyl group can be mentioned, and conventional ones can be used.

Specifically, for example, a photocurable thermosetting resin containing a carboxyl group-containing resin or a carboxyl group-containing photosensitive resin used as a solder resist composition, a compound having an ethylenically unsaturated bond, a photopolymerization initiator, and a thermoreactive compound Composition. In addition, a resin composition containing a carboxyl group-containing urethane resin, a resin having a carboxyl group, a photobase generator, and a thermosetting component can also be used. Here, as for the carboxyl group-containing resin or the carboxyl group-containing photosensitive resin, the compound having an ethylenically unsaturated bond, the photopolymerization initiator, and the photobase generator, conventionally used compounds can be used, and as the heat-reactive compound, A conventionally used compound having a functional group such as a cyclic (thio) ether group that can undergo a curing reaction by heat is used.

The subsequent layer (A2) preferably contains (meth)acrylate monomers. The (meth)acrylate monomer is the same as the above-mentioned adhesive layer (A1), and conventional ones can be used.

The subsequent layer (A2) contains a flame retardant. Regarding flame retardants, conventional flame retardants can be used. The conventionally used flame retardants include, for example, phosphoric acid esters and condensed phosphoric acid esters, phosphorus-containing (meth)acrylates, phosphorus-containing compounds with phenolic hydroxyl groups, cyclic phosphazene compounds, azo oligomers, and secondary Phosphorus compounds such as phosphonic acid metal salts, antimony compounds such as antimony trioxide and antimony pentoxide, halogen compounds such as pentabromodiphenyl ether, octabromodiphenyl ether, and metals such as aluminum hydroxide and magnesium hydroxide Layered double hydroxides such as hydroxides, magnesia and magnesia-like compounds.

The resin composition used in the adhesive layer (A2) and the protective layer (B2) described above is the same as the above-mentioned adhesive layer (A1) and protective layer (B1). Polymer resin, inorganic filler, colorant, Organic solvents. In addition, similar to the above-mentioned adhesive layer (A1) and protective layer (B1), if necessary, components such as mercapto compounds, adhesion promoters, antioxidants, and ultraviolet absorbers can be further combined. For this, you can use the familiar ones. In addition, it can be used with conventionally used tackifiers such as micronized silica, magnesia, organic bentonite, montmorillonite, silicone-based, fluorine-based, polymer-based defoamers and/or flat Conventional additives such as chemical agents, silane coupling agents, rust inhibitors, etc.

In the second dry film of the present invention, the adhesive layer (A2) is preferably thicker than the protective layer (B2) from the viewpoint of followability to copper circuits.

The dry film of the present invention can be used for at least one of the curved portion and the non-curved portion of a flexible printed wiring board, and preferably used for both. By this, the cost and the workability are improved while obtaining a double folding Flexible printed wiring board with sufficient durability. Specifically, the dry film of the present invention can be used for at least any one of cover films, solder resists, and interlayer insulating materials for flexible printed wiring boards.

The dry film of the present invention can be supported or protected by a film on at least one side. For the manufacture of dry film, for example, the resin composition constituting the protective layer (B1) or (B2) (hereinafter, collectively referred to as "protective layer B") is diluted with an organic solvent and adjusted to a proper viscosity. The carrier film is coated with a uniform thickness. The coating layer is dried to form a protective layer on the carrier film. Similarly, on the protective layer to form an adhesive layer (A1) or The resin of (A2) (hereinafter, collectively referred to as "adhesive layer A") forms the adhesive layer (A) to obtain the dry film of the present invention. From the viewpoint of the strength of the coating film, the interface between the layers can also be blurred. After the dry film is formed on the carrier film, a peelable cover film may be laminated on the surface of the dry film. Furthermore, after forming a dry film on the cover film, a peelable carrier film may be laminated on the surface of the dry film.

The coating method of the resin composition may be a conventional method such as a knife coating method, a lip coating method, a chipping wheel coating method, and a film coating method. In addition, the drying method can be a hot air circulation type drying oven, IR furnace, heating plate, convection oven, etc., which are equipped with a steam heating method, a method of contacting the hot air in the dryer in countercurrent, and a method of blowing the support with a nozzle And other known methods. As the carrier film, thermoplastic films such as polyester films with a thickness of 2 to 150 μm can be used. Although polyethylene film, polypropylene film, etc. can be used as the cover film, it is preferable that the adhesion to the dry coating film is smaller than that of the carrier film.

