Flux for resin-cored solder, resin-cored solder, and soldering method

Abstract

The purpose of the present invention is to provide flux by which discharge of sediment is promoted, resin-cored solder in which the flux is used, and a soldering method. This flux for resin-cored solder contains 60-99.9 mass% (inclusive) of a rosin ester relative to the mass of the entire flux, and contains 0.1-15 mass% (inclusive) of covalent-bond halides relative to the mass of the entire flux. The flux for the resin-cored solder is used in linear resin-cored solder that is supplied to through-holes formed along the central axis of a soldering iron.

Description

TECHNICAL FIELD

[0001] The present invention relates to a flux forresin-cored solder, resin-cored solder, and a solderingmethod.BACKGROUND ART

[0002] In general, a flux used for soldering hasproperties of chemically removing metal oxides present onsolder and the metal surface of a joining object to besoldered, and moving metal elements at the boundarytherebetween. Hence, soldering using a flux can formintermetallic compounds between solder and the metal surfaceof a joining object, thereby producing a strong joint.

[0003] As solder used for soldering, there has beenwire-shaped solder filled with a flux, which is referred toas resin-cored solder. A flux supposed to be used in suchresin-cored solder has been proposed (e.g., in PatentLiteratures 1 and 2).

[0004] As a soldering method using resin-cored solder,there has been known using a heating member, which isreferred to as a soldering iron. Regarding this, there hasbeen proposed a technique of providing a through hole at thecentral axis of a soldering iron and supplying resin-coredsolder into the through hole to perform soldering (e.g., inPatent Literature 3).CITATION LISTPatent Literature

[0005] Patent Literature 1: JP H05-42388 APatent Literature 2: JP H05-42389 APatent Literature 3: JP 2009-195938 ASUMMARY OF INVENTIONProblem to Solve

[0006] If soldering is performed using a soldering ironsuch as the one disclosed in Patent Literature 3, rosin thatis contained in a flux for resin-cored solder to be suppliedinto the through hole and hardly volatilizes in a thermalhistory expected during soldering may become residues afterheated and adhere to the inner surface of the through holeof the soldering iron. In the soldering using the solderingiron disclosed in Patent Literature 3, soldering is performedcontinuously with resin-cored solder supplied into thethrough hole of the soldering iron in a state in which thesoldering iron is controlled so as to keep a predeterminedtemperature exceeding the melting point of solder. As aresult, adhered matters, such as the residues, keep beingheated and become carbide. This is a cause of burning in thethrough hole. The carbide is accumulated in the through holeof the soldering iron, which makes the diameter of thethrough hole small. This may cause the resin-cored solder tobe unable to be supplied.

[0007] There has been proposed therefore a technique ofusing volatile rosin as the main component of a flux that isused by a soldering iron such as the one disclosed in PatentLiterature 3 in order to volatilize the flux during soldermelting, thereby preventing carbide from being accumulatedin the through hole of the soldering iron.

[0008] By using volatile rosin as the main component,most of the flux volatilizes as intended. However, the fluxresidues, which are the remaining part of the flux, becomecarbide and are accumulated in the through hole of asoldering iron, and the through hole of the soldering ironis eventually clogged with deposits thereof.

[0009] The present invention has been conceived in orderto solve such a problem(s), and objects thereof includeproviding a flux that facilitates discharge of deposits, andresin-cored solder and a soldering method using this flux.Solution to Problem

[0010] A flux containing nonvolatile rosin, whichhardly volatilizes, has been considered unsuitable as a fluxfor resin-cored solder that is used by a soldering iron suchas the one disclosed in Patent Literature 3. Regarding this,the present inventors have found that, of nonvolatile rosin,a rosin ester(s) can liquefy deposits of flux residues inthe through hole of a soldering iron and facilitate dischargeof the deposits to the outside, thereby preventing thedeposits from adhering to the inside of the through hole ofthe soldering iron.

[0011] Hence, the present invention is a flux for resin-coredsolder that is used in resin-cored solder that is supplied into athrough hole formed along the central axis of a soldering iron,including: 60% by mass to 99.9% by mass of a rosin ester(s) to thetotal mass of the flux; 0.1% by mass to 15% by mass of a covalenthalogen compound(s) to the total mass of the flux; and more than 0%by mass to 10% by mass of rosin amine, N,N-diethyloctylamine, orrosin amine and N,N-diethyloctylamine to the total mass of the flux.

[0012] The covalent halogen compound is one type or twoor more types of trans-2,3-dibromo-1,4-butenediol, triallylisocyanurate hexabromide, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, 2,3-dibromo-2-butene1,4-diol, trans-2,3-dibromo-2-butene-1,4-diol, cis-2,3-dibromo-2-butene-1,4-diol, 2,2-bis(bromomethyl)-1,3-propanediol, tetrabromoethane, tetrabromobutane,tetrabromophthalic acid, bromosuccinic acid, and 2,2,2-tribromoethanol.

