JP2022060053A - Flux and solder paste - Google Patents

Abstract

To provide a flux which can realize soldering with less voids, and improves wettability of solder, and in which missing is suppressed, and a solder paste using the flux.SOLUTION: A flux, which is used in solder paste, contains: hydrogenated rosin methacrylate; a compound represented by general formula (p1); and a solvent. In the general formula (p1), R1, R2, R3 and R4 independently represent hydrogen atom or alkyl group with a carbon number of 1 to 4.[chemical formula 1]SELECTED DRAWING: None

Description

The present invention relates to flux and solder paste.

As the solder material, a solder paste containing solder powder and flux is used.
Electronic components mounted on printed circuit boards are increasingly required to be smaller and have higher performance. Examples of such electronic components include semiconductor packages. In a semiconductor package, a semiconductor element having an electrode is sealed with a resin component. Solder bumps made of a solder material are formed on this electrode. With this solder material, the semiconductor element and the printed circuit board are soldered, and both are connected.

In the solder material, various characteristics are required depending on the usage conditions, applications, and the like.
For example, Patent Document 1 proposes a composition containing a flux containing a rosin-based resin, an activator and a solvent, and a solder powder for the purpose of improving solder wettability.

Japanese Unexamined Patent Publication No. 2018-167297

The flux used for soldering has the effect of chemically removing metal oxides present on the metal surface of the solder and the object to be soldered, and enabling the movement of metal elements at the boundary between the two. .. Therefore, by soldering using a flux, an intermetallic compound can be formed between the solder and the metal surface of the object to be joined, and a strong bond can be obtained.

As electronic components become smaller and have higher performance, it is required to further improve the characteristics of conventional solder materials.
In the flux, it is required that the solder wetting speed is high and the solder wetting property is good with respect to the metal surface of the object to be joined.
When soldering using solder paste, if the wettability of the solder cannot be ensured on the metal surface of the object to be joined, it becomes difficult for the solder to evenly wet and spread on the electrodes. When the wettability and spreadability of the solder deteriorates, the solder paste is misaligned with respect to the electrode, and the solder paste is in a state of being detached from the electrode pad (missing bump), which causes a problem that bonding failure and conductivity failure are likely to occur.

In the case of soldering by the reflow method, the flux component is volatilized or decomposed by heating and gasified during the paste reflow. Then, there is a problem that voids caused by this gasified flux component are generated in the soldered portion.
The above problems are becoming more prominent due to the narrowing of the electrode pitch.

The present invention has been made in view of the above circumstances, and is capable of realizing soldering with less generation of voids, improving the wettability of the solder, suppressing missing, and a solder paste using this flux. The purpose is to provide.

According to the study, the present inventors can reduce the melt viscosity of the solder paste by using a specific rosin and an activator in combination, suppress the generation of voids, improve the wetting speed of the solder, and reflow. And, it has been found that missing after washing the flux residue is suppressed, and the present invention has been completed.
That is, the present invention employs the following means in order to solve the above problems.

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

［式（ｐ１）中、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４は、それぞれ独立に、水素原子又は炭素数１～４のアルキル基を示す。］

[In the 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. ]

Further, another aspect of the present invention is a solder paste comprising the flux according to the one aspect of the present invention and the solder powder, and the solder powder has an α dose of 0.02 cf / cm ² or less. A solder paste characterized by being made of a solder alloy.

According to one aspect of the present invention, it is possible to realize soldering with less generation of voids, improve the wettability of the solder, and provide a flux in which missing is suppressed.
According to another aspect of the present invention, it is possible to provide a solder paste containing the flux according to one aspect of the present invention and useful as a low α-dose material.

The present invention will be described in more detail below.
In the present specification, "ppb" relating to the solder alloy composition is "mass ppb" unless otherwise specified. "Ppm" is "mass ppm" unless otherwise specified. “%” Is “mass%” unless otherwise specified.

(flux)
The flux according to one aspect of the present invention is used for solder paste.
The flux of the present embodiment contains methyl hydrogenated rosinate, a compound represented by the general formula (p1), and a solvent.

≪Methyl hydrogenated rosinate≫
The flux of this embodiment contains methyl hydrogenated rosinate.
This methyl hydrogenated rosinate is an ester obtained from a hydrogenated cyclic fatty acid obtained from rosin and a methyl alcohol, also known as methyl hydrogenated abietic acid, and has a CAS number: 8050-15-5. be.
The content of hydrogenated methyl rosinate in the flux is preferably 5% by mass or more and 20% by mass or less with respect to the total amount (100% by mass) of the flux, and more preferably 5% by mass or more and 15% by mass or less. preferable.
When the content of hydrogenated methyl rosinate is in the above-mentioned preferable range, the generation of voids is more likely to be suppressed in soldering.

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

［式（ｐ１）中、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４は、それぞれ独立に、水素原子又は炭素数１～４のアルキル基を示す。］

[In the 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 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 a methyl group, an ethyl group, a propyl group, a cyclopropyl group, a butyl group and a cyclobutyl group. 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 picolinic acid, 6-methylpicolinic acid, 6-ethylpicolinic acid, 3-cyclopropylpicolinic acid, 4-cyclopropylpicolinic acid, and 6-cyclopropylpicolinic acid. Examples thereof include 5-butylpicolinic acid and 6-cyclobutylpicolinic acid. Of these, picolinic acid is particularly preferred.
As the compound represented by the general formula (p1), one kind may be used alone, or two or more kinds may be mixed and used.

The content of the compound represented by the general formula (p1) in the flux is preferably more than 0% by mass and 5% by mass or less with respect to the total amount (100% by mass) of the flux, and is preferably 1% by mass or more. 5% by mass or less is more preferable, and 2% by mass or more and 5% by mass or less is further preferable.
When the content of the compound represented by the general formula (p1) is in the above-mentioned preferable range, the wettability of the solder is further enhanced and the missing is further suppressed in the soldering.

The total content of the hydrogenated methyl rosinate in the flux and the compound represented by the general formula (p1) is more than 5% by mass and 25% by mass or less with respect to the total amount (100% by mass) of the flux. Is more preferable, 6% by mass or more and 25% by mass or less is more preferable, and 7% by mass or more and 20% by mass or less is further preferable.
If the total content of these two components is within the above-mentioned preferable range, the effects of suppressing void generation, solder wettability, and suppressing missing can be more easily enhanced.

≪Solvent≫
In the flux of the present embodiment, examples of the solvent include water, alcohol-based solvents, glycol ether-based solvents, terpineols, and the like.
Examples of the alcohol solvent include isopropyl alcohol, 1,2-butanediol, isobornylcyclohexanol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, and the like. 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexine-2,5-diol, 2,3-dimethyl-2,3-butanediol, 1,1,1-tris ( Hydroxymethyl) ether, 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, tretol, guayacol glycerol ether, 3,6-dimethyl-4-octine-3,6-diol, 2,4,7,9-tetramethyl-5- Descin-4,7-diol and the like can be mentioned.
Examples of the glycol ether-based solvent include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol monohexyl ether (hexyl diglycol), diethylene glycol monobutyl ether, and diethylene glycol di. Examples thereof include butyl ether and triethylene glycol monobutyl ether.

≪Other ingredients≫
The flux of the present embodiment may contain other components, if necessary, in addition to the hydrogenated methyl rosinate, the compound represented by the general formula (p1) and the solvent.
Other components include rosins other than methyl hydrogenated rosin, organic acids other than compounds represented by the general formula (p1), amines, thixo agents, halogen-based activators, resin components other than rosin-based resins, and metal inactivity. Examples thereof include agents, surfactants, silane coupling agents, antioxidants, colorants and the like.
For example, a suitable flux includes a form containing methyl hydrogenated rosinate, a compound represented by the general formula (p1), a solvent, a rosin other than methyl hydrogenated rosinate, and a thixo agent.

