WO2006088230A1

WO2006088230A1 - Thermosetting composition for solder resist and cured product thereof

Info

Publication number: WO2006088230A1
Application number: PCT/JP2006/303210
Authority: WO
Inventors: Yoshio Miyajima; Tetsuo Wada; Ayako Nakamura
Original assignee: Showa Denko KK
Current assignee: Resonac Holdings Corp
Priority date: 2005-02-21
Filing date: 2006-02-16
Publication date: 2006-08-24
Anticipated expiration: 2007-08-21
Also published as: EP1858950A1; TW200635975A; JP2006229127A; KR20070103399A; CN101124258A

Abstract

There is provided a novel thermosetting composition for a solder resist with excellent flexibility, low warping upon curing, soldering heat resistance, PCT resistance and HHBT resistance, which is suitable as a thermosetting solder resist ink for printed circuit boards and particularly FPC boards. The thermosetting composition for a solder resist according to the invention comprises as essential components: (A) an epoxy resin having two or more epoxy groups in the molecule, (B) a polyacid anhydride represented by general formula (I) as defined in claims, wherein R represents a divalent organic group and n represents an integer of 2-30, and (C) a coupling agent.

Description

DESCRIPTION

THERMOSETTING COMPOSITION FOR SOLDER RESIST

AND CURED PRODUCT THEREOF

Cross-References to Related Applications

This application claims benefit under 35 U. S. C. §119 (e) to United States Provisional Application Serial No. 60/657,733 filed March 3, 2005

Technical Field

The present invention relates to a thermosetting composition for formation of a protective film to be used for manufacture of printed circuit boards and the like, as well as to its cured products and use. Background Art

Manufacture of printed circuit boards has conventionally required various board-protecting means such as resists used during etching and solder resists used in soldering steps. The manufacturing processes for film-like printed circuit boards (flexible printed circuit boards: hereinafter abbreviated as "FPC") used in miniature devices and the like have also required solder resists for protrusion of unrelated circuits during soldering steps.

Cover lays formed by laminating polyimide films punched into specific shapes have been employed as such board-protecting means. A cover lay also serves as a circuit protecting film after soldering, and must be heat-resistant and insulative during the soldering while being flexible without bend cracking when the board is integrated.

Cover lays formed by punching polyimide films satisfy these requirements and are currently the most commonly used type, but because expensive dies are needed for punching and the punched films are attached while positioning by hand, increased costs are incurred and it is difficult to form fine patterns.

Methods proposed for solving these problems include a method of coating a photosensitive resin composition as a liquid, or attaching it as a film, onto the base. According to such methods, formation of the coating on the base may be followed by photographic exposure, development and heating to easily form a fine patterned cover lay, and therefore many different types of photosensitive resin compositions have been developed in the prior art.

However, while photosensitive resin compositions allow formation of fine patterns, the drying, exposure, development and rinsing steps required render the process inconveniently complex. On the other hand, soluble aromatic polyimides have been proposed as thermosetting solder resists (Japanese ϋnexamined Patent Publication (Kokai) HEI No. 1-121364; Patent document 1) , but these are associated with problems such as poor solubility in solvents commonly employed for ordinary screen printing, high cost, bleed- out during printing, and unsatisfactory workability.

Epoxy resin-based resist inks are also known which comprise epoxy resins and dibasic acid anhydrides as essential components (Japanese Examined Patent Publication (Kokai) HEI No. 5-75032; Patent document 2), but although they have excellent flexibility their drawbacks include low PCT resistance and HHBT resistance.

Also known are resist inks having an acid value of 20-120 mgKOH/g, a glass transition temperature of -60 to 4O⁰C and a weight-average molecular weight of 5,000-

100,000, and which comprise a polycarboxylic acid resin and an epoxy resin as essential components (Japanese Unexamined Patent Publication (Kokai) HEI No. 11-158252; Patent document 3) , but the solvent resistance of such inks is unsatisfactory.

Thus, since it has not been easy to obtain resists simultaneously exhibiting excellent flexibility, soldering heat resistance, PCT resistance and HHBT resistance, a demand has existed for further improvement. [Patent document 1]

Japanese Unexamined Patent Publication (Kokai) HEI No. 1-121364

[Patent document 2]

Japanese Examined Patent Publication (Kokai) HEI No. 5-75032

[Patent document 3] Japanese Unexamined Patent Publication (Kokai) HEI No. 11-158252 Summary of the Invention

It is an object of the present invention to provide a thermosetting composition with excellent flexibility and low warping upon curing, as well as excellent PCT resistance and HHBT resistance, and particularly a thermosetting composition which can be suitably used as a solder resist for FPC. It is another object of the invention to provide a satisfactory method for forming heat-resistant protective films using the thermosetting composition.