[0013] The rosin ester is one or more types of rosinesters each being one type of rosin esterified or one ormore types of rosin esters each being a mixture of two ormore types of rosin esterified, and the rosin to beesterified is any or any mixture of natural rosin and rosinderivatives obtained from the natural rosin, wherein therosin derivatives are: purified rosin; polymerized rosin;hydrogenated rosin; disproportionated rosin, hydrogenateddisproportionated rosin; acid-modified rosin; phenolmodified rosin; an α, β-unsaturated carboxylic acid-modifiedproduct; a purified product, a hydride and adisproportionated product of the polymerized rosin; and apurified product, a hydride and a disproportionated productof the α, β-unsaturated carboxylic acid-modified product.

[0014] The flux may further include 0% by mass to 39%by mass of other rosin to the total mass of the flux and / orfurther include 0% by mass to 39% by mass of an activator(s)other than the covalent halogen compound to the total massof the flux.

[0015] Further, the present invention is (a) resincored solder including solder filled with the abovedescribed flux for resin-cored solder.

[0016] Still further, the present invention is a solderingmethod including: supplying resin-cored solder that is solder filledwith a flux for resin-cored solder including 60% by mass to 99.9% bymass of a rosin ester(s) to the total mass of the flux, 0.1% by massto 15% by mass of a covalent halogen compound(s) to the total massof the flux; and more than 0% by mass to 10% by mass of rosin amine,N,N-diethyloctylamine, or rosin amine and N,N-diethyloctylamine tothe total mass of the flux into a through hole formed along thecentral axis of a soldering iron; and heating the resin-cored solderto a temperature exceeding the melting point of the solder with thesoldering iron, thereby heating a joining object and melting theresin-cored solder.Advantageous Effects of Invention

[0017] The rosin ester can liquefy deposits of the fluxresidues in the through hole of a soldering iron andfacilitate discharge of the deposits to the outside, therebypreventing the deposits from adhering to the inside of thethrough hole of the soldering iron.

[0018] Further, addition of the covalent halogencompound, which is a halogen compound not classified as ahalide (halogen element that does not bind), can achieveexcellent usability without impairing reliability.BRIEF DESCRIPTION OF DRAWINGS

[0019] [FIG. 1] This illustrates an example of a solderingiron that is used in a soldering method of an embodiment.[FIG. 2A] This illustrates the soldering method of theembodiment.[FIG. 2B] This illustrates the soldering method of theembodiment.[FIG. 2C] This illustrates the soldering method of theembodiment.[FIG. 2D] This illustrates the soldering method of theembodiment.DESCRIPTION OF EMBODIMENTS

[0020] <Examples of Flux for Resin-cored Solder ofEmbodiment>A flux for resin-cored solder of an embodiment containsa rosin ester(s) and a covalent halogen compound(s), whichis a halogen compound not classified as a halide.

[0021] Rosin esters can liquefy deposits of fluxresidues in a through hole of a soldering iron and facilitatedischarge of the deposits to the outside, thereby preventingthe deposits from adhering to the inside of the through holeof the soldering iron.

[0022] However, a flux containing a rosin ester(s) hasa problem that the acid value of the base material (rosinester and other rosin) in the flux decreases. For the fluxcontaining a predetermined amount of the rosin ester thatcan liquefy deposits of the flux residues, a conventionaladditive amount of an amine halogen salt(s) is insufficientfor activity, and no wetting is likely to occur in asoldering process of supplying resin-cored solder into athrough hole formed along the central axis of a solderingiron to perform soldering. In order to improve wettability,increasing the amount of the amine halogen salt could bedone, but increasing the amount of the amine halogen saltincreases the content of a halide(s) (halogen element thatdoes not bind). As a result, reliability may decrease.

[0023] To overcome this, the flux for resin-cored solderof this embodiment, which is used in resin-cored solder thatis supplied into a through hole formed along the centralaxis of a soldering iron, contains 60% by mass to 99.9% bymass of the rosin ester to the total mass of the flux and0.1% by mass to 15% by mass of the covalent halogen compound,which is a halogen compound not classified as a halide, tothe total mass of the flux. This can prevent the throughhole of a soldering iron from being clogged with the deposits,and also achieve excellent usability without impairingreliability.

[0024] If the content of the rosin ester is less than60% by mass, which is the lower limit specified in thepresent invention, the effect of preventing the through holeof a soldering iron from being clogged with the deposits isnot sufficient. If the content of the rosin ester is morethan 99.9% by mass, which is the upper limit specified inthe present invention, solder’s wettability decreases.

[0025] If the content of the covalent halogen compoundis less than 0.1% by mass, which is the lower limit specifiedin the present invention, usability decreases. If the contentof the covalent halogen compound is more than 15% by mass,which is the upper limit specified in the present invention,reliability decreases.

[0026] It is preferable that the rosin ester be one ormore types of rosin esters each being one type of rosinesterified or one or more types of rosin esters each beinga mixture of two or more types of rosin esterified. Examplesof the rosin to be esterified include natural rosin, such asgum rosin, wood rosin and tall oil rosin, and derivativesobtained from the natural rosin. Examples of the rosinderivatives include: purified rosin; polymerized rosin;hydrogenated rosin; disproportionated rosin; hydrogenateddisproportionated rosin; acid-modified rosin; phenolmodified rosin; α, β-unsaturated carboxylic acid-modifiedproducts (acrylated rosin, maleated rosin, fumarated rosin,etc.); purified products, hydrides and disproportionatedproducts of polymerized rosin; purified products, hydridesand disproportionated products of α, β-unsaturatedcarboxylic acid-modified products; and mixtures of any ofthese. The rosin ester is preferably solid, but may be liquidif the flux can have a viscosity to be processed to formresin-cored solder. The viscosity required for the flux forresin-cored solder is 3,500 Pa·s or more, for example.