Rosin other than methyl hydrogenated rosin:
Examples of the rosin other than the hydrogenated methyl rosinate include raw material rosins such as gum rosin, wood rosin and tall oil rosin, and derivatives obtained from the raw material rosin.
Examples of the derivative include purified rosin, polymerized rosin, hydrogenated rosin, disproportionated rosin and α, β-unsaturated carboxylic acid modified products (acrylicated rosin, maleated rosin, fumarized rosin, etc.), and the polymerized rosin. Examples thereof include purified products, hydrides and disproportionated products of the above, and purified products, hydrides and disproportionated products of the α, β unsaturated carboxylic acid modified products.
In the flux of the present embodiment, one or more rosins other than methyl hydrogenated rosinate can be used.
Among the above, examples of rosins other than methyl hydrogenated rosin include polymerized rosins, acrylic acid-modified rosins, acrylic acid-modified hydrogenated rosins, acrylic acid-modified disproportionated rosins, hydrogenated rosins, disproportionated rosins and hydrogenated rosins. It is preferable to use at least one selected from the group consisting of glycerin esters.

The content of rosin other than methyl hydrogenated rosin in the flux is preferably 20% by mass or more and 40% by mass or less, and 25% by mass or more and 40% by mass with respect to the total amount (100% by mass) of the flux. % Or less is more preferable, and 25% by mass or more and 35% by mass or less is further preferable.

In the flux of the present embodiment, the mixing ratio of methyl hydrogenated rosinate and rosin other than methyl hydrated rosin (hereinafter, also referred to as “other rosin”) is represented by methyl hydrated rosin / other rosin. The mass ratio is preferably 0.16 or more and 1.0 or less, more preferably 0.16 or more and 0.60 or less, and further preferably 0.16 or more and 0.40 or less.

The ratio of the content of other rosins in the flux to the total content of methyl hydrogenated rosin and the compound represented by the general formula (p1) is the ratio of other rosins / (methyl rosinated and general formula). The mass ratio represented by (the compound represented by (p1)) is preferably 0.80 or more and 4.0 or less, more preferably 1.0 or more and 3.0 or less, and 1.5 or more and 2. 5 or less is more preferable.

Organic acids other than compounds represented by the general formula (p1):
Examples of the organic acid other than the compound represented by the general formula (p1) include glutaric acid, adipic acid, azelaic acid, eicosandiic acid, citric acid, glycolic acid, succinic acid, salicylic acid, diglycolic acid, dipicolinic acid, and the like. Dibutylaniline diglycolic acid, suberic acid, sebacic acid, thioglycolic acid, dithioglycolic acid, terephthalic acid, dodecanedioic acid, parahydroxyphenylacetic acid, phenylsuccinic acid, phthalic acid, fumaric acid, maleic acid, malonic acid, lauric acid , Saccharic acid, tartrate acid, tris isocyanurate (2-carboxyethyl), glycine, 1,3-cyclohexanedicarboxylic acid, 2,2-bis (hydroxymethyl) propionic acid, 2,2-bis (hydroxymethyl) butanoic acid, 2,3-Dihydroxybenzoic acid, 2,4-diethylglutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, propionic acid, malic acid, p-anisic acid, stearic acid, 12-hydroxystearic acid, oleic acid , Linol acid, linolenic acid, palmitic acid, pimelic acid, dimer acid, trimer acid, hydrogenated dimer acid which is a hydrogenated dimer acid, and hydrogenated which is a hydrogenated trimer acid. Examples include trimer acid.
In the flux of the present embodiment, the organic acid can be used alone or in two or more kinds.
Among the above, as the organic acid, it is preferable to use at least one selected from the group consisting of malonic acid, suberic acid, azelaic acid, stearic acid and hydrogenated dimer acid.

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

Amine:
Examples of the amine include ethylamine, triethylamine, ethylenediamine, N, N, N', N'-tetrakis (2-hydroxypropyl) ethylenediamine, triethylenetetramine, diphenylguanidine, ditrilguanidine, 2-methylimidazole, 2-un. Decylimidazole, 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-cyanoethyl-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'-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-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-methylimidazolin, 2-phenylimidazolin, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanul Acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methylbenzoimidazole, 2-octylbenzoimidazole, 2-pentylbenzoimidazole, 2- (1-ethylpentyl) ) Benzoimidazole, 2-nonylbenzoimidazole, 2- (4-thiazolyl) benzoimidazole, benzoimidazole, 2- (2'-hydroxy-5) '-Methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3', 5'- Di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-octylphenyl) benzotriazole, 2,2'-methylenebis [6- (2H-benzotriazole-2-yl) -4 -Tert-octylphenol], 6- (2-benzotriazolyl) -4-tert-octyl-6'-tert-butyl-4'-methyl-2,2'-methylenebisphenol, 1,2,3-benzo Triazole, 1- [N, N-bis (2-ethylhexyl) aminomethyl] benzotriazole, carboxybenzotriazole, 1- [N, N-bis (2-ethylhexyl) aminomethyl] methylbenzotriazole, 2,2'- [[(Methyl-1H-benzotriazole-1-yl) methyl] imino] bisethanol, 1- (1', 2'-dicarboxyethyl) benzotriazole, 1- (2,3-dicarboxypropyl) benzotriazole , 1-[(2-ethylhexylamino) methyl] benzotriazole, 2,6-bis [(1H-benzotriazole-1-yl) methyl] -4-methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole, etc. Can be mentioned.
In the flux of the present embodiment, the amine can be used alone or in two or more kinds.

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

Thixotropy:
Examples of the thixotropic agent include wax-based thixotropic agents, amide-based thixotropic agents, sorbitol-based thixotropic agents, and the like.

Examples of the wax-based thixotropic agent include ester compounds, and specific examples thereof include castor oil.

Examples of the amide-based thixo agent include monoamides, bisamides, and polyamides, and specific examples thereof include lauric acid amides, palmitic acid amides, stearic acid amides, behenic acid amides, hydroxystearic acid amides, saturated fatty acid amides, and oleic acids. Monoamides such as amides, erucic acid amides, unsaturated fatty acid amides, p-toluamides, p-toluenemethane amides, aromatic amides, hexamethylene hydroxystearate amides, substituted amides, methylol stearate amides, methylol amides, fatty acid ester amides; Methylene bisstearic acid amide, ethylene bislauric acid amide, ethylene bishydroxy fatty acid (carbon number C6 to 24 of fatty acid) amide, ethylene bishydroxystearic acid amide, saturated fatty acid bisamide, methylene bisoleic acid amide, unsaturated fatty acid bisamide, m -Bisamides such as xylylene bisstearic acid amides and aromatic bisamides; saturated fatty acid polyamides, unsaturated fatty acid polyamides, aromatic polyamides, tris 1,2,3-propanetricarboxylate (2-methylcyclohexylamide), cyclic amide oligomers, Examples thereof include polyamides such as acyclic amide oligomers.

The cyclic amide oligomer includes an amide oligomer in which dicarboxylic acid and diamine are cyclically polycondensed, an amide oligomer in which tricarboxylic acid and diamine are cyclically polycondensed, an amide oligomer in which dicarboxylic acid and triamine are cyclically polycondensed, and tricarboxylic acid. Amido oligomer in which triamine is cyclically polycondensed, dicarboxylic acid and amide oligomer in which tricarboxylic acid and diamine are cyclically polycondensed, amide oligomer in which dicarboxylic acid and tricarboxylic acid and triamine are cyclically polycondensed, dicarboxylic acid and diamine Examples thereof include an amide oligomer in which triamine is cyclically polycondensed, an amide oligomer in which tricarboxylic acid and diamine and triamine are cyclically polycondensed, and an amide oligomer in which dicarboxylic acid and tricarboxylic acid and diamine and triamine are cyclically polycondensed. ..

When the acyclic amide oligomer is an amide oligomer in which a monocarboxylic acid and diamine and / or triamine are polycondensed in an acyclic manner, the amide in which the dicarboxylic acid and / or the tricarboxylic acid and the monoamine are polycondensed in an acyclic manner. Examples thereof include the case of an oligomer. When it is an amide oligomer containing a monocarboxylic acid or a monoamine, the monocarboxylic acid and the monoamine function as terminal molecules (terminal molecules), and become an acyclic amide oligomer having a reduced molecular weight. When the acyclic amide oligomer is an amide compound in which a dicarboxylic acid and / or a tricarboxylic acid and a diamine and / or a triamine are cyclically polycondensed, the acyclic amide oligomer is an acyclic polymer amide polymer. Further, the acyclic amide oligomer also includes an amide oligomer in which a monocarboxylic acid and a monoamine are cyclically condensed.

