CN106796395B

CN106796395B - Dry film and flexible printed circuit board

Info

Publication number: CN106796395B
Application number: CN201580055821.8A
Authority: CN
Inventors: 宫部英和; 小池直之; 内山强; 笠间美智子
Original assignee: Taiyo Ink Mfg Co Ltd
Current assignee: Taiyo Holdings Co Ltd
Priority date: 2014-10-14
Filing date: 2015-10-13
Publication date: 2020-12-18
Anticipated expiration: 2035-10-13
Also published as: JP2016080803A; KR20170070134A; CN106796395A; KR102408242B1; WO2016060138A1; TW201632988A; TWI696035B

Abstract

A dry film which satisfies the performance required as an insulating film for a flexible printed wiring board and is suitable for a process of simultaneously forming a bending portion and a mounting portion is provided. Also provided is a flexible printed wiring board provided with the dry film as a protective film, for example, a coverlay or a solder resist. A dry film of a laminated structure in which two or more different resin compositions are laminated, the dry film having at least one glass transition temperature as a cured product at a temperature lower than 100 ℃ and at a temperature higher than 100 ℃, and a flexible printed wiring board using the same.

Description

Dry film and flexible printed circuit board

Technical Field

The present invention relates to a dry film and a flexible printed circuit board, and more particularly, to a dry film which can be used as an insulating film of a flexible printed circuit board, and a flexible printed circuit board using the same.

Background

In recent years, with the miniaturization and thinning of electronic devices due to the spread of smart phones and tablet terminals, there is a growing need for a smaller space for a circuit board. Therefore, the flexible printed circuit board which can be stored in a bent state has been used in a wide range of applications, and the flexible printed circuit board also has been required to have a reliability as high as that of the conventional flexible printed circuit board.

In contrast, a hybrid process has been widely used in which a cover layer made of polyimide having excellent mechanical properties such as heat resistance and flexibility is used for a bending portion (flexible portion) (see, for example, patent documents 1 and 2), and a photosensitive resin composition having excellent electrical insulation properties and capable of being finely processed is used for a mounting portion (non-flexible portion) as an insulating film for ensuring insulation reliability of a flexible printed circuit board.

That is, a cover layer having a polyimide substrate excellent in mechanical properties such as heat resistance and flexibility requires processing by die pressing, and is therefore not suitable for fine wiring. Therefore, for a chip mounting portion requiring fine wiring, it is necessary to partially use an alkali development type photosensitive resin composition (solder resist) which can be processed by photolithography.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 62-263692

Patent document 2: japanese laid-open patent publication No. 63-110224

Disclosure of Invention

Problems to be solved by the invention

In this way, in the manufacturing process of the flexible printed circuit board, a mixed mounting process of a step of attaching the cover layer and a step of forming the solder resist layer has to be adopted, and there is a problem that the cost and the workability are poor.

In contrast, although it has been studied to apply an insulating film as a solder resist layer or an insulating film as a coverlay layer to both a solder resist layer and a coverlay layer of a flexible printed circuit board, a material that can sufficiently satisfy both required performances has not been put to practical use. In particular, for flexible printed wiring boards, there is a demand for materials that have both alkali developability required for insulating films as solder resists and mechanical properties such as heat resistance and flexibility required for insulating films as coverlays.

Accordingly, an object of the present invention is to provide a dry film which improves the lamination property of an insulating film for forming a flexible printed wiring board, satisfies the required performance as an insulating film, is suitable for a process of simultaneously forming a bending portion and a mounting portion, and further provides a flexible printed wiring board including the dry film as a protective film, for example, a coverlay or a solder resist.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that: the present inventors have completed the present invention by solving the above-described problems by forming a dry film used for a flexible printed wiring board into a laminated structure in which two or more different resin compositions are laminated and setting the glass transition temperature (Tg) of each layer as a cured product within a predetermined range.

That is, the dry film of the present invention is a dry film of a laminate structure in which two or more different resin compositions are laminated, and is characterized in that at least one of the glass transition temperatures (Tg) of the cured product is lower than 100 ℃ and higher than 100 ℃.

The dry film of the present invention preferably has at least one of the above glass transition temperatures in the range of 40 to 90 ℃ and in the range of 110 to 200 ℃. In addition, the laminated structure is preferably a two-layer structure. Further, the two-layer structure preferably includes: an adhesive layer (A) formed of an alkali-developable resin composition, and a protective layer (B) formed of a photosensitive resin composition. In addition, the laminated structure is preferably patterned by light irradiation.

The dry film of the present invention is suitably used for at least either one of a flexible portion and a non-flexible portion of a flexible printed circuit board. In addition, the dry film of the present invention is suitably used for at least any one of a coverlay layer, a solder resist layer and an interlayer insulating material of a flexible printed circuit board. Further, the dry film of the present invention is preferably supported or protected on at least one side by a film.

The flexible printed wiring board of the present invention is characterized by comprising an insulating film obtained by forming a layer of a laminated structure on a flexible printed wiring board by using the dry film of the present invention, patterning the layer by light irradiation, and forming a pattern at a time by a developing solution.

In the present invention, the term "pattern" refers to a pattern-like cured product, i.e., an insulating film.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a dry film which satisfies required performance as an insulating film of a flexible printed circuit board and is also suitable for a process of simultaneously forming a bending portion and a mounting portion, and a flexible printed circuit board using the same can be realized.

Drawings

Fig. 1 is a process diagram schematically showing an example of a method for manufacturing a flexible printed wiring board according to the present invention.

Fig. 2 is a graph showing the glass transition temperatures based on the results of dynamic viscoelasticity measurement (DMA) of the dry films of (a) example 1, (b) example 2, (c) example 3, (d) comparative example 1, (e) comparative example 2, and (f) comparative example 3, respectively.

Detailed Description

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

(Dry film)

The dry film of the present invention is a dry film of a laminated structure in which two or more different resin compositions are laminated, and has at least one glass transition temperature of a cured product thereof at a temperature lower than 100 ℃ and at a temperature higher than 100 ℃.

