Manufacturing method of flux and joint body

Abstract

The present invention provides a flux that can increase the fillet size during soldering and suppresses the occurrence of bridges, and a method for manufacturing a joint using the flux. [Solution] A flux containing rosin, an activator, and a solvent, the activator containing an imidazole compound and two kinds of dicarboxylic acids, the two kinds of dicarboxylic acids being a combination of one selected from the group consisting of succinic acid, adipic acid, and sebacic acid, and malonic acid. Alternatively, a flux containing rosin, an activator, and a solvent, the activator containing an imidazole compound and two kinds of dicarboxylic acids, the two kinds of dicarboxylic acids being a combination of one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid, and succinic acid.

Description

[Technical field]

[0001] The present invention relates to a method for producing a flux and a joint body. [Background technology]

[0002] Fixing components to a board and electrically connecting the components to the board are generally performed by soldering. For soldering, a method such as flow soldering or reflow soldering is adopted depending on the size of the objects to be joined. For example, in flow soldering, flux is first applied to a board on which components are mounted, and then, while the board on which the components are mounted is being transported, molten solder is jetted from below the board and brought into contact with the surface to be soldered, thereby performing soldering.

[0003] Fluxes used in soldering generally contain a resin component, a solvent, an activator, etc. For example, Patent Document 1 discloses a flux that contains rosin as a resin component, a solvent, and a specific hydroxybenzoic acid and a monocarboxylic acid as activators. The flux disclosed in Patent Document 1 is suitable for flow soldering. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2024-34098 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, from the viewpoint of energy saving, Sn-Bi based solders that contain Sn and Bi and enable soldering at lower temperatures have been used. When using Sn-Bi based solders that contain a large amount of Bi, the disadvantage is that they are hard and brittle, which causes problems with the joining strength of the objects to be joined. To address this problem, a method of increasing the joint strength by increasing the fillet size has been considered, but when soldering is performed using conventional flux, it is difficult to achieve both goals at the same time, as the fillet shape may be poor or bridging may occur even if the fillet size can be increased.

[0006] The present invention has been made in consideration of the above circumstances, and provides a flux that makes it possible to increase the fillet size during soldering and suppresses the occurrence of bridges, and a method for manufacturing a joint using the same. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention employs the following configuration.

[0008] [1] A flux comprising rosin, an activator, and a solvent, the activator comprising an imidazole compound and two dicarboxylic acids, the two dicarboxylic acids being a combination of one selected from the group consisting of succinic acid, adipic acid, and sebacic acid, and malonic acid.

[0009] [2] A flux comprising rosin, an activator, and a solvent, the activator comprising an imidazole compound and two kinds of dicarboxylic acids, the two kinds of dicarboxylic acids being a combination of one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid, and succinic acid.

[0010] [3] The flux according to [1] or [2], wherein a mass ratio of the two types of dicarboxylic acids to the imidazole compound is two types of dicarboxylic acids / imidazole compound=0.30 or more and 50 or less.

[0011] [4] The flux according to any one of [1] to [3], wherein the content of the imidazole compound is 0.1 mass % or more and 1.5 mass % or less with respect to the total mass (100 mass %) of the flux. [5] The flux according to any one of [1] to [4], wherein a total content of the two kinds of dicarboxylic acids is 0.5 mass % or more and 6 mass % or less with respect to a total mass (100 mass %) of the flux. [6] The flux according to any one of [1] to [5], wherein the rosin content is 3 mass % or more and 25 mass % or less with respect to the total mass (100 mass %) of the flux.

[0012] [7] A method for producing a joined body, comprising the step of obtaining a joined body by soldering a solder alloy to a surface of a substrate treated with the flux according to any one of [1] to [6], wherein the solder alloy is an alloy containing Sn and Bi. Effect of the Invention

[0013] According to the present invention, it is possible to provide a flux that can increase the fillet size during soldering and suppress the occurrence of bridges, and a method for manufacturing a joint using the flux. This flux is suitable for use with Sn-Bi based solder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Flux) The flux according to a first aspect of the present invention contains rosin, an activator, and a solvent, and the activator contains an imidazole compound and two kinds of dicarboxylic acids. The two dicarboxylic acids contained in this flux are specified as the following combination (1) or combination (2).

[0015] Combination of two dicarboxylic acids (1): A combination of one selected from the group consisting of succinic acid, adipic acid, and sebacic acid with malonic acid

[0016] Combination of two dicarboxylic acids (2): A combination of one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid with succinic acid

[0017] In other words, even if a flux contains a dicarboxylic acid, a flux containing only one dicarboxylic acid, two dicarboxylic acids in a combination other than the above combination (1) or combination (2), or three or more dicarboxylic acids is outside the scope of the flux according to this embodiment. Therefore, a flux containing the combination (1) of two dicarboxylic acids and a dicarboxylic acid other than the two dicarboxylic acids in the combination (1) is also outside the scope of the flux according to this embodiment, and a flux containing two or three acids selected from the group consisting of succinic acid, adipic acid, and sebacic acid and malonic acid is also outside the scope of the flux according to this embodiment. Similarly, a flux containing the combination (2) of two dicarboxylic acids and a dicarboxylic acid other than the two in the combination (2) is outside the scope of the flux according to this embodiment, and a flux containing two or more selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid, and succinic acid is also outside the scope of the flux according to this embodiment.