Examples of the sorbitol-based thixo agent include dibenzylidene-D-sorbitol, bis (4-methylbenzylidene) -D-sorbitol, (D-) sorbitol, monobenzylidene (-D-) sorbitol, and mono (4-methylbenzylidene). -(D-) Sorbitol and the like can be mentioned.

In the flux of the present embodiment, the thixotropic agent can be used alone or in combination of two or more.
Among the above, the thixotropic agent preferably contains at least one selected from the group consisting of wax-based thixotropic agents and amide-based thixotropic agents.
The wax-based thixotropic agent preferably contains castor oil.
The amide thixotropic agent preferably contains at least one selected from the group consisting of polyamide, bisamide and monoamide.

The content of the thixo agent in the flux is preferably 3% by mass or more and 10% by mass or less, more preferably 5% by mass or more and 10% by mass or less, based on the total amount (100% by mass) of the flux. , 6% by mass or more and 9% by mass or less is more preferable.

Halogen activator:
Examples of the halogen-based activator include an organic halogen compound, an amine hydrohalide, 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, Examples thereof include 3-dibromo-1,4-butanediol and 2,3-dibromo-2-butene-1,4-diol.
Examples of the organic halogen compound include halogenated carboxyl compounds, for example, iodide such as 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, and 5-iodoanthranyl acid. Carboxyl compounds; carboxyl chloride compounds such as 2-chlorobenzoic acid and 3-chloropropionic acid; brominated carboxyl compounds such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid and 2-bromobenzoic acid. Be done.

Amine hydrohalide is a compound obtained by reacting an amine with hydrogen halide. Examples of the amine here include ethylamine, ethylenediamine, triethylamine, diphenylguanidine, ditrilguanidine, methylimidazole, 2-ethyl-4-methylimidazole and the like, and examples of the hydrogen halide include chlorine, bromine and the like. Examples include hydrides of iodine.

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

In the flux of the present embodiment, the halogen-based activator can be used alone or in combination of two or more.
The content of the organic halogen compound in the flux is preferably 0% by mass or more and 5% by mass or less, and 0.5% by mass or more and 5% by mass or less, based on the total amount (100% by mass) of the flux. Is more preferable, and 0.5% by mass or more and 3% by mass or less is further preferable.
The content of the amine halide hydrochloride in the flux is preferably 0% by mass or more and 1% by mass or less with respect to the total amount (100% by mass) of the flux.

Resin components other than rosin-based resin:
Resin components other than the rosin-based resin include, for example, terpene resin, modified terpene resin, terpenephenol resin, modified terpenephenol resin, styrene resin, modified styrene resin, xylene resin, modified xylene resin, acrylic resin, polyethylene resin, acrylic-. Examples thereof include polyethylene copolymer resin and epoxy resin.
Examples of the modified terpene resin include aromatic modified terpene resin, hydrogenated terpene resin, hydrogenated aromatic modified terpene resin and the like. Examples of the modified terpene phenol resin include hydrogenated terpene phenol resin and the like. Examples of the modified styrene resin include styrene acrylic resin and styrene maleic acid resin. Examples of the modified xylene resin include a phenol-modified xylene resin, an alkylphenol-modified xylene resin, a phenol-modified resol-type xylene resin, a polyol-modified xylene resin, and a polyoxyethylene-added xylene resin.

Metal inactivating agent:
Examples of the metal inactivating agent include hindered phenolic compounds and nitrogen compounds. When the flux contains either a hindered phenolic compound or a nitrogen compound, the effect of suppressing the thickening of the solder paste can be easily enhanced.
The term "metal inactivating agent" as used herein refers to a compound having the ability to prevent the metal from deteriorating due to contact with a certain compound.

The hindered phenol-based compound refers to a phenol-based compound having a bulky substituent (for example, a branched or cyclic alkyl group such as a t-butyl group) at at least one of the ortho positions of the phenol.
The hindered phenolic compound is not particularly limited, and is, for example, bis [3- (3-tert-butyl-4-hydroxy-5-methylphenyl) propionic acid] [ethylenebis (oxyethylene)], 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 (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-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-) Butylanilino) -1,3,5-triazine, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 2,2-thio-diethylenebis [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-t-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] oxamid, compounds represented by the following chemical formulas and the like.

［式中、Ｚは、置換されてもよいアルキレン基である。Ｒ^１１及びＲ^１２は、それぞれ独立して、置換されてもよい、アルキル基、アラルキル基、アリール基、ヘテロアリール基、シクロアルキル基又はヘテロシクロアルキル基である。Ｒ^１３及びＲ^１４は、それぞれ独立して、置換されてもよいアルキル基である。］

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

Examples of the nitrogen compound in the metal deactivating agent include hydrazide-based nitrogen compounds, amide-based nitrogen compounds, triazole-based nitrogen compounds, and melamine-based nitrogen compounds.

The hydrazide-based nitrogen compound may be any nitrogen compound having a hydrazide skeleton, and is bis dodecanoate [N2- (2-hydroxybenzoyl) hydrazide], N, N'-bis [3- (3,5-di-tert). -Butyl-4-hydroxyphenyl) propionyl] hydrazine, decandicarboxylic acid disalicyloyl hydrazide, N-salicylidene-N'-salityl hydrazide, m-nitrobenzhydrazide, 3-aminophthalhydrazide, phthalic acid dihydrazide, adipate hydrazide , Oxalobis (2-hydroxy-5-octylbenzylidene hydrazide), N'-benzoylpyrrolidone carboxylic acid hydrazide, N, N'-bis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyl) Hydrazide and the like can be mentioned.

The amide-based nitrogen compound may be any nitrogen compound having an amide skeleton, and N, N'-bis {2- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxyl] ethyl. } Oxamide and the like can be mentioned.

The triazole-based nitrogen compound may be a nitrogen compound having a triazole skeleton, and may be N- (2H-1,2,4-triazole-5-yl) salicylamide, 3-amino-1,2,4-triazole, Examples thereof include 3- (N-salicyloyl) amino-1,2,4-triazole.

The melamine-based nitrogen compound may be any nitrogen compound having a melamine skeleton, and examples thereof include melamine and melamine derivatives. More specifically, for example, trisaminotriazine, alkylated trisaminotriazine, alkoxyalkylated trisaminotriazine, melamine, alkylated melamine, alkoxyalkylated melamine, N2-butyl melamine, N2, N2-diethyl melamine, N, Examples thereof include N, N', N', N'', N''-hexax (methoxymethyl) melamine and the like.

Surfactant:
Examples of the surfactant include nonionic surfactants, weak cationic surfactants and the like.
Examples of the nonionic surfactant include polyethylene glycol, polyethylene glycol-polypropylene glycol copolymer, aliphatic alcohol polyoxyethylene adduct, aromatic alcohol polyoxyethylene adduct, and polyhydric alcohol polyoxyethylene adduct. Be done.
Examples of the weak cationic surfactant include terminal diamine polyethylene glycol, terminal diamine polyethylene glycol-polypropylene glycol copolymer, aliphatic amine polyoxyethylene adduct, aromatic amine polyoxyethylene adduct, and polyvalent amine polyoxy. Examples include polyethylene adducts.

Examples of the surfactant other than the above include polyoxyalkylene acetylene glycols, polyoxyalkylene glyceryl ether, polyoxyalkylene alkyl ether, polyoxyalkylene ester, polyoxyalkylene alkyl amine, polyoxyalkylene alkyl amide and the like. ..

By applying the flux of the present embodiment described above, it is possible to realize soldering with less voids, improve the wettability of the solder, and suppress missing. Further, the flux of the present embodiment is suitable for solder paste using a solder alloy having a low α dose, as will be described later.

