Flux and bonded body

Abstract

Disclosed are a flux containing rosin, an active agent, and a solvent, the active agent containing an imidazole compound and two dicarboxylic acids, the two dicarboxylic acids being combined with malonic acid using one selected from succinic acid, adipic acid, and sebacic acid, and a method for preparing a joined body using the flux. Or the soldering flux contains rosin, an active agent and a solvent, the active agent contains an imidazole compound and two dicarboxylic acids, and the two dicarboxylic acids are combined with succinic acid and one selected from suberic acid, sebacic acid, methylsuccinic acid, malic acid and malonic acid. According to the present invention, it is possible to provide a flux capable of increasing the leg size and suppressing the occurrence of bridging during soldering.

Description

Technical Field

[0001] This invention relates to a method for preparing flux and a bonding agent. Background Technology

[0002] Components are typically fixed to a substrate and electrically connected to the substrate by soldering. During soldering, methods such as flow soldering and reflow soldering are used, depending on the dimensions of the objects being joined.

[0003] For example, in flow soldering, flux is first applied to a substrate on which the component is mounted. Then, while conveying the substrate with the component, molten flux jetted from below the substrate is brought into contact with the soldering surface, thereby performing soldering.

[0004] Fluxes used in welding typically contain resin components, solvents, activators, etc. For example, Patent Document 1 discloses a flux containing rosin as a resin component, a solvent, and specific hydroxybenzoic acid and monocarboxylic acid as activators. The flux disclosed in Patent Document 1 is considered to be suitable for flow welding.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2024-34098 Summary of the Invention

[0008] The problem to be solved by the present invention

[0009] However, in recent years, from an energy-saving perspective, Sn-Bi-based solders containing Sn and Bi, which can be soldered at lower temperatures, have been used. When using Sn-Bi-based solders containing more Bi, their hard and brittle properties become a disadvantage, and the bond strength of the joined objects becomes a problem.

[0010] To address this issue, one approach is to increase the solder lead size (the size of the molten and solidified solder) to improve the joint strength. However, when using existing fluxes for soldering, issues such as poor solder lead shape or bridging may occur even if the solder lead size is increased, making it difficult to achieve both goals simultaneously.

[0011] The present invention was made in view of the above circumstances, and provides a flux that can increase the size of the solder leg and suppress the generation of bridging during soldering, as well as a method for preparing a joint using the flux.

[0012] Problem-solving methods

[0013] To address the aforementioned issues, the present invention employs the following structure.

[0014] [1] A flux containing rosin, an activator and a solvent, wherein the activator contains an imidazole compound and two dicarboxylic acids, wherein the two dicarboxylic acids are composed of a combination of dicarboxylic acid (1c) and malonic acid, wherein the dicarboxylic acid (1c) is selected from succinic acid, adipic acid and sebacic acid.

[0015] [2] A flux containing rosin, an activator and a solvent, wherein the activator contains an imidazole compound and two dicarboxylic acids, wherein the two dicarboxylic acids are composed of a combination of a dicarboxylic acid (2c) and succinic acid, wherein the dicarboxylic acid (2c) is selected from octanoic acid, sebacic acid, methylsuccinic acid, malic acid and malonic acid.

[0016] [3] According to the flux described in [1] or [2], wherein the mass ratio of the two dicarboxylic acids to the imidazole compound is 0.30 or more and 50 or less, expressed as a mass ratio of the two dicarboxylic acids / imidazole compound.

[0017] [4] The flux according to any one of [1] to [3], wherein the content of the imidazole compound is 0.1% by mass or more and 1.5% by mass or less relative to the total mass of the flux expressed in 100% by mass.

[0018] [5] The flux according to any one of [1] to [4], wherein the total content of the two dicarboxylic acids is 0.5% by mass or more and 6% by mass or less relative to the total mass of the flux expressed in 100% by mass.

[0019] [6] The flux according to any one of [1] to [5], wherein the rosin content is 3% by mass or more and 25% by mass or less relative to the total mass of the flux expressed in 100% by mass.

[0020] [7] The flux according to any one of [1] to [6], wherein the flux is a welding flux using Sn-Bi solder.

[0021] [8] The flux according to any one of [1] to [7], wherein the flux does not contain more than three dicarboxylic acids.

[0022] [9] The flux according to any one of [1], [3] to [8], wherein the mass ratio of the dicarboxylic acid (1c) to malonic acid is 10 / 90 or more and 90 / 10 or less, expressed as a mass ratio of dicarboxylic acid (1c) / malonic acid.

[0023]

[10] The flux according to any one of [2] to [8], wherein the mass ratio of the dicarboxylic acid (2c) to succinic acid is 10 / 90 or more and 90 / 10 or less, expressed as a mass ratio of dicarboxylic acid (2c) / succinic acid.

