TW202216341A - Flux and solder paste - Google Patents

Abstract

The flux is used for solder paste and contains hydrogenated methyl rosinate, a compound represented by the general formula (p1), and a solvent. In the general formula (p1), R¹, R², R³, and R⁴ each independently represent a hydrogen atom or an alkyl group with 1-4 carbon atoms.

Description

Flux and Solder Paste

The present invention relates to fluxes and solder pastes.

As the solder material, a solder paste containing solder powder and flux was used.

Electronic components mounted on printed circuit boards are required to be miniaturized and high-performance. The electronic component may, for example, be a semiconductor package. The semiconductor package seals a semiconductor element having electrodes with a resin composition. Solder bumps formed of solder material are formed in the electrodes. The semiconductor element and the printed circuit board are soldered and connected by the solder material.

Various properties of solder materials are required depending on the conditions of use, applications, and the like. For example, Patent Document 1 proposes a composition including a flux containing a rosin-based resin, an activator and a solvent, and a solder powder for the purpose of improving solder wettability.

[Prior Art Literature]

[Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2018-167297.

The flux used for soldering has the effect of chemically removing metal oxides existing on the metal surface of the solder and the metal surface of the object to be welded, so that the metal elements can move at the boundary between the two. Therefore, by soldering with a flux, an intermetallic compound can be formed between the solder and the metal surface of the object to be joined, and a strong joint can be obtained.

With the miniaturization and higher performance of electronic components, further improvement in properties is required for conventional solder materials.

In the aforementioned flux, it is required to increase the wetting speed of the solder on the metal surface of the object to be joined, and to have better solder wettability.

When soldering with solder paste, if the wettability of the solder to the metal surface of the object to be joined cannot be ensured, the solder cannot be uniformly wetted and spread on the electrodes. If the wettability of the solder deteriorates, the position of the solder paste on the counter electrode will be deviated, and the solder paste will be separated from the electrode pad (bump missing), which may cause poor bonding or poor electrical conductivity. .

When soldering by reflow, the flux components will be vaporized or decomposed by heat during the paste reflow. Therefore, there is a problem that voids are generated in the soldered portion due to the vaporized flux component.

The above-mentioned problems are more pronounced in the narrowing of the electrode pitch.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a soldering flux that can reduce the generation of voids, improve solder wettability, and suppress peeling, and a solder paste using the soldering flux.

The present inventors have examined and found that by using a specific rosin and an active agent in combination, the melt viscosity of the solder paste can be reduced, the generation of voids can be suppressed, the wetting speed of the solder can be improved, and the reflow and flux residues can be suppressed from falling off after cleaning. , thereby completing the present invention.

That is, this invention employs the following means in order to solve the said subject.

One aspect of the present invention is a flux, which is used in a solder paste, and contains methyl hydrogenated rosinate, a compound represented by the following general formula (p1), and a solvent.

[In formula (p1), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ]

Another aspect of the present invention is a solder paste comprising the flux and solder powder of the aforementioned aspect of the present invention, wherein the solder powder is formed of a solder alloy with an alpha radiation dose of 0.02 cph/cm ² or less.

According to an aspect of the present invention, a soldering flux capable of reducing void generation, improving solder wettability, and suppressing peeling can be provided.

According to other aspects of the present invention, there can be provided a solder paste containing the flux of one aspect of the present invention, which can be used as a low alpha radiation dose material.

The present invention will be described in detail below.

In this specification, the "ppb" of the solder alloy composition is "mass ppb" unless otherwise specified. "ppm" means "mass ppm" unless otherwise specified. "%" means "mass %" unless otherwise specified.

(flux)

The flux of one aspect of the present invention is used in solder paste.

The flux of this embodiment contains hydrogenated methyl rosinate, a compound represented by the general formula (p1), and a solvent.

≪Methyl Hydrogenated Rosinate≫

The flux of this embodiment contains hydrogenated methyl rosinate.

The hydrogenated methyl rosinate is an ester of hydrogenated cyclic fatty acid obtained from rosin and methanol, also known as hydrogenated methyl rosinate, CAS number: 8050-15-5.

The content of the hydrogenated methyl rosinate in the flux is preferably 5 mass % or more and 20 mass % or less, more preferably 5 mass % or more and 15 mass % or less with respect to the total amount (100 mass %) of the flux.

When the content of methyl hydrogenated rosinate is in the above-mentioned preferred range, it is easy to suppress the generation of voids in welding.

≪Compounds represented by general formula (p1)≫

The flux of this embodiment contains a compound represented by the following general formula (p1).

[In formula (p1), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ]

In the aforementioned general formula (p1), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Examples of the alkyl group having 1 to 4 carbon atoms include methyl, ethyl, propyl, cyclopropyl, butyl, and cyclobutyl. Among them, R ¹ , R ² , R ³ and R ⁴ are preferably a hydrogen atom, a methyl group, an ethyl group, or a cyclopropyl group, more preferably a hydrogen atom or a methyl group, and particularly preferably a hydrogen atom. R ¹ , R ² , R ³ and R ⁴ may be the same or different.

Examples of the compound represented by the general formula (p1) include 2-picolinic acid, 6-methyl-2-picolinic acid, 6-ethyl-2-picolinic acid, 3-cyclopropyl-2-picolinic acid, 4-picolinic acid Cyclopropyl-2-picolinic acid, 6-cyclopropyl-2-picolinic acid, 5-butyl-2-picolinic acid, 6-cyclobutyl-2-picolinic acid, etc. Of these, 2-picolinic acid is particularly preferred.

The compound represented by the general formula (p1) may be used alone or in combination of two or more.

The content of the compound represented by the general formula (p1) in the flux is preferably more than 0 mass % and 5 mass % or less, more preferably 1 mass % or more, relative to the total amount (100 mass %) of the flux. It is not more than 2 mass %, and more preferably not less than 2 mass % and not more than 5 mass %.

When the content of the compound represented by the general formula (p1) is in the above-mentioned preferred range, the wettability of the solder can be improved during soldering and the peeling can be suppressed.

The total content of the hydrogenated methyl rosinate and the compound represented by the general formula (p1) in the flux is preferably more than 5% by mass and not more than 25% by mass relative to the total amount (100% by mass) of the flux. More preferably, it is 6 mass % or more and 25 mass % or less, and still more preferably 7 mass % or more and 20 mass % or less.

When the total content of these two components is in the above-mentioned preferred range, the generation of voids can be suppressed, and the wettability of the solder and the effect of suppressing peeling can be improved.

≪Solvents≫

In the flux of the present embodiment, the solvent includes, for example, water, alcohol-based solvents, glycol ether-based solvents, terpineols, and the like.

Examples of the alcohol-based solvent include isopropanol, 1,2-butanediol, isocamphenylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1 ,3-Propanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,3-dimethyl-2 ,3-Butanediol, 1,1,1-Tris(hydroxymethyl)ethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 2,2'-oxybis(methylene ) bis(2-ethyl-1,3-propanediol), 2,2-bis(hydroxymethyl)-1,3-propanediol, 1,2,6-trihydroxyhexane, bis[2,2,2 -Tris(hydroxymethyl)ethyl]ether, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, erythritol, threitol, Guaifenesin, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol Wait.

The glycol ether-based solvent includes, for example, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, and diethylene glycol monohexyl ether. (hexyl diethylene glycol), diethylene glycol monobutyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, and the like.

≪Other ingredients≫

In addition to the hydrogenated methyl rosinate, the compound represented by the general formula (p1), and the solvent, the flux of this embodiment may contain other components as needed.

Other components include rosin other than hydrogenated methyl rosinate, organic acids other than compounds represented by the general formula (p1), amines, thixotropic agents, halogen-based activators, resin components other than rosin-based resins, and metal deactivators. agents, surfactants, silane coupling agents, antioxidants, colorants, etc.

For example, a suitable flux includes a form containing hydrogenated methyl rosinate, a compound represented by the general formula (p1), a solvent, rosin other than hydrogenated methyl rosinate, and a thixotropic agent.

Rosin other than Methyl Hydrogenated Rosinate:

Examples of rosins other than hydrogenated methyl rosinate include raw material rosins such as gum rosin, wood rosin, and turpentine rosin, and derivatives obtained from the raw material rosin. The derivatives include, for example, purified rosin, polymerized rosin, hydrogenated rosin, disproportionated rosin, and α,β-unsaturated carboxylic acid modified products (acrylated rosin, maleated rosin, fumaric acidified rosin, etc.), and the polymerization Refined product, hydrogenated product and disproportionate of rosin, and refined product, hydrogenated product and disproportionated product of the α,β-unsaturated carboxylic acid modified product, etc.