(Solder paste)
The solder paste according to another aspect of the present invention comprises the flux according to one aspect described above and the solder powder. In addition, the solder powder is made of a solder alloy having an α dose of 0.02 cf / cm ² or less.

<Flux>
The solder paste of the present embodiment contains the flux of the above-mentioned embodiment.
The content of the flux in the solder paste of the present embodiment is preferably 5 to 95% by mass, more preferably 5 to 50% by mass, based on the total mass (100% by mass) of the solder paste. It is more preferably 5 to 15% by mass.
When the content of the flux in the solder paste is within this range, the effects of the components blended in the flux, that is, the effects of suppressing the generation of voids, the wettability of the solder, and the suppression of missing during soldering are all enhanced. It will be easier.

<Solder powder>
The solder powder used in the solder paste of the present embodiment is made of a solder alloy having an α dose of 0.02 cf / cm ² or less.
The solder powder in the present embodiment is a solder powder of Sn alone, or an alloy powder of Sn-Ag type, Sn-Cu type, Sn-Ag-Cu type, Sn-Bi type, Sn-In type and the like. Alternatively, it may be a powder of a solder alloy obtained by adding Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, P and the like to these alloys.
Further, the solder powder may be a solder containing no Pb, a solder containing Pb, or a Sn—Pb system or a Sn—Pb system with Sb, Bi, In, Cu, Zn, As, Ag, Cd, and the like. It may be a powder of a solder alloy to which Fe, Ni, Co, Au, Ge, P and the like are added.

One 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 or more and 600 mass ppm or less, and Fe. : Solder powder made of a solder alloy having an alloy composition of 0% by mass or more and 100% by mass or less and the balance of Sn, satisfying the following formula (1), and having an α dose of 0.02 cph / cm ² or less. (Hereinafter also referred to as "solder powder (SP)") is preferably mentioned.
20 ≦ Ni + Fe ≦ 700 (1)
In the formula (1), Ni and Fe each represent the content (mass ppm) in the alloy composition.

By using the solder powder (SP), it is possible to suppress an increase in the viscosity of the solder paste over time. In addition, it is possible to suppress the occurrence of soft errors.

≪U: less than 5 mass ppb, Th: less than 5 mass ppb≫
U and Th are radioactive elements. In order to suppress the occurrence of soft errors, it is necessary to suppress these contents in the solder alloy.
In the solder powder (SP), the content of U and Th in the solder alloy is the total mass (100% by mass) of the solder alloy from the viewpoint that the α dose generated from the solder alloy is 0.02 cf / cm ² or less. On the other hand, each is less than 5 ppb. From the viewpoint of suppressing the occurrence of soft errors in high-density mounting, the contents of U and Th are preferably 2 ppb or less, respectively, and the lower the better.

≪Pb: less than 5 mass ppm≫
Generally, Sn contains Pb as an impurity. The radioactive isotope in this Pb undergoes β-decay to become ²¹⁰ Po, and ²¹⁰ Po undergoes α-decay to generate α rays when ²⁰⁶ Pb is generated. For this reason, it is preferable that the content of Pb, which is an impurity, in the solder alloy is as small as possible.
In the solder powder (SP), the content of Pb in the solder alloy is less than 5 ppm, preferably less than 2 ppm, and more preferably less than 1 ppm with respect to the total mass (100% by mass) of the solder alloy. be. 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 is effective in suppressing the thickening of the solder paste over time, but with the addition of As, the alloy also contains radioactive elements from impurities derived from As, and the solder material The α-dose generated from the solder increases.
The purpose of the solder powder (SP) is to suppress the thickening of the solder paste over time without adding As with impurities containing radioactive elements.
In the solder powder (SP), the content of As in the solder alloy is less than 5 ppm, preferably less than 2 ppm, and more preferably less than 1 ppm with respect to the total mass (100% by mass) of the solder alloy. be. The lower limit of the content of As 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, equation (1) >>
By soldering, the formation of Sn-containing intermetallic compounds (intermetallic compounds containing Sn) progresses in the vicinity of the bonding interface in the solder alloy, and when the Sn-containing intermetallic compounds precipitate, the mechanical strength of the solder joint deteriorates. ..

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.
When the solder alloy contains Ni, the formation of the Sn-containing intermetallic compound is suppressed, and the mechanical strength of the solder joint is 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 bonding interface in the solder alloy, and the mechanical strength of the solder joint may deteriorate.
In the solder powder (SP), the content of Ni 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, with respect to the total mass (100% by mass) of the solder alloy. Is 40 ppm or more and 600 ppm or less.

Fe: 0 mass ppm or more and 100 mass ppm or less Fe is an element that suppresses the formation of Sn-containing intermetallic compounds at the bonding interface, similar to Ni. In addition, within a predetermined content range, precipitation of needle-like crystals due to the SnFe compound is suppressed, and short circuit of the circuit can be prevented.
The term "acicular crystal" as used herein refers to a crystal derived from one SnFe compound having an aspect ratio of 2 or more, which is the ratio of the major axis to the minor axis.
In the solder powder (SP), the content of Fe 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, with respect to the total mass (100% by mass) of the solder alloy. Is 40 ppm or more and 80 ppm or less.

Regarding the solder alloy in the solder powder (SP), the alloy composition satisfies the following formula (1).
20 ≦ Ni + Fe ≦ 700 (1)
In the formula (1), Ni and Fe each represent the content (mass ppm) in the alloy composition.

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 solder powder (SP), both Ni and Fe also contribute to the effect of suppressing the thickening of the solder paste over time.
In order to obtain the effect of suppressing the formation of the Sn-containing intermetallic compound and the effect of suppressing the thickening of the solder paste over time, the total content of Ni and Fe in the solder alloy is the total mass of the solder alloy. It is necessary to be 20 ppm or more and 700 ppm or less with respect to (100% by mass). 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 above-mentioned "total content of Ni and Fe" is the content of Fe when the content of Ni in the solder alloy is 0 ppm, and the content of Fe in the solder alloy is 0 ppm. Is the content of Ni, and when both Ni and Fe are present, the total content of these is obtained.

When both Ni and Fe are contained in the solder powder (SP), the ratio of Ni and Fe in the solder alloy is preferably 0.4 or more and 30 or less as the mass ratio expressed by Ni / Fe. Yes, more preferably 0.4 or more and 10 or less, still more preferably 0.4 or more and 5 or less, and particularly preferably 0.4 or more and 2 or less.
When Ni / Fe having such a mass ratio is in the above-mentioned preferable range, the effect of suppressing the increase in viscosity of the solder paste over time can be more easily obtained.

≪Arbitrary element≫
Regarding the solder alloy in the solder powder (SP), the alloy composition may contain an element other than the above-mentioned elements, if necessary.
For example, with respect to the solder alloy in the solder powder (SP), the alloy composition is, in addition to the above-mentioned elements, Ag: 0% by mass or more and 4% by mass or less, and Cu: 0% by mass or more and 0.9% by mass or less. May contain at least one of the above.

Ag: 0% by mass or more and 4% by mass or less Ag is an optional element capable of forming Ag ₃ Sn at the crystal interface to improve the reliability of the solder alloy. Further, Ag is an element whose ionization tendency is noble with respect to Sn, and when it coexists with Ni and Fe, it enhances the effect of suppressing the thickening of the solder paste over time. Further, when the Ag content in the solder alloy is within the above range, it is possible to suppress an increase in the melting point of the alloy, so that it is not necessary to raise the reflow temperature excessively.
In the solder powder (SP), the content of Ag in the solder alloy is preferably 0% or more and 4% or less, more preferably 0.5% or more 3 with respect to the total mass (100% by mass) of the solder alloy. It is 5.5% or less, more preferably 1.0% or more and 3.0% or less, and particularly preferably 2.0% or more and 3.0% or less.