In the dry film, at least one of the glass transition temperatures of the cured products is lower than 100 ℃ and higher than 100 ℃, so that the resin composition having the glass transition temperature of the cured product lower than 100 ℃ can exert a good adhesive function to a printed wiring board, while the resin composition having the glass transition temperature of the cured product of 100 ℃ or higher can exert good mechanical properties such as heat resistance and flexibility required for an insulating film as a cover layer. In order to achieve the above-mentioned properties such as the adhesive function and heat resistance, the dry film of the present invention preferably has at least one of the glass transition temperatures in the ranges of 40 to 90 ℃ and 110 to 200 ℃. In the temperature range of the glass transition temperature, the range on the low temperature side is more preferably 45 to 80 ℃, and the range on the high temperature side is more preferably 120 to 180 ℃. The number of layers of the laminated structure is not limited to two, and may be 3 or more.

The laminated structure preferably has a two-layer structure, preferably has an adhesive layer (a) formed from an alkali-developable resin composition and a protective layer (B) formed from a photosensitive resin composition, and further preferably can be patterned by light irradiation. Thus, a dry film having both of the alkali developability required for an insulating film as a solder resist layer and the heat resistance and mechanical properties such as flexibility required for an insulating film as a cover layer can be realized for a flexible printed wiring board.

Hereinafter, a dry film suitable for the present invention in which the adhesive layer (a) is composed of an alkali-developable resin composition and the protective layer (B) is composed of a photosensitive resin composition will be specifically described.

The following components may be used to control Tg so that the Tg becomes high (or low Tg) as exemplified as the components in the resin composition. For example, it is useful to use imide or imide precursor for producing a coating film having a high Tg, and a method of forming a dense crosslinked structure using a polyfunctional acrylate or a polyfunctional epoxide is also conceivable. On the other hand, in order to keep the Tg low, a resin having a flexible skeleton, a bifunctional acrylate, or a monofunctional component may be used.

(protective layer (B))

The photosensitive resin composition constituting the protective layer (B) may have any composition as long as the glass transition temperature of the cured product of the dry film can be maintained at 100 ℃ or higher, preferably 110 to 200 ℃, more preferably 120 to 180 ℃, and for example, "a photocurable thermosetting resin composition 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 thermally reactive compound, which has been conventionally used as a solder resist composition; a photosensitive thermosetting resin composition comprising a carboxyl group-containing resin, a photobase generator and a thermally reactive compound.

Among them, the protective layer (B) is preferably formed of a resin composition containing an alkali-soluble resin having an imide ring or an imide precursor skeleton.

In the present invention, the alkali-soluble resin having an imide ring or an imide precursor skeleton means a resin having an alkali-soluble group such as a carboxyl group or an acid anhydride group and an imide ring or an imide precursor skeleton. For introducing the imide ring or the imide precursor skeleton into the alkali-soluble resin, a known and commonly used method can be used. Examples thereof include: a resin obtained by reacting a carboxylic acid anhydride component with either or both of an amine component and an isocyanate component. The imidization may be performed by thermal imidization, may be performed by chemical imidization, or may be performed by using these in combination.

Among them, examples of the carboxylic anhydride component include: tetracarboxylic anhydride, tricarboxylic anhydride, etc., but are not limited to these anhydrides, and any derivatives thereof may be used as long as they are compounds having an acid anhydride group and a carboxyl group which react with an amino group and an isocyanate group. These carboxylic anhydride components may be used alone or in combination.

Examples of the tetracarboxylic anhydride include: pyromellitic dianhydride, 3 ', 4,4 ' -benzophenonetetracarboxylic dianhydride, 3 ', 4,4 ' -biphenyltetracarboxylic dianhydride, 4,4 ' -oxydiphthalic dianhydride, 1,2,3, 4-benzenetetracarboxylic dianhydride, 3 ', 4,4 ' -terphenyltetracarboxylic dianhydride, 3 ', 4,4 ' -quaterphenyltetracarboxylic dianhydride, 3 ', 4,4 ' -pentabiphenyltetracarboxylic dianhydride, methylene-4, 4 ' -bisphthalic dianhydride, 1-ethylidene-4, 4 ' -bisphthalic dianhydride, 2-propylidene-4, 4 ' -bisphthalic dianhydride, 1, 2-ethylidene-4, 4 ' -bisphthalic dianhydride, 1, 3-trimethylene-4, 4 ' -biphthalic dianhydride, 1, 4-tetramethylene-4, 4 ' -biphthalic dianhydride, 1, 5-pentamethylene-4, 4 ' -biphthalic dianhydride, thio-4, 4 ' -biphthalic dianhydride, sulfonyl-4, 4 ' -biphthalic dianhydride, 1, 3-bis (3, 4-dicarboxyphenyl) -1,1,3, 3-tetramethylsiloxane dianhydride, 1, 3-bis (3, 4-dicarboxyphenyl) benzene dianhydride, 1, 4-bis (3, 4-dicarboxyphenyl) benzene dianhydride, 1, 3-bis (3, 4-dicarboxyphenoxy) benzene dianhydride, 1, 4-bis (3, 4-dicarboxyphenoxy) benzene dianhydride, 1, 3-bis [ 2- (3, 4-dicarboxyphenyl) -2-propyl ] benzene dianhydride, 1, 4-bis [ 2- (3, 4-dicarboxyphenyl) -2-propyl ] benzene dianhydride, bis [ 3- (3, 4-dicarboxyphenoxy) phenyl ] methane dianhydride, 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 1,2,5, 6-naphthalenetetracarboxylic dianhydride, 3,4,9, 10-perylenetetracarboxylic dianhydride, 2,3,6, 7-anthracenetetracarboxylic dianhydride, 1,2,7, 8-phenanthrenetetracarboxylic dianhydride, 1,2,3, 4-butanetetracarboxylic dianhydride, 1,2,3, 4-cyclobutanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexane-1, 2,3, 4-tetracarboxylic dianhydride, Cyclohexane-1, 2,4, 5-tetracarboxylic dianhydride, 3 ', 4,4 ' -dicyclohexyltetracarboxylic dianhydride, carbonyl-4, 4 ' -bis (cyclohexane-1, 2-dicarboxylic acid) dianhydride, methylene-4, 4 ' -bis (cyclohexane-1, 2-dicarboxylic acid) dianhydride, 1, 2-ethylene-4, 4 ' -bis (cyclohexane-1, 2-dicarboxylic acid) dianhydride, 1-ethylidene-4, 4 ' -bis (cyclohexane-1, 2-dicarboxylic acid) dianhydride, 2-propylidene-4, 4 ' -bis (cyclohexane-1, 2-dicarboxylic acid) dianhydride, ethylene glycol bis (trimellitic acid dianhydride), 1,2- (ethylene) bis (trimellitic acid anhydride), 1,3- (trimethylene) bis (trimellitic anhydride), 1,4- (tetramethylene) bis (trimellitic anhydride), 1,5- (pentamethylene) bis (trimellitic anhydride), 1,6- (hexamethylene) bis (trimellitic anhydride), 1,7- (heptamethylene) bis (trimellitic anhydride), 1,8- (octamethylene) bis (trimellitic anhydride), 1,9- (nonamethylene) bis (trimellitic anhydride), 1,10- (decamethylene) bis (trimellitic anhydride), 1,12- (dodecamethylene) bis (trimellitic anhydride), 1,16- (hexadecamethylene) bis (trimellitic anhydride), 1,18- (octadecamethylene) bis (trimellitic anhydride), and the like.