[0018] One embodiment of the flux according to the present aspect includes a flux containing rosin, an activator, a solvent, and other components as necessary, and further includes a flux in which the activator contains an imidazole compound and the combination (1) of two kinds of dicarboxylic acids (first embodiment). Another embodiment of the flux according to the present aspect includes a flux containing rosin, an activator, a solvent, and other components as necessary, and in addition, the activator contains an imidazole compound and the combination (2) of two kinds of dicarboxylic acids (second embodiment).

[0019] First Embodiment The flux of the first embodiment contains rosin, an activator, a solvent, and other components as necessary. The activator in the first embodiment contains an imidazole compound and the combination (1) of two dicarboxylic acids.

[0020] <Rosin> In this embodiment, "rosin" includes natural resins containing abietic acid as the main component or a mixture of abietic acid and its isomers, as well as chemically modified natural resins (sometimes referred to as rosin derivatives).

[0021] The term "main component" as used herein refers to a component that is contained in a compound at a content of 40 mass % or more among the components that constitute the compound. The content of abietic acid in the natural resin is 40% by mass or more, and as an example, is 40% by mass or more and 80% by mass or less with respect to the natural resin.

[0022] Representative isomers of abietic acid include neoabietic acid, palustric acid, and levopimaric acid. Examples of the "natural resin" include gum rosin, wood rosin, tall oil rosin, and the like.

[0023] In the present invention, the term "chemically modified natural resin (rosin derivative)" includes the "natural resin" that has been subjected to one or more treatments selected from the group consisting of hydrogenation, dehydrogenation, neutralization, alkylene oxide addition, amidation, dimerization, oligomerization, esterification, and Diels-Alder cycloaddition.

[0024] Examples of rosin derivatives include purified rosin and modified rosin. Examples of modified rosins include hydrogenated rosin, polymerized rosin, polymerized hydrogenated rosin, disproportionated rosin, acid-modified rosin, rosin ester, acid-modified hydrogenated rosin, acid anhydride-modified hydrogenated rosin, acid-modified disproportionated rosin, acid anhydride-modified disproportionated rosin, phenol-modified rosin and α,β-unsaturated carboxylic acid modified products (acrylated rosin, maleated rosin, fumarated rosin, etc.), as well as purified products, hydrogenated products and disproportionated products of the polymerized rosins, as well as purified products, hydrogenated products and disproportionated products of the α,β-unsaturated carboxylic acid modified products, rosin alcohol, rosin amine, hydrogenated rosin alcohol, rosin ester, hydrogenated rosin ester, rosin soap, hydrogenated rosin soap, acid-modified rosin soap, etc.

[0025] Examples of rosin amines include dehydroabietylamine, dihydroabietylamine, etc. The rosin amine refers to a so-called disproportionated rosin amine.

[0026] In the flux of the first embodiment, the rosin may be used alone or in combination of two or more kinds. The rosin preferably contains a rosin derivative, more preferably contains at least one selected from the group consisting of acid-modified rosin, hydrogenated rosin, polymerized rosin, and acid-modified hydrogenated rosin, and further preferably contains at least one selected from the group consisting of acid-modified hydrogenated rosin, hydrogenated rosin, and polymerized rosin. From the viewpoint of solderability, the acid-modified hydrogenated rosin is preferably acrylic acid-modified hydrogenated rosin, that is, the rosin preferably contains at least one selected from the group consisting of acrylic acid-modified hydrogenated rosin, hydrogenated rosin, and polymerized rosin. The rosin used in the flux of the present embodiment may be, for example, a combination of acid-modified hydrogenated rosin and hydrogenated rosin, a combination of acid-modified hydrogenated rosin and partially hydrogenated rosin, or a polymerized rosin.

[0027] The content of rosin in the flux of the first embodiment is preferably 3 mass % or more and 25 mass % or less, and more preferably 4 mass % or more and 20 mass % or less, relative to the total mass (100 mass %) of the flux.

[0028] <Stimulant> The activator in the first embodiment contains an imidazole compound and the following combination (1). Combination of two dicarboxylic acids (1): A combination of one selected from the group consisting of succinic acid, adipic acid, and sebacic acid with malonic acid

[0029] Imidazole compounds Examples of the imidazole compound include 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole; 2-phenylimidazole, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-cyanoethyl-2-phenylimidazo benzimidazole, 1-benzyl-2-phenylimidazole, 1-benzyl-2-methylimidazole; epoxy-imidazole adduct; benzimidazole, 2-methylbenzimidazole, 2-pentylbenzimidazole, 2-octylbenzimidazole, 2-nonylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-(4-thiazolyl)benzimidazole; 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole; 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate; and the like.

[0030] In the flux of the first embodiment, the imidazole compounds may be used alone or in combination of two or more kinds. Among the above, the imidazole compound is preferably an alkyl group-substituted imidazole compound, more preferably an imidazole compound selected from the group consisting of 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole and 1-cyanoethyl-2-ethyl-4-methylimidazole, even more preferably an imidazole compound selected from the group consisting of 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole and 2-ethyl-4-methylimidazole, and most preferably 2-undecylimidazole.