(Method of manufacturing wiring board)

In the present invention, by laminating the dry film of the present invention on a flexible printed wiring board and patterning by light irradiation, the pattern is formed at one time with a developer to form an insulating film, and a flexible printed wiring board can be obtained. According to the first dry film of the present invention, by using the dry film in the infrared absorption spectrum, the adhesive surface (a1) does not have a peak derived from imidine and the protective surface (b1) has a peak derived from imidine It can provide an insulating film for a flexible printed wiring board that satisfies the required performance as an insulating film for a flexible printed wiring board and is suitable for the primary forming process of the folded part and the mounting part. Also, according to this Ming’s second dry film is provided by using a dry film in which the adhesive surface (a2) has a peak derived from the flame retardant and the protective surface (b2) does not have a peak derived from the flame retardant in the infrared absorption spectrum. Insulating film for flexible printed wiring boards with excellent flame retardancy and folding resistance.

The following is an example of a method for manufacturing a flexible printed wiring board using the dry film of the present invention. The protective layer (B) is made of a photosensitive thermosetting resin containing an alkali-soluble resin, a photopolymerization initiator, and a thermoreactive compound. When the adhesive layer (A) is composed of an alkali-developable resin composition containing an alkali-soluble resin and a heat-reactive compound and not containing a photopolymerization initiator, it is the flow of the step diagram of FIG. 2. That is, it includes a step of laminating the dry film of the present invention on a flexible wiring substrate formed with a conductor circuit and forming a layer (laminating step), a step of irradiating the pattern of the layer with active energy rays (exposing step), and using A manufacturing method of the step of forming a patterned layer (development step) at one time after alkali development of the layer. In addition, if necessary, after alkali development, photocuring or thermal curing (post-curing step) is performed to completely cure the patterned layer, and a highly reliable flexible printed wiring board can be obtained.

In addition, when a photopolymerization initiator having a function as a photobase generator is used in the protective layer (B), or a photopolymerization initiator and a photobase generator are used in combination, follow the flow shown in the step diagram of FIG. 3, It can also manufacture flexible printed wiring boards. That is, it includes the step of laminating the dry film of the present invention on a flexible wiring substrate formed with a conductive circuit and forming a layer (laminating step), a step of irradiating the pattern of the layer with active energy rays (exposing step), and heating the Layer step (heating (PEB) step), and after alkali development of the layer A manufacturing method for the step of forming a patterned layer (development step). In addition, if necessary, photo-curing or thermal curing (post-curing step) is performed after alkali development to completely cure the patterned layer, and a highly reliable flexible printed wiring board can be obtained. In particular, when the protective layer (B) uses an alkali-soluble resin containing an amide ring or a skeleton of an amide precursor, it is better to use the process shown in the step diagram of FIG. 3.

The steps shown in FIG. 3 or FIG. 4 are described in detail below.

[Laminating Step]

In this step, by laminating the dry film of the present invention on the flexible printed wiring board 1 on which the conductor circuit 2 is formed, a resin composed of an alkali-developable resin composition containing alkali-soluble resin or the like is formed Layer 3 (adhesive layer (A)) and resin layer 4 (protective layer (B)) composed of photosensitive thermosetting resin composition such as alkali-containing soluble resin on resin layer 3 body.

[Exposure Step]

In this step, the photopolymerization initiator contained in the resin layer 4 is activated into a negative pattern by irradiation of active energy rays, and then the exposed portion is cured. Exposure machine can use direct drawing device, exposure machine equipped with metal halide lamp, etc. The mask for patterned exposure is a negative mask.

Regarding the active energy rays used for exposure, it is better to use laser light or scattered light with a maximum wavelength in the range of 350 to 450 nm. When the maximum wavelength is in this range, the photopolymerization initiator can be efficiently activated. In addition, although the amount of exposure varies depending on the film thickness, etc., it can usually be 100 to 1500 mJ/cm ² .

[PEB step]

In this step, the resin layer is heated after exposure to harden the exposed part. After this step, it is produced by the exposure step using a photopolymerization initiator having the function of a photobase generator, or a protective layer (B) composed of a combination of a photopolymerization initiator and a photobase generator The alkali can harden the protective layer (B) to the deep part. The heating temperature is, for example, 80 to 140°C. The heating time is, for example, 10 to 100 minutes. The curing of the PEB step is, for example, a ring-opening reaction of the epoxy resin caused by a thermal reaction, so it can suppress distortion or curing shrinkage compared with the curing by a light radical reaction.

[Development step]

In this step, after removing the unexposed parts by alkali development, a negative pattern-like insulating film, especially a cover film and a solder resist are formed. The development method can be performed by conventional methods such as immersion. In addition, as the developer, sodium carbonate, potassium carbonate, potassium hydroxide, amines, imidazoles such as 2-methylimidazole, alkali aqueous solutions such as tetramethylammonium hydroxide aqueous solution (TMAH), or a mixture of these can be used.