Examples of the tricarboxylic acid anhydride include: trimellitic anhydride, nuclear hydrogenated trimellitic anhydride, and the like.

As amine components, it is possible to use: diamines such as aliphatic diamines and aromatic diamines; and polyamines such as aliphatic polyether amines, but are not limited to these amines. In addition, these amine components may be used alone or in combination.

Examples of the diamine include: p-phenylenediamine (PPD), 1, 3-diaminobenzene, 2, 4-tolylenediamine, 1-nucleus-containing diamines such as 2, 5-tolylenediamine and 2, 6-tolylenediamine, diaminodiphenyl ethers such as 4,4 ' -diaminodiphenyl ether, 3 ' -diaminodiphenyl ether and 3,4 ' -diaminodiphenyl ether, diaminodiphenyl ethers such as 4,4 ' -diaminodiphenylmethane, 3 ' -dimethyl-4, 4 ' -diaminobiphenyl, 2 ' -dimethyl-4, 4 ' -diaminobiphenyl, 3 ' -diaminodiphenyl ether, 3,4 ' -diaminodiphenyl ether, 4 ' -diaminodiphenyl ether, 3 ' -diaminodiphenyl sulfide, 3,4 ' -diaminodiphenyl sulfide and other 2-nucleus-containing diamines, such as p-phenylenediamine, 1, 3-diaminobenzene, 2, 4-tolylenediamine, 2, 5-tolylenediamine and 2, 6-tolyl, Aromatic diamines such as 3-nucleus diamines including 1, 3-bis (3-aminophenylsulfide) benzene, 1, 3-bis (4-aminophenylsulfide) benzene and 1, 4-bis (4-aminophenylsulfide) benzene, 3 ' -bis (3-aminophenoxy) biphenyl, 3 ' -bis (4-aminophenoxy) biphenyl, 4 ' -bis (3-aminophenoxy) biphenyl, 2-bis [ 3- (3-aminophenoxy) phenyl ] propane, 2-bis [ 3- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2-bis [4- (4-aminophenoxy) phenyl ] propane and the like, Aliphatic diamines such as 1, 2-diaminoethane, 1, 3-diaminopropane, 1, 4-diaminobutane, 1, 5-diaminopentane and 1, 6-diaminohexane, and examples of the aliphatic polyether amines include: and ethylene glycol and/or propylene glycol based polyamines. Further, as polyoxyalkylene diamine, there may be mentioned: polyoxyethylene diamine, polyoxypropylene diamine, polyoxybutylene diamine, and the like, and commercially available products include: JEFFAMINE EDR-148, EDR-176, JEFFAMINE D-230, D-400, D-2000, D-4000, JEFFAMINE ED-600, ED-900, ED-2003, JEFFAMINE XTJ-542 and the like manufactured by HUNTSMAN CORPORATION. In addition, as described below, an amine having a carboxyl group may also be used.

Examples of the amine having a carboxyl group include: diaminobenzoic acids such as 3, 5-diaminobenzoic acid, 2, 5-diaminobenzoic acid, and 3, 4-diaminobenzoic acid; aminophenoxybenzoic acids such as 3, 5-bis (3-aminophenoxy) benzoic acid and 3, 5-bis (4-aminophenoxy) benzoic acid; carboxybiphenyl compounds such as 3,3 '-diamino-4, 4' -dicarboxybiphenyl; carboxydiphenylalkanes such as 3,3 '-diamino-4, 4' -dicarboxydiphenylmethane, 3 '-dicarboxydiphenyl-4, 4' -diaminodiphenylmethane and 2, 2-bis [ 4-amino-3-carboxyphenyl ] propane; carboxyl diphenyl ether compounds such as 3,3 '-diamino-4, 4' -dicarboxydiphenyl ether and 4,4 '-diamino-3, 3' -dicarboxydiphenyl ether; and diphenyl sulfone compounds such as 3,3 '-diamino-4, 4' -dicarboxydiphenyl sulfone and 4,4 '-diamino-3, 3' -dicarboxydiphenyl sulfone.

As the isocyanate component, there can be used: diisocyanates such as aromatic diisocyanates and isomers, polymers thereof, aliphatic diisocyanates, alicyclic diisocyanates and isomers thereof, and other general-purpose diisocyanates, but are not limited to these isocyanates. In addition, these isocyanate components may be used alone or in combination.

Examples of the diisocyanate include: aromatic diisocyanates such as 4, 4' -diphenylmethane diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, biphenyl diisocyanate, diphenylsulfone diisocyanate, and diphenylether diisocyanate, and aliphatic diisocyanates such as isomers, polymers, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate thereof; or alicyclic diisocyanates and isomers obtained by hydrogenating aromatic diisocyanates, or other general-purpose diisocyanates.

