JP7705033B2 - Flux and solder paste using same - Google Patents

Description

The present invention relates to a flux and a solder paste using the same.

Conventionally, the fixing and electrical connection of electronic components in electronic devices, such as mounting electronic components on a printed circuit board, has generally been performed by soldering. In soldering, a flux is used as an auxiliary agent to facilitate adhesion of solder to the printed circuit board and electronic components, and various soldering fluxes have been developed to date.
On the other hand, such soldering flux is heated to a high temperature during soldering, and the solvent components contained therein may bump, causing the molten flux to scatter. As such, a technique for suppressing scattering of the flux is known, for example, as described in Patent Document 1. Patent Document 1 discloses a flux containing a base resin, a solvent, an activator, a thixotropic agent, and a predetermined amount of a polyalkylene oxide polymer having a weight average molecular weight of 2,000 Mw or more and 1,000,000 Mw or less (claim 1 of Patent Document 1).

JP 2020-157310 A

However, as a result of the inventor's investigations, it was found that even the flux described in Patent Document 1 above has room for improvement in terms of suppressing scattering of the flux during reflow. Furthermore, when flux is applied to a solder paste, the flux components may seep out during storage and preservation of the solder paste, causing the flux and solder powder to separate. Therefore, there is a demand for suppressing the separation of the flux and solder powder to improve the storage properties of the solder paste.

After further investigation, the inventors unexpectedly discovered that by using an alkylene oxide copolymer having an allyl group and/or a phenyl group in the side chain as a flux, it is possible to more effectively prevent the flux from scattering during reflow while improving the storage stability of the solder paste.

According to the present invention,
A flux containing a thixotropic agent,
There is provided a flux, in which the thixotropic agent comprises an alkylene oxide copolymer (A) having an allyl group and/or a phenyl group in a side chain.

Further, according to the present invention,
A solder paste is provided that includes the above flux and a metal powder.

The present invention provides a flux that can more effectively suppress flux scattering during reflow while improving the storage properties of the solder paste, and a solder paste using the flux.

The following describes in detail an embodiment of the present invention. In this specification, the term "approximately" means that the range includes consideration of manufacturing tolerances and assembly variations, unless otherwise specified. In this specification, the notation "a to b" in the explanation of a numerical range means a to b, unless otherwise specified. For example, "1 to 5% by mass" means "1% by mass to 5% by mass."

<Flux>
The flux of the present embodiment is a flux containing a thixotropic agent, and the thixotropic agent contains an alkylene oxide copolymer (A) having an allyl group and/or a phenyl group in the side chain, which can more effectively suppress scattering of the flux during reflow and improve storage stability of the solder paste.

The components contained in flux are explained below.

[Thixotropic agent]
Thixotropic agents are used to impart thixotropic properties to fluxes and solder pastes.
The thixotropic agent of this embodiment includes at least an alkylene oxide copolymer (A) having an allyl group and/or a phenyl group in the side chain. That is, the alkylene oxide copolymer (A) has a bulky hydrophobic group such as an allyl group and/or a phenyl group in the side chain, and thus a surface active effect is obtained, which improves the dispersibility of the solder powder, and makes it easier to suppress the separation of the flux components from the solder powder, and it is considered that the scattering of small lumps of the flux components can be suppressed by improving the spinnability. In addition, by using polyalkylene oxide as the main skeleton, a good viscosity can be obtained, and even at high temperatures due to reflow, it is easy to suppress the scattering of the flux components, and during storage of the flux, the sedimentation of the solder powder due to the improvement of the viscosity and thixotropy can be suppressed, making it difficult for separation from the flux components to occur. In this embodiment, there is no problem with the solder powder and the flux components being separated during reflow.

(Alkylene oxide copolymer (A))
The alkylene oxide copolymer (A) is preferably a copolymer of a polyalkylene oxide and a glycidyl ether having an allyl group and/or a phenyl group in a side chain. The content of the allyl group and/or the phenyl group in the side chain in the alkylene oxide copolymer (A) is preferably 1 to 12 mass%.