[0024]

[11] The flux according to any one of [1], [3] to [9], wherein the mass ratio of dicarboxylic acid (1c) / malonic acid is 40 / 60 or more and 75 / 25 or less.

[0025]

[12] The flux according to any one of [2] to [8] and

[10] , wherein the mass ratio of dicarboxylic acid (2c) to succinic acid is 10 / 90 or more and 60 / 40 or less.

[0026]

[13] A method for preparing a bonding body includes a step of obtaining the bonding body by welding a solder alloy onto the surface of a substrate treated with any one of the fluxes described in [1] to

[12] , wherein the solder alloy is composed of an alloy containing Sn and Bi.

[0027] Effects of the present invention

[0028] According to the present invention, a flux that can increase the size of the solder leg and suppress the formation of bridging during welding, and a method for preparing a joint using the flux, are provided.

[0029] This flux is suitable for use as a Sn-Bi based flux. Detailed Implementation

[0030] The following describes preferred examples of the preparation method of the flux and the bonding agent of the present invention. These examples are provided to better understand the spirit of the invention and are not intended to limit the invention unless otherwise specified. Changes, additions, omissions, etc., in quantity, material, amount, value, ratio, etc., are possible without departing from the spirit of the invention.

[0031] (Fluoride)

[0032] The flux of the first aspect of the present invention contains rosin, an activator, and a solvent, wherein the activator contains an imidazole compound and two dicarboxylic acids.

[0033] The flux contains two dicarboxylic acids, specifically a combination (1) or a combination (2) as described below.

[0034] Combination of two dicarboxylic acids (1): a combination of one of succinic acid, adipic acid, and sebacic acid (hereinafter sometimes referred to as dicarboxylic acid (1c)) and malonic acid.

[0035] Combination of two dicarboxylic acids (2): a combination of one of the following (hereinafter sometimes referred to as dicarboxylic acid (2c)) and succinic acid: octanoic acid, sebacic acid, methylsuccinic acid, malic acid and malonic acid.

[0036] That is, even if it is a flux containing dicarboxylic acid, flux containing only one dicarboxylic acid, flux containing two dicarboxylic acids that are different from the combination (1) or combination (2) said, or flux containing three or more dicarboxylic acids, are outside the scope of fluxes in this manner.

[0037] Therefore, for example, fluxes containing a combination (1) of the two dicarboxylic acids and two or more other dicarboxylic acids of the combination (1) are outside the scope of fluxes of this type because they also contain three or more dicarboxylic acids. In addition, fluxes containing two or three selected from succinic acid, adipic acid and sebacic acid and malonic acid also contain three or more dicarboxylic acids and are therefore outside the scope of fluxes of this type.

[0038] Similarly, fluxes containing a combination (2) of the two dicarboxylic acids and two or more other dicarboxylic acids of the combination (2) are also outside the scope of fluxes of this type. Fluxes containing two or more of octanoic acid, sebacic acid, methylsuccinic acid, malic acid and malonic acid and succinic acid are also outside the scope of fluxes of this type.

[0039] As one embodiment of the flux of this method, a flux containing rosin, an activator, a solvent and other ingredients as needed, wherein the activator contains an imidazole compound and a combination of the two dicarboxylic acids (1) (first embodiment).

[0040] As another embodiment of the flux of this method, a flux containing rosin, an activator, a solvent and other ingredients as needed, wherein the activator contains an imidazole compound and a combination of the two dicarboxylic acids (2) (second embodiment).

[0041] <First Implementation>

[0042] The flux of the first embodiment contains rosin, an activator, a solvent, and other ingredients as needed. The activator in the first embodiment contains an imidazole compound and a combination of the two dicarboxylic acids (1).

[0043] "rosin"

[0044] In this embodiment, "rosin" includes natural resins containing a mixture of abrasive acid and its isomers, with abrasive acid as the main component, as well as substances that have been chemically modified from natural resins (sometimes referred to as rosin derivatives).

[0045] The term "main component" as used here refers to the component that constitutes the compound and accounts for 40% or more of the compound by mass.

[0046] The content of rosin acid in natural resin is 40% by mass or more, which, as an example, is 40% by mass or more and less than 80% by mass relative to natural resin.

[0047] Representative examples of isomers of abietic acid include neorosinic acid, longleaf abietic acid, and L-piperidine.

[0048] Examples of the aforementioned "natural resins" include, for example, rosin, wood rosin, and oil rosin.