The alkali-soluble resin having an imide ring or an imide precursor skeleton described above may have an amide bond. The amide bond may be an amide bond obtained by reacting an isocyanate with a carboxylic acid, or an amide bond obtained by another reaction. Further, the polymer may have a bond formed by other addition and condensation.

In addition, as the imide ring or imide precursor skeleton introduced into the alkali-soluble resin, there can be used a publicly known and commonly used alkali-soluble polymer, oligomer, or monomer having either or both of a carboxyl group and an acid anhydride group, and for example, a resin obtained by reacting these publicly known and commonly used alkali-soluble resins with the above-mentioned amine/isocyanate alone or in combination with the above-mentioned carboxylic acid anhydride component.

In the synthesis of such an alkali-soluble resin having an alkali-soluble group and an imide ring or an imide precursor skeleton, a known and commonly used organic solvent can be used. The organic solvent is not particularly limited in structure as long as it does not react with the carboxylic acid anhydride, amine, or isocyanate as the raw material and can dissolve the raw material. Among them, from the viewpoint of high solubility of the raw materials, preferred are: aprotic solvents such as N, N-dimethylformamide, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and γ -butyrolactone.

The alkali-soluble resin having an alkali-soluble group such as a carboxyl group or an acid anhydride group and an imide ring or an imide precursor skeleton described above preferably has an acid value of 20 to 200mgKOH/g, more preferably 60 to 150mgKOH/g, in order to cope with the photolithography step. When the acid value is 20mgKOH/g or more, solubility to alkali increases, and developability becomes good, and further, the degree of crosslinking with a thermosetting component after light irradiation becomes high, and therefore, sufficient development contrast can be obtained. When the acid value is 200mgKOH/g or less, so-called thermal fogging in a POST EXPOSURE BAKE (POST EXPOSURE BAKE) step of PEB after light irradiation, which will be described later, can be suppressed, and a process margin (process margin) can be increased.

The molecular weight of the alkali-soluble resin is preferably 1000 to 100000, more preferably 2000 to 50000, in view of developability and cured coating properties. When the molecular weight is 1000 or more, sufficient development resistance and curing properties can be obtained after exposure to light and PEB. When the molecular weight is 100000 or less, the alkali solubility increases and the developability improves.

When the photobase generator is used for the resin composition containing the alkali-soluble resin having an imide ring or an imide precursor skeleton, the photobase generator and the thermally reactive compound are generally contained in addition to the alkali-soluble resin, and when the photopolymerization initiator is used, the photopolymerization initiator and the compound having an ethylenically unsaturated bond are contained in addition to the alkali-soluble resin. In addition, as the resin component, a carboxyl group-containing urethane resin, a carboxyl group-containing novolac resin, or the like may be used in combination.

The photobase generator is a compound that generates 1 or more basic substances that function as a catalyst for a polymerization reaction of a thermally reactive compound to be described later by changing a molecular structure or cleaving molecules thereof by irradiation with light such as ultraviolet light or visible light. Examples of the basic substance include: secondary amines, tertiary amines.

Examples of the photobase generator include: an alpha-aminoacetophenone compound; an oxime ester compound; and compounds having a substituent such as acyloxyimino group, N-formylated aromatic amino group, N-acylated aromatic amino group, nitrobenzylcarbamate group, alkoxybenzylcarbamate group, and the like. Among them, oxime ester compounds and α -aminoacetophenone compounds are preferable. As the α -aminoacetophenone compound, a compound having 2 or more nitrogen atoms is particularly preferable.

The molecules of the alpha-amino acetophenone compound have benzoin ether bonds, and when the alpha-amino acetophenone compound is irradiated by light, intramolecular cracking occurs to generate an alkaline substance (amine) which plays a role in curing catalysis. As specific examples of the α -aminoacetophenone compound, there can be used: commercially available compounds such as (4-morpholinobenzoyl) -1-benzyl-1-dimethylaminopropane (IRGACURE 369, trade name, manufactured by BASF JAPAN ltd.), 4- (methylthiobenzoyl) -1-methyl-1-morpholinoethane (IRGACURE 907, trade name, manufactured by BASF JAPAN ltd.), 2- (dimethylamino) -2- [ (4-methylphenyl) methyl ] -1- [4- (4-morpholino) phenyl ] -1-butanone (IRGACURE 379, trade name, manufactured by BASF JAPAN ltd.) and the like, and solutions thereof.

The oxime ester compound may be any compound that generates a basic substance by light irradiation. Examples of the oxime ester compound include commercially available products such as: CGI-325 manufactured by BASF JAPAN LTD, IRGACURE OXE01, IRGACURE OXE02, N-1919 manufactured by ADEKA CORPORATION, NCI-831, and the like. Further, a compound having 2 oxime ester groups in the molecule as described in Japanese patent No. 4344400 can also be preferably used.

Such photobase generators may be used alone in 1 kind, or in combination of 2 or more kinds. The amount of the photobase generator to be blended in the resin composition is preferably 0.1 to 40 parts by mass, more preferably 0.1 to 30 parts by mass, per 100 parts by mass of the thermally reactive compound. When the amount is 0.1 parts by mass or more, the contrast of the development resistance of the irradiated portion/non-irradiated portion can be favorably obtained. When the amount is 40 parts by mass or less, the properties of the cured product are improved.

The thermally reactive compound is a resin having a functional group capable of undergoing a curing reaction by heat, and examples thereof include: epoxy resins, polyfunctional oxetane compounds, and the like.

The epoxy resin is a resin having an epoxy group, and any known resin can be used. Specifically, there may be mentioned: a 2-functional epoxy resin having 2 epoxy groups in the molecule, a polyfunctional epoxy resin having a plurality of epoxy groups in the molecule, and the like. The epoxy compound may be a hydrogenated 2-functional epoxy compound.