Examples of polyalkylene oxides include ethylene oxide, propylene oxide, and 1,4-butylene oxide (tetrahydrofuran). Of these, ethylene oxide and propylene oxide are preferred, and those containing both ethylene oxide and propylene oxide are more preferred.

Specific examples of the alkylene oxide copolymer (A) include one or two selected from the group consisting of a terpolymer (a1) of ethylene oxide, propylene oxide, and allyl glycidyl ether, and a terpolymer (a2) of ethylene oxide, propylene oxide, and phenyl glycidyl ether.

When the copolymerization ratios of ethylene oxide, propylene oxide, and allyl glycidyl ether in the terpolymer (a1) of ethylene oxide, propylene oxide, and allyl glycidyl ether are n, m, and l (mol %), it is preferable that n:m:l = 96-93:1-6:3-1.

When the copolymerization ratios of ethylene oxide, propylene oxide, and phenyl glycidyl ether in the terpolymer (a2) of ethylene oxide, propylene oxide, and phenyl glycidyl ether are x, y, and z (mol %), it is preferable that x:y:z = 98-97:1:1-2.

Alkylene oxide copolymer (A) is a random copolymer containing ethylene oxide, propylene oxide, and phenyl or allyl glycidyl ether as repeating units.

The weight average molecular weight of the alkylene oxide copolymer (A) is preferably 50,000 to 800,000, more preferably 60,000 to 600,000, even more preferably 70,000 to 500,000, even more preferably 80,000 to 200,000, and particularly preferably 90,000 to 150,000. This reduces the difference in specific gravity between the solder powder and the flux components, improving storage properties.

The viscosity of the aqueous solution of the alkylene oxide copolymer (A) (at a concentration of 10% by mass) is preferably 50 to 3,000 mPa·s, and more preferably 100 to 2,000 mPa·s.

The content of the alkylene oxide copolymer (A) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 98% by mass or more, based on the total amount of the thixotropic agent, and may be 100% by mass.

The thixotropic agent of this embodiment may further contain a thixotropic agent other than the alkylene oxide copolymer (A) described above. The other thixotropic agents are not particularly limited and may be any known agent, such as amide compounds, ester compounds, sorbitol-based thixotropic agents, carnauba wax, beeswax, and other wax-based thixotropic agents.

Examples of the amide compounds that are thixotropic agents include monoamides, bisamides, and polyamides. More specifically, for example, such amide compounds include monoamides such as lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, saturated fatty acid amide, oleic acid amide, erucic acid amide, unsaturated fatty acid amide, p-toluamide, p-toluenemethane amide, aromatic amide, hexamethylene hydroxystearic acid amide, substituted amide, methylol stearic acid amide, methylol amide, and fatty acid ester amide; bisamides such as methylene bisstearic acid amide, ethylene bislauric acid amide, ethylene bishydroxy fatty acid (fatty acid carbon number 6 to 24) amide, ethylene bishydroxystearic acid amide, saturated fatty acid bisamide, methylene bisoleic acid amide, unsaturated fatty acid bisamide, m-xylylene bisstearic acid amide, and aromatic bisamide; and polyamides such as saturated fatty acid polyamides, unsaturated fatty acid polyamides, aromatic polyamides, 1,2,3-propanetricarboxylic acid tris(2-methylcyclohexylamide), cyclic amide oligomers, and non-cyclic amide oligomers.

An example of the ester compound that is the thixotropic agent is hydrogenated castor oil.

Examples of the sorbitol-based thixotropic agents include dibenzylidene sorbitol, bis(4-methylbenzylidene) sorbitol, (D-) sorbitol, monobenzylidene (-D-) sorbitol, mono(4-methylbenzylidene)-(D-) sorbitol, etc.