[0049] In this invention, "substances obtained by chemically modifying natural resins (rosin derivatives)" include substances obtained by subjecting the "natural resins" to one or more treatments selected from hydrogenation, dehydrogenation, neutralization, alkyl epoxide addition, amidation, dimerization and polymerization, esterification and Diels-Alder cyclization addition.

[0050] Examples of rosin derivatives include purified rosin and modified rosin.

[0051] Examples of modified rosin include, for example, hydrogenated rosin, polymerized rosin, polymerized hydrogenated rosin, disproportionated rosin, acid-modified rosin, rosin esters, 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, fumaric acid-modified rosin, etc.), as well as purified products, hydrides and disproportions of the polymerized rosin, as well as purified products, hydrides and disproportions of the α,β-unsaturated carboxylic acid modified products, rosin alcohol, rosin amine, hydrogenated rosin alcohol, rosin esters, hydrogenated rosin esters, rosin soap, hydrogenated rosin soap, acid-modified rosin soap, etc.

[0052] Examples of rosin amines include, for example, dehydrorosin amines and dihydrorosin amines. Rosin amines refer to so-called disproportionated rosin amines.

[0053] In the flux of the first embodiment, rosin can be used alone or in combination with two or more types.

[0054] The rosin preferably contains rosin derivatives, more preferably contains at least one selected from acid-modified rosin, hydrogenated rosin, polymerized rosin and acid-modified hydrogenated rosin, and even more preferably contains at least one selected from acid-modified hydrogenated rosin, hydrogenated rosin and polymerized rosin.

[0055] From a weldability viewpoint, acrylic acid-modified hydrogenated rosin is preferred as an acid-modified hydrogenated rosin. That is, the rosin preferably contains at least one selected from acrylic acid-modified hydrogenated rosin, hydrogenated rosin, and polymerized rosin.

[0056] The rosin used in the flux of this 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 polymerized rosin.

[0057] The rosin content in the flux of the first embodiment can be arbitrarily selected, and is preferably 3% or more and 25% or less relative to the total mass (100% by mass) of the flux, more preferably 4% or more and 20% or less by mass. It can also be 5% or more and 17% or less by mass, 8% or more and 15% or less by mass, etc.

[0058] Surfactants

[0059] The active agent in the first embodiment contains an imidazole compound and the following combination (1).

[0060] Imidazole compounds can refer to imidazoles, preferably compounds containing an imidazole ring. They also include compounds in which the nitrogen or carbon atoms on the imidazole ring are substituted with substituents.

[0061] Combination of two dicarboxylic acids (1): a combination of succinic acid, adipic acid, and sebacic acid with malonic acid.

[0062] ·Imidazole compounds

[0063] Examples of imidazole compounds include, for example, 2-methylimidazolium, 2-ethylimidazolium, 2-undecylimidazolium, 2-heptadecylimidazolium, 1,2-dimethylimidazolium, 2-ethyl-4-methylimidazolium, 1-cyanoethyl-2-methylimidazolium, 1-cyanoethyl-2-undecylimidazolium, 1-cyanoethyl-2-ethyl-4-methylimidazolium; 2-phenylimidazolium, 2-phenylimidazolium isocyanuric acid adduct, 2-phenyl-4-methylimidazolium, 2-phenyl-4,5-dihydroxymethylimidazolium, 2-phenyl-4-methyl-5-hydroxymethylimidazolium, and 1-cyanoethyl-2-phenylimidazolium. Imidazole, 1-benzyl-2-phenylimidazolium, 1-benzyl-2-methylimidazolium; epoxy-imidazolium adducts; 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; etc.

[0064] In the flux of the first embodiment, the imidazole compound may be used alone or in combination with two or more.

[0065] Of the above, as an imidazole compound, an alkyl-substituted imidazole compound is preferred, more preferably an imidazole compound selected from 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 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole and 2-ethyl-4-methylimidazole, and most preferably 2-undecylimidazole.

[0066] • Combination of two dicarboxylic acids (1)

[0067] The combination of two dicarboxylic acids (1) is any one of the following: a combination of succinic acid and malonic acid, a combination of adipic acid and malonic acid, or a combination of sebacate and malonic acid.

[0068] In the combination (1), from the viewpoint of solder lead size, the combination of succinic acid and malonic acid, the combination of sebacic acid and malonic acid are more preferred, and the combination of succinic acid and malonic acid is even more preferred.

[0069] The mass ratio of succinic acid, adipic acid, and sebacic acid (also referred to as "dicarboxylic acid (1c)") to malonic acid in the combination (1) 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.

[0070] The content of the imidazole compound in the flux of the first embodiment can be arbitrarily selected. Relative to the total mass (100% by mass) of the flux, it is preferably 0.1% by mass or more and 2.0% by mass or less, more preferably 0.3% by mass or more and 1.8% by mass or less, even more preferably 0.5% by mass or more and 1.5% by mass or less, and even more preferably 0.7% by mass or more and 1.5% by mass or less.