[Post curing step]

In addition, the insulating film may be further irradiated with light after the development step. Moreover, it can heat at 150 degreeC or more, for example.

Example

Hereinafter, the present invention will be described in detail with examples.

[Example 1] <Synthesis of Alkali Soluble Resin with Imidine Ring>

Add 12.2g of 3,5-diaminobenzoic acid and 2,2'-bis[4-(4-amine) to a detachable 3-necked flask equipped with a stirrer, nitrogen introduction tube, fractionating ring and cooling ring. (Phenoxy)phenyl)propane 8.2g, N-methyl-2-pyrrolidone (NMP) 30g, γ-butyrolactone 30g, 4,4'-oxydiphthalic anhydride 27.9g, trimellitic anhydride 3.8g , Stir for 4 hours at room temperature and 100 rpm in a nitrogen environment. Next, 20 g of toluene was added, and stirring was performed for 4 hours while distilling off toluene and water at a silicon bath temperature of 180°C and 150 rpm to obtain an alkali-soluble resin solution having an imine ring. After that, γ-butyrolactone was added until the solid content became 30% by mass. The obtained resin solution had a solid acid value of 86 mgKOH/g and a Mw of 10,000.

<Adjustment of a resin composition (α1-1) that does not have a peak derived from amide>

After mixing the following ingredients and pre-mixing with a mixer, they are kneaded and prepared with a 3-roll roller mill.

<Adjustment of a resin composition ( β 1-1) having a peak derived from imidine>

After mixing the following ingredients and pre-mixing with a mixer, they are kneaded and prepared with a 3-roll roller mill.

<Adjustment of a resin composition ( β 1-2) having a peak derived from imidine>

After mixing the following ingredients and pre-mixing with a mixer, they are kneaded and prepared with a 3-roll roller mill.

<Production of Dry Film>

On the carrier film, the resin composition constituting the protective layer shown in Table 1 was coated so that the film thickness after drying was 10 μm . After that, it was dried at 90°C/30 minutes in a hot-air circulation type drying oven to form a protective layer (B1). On the surface of the protective layer (B1), the resin composition constituting the adhesive layer shown in Table 1 was applied so that the film thickness after drying became 25 μm . After that, it was dried at 90° C./30 minutes in a hot-air circulation type drying furnace to form an adhesive layer (A1) to produce a dry film.

<Infrared absorption spectrum measurement by FT-IR ATR method>

The FT-IR measurement of the dry film obtained above was performed using Spectrum 100 manufactured by PerkinElmer. The measurement is performed by directly contacting the surface of the dry film to be measured on the Dura Sample IRII of the ATR measurement unit Dura Sample IRII, and incident infrared light.

<Judgment of the presence or absence of peaks from imidine>

In the infrared absorption spectrum obtained above, those with a peak in the range of 1785 to 1765 cm ^-1 were evaluated as "○", and those without a peak were evaluated as "×".

<Judgment of the presence or absence of acrylic peaks>

In the infrared absorption spectrum obtained above, those with a peak in the range of 1420 to 1400 cm ^-1 were evaluated as "○", and those without a peak were evaluated as "×".

<Alkali developability (patterning) and foldability evaluation>

The dry film obtained above was laminated on a flexible printed wiring board at 60°C using a vacuum laminator, and then used HMW680GW (metal halide lamp, scattered light) manufactured by ORC, with an exposure amount of 500mJ/cm ² against the negative type The pattern is illuminated by light. Next, heat treatment was performed at 90°C for 60 minutes. After that, the substrate was immersed in an aqueous solution of sodium carbonate at 30°C and 1% by mass, and then developed for 3 minutes, and the alkali developability was evaluated.

Next, use a hot air circulation type drying oven to perform 150°C /60 minutes heat treatment to obtain an evaluation substrate with a patterned cured coating film. Use the obtained evaluation substrate to bend, and record the number of times before the cured coating film cracks. It was evaluated as ○ when it was folded 3 or more times, and it was evaluated as × when the number of folding was 2 or less.

<Laminating Evaluation>

The dry film obtained above was vacuum-laminated under the following conditions using a film transport pressure vacuum laminator (CPV-300) manufactured by Nichigo Morton Co., with the adhesive surface (b) of the dry film in contact with the copper-clad laminate. To confirm whether there is a gap. The results obtained are shown in Table 1 below.