The content of the thixotropic agent in this embodiment is preferably 0.1 to 20 mass %, more preferably 2 to 15 mass %, and even more preferably 8 to 12 mass %, based on the total weight of the flux.
By setting the content of the thixotropic agent to the above upper limit or less, scattering can be easily suppressed, whereas by setting the content of the thixotropic agent to the above lower limit or more, the balance between storage stability and scattering suppression can be improved.

The weight average molecular weight of the thixotropic agent of this embodiment is preferably 50,000 to 800,000, more preferably 60,000 to 600,000, even more preferably 70,000 to 500,000, particularly preferably 80,000 to 200,000, and particularly preferably 90,000 to 150,000. The flux of this embodiment may contain multiple types of thixotropic agents having different weight average molecular weights.
As a method for measuring the weight-average molecular weight, a method is generally known in which the results of gel permeation chromatography (GPC) are converted using a calibration curve of standard polyethylene glycol.
For example, the measurement can be performed under the following conditions.
Measurement device: Agilent 1260 Infinity
Columns used: Tosoh TSKguardcolumn SWXL (guard column), Tosoh TSKgel G5000PWXL-CP, Tosoh TSKgel G3000PWXL-CP
Mobile phase: 0.1 M sodium nitrate aqueous solution Standard substance: polyethylene glycol Detector: RI detector, Pol(+)
Injection volume: 20μl
Calibration curve: Polyethylene glycol standard

[Activator]
The flux of the present embodiment preferably contains an activator.
The activator has the property of removing metal oxides and can enhance solder wettability during the solder joining process.
That is, in general, the soldering process is known to be carried out in a reducing gas atmosphere such as formic acid gas, in an inert gas atmosphere containing nitrogen gas, argon gas, or the like and not substantially containing a reducing gas, or in a reduced pressure atmosphere, or in an atmospheric pressure environment. Therefore, by including an activator in the flux, it becomes possible to use the flux in a soldering process in an inert gas atmosphere or a reduced pressure atmosphere that is not substantially containing a reducing gas.

The activator may be one or more selected from organic acids, amines, halogen-based activators, and phosphorus-based activators. Although the detailed mechanism is unclear, it is believed that these activators can remove the metal oxide film from the solder and the metal surface of the soldering target by forming a salt or chelate with the metal oxide.

Examples of organic acids include monocarboxylic acids, dicarboxylic acids, anhydrides of dicarboxylic acids, oxyacids, etc. These may be used alone or in combination of two or more. Among these, polyvalent organic acids having two or more hydroxyl groups and/or carboxyl groups in the molecule may be used.

Specific examples of organic acids include glutaric acid, adipic acid, azelaic acid, eicosane diacid, citric acid, glycolic acid, succinic acid, salicylic acid, diglycolic acid, dipicolinic acid, dibutylaniline diglycolic acid, suberic acid, sebacic acid, thioglycolic acid, terephthalic acid, dodecanedioic acid, parahydroxyphenylacetic acid, picolinic acid, phenylsuccinic acid, phthalic acid, fumaric acid, maleic acid, malonic acid, lauric acid, benzoic acid, tartaric acid, isopropyl alcohol, and ethyl alcohol. Examples include tris(2-carboxyethyl) cyanurate, 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, malic acid, p-anisic acid, stearic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, and linolenic acid.