[0031] Combination of two dicarboxylic acids (1) The combination of two dicarboxylic acids (1) is either a combination of succinic acid and malonic acid, a combination of adipic acid and malonic acid, or a combination of sebacic acid and malonic acid. Among the above combinations (1), from the viewpoint of fillet size, the combination of succinic acid and malonic acid, and the combination of sebacic acid and malonic acid are more preferable, and the combination of succinic acid and malonic acid is even more preferable. The mass ratio of one selected from the group consisting of succinic acid, adipic acid, and sebacic acid (hereinafter also referred to as "dicarboxylic acid (1c)") to malonic acid in the combination (1), expressed as a mass ratio of dicarboxylic acid (1c) / malonic acid, is preferably 10 / 90 or more and 90 / 10 or less, more preferably 25 / 75 or more and 75 / 25 or less, and even more preferably 40 / 60 or more and 60 / 40 or less.

[0032] The content of the imidazole compound in the flux of the first embodiment is preferably 0.1 mass % or more and 1.5 mass % or less, and more preferably 0.5 mass % or more and 1.5 mass % or less, relative to the total mass (100 mass %) of the flux.

[0033] The total content of the two dicarboxylic acids in the flux of the first embodiment is preferably 0.5% by mass or more and 6% by mass or less, and more preferably 1% by mass or more and 4% by mass or less, relative to the total mass (100% by mass) of the flux.

[0034] In the flux of the first embodiment, the mass ratio of the combination (1) of two dicarboxylic acids to the imidazole compound, expressed as the mass ratio of two dicarboxylic acids / imidazole compound, is preferably 0.30 or more and 50 or less, more preferably 0.50 or more and 45 or less, and even more preferably 1 or more and 40 or less. When the mass ratio of the two dicarboxylic acids to the imidazole compound is within the above-mentioned preferred range, the fillet size can be easily controlled.

[0035] Other activators The activator in the first embodiment may contain other activators as necessary in addition to the combination (1) of the imidazole compound and two kinds of dicarboxylic acids. Other examples of the activator include halogen compounds, organic acids other than dicarboxylic acids, and organic phosphorus compounds.

[0036] Examples of the halogen compound include amine hydrohalides and organic halogen compounds other than amine hydrohalides.

[0037] Amine hydrohalides are compounds obtained by reacting amines with hydrogen halides. Examples of amines include aliphatic amines, guanidines, azoles, etc. Examples of hydrogen halides include chlorine, bromine, and iodine hydrides. Examples of the aliphatic amines include ethylamine, dimethylamine, diethylamine, triethylamine, 2-ethylhexylamine, cyclohexylamine, ethylenediamine, etc. Examples of the guanidines include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, 1,3-di-o-cumenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc.

[0038] Examples of organic halogen compounds other than amine hydrohalides include halogenated aliphatic compounds, which are compounds in which some or all of the hydrogen atoms constituting the aliphatic hydrocarbon group have been substituted with halogen atoms. Examples of halogenated aliphatic compounds include halogenated aliphatic alcohols and halogenated heterocyclic compounds. Examples of halogenated aliphatic alcohols include 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1-bromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, 1,4-dibromo-2-butanol, and trans-2,3-dibromo-2-butene-1,4-diol.

[0039] Furthermore, examples of the halogen compound that can be used include salts obtained by reacting an amine with tetrafluoroboric acid (HBF4) and complexes obtained by reacting an amine with boron trifluoride (BF3).

[0040] When a halogen compound is used as an additional activator, one type may be used alone, or two or more types may be used in combination. The halogen compound is preferably at least one selected from the group consisting of amine hydrohalides and halogenated aliphatic alcohols, and more preferably an amine hydrohalide and a halogenated aliphatic alcohol are used in combination. The content of the halogen compound in the flux of the first embodiment is preferably 0.1 mass % or more and 2 mass % or less, and more preferably 0.5 mass % or more and 1.5 mass % or less, relative to the total mass (100 mass %) of the flux.

[0041] Examples of the organic acid other than the dicarboxylic acid include carboxylic acid and organic sulfonic acid. The carboxylic acid includes aliphatic monocarboxylic acid and aromatic carboxylic acid.

[0042] Examples of aliphatic monocarboxylic acids include caproic acid, enanthic acid, caprylic acid, pelargonic acid, isopelargonic acid, capric acid, caproleic acid, lauric acid (dodecanoic acid), undecanoic acid, Linderic acid, tridecanoic acid, myristoleic acid, pentadecanoic acid, isopalmitic acid, palmitoleic acid, hiragonic acid, hydnocarpic acid, margaric acid, isostearic acid, elaidic acid, petroselinic acid, moroctic acid, eleostearic acid, taliric acid, vaccenic acid, ricinoleic acid, vernolic acid, sterculic acid, nonadecanoic acid, eicosanoic acid, stearic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, linolenic acid, myristic acid, 2,2-bis(hydroxymethyl)propionic acid, and 2,2-bis(hydroxymethyl)butanoic acid. Examples of aromatic monocarboxylic acids include salicylic acid, p-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, benzoic acid, 2,3-dihydroxybenzoic acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, p-anisic acid, picolinic acid, and 3-hydroxypicolinic acid.

[0043] Examples of organic sulfonic acids include aliphatic sulfonic acids, aromatic sulfonic acids, etc. Examples of aliphatic sulfonic acids include alkanesulfonic acids, alkanolsulfonic acids, etc. Examples of aromatic sulfonic acids include 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, p-toluenesulfonic acid, xylenesulfonic acid, p-phenolsulfonic acid, cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, and diphenylamine-4-sulfonic acid, etc.

[0044] When an organic acid other than a dicarboxylic acid is used as the other activator, one type may be used alone, or two or more types may be used in combination. The content of the organic acid, excluding dicarboxylic acids, in the flux of the first embodiment is preferably 0.1 mass % or more and 2 mass % or less, and more preferably 0.5 mass % or more and 1.5 mass % or less, relative to the total mass (100 mass %) of the flux.