Examples of the epoxy resin include: bisphenol a type epoxy resin, brominated epoxy resin, novolac type epoxy resin, bisphenol F type epoxy resin, hydrogenated bisphenol a type epoxy resin, glycidylamine type epoxy resin, hydantoin type epoxy resin, alicyclic epoxy resin, trihydroxyphenyl methane type epoxy resin, bixylenol type epoxy resin or biphenol type epoxy resin or a mixture thereof; bisphenol S type epoxy resin, bisphenol a novolac type epoxy resin, bisphenol novolac type epoxy resin, tetrahydroxyphenylethane type epoxy resin, heterocyclic epoxy resin, diglycidyl phthalate resin, tetraglycidyl xylenol ethane resin, naphthyl-containing epoxy resin, epoxy resin having a dicyclopentadiene skeleton, glycidyl methacrylate copolymer epoxy resin, copolymer epoxy resin of cyclohexylmaleimide and glycidyl methacrylate, CTBN-modified epoxy resin, and the like.

The amount of the thermally reactive compound to be blended is preferably 1:0.1 to 1:10 in terms of equivalent ratio to the alkali-soluble resin (alkali-soluble group such as carboxyl group: thermally reactive group such as epoxy group). By setting the compounding ratio in such a range, development becomes favorable, and a fine pattern can be easily formed. The equivalent ratio is more preferably 1:0.2 to 1: 5.

As the photopolymerization initiator, known photopolymerization initiators can be used, and examples thereof include: α -aminoacetophenone-based photopolymerization initiator, acylphosphine oxide-based photopolymerization initiator, benzoin compound, acetophenone compound, anthraquinone compound, thioxanthone compound, ketal compound, benzophenone compound, tertiary amine compound, xanthone compound, and the like.

As the compound having an ethylenically unsaturated bond, known compounds can be used, and examples thereof include: hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate; monoacrylates or diacrylates of glycols such as ethylene glycol, methoxyethylene glycol, polyethylene glycol, and propylene glycol; polyhydric alcohols such as hexanediol, trimethylolpropane, pentaerythritol, dipentaerythritol, and trishydroxyethyl isocyanurate, and polyvalent acrylates such as ethylene oxide adducts and propylene oxide adducts thereof; acrylic esters such as phenoxy acrylate, bisphenol a diacrylate, and ethylene oxide adducts and propylene oxide adducts of these phenols.

(adhesive layer (A))

The alkali developable resin composition constituting the adhesive layer (a) may be any composition as long as it contains a resin that contains 1 or more functional groups selected from a phenolic hydroxyl group, a thiol group, and a carboxyl group and is developable with an alkali solution, and the glass transition temperature of a cured product as a dry film is lower than 100 ℃, preferably 40 to 90 ℃, more preferably 45 to 80 ℃, and a photocurable resin composition or a thermosetting resin composition may be used. Preferably, the resin composition contains a compound having 2 or more phenolic hydroxyl groups, a carboxyl group-containing resin, a compound having a phenolic hydroxyl group and a carboxyl group, and a compound having 2 or more thiol groups, and known and commonly used compounds can be used.

Specifically, for example, a photocurable thermosetting resin composition conventionally used as a solder resist composition, which comprises: a carboxyl group-containing resin or a carboxyl group-containing photosensitive resin, a compound having an ethylenically unsaturated bond, a photopolymerization initiator, and a thermally reactive compound. In addition, a resin composition containing a carboxyl group-containing urethane resin, a carboxyl group-containing resin, a photobase generator, and a thermosetting component may also be used. The resin composition is as follows: the polyurethane resin having a carboxyl group and the thermosetting component are subjected to an addition reaction by heating after exposure using a base generated from the photobase generator as a catalyst, and an unexposed portion is removed by an alkali solution, whereby development can be performed.

As each material constituting the resin composition used for the adhesive layer (a), a known and commonly used material can be used, and the material used for the protective layer (B) can be similarly used.

The resin composition used for the adhesive layer (a) and the protective layer (B) may contain a known and commonly used polymer resin in order to improve flexibility and dry-to-touch properties of the resulting cured product. Examples of such a polymer resin include: cellulose-based, polyester-based, phenoxy resin-based, polyvinyl acetal-based, polyvinyl butyral-based, polyamide-based, polyamideimide-based binder polymers, block copolymers, elastomers, and the like. The polymer resin may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

In the resin composition used for the adhesive layer (a), the protective layer (B), and the like, an inorganic filler may be blended in order to suppress curing shrinkage of a cured product and improve properties such as adhesion and hardness. Examples of such inorganic fillers include: barium sulfate, amorphous silica, fused silica, spherical silica, talc, clay, magnesium carbonate, calcium carbonate, alumina, aluminum hydroxide, silicon nitride, aluminum nitride, boron nitride, Nojenberg silica, and the like.

In the resin composition used for the adhesive layer (a), the protective layer (B), and the like, an organic solvent may be used for preparing the resin composition and for adjusting the viscosity for application to a substrate or a carrier film. Examples of such organic solvents include: ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, petroleum solvents, and the like. Such organic solvents may be used alone in 1 kind, or may be used in the form of a mixture of 2 or more kinds.

The resin composition used for the adhesive layer (a), the protective layer (B), and the like may further contain, as necessary, components such as a colorant, a mercapto compound, an adhesion promoter, an antioxidant, and an ultraviolet absorber. The components may be those commonly used in the field of electronic materials. In addition, it is possible to suitably compound: known and commonly used additives such as a thickener such as fine powder silica, hydrotalcite, organobentonite, and montmorillonite, a defoaming agent such as silicone-based, fluorine-based, and polymer-based ones, a leveling agent, a silane coupling agent, and a rust preventive.

In the dry film of the present invention, the adhesive layer (a) is preferably thicker than the protective layer (B) from the viewpoint of conformability to a copper circuit.

The dry film of the present invention can be used for at least one of a flexible portion and a non-flexible portion of a flexible printed wiring board, preferably both of them, and thus a flexible printed wiring board having sufficient durability against bending can be obtained and the cost and workability can be improved. Specifically, the dry film of the present invention can be used for at least any one of a coverlay layer, a solder resist layer and an interlayer insulating material of a flexible printed circuit board.