Cu: 0% by mass or more and 0.9% by mass or less Cu is an optional element used in general solder alloys and capable of improving the bonding strength of solder joints. Further, Cu is an element whose ionization tendency is noble with respect to Sn, and when it coexists with Ni and Fe, it enhances the effect of suppressing the thickening of the solder paste over time.
In the solder powder (SP), the content of Cu in the solder alloy is preferably 0% or more and 0.9% or less, more preferably 0.1%, based on the total mass (100% by mass) of the solder alloy. It is 0.8% or more, more preferably 0.2% or more and 0.7% or less.

When Cu and Ni are contained together in the solder powder (SP), the ratio of Cu and Ni in the solder alloy is preferably 8 or more and 175 or less as the mass ratio represented by Cu / Ni, which is more preferable. Is 10 or more and 150 or less.
When Cu / Ni having such a mass ratio is in the above-mentioned preferable range, the effect of suppressing the increase in viscosity of the solder paste over time can be more easily obtained.

When Cu and Fe are contained together in the solder powder (SP), the ratio of Cu and Fe in the solder alloy is preferably 50 or more and 350 or less as the mass ratio expressed by Cu / Fe, which is more preferable. Is 70 or more and 250 or less.
When Cu / Fe having such a mass ratio is in the above-mentioned preferable range, the effect of suppressing the increase in viscosity of the solder paste over time can be more easily obtained.

When Cu, Ni, and Fe are contained together in the solder powder (SP), the ratio of Cu, Ni, and Fe in the solder alloy is preferably 7 or more and 350 as the mass ratio expressed by Cu / (Ni + Fe). It is less than or equal to, and more preferably 10 or more and 250 or less.
When Cu / (Ni + Fe) having such a mass ratio is in the above-mentioned preferable range, the effect of suppressing the increase in viscosity of the solder paste over time can be more easily obtained.

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

Bi: 0% by mass or more and 0.3% by mass or less Bi is an element that has low reactivity with flux and exhibits an effect of suppressing thickening of solder paste over time. Further, Bi is an element capable of suppressing deterioration of wettability because it lowers the liquidus temperature of the solder alloy and reduces the viscosity of the molten solder.
In the solder powder (SP), the Bi content in the solder alloy is preferably 0% or more and 0.3% or less, more preferably 0.0020%, based on the total mass (100% by mass) of the solder alloy. It is 0.3% or more, more preferably 0.01% or more and 0.1% or less, and most preferably 0.01% or more and 0.05% or less.

Sb: 0% by mass or more and 0.9% by mass or less Sb is an element that has low reactivity with flux and exhibits an effect of suppressing thickening of solder paste over time, like Bi. If the content of Sb in the solder alloy is too large, the wettability deteriorates. Therefore, when adding Sb, it is necessary to make the content appropriate.
In the solder powder (SP), the content of Sb in the solder alloy is preferably 0% or more and 0.9% or less, more preferably 0.0020%, based on the total mass (100% by mass) of the solder alloy. It is 0.9% or more, more preferably 0.01% or more and 0.1% or less, and most 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% by mass or more and 0.3% by mass or less and Sb: 0% by mass or more and 0.9% by mass or less. The alloy composition preferably satisfies the following formula (2).
0.03 ≤ Bi + Sb ≤ 1.2 (2)
In the formula (2), Bi and Sb each represent the content (mass%) in the alloy composition.

Both Bi and Sb in the formula (2) are elements showing the effect of suppressing the thickening of the solder paste over time. In addition, in the solder powder (SP), both Bi and Sb also contribute to the wettability of 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, based on the total mass (100% by mass) of the solder alloy. It is 0.9% or less, more preferably 0.3% or more and 0.9% or less.

However, the above-mentioned "total content of Bi and Sb" is the content of Sb when the content of Bi in the solder alloy is 0%, and the content of Sb in the solder alloy is 0%. In some cases, it is the content of Bi, and in the case of having both Bi and Sb, it is the total content of these.

When Bi and Sb are co-existed in the solder powder (SP), the ratio of Bi and Sb in the solder alloy is preferably 0.01 or more and 10 or less as the mass ratio expressed by Sb / Bi. More preferably, it is 0.1 or more and 5 or less.
If the mass ratio of Sb / Bi is in the above-mentioned preferable range, the effect of suppressing the increase in viscosity of the solder paste over time can be more easily obtained.

≪Remaining part: Sn≫
Regarding the solder alloy in the solder powder (SP), the alloy composition is composed of Sn as the balance. In addition to the above-mentioned elements, unavoidable impurities may be contained. Even if it contains unavoidable impurities, it does not affect the above-mentioned effects.

≪α dose≫
The α dose of the solder alloy in the solder powder (SP) is 0.02 cph / cm ² or less.
This is an α-dose that does not cause soft errors in high-density mounting of electronic components.
The α-dose generated from the solder alloy in the solder powder (SP) is preferably 0.01 cph / cm ² or less, more preferably 0.002 cph / cm, from the viewpoint of suppressing soft errors in further high-density mounting. It is cm ² or less, more preferably 0.001 cph / cm ² or less.

The α dose generated from the solder alloy can be measured as follows. The method for measuring the α dose is based on the international standard JEDEC STANDARD.

Procedure (i):
A gas flow type α dosimetry device is used.
As a measurement sample, a solder alloy sheet formed by melting a solder alloy into a sheet having an area of 900 cm ² on one side is used.
The solder alloy sheet is installed as a measurement sample in the α-dose measuring device, and PR gas is purged therein.

As the PR gas, a gas that complies with the international standard JEDEC STANDARD is used. That is, the PR gas used for the measurement is assumed to be the disintegration of the impurity radon (Rn) in the gas after 3 weeks or more have passed since the gas cylinder was filled with the mixed gas of 90% argon and 10% methane.

Procedure (ii):
The PR gas is allowed to flow in the α-dose measuring device on which the solder alloy sheet is installed for 12 hours, and then the α-dose is measured for 72 hours.

Procedure (iii):
The average α-dose is calculated as “cph / cm ² ”. Abnormal points (counts due to device vibration, etc.) are removed from the count for one hour.

The solder alloy in the solder powder (SP) has an α-dose after being heat-treated at 100 ° C. for 1 hour on a solder alloy sheet formed into a sheet having an area of 900 cm ² on one side. It is preferably 0.02 cf / cm ² or less, more preferably 0.01 cf / cm ² or less, still more preferably 0.002 cf / cm ² or less, and particularly preferably 0. It is 001 cph / cm ² or less.
Solder alloys exhibiting such an α dose are useful because they are less likely to segregate ²¹⁰ Po in the alloy and are less affected by changes in the α dose over time. By applying a solder alloy exhibiting such an α dose, the occurrence of soft errors is further suppressed, and it becomes easier to secure stable operation of the semiconductor element.

[Manufacturing method of solder alloy]
The solder alloy in the solder powder (SP) can be produced, for example, by using a production method having a step of melt-mixing at least one of Ni and Fe and a raw material metal containing Sn.
Since the purpose is to design a solder alloy with a low α-dose, it is preferable to use a low-α-dose material as the raw material metal. Further, it is preferable to use one from which U, Th and Pb have been removed.
As the Sn as the raw material metal, for example, one manufactured according to the manufacturing method described in Japanese Patent Application Laid-Open No. 2010-156052 (Patent Document 1) can be used.
As the raw material metals Ni and Fe, for example, those manufactured according to Japanese Patent No. 5692467 can be used.
A conventionally known method can be used for the operation of melting and mixing the raw metal.

The solder powder (SP) is manufactured by a dropping method of dropping a molten solder alloy to obtain particles, a spraying method of centrifugal spraying, an atomizing method, an in-liquid granulation method, a method of crushing a bulk solder alloy, and the like. , A known method can be adopted. The dropping or spraying in the dropping method or the spraying method is preferably carried out in an inert atmosphere or a solvent in order to form particles.

The solder powder (SP) is preferably a spherical powder. The spherical powder improves the fluidity of the solder alloy.
When the solder powder (SP) is a spherical powder, it is preferable that the symbols 1 to 8 are satisfied, and the symbols 4 to 8 are satisfied in the powder size classification (Table 2) in JIS Z 3284-1: 2014. It is more preferable to be there. When the particle size of the solder powder satisfies this condition, the surface area of the powder is not too large, the increase in the viscosity of the solder paste over time is suppressed, and the aggregation of the fine powder is suppressed, so that the viscosity of the solder paste is increased. May be suppressed. Therefore, it is possible to solder to finer parts.