[0045] Examples of the organic phosphorus compound include acid phosphate esters, acid phosphonate esters, and acid phosphinate esters.

[0046] The total content of all the activators in the flux of the first embodiment is, for example, 2 mass % or more and 10 mass % or less, and may be 2 mass % or more and 9 mass % or less, relative to the total mass (100 mass %) of the flux.

[0047] <Solvent> Examples of the solvent in the first embodiment include water, alcohol-based solvents, glycol ether-based solvents, and terpineols.

[0048] Alcohol-based solvents include ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-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, 2-methylpentane-2,4-diol, 1,1,1-tris(hydroxymethyl)propanediol, and 1,2,3-tris(hydroxymethyl)propanediol. propane, 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, 1-ethynyl-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2-hexyl-1-decanol, 2-methyl-2,4-pentanediol (hexylene glycol), octanediol, and the like.

[0049] Examples of glycol ether solvents include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, ethylene glycol monobutyl ether (butyl glycol), ethylene glycol monohexyl ether (hexyl glycol), diethylene glycol monohexyl ether (hexyl diglycol), diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, methylpropylene triglycol, triethylene glycol butyl methyl ether, tetraethylene glycol, tetraethylene glycol dimethyl ether, and tripropylene glycol-n-butyl ether.

[0050] Examples of terpineols include α-terpineol, β-terpineol, γ-terpineol, and terpineol mixtures (that is, mixtures whose main component is α-terpineol and contain β-terpineol or γ-terpineol). Other examples of the solvent include di(2-ethylhexyl) sebacate and liquid paraffin.

[0051] In the flux of the first embodiment, the solvent may be used alone or in combination of two or more kinds. The solvent preferably contains a solvent having a boiling point of 100° C. or less, and among these, an alcohol-based solvent is more preferable, and it is even more preferable that the solvent contains at least one selected from the group consisting of ethanol and 2-propanol, and it is particularly preferable that the solvent contains 2-propanol. The content of the solvent in the flux of the first embodiment is, for example, 60 mass % or more, may be 70 mass % or more and 95 mass % or less, or may be 75 mass % or more and 95 mass % or less, relative to the total mass (100 mass %) of the flux.

[0052] <Other ingredients> The flux of the first embodiment may contain other components as necessary in addition to the rosin, activator, and solvent. Examples of the other components include resin components other than rosin, a thixotropic agent, a surfactant, a metal deactivator, an antioxidant, a silane coupling agent, a colorant, etc. The flux of the first embodiment may be a composition that contains rosin, an imidazole compound, the combination (1) of two kinds of dicarboxylic acids, and a solvent, but does not contain a thixotropic agent.

[0053] As described above, in the flux of the first embodiment, the specific amine is combined with the specific organic acid. An imidazole compound is selected as the specific amine, and one selected from the group consisting of succinic acid, adipic acid, and sebacic acid is used as the specific organic acid in combination with malonic acid. Although the reason is unclear, the flux of the first embodiment obtains a unique interaction by combining the specific amine and the specific organic acid. For this reason, it is believed that it is possible to increase the fillet size during soldering and to suppress the occurrence of bridges. The effect of the flux of the first embodiment is particularly remarkable when an alloy containing Sn and Bi is used, that is, the flux of the first embodiment is suitable for use with Sn-Bi based solder.

[0054] <Second embodiment> The flux of the second embodiment contains rosin, an activator, a solvent, and other components as necessary. The activator in the second embodiment contains an imidazole compound and the combination (2) of two dicarboxylic acids.

[0055] <Rosin> The description of the rosin in the second embodiment is similar to the description of the rosin in the above-mentioned first embodiment. In the flux of the second embodiment, the rosin may be used alone or in combination of two or more kinds. The rosin preferably contains a rosin derivative, more preferably contains at least one selected from the group consisting of acid-modified rosin, hydrogenated rosin, polymerized rosin, and acid-modified hydrogenated rosin, and further preferably contains at least one selected from the group consisting of acid-modified hydrogenated rosin, hydrogenated rosin, and polymerized rosin. From the viewpoint of solderability, the acid-modified hydrogenated rosin is preferably acrylic acid-modified hydrogenated rosin, that is, the rosin preferably contains at least one selected from the group consisting of acrylic acid-modified hydrogenated rosin, hydrogenated rosin, and polymerized rosin. The rosin used in the flux of the present embodiment may be, for example, a combination of acid-modified hydrogenated rosin and hydrogenated rosin, or a combination of acid-modified hydrogenated rosin and partially hydrogenated rosin.

[0056] The rosin content in the flux of the second embodiment is preferably 3 mass% or more and 25 mass% or less, more preferably 4 mass% or more and 20 mass% or less, and even more preferably 5 mass% or more and 15 mass% or less, relative to the total mass (100 mass%) of the flux.

[0057] <Stimulant> The activator in the second embodiment contains an imidazole compound and the following combination (2). Combination of two dicarboxylic acids (2): A combination of one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid with succinic acid

[0058] Imidazole compounds Examples of the imidazole compound include the same compounds as those exemplified in the description of the imidazole compound in the first embodiment. In the flux of the second embodiment, the imidazole compounds may be used alone or in combination of two or more kinds. Among them, the imidazole compound is preferably an alkyl group-substituted imidazole compound, more preferably an imidazole compound selected from the group consisting of 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole and 1-cyanoethyl-2-ethyl-4-methylimidazole, even more preferably an imidazole compound selected from the group consisting of 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole and 2-ethyl-4-methylimidazole, and most preferably 2-undecylimidazole.