As a result of much diligent research, the present inventors have discovered that the aforementioned problems can be overcome by using an epoxy curing agent with a specific composition and a coupling agent, and have thereupon completed this invention. Specifically, the present invention relates to a thermosetting composition for a solder resist as laid out in [1] to [17] below, and to its cured products and use. [1] A thermosetting composition for a solder resist comprising as essential components: (A) an epoxy resin having two or more epoxy groups in the molecule, (B) a polyacid anhydride represented by the following general formula (I) :

(wherein R represents a divalent organic group and n represents an integer of 2-30), and (C) a coupling agent. [2] A thermosetting composition for a solder resist according to [1] above, wherein 5-100 wt% of the epoxy resin (A) is a catechol-type epoxy resin (A-I) represented by the following general formula (II) :

(wherein each R independently represents hydrogen or a

Cl-10 organic group, and n represents an integer of 0-3) , [3] A thermosetting composition for a solder resist according to [1] or [2] above, which further comprises

(D) an inorganic ion exchanger.

[4] A thermosetting composition for a solder resist according to any one of [1] to [3] above, which further comprises (E) a flame retardant.

[5] A thermosetting composition for a solder resist according to any one of [1] to [4] above, which further comprises (F) a hydrated metal compound.

[6] A thermosetting composition for a solder resist according to [5] above, wherein the endotherm upon thermal decomposition of the hydrated metal compound (F) is 400-2,500 J/g. [7] A thermosetting composition for a solder resist according to [5] above, wherein the hydrated metal compound (F) is aluminum hydroxide and/or magnesium hydroxide . [8] A thermosetting composition for a solder resist according to any one of [1] to [7] above, which further comprises (G) a binder polymer.

[9] A thermosetting composition for a solder resist according to any one of [1] to [8] above, which further comprises (H) a diluting agent.

[10] A thermosetting composition for a solder resist according to any one of [1] to [9] above, which has a viscosity of 500-500,000 mPa-s (25°C) .

[11] An interlayer insulating film comprising a thermosetting layer formed from a thermosetting composition for a solder resist according to any one of [1] to [10] above, on a base.

[12] A cured product of a thermosetting composition for a solder resist according to any one of [1] to [10] above.

[13] A cured product of an interlayer insulating film according to [11] above.

[14] An insulating protective coating comprising a cured product according to [12] or [13] above. [15] A printed circuit board which is partially or fully covered by a cured product according to [12] or [13] above.

[16] A flexible printed circuit board which is partially or fully covered by a cured product according to [12] or [13] above.

[17] An electronic part comprising a cured product according to [12] or [13] above. Detailed Description of the Invention

1. Epoxy resin with two or more epoxy groups in the molecule (A)

As epoxy resins with two or more epoxy groups in the molecule (A) there may be mentioned bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, tetramethylbisphenol A-type epoxy resins and bisphenol S- type epoxy resins; other difunctional epoxy resins such as resorcinol diglycidylether and dimethylbisphenol C diglycidylether; epoxy resins with fused ring skeletons such as 1, β-dihydroxynaphthalene diglycidylether, 1,6- diglycidyloxynapthalene-type epoxy resins, l-(2,7- diglycidyloxynaphthyl) -1- (2-glycidyloxynaphthyl) methane, 1, 1-bis (2, 7-diglycidyloxynaphthyl) methane and 1,1- bis (2, 7-diglycidyloxynaphthyl) -1-phenylmethane; novolac- type epoxy resins such as phenol-novolac type epoxy resins, cresol-novolac type epoxy resins, bisphenol A- novolac type epoxy resins and bisphenol AD-novolac resins; and phenolaralkyl-type epoxy resins such as phenol-p-xyleneglycol dimethylether polycondensate polyglycidyl ether; epoxy resins with cyclic aliphatic skeletons such as epoxy resins with cyclohexene oxide groups, epoxy resins with tricyclodecene oxide groups, epoxy resins with cyclopentene oxide groups and dicyclopentadiene epoxy compounds; glycidyl ester-type epoxy resins such as phthalic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, diglycidyl-p-oxybenzoic acid, dimer acid glycidyl ester and triglycidyl esters; glycidylamine-type epoxy resins such as diglycidylaniline, tetraglycidylaminodiphenylmethane, triglycidyl-p- aminophenol, tetraglycidylmetaxylylenediamine, diglycidyltoluidine and tetraglycidylbisaminomethylcyclohexane; hydantoin-type epoxy resins such as diglycidylhydantoin and glycidylglycidoxyalkylhydantoin; heterocyclic epoxy resins such as triallyl isocyanurate and triglycidyl isocyanurate; trifunctional-type epoxy resins such as fluoroglycinol triglycidyl ether, trihydroxybiphenyl triglycidylether, trihydroxyphenylmethane triglycidylether, glycerin triglycidylether, 2- [4- (2,3- epoxypropoxy) phenyl] -2- [4- [1, 1-bis [4- (2, 3- epoxypropoxy) phenyl] ethyl] phenyl] propane and l,3-bis[4- [1- [4- (2, 3-epoxypropoxy) phenyl] -1- [4- [1- [4- (2, 3- epoxypropoxy) phenyl] -1-methylethyl] phenyl] ethyl] phenoxy] - 2-propanol; and tetrafunctional-type epoxy resins such as tetrahydroxyphenylethane tetraglycidylether, tetraglycidylbenzophenone, bisresorcinol tetraglycidylether and tetraglycidoxybiphenyl. These epoxy resins are not limited to use alone, as two or more thereof may be used in combination, or modified forms thereof may be used. Preferred among these epoxy resins are catechol-type epoxy resins (A-I) represented by the following general formula (II) :