Among these, from the viewpoint of low residue, the organic acid may include an organic acid having 11 or less carbon atoms.
Examples of organic acids having 11 or less carbon atoms include glycolic acid (2 carbon atoms), thioglycolic acid (2 carbon atoms), glycine (2 carbon atoms), malonic acid (3 carbon atoms), fumaric acid (4 carbon atoms), maleic acid (4 carbon atoms), succinic acid (4 carbon atoms), diglycolic acid (4 carbon atoms), tartaric acid (4 carbon atoms), malic acid (4 carbon atoms), glutaric acid (5 carbon atoms), 2,2-bis(hydroxymethyl)propionic acid (5 carbon atoms), adipic acid (6 carbon atoms), citric acid (6 carbon atoms), picolinic acid (6 carbon atoms), benzoic acid (7 carbon atoms), 2,2-bis(hydroxymethyl)butanoic acid (6 carbon atoms), salicylic acid (7 carbon atoms), and diglycolic acid (4 carbon atoms). Examples of such an acid include picolinic acid (7 carbon atoms), 2,3-dihydroxybenzoic acid (7 carbon atoms), 3-hydroxybenzoic acid (7 carbon atoms), suberic acid (8 carbon atoms), phthalic acid (8 carbon atoms), isophthalic acid (8 carbon atoms), terephthalic acid (8 carbon atoms), parahydroxyphenylacetic acid (8 carbon atoms), 1,3-cyclohexanedicarboxylic acid (8 carbon atoms), p-anisic acid (8 carbon atoms), azelaic acid (9 carbon atoms), 2,4-diethylglutaric acid (9 carbon atoms), sebacic acid (10 carbon atoms), phenylsuccinic acid (10 carbon atoms), 2-quinolinecarboxylic acid (10 carbon atoms), and 4-tert-butylbenzoic acid (11 carbon atoms).

Examples of organic acids include dimer acid, trimer acid, hydrogenated dimer acid, which is a hydrogenated product of dimer acid with hydrogen added, and hydrogenated trimer acid, which is a hydrogenated product of trimer acid with hydrogen added.

The organic acid content in the flux may be, for example, 0 to 15 mass %, or 1 to 10 mass %.

Examples of amines include monoethanolamine, diphenylguanidine, ethylamine, triethylamine, ethylenediamine, triethylenetetramine, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 1-benzyl-2-methylimidazo 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-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'-methyl imidazolyl-(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 imidazoline, 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-triazine, 2,4-diamino-6-vinyl-s-triazine isoform Cyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-nonylbenzimidazole, 2-(4-thiazolyl)benzimidazole, benzimidazole, 2-(2'-hydroxy-5'-methylphenyl)benzimidazole, 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-benzotriazol-2-yl)-4-tert-octylphenol] 1, 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-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, 1-(1',2'-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-bis[(1H-benzotriazol-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, and 5-phenyltetrazole.

The content of amines in the flux may be, for example, 0 to 15 mass %, or 0.5 to 5 mass %.

Halogen-based activators include organic halogen compounds or amine hydrohalides.

Examples of the organic halogen compound include trans-2,3-dibromo-1,4-butenediol, triallyl isocyanurate hexabromide, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, and 2,3-dibromo-2-butene-1,4-diol.
Other organic halogen compounds include, for example, organic chloro compounds such as chloroalkanes, chlorinated fatty acid esters, HET acids, HET acid anhydrides, etc. Furthermore, organic fluoro compounds such as fluorine-based surfactants, surfactants having perfluoroalkyl groups, polytetrafluoroethylene, etc.

Examples of amine hydrohalide salts include salts obtained by combining hydrohalic acids such as hydroiodic acid (HI), hydrobromic acid (HBr), hydrochloric acid (HCl), and hydrofluoric acid (HF) with amine compounds such as aniline, diphenylguanidine, diethylamine, and isopropylamine. In addition, salts obtained by combining tetrafluoroboric acid (HBF4) with amine compounds can also be used as equivalents to amine hydrohalide salts.

The content of the halogen-based activator in the flux may be, for example, 0 to 10 mass %, or 0.5 to 5 mass %.
The content of the organic halogen compound in the flux may be, for example, 0 to 5 mass %.
The content of the amine hydrohalide in the flux may be, for example, 0 to 1 mass %.

Examples of phosphorus-based activators include phosphonic acid esters, phenyl-substituted phosphinic acids, and phosphoric acid esters.

Examples of phosphonate esters include 2-ethylhexyl (2-ethylhexyl) phosphonate, n-octyl (n-octyl) phosphonate, n-decyl (n-decyl) phosphonate, and n-butyl (n-butyl) phosphonate.
Phenyl-substituted phosphinic acids include, for example, phenylphosphinic acid and diphenylphosphinic acid.