One or two or more kinds of rosin other than methyl rosinate can be used in the flux of this embodiment.

Among the above, rosin other than hydrogenated rosin acid methyl ester is preferably used in the group consisting of polymerized rosin, acrylic modified rosin, acrylic modified hydrogenated rosin, acrylic modified disproportionated rosin, hydrogenated rosin, disproportionated rosin and hydrogenated rosin glyceride At least one of the selected.

The content of rosin other than hydrogenated methyl rosinate in the flux with respect to the total amount (100% by mass) of the flux is preferably 20% by mass or more and 40% by mass or less, more preferably 25% by mass or more and 40% by mass or less. , and more preferably not less than 25% by mass and not more than 35% by mass.

In the flux of this embodiment, the mixing ratio of hydrogenated methyl rosinate and rosin other than hydrogenated methyl rosinate (hereinafter referred to as "other rosin") is preferably hydrogenated methyl rosinate/other rosin by mass ratio. 0.16 or more and 1.0 or less, more preferably 0.16 or more and 0.60 or less, still more preferably 0.16 or more and 0.40 or less.

The ratio of the content of other rosin to the total content of hydrogenated methyl rosinate and the compound represented by the general formula (p1) in the aforementioned flux is represented by other rosin/(methyl hydrogenated rosinate and the compound represented by the general formula (p1)) The mass ratio is preferably 0.80 or more and 4.0 or less, more preferably 1.0 or more and 3.0 or less, and still more preferably 1.5 or more and 2.5 or less.

Organic acids other than compounds represented by general formula (p1):

Examples of organic acids other than the compound represented by the general formula (p1) include glutaric acid, adipic acid, azelaic acid, eicosanedioic acid, citric acid, glycolic acid, succinic acid, salicylic acid, and diethylene glycol. acid, pyridinedicarboxylic acid, dibutylaniline diglycolic acid, suberic acid, sebacic acid, thioglycolic acid, dithioglycolic acid, terephthalic acid, dodecanedioic acid, p-hydroxyphenylacetic acid, Phenylsuccinic acid, phthalic 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)butyric acid, 2,3-dihydroxybenzoic acid, 2,4-diethyl Glutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, propionic acid, malic acid, p-anisic acid, stearic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, threonoleic acid , palmitic acid, pimelic acid, dimer acid, trimer acid, hydrogenated dimer acid of the hydride of dimer acid added hydrogen, hydrogenated trimer acid of the hydride of trimer acid added hydrogen, etc.

One or two or more kinds of organic acids can be used in the flux of this embodiment. The above-mentioned organic acid is preferably at least one selected from the group consisting of malonic acid, suberic acid, azelaic acid, stearic acid and hydrogenated dimer acid.

The organic acid content in the flux is preferably 0 mass % or more and 15 mass % or less, more preferably 5 mass % or more and 15 mass % or less, more preferably 7 mass % or less with respect to the total amount of the flux (100 mass %) mass % or more and 10 mass % or less.

amine:

Examples of the amine include ethylamine, triethylamine, ethylenediamine, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine, triethylenetetramine, diphenylguanidine, and xylene. guanidine, 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-cyanoethyl-2-methylimidazole, 1-cyano ethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl- 2-Undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazole yl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine , 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6- [2'-Methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric 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-benzylimidazolium chloride, 2-methylimidazoline, 2-phenylimidazoline, 2,4-diamino-6-vinyl-s-tri oxazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine oxazine, 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-tert-pentylphenyl)benzene Triazole, 2-(2'- Hydroxy-5'-tert-octylphenyl)benzotriazole, 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol] , 6-(2-benzotriazolyl)-4-tert-octyl-6'-tert-butyl-4'-methyl-2,2'-methylenebisphenol, 1,2,3 - Benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N-bis(2-ethyl Hexyl)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 azole, 2,6-bis[(1H-benzotriazol-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole, and the like.

One or two or more kinds of amines can be used in the flux of this embodiment.

The amine content in the flux is preferably 0 mass % or more and 30 mass % or less, more preferably 0 mass % or more and 20 mass % or less with respect to the total amount (100 mass %) of the flux.

Thixotropic agent:

The thixotropic agent includes, for example, a wax-based thixotropic agent, an amide-based thixotropic agent, and a sorbitol-based thixotropic agent.

As a wax-type thixotropic agent, an ester compound is mentioned, for example, Specifically, a castor hydrogenated oil etc. are mentioned.

Examples of the amide-based thixotropic agent include monoamide, diamide, and polyamide, and specifically, lauramide, palmamide, stearylamide, behenylamide, and hydroxystearin amide, saturated aliphatic amide, oleamide, sinacinamide, unsaturated aliphatic amide, p-toluamide, p-toluamide, aromatic amide, hexamethylene hydroxystearylamine, substituted amide Monoamides such as amine, hydroxymethyl stearyl amide, hydroxymethyl amide, fatty acid ester amide; Fatty acid carbon number C6 to 24) amide, ethylidene bishydroxystearylamine, saturated aliphatic diamide, methylene dioleamide, unsaturated aliphatic diamide, Meta-xylyl bis-stearylamine, aromatic bis-amide and other diamides; saturated aliphatic polyamides, unsaturated aliphatic polyamides, aromatic polyamides, 1,2,3-propanetricarboxytris( 2-methylcyclohexyl amide), cyclic amide oligomers, acyclic amide oligomers and other polyamides.

The aforementioned cyclic amide oligomers include amide oligomers obtained by cyclic polycondensation of dicarboxylic acids and diamines, amide oligomers obtained by cyclic polycondensation of tricarboxylic acids and diamines, and dicarboxylic acids and triamines. amide oligomers obtained by cyclic polycondensation of amines, amide oligomers obtained by cyclic polycondensation of tricarboxylic acids and triamines, amide oligomers obtained by cyclic polycondensation of dicarboxylic acids and tricarboxylic acids and diamines, Dicarboxylic acid and tricarboxylic acid and triamine through cyclic polycondensation amide oligomer, dicarboxylic acid and diamine and triamine through cyclic polycondensation amide oligomer, tricarboxylic acid and diamine and triamine Amide oligomers by cyclic polycondensation, amide oligomers by cyclic polycondensation of dicarboxylic acid and tricarboxylic acid with diamine and triamine, etc.

In addition, the aforementioned acyclic amide oligomers include amide oligomers obtained by acyclic polycondensation of monocarboxylic acids and diamines and/or triamines, dicarboxylic acids and/or tricarboxylic acids and monoamines. Acyclic polycondensation of amide oligomers, etc. In the case of an amide oligomer containing a monocarboxylic acid or a monoamine, the monocarboxylic acid and the monoamine can function as terminal molecules, and an acyclic amide oligomer with a relatively small molecular weight can be formed. In addition, when the acyclic amide oligomer is an amide compound obtained by acyclic polycondensation of dicarboxylic acid and/or tricarboxylic acid and diamine and/or triamine, it can form an acyclic polymer system of amide polymerization thing. In addition, the acyclic amide oligomer also includes an amide oligomer obtained by acyclic condensation of a monocarboxylic acid and a monoamine.

The sorbitol-based thixotropic agent includes, for example, dibenzylidene-D-sorbitol, bis(4-methylbenzylidene)-D-sorbitol, (D-)sorbitol, monobenzylidene (-D- ) sorbitol, mono(4-methylbenzylidene)-(D-)sorbitol, etc.

One or two or more thixotropic agents can be used in the flux of this embodiment. Among the above, the aforementioned thixotropic agent preferably contains at least one selected from the group consisting of a wax-based thixotropic agent and an amide-based thixotropic agent.

The wax-based thixotropic agent preferably contains castor hydrogenated oil.

The amide-based thixotropic agent preferably contains at least one selected from the group consisting of polyamide, diamide and monoamide.

The content of the thixotropic agent in the flux is preferably not less than 3% by mass and not more than 10% by mass, more preferably not less than 5% by mass and not more than 10% by mass relative to the total amount (100% by mass) of the flux It is 6 mass % or more and 9 mass % or less.

Halogen-based activator:

Examples of the halogen-based activator include organic halogen compounds, amine hydrohalide salts, and the like.

Examples of the organic halogen compound include trans-2,3-dibromo-2-butene-1,4-diol, triallyl isocyanurate 6 bromide, 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, etc.

In addition, halogenated carboxyl compounds may also be mentioned as the organic halogen compound, and examples thereof include iodine such as 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, and 5-iodoanthranilic acid. Carboxyl compounds; chlorinated carboxyl compounds such as 2-chlorobenzoic acid and 3-chloropropionic acid; brominated carboxyl compounds such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid, 2-bromobenzoic acid, etc. .