(wherein each R independently represents hydrogen or a Cl-IO organic group, and n represents an integer of 0-3) . As a specific example of a catechol-type epoxy resin there may be mentioned EPICLON HP-820 (Dainippon Ink & Chemical Co., Ltd.) which is a 4-t-butylcatechol-type epoxy resin. The content of the catechol-type epoxy resin is preferably 5-100 wt% of the epoxy resin. If the catechol-type epoxy resin content is less than 5 wt% of the epoxy resin, the formed solder resist will tend to have low flexibility and exhibit warping upon thermosetting . 2. Polyacid anhydride (B)

The polyacid anhydride (B) used for the invention may be a compound represented by the following formula (I) :

(wherein R represents a divalent organic group and n represents an integer of 2-30).

As specific examples there may be mentioned polydecanedioic anhydride, polyoctadecanedioic anhydride, poly-8-ethyloctadecanedioic anhydride, polyeicosanedioic anhydride and poly-8, 13-dimethyl-8, 12-eicosadienedioic anhydride .

As curing agents other than the polyacid anhydride (B) there may be used amine-based compounds, acid anhydride-based curing agents, phenol-based curing agents, imidazole-based compounds and the like, which are ordinarily used as epoxy resin curing agents.

The content of the polyacid anhydride (B) is preferably in an amount with acid anhydride groups in the range of 0.05-2.0 (equivalent ratio) with respect to the epoxy groups of the epoxy resin (A) . If the ratio is greater than 2.0 the soft components will be too abundant and heat resistance will be insufficient, while if it is less than 0.05 the flexibility will be inadequate. The value for acid anhydride groups of the polyacid anhydride (B) referred to here is the reciprocal of the acid anhydride equivalents.

3. Coupling agent (C)

The coupling agent (C) used for the invention may be a silane coupling agent, titanate-based coupling agent, aluminum-based coupling agent or the like. As specific examples of silane coupling agents there may be mentioned vinyltrichlorosilane, vinyltris (β-methoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ- (methacryloxypropyl) trimethoxysilane, β- (3, 4- epoxycyclohexyl) ethyltrimethoxysilane, γ- glycidoxypropyltrimethoxysilane, γ- glycidoxypropylmethyldiethoxysilane, N-β- (aminoethyl) -γ- aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ- aminopropylmethyldimethoxysilane, γ- aminopropyltriethoxysilane, N-phenyl-γ- aminopropyltrimethoxysilane, γ- mercaptopropyltrimethoxysilane, γ- chloropropyltrimethoxysilane, or the imidazolesilanes IS- 1000, IS-1000D, IM-1000, SP-1000, IA-100A, IA-100P, IA- 100F, IA-100AD, IA-100FD, IM-100F, IS-3000 and IS-4000 by Japan Energy Corp., as titanate-based coupling agents there may be mentioned isopropyltriisostearoyl titanate, isopropyl tri-n-dodecylbenzenesulfonyltitanate, isopropyl tris (dioctylpyrophosphate) titanate, tetraisopropyl bis (dioctylphosphite) titanate, tetraoctyl bis (ditridecylphosphite) titanate, tetra (2,2- diallyloxymethyl-1-butyl) bis (di-tridecyl) phosphite titanate, bis (dioctylpyrophosphate) oxyacetate titanate, bis (dioctylpyrophosphate) ethylene titanate and isopropyltri (N-aminoethyl-aminoethyl) titanate, and as aluminum-based coupling agents there may be mentioned Plenacuto AL-M by Ajinomoto Fine Techno Corp. These may be used alone or in combinations of two or more.