(method of manufacturing Flexible printed Circuit Board)

In the present invention, a flexible printed wiring board can be obtained by forming a layer of the laminated structure of the dry film of the present invention described above on a flexible printed wiring substrate, patterning the layer by light irradiation, and forming a pattern at a time by a developing solution to form an insulating film. In the conventional solder resist, the properties such as flexibility are poor in a single layer, but according to the present invention, a dry film of a laminated structure having at least an adhesive layer (a) and a protective layer (B) is produced, in which at least two glass transition temperatures as cured products are independently set to be lower than 100 ℃ and higher than 100 ℃, so that a resin composition having a glass transition temperature as a cured product of lower than 100 ℃ can exhibit a good adhesive function to a printed wiring board, and on the other hand, a resin composition having a glass transition temperature as a cured product of higher than 100 ℃ can exhibit good mechanical properties such as heat resistance and flexibility required for an insulating film as a cover layer.

Hereinafter, an example of the method for producing the flexible printed wiring board of the present invention from the dry film of the present invention will be described based on the process diagram shown in fig. 1, in the case where a resin composition containing a photobase generator and a thermally reactive compound is used for both the adhesive layer (a) and the protective layer (B) constituting the dry film. When a photocurable thermosetting resin composition 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 thermally reactive compound, which is used as a conventional solder resist composition, is used, the same steps as those for a solder resist layer can be employed.

[ laminating Process ]

The laminating step is a step of forming a laminated structure on a substrate by using the dry film of the present invention. The laminating step in fig. 1 shows a state in which a laminated structure composed of an adhesive layer 3 and a protective layer 4 is formed on a flexible printed circuit substrate 1 on which a copper circuit 2 is formed, and the adhesive layer 3 is formed of an alkali-developable resin composition.

The layers constituting the laminated structure can be formed by laminating the resin compositions constituting the adhesive layer 3 and the protective layer 4 to the base material in the dry film form of the present invention. At this time, at least one surface of the laminated structure may be supported or protected by a thin film. As the film to be used, a plastic film peelable from a laminated structure can be used. The thickness of the thin film is not particularly limited, but is usually suitably selected within the range of 10 to 150 μm. The interfaces between the layers may also be fused from the viewpoint of the strength of the coating film.

The method for coating the substrate with the resin composition may be any known method such as a blade coater, a lip coater, a comma coater, or a film coater. The drying method may be a method of bringing hot air in a dryer into convective contact with each other by using a device having a heat source using a heating method of steam, such as a hot air circulation drying furnace, an IR furnace, a hot plate, or a convection oven; and a method of blowing the gas to the support body through the nozzle.

In the present invention, the reason why the dry film is formed into at least two layers is not only because the lamination can be performed by a vacuum laminator as shown in the following examples, but also because the dry film can be suitably used in various lamination methods. Further, a PET film is often used in a vacuum laminator used for printed wiring boards and the like during conveyance, and in this case, the upper limit of the heating temperature to be applied is about 120 ℃.

Further, in the lamination, since the resin must sufficiently flow into the fine inter-circuit and high aspect ratio circuits, the resin must be sufficiently softened and fluidized in the lamination under atmospheric pressure in a roll laminator or the like. Therefore, the use of a heat-resistant resin having a high softening point makes the above lamination difficult, and therefore, it is preferable to realize a lamination-enabling state having fluidity even at a relatively low temperature in a dry film. In the dry film of the present invention, a component that flows by heating is used on the side of the adhesive layer 3 in contact with the substrate (circuit), and the protective layer 4 can realize mechanical properties such as heat resistance and flexibility.

The substrate is a flexible printed circuit substrate on which a circuit is formed in advance. In addition, a further layer may be provided between the adhesive layer 3 and the protective layer 4 in order to obtain other effects than the desired effects.

[ light irradiation Process ]

The light irradiation step is as follows: the photobase generator contained in the resin composition is activated by light irradiation in a negative pattern, thereby curing the irradiated portion. In this light irradiation step, a mask 5 is disposed on the protective layer 4, and light irradiation is performed in a negative pattern shape to activate the photobase generator contained in the resin composition, thereby curing the light irradiated portion.

In this step, the photobase generator is destabilized by the base generated in the light irradiation section, and a basic substance (hereinafter, may be simply referred to as "base") is generated from the photobase generator. It is considered that by generating the alkali in this manner and chemically growing the alkali to the deep part of each layer, sufficient curing to the deep part of each layer can be achieved. In the subsequent thermal curing, since the alkali acts as a catalyst for the addition reaction of the alkali-developable resin and the thermally reactive compound and the addition reaction proceeds, the layers are thermally cured sufficiently to the deep part in the light irradiation part. In this case, the curing of the resin composition is, for example, a ring-opening reaction of epoxy by a thermal reaction, and therefore, strain and curing shrinkage can be suppressed as compared with the case of proceeding by a photoreaction.

As a light irradiator used for light irradiation, a direct drawing device (for example, a laser direct imaging device which directly draws an image with a laser beam by CAD data from a computer), a light irradiator equipped with a metal halide lamp, a light irradiator equipped with a (ultra) high-pressure mercury lamp, a light irradiator equipped with a mercury short-arc lamp, or a direct drawing device using an ultraviolet lamp such as a (ultra) high-pressure mercury lamp can be used. The mask for pattern-like light irradiation is a negative mask.

As the active energy ray, a laser beam or scattered light having a maximum wavelength in the range of 350 to 410nm is preferably used. By setting the maximum wavelength to this range, the photobase generator can be efficiently activated. The laser beam in this range may be used, and the laser type may be gas laser or solid laser. The amount of light irradiation varies depending on the film thickness, and can be usually set to 100 to 1500mJ/cm²Preferably 300 to 1500mJ/cm²Within the range of (1).

[ heating Process ]

In the heating step, the light-irradiated portion is cured by heating, and the light-irradiated portion can be cured to a deep portion by the alkali generated in the light-irradiating step. This heating step is a step of heating the adhesive layer 3 and the protective layer 4 after the light irradiation step to cure the light-irradiated portion, and is a step called a so-called PEB (POST EXPOSURE BAKE) step. Thus, the respective layers are sufficiently cured to the deep part by the alkali generated in the light irradiation step, and a pattern layer having excellent curing properties can be obtained.