The content of the phosphorus-based activator in the flux may be, for example, 0 to 10 mass %, or 1 to 5 mass %.

The content of the activator may be 0 to 30 mass % relative to the total amount of the flux, 1 to 20 mass %, or 5 to 15 mass %.

[solvent]
The flux of the present embodiment contains a solvent. The solvent is not particularly limited, but examples thereof include solid solvents and liquid solvents. These may be used alone or in combination of two or more.

The solid solvent may be any solvent that is solid at 25°C, and the lower limit of the melting point may be, for example, 30°C or higher, 40°C or higher, or 50°C or higher. The upper limit of the melting point may be, for example, 280°C or lower.

As the solid solvent, for example, an alcohol-based solid solvent or a phenol-based solid solvent is used.
The alcohol-based solid solvent may be any solid solvent having one or more hydroxyl groups in the molecule, and is preferably a polyhydric alcohol-based solid solvent having two or more hydroxyl groups. Specific examples of polyhydric alcohol-based solid solvents include pentaerythritol, trimethylolpropane, 2,5-dimethyl-2,5-hexanediol, and neopentyl glycol.
The above-mentioned phenol-based solid solvent may be a solid solvent having one or more phenol groups in the molecule, and one or more hydroxy groups may be bonded to the benzene ring of the phenol group.

The content of the solid solvent in the flux may be, for example, 0 to 40 mass %, or 1 to 30 mass %.

The liquid solvent is a solvent that is liquid at 25°C, and examples of the liquid solvent include alcohol-based solvents, glycol ether-based solvents, terpineols, hydrocarbons, esters, water, etc. These may be used alone or in combination of two or more. Among these, at least one of alcohol-based solvents and glycol ether-based solvents may be used as the liquid solvent.

Examples of the alcohol-based solvents include isopropyl alcohol, 1,2-butanediol, isobornylcyclohexanol, 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, guaiacol glycerol ether, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, etc.

Examples of the glycol ether solvents include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol monomethyl ether.

The liquid solvent content in the flux may be, for example, 0 to 50 mass %, or 1 to 45 mass %.

[Base resin]
The flux may include a base resin.
Examples of the base resin include rosin resins, (meth)acrylic resins, urethane resins, polyester resins, phenoxy resins, vinyl ether resins, terpene resins, modified terpene resins (e.g., aromatic modified terpene resins, hydrogenated terpene resins, hydrogenated aromatic modified terpene resins, etc.), terpene phenol resins, modified terpene phenol resins (e.g., hydrogenated terpene phenol resins, etc.), styrene resins, modified styrene resins (e.g., styrene acrylic resins, styrene maleic resins, etc.), xylene resins, modified xylene resins (e.g., phenol modified xylene resins, alkylphenol modified xylene resins, phenol modified resol type xylene resins, polyol modified xylene resins, polyoxyethylene adduct xylene resins, etc.), etc. These may be used alone or in combination of two or more.
In this specification, the term "(meth)acrylic resin" refers to a concept that includes methacrylic resins and acrylic resins.

Among these, the base resin preferably contains a rosin-based resin.
Examples of rosin-based resins include raw rosins such as gum rosin, wood rosin, and tall oil rosin, and derivatives obtained from raw rosins. Examples of derivatives include refined rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, and α,β-unsaturated carboxylic acid modified products (acrylated rosin, maleated rosin, fumarated rosin, etc.), as well as refined products, hydrogenated products, and disproportionated products of polymerized rosin, and refined products, hydrogenated products, and disproportionated products of α,β-unsaturated carboxylic acid modified products. These rosin-based resins may be used alone or in combination of two or more.

The content of the base resin in the flux may be, for example, 10 to 70% by mass, or 20 to 50% by mass. The content of the base resin is adjusted appropriately depending on the other components in the flux.