The content of the coupling agent is preferably 0.05-5 wt% of the effective components of the thermosetting composition for a solder resist. The content is more preferably 0.1-3 wt%. 4. Inorganic ion exchanger (D)

As inorganic ion exchangers (D) to be used for the invention there may be mentioned aluminosilicates such as natural zeolite or synthetic zeolite, metal oxides such as aluminum oxide or magnesium oxide, hydroxides such as hydrous titanium oxide, hydrous bismuth oxide or hydrous antimony oxide, acidic salts such as zirconium phosphate or titanium phosphate, basic salts such as hydrotalcites, compound hydrous oxides, heteropolyphosphoric acids such as ammonium molybdophosphate, or hexacyanoiron (III) salts or hexacyanozinc. Among these, hydroxides and hydrous oxides are preferred because of their high heat resistance, chemical resistance and moisture resistance, and specifically hydrous titanium oxide, hydrous bismuth oxide and hydrous antimony oxide are preferred.

The inorganic ion exchanger (D) used for the invention preferably has a cation exchange capacity of at least 0.1 meq/g based on Na ion and/or an anion exchange capacity of at least 0.1 meq/g based on Cl ion. If the ion-exchange capacity is less than 0.1 meq/g are large amount of addition will be necessary, possibly impairing the properties such as mechanical strength and flexibility of the cured product. These may be used alone or in combinations of two or more. The content of the inorganic ion exchanger (D) is preferably 0.01-10 wt% of the effective components of the thermosetting composition for a solder resist. 5. Flame retardant (E) There are no particular restrictions on the flame retardant (E) used for the invention, and there may be mentioned bromine compounds, phosphorus compounds, antimony-based compounds and the like. As specific examples of bromine compounds there may be mentioned brominated epoxy compounds, tetrabromobisphenol A carbonate oligomer, tetrabromobisphenol A, tetrabromobisphenol A-bis (2, 3-dibromopropyl ether), tetrabromobisphenol A-bis (allyl ether) , tetrabromobisphenol A-bis (ethoxylate) , tetrabromobisphenol S, tetrabromobisphenol S-bis(2,3- dibromopropyl ether) , hexabromobenzene, hexabromocyclododecane, decabromodiphenyl oxide, octabromodiphenyl oxide, ethylenebis (pentabromophenyl) , ethylenebis (tetrabromophthalimide) , tetrabromophthalic anhydride, tribromophenol, tris (tribromophenoxy) triazine, polybromophenylene oxide, bis (tribromophenoxyethane) , tribromoneopentyl glycol, dibromoneopentyl glycol, pentabromobenzyl acrylate, dibromostyrene, tribromostyrene, poly (pentabenzyl acrylate) and brominated polystyrene. Brominated epoxy resins and phosphorus compounds are preferred among these.

As specific examples of brominated epoxy resins there may be mentioned brominated bisphenol A-type epoxy resins, brominated cresol-novolac type epoxy resins and brominated phenylglycidyl ethers. Particularly preferred are brominated bisphenol A-type ^' epoxy resins. The content of brominated epoxy resins of the solid content of the thermosetting composition for a solder resist is preferably in the range of 4-15 wt% in terms of bromine content .

Phosphorus compounds which may be used are not particularly limited but preferred specific examples include phosphoric acid ester compounds and phosphazene compounds. Phosphoric acid ester compounds and phosphazene compounds are preferably used in combination in order to increase the flexibility without impairing the flame retardance. As specific examples of phosphoric acid esters there may be mentioned tributyl phosphate, tris (2-ethylhexyl) phosphate, tris (butoxyethyl) phosphate, tricresyl phosphate, trixylenyl phosphate, 2- ethylhexyldiphenyl phosphate, cresyl di-2,6- xylenylphosphate, and CR-733S, CR-741, CR-747 and PX-200 by Daihachi Chemical Industry Co., Ltd. As specific examples of phosphazenes there may be mentioned SPH-100 and SBP-100 by Otsuka Chemical Co., Ltd. These phosphoric acid ester compounds and phosphazene compounds may be used alone or in mixtures of two or more. The content of phosphorus compounds of the solid content of the thermosetting composition for a solder resist is preferably in the range of 2-10 wt%. If the phosphorus compound content is less than 2 wt% a flame retarding effect will not be achieved, and if it is greater than 10 wt% the outer appearance of the cured film may be impaired by bleed-out. 6. Hydrated metal compound (F)

The hydrated metal compound (F) used in the thermosetting composition for a solder resist according to the invention is a metal compound containing water of crystallization, and for example, the water of crystallization content may be in the range of 12-60 wt% per mole based on thermal analysis, although this is not a restriction. From the standpoint of the flame retardant effect, a hydrated metal with an endotherm of 400 J/g or greater and preferably 600-2,500 J/g during thermal decomposition is preferably used. As specific examples of hydrated metals there may be mentioned aluminum hydroxide, magnesium hydroxide, calcium hydroxide, dawsonite, calcium aluminate, dihydrated gypsum, zinc borate, barium metaborate, zinc hydroxystannate, kaolin, vermiculite and the like.