[0059] Combination of two dicarboxylic acids (2) The combination of two dicarboxylic acids (2) is any one of a combination of suberic acid and succinic acid, a combination of sebacic acid and succinic acid, a combination of methylsuccinic acid and succinic acid, a combination of malic acid and succinic acid, and a combination of malonic acid and succinic acid. Among the combinations (2), from the viewpoint of fillet size, the combinations of malonic acid and succinic acid, suberic acid and succinic acid, sebacic acid and succinic acid, and methylsuccinic acid and succinic acid are more preferable, and the combinations of malonic acid and succinic acid and sebacic acid and succinic acid are even more preferable. The mass ratio of one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid (hereinafter also referred to as "dicarboxylic acid (2c)") to succinic acid in the combination (2) is preferably 10 / 90 or more and 90 / 10 or less, more preferably 25 / 75 or more and 75 / 25 or less, and even more preferably 40 / 60 or more and 60 / 40 or less, expressed as a mass ratio of dicarboxylic acid (2c) / succinic acid.

[0060] The content of the imidazole compound in the flux of the second embodiment is preferably 0.1 mass % or more and 1.5 mass % or less, and more preferably 0.5 mass % or more and 1.5 mass % or less, relative to the total mass (100 mass %) of the flux.

[0061] The total content of the two dicarboxylic acids in the flux of the second embodiment is preferably 0.5% by mass or more and 6% by mass or less, and more preferably 1% by mass or more and 4% by mass or less, relative to the total mass (100% by mass) of the flux.

[0062] In the flux of the second embodiment, the mass ratio of the combination (2) of two dicarboxylic acids to the imidazole compound, expressed as the mass ratio of two dicarboxylic acids / imidazole compound, is preferably 0.30 or more and 50 or less, more preferably 0.50 or more and 45 or less, and even more preferably 1 or more and 40 or less. When the mass ratio of the two dicarboxylic acids to the imidazole compound is within the above-mentioned preferred range, the fillet size can be easily controlled.

[0063] Other activators The activator in the second embodiment may contain other activators as necessary in addition to the combination (2) of the imidazole compound and two kinds of dicarboxylic acids. Examples of the other activators include halogen compounds, organic acids other than dicarboxylic acids, organic phosphorus compounds, etc. The explanation of the other activators in the second embodiment includes the same ones as those exemplified in the explanation of the other activators in the first embodiment.

[0064] When a halogen compound is used as an additional activator, one type may be used alone, or two or more types may be used in combination. The halogen compound is preferably at least one selected from the group consisting of amine hydrohalides and halogenated aliphatic alcohols, and more preferably an amine hydrohalide and a halogenated aliphatic alcohol are used in combination. The content of the halogen compound in the flux of the second embodiment is preferably 0.1 mass % or more and 2 mass % or less, and more preferably 0.5 mass % or more and 1.5 mass % or less, relative to the total mass (100 mass %) of the flux.

[0065] The total content of all the activators in the flux of the second embodiment is, for example, 2 mass % or more and 10 mass % or less, and may be 2 mass % or more and 9 mass % or less, relative to the total mass (100 mass %) of the flux.

[0066] <Solvent> Examples of the solvent in the second embodiment include water, alcohol-based solvents, glycol ether-based solvents, terpineols, etc. The solvent in the second embodiment may be the same as those exemplified in the description of the solvent in the first embodiment. In the flux of the second embodiment, the solvent may be used alone or in combination of two or more kinds. The solvent preferably contains a solvent having a boiling point of 100° C. or less, and among these, an alcohol-based solvent is more preferable, and it is even more preferable that the solvent contains at least one selected from the group consisting of ethanol and 2-propanol, and it is particularly preferable that the solvent contains 2-propanol. The content of the solvent in the flux of the second embodiment is, for example, 60 mass % or more, may be 70 mass % or more and 95 mass % or less, or may be 75 mass % or more and 95 mass % or less, relative to the total mass (100 mass %) of the flux.

[0067] <Other ingredients> The flux of the second embodiment may contain other components as necessary in addition to the rosin, activator, and solvent. Examples of the other components include resin components other than rosin, a thixotropic agent, a surfactant, a metal deactivator, an antioxidant, a silane coupling agent, a colorant, etc. The flux of the second embodiment may be a composition that contains rosin, an imidazole compound, the combination (2) of two kinds of dicarboxylic acids, and a solvent, but does not contain a thixotropic agent.

[0068] As described above, in the flux of the second embodiment, the specific amine is combined with the specific organic acid. An imidazole compound is selected as the specific amine, and one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid is used in combination with succinic acid as the specific organic acid. Although the reason is unclear, the flux of the second embodiment obtains a unique interaction by combining the specific amine and the specific organic acid. For this reason, it is believed that the fillet size can be increased during soldering, and the occurrence of bridges is suppressed. The effect of the flux of the second embodiment is particularly remarkable when an alloy containing Sn and Bi is used, that is, the flux of the second embodiment is suitable for use with Sn-Bi based solder.