Laminating temperature: 60℃

Vacuum degree: 4hPa

Vacuum time: 30 seconds

Laminating pressure: 0.3MPa

Laminating press time: 25 seconds

<Evaluation of Soldering Heat Resistance>

The evaluation substrate obtained above was coated with a rosin-based flux, and immersed in a soldering tank preset at 260°C for 20 seconds (10 seconds × 2 times) to evaluate the expansion and peeling of the cured coating film. The criterion is as follows. The results obtained are shown in Table 1 below.

◎: There is no swelling and peeling even after immersion for 10 seconds × 2 times.

○: No expansion and peeling occurred after 10 seconds × 1 immersion, but expansion and peeling occurred after 10 seconds × 2 immersion.

×: 10 seconds × 1 immersion, swelling and peeling occurred.

<Pencil Hardness Evaluation>

With respect to the evaluation substrate obtained above, the pencil hardness of the cured coating film was evaluated in accordance with JIS K5400. The results obtained are shown in Table 1 below.

From the evaluation results shown in Table 1 above, it can be understood that the dry film of the example is excellent in alkali developability, and its cured coating film satisfies the required performance as an insulating film such as solder heat resistance. On the other hand, the dry film of Comparative Example 1-1 in which both the adhesive surface and the protective surface have a peak derived from imidine is one of poor alkali developability. In addition, the dry film of Comparative Example 1-2 in which neither the adhesive surface nor the protective surface had a wave peak derived from imidine was inferior in solder heat resistance and the like.

[Example 2] <Synthesis of Alkali Soluble Resin with Imidine Ring>

As in Example 1, an alkali-soluble resin solution with an imine ring having a solid content of 30% by mass, a solid content of 86 mgKOH/g, and a Mw of 10000 was obtained.

<Adjustment of the resin composition (α2-1) having a peak derived from the flame retardant>

After mixing the following ingredients and pre-mixing with a mixer, they are kneaded and prepared with a 3-roll roller mill.

<Adjustment of the resin composition (α2-2) having a peak derived from the flame retardant>

After mixing the following ingredients and pre-mixing with a mixer, they are kneaded and prepared with a 3-roll roller mill.

<Adjustment of resin composition (β2-1) that does not have a peak derived from flame retardant>

After mixing the following ingredients and pre-mixing with a mixer, they are kneaded and prepared with a 3-roll roller mill.

<Adjustment of a resin composition (β2-2) that does not have a peak derived from a flame retardant>

After mixing the following ingredients and pre-mixing with a mixer, they are kneaded and prepared with a 3-roll roller mill.

<Production of Dry Film>

On the carrier film, the resin composition constituting the protective layer shown in Table 2 was applied so that the film thickness after drying became 10 μm. After that, it was dried at 90°C/30 minutes in a hot-air circulation type drying oven to form a protective layer (B2). The resin composition constituting the adhesive layer shown in Table 2 was applied to the surface of the protective layer (B2) so that the film thickness after drying would be 25 μm. After that, it was dried at 90° C./30 minutes in a hot-air circulation type drying oven to form an adhesive layer (A2) to produce a dry film.

<Infrared absorption spectrum measurement by FT-IR ATR method>

As in Example 1, the FT-IR measurement of the dry film obtained above was performed using Spectrum 100 manufactured by PerkinElmer.

<Judgment of the presence or absence of acrylic peaks>

In the infrared absorption spectrum obtained above, those with a peak in the range of 1420 to 1400 cm ^-1 were evaluated as "○", and those without a peak were evaluated as "×".

<Judgment of the presence or absence of peaks from flame retardants>

In the infrared absorption spectrum obtained above, those with peaks in 3630~3605cm ^-1 , 3535~3510 cm ^-1 , 3450-3425 cm ^-1 , and 3380-3355 cm ^-1 were evaluated as "○", and those without crests were evaluated as "×".

<Flame retardant>

The dry film obtained above was laminated on both sides of a 25 μm-thick polyimide film (manufactured by Du Pont-Toray, Kapton 100H (25 μm)) at 60° C. using a vacuum laminator. A metal halide lamp was used on both sides of the obtained substrate The exposure device (HMW-680-GW20) was irradiated with light at an exposure amount of 500mJ/cm ² and heated at 90°C for 60 minutes. Then a hot air circulating drying furnace was used to heat treat at 150°C/60 minutes to obtain a test piece The flame retardancy test of this test piece is carried out according to the UL94 standard thin material vertical burning test. The evaluation is based on the UR94 standard, which is expressed as "VTM-0" ~ "burning".