Amine hydrohalides are compounds in which amines are reacted with hydrogen halide. Examples of the amine here include ethylamine, ethylenediamine, triethylamine, diphenylguanidine, xylylguanidine, methylimidazole, 2-ethyl-4-methylimidazole, and the like, and examples of the hydrogen halide include chlorine , bromine, iodine hydride.

In addition, as the halogen-based activator, for example, a salt prepared by reacting an amine with tetrafluoroboric acid (HBF ₄ ) or a complex prepared by reacting an amine with boron trifluoride (BF ₃ ) can also be used.

One or two or more halogen-based activators can be used in the flux of this embodiment.

The content of the organic halogen compound in the flux is preferably 0 mass % or more and 5 mass % or less, more preferably 0.5 mass % or more and 5 mass % or less, with respect to the total amount (100 mass %) of the flux. Preferably it is 0.5 mass % or more and 3 mass % or less.

The content of the aforementioned amine hydrohalide in the aforementioned flux is preferably 0 mass % or more and 1 mass % or less with respect to the total amount (100 mass %) of the aforementioned flux.

Resin components other than rosin resin:

Resin components other than rosin-based resins include, for example, terpene resins, modified terpene resins, terpene phenol resins, modified terpene phenol resins, styrene resins, modified styrene resins, xylene resins, and modified xylenes Resin, acrylic resin, polyethylene resin, acrylic polyethylene copolymer resin, epoxy resin, etc.

As a modified terpene resin, an aromatic modified terpene resin, a hydrogenated terpene resin, a hydrogenated aromatic modified terpene resin, etc. are mentioned. Hydrogenated terpene phenol resin etc. are mentioned as a modified terpene phenol resin. As a modified styrene resin, a styrene acrylic resin, a styrene maleic acid resin, etc. are mentioned. The modified xylene resins include phenol-modified xylene resins, alkylphenol-modified xylene resins, phenol-modified resole-type xylene resins, polyol-modified xylene resins, and polyoxyethylene Addition of xylene resin, etc.

Metal Deactivator:

As a metal deactivator, a hindered phenol type compound, a nitrogen compound, etc. are mentioned, for example. The flux contains either a hindered phenol compound or a nitrogen compound, whereby the thickening inhibitory effect of the solder paste can be easily enhanced.

The term "metal deactivator" as used herein refers to a compound having a property of preventing metal deterioration by contact with a certain compound.

The hindered phenolic compound refers to a phenolic compound having a bulky substituent (for example, a branched or cyclic alkyl group such as tert-butyl group) at at least one of the normal positions of the phenol.

The hindered phenol-based compound is not particularly limited, and examples thereof include bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylidenebis(oxyethylidene)], N,N'-Hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], 1,6-hexanediolbis[3-(3,5 -Di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-methylenebis[6-(1-methylcyclohexyl)-p-cresol], 2,2'-methylenebis Methylbis(6-tert-butyl-p-cresol), 2,2'-methylenebis(6-tert-butyl-4-ethylphenol), triethylene glycol-bis[3-( 3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis-[3-(3,5-di-tert-butyl-4-hydroxy phenyl)propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine , Neotaerythritol-tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2-thio-dieneethylbis[3-(3, 5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N '-Hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 3,5-di-tert-butyl-4-hydroxybenzylphosphonate diethyl ester, 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, N,N'-bis[2-[2-(3 , 5-di-tert-butyl-4-hydroxyphenyl)ethylcarbonyloxy]ethyl]oxamide, a compound represented by the following chemical formula, and the like.

[In the formula, Z is a substituted alkylene group. R ¹¹ and R ¹² are each independently alkyl, aralkyl, aryl, heteroaryl, cycloalkyl, or heterocycloalkyl, which may be substituted. R ¹³ and R ¹⁴ are each independently a substituted alkyl group. ]

As the nitrogen compound in the metal deactivator, for example, a hydrazide-based nitrogen compound, an amide-based nitrogen compound, a triazole-based nitrogen compound, a melamine-based nitrogen compound, etc. may be mentioned.

As long as the hydrazine-based nitrogen compound is a nitrogen compound having a hydrazine skeleton, dodecanedioic acid bis[N2-(2-hydroxybenzyl)hydrazine], N,N'-bis[3- (3,5-Di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, decanedicarboxylate disalicylhydrazine, N-salylidene-N'-salicylhydrazine, m Nitrobenzohydrazine, 3-aminophthalic hydrazine, phthalic hydrazine, adipic hydrazine, oxalobis(2-hydroxy-5-octylbenzylidene hydrazine), N'-benzylpyrrolidone carboxyhydrazine, N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine, etc.

The amide-based nitrogen compound may be a nitrogen compound having an amide skeleton, and examples thereof include N,N'-bis{2-[3-(3,5-ditert-butyl-4-hydroxyphenyl)propane] Acyloxy] ethyl} oxalamide and the like.

As long as the triazole-based nitrogen compound is a nitrogen compound having a triazole skeleton, N-(2H-1,2,4-triazol-5-yl)salicylamide, 3-amino-1, 2,4-triazole, 3-(N-salicyl)amino-1,2,4-triazole, etc.

The melamine-based nitrogen compound only needs to be a nitrogen compound having a melamine skeleton, and examples thereof include melamine, melamine derivatives, and the like. More specifically, triaminotriazine, alkylated triaminotriazine, alkoxyalkylated triaminotriazine, melamine, alkylated melamine, alkoxyalkylated melamine, N2 -Butyl melamine, N2,N2-diethylmelamine, N,N,N',N',N",N"-hexa(methoxymethyl)melamine, etc.

Surfactant:

The surfactant includes a nonionic surfactant, a weak cationic surfactant, and the like.

Examples of nonionic surfactants include polyethylene glycol, polyethylene glycol/polypropylene glycol copolymer, aliphatic alcohol polyoxyethylene adduct, aromatic alcohol polyoxyethylene adduct, polyol Polyoxyethylene adduct.

Examples of weak cationic surfactants include terminal diamine polyethylene glycol, terminal diamine polyethylene glycol/polypropylene glycol copolymer, aliphatic amine polyoxyethylene adduct, aromatic amine polyoxyethylene Adduct, polyamine polyoxyethylene adduct.

Surfactants other than the above include, for example, polyalkylene oxide acetylene glycols, polyalkylene oxide glyceryl ethers, polyalkylene oxide alkyl ethers, polyalkylene oxide esters, polyalkylene oxide alkylamines, polycyclic Oxyalkaneamide, etc.

By using the flux of the present embodiment described above, it is possible to achieve soldering that reduces the generation of voids, improves solder wettability, and suppresses peeling during soldering. In addition, the flux of this embodiment is suitable for use in a solder paste using a solder alloy with a low alpha radiation dose, as will be described later.

(Solder Paste)

The solder paste of another aspect of the present invention is composed of the flux and solder powder of the above-mentioned aspect. Moreover, the said solder powder consists of the solder alloy whose alpha radiation dose is 0.02cph/cm< ² > or less.

<Flux>

The solder paste of this embodiment contains the flux of the above-mentioned embodiment.

The flux content in the solder paste of the present embodiment is preferably 5 to 95% by mass, more preferably 5 to 50% by mass, and still more preferably 5 to 15% by mass relative to the total mass of the solder paste (100% by mass). .

If the flux content in the solder paste is within this range, the effect of the components mixed in the flux can be enhanced, that is, the generation of voids during soldering is easily suppressed, and the wettability of the solder and the effect of suppressing peeling are easily improved.

<Solder powder>

The solder powder used in the solder paste of the present embodiment is composed of a solder alloy with an alpha radiation dose of 0.02 cph/cm ² or less.

The solder powder in this embodiment may be a powder of a Sn-based solder, or a powder of an alloy such as Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Bi, and Sn-In. powder, or a powder of a solder alloy in which Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, P, etc. are added to these alloys.

In addition, the solder powder may be a solder that does not contain Pb, may be a solder that contains Pb, or may be Sn-Pb based or Sn-Pb based with Sb, Bi, In, Cu, Zn, As, Ag, Cd added. , Fe, Ni, Co, Au, Ge, P and other solder alloy powders.

One preferred embodiment of the solder powder includes U: less than 5 mass ppb, Th: less than 5 mass ppb, Pb: less than 5 mass ppm, As: less than 5 mass ppm, Ni: 0 mass ppm Solder having an alloy composition of 600 mass ppm or more, Fe: 0 mass ppm or more and 100 mass ppm or less, and residual content of Sn, satisfying the following formula (1) and having an α radiation dose of 0.02 cph/cm ² or less Solder powder composed of an alloy (hereinafter referred to as "solder powder (SP)").