For example, in the heating step, the heating is preferably performed at a temperature lower than the heat release starting temperature or the heat release peak temperature of the resin composition that has not been irradiated and higher than the heat release starting temperature or the heat release peak temperature of the resin composition that has been irradiated with light. By thus heating, only the light irradiation portion can be selectively cured.

The heating temperature in this case is preferably a temperature at which the irradiated portion of the resin composition is thermally cured, but the unirradiated portion is not thermally cured. The heating temperature is, for example, 80 to 140 ℃. By setting the heating temperature to 80 ℃ or higher, the light irradiation part can be sufficiently cured. On the other hand, by setting the heating temperature to 140 ℃ or lower, only the light irradiation part can be selectively cured. The heating time is, for example, 10 to 100 minutes. The heating method is the same as the above-described drying method. In addition, since alkali derived from the photobase generator is not generated in the non-irradiated portion, thermosetting is suppressed.

[ developing Process ]

In the developing step, the non-irradiated portion is removed by alkali development to form a negative pattern layer. The developing step in fig. 1 is a step of developing the adhesive layer 3 and the protective layer 4 with an aqueous alkali solution to remove the non-irradiated portion and form a negative pattern layer. As the developing method, known methods such as a dipping method, a shower method, a spray method, and a brush method can be used. The developer may be an aqueous alkaline solution or a mixture thereof of an amine such as potassium hydroxide, sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, ammonia, or ethanolamine, an imidazole such as 2-methylimidazole, or a tetramethylammonium hydroxide aqueous solution (TMAH).

[ 2 nd light irradiation step ]

After the developing step, a 2 nd light irradiation step is preferably included. The 2 nd light irradiation step is a step of irradiating ultraviolet rays as necessary so as to activate the photobase generator remaining in the pattern layer in the light irradiation step without being activated and to generate a base. The wavelength and the light irradiation amount (exposure amount) of the ultraviolet ray in the 2 nd light irradiation step may be the same as or different from those in the above light irradiation step. The amount of light irradiation (exposure amount) is, for example, 150 to 2000mJ/cm²。

[ Heat curing Process ]

After the development step, a thermal curing (post-curing) step is preferably further included. The thermosetting step is a step of performing thermosetting (post-curing) as necessary in order to sufficiently thermally cure the pattern layer. When the 2 nd light irradiation step and the thermosetting step are both performed after the development step, the thermosetting step is preferably performed after the 2 nd light irradiation step.

In the thermosetting step, the pattern layer is thermally cured sufficiently by the alkali generated from the photobase generator in the light irradiation step or in the light irradiation step and the 2 nd light irradiation step. At the time of the thermosetting step, since the non-irradiated portion is already removed, the thermosetting step may be performed at a temperature equal to or higher than the curing reaction start temperature of the non-irradiated resin composition. Thereby, the pattern layer can be sufficiently thermally cured. The heating temperature is, for example, 150 ℃ or higher.

Examples

The present invention will be described in further detail below with reference to examples.

(Synthesis example 1)

< Synthesis of alkali-soluble resin having imide Ring >

Into a separable three-necked flask equipped with a stirrer, a nitrogen inlet, a fractionating tube and a condenser were charged 12.5g of 3, 5-diaminobenzoic acid, 4.0g of polyetherdiamine (manufactured by HUNTSMAN CORPORATION, JEFFAMINE D230), 30g of NMP, 30g of γ -butyrolactone, 27.9g of 4, 4' -oxydiphthalic anhydride and 3.8g of trimellitic anhydride, and the mixture was stirred at 100rpm under a nitrogen atmosphere at room temperature for 4 hours. Subsequently, 20g of toluene was added thereto, and the mixture was stirred at a silicon bath temperature of 180 ℃ and 150rpm for 4 hours while removing toluene and water by distillation to obtain an alkali-soluble resin solution having an imide ring. Then, γ -butyrolactone was added so that the solid content became 30 mass%. The solid acid value of the obtained resin solution was 117mgKOH/g, and Mw was 10000.

(Synthesis example 2)

< Synthesis of carboxyl group-containing polyurethane resin >

Into a reaction vessel equipped with a stirrer, a thermometer and a condenser were charged 2400g (3 moles) of a polycarbonate diol derived from 1, 5-pentanediol and 1, 6-hexanediol (manufactured by Asahi Kasei Chemicals Corporation, T5650J, number average molecular weight 800), 603g (4.5 moles) of dimethylolpropionic acid, and 238g (2.6 moles) of 2-hydroxyethyl acrylate as a monohydroxy compound. Subsequently, 1887g (8.5 mol) of isophorone diisocyanate as a polyisocyanate was charged, the heating was stopped to 60 ℃ while stirring, the heating was resumed at the point when the temperature in the reaction vessel started to decrease, the stirring was continued at 80 ℃ and the isocyanate was confirmed by infrared absorption spectroscopyAbsorption spectrum of the ester group (2280 cm)^-1) The reaction was terminated after disappearance. Next, carbitol acetate was added so that the solid content became 50 mass%. The solid content of the resulting carboxyl group-containing polyurethane resin had an acid value of 50 mgKOH/g.

< preparation of resin composition for Forming layers >

The materials shown in examples and comparative examples were compounded according to the formulation shown in table 1 below, premixed with a mixer, and kneaded with a three-roll mill to prepare resin compositions constituting the adhesive layer and the protective layer. The values in the table are parts by mass unless otherwise specified.

< preparation of Dry film >

The resin composition obtained above and constituting the protective layer was applied to the carrier film so that the dried film thickness became 10 μm. Then, the resultant was dried at 90 ℃ for 30 minutes in a hot air circulation drying furnace to form a protective layer (B). The resin composition constituting the adhesive layer thus obtained was applied to the surface of the protective layer (B) so that the film thickness after drying became 25 μm. Then, the resultant was dried at 90 ℃ for 30 minutes in a hot air circulation drying furnace to form an adhesive layer (A), thereby producing a dry film.