<Foldability Evaluation>

In the same manner as in Example 1 above, an evaluation substrate with a patterned cured coating film was obtained. Using the obtained evaluation substrate, bend it and observe it visually and with a ×200 optical microscope, and record the number of times the cured coating film has cracked. It was evaluated as ○ when it was folded three times or more, and it was evaluated as × when the number of folding times was less than 2 times.

From the evaluation results shown in Table 2 above, it can be understood that the protection The cured coating film obtained by the dry film of the example which does not have the peak derived from the flame retardant is excellent in foldability, and the flame retardancy is also VTM-0. On the other hand, the cured product obtained by the dry film of Comparative Example 2-1 in which both of the adhesive surface and the protective surface have peaks derived from the flame retardant has poor foldability. In addition, the cured product obtained by the dry film of Comparative Example 2-2 in which both the adhesive surface and the protective surface have peaks derived from the flame retardant is slightly low in flame resistance and poor in folding resistance. The cured product obtained by the dry film of Comparative Example 2-3 in which neither the adhering surface nor the protective surface has a peak derived from the flame retardant is one of poor flame retardancy.

Claims (16)

A dry film that has an adhesive surface (a1) for bonding with the object to be protected and a protective surface (b1) on the opposite side of the aforementioned adhesive surface. It is characterized by FT-IR (Fourier Transform Infrared In the infrared absorption spectrum obtained by the ATR method (total reflection method) of the spectrum), the bonding surface (a1) does not have a peak derived from imidine, and the protective surface (b1) has a peak derived from imidine, and is alkali Soluble. The dry film according to claim 1, wherein in the infrared absorption spectrum, the adhesive surface (a1) has a peak derived from acrylic acid. The dry film according to claim 1, wherein, in the infrared absorption spectrum, the adhesive surface (a1) has a peak derived from a flame retardant, and the protective surface (b1) does not have a peak derived from a flame retardant. The dry film according to claim 1, wherein the adhesive layer (A1) having the adhesive surface (a1) and the protective layer (B1) having the protective surface (b1) are provided, and the adhesive layer (A1) is developed by alkali The adhesive layer (B1) is composed of a resin composition containing an alkali-soluble resin having an amide ring or a skeleton of an amide precursor. A dry film, which is a photosensitive dry film having an adhesive surface (a2) for bonding an adherend and a protective surface (b2) on the opposite side of the adhesive surface, characterized by the ATR method (total reflection method) In the infrared absorption spectrum obtained by FT-IR (Fourier Transform Infrared Spectroscopy) of ), the adhesive surface (a2) has a peak derived from the flame retardant, and the protective surface (b2) does not have a peak derived from the flame retardant. In addition, the aforementioned adhesive surface (a2) does not have a wave peak derived from amide, and the aforementioned protective surface (b2) has a wave peak derived from amide peak. The dry film according to claim 5, wherein in the infrared absorption spectrum, the adhesive surface (a2) has a peak derived from acrylic acid. The dry film according to claim 5, wherein the adhesive layer (A2) having the adhesive surface (a2) and the protective layer (B2) having the protective surface (b2), and the adhesive layer (A2) contains a flame retardant, The aforementioned protective layer (B2) does not contain a flame retardant. The dry film according to claim 5, wherein the adhesive layer (A2) is composed of an alkali-developable resin composition, and the protective layer (B2) is composed of a skeleton having an amide ring or a precursor of amide It is composed of a resin composition of alkali-soluble resin. The dry film according to claim 1 or 5, wherein the aforementioned wave peak derived from imidine is a wave peak observed in the range of 1785 to 1765 cm ^-1 . The dry film according to claim 2 or 6, wherein the aforementioned wave peak derived from acrylic is a wave peak observed in the range of 1420 to 1400 cm ^-1 . Such as the dry film described in claim 3 or 5, wherein the aforementioned wave peak from the flame retardant is in any range of 3630~3605cm ^-1 , 3535~3510cm ^-1 , 3450~3425cm ^-1 , 3380~3355cm ^-1 Observed. The dry film described in claim 1 or 5 can be patterned by light irradiation. The dry film described in claim 1 or 5 is used for at least any one of the bent portion and the non-curved portion of a flexible printed wiring board. The dry film as described in claim 1 or 5, which is used for at least one of the cover film, solder resist and interlayer insulating material of a flexible printed wiring board use. The dry film described in claim 1 or 5 is constituted by supporting or protecting at least one of the aforementioned adhesive surface and protective surface with a film. A flexible printed wiring board, characterized by: laminating the dry film described in claim 1 or 5 on a flexible printed wiring board, and patterning by light irradiation, and then patterning the pattern once with a developer Insulating film formed.

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