Particularly preferred among these are aluminum hydroxide and magnesium hydroxide.

There are no particular restrictions on the particle size of the hydrated metal compound (F) used in the thermosetting composition for a solder resist according to the invention, but the mean particle size is preferably no greater than 40 μm and more preferably no greater than 2 μm. If the mean particle size exceeds 40 μm, the transparency and light transmittance of the cured resist will be lowered, often impairing the outer appearance and smoothness of the coated film surface.

As hydrated metal compounds to be used for the invention there are particularly preferred those that have been surface treated with polar surface treatment agents, from the standpoint of improving transparency. As specific examples of surface treatment agents there may be mentioned silane coupling agents such as epoxysilane, aminosilane, vinylsilane and mercaptosilane, and titanate coupling agents.

Their content in the thermosetting composition for a solder resist according to the invention is preferably 5- 30 wt%.

7. Binder polymer (G)

The binder polymer (G) is not particularly restricted, and for example, there may be used (meth)acryl resins, styrene-based resins, polybutadiene resins, acrylonitrile-butadiene copolymers, polyesters, polyacetals, polyurethanes, polyamides, polyamideimides, polycarbonates, polyimides, phenol resins, cresol resins, xylene resins, acetophenoneformaldehyde resins, alkylacetalated polyvinylalcohols and the like.

Their content in the thermosetting composition for a solder resist according to the invention is preferably 1- 20 wt%.

8. Diluting agent (H) Solvents, polymerizable monomers and the like may be used as diluting agents (H) . As solvents there may be mentioned ketone-based solvents such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ester- based solvents such as ethyl acetate, ethyl acetoacetate, γ-butyrolactone and butyl acetate; alcohol-based solvents such as butanol and benzyl alcohol; cellosolve-based and carbitol-based solvents and their ester and ether derivatives; amide-based solvents such as N, N- dimethylformamide, N, N-dimethylacetamide and N-methyl-2- pyrrolidone; dimethylsulfoxide; phenol-based solvents such as phenol and cresol; nitro compound-based solvents; toluene, xylene, hexamethylbenzene and cumene aromatic- based solvents; and aromatic-based or alicyclic-based solvents composed of hydrocarbons such as tetralin, decalin and dipentene. As polymerizable monomers there may be mentioned hydroxyalkyl (meth) acrylates such as 2- hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate, glycol mono- or di (meth) acrylates such as ethylene glycol, methoxytetraethylene glycol and polyethylene glycol, (meth) acrylamides such as N, N- dimethyl (meth) acrylamide and N-methylol (meth) acrylamide, aminoalkyl (meth) acrylates such as N, N-dimethylaminoethyl (meth) acrylate, polyvalent (meth) acrylates of polyhydric alcohols such as hexanediol, trimethylolpropane, pentaerythritol, ditrimethylolpropane, dipentaerythritol and trishydroxyethyl isocyanurate, or their ethylene oxide or propylene oxide addition products,

(meth) acrylates of phenol ethylene oxide or propylene oxide addition products such as phenoxyethyl (meth) acrylate or bisphenol A polyethoxydi (meth) acrylate, (meth) acrylates of glycidyl ethers such as glycerin diglycidylether, trimethylolpropane triglycidylether and triglycidyl isocyanurate, and ε-caprolactone-modified (meth) acrylates such as caprolactone-modified tris (acryloxyethyl) isocyanurate, and melamine (meth) acrylate . These may be used alone or in combinations of two or more.

The amount of diluting agent (H) used is preferably adjusted so that the viscosity of the thermosetting composition for a solder resist is 500-500,000 mPa*s [measured at 25°C with a Brookfield Viscometer] . The value is more preferably 800-30,000 mPa-s. This range of viscosity is more suitable and convenient for coating and printing onto objects. The preferred amount of diluting agent (H) for this range of viscosity is 0-40 wt% in the thermosetting composition. 9. Other additives

The thermosetting composition for a solder resist according to the invention may also contain other additives such as ordinary publicly known epoxy curing catalysts, inorganic fillers, organic fillers, waxes or surfactants, as necessary for the purpose of enhancing the properties such as heat resistance, hardness, flow properties (thixotropicity and viscosity) or flame retardance .