20≦Ni+Fe≦700 (1)

In formula (1), Ni and Fe represent contents (mass ppm) in each of the aforementioned alloy compositions.

By using the aforementioned solder powder (SP), the viscosity increase with time of the solder paste can be suppressed. In addition, the generation of soft errors can be suppressed.

≪U: Less than 5 quality ppb, Th: less than 5 quality ppb≫

U and Th are radioactive elements. To suppress the generation of soft errors, it is necessary to suppress the content of these in the solder alloy.

In the above-mentioned solder powder (SP), the U and Th contents in the solder alloy relative to the total mass (100 mass %) of the solder alloy are respectively from the viewpoint of making the amount of α radiation generated by the solder alloy 0.02 cph/cm ² or less. less than 5ppb. From the viewpoint of suppressing the occurrence of soft errors in high-density mounting, the U and Th contents are preferably 2 ppb or less, respectively, and the lower the better.

≪Pb: Less than 5 mass ppm≫

Generally speaking, Sn contains impurities of Pb. The radioactive isotopes in the Pb decay into ²¹⁰ Po through β decay, and when ²¹⁰ Po decays through α to generate ²⁰⁶ Pb, α rays are generated. From this point of view, the content of Pb, which is an impurity, in the solder alloy is preferably as small as possible.

In the aforementioned solder powder (SP), the content of Pb in the solder alloy is less than 5 ppm, preferably less than 2 ppm, more preferably less than 1 ppm relative to the total mass of the solder alloy (100 mass %). Furthermore, the lower limit of the Pb content in the solder alloy may be 0 ppm or more.

≪As: Less than 5 mass ppm≫

Adding As to the solder alloy can effectively suppress the thickening of the solder paste over time, but with the addition of As, the alloy will contain radioactive elements derived from As impurities, which will cause alpha rays generated by the solder material. volume increase.

The purpose of the aforementioned solder powder (SP) is to suppress the thickening of the solder paste over time without adding As as an impurity containing a radioactive element.

In the aforementioned solder powder (SP), the content of As in the solder alloy is less than 5 ppm, preferably less than 2 ppm, more preferably less than 1 ppm relative to the total mass (100 mass %) of the solder alloy. Furthermore, the lower limit of the As content in the solder alloy may be 0 ppm or more.

≪Ni: 0 mass ppm or more and 600 mass ppm or less, Fe: 0 mass ppm or more and 100 mass ppm or less, formula (1)≫

The formation of Sn-containing intermetallic compounds (Sn-containing intermetallic compounds) near the joint interface in solder alloys has progressed. If the Sn-containing intermetallic compounds are precipitated, the mechanical Deterioration of sexual strength.

Ni: 0 mass ppm or more and 600 mass ppm or less

Ni is an element that suppresses the formation of Sn-containing intermetallic compounds at the bonding interface.

The solder alloy contains Ni, whereby the formation of the aforementioned Sn-containing intermetallic compound can be suppressed, and the mechanical strength of the solder joint can be maintained. On the other hand, if the Ni content in the solder alloy exceeds 600 ppm, the SnNi compound may precipitate in the vicinity of the joint interface in the solder alloy, and the mechanical strength of the solder joint may be degraded.

In the solder powder (SP), the Ni content in the solder alloy is 0 ppm or more and 600 ppm or less, preferably 20 ppm or more and 600 ppm or less, more preferably 40 ppm or more and 600 ppm or less, relative to the total mass of the solder alloy (100 mass %).

Fe: 0 mass ppm or more and 100 mass ppm or less

Like Ni, Fe is an element that suppresses the formation of Sn-containing intermetallic compounds at the bonding interface. In addition, within the range of a specific content, the precipitation of needle-like crystals from the SnFe compound can be suppressed, and the short circuit of the circuit can be prevented.

The "needle crystal" as used herein refers to a crystal in which the aspect ratio of the ratio of the major axis to the minor axis in one crystal derived from the SnFe compound is 2 or more.

In the solder powder (SP), the Fe content in the solder alloy is 0 ppm or more and 100 ppm or less, preferably 20 ppm or more and 100 ppm or less, more preferably 40 ppm or more and 80 ppm or less, relative to the total mass of the solder alloy (100 mass %).

Regarding the solder alloy in the above-mentioned solder powder (SP), the alloy composition system satisfies the following formula (1).

20≦Ni+Fe≦700 (1)

In formula (1), Ni and Fe represent contents (mass ppm) in each of the aforementioned alloy compositions.

Both Ni and Fe in the formula (1) are elements that suppress the formation of Sn-containing intermetallic compounds at the bonding interface. In addition, in the above-mentioned solder powder (SP), both Ni and Fe can provide the effect of suppressing the thickening over time of the solder paste.

In order to obtain the effect of suppressing the formation of intermetallic compounds containing Sn and the effect of suppressing the thickening over time of the solder paste, the total content of Ni and Fe in the solder alloy needs to be 20 ppm or more relative to the total mass of the solder alloy (100% by mass). Below 700ppm. The total content of Ni and Fe is preferably 40 ppm or more and 700 ppm or less, more preferably 40 ppm or more and 600 ppm or less, and most preferably 40 ppm or more and 200 ppm or less.

However, the aforementioned "total content of Ni and Fe" is the Fe content when the Ni content in the solder alloy is 0 ppm, the Ni content when the Fe content in the solder alloy is 0 ppm, and the total when Ni and Fe are present content.

In addition, when the solder powder (SP) contains Ni and Fe, the ratio of Ni to Fe in the solder alloy is preferably 0.4 or more and 30 or less, more preferably 0.4 or more and 10 or less, in terms of the mass ratio represented by Ni/Fe. 0.4 or more and 5 or less, particularly preferably 0.4 or more and 2 or less.

If the mass ratio of Ni/Fe is within the aforementioned preferred range, the effect of suppressing the increase in the viscosity of the solder paste over time can be easily obtained.

≪Any element≫

Regarding the solder alloy in the aforementioned solder powder (SP), the alloy composition may contain elements other than the above-mentioned elements as necessary.

For example, in the solder alloy in the solder powder (SP), the alloy composition may further contain at least one of Ag: 0 mass % or more and 4 mass % or less and Cu: 0 mass % or more and 0.9 mass % or less in addition to the above elements.

Ag: 0 mass % or more and 4 mass % or less

Ag is any element that forms Ag ₃ Sn at the crystal interface and improves the reliability of the solder alloy. In addition, Ag is a noble element with respect to Sn in the ionization tendency, and by coexisting with Ni and Fe, the effect of suppressing the thickening over time of the solder paste can be enhanced. In addition, if the Ag content in the solder alloy is within the above range, the melting point of the alloy can be suppressed from rising, so the reflow temperature does not need to be too high.

In the aforementioned solder powder (SP), the Ag content in the solder alloy is preferably 0% or more and 4% or less, more preferably 0.5% or more and 3.5% or less, and still more preferably 1.0% relative to the total mass (100% by mass) of the solder alloy. % or more and 3.0% or less, particularly preferably 2.0% or more and 3.0% or less.

Cu: 0 mass % or more and 0.9 mass % or less

Cu is an arbitrary element used in general solder alloys that can improve the bonding strength of solder joints. In addition, the ionization tendency of Cu is a noble element relative to Sn, and by coexisting with Ni and Fe, the effect of suppressing the thickening over time of the solder paste can be enhanced.

In the aforementioned solder powder (SP), the Cu content in the solder alloy is preferably 0% or more and 0.9% or less, more preferably 0.1% or more and 0.8% or less, and still more preferably 0.2% relative to the total mass of the solder alloy (100% by mass). % above and 0.7% below.

When the solder powder (SP) contains Cu and Ni, the ratio of Cu to Ni in the solder alloy is preferably 8 or more and 175 or less, more preferably 10 or more and 150 or less, in terms of the mass ratio represented by Cu/Ni.

If the mass ratio of Cu/Ni is within the aforementioned preferred range, the effect of suppressing the increase in the viscosity of the solder paste over time can be easily obtained.

When the solder powder (SP) contains Cu and Fe, the ratio of Cu to Fe in the solder alloy is preferably 50 or more and 350 or less, more preferably 70 or more and 250 or less, in terms of mass ratio represented by Cu/Fe.

If the mass ratio of Cu/Fe is within the aforementioned preferred range, the effect of suppressing the increase in the viscosity of the solder paste over time can be easily obtained.