Further, it is preferable to use the solder powder (SP) having a solder alloy particle group having an average particle diameter of 0.1 to 50 μm, and using a solder alloy particle group having an average particle diameter of 1 to 25 μm. It is more preferable to use a group of solder alloy particles having an average particle diameter of 1 to 15 μm.
When the particle size of the solder powder is in the above-mentioned preferable range, the increase in viscosity of the solder paste with time is likely to be suppressed.
The average particle size of the solder powder referred to here means the particle size at an integrated value of 50% in the particle size distribution measured by the laser diffraction / scattering type particle size distribution measuring device.

Further, it is preferable that the solder powder (SP) also has two or more kinds of solder alloy particle groups having different particle size distributions. As a result, the slipperiness of the solder paste is enhanced, and workability such as easy printing is improved.
For example, the solder powder may have two or more kinds of solder alloy particles having different average particle diameters. As an example, a solder powder having both 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 preferably mentioned.
The mixing ratio of the solder alloy particle group (S1) and the solder alloy particle group (S2) is (S1) / (S2) = 9/1 to 1 / as the mass ratio represented by (S1) / (S2). 9 is preferable, 9/1 to 3/7 is more preferable, and 9/1 to 5/5 is even more preferable.

Regarding the solder powder in the present embodiment, the sphericity of the spherical powder is preferably 0.8 or more, more preferably 0.9 or more, further preferably 0.95 or more, and particularly preferably 0.99 or more.

The "spherical degree of spherical powder" referred to here can be measured using a CNC image measurement system (Ultra Quick Vision ULTRA QV350-PRO measuring device manufactured by Mitutoyo Co., Ltd.) using the minimum region center method (MZC method). can.
The sphericity represents the deviation from the sphere, and is an arithmetic mean value calculated when, for example, the diameter of each of 500 solder alloy particles is divided by the major axis, and the value is 1.00, which is the upper limit. The closer it is, the closer it is to a true sphere.

The solder paste of the present embodiment can be produced by a production method common in the art.
A solder paste can be obtained by heating and mixing the compounding components constituting the flux to prepare a flux, and stirring and mixing the solder powder in the flux. Further, in anticipation of the effect of suppressing thickening over time, zirconium oxide powder may be further blended in addition to the solder powder.

As described above, in the solder paste of the present embodiment, a flux having a specific rosin and an activator is adopted. With a solder paste that combines such a flux and a solder powder made of a solder alloy having an α dose of 0.02 cf / cm ² or less, it is possible to realize soldering with less voids in soldering, and the wettability of the solder. Can be enhanced and missing can be suppressed. Further, according to the solder paste of the present embodiment, it is possible to suppress the occurrence of soft errors.
In the flux in the present embodiment, the melt viscosity of the solder paste tends to decrease by selecting a specific rosin, that is, methyl hydrogenated rosinate. Therefore, the gasified flux component can be easily removed from the paste, and the generation of voids can be suppressed. In addition, in the flux in the present embodiment, the wettability of the solder is enhanced by selecting a specific activator, that is, a compound represented by the general formula (p1). Therefore, the wetting speed of the solder can be improved, and the reflow and the missing after the flux residue cleaning are suppressed.

Further, in the solder paste of the above-described embodiment, the form in which the solder powder (SP) is used as the solder powder is less likely to cause a change with time such as an increase in viscosity, and it is possible to suppress the occurrence of soft errors. Will be. That is, the solder paste of the present embodiment is also suitable as a low α-dose material.

Generally, in a solder alloy, each constituent element constituting the solder alloy does not function independently, and various effects can be exhibited only when the content of each constituent element is all within a predetermined range. .. According to the solder alloy in the solder powder (SP), when the content of each constituent element is in the above range, the increase in viscosity of the solder paste over time is suppressed and the occurrence of soft errors is suppressed. Can be done. That is, the solder alloy in the solder powder (SP) is useful as a target low α-dose material, and by applying it to the formation of solder bumps around the memory, it is possible to suppress the occurrence of soft errors. ..

Further, the solder powder (SP) contains Ni and Fe, which are refractory metals that are heated at a high temperature during refining or processing of the bare metal, in a specific ratio without actively adding As. By adopting a solder alloy, the thickening of solder paste can be suppressed over time.
The reason why such an effect is obtained is not clear, but it is presumed as follows.
Sn for low α-dose solder alloys has very high purity, and when the molten alloy is solidified, the crystal size of Sn becomes large. Further, the oxide film in Sn also forms a sparse oxide film corresponding to the oxide film. Therefore, by adding the refractory metals Ni and Fe, the crystal size is reduced and a dense oxide film is formed, so that the reactivity between the alloy and the flux is suppressed, so that the solder paste can be used over time. It is possible to suppress thickening.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.
In this embodiment, unless otherwise specified, "ppb" for the solder alloy composition is "mass ppb", "ppm" is "mass ppm", and "%" is "mass%".

<Manufacturing of solder alloy>

(Manufacturing Examples 1 to 460)
The raw metal was melted and stirred to prepare solder alloys having the respective alloy compositions shown in Tables 1 to 19.

For the solder alloys of each production example, the α dose was evaluated as follows. The evaluation results are shown in Tables 1 to 19.

[Α dose]
(1) Verification method 1
The α-dose was measured by using the α-dose measuring device of the gas flow proportional counter and following the above-mentioned procedures (i), (ii) and (iii).
As a measurement sample, a solder alloy sheet immediately after production was used.
This solder alloy sheet was manufactured by melting the solder alloy immediately after production and forming it into a sheet having an area of 900 cm ² on one surface.
This measurement sample was placed in an α-dose measuring device, PR-10 gas was allowed to flow for 12 hours, and the mixture was allowed to stand, and then the α-dose was measured for 72 hours.

(2) Judgment criteria 1
〇 〇: The α dose generated from the measurement sample was 0.002 cph / cm ² or less.
◯: The α dose generated from the measurement sample was more than 0.002 cf / cm ² and 0.02 cf / cm ² or less.
X: The α dose generated from the measurement sample was more than 0.02 cph / cm ² .
If this determination is "○○" or "○", it can be said that the solder material has a low α dose.

(3) Verification method 2
The α dose was measured in the same manner as in (1) Verification method 1 above, except that the measurement sample was changed.
As a measurement sample, a solder alloy sheet formed by melting a solder alloy immediately after production and forming a sheet having an area of 900 cm ² on one side is heat-treated at 100 ° C. for 1 hour and then allowed to cool. board.

(4) Judgment criteria 2
〇 〇: The α dose generated from the measurement sample was 0.002 cph / cm ² or less.
◯: The α dose generated from the measurement sample was more than 0.002 cf / cm ² and 0.02 cf / cm ² or less.
X: The α dose generated from the measurement sample was more than 0.02 cph / cm ² .
If this determination is "○○" or "○", it can be said that the solder material has a low α dose.

(5) Verification method 3
After storing the solder alloy sheet of the measurement sample whose α-dose was measured in the above (1) verification method 1 for one year, the α-dose is again followed in the above-mentioned procedures (i), (ii) and (iii). Was measured to evaluate the change over time in the α dose.

(6) Judgment criteria 3
〇 〇: The α dose generated from the measurement sample was 0.002 cph / cm ² or less.
◯: The α dose generated from the measurement sample was more than 0.002 cf / cm ² and 0.02 cf / cm ² or less.
X: The α dose generated from the measurement sample was more than 0.02 cph / cm ² .
If this determination is "○○" or "○", it can be said that the generated α-dose does not change with time and is stable. That is, it is possible to suppress the occurrence of soft errors in electronic devices.

As shown in Tables 1 to 19, as a result of evaluating the α dose for the solder alloys of each production example, the solder alloys of production examples 1 to 460 are the solder alloy sheets immediately after production, after heat treatment at 100 ° C. for 1 hour. It was confirmed that the judgment was "○○" for all the solder alloy sheets and the solder alloy sheets after being stored for one year.