[0027] It is preferable that the covalent halogencompound be one type or two or more types of trans-2,3-dibromo-1,4-butenediol, triallyl isocyanurate hexabromide,1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol,3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo1,4-butanediol, 2,3-dibromo-2-butene-1,4-diol, trans-2,3-dibromo-2-butene-1,4-diol, cis-2,3-dibromo-2-butene-1,4-diol, 2,2-bis(bromomethyl)-1,3-propanediol,tetrabromoethane, tetrabromobutane, tetrabromophthalic acid,bromosuccinic acid, and 2,2,2-tribromoethanol.

[0028] The flux for resin-cored solder of thisembodiment may further contain 0% by mass to 39% by mass ofrosin or resin other than the rosin ester to the total massof the flux. Examples of the other rosin include naturalrosin, such as gum rosin, wood rosin and tall oil rosin, andderivatives obtained from the natural rosin. Examples of therosin derivatives include: purified rosin; polymerizedrosin; hydrogenated rosin; disproportionated rosin;hydrogenated disproportionated rosin; acid-modified rosin;phenol-modified rosin; α, β-unsaturated carboxylic acidmodified products (acrylated rosin, maleated rosin,fumarated rosin, etc.), purified products, hydrides anddisproportionated products of polymerized rosin; andpurified products, hydrides and disproportionated productsof α, β-unsaturated carboxylic acid-modified products. Oneor more types of these can be used.

[0029] Examples of the resin other than the other rosininclude terpene resin, modified terpene resin, terpenephenol resin, modified terpene phenol resin, styrene resin,modified styrene resin, xylene resin, and modified xyleneresin, and at least one type selected from these can befurther contained in the flux. Examples of the modifiedterpene resin usable include aromatic modified terpene resin,hydrogenated terpene resin, and hydrogenated aromaticmodified terpene resin. Examples of the modified terpenephenol resin usable include hydrogenated terpene phenolresin. Examples of the modified styrene resin usable includestyrene acrylic resin and styrene maleic acid resin. Examplesof the modified xylene resin usable include phenol-modifiedxylene resin, alkylphenol-modified xylene resin, phenolmodified resol-type xylene resin, polyol-modified xyleneresin, and polyoxyethylene-added xylene resin.

[0030] The flux for resin-cored solder of thisembodiment may further contain 0% by mass to 39% by mass ofan activator(s) other than the covalent halogen compound tothe total mass of the flux.

[0031] The other activators refer to an organic acid(s),amine(s), a halogen compound(s) other than the covalenthalogen compound, which is a halogen compound not classifiedas a halide, and the like. It is preferable that the fluxcontain, as the other activators, 0% by mass to 20% by massof an organic acid(s), 0% by mass to 10% by mass of anamine(s), and 0% by mass to 3% by mass of an amine halogensalt(s).

[0032] Examples of the organic acid include glutaricacid, adipic acid, azelaic acid, eicosane diacid, citricacid, glycolic acid, succinic acid, salicylic acid,diglycolic acid, dipicolinic acid, dibutyl anilinediglycolic acid, suberic acid, sebacic acid, thioglycol acid,phthalic acid, isophthalic acid, terephthalic acid,dodecanedioic acid, parahydroxyphenylacetic acid, picolinicacid, phenylsuccinic acid, fumaric acid, maleic acid,malonic acid, lauric acid, benzoic acid, tartaric acid,tris(2-carboxyethyl)isocyanurate, glycine, 1,3-cyclohexanedicarboxylic acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butanoic acid, 4-tert-butylbenzoic acid,2,3-dihydroxybenzoic acid, 2,4-diethylglutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, malic acid,p-anisic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, andlinolenic acid.