When the solder powder (SP) contains Cu, Ni, and Fe, the ratio of Cu, Ni, and Fe in the solder alloy is preferably 7 or more and 350 or less, more preferably 10 or more and 250, in terms of the mass ratio represented by Cu/(Ni+Fe) the following.

If the mass ratio of Cu/(Ni+Fe) is within the aforementioned preferred range, the effect of suppressing the increase in the viscosity of the solder paste over time can be easily obtained.

For example, regarding the solder alloy in the above-mentioned solder powder (SP), the alloy composition may further contain at least one of Bi: 0 mass % or more and 0.3 mass % or less and Sb: 0 mass % or more and 0.9 mass % or less in addition to the above elements.

Bi: 0 mass % or more and 0.3 mass % or less

Bi has low reactivity with the flux, and is an element that exhibits the effect of suppressing the thickening over time of the solder paste. In addition, Bi can reduce the liquidus temperature of the solder alloy and reduce the viscosity of the molten solder, so it is an element that can suppress the deterioration of wettability.

In the aforementioned solder powder (SP), the content of Bi in the solder alloy is preferably 0% or more and 0.3% or less, more preferably 0.0020% or more and 0.3% or less, and still more preferably 0.01% with respect to the total mass of the solder alloy (100% by mass). % or more and 0.1% or less, preferably 0.01% or more and 0.05% or less.

Sb: 0 mass % or more and 0.9 mass % or less

Like Bi, Sb has low reactivity with flux, and is an element that exhibits an effect of suppressing the thickening of solder paste over time. If the content of Sb in the solder alloy is too large, the wettability will be deteriorated, so Sb needs to be added in an appropriate amount.

In the aforementioned solder powder (SP), the Sb content in the solder alloy is preferably 0% or more and 0.9% or less, more preferably 0.0020% or more and 0.9% or less, and still more preferably 0.01% relative to the total mass of the solder alloy (100% by mass). % or more and 0.1% or less, preferably 0.01% or more and 0.05% or less.

Regarding the solder alloy in the solder powder (SP), when the alloy composition further contains at least one of Bi: 0 mass % or more and 0.3 mass % or less, and Sb: 0 mass % or more and 0.9 mass % or less, the alloy composition is preferably The following formula (2) is satisfied.

0.03≦Bi+Sb≦1.2 (2)

In formula (2), Bi and Sb represent contents (mass %) in each of the aforementioned alloy compositions.

Both Bi and Sb in the formula (2) are elements that exhibit the effect of suppressing the thickening over time of the solder paste. In addition, in the aforementioned solder powder (SP), both Bi and Sb can impart wettability to the solder alloy.

The total content of Bi and Sb in the solder alloy is preferably 0.03% or more and 1.2% or less, more preferably 0.03% or more and 0.9% or less, and still more preferably 0.3% or more and 0.9%, with respect to the total mass of the solder alloy (100% by mass). the following.

However, the aforementioned "total content of Bi and Sb" is the Sb content when the Bi content in the solder alloy is 0%, the Bi content when the Sb content in the solder alloy is 0%, and the combination when Bi and Sb are present. total content.

When Bi and Sb are included in the solder powder (SP), the ratio of Bi to Sb in the solder alloy is preferably 0.01 or more and 10 or less, more preferably 0.1 or more and 5 or less, in terms of mass ratio represented by Sb/Bi.

If the mass ratio of Sb/Bi is within the aforementioned preferred range, the effect of suppressing the increase in the viscosity of the solder paste over time can be easily obtained.

≪Residual: Sn≫

Regarding the solder alloy in the aforementioned solder powder (SP), the remainder of the alloy composition is composed of Sn. Inevitable impurities other than the above-mentioned elements may be contained. Even the case of containing unavoidable impurities does not affect the above-mentioned effects.

≪Alpha radiation dose≫

The alpha radiation dose of the solder alloy in the solder powder (SP) is 0.02 cph/cm ² or less.

This is the amount of alpha rays that is such that there is no problem of soft errors in high-density mounting of electronic components.

From the viewpoint of further suppressing soft errors in high-density mounting, the amount of α radiation generated by the solder alloy in the solder powder (SP) is preferably 0.01 cph/cm ² or less, more preferably 0.002 cph/cm ² or less, Still more preferably, it is 0.001 cph/cm ² or less.

The amount of alpha radiation generated by the solder alloy can be measured in the following manner. The measurement method of the alpha radiation dose is based on the international standard JEDEC STANDARD.

Procedure (i):

An air-flow type alpha dose measuring device was used.

The measurement samples are solder alloy flakes formed into flakes with a surface area of 900 cm ² using molten solder alloy.

The above-mentioned solder alloy sheet as a measurement sample was set in the above-mentioned α-ray dose measuring apparatus, and flushed with PR gas.

Furthermore, the PR gas system uses JEDEC STANDARD according to international standards. That is, as the PR gas system used for the measurement, the gas cylinder was filled with a mixed gas of 90% argon-10% methane, and the impurity radon (Rn) in the gas was decayed over 3 weeks.

Procedure (ii):

After the PR gas was circulated for 12 hours in the α-ray dose measuring apparatus in which the solder alloy flakes were installed, and then left to stand, the α-ray dose measurement was performed for 72 hours.

Procedure (iii):

The average alpha radiation dose was calculated as "cph/cm ² ". Abnormal points (counts due to vibration of the apparatus, etc.) are the counts excluding the one-hour period.

In the solder alloy in the above-mentioned solder powder (SP), the α radiation dose is preferably 0.02 cph/cm after heat treatment at 100° C. for 1 hour with respect to the solder alloy flake formed into a flake with a surface area of 900 cm ^{2 2} or less, more preferably 0.01 cph/cm ² or less, more preferably 0.002 cph/cm ² or less, and particularly preferably 0.001 cph/cm ² or less.

The solder alloy with such a dose of α radiation is not likely to produce segregation of ²¹⁰ Po in the alloy, and the influence of the temporal change of the dose of α radiation is small, so it is useful. The occurrence of soft errors can be suppressed by applying the solder alloy exhibiting the α radiation dose, and stable operation of the semiconductor element can be easily ensured.

[Manufacturing method of solder alloy]

The solder alloy in the above-mentioned solder powder (SP) can be produced, for example, by using a production method having a step of melt-mixing a raw material metal containing at least one of Ni and Fe and Sn.

For the purpose of designing a solder alloy with low alpha radiation dose, the raw material metal is preferably a low alpha radiation dose material, such as Sn, Ni and Fe of high purity and U, Th and Pb removed. Sn which is the raw material metal can be produced by, for example, the production method described in Japanese Patent Laid-Open No. 2010-156052 (Patent Document 1).

As the raw material metals, Ni and Fe can be used, for example, respectively, and those produced according to Patent No. 5,692,467 can be used.

A conventionally known method can be used for the operation system for melt-mixing the raw materials.

The above-mentioned solder powder (SP) can be produced by the dropping method of dropping molten solder alloy to obtain particles, or the spray method of centrifugal spray, the atomization method, the granulation method in liquid, the method of crushing the bulk solder alloy, etc. known methods. The dropping or spraying in the dropping method or the spraying method is preferably performed in an inert environment or a solvent in order to form particles.

The aforementioned solder powder (SP) is preferably spherical powder. The fluidity of the solder alloy can be improved by being a spherical powder.

When the above-mentioned solder powder (SP) is spherical powder, it is preferable to satisfy symbols 1 to 8 in the classification of powder size in JIS Z 3284-1:2014 (Table 2), and it is more preferable to satisfy symbols 4 to 8 . If the particle size of the solder powder satisfies this condition, the surface area of the powder will not be too large, the increase in the viscosity of the solder paste over time can be suppressed, and the aggregation of the fine powder can be suppressed, thereby suppressing the increase in the viscosity of the solder paste. Therefore, it can be welded to finer parts.

In addition, the above-mentioned solder powder (SP) is preferably composed of a group of solder alloy particles with an average particle size of 0.1 to 50 μm, more preferably composed of a group of solder alloy particles with an average particle size of 1 to 25 μm, and even more It is preferable to use a group of solder alloy particles with an average particle size of 1 to 15 μm.

If the particle size of the solder powder is within the aforementioned preferable range, it is easy to suppress the increase in the viscosity of the solder paste with time.

Here, the average particle size of the solder powder is a particle size of 50% of the cumulative value in the particle size distribution measured by a laser diffraction scattering particle size distribution analyzer.

Moreover, it is preferable that the said solder powder (SP) has 2 or more types of solder alloy particle groups which differ in particle size distribution. Thereby, the lubricity of the solder paste can be improved, and the operability such as easy printing can be improved.