[Additives]
The flux may contain additives that are usually added to fluxes as long as they do not impair the effects of the present invention.
Examples of the additives include antioxidants such as hindered phenol-based antioxidants and phosphorus-based antioxidants, rust inhibitors, antifoaming agents, matting agents, surfactants, and colorants. These may be used alone or in combination of two or more.

[Application]
The flux of this embodiment can be used, for example, by mixing with metal powder to form a solder paste, or as a flux for ball attachment or chip attachment.

<Solder paste>
The solder paste of this embodiment contains the above-mentioned flux and metal powder.

The metal powder may be composed of solder powder consisting of Sn alone, or Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Bi, Sn-In, etc., or alloys of these with the addition of Pb, Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, P, etc.

The solder alloy preferably has an alloy composition consisting of As: 25 to 300 ppm by weight, and at least one of Sb: more than 0 ppm by weight and 3000 ppm by weight or less, Bi: more than 0 ppm by weight and 10000 ppm by weight or less, and Pb: more than 0 ppm by weight and 5100 ppm by weight or less, with the balance being Sn. The solder alloy may further contain at least one of Ag: 0 to 4 mass% and Cu: 0 to 0.9 mass%.

There is no limit to the amount of metal powder and flux contained in the solder paste; for example, the amount of metal powder can be 5 to 95 mass % and the amount of flux can be 5 to 95 mass %.

There is no limitation on the method for producing the flux and solder paste, and they can be produced by mixing the raw materials simultaneously or sequentially by any method.
For example, the method of producing the flux may be such that all of the components of the flux are ultimately mixed together, and the other components may be mixed sequentially into the solvent, or the mixture of the other components may be added to the solvent, or the solvent and all of the other components may be mixed at the same time.
Furthermore, in the method of manufacturing a solder paste, it is not necessary to prepare a flux in advance and mix it with a metal powder. As long as all components of the flux, the metal powder, and additives to be added to the solder paste as necessary are ultimately mixed, the order of mixing is not important. For example, some of the components of the flux may be mixed with the metal powder, and then the remaining components of the flux may be added.

The flux and solder paste of the present embodiment can be used, for example, in a method for manufacturing a semiconductor device.
A method for manufacturing a semiconductor device may include a step of applying flux or solder paste to an electrode, placing a solder ball on the electrode, and heat-treating a substrate, such as a lead frame or a printed wiring board, and a semiconductor element to join them via the molten solder ball.
The heat treatment may be carried out in a nitrogen atmosphere or a reduced pressure atmosphere, and may be carried out under conditions where the temperature rise rate is, for example, 3° C./sec or more.
The method for manufacturing a semiconductor device may be configured so as not to include a step of washing away the flux or solder paste after the bonding step.

The above describes the embodiments of the present invention, but these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements that can achieve the object of the present invention are included in the present invention.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the description of these examples.

1. Preparation of Flux The raw materials shown below were mixed in the proportions shown in Tables 1 and 2 by a known method to obtain fluxes.
(Base resin)
Base resin 1: Acrylic acid modified hydrogenated rosin Base resin 2: Hydrogenated rosin Base resin 3: Rosin ester Base resin 4: Polymerized rosin (solvent)
Solvent 1: Hexyl diglycol (diethylene glycol monohexyl ether)
Solvent 2: Hexylene glycol (2-methylpentane-2,4-diol)
(Activator)
Organic acid 1: glutaric acid Organic acid 2: adipic acid Amines: 2-ethylimidazole Halogen-based activator: 2,3-dibromo-1,4-butanediol (thixotropic agent)
Thixotropic agent 1: hydrogenated castor oil Thixotropic agent 2: polyamide-based thixotropic agent Thixotropic agent 3: polyethylene oxide ("Alcox L-11" manufactured by Meisei Chemical Industry Co., Ltd., weight average molecular weight 110,000 (catalog value))
Alkylene oxide copolymer (A) 1: Thixotropic agent ethylene oxide-propylene oxide-allyl glycidyl ether random copolymer ("Alkox CP-A1H" manufactured by Meiwa Chemical Industry Co., Ltd., weight average molecular weight 100,000 (catalog value))
Alkylene oxide copolymer (A) 2: Ethylene oxide-propylene oxide-phenyl glycidyl ether random copolymer ("Alkox CP-B1" manufactured by Meiwa Chemical Industry Co., Ltd., weight average molecular weight 100,000 (catalog value))