[0071] The total content of the two dicarboxylic acids in the flux of the first embodiment can be arbitrarily selected, and is preferably 0.5% by mass or more and 6% by mass or less, more preferably 1% by mass or more and 4% by mass or less, relative to the total mass (100% by mass) of the flux. For example, it can be 0.7% by mass or more and 5% by mass or 2.0% by mass or more and 3.0% by mass or less.

[0072] In the flux of the first embodiment, the mass ratio of the combination of two dicarboxylic acids (1) to the imidazole compound, expressed as a 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. For example, it may also be 1 or more and 20 or less, 1 or more and 5 or less, 1 or more and 3 or less, etc.

[0073] When the mass ratio of the two dicarboxylic acid / imidazolium compounds is within the preferred range described above, the solder lead size can be easily controlled.

[0074] Other surfactants

[0075] In the first embodiment, in addition to the combination of imidazole compound and two dicarboxylic acids (1), other active agents may be included as needed.

[0076] Other active agents include halogenated compounds, organic acids other than dicarboxylic acids, and organophosphorus compounds.

[0077] Examples of halogen compounds include, for example, hydrohalates and other organic halogen compounds.

[0078] Amino halides are compounds formed by reacting amines with hydrogen halides. Examples of amines include aliphatic amines, guanidines, and azoles. Examples of hydrogen halides include, for example, hydrides of chlorine, bromine, and iodine.

[0079] Examples of aliphatic amines include ethylamine, dimethylamine, diethylamine, triethylamine, 2-ethylhexylamine, cyclohexylamine, and ethylenediamine. Examples of guanidines include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylguanidine, 1,3-di-o-isopropylphenylguanidine, and 1,3-di-o-isopropylphenyl-2-propionylguanidine.

[0080] Other than amine hydrohalides, organohalogen compounds include, for example, halogenated aliphatic compounds. Halogenated aliphatic compounds are compounds in which some or all of the hydrogen atoms constituting the aliphatic hydrocarbon group are replaced by halogen atoms.

[0081] Examples of halogenated aliphatic compounds include halogenated aliphatic alcohols and halogenated heterocyclic compounds. Examples of halogenated aliphatic alcohols include, for instance, 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-1,4-butanediol, 1,4-dibromo-2-butanol, and trans-2,3-dibromo-2-buten-1,4-diol.

[0082] Alternatively, halogen compounds may be used, for example, as salts formed by reacting amines with tetrafluoroboric acid (HBF4) or complexes formed by reacting amines with boron trifluoride (BF3).

[0083] In addition, when using halogen compounds as activators, one type can be used alone, or two or more types can be used in combination.

[0084] As a halogen compound, it is preferably selected from at least one of amine hydrohalates and halogenated aliphatic alcohols, and more preferably, amine hydrohalates and halogenated aliphatic alcohols are used together.

[0085] The content of halogen compounds in the flux of the first embodiment can be arbitrarily selected, and is preferably 0.1% by mass or more and 2% by mass or less, more preferably 0.5% by mass or more and 1.5% by mass or less, relative to the total mass (100% by mass) of the flux. For example, it can be 0.3% by mass or more and 1.2% by mass or 0.7% by mass or more and 1.5% by mass or less, etc.

[0086] Examples of organic acids other than dicarboxylic acids include carboxylic acids and organic sulfonic acids. Examples of carboxylic acids include aliphatic monocarboxylic acids and aromatic carboxylic acids.

[0087] Examples of aliphatic monocarboxylic acids include, for example, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, isononanoic acid, decanoic acid, decenoic acid, lauric acid (dodecanoic acid), undecanoic acid, 5-dodecenoic acid, tridecanoic acid, myristone acid, pentadecanoic acid, isopalmitic acid, palmitoleic acid, hexadecanetrienoic acid, cyclopentene undecanoic acid, heptadecanic acid, isostearic acid, transoleic acid, parsleyic acid, stearatetraenoic acid, tung acid, tarric acid, isoleic acid, ricinoleic acid, piperidinic acid, styracidin, styracidin, isoleic acid, ricinoleic acid, piperidinic acid, styracidin, nonadecanic 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)butyric acid.

[0088] Examples of aromatic monocarboxylic acids include, for example, 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-anesic acid; pyridinecarboxylic acid, 3-hydroxypyridinecarboxylic acid, etc.

[0089] Examples of organic sulfonic acids include, for example, aliphatic sulfonic acids and aromatic sulfonic acids. Examples of aliphatic sulfonic acids include, for example, alkyl sulfonic acids and alkanol sulfonic acids. Examples of aromatic sulfonic acids include, for example, 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.