[0069] (Method of Manufacturing Joint) A method for producing a joint body according to a second aspect of the present invention is a method including a step of obtaining a joint body by soldering a solder alloy to a surface of a substrate treated with the flux according to the first aspect described above, the solder alloy being an alloy containing Sn and Bi. One embodiment of the method for producing a bonded body according to the present aspect includes a manufacturing method including, in this order, a component mounting step, a flux application step, a preheating step, and a soldering step, in which the flux of the first embodiment or the flux of the second embodiment is used as the flux.

[0070] In the component mounting process, the components are mounted on the board. One example of a component mounting process involves using an automatic insertion machine to insert the leads or terminals of an insertion-mount component into through holes drilled in a board, and then clinching the protruding leads or terminals to secure the component to the board. The substrate may be, for example, a printed wiring board. Examples of components include integrated circuits, transistors, diodes, resistors, and capacitors.

[0071] In the flux application step, the flux of the above-described embodiment is applied to the soldering surface of the board on which the components are attached. Examples of flux application devices include spray fluxers, foaming fluxers, etc. Among these, spray fluxers are preferred from the viewpoint of the stability of the amount of application. The amount of flux to be applied should be 30 to 180 mL / m from the viewpoint of solderability. 2 is preferably 40 to 150 mL / m 2 or 50-120mL / m 2 That's fine too.

[0072] In the preheating step, the substrate on which the components are attached is preheated. The temperature to which the substrate is heated in the preheating step is preferably 80 to 130°C, and more preferably 90 to 120°C.

[0073] In the soldering process, the surface to be soldered of the board on which the components are mounted is brought into contact with molten solder which is a melted solder alloy. The method for bringing the molten solder into contact with the surface to be soldered is not particularly limited as long as it is a method that can bring the molten solder into contact with the board. Examples of such a method include a jet method and an immersion method. The jet method is a method in which the soldering surface of a board with components attached is brought into contact with a jet of molten solder, while the immersion method is a method in which the soldering surface of a board with components attached is brought into contact with the liquid surface of stationary molten solder.

[0074] The manufacturing method of the joint body of this embodiment is useful when an alloy containing Sn and Bi is used as the solder alloy, and is particularly useful when an alloy of Sn and Bi (Sn-Bi based solder) is used.

[0075] In the soldering step, the soldering conditions may be appropriately set according to the melting point of the solder alloy. For example, when a Sn-Bi based solder is used, the temperature of the molten solder is preferably 170 to 220°C, and more preferably 180 to 200°C.

[0076] As described above, in the manufacturing method of the bonded body of this embodiment, the flux of the first embodiment or the flux of the second embodiment is applied to the soldering surface. Therefore, when soldering using an alloy containing Sn and Bi, it is possible to increase the fillet size and suppress the occurrence of bridges. This makes it possible to manufacture a bonded body with increased bonding strength. In addition, it is possible to manufacture a highly reliable bonded body that is less likely to cause short circuits and insulation deterioration. EXAMPLES

[0077] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0078] <Preparation of flux> (Examples 1 to 16, Comparative Examples 1 to 12) The fluxes of the examples and comparative examples were prepared with the compositions shown in Tables 1 to 5. In the table, the content of each component is shown as a percentage (mass%) relative to the total mass (100 mass%) of the flux. The raw materials used are shown below.

[0079] Rosin Polymerized rosin, acrylic acid modified hydrogenated rosin, partially hydrogenated rosin

[0080] ·Activators Imidazole Compounds: 2-Undecylimidazole

[0081] Dicarboxylic acids: succinic acid, adipic acid, glutaric acid, suberic acid, sebacic acid, malonic acid, maleic acid, methylsuccinic acid, malic acid

[0082] Other activators: 1,3-diphenylguanidine, monoisopropanolamine; ethylamine hydrobromide, 1,3-diphenylguanidine hydrobromide, trans-2,3-dibromo-2-butene-1,4-diol; palmitic acid

[0083] ·solvent 2-Propanol (Isopropyl Alcohol)

[0084] <Preparation of test solder> · Sn-Bi solder An ingot of an alloy (Sn-58Bi) containing 58 mass % Bi and the remainder Sn was prepared as a master alloy, and the ingot was melted to prepare a molten solder.

[0085] · Sn-Ag-Cu solder An ingot of an alloy (Sn-3Ag-0.5Cu) containing 3 mass % Ag, 0.5 mass % Cu, and the remainder Sn was prepared as a master alloy, and the ingot was melted to prepare a molten solder.

[0086] <Evaluation> The fillet size and bridge occurrence were evaluated as described below. The evaluation results are shown in Tables 1 to 5.

[0087] [Evaluation of fillet size and bridge occurrence] 900 μL of the flux of each example was sprayed onto a substrate having the following through-hole lands to obtain a pretreated substrate. <Through-hole land> Contour shape:Circular Inner diameter (hole diameter): 0.5mm Through hole land width (half the difference between the inner and outer diameters of the through hole land): 0.25 mm Through hole pitch: 2.5mm Number of through hole lands: 48 Surface treatment: Cu-OSP

[0088] Next, the pretreated substrate was subjected to flow soldering by contacting molten solder in a nitrogen atmosphere. Thereafter, the fillet volumes of the boards that had been flow soldered were measured using a laser microscope (VK-X1050) manufactured by Keyence Corporation, and the average value of the fillet volumes was calculated. Furthermore, the number of bridges was visually counted for each board that had been subjected to flow soldering.

[0089] The evaluation criteria for fillet size and bridge occurrence are shown below.