As specific examples of inorganic fillers there may be mentioned talc, barium sulfate, barium titanate, silica, alumina, clay, magnesium carbonate, calcium carbonate, aluminum hydroxide and silicate compounds. As specific examples of organic fillers there may be mentioned silicone resins, silicone rubber and fluorine resins. As specific examples of waxes there may be mentioned polyamide waxes and polyethylene oxide waxes. As specific examples of surfactants there may be mentioned silicone oils, higher fatty acid esters and amides. These flow property adjustors may be used alone or in combinations of two or more. Using an inorganic filler is advantageous not only for the flow properties of the thermosetting composition for a solder resist, but also for enhanced cohesion and hardness.

As thickeners there may be mentioned asbestos, orben, bentone, montmorillonite and the like. Defoaming agents are used to eliminate foam produced during printing, application and curing, and specifically there may be mentioned acrylic-based and silicone-based surfactants. Leveling agents are used to eliminate unevenness of the film surface formed during printing and application, and as specific examples there may be mentioned acrylic-based and silicone-based surfactants. As tackifiers there may be mentioned imidazole-based, thiazole-based, triazole-based and silane coupling agents .

If necessary, additives such as coloring agents, thermopolymerization inhibitors, radical polymerization initiators, thickeners, defoamers, leveling agents and tackifiers can be added to the thermosetting composition for a solder resist according to the invention. As coloring agents there may be mentioned phthalocyanine blue, phthalocyanine green, iodine green, disazo yellow, crystal violet, titanium oxide, carbon black and naphthalene black. As thermopolymerization inhibitors there may be mentioned hydroquinone, hydroquinone monomethyl ether, tert-butyl catechol, pyrogallol and phenothiazine . As radical polymerization initiators there may be mentioned azobis-based and peroxide-based compounds. As thickeners there may be mentioned asbestos, orben, bentone, montmorillonite and the like. Defoaming agents are used to eliminate foam produced during printing, application and curing. Specifically there may be mentioned acrylic-based and silicone-based surfactants. Leveling agents are used to eliminate unevenness of the film surface formed during printing and application. Specifically there may be mentioned acrylic-based and silicone-based surfactants. As tackifiers there may be mentioned imidazole-based, thiazole-based, triazole-based and silane coupling agents .

Other additives such as ultraviolet absorbers and plasticizers can be added to impart storage stability, so long as the effect of the invention is not impaired. 10. Process for production of thermosetting composition for solder resist

The thermosetting composition for a solder resist according to the invention may be produced by mixing the aforementioned components by an ordinary method. There are no particular restrictions on the mixing method, and a portion of the components may be mixed before adding the remaining components, or all of the components may be mixed together at once.

Specifically, the production may be carried out by a publicly known kneading method using a kneader, triple roll, bead mill or the like after mixing the aforementioned components.

11. Cured products of thermosetting composition for solder resist, and their use The thermosetting composition for a resist according to the invention may be coated onto a base to an appropriate thickness and then heat treated to produce a cured product.

The thermosetting composition for a resist according to the invention can form a cured film having excellent flexibility, as well as satisfactory performance in terms of heat resistance, electrical insulating properties and adhesion to circuit boards. The cured film exhibits particularly superior flexibility and electrical insulating properties, and therefore produces no curling even when used on a thin circuit board such as an FPC board, and can form satisfactory flexible insulating protective films which also have excellent electrical performance and handling properties. The composition of the invention may also be suitably used as an interlayer insulating resin layer for a multilayer printed circuit board.

An insulating protective film may be formed by first coating the thermosetting composition for a solder resist onto the circuit-formed board to a thickness of 10-100 μm, and then heat treating it in a temperature range of 100-200°C for 10-60 minutes for curing.

The thermosetting composition for a solder resist according to the invention may be used for a variety of purposes, but is particularly suited for use as an insulating protective film for a printed circuit board or as an interlayer insulating resin layer for a multilayer printed circuit board, which require excellent thermosetting properties, adhesion with boards, insulating properties, heat resistance, warping deformation resistance and flexibility. Cured products of the thermosetting composition for a solder resist according to the invention are suitable for use in electronic parts that require especially high durability. Examples Examples 1-6 and Comparative Examples 1-4

Thermosetting compositions were prepared by kneading the main ingredients and curing agents separately three — 1J. QO ""

times using a triple roll mill (Model RIII-I RM-2 by Kodaira Seisakusho Co., Ltd. ) , in the ^' proportions listed in Table 1 below.

The obtained thermosetting compositions were evaluated in the following manner.