<Manufacturing of solder powder>
The solder alloys of each production example were melted, and a solder powder composed of solder alloy particles having the alloy compositions shown in Tables 1 to 19 and having an average particle diameter of 6 μm was produced by an atomizing method.

For the solder alloys of Production Examples 241 to 296 and Production Examples 445 to 448, the solder alloys of each production example are melted, and the alloy compositions shown in Tables 10, 11, 12, and 19 are obtained by the atomization method, respectively. A solder powder composed of a group of solder alloy particles having an average particle diameter of 4 μm was produced.

<Preparation of flux>
(Examples 1 to 28, comparative examples 1 to 3)
As the resin component, rosins other than methyl hydrogenated rosinate and methyl hydrogenated rosinate were used.
As rosins other than methyl hydrogenated rosin, polymerized rosin, acrylic acid-modified rosin, acrylic acid-modified hydrogenated rosin, hydrogenated rosin, disproportionated rosin, and hydrogenated rosing lysellin ester were used.
As the organic acid, picolinic acid, malonic acid, suberic acid, azelaic acid, stearic acid, and hydrogenated dimer acid were used.
As the amine, N, N, N', N'-tetrakis (2-hydroxypropyl) ethylenediamine, 2-phenylimidazole, and ditrilguanidine were used.
Ethylene bishydroxystearic acid amide and castor oil were used as thixotropic agents.
Diethylene glycol monobutyl ether and hexyl diglycol were used as solvents.
As the halogen-based activator, trans-2,3-dibromo-2-butene-1,4-diol, which is an organic halogen compound, was used. In addition, a diphenylguanidine / HBr salt, which is an amine hydrohalide, was used.
Then, each component shown in Tables 20 to 25 was mixed to prepare the flux of each example.

<Manufacturing of solder paste>
(Example 101)
A solder paste was produced by mixing the flux of Example 1 and the solder powder composed of the solder alloys of Production Examples 445 to 448 and the solder alloy particles having an average particle diameter of 6 μm.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(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 the flux 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 the flux 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 the flux of Comparative Example 3.

(Examples 102 to 128)
Each solder paste was produced in the same manner as in Example 1 except that the flux in Example 1 was changed to each flux of Examples 2 to 28.

(Example 129)
Each of the fluxes of Examples 1 to 28 and the solder powder of the solder alloy particles of Production Examples 445 to 448 having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 35:65 as a mass ratio.

(Example 130)
Each flux of Examples 1 to 28 and a solder powder composed of solder alloys of Production Examples 449 to 452 and having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 131)
Each flux of Examples 1 to 28 and a solder powder composed of solder alloys of Production Examples 453 to 456 and having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 132)
Each flux of Examples 1 to 28 and a solder powder composed of solder alloys of Production Examples 457 to 460 and having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 133)
Each flux of Examples 1 to 28 and a solder powder composed of solder alloys of Production Examples 1 to 74 and having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 134)
Each flux of Examples 1 to 28 and a solder powder composed of the solder alloys of Production Examples 371 to 444 and having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 135)
Each of the fluxes of Examples 1 to 28 and the solder powder of the solder alloy particles of Production Examples 75 to 148 having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 136)
Each flux of Examples 1 to 28 and a solder powder composed of solder alloy particles of Production Examples 223 to 296 having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 137)
Each of the fluxes of Examples 1 to 28 and the solder powder of the solder alloy particles of Production Examples 149 to 222 having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 138)
Each flux of Examples 1 to 28 and a solder powder composed of solder alloys of Production Examples 297 to 370 and having an average particle diameter of 6 μm were mixed to produce each solder paste.
The mixing ratio of the flux and the solder powder was set to flux: solder powder = 11:89 as a mass ratio.

(Example 139)
In each case, a mixed solder powder made of the solder alloy of Production Example 445 and having two kinds of solder alloy particle groups having different average particle diameters was produced.
Specifically, a solder alloy particle group (S1b) made of the solder alloy of Production Example 445 and having an average particle diameter of 6 μm and a solder alloy particle group (S2b) made of the solder alloy of Production Example 445 and having an average particle diameter of 4 μm. Was mixed at a mass ratio (S1b) / (S2b) = 90/10 to obtain a mixed solder powder.
Next, each of the fluxes of Examples 1 to 28 and the mixed solder powder mixed at a mass ratio (S1b) / (S2b) = 90/10 were mixed to produce each solder paste.
The mixing ratio of the flux and the mixed solder powder was set to flux: mixed solder powder = 11:89 as a mass ratio.

(Example 140)
The mass ratio (S1b) is the mixing ratio of the solder alloy particle group (S1b) having an average particle diameter of 6 μm and the solder alloy particle group (S2b) having an average particle diameter of 4 μm, all of which are made of the solder alloy of Production Example 445. Each solder paste was produced in the same manner as in Example 139 except that / (S2b) was changed to 50/50.

(Example 141)
In each case, a mixed solder powder made of the solder alloy of Production Example 257 and having two kinds of solder alloy particle groups having different average particle diameters was produced.
Specifically, the solder alloy particle group (S1a) made of the solder alloy of Production Example 257 and having an average particle diameter of 6 μm and the solder alloy particle group (S2a) made of the solder alloy of Production Example 257 and having an average particle diameter of 4 μm. Was 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 powder mixed at a mass ratio (S1a) / (S2a) = 90/10 were mixed to produce each solder paste.
The mixing ratio of the flux and the mixed solder powder was set to flux: mixed solder powder = 11:89 as a mass ratio.

(Example 142)
The mass ratio (S1a) is the mixing ratio of the solder alloy particle group (S1a) having an average particle diameter of 6 μm and the solder alloy particle group (S2a) having an average particle diameter of 4 μm, all of which are made of the solder alloy of Production Example 257. Each solder paste was produced in the same manner as in Example 141 except that / (S2a) was changed to 50/50.

<Evaluation (1)>
Using the flux and solder paste of each example, the resistance to void generation, the wetting speed of the solder, and the suppression of missing were evaluated. Comprehensive evaluation was performed from these evaluation results.
The details are as follows. The evaluation results are shown in Tables 20 to 28.

[Difficulty in generating voids]
The solder paste was printed on a Cu-OSP electrode (N = 15) having a diameter of 80 μm and a pitch of 150 μm at a height of 40 μm using a metal mask. After that, it reflowed in a nitrogen atmosphere. The reflow profile was held at 160 ° C. for 2 minutes and then heated to 260 ° C. at 1.5 ° C./sec.
A transmission image of the soldered portion (solder bump) after reflow was observed using Micro Focus X-ray System XVR-160 manufactured by UNITE SYSTEM, and the void generation rate was determined.
Specifically, transmission observation is performed on the solder bumps from the upper part to the lower part, a circular solder bump transmission image is obtained, the metal filling portion and the void portion are distinguished based on the contrast of the color tone, and the void area is automatically analyzed. The rate was calculated and used as the void occurrence rate.

Using the void generation rate obtained in this way, the difficulty of void generation was evaluated according to the following criteria.
〇: When the void generation rate is 10% or less in all 15 soldered parts ×: When the void generation rate exceeds 10% in all 15 soldered parts

[Solder wetting speed]
(1) Verification method The evaluation test of the wetting speed of the solder was carried out as follows.
According to the method of the meniscograph test, a copper plate having a width of 5 mm, a length of 25 mm and a thickness of 0.5 mm was oxidized at 150 ° C. for 1 hour to obtain a copper oxide plate as a test plate, and the Solder Checker SAT-5200 was used as a test apparatus. (Manufactured by RHESCA) was used, and a solder alloy having an alloy composition Sn-3Ag-0.5Cu (each numerical value is mass%; the balance Sn) was used and evaluated as follows.
First, the test plate was immersed in the flux of each example measured in a beaker by 5 mm, and the flux was applied to the test plate. Subsequently, after the flux was applied, the test plate to which the flux was applied was immediately immersed in a solder bath of a solder alloy having the alloy composition to obtain a zero cross time (sec).
Subsequently, the flux of each example was measured 5 times, and the average value of the obtained 5 zero cross times (sec) was calculated. The test conditions were set as follows.
Immersion speed in solder bath: 5 mm / sec (JIS Z 3198-4: 2014)
Immersion depth in solder bath: 2 mm (JIS Z 3198-4: 2014)
Immersion time in solder bath: 10 sec (JIS Z 3198-4: 2014)
Solder tank temperature: 245 ° C (JIS C 60068-2-69: 2019 Annex B)
The shorter the average value of the zero cross time (sec), the higher the wetting speed and the better the solder wetting property.