[0033] Examples of the organic acid further includedimer acid that is a reactant of oleic acid and linoleicacid, trimer acid that is a reactant of oleic acid andlinoleic acid, hydrogenated dimer acid that is obtained byadding hydrogen to dimer acid that is a reactant of oleicacid and linoleic acid, and hydrogenated trimer acid that isobtained by adding hydrogen to trimer acid that is a reactantof oleic acid and linoleic acid. Examples of the organicacid still further include, as dimer acid that is not areactant of oleic acid and linoleic acid, trimer acid thatis not a reactant of oleic acid and linoleic acid,hydrogenated dimer acid that is obtained by adding hydrogento dimer acid that is not a reactant of oleic acid andlinoleic acid, and hydrogenated trimer acid that is obtainedby adding hydrogen to trimer acid that is not a reactant ofoleic acid and linoleic acid, dimer acid that is a reactantof acrylic acid, trimer acid that is a reactant of acrylicacid, dimer acid that is a reactant of methacrylic acid,trimer acid that is a reactant of methacrylic acid, dimeracid that is a reactant of acrylic acid and methacrylic acid,trimer acid that is a reactant of acrylic acid andmethacrylic acid, dimer acid that is a reactant of oleicacid, trimer acid that is a reactant of oleic acid, dimeracid that is a reactant of linoleic acid, trimer acid thatis a reactant of linoleic acid, dimer acid that is a reactantof linolenic acid, trimer acid that is a reactant oflinolenic acid, dimer acid that is a reactant of acrylicacid and oleic acid, trimer acid that is a reactant ofacrylic acid and oleic acid, dimer acid that is a reactantof acrylic acid and linoleic acid, trimer acid that is areactant of acrylic acid and linoleic acid, dimer acid thatis a reactant of acrylic acid and linolenic acid, trimeracid that is a reactant of acrylic acid and linolenic acid,dimer acid that is a reactant of methacrylic acid and oleicacid, trimer acid that is a reactant of methacrylic acid andoleic acid, dimer acid that is a reactant of methacrylicacid and linoleic acid, trimer acid that is a reactant ofmethacrylic acid and linoleic acid, dimer acid that is areactant of methacrylic acid and linolenic acid, trimer acidthat is a reactant of methacrylic acid and linolenic acid,dimer acid that is a reactant of oleic acid and linolenicacid, trimer acid that is a reactant of oleic acid andlinolenic acid, dimer acid that is a reactant of linoleicacid and linolenic acid, trimer acid that is a reactant oflinoleic acid and linolenic acid, hydrogenated dimer acidthat is obtained by adding hydrogen to any of theabovementioned dimer acids that are each not a reactant ofoleic acid and linoleic acid, and hydrogenated trimer acidthat is obtained by adding hydrogen to any of theabovementioned trimer acids that are each not a reactant ofoleic acid and linoleic acid. The present invention maycontain any one or more types of the abovementioned organicacids.

[0034] Examples of the amine include monoethanolamine,diphenylguanidine, ethylamine, triethylamine,ethylenediamine, triethylenetetramine, 2-methylimidazole,2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazoliumtrimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate,2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-[2′-undecylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-striazine, 2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-striazine isocyanuric acid adduct, 2-phenylimidazoleisocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazoliumchloride, 2-methylimidazoline, 2-phenylimidazoline, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazineisocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-nonylbenzimidazole, 2-(4-thiazolyl)benzimidazole,benzimidazole, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole, 2-(2′-hydroxy-3′,5′-di-tertamylphenyl)benzotriazole, 2-(2′-hydroxy-5′-tertoctylphenyl)benzotriazole, 2,2′-methylenebis[6-(2Hbenzotriazol-2-yl)-4-tert-octylphenol], 6-(2-benzotriazolyl)-4-tert-octyl-6′-tert-butyl-4′-methyl-2,2′-methylene bisphenol, 1,2,3-benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole,1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole,2,2′-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol,1-(1′,2′-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-bis[(1Hbenzotriazol-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole, rosin amine, N,Ndimethyloctylamine, N,N-diethyloctylamine, and N,Ndiethylaniline. The present invention may contain any one ormore types of the abovementioned amines.

[0035] The amine halide salt is a compound obtained byreacting an amine with a hydrogen halide, and examplesthereof include aniline hydrochloride and anilinehydrobromide. Examples of the amine of the amine-hydrogenhalide salt usable include the abovementioned amines, suchas ethylamine, ethylenediamine, triethylamine,methylimidazole, 2-ethyl-4-methylimidazole, and N,Ndiethylaniline, and examples of the hydrogen halide thereofinclude hydrides of chlorine, bromine, iodine and fluorine(hydrogen chloride, hydrogen bromide, hydrogen iodide andhydrogen fluoride). Further, borofluoride may also be used.Examples of the borofluoride include fluoroboric acid. Thepresent invention may contain any one or more of aminehalogen salts that are each a compound obtained by reactingany of the abovementioned amines with any of theabovementioned hydrogen halides. Examples of the aminehalogen salts, which are each a compound obtained by reactingan amine with a hydrogen halide, include N,N-diethylaniline.HBr.

[0036] When an organic acid and an amine are added tothe flux, predetermined amounts of the organic acid and theamine are reacted to be salt. Therefore, two or more typesof organic acids and amines may be reacted to be salt andthen added to the flux in order to prevent or reduce reactionof the organic acid(s) and the amine(s).

[0037] The flux for resin-cored solder of thisembodiment may further contain, as an additive(s), 0% bymass to 10% by mass of a phosphate ester(s), 0% by mass to5% by mass of a silicone(s), 0% by mass to 5% by mass of asurfactant(s), 0% by mass to 13% by mass of a solvent(s),and 0% by mass to 3% by mass of a defoamer(s).

[0038] Examples of the phosphate ester include methylacid phosphate, ethyl acid phosphate, isopropyl acidphosphate, monobutyl acid phosphate, butyl acid phosphate,dibutyl acid phosphate, butoxyethyl acid phosphate, 2-ethylhexy acid phosphate, bis(2-ethylhexy) phosphate,monoisodecyl acid phosphate, isodecyl acid phosphate, laurylacid phosphate, isotridecyl acid phosphate, stearyl acidphosphate, oleyl acid phosphate, beef tallow phosphate,coconut oil phosphate, isostearyl acid phosphate, alky acidphosphate, tetracosyl acid phosphate, ethylene glycol acidphosphate, 2-hydroxyethyl methacrylate acid phosphate,dibutyl pyrophosphate acid phosphate, 2-ethylhexylphosphonicacid mono-2-ethylhexyl, and alkyl(alkyl)phosphonate. Thepresent invention may contain any one or more types of theabovementioned phosphate esters.