• Thermosetting property

Each thermosetting composition for a solder resist was coated onto a 25 μm polyimide film (CAPTONE™ 10OH, Toray-DuPont Co., Ltd.) by screen printing with a 150 mesh polyester plate, and set in a 15O⁰C hot-air circulating drier for thermosetting for 20 minutes, 40 minutes and 60 minutes. A few drops of ethyl acetate were then dropped onto the thermoset film and the condition of the film after rubbing with a cloth was visually observed. If cured, the film exhibits no change. The evaluation criteria for thermosetting were as follows.

A: No change in film observed B: Whitening of film C: Dissolution of film

• Flexibility

Each thermosetting composition for a solder resist was coated onto a board by screen printing with a 150 mesh polyester plate, and thermoset for 40 minutes at 150⁰C. The board used was an approximately 25 μm-thick polyimide film. The obtained polyimide film was folded 180° with the coated side outward and visually judged for the occurrence of whitening. The criteria used for judgment were as follows. A: No whitening of cured film

C: Whitening or cracking of cured film

• Soldering heat resistance

Each thermosetting composition for a solder resist was coated onto a board by screen printing with a 150 mesh polyester plate, and thermoset for 40 minutes at

150°C, according to the test method of JIS-C-6481. The board used was a print board (UPISEL™ N, Ube Kosan Co., Ltd.) composed of a polyimide film (41 μm thickness) with a copper foil (35 μm thickness) laminated on one side, which had been cleaned with 1% aqueous sulfuric acid, rinsed with water and dried with an air stream.

The cycle of application of a rosin-based flux onto the obtained test piece and floating for 5 seconds in a soldering bath at 260°C, was repeated while visually observing the cured film after each cycle to confirm the complete absence of "blistering" and "solder sinking" or other types of changes, and the maximum number of cycles without change was recorded. • Flammability

A flammable test piece was prepared in the following manner. A 20 μm-thick cured thermosetting composition for a solder resist was formed on both sides of a 25 μm- thick, 200 mm x 50 mm polyimide film (CAPTONE™ 10OH, Toray-DuPont Co., Ltd.), to prepare a test piece. The flammable characteristics were evaluated according to the Tests for Flammability of Plastic

Materials (94UL-VTM) of the Underwriters Laboratories Inc. U.S.A. (UL) .

The "VTM" and "NOT" abbreviations in Table 1 signify the following. VTM-O: Rating that satisfies all of the following requirements .

(1) Flaming combustion time of no greater than 10 seconds for any test piece after first burner flame application. (2) Total flaming combustion time of no greater than 50 seconds after applying a total of 10 burner flames to 5 test pieces of any set.

(3) Flaming or glowing combustion failed to reach 125 mm mark line. (4) Flaming drops failed to ignite absorbent cotton. (5) Total flaming and glowing combustion time for each test piece of no greater than 30 seconds after second burner flame application.

(6) Where only one of five test pieces in a set failed to satisfy the requirements or the total flaming combustion time ranges from 51 to 55 seconds, upon retesting all of the five test pieces satisfied requirements (1) to (5) .

VTM-I: Rating that satisfies all of the following requirements . (1) Flaming combustion time of no greater than 30 seconds for any test piece after first burner flame application.

(2) Total flaming combustion time of no greater than 250 seconds after applying a total of 10 burner flames to 5 test pieces of any set.

(3) Flaming or glowing combustion failed to reach 125 mm mark line.

(4) Flaming drops failed to ignite absorbent cotton.

(5) Total flaming and glowing combustion time for each test piece of no greater than 60 seconds after second burner flame application.

(6) Where only one of five test pieces in a set failed to satisfy the requirements or the total flaming combustion time ranges from 251 to 255 seconds, upon retesting all of the five test pieces satisfied requirements (1) to (5) .

VTM-2: Rating that satisfies all of the following requirements .

(1) Flaming combustion time of no greater than 30 seconds for any test piece after first burner flame application.

(2) Total flaming combustion time of no greater than 250 seconds after applying a total of 10 burner flames to 5 test pieces of any set. (3) Flaming or glowing combustion failed to reach 125 mm mark line.

(4) Flaming drops may ignite absorbent cotton. (5) Total flaming and glowing combustion time for each test piece of no greater than 60 seconds after second burner flame application.

NOT: Cases which fall in none of the above ratings. • PCT resistance

Each thermosetting composition for a solder resist was coated onto UPISEL N by screen printing with a 150 mesh polyester plate, and thermoset for 40 minutes at 150°C. The obtained test piece was treated with a PCT apparatus (ESPEC HAST CHAMBER EHS-411M by Tabai Corp.) for 96 hours under conditions of 121°C, 0.2 MPa and the condition of the cured film was evaluated. A: No peeling, coloration or elution B: Peeling, coloration or elution C". Extensive peeling, coloration and elution • HHBT resistance

Each thermosetting composition for a solder resist was coated onto an IPC-C (comb-shaped pattern) of a commercially available board (IPC conforming) by screen printing with a 150 mesh polyester plate, and thermoset for 40 minutes at 15O⁰C. A 100 V direct current was applied to the test piece in an atmosphere of 85°C, 85% relative humidity. The intralayer insulation resistance value was measured after 1,000 hours to evaluate the HHBT resistance. The insulation resistance value was determined by maintaining application of the 100 V current voltage for one minute and then performing measurement with an electrical resistance tester with the voltage still applied. The judgment criteria were as follows.