[0090] Evaluation criteria for fillet size Passed: Fillet size is 1.400mm 3 End Rejected: Fillet size is 1.400mm 3 less than

[0091] Criteria for assessing bridge occurrence Pass: Zero bridges Fail: 1 or more bridges

[0092] [Table 1]

[0093] The flux of Example 1 contains rosin, an activator, and a solvent. The activator contains an imidazole compound and two kinds of dicarboxylic acids. 2-undecylimidazole is used as the imidazole compound, and succinic acid and malonic acid are used in combination as the two kinds of dicarboxylic acids. The flux of Comparative Example 7 contains rosin, an activator, and a solvent. The activator contains an imidazole compound and one kind of dicarboxylic acid. As the imidazole compound, 2-undecylimidazole is used. As the one kind of dicarboxylic acid, only malonic acid is used. The flux of Reference Example 1 has the same composition as the flux of Example 1. The flux of Reference Example 2 has the same composition as the flux of Comparative Example 7.

[0094] Comparison of Example 1 and Comparative Example 7: During flow soldering in which Sn-Bi solder is brought into contact with a pretreated substrate, it can be confirmed that the fillet size is larger when the flux of Example 1 is used than when the flux of Comparative Example 7 is used. It can also be seen that the occurrence of bridging was suppressed when the flux of Example 1 was used, whereas bridging occurred when the flux of Comparative Example 7 was used.

[0095] Reference Examples 1 and 2: When Sn-Ag-Cu based solder was brought into contact with a pretreated substrate for flow soldering, the fillet size was increased when the flux of Example 1 was used as well as when the flux of Comparative Example 7 was used, but bridging occurred.

[0096] From the results shown in Table 1, it was confirmed that when Sn-Bi based solder was brought into contact with a pretreated substrate and flow soldering was performed, the fillet size could be increased and the occurrence of bridges was suppressed only when the flux of Example 1 was used.

[0097] [Table 2]

[0098] Both the fluxes of Example 2 and Reference Example 3 contain rosin, an activator, and a solvent, the activator contains an imidazole compound and two dicarboxylic acids, 2-undecylimidazole is used as the imidazole compound, and adipic acid and malonic acid are used in combination as the two dicarboxylic acids. That is, the flux of Example 2 and the flux of Reference Example 3 have the same composition. When Sn-Ag-Cu solder was brought into contact with a pretreated substrate for flow soldering, the fillet size was increased, but bridging occurred (Reference Example 3). In contrast, it was confirmed that when Sn-Bi based solder was brought into contact with a pretreated substrate during flow soldering, the fillet size was increased and the occurrence of bridging was suppressed (Example 2).

[0099] Both the fluxes of Example 3 and Reference Example 4 contain rosin, an activator, and a solvent, the activator contains an imidazole compound and two kinds of dicarboxylic acids, 2-undecylimidazole is used as the imidazole compound, and sebacic acid and malonic acid are used in combination as the two kinds of dicarboxylic acids. That is, the flux of Example 3 and the flux of Reference Example 4 have the same composition. When Sn-Ag-Cu solder was brought into contact with a pretreated substrate for flow soldering, the fillet size was increased, but bridging occurred (Reference Example 4). In contrast, it was confirmed that when Sn-Bi based solder was brought into contact with a pretreated substrate during flow soldering, the fillet size was increased and the occurrence of bridging was suppressed (Example 3).

[0100] Both the fluxes of Example 13 and Reference Example 5 contain rosin, an activator, and a solvent, the activator contains an imidazole compound and two kinds of dicarboxylic acids, 2-undecylimidazole is used as the imidazole compound, and succinic acid and suberic acid are used in combination as the two kinds of dicarboxylic acids. That is, the flux of Example 13 and the flux of Reference Example 5 have the same composition. When Sn-Ag-Cu solder was brought into contact with a pretreated substrate for flow soldering, the fillet size was increased, but bridging occurred (Reference Example 5). In contrast, it was confirmed that when Sn-Bi based solder was brought into contact with a pretreated substrate during flow soldering, the fillet size was increased and the occurrence of bridging was suppressed (Example 13).

[0101] Both the fluxes of Example 14 and Reference Example 6 contain rosin, an activator, and a solvent, the activator contains an imidazole compound and two kinds of dicarboxylic acids, 2-undecylimidazole is used as the imidazole compound, and succinic acid and methylsuccinic acid are used in combination as the two kinds of dicarboxylic acids. That is, the flux of Example 14 and the flux of Reference Example 6 have the same composition. When Sn-Ag-Cu solder was brought into contact with a pretreated substrate for flow soldering, the fillet size was increased, but bridging occurred (Reference Example 6). In contrast, it was confirmed that when Sn-Bi based solder was brought into contact with a pretreated substrate during flow soldering, the fillet size was increased and the occurrence of bridging was suppressed (Example 14).

[0102] Both the fluxes of Example 15 and Reference Example 7 contain rosin, an activator, and a solvent, the activator contains an imidazole compound and two dicarboxylic acids, 2-undecylimidazole is used as the imidazole compound, and succinic acid and malic acid are used in combination as the two dicarboxylic acids. That is, the flux of Example 15 and the flux of Reference Example 7 have the same composition. When Sn-Ag-Cu solder was brought into contact with a pretreated substrate for flow soldering, the fillet size was increased, but bridging occurred (Reference Example 7). In contrast, it was confirmed that when Sn-Bi based solder was brought into contact with a pretreated substrate during flow soldering, the fillet size was increased and the occurrence of bridging was suppressed (Example 15).