[0039] Examples of the silicone include dimethylsilicone oil, cyclic silicone oil, methylphenyl silicone oil,methyl hydrogen silicone oil, higher fatty acid-modifiedsilicone oil, alkyl-modified silicone oil, alkyl aralkylmodified silicone oil, amino-modified silicone oil, epoxymodified silicone oil, polyether-modified silicone oil,alkyl polyether-modified silicone oil, and carbinol-modifiedsilicone oil. The present invention may contain any one ormore types of the abovementioned silicones.

[0040] Examples of the surfactant include acrylicpolymer, vinyl ether polymer, olefin polymer, and butadienepolymer, and examples of the acrylic polymer includepolyoxyalkylene polyalkylamide. The present invention maycontain any one or more types of the abovementionedsurfactants.

[0041] Examples of the solvent include various glycolether-based solvents, such as phenyl glycol, hexylene glycol,and hexyldiglycol, but not limited thereto, and any wellknown solvents can be used. The solvent may be either solidor liquid. Examples of the solid solvent include neopentylglycol (2,2-dimethyl-1,3-propanediol), dioxane glycol, 4-(1,1,3,3-tetramethylbutyl)phenol, and catechol. The presentinvention may contain any one or more types of theabovementioned solvents.

[0042] Examples of the defoamer include acrylic polymer,vinyl ether polymer, and butadiene polymer. The presentinvention may contain any one or more types of theabovementioned defoamers.

[0043] <Configuration Example of Resin-cored Solder ofEmbodiment>Resin-cored solder of an embodiment is wire-shapedsolder filled with the above-described flux for resin-coredsolder. The flux for resin-cored solder is required to besolid at room temperature (e.g., 25°C) in order not to flowout in a step of processing solder, or required to have apredetermined high viscosity with which the flux does notflow out. The viscosity required for the flux for resincored solder be 3,500 Pa·s or more, for example. If the fluxfor resin-cored solder is a low-viscosity liquid (viscosityof less than 3,500 Pa·s) at 25°C, workability of the resincored solder decreases, which is undesirable. As far as theresin-cored solder can be supplied into a through hole formedalong the central axis of a soldering iron described below,the shape of the resin-cored solder is not limited to theshape of a continuous wire having a circular cross section,and hence can be changed to another as appropriate. Examplesof the shape include: the shape of a continuous wire havinga cross section of a shape having corners such as a square;the shape of a continuous wire having a cross section of acertain shape such as a star shape; the shape ofdiscontinuous pellets, such as cylindrical pellets orprismatic pellets, each having a cross section of a certainshape; the shape of a continuous sheet; the shape ofdiscontinuous sheets; the shape of a continuous sphere; andthe shape of discontinuous spheres.

[0044] The wire diameter of the resin-cored solder is0.1 mm to 3.0 mm, preferably 0.3 mm to 1.6 mm. The contentof the flux with which the resin-cored solder is filled is,with the resin-cored solder as 100, 0.5% by mass to 6% bymass, preferably 1.5% by mass to 4.5% by mass, and furtherpreferably 2.0% by mass to 4.0% by mass.

[0045] Solder thereof is composed of Sn alone or an SnAg-based alloy, an Sn-Cu-based alloy, an Sn-Ag-Cu-basedalloy, an Sn-Bi-based alloy, an Sn-In-based alloy, an Sn-Znbased alloy, an Sn-Pb-based alloy or the like or an alloycomposed of Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au,Ge, Ga, Al, Mn, Ti, P, Pb, Zr or the like added to any ofthe abovementioned alloys.

[0046] <Example of Soldering Method of Embodiment>FIG. 1 illustrates an example of a soldering iron thatis used in a soldering method of an embodiment. FIG. 2A, FIG.2B, FIG. 2C and FIG. 2D illustrate the soldering method ofthis embodiment.

[0047] The soldering method of this embodiment isapplied to through-hole technology, single-sided boards, andso forth. A soldering iron 1A that is used in the solderingmethod of this embodiment has a through hole 2 formed alongthe central axis of the soldering iron 1A and a heater 3 asa heating means that heats the soldering iron 1A.

[0048] The diameter D of the through hole 2 of thesoldering iron 1A is larger than the diameter d1 of a resincored solder H. Hence, the resin-cored solder H can besupplied to a tip 10 of the soldering iron 1A through thethrough hole 2. Also, the diameter D of the through hole 2of the soldering iron 1A is larger than the diameter d2 of alead terminal 101 of an electronic component 100. Hence, thelead terminal 101 can be inserted into the through hole 2.

[0049] In the soldering method of this embodiment, asshown in FIG. 2A, the lead terminal 101 of the electroniccomponent 100 is inserted into a through hole 201 formed ina substrate 200. Meanwhile, the soldering iron 1A is heatedby the heater 3 to a temperature exceeding the melting pointof solder, and controlled so as to keep a predeterminedtemperature exceeding the melting point of solder. Next, asshown in FIG. 2B, the tip 10 of the soldering iron 1A isbrought into contact with or near the through hole 201, inwhich the lead terminal 101 is inserted, so that the leadterminal 101 is inserted into the through hole 2 of thesoldering iron 1A.