[0090] When using organic acids other than dicarboxylic acids as other active agents, one can be used alone or in combination with two or more.

[0091] The content of organic acids other than dicarboxylic acids in the flux of the first embodiment can be arbitrarily selected, and is preferably 0.1% by mass or more and 2% by mass or less, more preferably 0.5% by mass or more and 1.5% by mass or less, relative to the total mass (100% by mass) of the flux. For example, it can be 0.3% by mass or more and 1.2% by mass or 0.7% by mass or more and 1.0% by mass or less. In addition, organic acids other than dicarboxylic acids may not be present in the flux. For example, the flux may not contain organic acids different from dicarboxylic acids.

[0092] Examples of organophosphorus compounds include, for example, acidic phosphate esters, acidic phosphonates, and acidic hypophosphonates.

[0093] The total content of the activator in the flux of the first embodiment can be arbitrarily selected. Relative to the total mass (100% by mass) of the flux, it can be, for example, 2% by mass or more and 10% by mass or less, or 2% by mass or more and 9% by mass or less. It can also be 3% by mass or more and 8% by mass or 4% by mass or more and 6% by mass or less.

[0094] Solvent

[0095] Examples of solvents used in the first embodiment include water, alcohol solvents, glycol ether solvents, and terpineols.

[0096] Examples of alcohol-based solvents include ethanol, 1-propanol, 2-propanol (isopropanol), 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-hexyn-2,5-diol, 2,3-dimethyl-2,3-butanediol, 2-methylpentane-2,4-diol, and 1,1,1-tris( Hydroxymethyl 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-cyclohexanediol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2-hexyl-1-decol, 2-methyl-2,4-pentanediol (hexanediol), octanediol, etc.

[0097] Examples of glycol ether solvents include diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, ethylene glycol monobutyl ether (ethylene glycol butyl ether), ethylene glycol monohexyl ether (ethylene glycol hexyl ether), diethylene glycol monohexyl ether (hexyl diethylene glycol), diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, methyl glycerol, triethylene glycol butyl methyl ether, tetraethylene glycol, tetraethylene glycol dimethyl ether, and tripropylene glycol n-butyl ether.

[0098] Examples of terpineols include α-terpineol, β-terpineol, γ-terpineol, and mixtures of terpineols (i.e., mixtures whose main component is α-terpineol and which contain β-terpineol or γ-terpineol).

[0099] Other solvents include, for example, di(2-ethylhexyl) sebacate and liquid paraffin.

[0100] In the flux of the first embodiment, a single solvent may be used, or two or more solvents may be used in combination.

[0101] As a solvent, it is preferred to contain a solvent with a boiling point below 100°C, more preferably an alcohol solvent, and even more preferably contains at least one selected from ethanol and 2-propanol, particularly preferably contains 2-propanol.

[0102] The solvent content in the flux of the first embodiment can be arbitrarily selected. Relative to the total mass (100% by mass) of the flux, it can be, for example, 60% by mass or more, 70% by mass or more and 95% by mass or less, 75% by mass or more and 95% by mass or less, or 80% by mass or more and 90% by mass or less.

[0103] Other Ingredients

[0104] In addition to rosin, activator, and solvent, the flux of the first embodiment may contain other ingredients as needed.

[0105] Other components may include, for example, resin components other than rosin, thixotropic agents, surfactants, metal passivators, antioxidants, silane coupling agents, colorants, etc. The flux of the first embodiment may also be a composition containing rosin, imidazole compounds, a combination of the two dicarboxylic acids (1), and a solvent, but without thixotropic agents.

[0106] As explained above, in the flux of the first embodiment, a specific organic acid is combined with a specific amine. That is, an imidazole compound is selected as the specific amine, and malonic acid, selected from succinic acid, adipic acid, and sebacic acid, is used as the specific organic acid. Although the reason is not yet clear, a unique interaction resulting from the combination of such a specific amine and a specific organic acid is obtained in the flux of the first embodiment. Therefore, it is believed that during soldering, the solder leg size can be increased and the generation of bridging can be suppressed.

[0107] The effects of the flux of the first embodiment are particularly significant when using an alloy containing Sn and Bi. That is, the flux of the first embodiment is suitable for use as a Sn-Bi based flux. Sn-Bi based solder may contain only Sn and Bi, or it may be an alloy composed only of Sn and Bi, or it may be an alloy containing Sn and Bi. The amount of Sn may be, for example, 30-80%, 40-70%, etc., and the amount of Bi may be, for example, 20-70%, 30-60%, etc.