As the solder powder, for example, two or more types of solder alloy particle groups having different average particle diameters can be used in combination. As an example, a solder powder having a solder alloy particle group (S1) having an average particle diameter of 5 μm or more and less than 10 μm and a solder alloy particle group (S2) having an average particle diameter of 1 μm or more and less than 5 μm can be mentioned.

The mixing ratio of the solder alloy particle group (S1) and the solder alloy particle group (S2) is preferably (S1)/(S2)=9/1 to 1/9 in terms of the mass ratio represented by (S1)/(S2), more preferably 9/1 to 3/7, more preferably 9/1 to 5/5.

For the solder powder in this embodiment, the spherical powder has a sphericity of preferably 0.8 or more, more preferably 0.9 or more, still more preferably 0.95 or more, and particularly preferably 0.99 or more.

The "sphericity of spherical powder" described herein can be measured using a minimum zone center method (MZC method) CNC image measurement system (ULTRA QUICK VISION ULTRA QV350-PRO measurement device manufactured by Mitutoyo Corporation).

The sphericity represents the deviation from a sphere, and is, for example, an arithmetic mean calculated by dividing the diameter of 500 solder alloy particles by the major axis, and the closer the value is to 1.00 of the upper limit, the closer it is to a sphere.

The solder paste of this embodiment can be manufactured according to the general manufacturing method in the technical field.

A solder paste can be obtained by heating and mixing the compounding components constituting the above-mentioned flux to prepare a flux, and stirring and mixing the above-mentioned solder powder in the flux. Furthermore, in order to obtain the effect of suppressing the thickening over time, zirconia powder may be further blended in addition to the above-mentioned solder powder.

As described above, the solder paste of the present embodiment uses a flux with specific rosin and activator. A solder paste combining the flux and solder powder composed of a solder alloy with an alpha radiation dose of 0.02 cph/cm ² or less can achieve soldering with reduced void generation, improve solder wettability and suppress peeling during soldering. In addition, the occurrence of soft errors can be suppressed by the solder paste of this embodiment.

In the present embodiment, a specific rosin is selected as the flux, that is, methyl rosinate is selected to easily reduce the melt viscosity of the solder paste. Therefore, the vaporized flux component is easily detached from the paste, thereby suppressing the generation of voids. In addition, a specific active agent is selected in the flux in this embodiment, that is, the compound represented by the general formula (p1) is selected, thereby improving the wettability of the solder. Therefore, the wetting speed of the solder can be increased, and the reflow and flux residue removal after cleaning can be suppressed.

In addition, in the solder paste of the above-described embodiment, the solder powder in the form of the solder powder (SP) is less likely to change with time, such as an increase in viscosity, and the occurrence of soft errors can be suppressed. That is, the solder paste of this embodiment is suitable as a low alpha radiation dose material.

Generally speaking, each constituent element constituting the solder alloy in the solder alloy does not function independently, and various effects can be exhibited only when the content of each constituent element is within a specific range. According to the solder alloy in the above-mentioned solder powder (SP), by making the content of each constituent element within the above-mentioned range, the increase in the viscosity of the solder paste with time can be suppressed, and the occurrence of soft errors can be suppressed. That is, the solder alloy in the aforementioned solder powder (SP) can be used as a low-α radiation material for the purpose, and is suitable for forming the solder bumps around the memory, thereby suppressing the occurrence of soft errors.

In addition, the above-mentioned solder powder (SP) does not actively add As, but uses a solder alloy containing Ni and Fe of the high melting point metal in a specific ratio by heating at a high temperature during refining or processing of the bare metal, thereby achieving suppression of Thickening of solder paste over time. The reason why this effect is obtained has not yet been determined, but is presumed as follows.

The purity of Sn for solder alloys with low α radiation dose is extremely high, and the crystal size of Sn becomes larger when the molten alloy solidifies. In addition, the oxide film in the Sn will also form a relatively sparse oxide film correspondingly. Therefore, by adding Ni and Fe of high melting point metals, the crystal size can be reduced and a dense oxide film can be formed, thereby suppressing the reactivity of the alloy and the flux, thereby suppressing the thickening of the solder paste over time.

(Example)

Hereinafter, the present invention will be described in further detail by way of examples, but the present invention is not limited to these examples.

In this example, unless otherwise specified, "ppb" of the solder alloy composition is "mass ppb", "ppm" is "mass ppm", and "%" is "mass %".

<Production of Solder Alloy>

(Production Examples 1 to 460)

The raw material metals were melted and stirred to prepare solder alloys having respective alloy compositions shown in Tables 1 to 19, respectively.

The α radiation dose evaluation of the solder alloys of the respective production examples was performed in the following manner. The evaluation results are shown in Tables 1 to 19.

[alpha radiation dose]

(1) Verification method 1

The measurement of the α-ray dose was performed using an α-ray dose measuring device of an airflow proportional counter and in accordance with the above-mentioned procedures (i), (ii) and (iii).

The measurement sample used the solder alloy flake immediately after manufacture.

This solder alloy sheet is produced by melting the solder alloy immediately after production and molding it into a sheet shape having a surface area of 900 cm ² .

The measurement sample was placed in an α-ray dose measuring apparatus, and after flowing PR-10 gas for 12 hours and standing, the α-ray dose measurement was performed for 72 hours.

(2) Judgment Criteria 1

○○: The amount of α radiation generated by the measurement sample is 0.002 cph/cm ² or less.

○: The amount of α radiation generated by the measurement sample exceeds 0.002 cph/cm ² and is 0.02 cph/cm ² or less.

×: The amount of α radiation generated by the measurement sample exceeded 0.02 cph/cm ² .

If the determination is "○○" or "○", it can be determined as a solder material with a low alpha radiation dose.

(3) Verification method 2

The α radiation dose was measured in the same manner as in (1) Verification Method 1 above, except that the measurement sample was changed.

The measurement samples were obtained by melting and molding the solder alloy immediately after fabrication into a sheet-like solder alloy sheet with a surface area of 900 cm ² , and heating the solder alloy sheet at 100° C. for 1 hour and letting it cool.

(4) Judgment Criteria 2

○○: The amount of α radiation generated by the measurement sample is 0.002 cph/cm ² or less.

○: The amount of α radiation generated by the measurement sample exceeds 0.002 cph/cm ² and is 0.02 cph/cm ² or less.

×: The amount of α radiation generated by the measurement sample exceeded 0.02 cph/cm ² .

If the determination is "○○" or "○", it can be determined as a solder material with a low alpha radiation dose.

(5) Verification method 3

After storing the solder alloy sheet of the measurement sample for the measurement of α radiation dose in the above (1) Verification method 1 for one year, measure the α radiation dose again according to the above procedures (i), (ii) and (iii), and evaluate the α radiation dose. change over time.

(6) Judgment Criteria 3

○○: The amount of α radiation generated by the measurement sample is 0.002 cph/cm ² or less.

○: The amount of α radiation generated by the measurement sample exceeds 0.002 cph/cm ² and is 0.02 cph/cm ² or less.

×: The amount of α radiation generated by the measurement sample exceeded 0.02 cph/cm ² .

If the judgment is "○○" or "○", it can be judged that the amount of α rays generated does not change over time and is stable. That is, the occurrence of soft errors in electronic devices can be suppressed.

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Table 11]

[Table 12]

[Table 13]

[Table 14]

[Table 15]

[Table 16]

[Table 17]

[Table 18]

[Table 19]

As shown in Tables 1 to 19, the α radiation dose of the solder alloys of each production example was evaluated. As a result, it was confirmed that the solder alloy sheets of the production examples 1 to 460 were at 100 in the solder alloy flakes immediately after production. ℃, the solder alloy flakes after heat treatment for 1 hour, and the solder alloy flakes after storage for 1 year were judged as "○○".

<Manufacture of solder powder>

The solder alloys of each production example were melted, and solder powders were produced by atomization. The solder powders were composed of solder alloys having the alloy compositions shown in Tables 1 to 19, respectively, and were solder alloy particles with an average particle size of 6 μm. composed of groups.

In addition, for the solder alloys of Production Examples 241 to 296 and Production Examples 445 to 448, the solder alloys of the production examples were melted, and solder powders were produced by the atomization method. It consists of solder alloys of the alloy compositions shown in Table 12 and Table 19, and consists of a group of solder alloy particles having an average particle diameter of 4 μm.