2. Preparation of solder paste The obtained flux and metal powder were mixed in a ratio of 13 mass% flux:87 mass% metal powder to obtain a solder paste. The metal powder used was a Sn-Ag-Cu solder alloy (average particle size of the metal powder was φ20 μm) with 3.0 mass% Ag, 0.5 mass% Cu, and the remainder Sn.
The particle size of the metal powder used was classified as symbol 6 in Table 2 (powder size classification) of JIS Z 3284-1:2014.

3. Evaluation The obtained solder paste was evaluated for the following evaluation items.

<Scatterability>
Each of the obtained solder pastes was printed on a FR-4 (Flame Retardant Type 4) board using a metal mask (mask thickness 0.15 mm, opening size 1.6 mm×1.6 mm).
Next, 30 chip capacitors measuring 3.2 mm×1.6 mm were mounted on the printed portion and mounted in a reflow furnace. The reflow temperature profile was as follows (i) to (iv).
(i) Heat up to 150°C at 2°C/sec (ii) Heat up from 150 to 180°C in 80 seconds (iii) Heat up from 180 to 240°C at 2°C/sec (iv) Hold at 220°C or higher for 40 seconds The number of flux residues scattered on the outside (surroundings) of each of the 30 chip capacitor mounting locations was counted, the measurements for the 30 locations were totaled, and the results were evaluated according to the following criteria. Note that the number of flux residues was counted as one lump, regardless of its size.
・Standards ○: 0 to 5 pieces △: 6 to 15 pieces ×: 16 or more pieces

<Storability (storability)>
100 g of each solder paste was placed in a paste container (cylindrical, inner diameter 58 mm) and stirred with a softener (Thinky Corporation ARV-930TWIN) at 200 rpm for 2 minutes. The container was then sealed with a lid and left at room temperature (25±3°C, 60% RH or less).
Thereafter, every 24 hours, the lid was opened and the paste container was tilted to visually check whether the flux components flowed out (or oozed out) from the solder paste. The time it took for the flux components to flow out was evaluated according to the following criteria.
Criteria: No flow occurred even after 168 hours or more.
Δ: Flowed out within 72 hours or more and less than 168 hours.
×: Flowed out within 72 hours.

Claims (10)

A flux containing a thixotropic agent,
A flux, wherein the thixotropic agent contains an alkylene oxide copolymer (A) having an allyl group and/or a phenyl group in a side chain. 2. The flux according to claim 1 ,
A flux, wherein the weight average molecular weight of the thixotropic agent is 50,000 to 800,000. The flux according to claim 1 or 2,
A flux, wherein the content of the thixotropic agent is 0.1 to 20 mass % based on the total weight of the flux. The flux according to any one of claims 1 to 3,
The alkylene oxide copolymer (A) is a copolymer of a polyalkylene oxide and a glycidyl ether having an allyl group and/or a phenyl group in the side chain, The flux according to any one of claims 1 to 4,
The alkylene oxide copolymer (A) is one or two selected from the group consisting of an ethylene oxide-propylene oxide-allyl glycidyl ether random copolymer and an ethylene oxide-propylene oxide-phenyl glycidyl ether random copolymer. The flux according to any one of claims 1 to 5,
The alkylene oxide copolymer (A) is a random copolymer. The flux according to any one of claims 1 to 6,
Also contains rosin and flux. The flux according to any one of claims 1 to 7,
The flux further contains one or more activators selected from organic acids, amines, halogen-based activators, and phosphorus-based activators. The flux according to claim 8,
The flux, wherein the activator comprises an organic acid having 11 or less carbon atoms. A solder paste comprising the flux according to any one of claims 1 to 9 and a metal powder.