[0050] Next, the resin-cored solder H, which has beencut to have a predetermined length, is supplied into thethrough hole 2 of the soldering iron 1A, thereby contactingthe lead terminal 101, which is inserted in the through hole2.

[0051] Since the soldering iron 1A is controlled so asto keep a predetermined temperature exceeding the meltingpoint of solder, the soldering iron 1A heats and melts theresin-cored solder H as shown in FIG. 2C, and also heats thethrough hole 201 and the lead terminal 101.

[0052] While the soldering iron 1A is heating the resincored solder H to the temperature exceeding the melting pointof solder, the viscosity of the flux in the resin-coredsolder decreases, and the flux flows to the through hole 201and the lead terminal 101, so that metal oxides on thesurfaces of the solder, the through hole 201 and the leadterminal 101 are removed, and the molten solder wetly spreads.

[0053] Next, as shown in FIG. 2D, the soldering iron 1Ais separated or made away from the through hole 201, so thatthe solder, which wetly spreads on / in the through hole 201and the lead terminal 101, is hardened.

[0054] <Examples of Effects of Flux for Resin-coredSolder, Resin-cored Solder and Soldering Method>A flux for resin-cored solder containing apredetermined amount of a rosin ester(s), the predeterminedamount being specified in the present invention, can, in theabove-described soldering method, liquefy deposits of theflux residues in the through hole of a soldering iron andfacilitate discharge of the deposits to the outside, therebypreventing the deposits from adhering to the inside of thethrough hole of the soldering iron.

[0055] Hence, even when soldering is performedcontinuously with the resin-cored solder H supplied into thethrough hole 2 in the state in which the soldering iron 1Ais controlled so as to keep a predetermined temperatureexceeding the melting point of solder, it is possible toprevent deposits of the residues from adhering in the throughhole 2, and accordingly prevent problems, such as a problemthat the through hole 2 of the soldering iron 1A is cloggedwith the deposits of the residues, from arising.

[0056] The flux for resin-cored solder furthercontaining a predetermined amount of a covalent halogencompound(s), which is a halogen compound not classified asa halide, the predetermined amount being specified in thepresent invention, can, in the above-described solderingmethod, achieve excellent usability without impairingreliability.Examples

[0057] Fluxes for resin-cored solder were prepared withcompositions of Examples and Comparative Examples shown inTABLES 1, 2, 3, 4 and 5 below, and a through-hole wettabilitytest and a reliability test were conducted with the solderingmethod of supplying resin-cored solder into a through holeformed along the central axis of a soldering iron to seewhether their resin-cored solders were supplied and to testreliability and usability of the resin-cored solderssupplied. In the reliability test, insulation reliability(insulation resistance value), halide amount (potentialdifference), solderability and deposition of activators weretested. The composition ratio in TABLES 1 to 5 is expressedin percent by mass with the total mass of a flux as 100.

[0058] <Through-hole Wettability Test>(1) Testing MethodThrough-hole substrates each having a thickness of 1.6mm with pins inserted were prepared and each soldered at 40points with a set temperature of 400°C of a soldering ironfor a soldering time of 1.0 second using J-CAT300SLVmanufactured by Apollo Seiko Ltd. The soldering at thethrough-hole wettability test was performed by supplyingeach resin-cored solder into the through hole formed alongthe central axis of the soldering iron, as described above.Each substrate after the test was observed under a digitalmicroscope VHX-6000 manufactured by Keyence Corporation, anddetermination was made with the following criteria.

[0059] (2) Criteria for Determination(double circle): Percentage of points where throughholes are filled with solder is 100%.(single circle): Percentage of points where throughholes are filled with solder is 95% or higher but lower than100%.(cross): Percentage of points where through holesare filled with solder is lower than 95%.

[0060] <Reliability Test>(a) Insulation Reliability(1) Testing MethodIn accordance with JIS Z 3197, comb-shaped substrateswere soldered with the respective resin-cored solders andplaced under conditions of a high temperature of 85°C and ahigh humidity of 85%RH, and a voltage of 100 V was appliedthereto and electrical insulation was measured using an ionmigration evaluation system AMI-150-U-5 manufactured byESPEC Corp. JIS Z 3283 specifies that an insulationresistance value of 1 × 108 Ω or more after a lapse of 168hours is JIS A class. Hence, determination was made with thefollowing criteria.

[0061] (2) Criteria for Determination(double circle): Insulation resistance value after168 hours is 1 × 108 Ω or more.(cross): Insulation resistance value after 168 hoursis less than 1 × 108 Ω.

[0062] (b) Potentiometry(1) Testing MethodIn accordance with JIS Z 3197, a 2-propanol solutionof each flux for resin-cored solder was titrated with anaqueous silver nitrate solution using an automaticpotentiometric titrator AT-610 manufactured by KyotoElectronics Manufacturing Co. Ltd., and the halide contentwas obtained from a changing point in potential difference.JIS Z 3283 specifies that a halide content of 0.5% or lessis JIS A class. Hence, determination was made with thefollowing criteria.

[0063] (2) Criteria for Determination(double circle): Halide content is 0.5% or less.(cross): Halide content is more than 0.5%.