[0108] <Second Implementation>

[0109] The flux of the second embodiment contains rosin, an activator, a solvent, and other ingredients as needed. The activator in the second embodiment contains an imidazole compound and a combination of the two dicarboxylic acids (2).

[0110] "rosin"

[0111] The description of rosin in the second embodiment is the same as that in the first embodiment described above.

[0112] In the flux of the second embodiment, rosin can be used alone or in combination with two or more types.

[0113] The rosin preferably contains rosin derivatives, more preferably contains at least one selected from acid-modified rosin, hydrogenated rosin, polymerized rosin and acid-modified hydrogenated rosin, and even more preferably contains at least one selected from acid-modified hydrogenated rosin, hydrogenated rosin and polymerized rosin.

[0114] From a weldability viewpoint, acrylic acid-modified hydrogenated rosin is preferred as an acid-modified hydrogenated rosin. That is, the rosin preferably contains at least one selected from acrylic acid-modified hydrogenated rosin, hydrogenated rosin, and polymerized rosin.

[0115] The rosin used in the flux of this 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.

[0116] Relative to the total mass (100% by mass) of the flux, the rosin content in the flux of the second embodiment is preferably 3% by mass or more and 25% by mass or less, more preferably 4% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less.

[0117] Surfactants

[0118] The active agent in the second embodiment contains an imidazole compound and the following combination (2). A combination of two dicarboxylic acids (2): a combination of one selected from succinic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid with succinic acid.

[0119] ·Imidazole compounds

[0120] As an imidazole compound, the same substances as those exemplified in the description of the imidazole compound in the first embodiment can be cited.

[0121] In the flux of the second embodiment, imidazole compounds may be used alone or in combination with two or more.

[0122] Among them, as an imidazole compound, an alkyl-substituted imidazole compound is preferred, more preferably an imidazole compound selected from 2-methylimidazolium, 2-ethylimidazolium, 2-undecylimidazolium, 2-heptadecylimidazolium, 1,2-dimethylimidazolium, 2-ethyl-4-methylimidazolium, 1-cyanoethyl-2-methylimidazolium, 1-cyanoethyl-2-undecylimidazolium and 1-cyanoethyl-2-ethyl-4-methylimidazolium, even more preferably an imidazole compound selected from 2-methylimidazolium, 2-ethylimidazolium, 2-undecylimidazolium, 2-heptadecylimidazolium, 1,2-dimethylimidazolium and 2-ethyl-4-methylimidazolium, and most preferably 2-undecylimidazolium.

[0123] • Combination of two dicarboxylic acids (2)

[0124] The combination of two dicarboxylic acids (2) is the combination of octanoic acid and succinic acid, the combination of sebacic acid and succinic acid, the combination of methyl succinic acid and succinic acid, the combination of malic acid and succinic acid, or the combination of malonic acid and succinic acid.

[0125] In the combination (2), from the viewpoint of solder lead size, the combination of malonic acid and succinic acid, the combination of octanoic acid and succinic acid, the combination of sebacic acid and succinic acid, and the combination of methylsuccinic acid and succinic acid are more preferred, and the combination of malonic acid and succinic acid and the combination of sebacic acid and succinic acid are even more preferred.

[0126] The mass ratio of succinic acid (selected from one of octanoic acid, sebacic acid, methylsuccinic acid, malic acid and malonic acid, also referred to as "dicarboxylic acid (2c)" as described above) to succinic acid in 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.

[0127] The content of the imidazole compound in the flux of the second embodiment can be arbitrarily selected. Relative to the total mass (100% by mass) of the flux, it is preferably 0.1% by mass or more and 2.0% by mass or less, more preferably 0.3% by mass or more and 1.8% by mass or less, even more preferably 0.5% by mass or more and 1.5% by mass or less, and even more preferably 0.7% by mass or more and 1.5% by mass or less.

[0128] The total content of the two dicarboxylic acids in the flux of the second embodiment can be arbitrarily selected, and is preferably 0.5% by mass or more and 6% by mass or less, more preferably 1% by mass or more and 4% by mass or less, relative to the total mass (100% by mass) of the flux. For example, it can be 0.7% by mass or more and 5% by mass or 2.0% by mass or more and 3.0% by mass or less.

[0129] In the second embodiment, the mass ratio of the combination of two dicarboxylic acids (2) to the imidazole compound in the flux 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. It may also be 1 or more and 20 or less, 1 or more and 5 or less, 1 or more and 3 or less, etc.

[0130] When the mass ratio of the two dicarboxylic acid / imidazolium compounds is within the preferred range described above, the solder lead size can be easily controlled.

[0131] Other surfactants

[0132] In the second embodiment, in addition to the combination of imidazole compounds and two dicarboxylic acids (2), other active agents may be included as needed.