A: Insulation resistance of 10⁸ Ω or greater. C: Insulation resistance of less than 10⁸ Ω.

The evaluation results are shown in Table 1 below.

Table 1

K) U)

*1 EPIKOTE : Bisphenol A-type epoxy resin (Japan Epoxy Resins Co., Ltd.)

*2 EPIKOTE 1001: Bisphenol A-type epoxy resin (Japan Epoxy Resins Co., Ltd.)

*3 ECA: Ethylcarbitol acetate (Tokyo Kasei Kogyo Co., Ltd.)

*4 EPICLON HP-820: Butylcatechol-type epoxy resin (Dainippon Ink and Chemicals, Inc.)

*5 IXE-100: Cation exchanger (Toa Gosei Co., Ltd.)

*6 EPIKOTE 5051: Tetrabromobisphenol A-type epoxy resin (Japan Epoxy Resins Co., Ltd.)

*7 PX-200: Aromatic condensed phosphoric acid ester (Daihachi Chemical Industry Co., Ltd.

*8 HIGILITE H43M: Aluminum hydroxide (Showa Denko K.K.)

*9 SG-2000: Talc (Nippon Talc Co., Ltd.)

*10 Aerosil #380: Silicon dioxide (Nippon Aerosil Co., Ltd.)

*11 Flowlen AO-40H: Defoaming agent (Kyoeisha Chemical Co., Ltd.)

*12 SB-20AH: 8-Ethyloctadecanedioic anhydride (Okamura Oil- Mill, Ltd.)

*13 Curezol 2PHZ-PW: 2-Phenyl-4, 5-dihydroxymethylimidazole (Shikoku Chemicals Corp.)

*14 Succinic anhydride: (New Japan Chemical Co., Ltd.)

Effect of the Invention

The thermosetting composition for a solder resist according to the invention has excellent flexibility, low warping upon curing, and excellent soldering heat resistance, PCT resistance and HHBT resistance, and is thus suitable as a thermosetting solder resist ink for printed circuit boards and especially FPC boards.

Claims

1. A thermosetting composition for a solder resist comprising as essential components: (A) an epoxy resin having two or more epoxy groups in the molecule, (B) a polyacid anhydride represented by the following general formula (I) :

wherein R represents a divalent organic group and n represents an integer of 2-30, and (C) a coupling agent.

2. A thermosetting composition for a solder resist according to claim 1, wherein 5-100 wt% of said epoxy resin (A) is a catechol-type epoxy resin (A-I) represented by the following general formula (II):

wherein each R independently represents hydrogen or a Cl- 10 organic group, and n represents an integer of 0-3.

3. A thermosetting composition for a solder resist according to claim 1, which further comprises (D) an inorganic ion exchanger.

4. A thermosetting composition for a solder resist according to claim 1, which further comprises (E) a flame retardant .

5. A thermosetting composition for a solder resist according to claim 1, which further comprises (F) a hydrated metal compound.

6. A thermosetting composition for a solder resist according to claim 5, wherein the endotherm upon thermal decomposition of said hydrated metal compound (F) is 400- 2500 J/g.

7. A thermosetting composition for a solder resist according to claim 5, wherein said hydrated metal compound (F) is aluminum hydroxide and/or magnesium hydroxide.

8. A thermosetting composition for a solder resist according to claim 1, which further comprises (G) a binder polymer.

9. A thermosetting composition for a solder resist according to claim 1, which further comprises (H) a diluting agent.

10. A thermosetting composition for a solder resist according to claim 1, which has a viscosity of 500- 500,000 mPa-s (25°C) .

11. An interlayer insulating film comprising a thermosetting layer formed from a thermosetting composition for a solder resist according to claim 1, on a base.

12. A cured product of a thermosetting composition for a solder resist according to claim 1.

13. A cured product of an interlayer insulating film according to claim 11. ^β

14. An insulating protective coating comprising a cured product according to claim 12 or 13.

15. A printed circuit board which is partially or fully covered by a cured product according to claim 12 or 13.

16. A flexible printed circuit board which is partially or fully covered by a cured product according to claim 12 or 13.

17. An electronic part comprising a cured product according to claim 12 or 13.