[0064] (c) Solderability(1) Testing MethodThrough-hole substrates each having a thickness of 1.6mm with tape attached to the back side without pins insertedwere prepared and each soldered by 15,000 shots with a settemperature of 400°C of the soldering iron for a solderingtime of 1.0 second. The soldering for solderability wasperformed by supplying each resin-cored solder into thethrough hole formed along the central axis of the solderingiron, as described above. When 15,000 shots finished, theinside diameter of the through hole of the soldering ironwas observed under the digital microscope and thereafter thethrough-hole wettability test was also conducted, anddetermination was made with the following criteria.

[0065] (2) Criteria for Determination(double circle): Inside diameter of through hole ofsoldering iron containing deposits is 60% or more of insidediameter of through hole thereof not containing deposits,and result of through-hole wettability test is (doublecircle).(single circle): Inside diameter of through hole ofsoldering iron containing deposits is 60% or more of insidediameter of through hole thereof not containing deposits,and result of through-hole wettability test is (singlecircle).(cross): Inside diameter of through hole of solderingiron containing deposits is less than 60% of inside diameterof through hole thereof not containing deposits, or resultof through-hole wettability test is × (cross).

[0066] (c) Deposition of Activator(1) Testing MethodThe prepared fluxes for resin-cored solder of Examplesand Comparative Examples were transferred to a container tobe cooled, and when they solidified, their appearances wereoverserved with eyes. Deposition of activators therein needsto be avoided because it deteriorates the appearance at thetime of soldering, and also increases influence onperformance stability and concern about reliability due toinhomogeneity / non-uniformity of the flux components. Hence,determination was made with the following criteria.

[0067] (2) Criteria for Determination(double circle): Deposition of activators is notobserved in solidified flux.(cross): Deposition of activators is observed insolidified flux.

[0068] [TABLE 1]

[0069] [TABLE 2]

[0070] [TABLE 3]

[0071] [TABLE 4]

[0072] [TABLE 5]

[0073] The flux for resin-cored solder of each Example,in which the flux contained 60% by mass to 99.9% by mass ofthe rosin ester to the total mass of the flux and 0.1% bymass to 15% by mass of the covalent halogen compound, whichis a halogen compound not classified as a halide, to thetotal mass of the flux, used in the resin-cored soldersupplied into the through hole formed along the central axisof the soldering iron showed excellent results in thethrough-hole wettability test and the reliability test(insulation reliability (insulation resistance value),halide amount (potential difference), solderability anddeposition of activators) with the soldering method ofsupplying resin-cored solder into a through hole formed onthe central axis of a soldering iron.

[0074] In contrast, Comparative Examples 1 and 2, ineach of which the content of the rosin ester was below thelower limit of its range specified in the present invention,did not have a desired solderability. Comparative Example 3,in which the flux did not contain the covalent halogencompound, which is a halogen compound not classified as ahalide, and contained the amine halogen salt, which is atype of halogen compound other than the covalent halogencompound, which is a halogen compound not classified as ahalide, above the upper limit of its range specified in thepresent invention, did not have a desired value regardingthe halide amount (potential difference) and accordingly didnot show an excellent result therein. Comparative Example 4,in which the flux contained the amine halogen salt withinits range specified in the present invention, but did notcontain the covalent halogen compound, which is a halogencompound not classified as a halide, did not have desiredvalues regarding the through-hole wettability test and thesolderability and accordingly did not show excellent resultstherein. In contrast, Example 2, in which the flux containedthe covalent halogen compound, which is a halogen compoundnot classified as a halide, within its range specified inthe present invention, and contained the amine halogen salt,which is a type of halogen compound other than the covalenthalogen compound, which is a halogen compound not classifiedas a halide, within its range specified in the presentinvention, showed excellent results in the through-holewettability test and the solderability with the solderingmethod of supplying resin-cored solder into a through holeformed along the central axis of a soldering iron. Example2 showed excellent results in the other items of thereliability test too.

[0075] Comparative Example 5, in which the fluxcontained trans-2,3-dibromo-2-butene-1,4-diol as thecovalent halogen compound, which is a halogen compound notclassified as a halide, above the upper limit of its rangespecified in the present invention, did not have a desiredvalue regarding the amount of deposition of activators andaccordingly did not show an excellent result therein.Comparative Example 6, in which the flux contained 2,2,2-tribromoethanol as the covalent halogen compound, which isa halogen compound not classified as a halide, above theupper limit of its range specified in the present invention,did not have a desired value regarding the insulationreliability (insulation resistance value) and accordinglydid not show an excellent result therein.

[0076] Comparative Example 7, in which the fluxcontained the rosin ester and the organic acid within theirranges specified in the present invention, but did notcontain the covalent halogen compound, which is a halogencompound not classified as a halide, did not have desiredvalues regarding the through-hole wettability test and thesolderability and accordingly did not show excellent resultstherein. Comparative Example 8, in which the flux containedthe rosin ester and the amine within their ranges specifiedin the present invention, but did not contain the covalenthalogen compound, which is a halogen compound not classifiedas a halide, did not have desired values regarding thethrough-hole wettability test and the solderability andaccordingly did not show excellent results therein.