[0133] Other active agents include halogenated compounds, organic acids other than dicarboxylic acids, and organophosphorus compounds. The description of other active agents in the second embodiment may include substances identical to those exemplified in the description of other active agents in the first embodiment described above.

[0134] When using halogen compounds as activators, one can be used alone, or two or more can be used in combination.

[0135] As a halogen compound, it is preferably selected from at least one of amine hydrohalates and halogenated aliphatic alcohols, and more preferably, amine hydrohalates and halogenated aliphatic alcohols are used together.

[0136] The content of halogen compounds in the flux of the second embodiment can be arbitrarily selected, and is preferably 0.1% by mass or more and 2% by mass or less relative to the total mass (100% by mass) of the flux, more preferably 0.5% by mass or more and 1.5% by mass or less. For example, it can be 0.3% by mass or more and 1.2% by mass or 0.7% by mass or more and 1.5% by mass or less, etc.

[0137] The total content of the activator in the flux of the second embodiment can be arbitrarily selected, and relative to the total mass (100% by mass) of the flux, for example, it is 2% by mass or more and 10% by mass or less, or it can be 2% by mass or more and 9% by mass or less. It can also be 3% by mass or more and 8% by mass or 4% by mass or 6% by mass or less.

[0138] Solvent

[0139] Examples of solvents used in the second embodiment include water, alcohol-based solvents, glycol ether-based solvents, and terpineols. Regarding the description of the solvent in the second embodiment, the same solvents exemplified in the description of the solvent in the first embodiment described above can be used.

[0140] In the flux of the second embodiment, a single solvent may be used, or two or more solvents may be used in combination.

[0141] As a solvent, it is preferred to contain a solvent with a boiling point below 100°C, more preferably an alcohol solvent, and even more preferably contains at least one selected from ethanol and 2-propanol, particularly preferably contains 2-propanol.

[0142] The solvent content in the flux of the second embodiment can be arbitrarily selected. Relative to the total mass (100% by mass) of the flux, it can be, for example, 60% by mass or more, 70% by mass or more and 95% by mass or less, 75% by mass or more and 95% by mass or less, or 80% by mass or more and 90% by mass or less.

[0143] Other Ingredients

[0144] In addition to rosin, activator, and solvent, the flux of the second embodiment may contain other ingredients as needed.

[0145] Other components may include, for example, resin components other than rosin, thixotropic agents, surfactants, metal passivators, antioxidants, silane coupling agents, colorants, etc. The flux of the second embodiment may also be a composition containing rosin, imidazole compounds, a combination of the two dicarboxylic acids mentioned above (2), and a solvent, but without thixotropic agents.

[0146] As explained above, in the flux of the second embodiment, a specific organic acid is combined with a specific amine. That is, an imidazole compound is selected as the specific amine, and succinic acid, selected from octanoic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid, is used as the specific organic acid. Although the reason is not yet clear, a unique interaction resulting from the combination of such a specific amine and a specific organic acid is obtained in the flux of the second embodiment. Therefore, it is believed that during soldering, the solder leg size can be increased and the generation of bridging can be suppressed.

[0147] The effects of the flux of the second embodiment are particularly significant when using alloys containing Sn and Bi. That is, the flux of the second embodiment is suitable for use as a Sn-Bi based flux.

[0148] (Preparation method of the conjugate)

[0149] The second embodiment of the present invention provides a method for preparing a bond comprising the following steps: obtaining a bond by soldering a solder alloy onto the surface of a substrate treated with the flux of the first embodiment described above. The flux alloy is composed of an alloy containing Sn and Bi.

[0150] As one embodiment of the method for preparing the joint in this manner, a preparation method comprising a component mounting step, a flux application step, a preheating step, and a welding step in sequence can be cited. The flux used is either the flux of the first embodiment or the flux of the second embodiment described above.

[0151] In the component mounting process, the component is mounted onto the substrate.

[0152] As an example of a component mounting process, an automatic insertion machine can be used to insert the lead or terminal of the component into a through hole in the substrate, and then nail the protruding lead or terminal to secure it, thereby fixing the component to the substrate.

[0153] The substrate can be chosen arbitrarily; for example, printed wiring substrates can be used.

[0154] The components can be chosen arbitrarily; for example, integrated circuits, transistors, diodes, resistors, capacitors, etc.

[0155] In the flux coating process, the flux of the above embodiment is applied to the soldering surface of the substrate on which the component is mounted.

[0156] Examples of flux coating devices include spray flux applicators and foam flux applicators. Among these, spray flux applicators are preferred from the viewpoint of coating amount stability.

[0157] From a weldability perspective, the preferred flux application rate is 30–180 mL / m. 2 It can be 40-150 mL / m 2 It can also be 50-120 mL / m 2 .