<Preparation of Flux>

(Examples 1 to 28, Comparative Examples 1 to 3)

As the resin component, hydrogenated methyl rosinate and rosin other than hydrogenated methyl rosinate were used. As the rosin system other than hydrogenated rosin acid methyl ester, polymerized rosin, acrylic-modified rosin, acrylic-modified hydrogenated rosin, hydrogenated rosin, disproportionated rosin, and hydrogenated rosin glyceride are used.

As the organic acid, 2-picolinic acid, malonic acid, suberic acid, azelaic acid, stearic acid, and hydrogenated dimer acid were used.

As the amines, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine, 2-phenylimidazole, and xylylguanidine were used.

Thixotropic agents used ethylene dihydroxystearic acid amide and castor hydrogenated oil.

As the solvent system, diethylene glycol monobutyl ether and hexyl diethylene glycol were used.

As the halogen-based activator, trans-2,3-dibromo-2-butene-1,4-diol, which is an organic halogen compound, is used. Also, diphenylguanidine HBr salt of amine hydrohalide was used.

Next, the components shown in Tables 20 to 25 were mixed to prepare the flux of each example.

<Manufacture of solder paste>

(Example 101)

Solder pastes were prepared by mixing the flux of Example 1 and each of the solder alloys of Production Examples 445 to 448 with solder powders composed of solder alloy particles having an average particle size of 6 μm.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Comparative Example 101)

A solder paste was produced in the same manner as in Example 1, except that the flux in Example 1 was changed to that of Comparative Example 1.

(Comparative Example 102)

A solder paste was produced in the same manner as in Example 1, except that the flux in Example 1 was changed to that of Comparative Example 2.

(Comparative Example 103)

A solder paste was produced in the same manner as in Example 1 except that the flux in Example 1 was changed to that of Comparative Example 3.

(Examples 102 to 128)

Each solder paste was produced in the same manner as in Example 1, except that the fluxes in Example 1 were changed to those of Examples 2 to 28, respectively.

(Example 129)

Each of the fluxes of Examples 1 to 28, each of the fluxes of Examples 1 to 28, and each of the solder alloys of Production Examples 445 to 448 were mixed with solders composed of solder alloy particles with an average particle size of 6 μm. powder to manufacture each solder paste.

The mixing ratio of flux and solder powder is flux: solder powder = 35:65 by mass.

(Example 130)

Each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 449 to 452 were mixed with solder powders composed of solder alloy particles having an average particle size of 6 μm to produce solder pastes.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 131)

Each solder paste was prepared by mixing each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 453 to 456 with solder powders composed of solder alloy particles having an average particle size of 6 μm.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 132)

Each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 457 to 460 were mixed with solder powders composed of solder alloy particles having an average particle size of 6 μm to produce solder pastes.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 133)

Each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 1 to 74 were mixed with solder powders composed of solder alloy particles having an average particle size of 6 μm to produce solder pastes.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 134)

Each solder paste was produced by mixing each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 371 to 444 with solder powders composed of solder alloy particles having an average particle size of 6 μm.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 135)

Each solder paste was prepared by mixing each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 75 to 148 with solder powders composed of solder alloy particles having an average particle size of 6 μm.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 136)

Each solder paste was prepared by mixing each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 223 to 296 with solder powders composed of solder alloy particles having an average particle size of 6 μm.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 137)

Each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 149 to 222 were mixed with solder powders composed of solder alloy particles having an average particle size of 6 μm to produce solder pastes.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 138)

Each of the fluxes of Examples 1 to 28 and each of the solder alloys of Production Examples 297 to 370 were mixed with solder powders composed of solder alloy particles having an average particle size of 6 μm to produce solder pastes.

The mixing ratio of flux and solder powder is flux: solder powder = 11:89 by mass.

(Example 139)

A mixed solder powder having two types of solder alloy particle groups composed of the solder alloy of Production Example 445 and having different average particle diameters was produced.

Specifically, the solder alloy particle group (S1b) composed of the solder alloy of Production Example 445 with an average particle size of 6 μm and the solder alloy of Production Example 445 composed of the average particle size of 4 μm The solder alloy particle group (S2b) is mixed at a mass ratio (S1b)/(S2b)=90/10 to obtain mixed solder powder.

Next, each of the fluxes of Examples 1 to 28 and the mixed solder powders mixed at a mass ratio (S1b)/(S2b)=90/10 were mixed to manufacture each solder paste.

The mixing ratio of flux and mixed solder powder is flux: mixed solder powder = 11:89 by mass.

(Example 140)

Except for changing the mixing ratio of the solder alloy particle group (S1b) having an average particle size of 6 μm and the solder alloy particle group (S2b) having an average particle size of 4 μm, which are all composed of the solder alloy of Production Example 445, to the mass ratio (S1b) Each solder paste was produced in the same manner as in Example 139 except that /(S2b)=50/50.

(Example 141)

Mixed solder powders having two types of solder alloy particle groups each consisting of the solder alloys of Production Example 257 and having different average particle diameters were produced.

Specifically, a group of solder alloy particles (S1a) with an average particle size of 6 μm composed of the solder alloy of Production Example 257 and a group of solder alloy particles composed of the solder alloy of Production Example 257 with an average particle size of 4 μm (S2a) ) are mixed at a mass ratio (S1a)/(S2a)=90/10 to obtain a mixed solder powder.

Next, each of the fluxes of Examples 1 to 28 and the mixed solder powders mixed at a mass ratio (S1a)/(S2a)=90/10 were mixed to manufacture each solder paste.

The mixing ratio of flux and mixed solder powder is flux: mixed solder powder = 11:89 by mass.

(Example 142)

The mixing ratio of the solder alloy particle group (S1a) with an average particle size of 6 μm and the solder alloy particle group (S2a) with an average particle size of 4 μm, both of which are composed of the solder alloy of Production Example 257, was changed to the mass ratio (S1a)/ Except (S2a)=50/50, each solder paste was produced in the same manner as in Example 141.

<Evaluation (Part 1)>

Using the fluxes and solder pastes of each example, various evaluations, such as difficulty of generation of voids, wetting speed of solder, and suppression of peeling, were performed. Based on these evaluation results, a comprehensive evaluation is carried out.

Details are as follows. The evaluation results are shown in Tables 20 to 28.

[Easy Difficulty of Void Generation]

Using a metal mask, the solder paste was printed with a height of 40 μm on Cu-OSP electrodes (N=15) with a φ80 μm and a pitch of 150 μm. It is then reflowed in a nitrogen atmosphere. The reflow profile was held at 160°C for 2 minutes, and then increased to 260°C at 1.5°C/sec.

The penetration image of the soldered portion (solder bump) after reflow was observed using Microfocus X-ray SystemXVR-160 manufactured by UNi-HiTE SYSTEM, and the void generation rate was obtained.

Specifically, the penetration observation of the solder bumps from the top to the bottom is carried out to obtain the penetration image of the circular solder bumps, and the metal filling part and the cavity part are identified by the color contrast, and the cavity area ratio is calculated by automatic analysis. , which is taken as the void generation rate.

Using the void generation rate obtained as described above, the difficulty of generating voids was evaluated by the following criteria.

○: In all 15 welded parts, the void generation rate was 10% or less.

×: The case where the void generation rate exceeded 10% was included in the 15 welded parts.

[Wetting speed of solder]

(1) Verification method

The evaluation test of the wetting speed of the solder was carried out in the following manner.

According to the meniscograph test method, a copper plate with a width of 5 mm × a length of 25 mm × a thickness of 0.5 mm was oxidized at 150° C. for 1 hour to obtain an oxidized copper plate of the test plate. The solder alloy of Sn-3Ag-0.5Cu (each value is mass %; the residual amount is Sn) was evaluated in the following manner.

First, with respect to the flux of each example measured in a beaker, the test board was dipped by 5 mm and the test board was coated with the flux. Next, immediately after the application of the flux, the test board coated with the flux was immersed in a solder bath having a solder alloy of the aforementioned alloy composition to obtain a zero crossing time (sec).

Next, the flux of each example was measured 5 times, and the average value of the obtained 5 zero crossing times (sec) was calculated. The test conditions were set in the following manner.

Immersion speed of solder bath: 5mm/sec (JIS Z 3198-4:2014).

Immersion depth of solder bath: 2mm (JIS Z 3198-4:2014).

Immersion time of solder bath: 10sec (JIS Z 3198-4:2014).

Solder bath temperature: 245°C (JIS C 60068-2-69:2019 Appendix B). The shorter the average value of the zero crossing time (sec), the higher the wetting speed and the better the solder wettability.

(2) Judgment criteria

○: The average value of the zero-crossing time (sec) is 6 seconds or less.

×: The average value of the zero crossing time (sec) exceeds 6 seconds.