< measurement of glass transition temperature >

The dry film obtained above was laminated on a PTFE film by CVP-300 made by Nichigo-Morton Co., Ltd., HMW680GW made by ORC CORPORATION (metal halide lamp, scattered light) at an exposure of 500mJ/cm²The light irradiation is performed in a negative pattern. Subsequently, heat treatment was performed at 90 ℃ for 60 minutes. Then, the substrate was immersed in a 1 mass% aqueous solution of sodium carbonate at 30 ℃ and developed for 3 minutes, and then heat-treated at 150 ℃ for 60 minutes in a hot air circulating drying furnace to obtain a pattern-like cured coating film. Using the obtained cured coating film, the glass transition temperature of the cured product was determined by dynamic viscoelasticity measurement (DMA) under the following conditions.

Measuring temperature: -30 to 300 DEG C

Temperature rise rate: 5 ℃ per minute

< laminating Property >

The dry film obtained above was laminated on a substrate using CVP-300 manufactured by nichogo-Morton co.

Lamination temperature: 60 deg.C

Vacuum: 4hPa, 30 seconds

Laminating: 0.3Pa, 25 seconds

O: without voids

X: with a gap

< alkali developability and solder Heat resistance >

The substrate having the dry film obtained above was subjected to HMW680GW (metal halide lamp, scattered light) manufactured by ORC CORPORATION, and exposed to an exposure of 500mJ/cm²The light irradiation is performed in a negative pattern. Subsequently, heat treatment was performed at 90 ℃ for 60 minutes. Then, the substrate was immersed in a 1 mass% aqueous solution of sodium carbonate at 30 ℃ and developed for 3 minutes, and the alkali developability was evaluated.

O: alkali developable

And (delta): alkali developable, but with a little residue remaining

X: with development residues

Subsequently, the resultant was heat-treated at 150 ℃ for 60 minutes in a hot air circulation drying furnace to obtain a pattern-like cured coating film. The obtained cured coating film was coated with rosin-based flux on the evaluation substrate, immersed in a solder bath set at 260 ℃ in advance for 20 seconds (10 seconds × 2 times), cleaned with isopropyl alcohol, and then subjected to a peel test using a transparent tape, and expansion, peeling, and discoloration of the resist layer were evaluated according to the following criteria.

O: no change at all was confirmed

X: with swelling, peeling

The results are shown in table 1 below.

[ Table 1]

In addition, the method is as follows: synthesis of the resin of example 1

In addition, 2: synthesis of the resin of example 2

And (2) in color: trimethylolpropane EO modified triacrylate (TOAGOSEI CO., LTD. manufactured)

In addition, 4: dicyclopentadiene type epoxy resin (DIC Co., Ltd.)

In addition, the method is as follows: bisphenol A type epoxy resin (molecular weight 400) (Mitsubishi chemical corporation)

In addition, 6: oxime photobase generators (BASF JAPAN LTD. manufactured)

In addition, the color is 7: 2- (dimethylamino) -2- [ (4-methylphenyl) methyl ] -1- [4- (4-morpholinyl) phenyl ] -1-butanone (manufactured by BASF JAPAN LTD., Ltd.)

In addition, the color is 8: bisphenol F type acid-modified epoxy acrylate (manufactured by Nippon Kabushiki Kaisha)

In addition, the color is 9: barium sulfate (made by Sakai chemical corporation)

The evaluation results shown in table 1 above show that the flexible printed circuit boards of examples 1 to 3 using the dry film satisfying the glass transition temperature Tg1 of less than 100 ℃ and the glass transition temperature Tg2 of 100 ℃ or higher in the present invention have good alkali developability, lamination property, and solder heat resistance. In contrast, comparative example 1, which did not satisfy Tg2, had poor welding heat resistance. In comparative example 2, which had no adhesive layer and exhibited Tg only of Tg2, alkali developability and laminatability were poor. Further, comparative example 3, which has no protective layer and only Tg1 showing Tg, has poor solder heat resistance.

Description of the reference numerals

1 Flexible printed Circuit substrate

2 copper circuit

3 adhesive layer

4 protective layer

5 mask

Claims

1. A dry film of a laminate structure in which two or more different resin compositions are laminated, characterized in that at least one of an adhesive layer (A) having a glass transition temperature of less than 100 ℃ as a cured product and a protective layer (B) having a glass transition temperature of 100 ℃ or higher as a cured product is provided,

the adhesive layer (A) is formed from a composition containing a resin which contains 1 or more functional groups selected from a phenolic hydroxyl group, a thiol group, and a carboxyl group and which can be developed with an alkaline solution, and the protective layer (B) is formed from a resin composition containing an alkaline-soluble resin having an imide ring or an imide precursor skeleton.

2. The dry film according to claim 1, wherein at least one of the adhesive layer (A) having a glass transition temperature of 40 to 90 ℃ as a cured product and the protective layer (B) having a glass transition temperature of 110 to 200 ℃ as a cured product is provided.

3. The dry film according to claim 1, wherein the laminate structure has a two-layer structure.

4. The dry film according to claim 3, wherein the two-layer structure laminated structure has: the adhesive layer (A) is formed from a composition containing a resin which contains 1 or more functional groups selected from a phenolic hydroxyl group, a thiol group and a carboxyl group and can be developed with an alkaline solution, and the protective layer (B) is formed from a resin composition containing an alkaline-soluble resin having an imide ring or an imide precursor skeleton.

5. The dry film according to claim 1, wherein the laminated structure can be patterned by light irradiation.

6. The dry film according to claim 1, which is used for at least any one of a flexible portion and a non-flexible portion of a flexible printed circuit board.

7. The dry film according to claim 1, which is used for at least any one of a coverlay layer, a solder resist layer and an interlayer insulating material of a flexible printed circuit board.

8. The dry film according to claim 1, which is supported or protected on at least one side by a film.

9. A flexible printed wiring board comprising an insulating film obtained by forming a layer of a laminated structure on a flexible printed wiring board with the dry film according to any one of claims 1 to 8, patterning the layer by light irradiation, and forming a pattern at a time by a developing solution.