(2) Judgment criteria 〇: The average value of zero cross time (sec) is 6 seconds or less.
X: The average value of zero cross time (sec) exceeds 6 seconds.

[Missing suppression]
(1) Verification method A substrate having a Cu-OSP electrode (N = 15) having a diameter of 80 μm and a pitch of 150 μm was immersed in isopropyl alcohol, and the OSP film was removed with a brush.
After removing the OSP film, it was baked for 1 hour in a constant temperature bath at 100 ° C.
On the obtained substrate electrode, the solder paste of each example was printed at a height of 40 μm using a metal mask. After that, it reflowed in a nitrogen atmosphere.
The reflow profile was held at 160 ° C. for 2 minutes and then heated to 260 ° C. at 1.5 ° C./sec.
Subsequently, it was observed with an optical microscope whether or not the solder paste was misaligned with respect to the electrodes.

(2) Judgment criteria 〇: Missing was not observed on any of the electrodes.
X: There was one or more electrodes in which missing was observed.

[Comprehensive evaluation]
◯: In Tables 20 to 28, each evaluation of the difficulty of generating voids, the wetting speed of solder, and the suppression of missing was 〇.
X: In Tables 20 to 28, at least one of the evaluations of the difficulty of generating voids, the wetting speed of the solder, and the suppression of missing was x.

As shown in Tables 20 to 28, in the solder pastes of Examples 101 to 142 containing the flux to which the present invention is applied, no voids are generated and the solder is wet, regardless of which solder paste is used. It was confirmed that the sex was enhanced and that the missing was suppressed.

On the other hand, when the solder paste of Comparative Example 1 containing a flux outside the scope of the present invention, which does not contain the compound represented by the general formula (p1), is used, the wettability of the solder and the effect of suppressing missing are obtained. Both showed inferior results.
Further, in the solder pastes of Comparative Examples 2 and 3 containing a flux which is outside the scope of the present invention and does not contain methyl hydrogenated rosinate, voids are less likely to occur regardless of which solder paste is used. The result was inferior in evaluation.

<Evaluation (2)>
For each example of solder paste, the suppression of thickening was evaluated as follows.

[Suppression of thickening]
(1) Verification Method For each solder paste immediately after production in Examples 133 to 142, the viscosity was measured for 12 hours in the air at a rotation speed of 10 rpm, 25 ° C., using PCU-205 manufactured by Malcolm Co., Ltd.

(2) Judgment criteria 〇: The viscosity after 12 hours is 1.2 times or less the viscosity when 30 minutes have passed immediately after the preparation of the solder paste.
X: The viscosity after 12 hours exceeds 1.2 times the viscosity when 30 minutes have passed immediately after preparing the solder paste.
If this determination is "〇", it can be said that a sufficient thickening suppressing effect has been obtained. That is, it is possible to suppress an increase in the viscosity of the solder paste over time.

As a result of evaluating the thickening suppression of the solder paste of each example, Examples 133 to 138 having both the flux to which the present invention is applied and the solder powder in which each of the solder alloys of Production Examples 1 to 444 are used. For the solder pastes of No. 141 and 142, the judgment was “◯”, and it was confirmed that the increase in viscosity of the solder paste over time was suppressed.

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

Claims (27)

A flux used in solder paste
A flux containing methyl hydrogenated rosinate, a compound represented by the following general formula (p1), and a solvent.

[In the 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 picolinic acid. The flux according to claim 1 or 2, wherein the content of the hydrogenated methyl 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% by mass and 5% by 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 a rosin other than methyl hydrogenated rosin and a thixotropic agent. The rosin other than methyl hydrogenated rosin is a group consisting of polymerized rosin, acrylic acid modified rosin, acrylic acid modified hydrogenated rosin, acrylic acid modified disproportionated rosin, hydrogenated rosin, disproportionated rosin and hydrogenated rosin lysellin ester. The flux according to claim 5, which is at least one selected from the above. The flux according to claim 5 or 6, wherein the content of the rosin other than the hydrogenated methyl rosinate is 20% by mass or more and 40% by mass or less with respect to the total amount of the flux. The mixing ratio of methyl hydrogenated rosin and rosin other than methyl hydrogenated rosin is
The flux according to any one of claims 5 to 7, wherein the mass ratio represented by rosin other than methyl hydrogenated rosinate / methyl hydrated rosinate 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 comprises 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 thixotropic agent contains at least one selected from the group consisting of polyamide, bisamide and monoamide. The flux according to claim 9 or 10, wherein the wax-based thixotropic agent contains castor oil. The flux according to any one of claims 5 to 11, wherein the content of the thixotropic agent is 3% by mass or more and 10% by mass or less with respect to the total amount of the flux. The flux according to any one of claims 5 to 12, further comprising 0% by mass or more and 15% by mass or less of an organic acid with respect to the total amount of the flux. Further, with respect to the total amount of the flux.
Amine is 0% by mass or more and 30% by mass or less,
The flux according to any one of claims 5 to 13, which contains 0% by mass or more and 5% by mass or less of an organic halogen compound and 0% by mass or more and 1% by mass or less of an amine hydrohalide. A solder paste comprising the flux according to any one of claims 1 to 14 and solder powder.
The solder powder is a solder paste made of a solder alloy having an α dose of 0.02 cf / cm ² or less. 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. The fifteenth aspect of claim 15, which comprises a solder alloy having an alloy composition of 100 mass ppm or less and the balance of Sn, satisfying the following formula (1), and having an α dose of 0.02 cph / cm ² or less. Solder paste.
20 ≦ Ni + Fe ≦ 700 (1)
In the formula (1), Ni and Fe each represent the content (mass ppm) in the alloy composition. The solder paste according to claim 16, wherein the alloy composition satisfies the following formula (1').
40 ≤ Ni + Fe ≤ 200 (1')
In the formula (1'), Ni and Fe each represent the content (mass ppm) in the alloy composition. Further, the solder paste according to claim 16 or 17, wherein the alloy composition has Pb of less than 2 parts by mass. Further, the solder paste according to any one of claims 16 to 18, wherein the alloy composition has As of less than 2 parts by mass ppm. Further, according to any one of claims 16 to 19, the alloy composition contains at least one of Ag: 0% by mass or more and 4% by mass or less, and Cu: 0% by mass or more and 0.9% by mass or less. Solder paste. Further, any one of claims 16 to 20, wherein the alloy composition contains at least one of Bi: 0% by mass or more and 0.3% by mass or less, and Sb: 0% by mass or more and 0.9% by mass or less. Solder paste described in. The solder paste according to claim 21, wherein the alloy composition satisfies the following formula (2).
0.03 ≤ Bi + Sb ≤ 1.2 (2)
In the formula (2), Bi and Sb each represent the content (mass%) in the alloy composition. The solder alloy has an α-dose of 0.02 cph / cm ² or less after being heat-treated at 100 ° C. for 1 hour on a solder alloy sheet formed into a sheet having an area of 900 cm ² on one surface. The solder paste according to any one of claims 16 to 22. The solder paste according to any one of claims 16 to 23, wherein the solder alloy has an α dose of 0.002 cf / cm ² or less. The solder paste according to claim 24, wherein the solder alloy has an α dose of 0.001 cf / 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 diameter of 0.1 to 15 μm. The solder paste according to any one of claims 16 to 25, wherein the solder powder has two or more kinds of solder alloy particle groups having different average particle diameters.