[falling off suppression]

(1) Verification method

80μm、間距150μm之Cu-OSP電極(N=15)之基板浸漬於異丙醇，以刷子去除OSP膜。 will have

The substrate of Cu-OSP electrode (N=15) with 80 μm and pitch of 150 μm was immersed in isopropanol, and the OSP film was removed with a brush.

After the OSP film was removed, it was baked in a constant temperature bath at 100°C for 1 hour.

The solder paste of each example was printed with a height of 40 μm using a metal mask on the obtained substrate electrodes. It is then reflowed in a nitrogen atmosphere.

The reflow temperature profile was held at 160°C for 2 minutes, and then increased to 260°C at 1.5°C/sec.

Next, it was observed with an optical microscope whether the positional deviation (dropping) of the solder paste with respect to the electrodes occurred.

(2) Judgment criteria

○: No dropout was observed in any of the electrodes.

×: One or more electrodes were observed to come off.

[Overview]

○: In Tables 20 to 28, each of the evaluations of the difficulty of generation of voids, the wetting speed of the solder, and the suppression of peeling are all ○.

×: In Tables 20 to 28, at least one of the evaluations of the difficulty of generation of voids, the wetting speed of the solder, and the suppression of peeling was rated as ×.

[Table 20]

[Table 21]

[Table 22]

[Table 23]

[Table 24]

[Table 25]

[Table 26]

[Table 27]

[Table 28]

As shown in Tables 20 to 28, in the solder pastes of Examples 101 to 142 containing the flux of the present invention, when any of the solder pastes was used, it was confirmed that the generation of voids was less, the solder wettability was improved, and the peeling was suppressed.

On the other hand, when using the solder paste of Comparative Example 1 which does not contain the compound represented by the general formula (p1) but contains a flux not within the scope of the present invention, both the solder wettability and the peeling inhibitory effect showed poor results.

In addition, in the solder pastes of Comparative Examples 2 to 3, which did not contain methyl rosinate but contained a flux not within the scope of the present invention, even when any solder paste was used, the evaluation of the difficulty of generating voids showed poor results. .

<Evaluation (Part 2)>

The evaluation of thickening inhibition was performed on the solder pastes of each example in the following manner.

[Thickening Inhibition]

(1) Verification method

The viscosity of each solder paste immediately after production in Examples 133 to 142 was measured for 12 hours in the atmosphere using PCU-205 manufactured by Malcom Co., Ltd., revolutions: 10 rpm, and 25°C.

(2) Judgment criteria

○: The viscosity after 12 hours was 1.2 times or less compared to the viscosity immediately after the preparation of the solder paste for 30 minutes.

×: The viscosity after 12 hours was 1.2 times higher than the viscosity at 30 minutes immediately after the preparation of the solder paste.

When this determination is "○", it can be said that a sufficient thickening inhibitory effect is obtained. That is, the viscosity increase with time of the solder paste can be suppressed.

The evaluation of thickening inhibition was carried out on the solder pastes of each example, and the results showed that the solder pastes of Examples 133 to 138, 141, and 142 all had the flux of the present invention and the solder powders used in the solder alloys of Production Examples 1 to 444. It was judged as "○", and it was confirmed that the increase in the viscosity of the solder paste over time could be suppressed.

On the other hand, the solder pastes of Examples 139 and 140 containing the solder powder used in the solder alloy of Production Example 445 in which the respective contents of Ni and Fe were less than 1 mass ppm were judged as "x".

Claims (27)

A flux is used for solder paste, and contains hydrogenated methyl rosinate, a compound represented by the following general formula (p1), and a solvent;

[In formula (p1), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms]. The flux according to claim 1, wherein the compound represented by the general formula (p1) is 2-picolinic acid. The flux according to claim 1 or 2, wherein the content of methyl hydrogenated rosinate is 5% by mass or more and 20% by mass or less with respect to the total amount of the flux. The flux according to any one of claims 1 to 3, wherein the content of the compound represented by the general formula (p1) is more than 0 mass % and 5 mass % or less with respect to the total amount of the flux. The flux according to any one of claims 1 to 4, further comprising rosin other than methyl rosinate, and a thixotropic agent. The flux according to claim 5, wherein the rosin other than hydrogenated methyl rosinate is composed of polymerized rosin, acrylic-modified rosin, acrylic-modified hydrogenated rosin, acrylic-modified disproportionated rosin, hydrogenated rosin, disproportionated rosin, and hydrogenated rosin glycerin At least one selected from the group consisting of esters. The flux according to claim 5 or 6, wherein the content of rosin other than methyl rosinate is 20% by mass or more and 40% by mass or less with respect to the total amount of the flux. The flux according to any one of claims 5 to 7, wherein the mixing ratio of hydrogenated methyl rosinate to rosin other than hydrogenated methyl rosinate is equal to hydrogenated methyl rosinate/hydrogenated rosin other than methyl rosinate The mass ratio is 0.16 or more and 1.0 or less. The flux according to any one of claims 5 to 8, wherein the thixotropic agent contains at least one selected from the group consisting of a wax-based thixotropic agent and an amide-based thixotropic agent. The flux according to claim 9, wherein the amide-based thixotropic agent contains at least one selected from the group consisting of polyamide, diamide and monoamide. The flux according to claim 9 or 10, wherein the wax-based thixotropic agent contains castor hydrogenated oil. The flux according to any one of claims 5 to 11, wherein the content of the thixotropic agent is 3 mass % or more and 10 mass % or less with respect to the total amount of the flux. The flux according to any one of claims 5 to 12, which further contains an organic acid of 0 mass % or more and 15 mass % or less with respect to the total amount of the flux. The flux according to any one of claims 5 to 13, which further contains 0 mass % or more and 30 mass % or less of an amine, 0 mass % or more and 5 mass % or less of an organic halogen compound with respect to the total amount of the flux, and The amine hydrohalide is 0 mass % or more and 1 mass % or less. A solder paste, which is composed of the flux according to any one of claims 1 to 14, and solder powder, The above-mentioned solder powder is composed of a solder alloy whose α radiation dose is 0.02 cph/cm ² or less. The solder paste according to claim 15, wherein the solder powder has U: less than 5 mass ppb, Th: less than 5 mass ppb, Pb: less than 5 mass ppm, As: less than 5 mass ppm, Ni: 0 mass ppm or more and 600 mass ppm or less, and Fe: 0 mass ppm or more and 100 mass ppm or less, and an alloy composition composed of Sn as a residual, satisfying the following formula (1) and having an α radiation dose of 0.02 cph/cm ² or less of solder alloys; 20≦Ni+Fe≦700 (1) In the formula (1), Ni and Fe represent contents (mass ppm) in each of the aforementioned alloy compositions. According to the solder paste of claim 16, the aforementioned alloy composition further satisfies the following formula (1'); 40≦Ni+Fe≦200 (1’) In the formula (1'), Ni and Fe represent the contents (mass ppm) in each of the aforementioned alloy compositions. The solder paste according to claim 16 or 17, wherein Pb in the aforementioned alloy composition is less than 2 mass ppm. The solder paste according to any one of claims 16 to 18, wherein the As in the aforementioned alloy composition is less than 2 mass ppm. The solder paste according to any one of claims 16 to 19, wherein the alloy composition further contains at least one of Ag: 0 mass % or more and 4 mass % or less, and Cu: 0 mass % or more and 0.9 mass % or less. The solder paste according to any one of claims 16 to 20, wherein the alloy composition further contains at least one of Bi: 0 mass % or more and 0.3 mass % or less, and Sb: 0 mass % or more and 0.9 mass % or less. According to the solder paste of claim 21, the aforementioned alloy composition further satisfies the following formula (2); 0.03≦Bi+Sb≦1.2 (2) In formula (2), Bi and Sb represent contents (mass %) in each of the aforementioned alloy compositions. The solder paste according to any one of Claims 16 to 22, wherein, in the solder alloy, after heat treatment at 100° C. for 1 hour is performed on the solder alloy sheet formed into a sheet with a surface area of 900 cm ² , the α-ray The amount is 0.02cph/ ^cm2 or less. The solder paste according to any one of claims 16 to 23, wherein the alpha radiation dose of the solder alloy is 0.002 cph/cm ² or less. The solder paste according to claim 24, wherein the alpha radiation dose of the solder alloy is 0.001 cph/cm ² or less. The solder paste according to any one of claims 16 to 25, wherein the solder powder is composed of a group of solder alloy particles having an average particle size of 0.1 to 15 μm. The solder paste according to any one of claims 16 to 25, wherein the solder powder further has two or more types of solder alloy particle groups having different average particle diameters.