[0077] As shown in Comparative Examples 4, 7 and 8described above, the flux not containing the covalent halogencompound, which is a halogen compound not classified as ahalide, did not show excellent results in the through-holewettability test and the solderability with the solderingmethod of supplying resin-cored solder to a through holeformed along the central axis of a soldering iron, althoughthe flux contained another activator(s) within its(their)range(s) specified in the present invention.

[0078] In contrast, as shown in Example 27, the fluxcontaining the covalent halogen compound, which is a halogencompound not classified as a halide, within its rangespecified in the present invention without containinganother activator showed excellent results in the throughhole wettability test and the solderability with thesoldering method of supplying resin-cored solder to a throughhole formed along the central axis of a soldering iron.Example 27 showed excellent results in the other items ofthe reliability test too.

[0079] Further, as shown in Example 1 or the like, theflux containing the covalent halogen compound, which is ahalogen compound not classified as a halide, within its rangespecified in the present invention and also containinganother activator(s) within its(their) range(s) specified inthe present invention showed excellent results in thethrough-hole wettability test and the solderability with thesoldering method of supplying resin-cored solder into athrough hole formed along the central axis of a solderingiron. Example 1 or the like showed excellent results in theother items of the reliability test too.

[0080] It is understand therefrom that a flux for resincored solder containing, in addition to a rosin ester(s)within its range specified in the present invention, acovalent halogen compound(s), which is a halogen compoundnot classified as a halide, within its range specified inthe present invention has a technical feature(s) in a fluxfor resin-cored solder that is used in a soldering method ofsupplying resin-cored solder into a through hole formed alongthe central axis of a soldering iron as well as in thesoldering method.

[0081] As described above, each of the fluxes for resincored solder containing 60% by mass to 99.9% by mass of therosin ester to the total mass of the flux and 0.1% by massto 15% by mass of the covalent halogen compound, which is ahalogen compound not classified as a halide, to the totalmass of the flux used in the resin-cored solder suppliedinto the through hole formed along the central axis of thesoldering iron showed excellent results in the through-holewettability test and the reliability test (insulationreliability (insulation resistance value), halide amount(potential difference), solderability and deposition ofactivators).

[0082] Further containing another activator(s), otherrosin or resin, and / or an additive(s) within its(their)range(s) specified in the present invention did not impairthe results.

Claims

1. A flux for resin-cored solder that is used in resin-cored solder that is supplied into a through hole formed along a central axis of a soldering iron, comprising: 60% by mass to 99.9% by mass of a rosin ester to a total mass of the flux; 0.1% by mass to 15% by mass of a covalent halogen compound to the total mass of the flux; and more than 0% by mass to 10% by mass of rosin amine, N,Ndiethyloctylamine, or rosin amine and N,N-diethyloctylamine to the total mass of the flux.

2. The flux for resin-cored solder as claimed in claim 1, wherein the covalent halogen compound is one or more types selected from the group consisting of trans-2,3-dibromo-1,4- butenediol, triallyl isocyanurate hexabromide, 1-bromo-2- butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2- propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, 2,3- dibromo-2-butene-1,4-diol, trans-2,3-dibromo-2-butene-1,4- diol, cis-2,3-dibromo-2-butene-1,4-diol, 2,2-bis(bromomethyl)- 1,3-propanediol, tetrabromoethane, tetrabromobutane, tetrabromophthalic acid, bromosuccinic acid, and 2,2,2- tribromoethanol.

3. The flux for resin-cored solder as claimed in claim 1 or 2, wherein the rosin ester is one or more types of rosin esters each being one type of rosin esterified, or one or more types of rosin esters each being a mixture of two or more types of rosin esterified, and the rosin to be esterified is any or any mixture of natural rosin and rosin derivatives obtained from the natural rosin, wherein the rosin derivatives are selected from the group of purified rosin; polymerized rosin; hydrogenated rosin; disproportionated rosin, hydrogenated disproportionated rosin; acid-modified rosin; phenol-modified rosin; an α, βunsaturated carboxylic acid-modified product; a purified product, a hydride and a disproportionated product of the polymerized rosin; and a purified product, a hydride and a disproportionated product of the α, β-unsaturated carboxylic acid-modified product.

4. The flux for resin-cored solder as claimed in any one of claims 1 to 3, wherein the flux further comprises 0% by mass to 39% by mass of another rosin with respect to the total mass of the flux.

5. The flux for resin-cored solder as claimed in any one of claims 1 to 4, wherein the flux further comprises 0% by mass to 39% by mass of an activator other than the covalent halogen compound with respect to the total mass of the flux.

6. A resin-cored solder comprising a solder filled with the flux for resin-cored solder as claimed in any one of claims 1 to 5.

7. A soldering method comprising: supplying a resin-cored solder that is a solder filled with a flux for resin-cored solder including 60% by mass to 99.9% by mass of a rosin ester with respect to a total amount of the flux, 0.1% by mass to 15% by mass of a covalent halogen compound with respect to the total mass of the flux, and more than 0% by mass to 10% by mass of rosin amine, N,N-diethyloctylamine, or rosin amine and N,N-diethyloctylamine with respect to the total mass of the flux, into a through hole formed along a central axis of a soldering iron; and heating the resin-cored solder to a temperature exceeding a melting point of the solder with the soldering iron, thereby heating a joining object, and melting the resin-cored solder.