[0103] From the results shown in Tables 1 and 2, it can be seen that the effect of the flux of the embodiment to which the present invention is applied is remarkable when Sn-Bi based solder is used.

[0104] [Table 3]

[0105] All of the fluxes of Examples 1 to 12 contain rosin, an activator, and a solvent. The activator contains an imidazole compound and two kinds of dicarboxylic acids. As the imidazole compound, 2-undecylimidazole is used. As the two kinds of dicarboxylic acids, one selected from the group consisting of succinic acid, adipic acid, and sebacic acid is used in combination with malonic acid (corresponding to the flux of the first embodiment). From the results shown in Table 3, it can be seen that when the fluxes of Examples 1 to 12 are used in flow soldering in which Sn-Bi solder is brought into contact with a pretreated substrate, the fillet size can be increased and the occurrence of bridges is suppressed.

[0106] [Table 4]

[0107] The fluxes of Examples 1, 13, 4, 5, 14, 15, 16, 6, and 12 all contain rosin, an activator, and a solvent. The activator contains an imidazole compound and two kinds of dicarboxylic acids. 2-undecylimidazole is used as the imidazole compound. As the two kinds of dicarboxylic acids, one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid is used in combination with succinic acid (corresponding to the flux of the second embodiment). From the results shown in Table 4, it can be seen that when the fluxes of Examples 1, 13, 4, 5, 14, 15, 16, 6, and 12 are used in flow soldering in which Sn-Bi based solder is brought into contact with a pretreated substrate, the fillet size can be increased and the occurrence of bridges is suppressed.

[0108] [Table 5]

[0109] The fluxes of Comparative Examples 1 to 3 and 8 all contain a combination of two dicarboxylic acids different from the combination (1) or combination (2) of two dicarboxylic acids, and are outside the scope of the present invention. The flux of Comparative Example 4 contains three types of dicarboxylic acids and is outside the scope of the present invention. The flux of Comparative Example 5 does not contain a dicarboxylic acid and is outside the scope of the present invention. The fluxes of Comparative Examples 6, 7 and 12 all contained only one dicarboxylic acid and are outside the scope of the present invention. The flux of Comparative Example 9 does not contain an imidazole compound and is outside the scope of the present invention. The fluxes of Comparative Examples 10 and 11 both contain an amine compound other than an imidazole compound, and are outside the scope of the present invention.

[0110] From the results shown in Table 5, when the fluxes of Comparative Examples 1 to 12 were used in flow soldering in which Sn-Bi solder was brought into contact with a pretreated substrate, either one or both of the evaluations of fillet size and bridge occurrence were poor.

[0111] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Addition, omission, substitution, and other modifications of the configuration are possible without departing from the spirit of the present invention. The present invention is not limited by the above description, but is limited only by the scope of the attached claims.

Claims

1. A flux for soldering using Sn-Bi based solder, comprising: Contains rosin, an activator, and a solvent; The activator comprises an imidazole compound and two dicarboxylic acids, The two dicarboxylic acids are a combination (1) of one selected from the group consisting of succinic acid, adipic acid, and sebacic acid (dicarboxylic acid (1c)) and malonic acid, The content of the rosin is 3 mass% or more and 25 mass% or less with respect to the total mass (100 mass%) of the flux, The content of the imidazole compound is 0.1 mass% or more and 1.5 mass% or less with respect to the total mass (100 mass%) of the flux, the total content of the two dicarboxylic acids is 0.5% by mass or more and 6% by mass or less with respect to the total mass (100% by mass) of the flux, A flux (excluding those containing three or more dicarboxylic acids) in which the mass ratio of the dicarboxylic acid (1c) to malonic acid, expressed as a mass ratio of dicarboxylic acid (1c) / malonic acid, is 10 / 90 or more and 90 / 10 or less.

2. The flux described in claim 1, wherein the mass ratio of the dicarboxylic acid (1c) / malonic acid is 40 / 60 or more and 75 / 25 or less.

3. A flux for soldering using a Sn-Bi based solder, comprising: Contains rosin, an activator, and a solvent, The activator comprises an imidazole compound and two dicarboxylic acids, The two dicarboxylic acids are a combination (2) of one selected from the group consisting of suberic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid (dicarboxylic acid (2c)) and succinic acid, The content of the rosin is 3 mass% or more and 25 mass% or less with respect to the total mass (100 mass%) of the flux, The content of the imidazole compound is 0.1 mass% or more and 1.5 mass% or less with respect to the total mass (100 mass%) of the flux, the total content of the two dicarboxylic acids is 0.5% by mass or more and 6% by mass or less with respect to the total mass (100% by mass) of the flux, A flux (excluding those containing three or more dicarboxylic acids) in which the mass ratio of the dicarboxylic acid (2c) to succinic acid, expressed as a mass ratio of dicarboxylic acid (2c) / succinic acid, is 10 / 90 or more and 90 / 10 or less.

4. The flux described in claim 3, wherein the mass ratio of the dicarboxylic acid (2c) / succinic acid is 10 / 90 or more and 60 / 40 or less.

5. The mass ratio of the two dicarboxylic acids to the imidazole compound is The flux according to any one of claims 1 to 4, wherein the mass ratio represented by two kinds of dicarboxylic acids / imidazole compound is 0.30 or more and 50 or less.

6. The method includes a step of obtaining a joint by soldering a solder alloy to a surface of a substrate treated with the flux according to any one of claims 1 to 4, The method for producing a joint, wherein the solder alloy is an alloy containing Sn and Bi.

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