[0158] In the preheating process, the substrate on which the components are mounted is preheated. In the preheating process, the temperature of the heating substrate is preferably 80 to 130°C, more preferably 90 to 120°C.

[0159] In the welding process, the welding surface of the substrate on which the component is mounted is brought into contact with molten solder formed by melting the solder alloy.

[0160] As a method for bringing molten solder into contact with the soldering surface, any method that enables the molten solder to contact the substrate is acceptable and is not particularly limited. Examples of such methods include jetting and dipping.

[0161] The jetting method involves bringing the soldering surface of a substrate with mounted components into contact with a jet of molten solder. The immersion method involves bringing the soldering surface of a substrate with mounted components into contact with the surface of a stationary molten solder.

[0162] The method for preparing the joint in this embodiment is useful when using a solder alloy composed of an alloy containing Sn and Bi, and is particularly useful when using an alloy of Sn and Bi (Sn-Bi-based solder).

[0163] The welding conditions in the welding process can be appropriately set according to the melting point of the solder alloy. For example, when using Sn-Bi-based solder, the temperature of the molten solder is preferably 170 to 220°C, and more preferably 180 to 200°C.

[0164] As explained above, in the method for preparing the joint in this embodiment, the flux of the first embodiment or the flux of the second embodiment is applied to the welding surface. Therefore, when welding with an alloy containing Sn and Bi, the weld leg size can be increased and bridging can be suppressed. As a result, a joint with improved joint strength can be prepared. Furthermore, a highly reliable joint that is less prone to short circuits and reduced insulation can be prepared.

[0165] Example

[0166] The present invention will be described below through embodiments, but the present invention is not limited to the following embodiments.

[0167] <Preparation of Flux>

[0168] (Examples 1-16, Comparative Examples 1-12)

[0169] The fluxes of the prepared examples and comparative examples were prepared with the compositions shown in Tables 1 to 5.

[0170] In the table, the content of each component is expressed as a percentage (mass%) relative to the total mass (100% by mass) of the flux. The raw materials used are shown below.

[0171] ·rosin

[0172] Polymerized rosin, acrylic acid-modified hydrogenated rosin, partially hydrogenated rosin

[0173] Surfactant

[0174] Imidazole compound: 2-Undecylimidazol

[0175] Dicarboxylic acids: succinic acid, adipic acid, glutaric acid, octanoic acid, sebacic acid, malonic acid, maleic acid, methylsuccinic acid, malic acid

[0176] Other active agents: 1,3-diphenylguanidine, monoisopropanolamine, ethylamine hydrobromide, 1,3-diphenylguanidine hydrobromide, trans-2,3-dibromo-2-buten-1,4-diol, palmitic acid

[0177] Solvent

[0178] 2-Propanol (Isopropanol)

[0179] <Preparation of Experimental Solder>

[0180] Sn-Bi solder

[0181] As the master alloy, an ingot is prepared consisting of an alloy (Sn-58Bi) with Bi of 58% by mass and the balance Sn. The ingot is then melted to prepare molten solder.

[0182] Sn-Ag-Cu based solder

[0183] As the master alloy, an ingot is prepared consisting of an alloy with 3% by mass Ag, 0.5% by mass Cu, and the balance Sn (Sn-3Ag-0.5Cu). The ingot is melted to prepare molten solder.

[0184] <Evaluation of Flux>

[0185] As shown below, evaluations were conducted on solder lead dimensions and bridging associated with each flux. The results of these evaluations are presented in Tables 1–5.

[0186] [Evaluation of solder lead size and bridging effects]

[0187] Prepare 900 μL of flux for each embodiment and comparative example, and apply it by spraying to a substrate having the following through-hole pads (holes penetrating the substrate and the copper foil around them) to obtain a pretreated substrate.

[0188] Through-hole pads

[0189] Outline shape: Circular

[0190] Inner diameter (bore): 0.5mm

[0191] Through-hole pad width (half the difference between the inner and outer diameters of the through-hole pad): 0.25mm

[0192] Through-hole spacing: 2.5mm

[0193] n-number of through-hole pads: 48

[0194] Surface treatment: Cu-OSP

[0195] Next, flow soldering is performed by bringing molten solder into contact with the pretreated substrate under a nitrogen atmosphere.

[0196] Then, for the substrates that have undergone flow soldering, the solder leg volume is measured using a laser microscope (VK-X1050) manufactured by Keyence Corporation, and the average value of the solder leg volume is calculated.

[0197] In addition, for substrates that underwent flow soldering, bridging (solder bridging) was visually counted. Bridging can refer to, for example, molten solder flowing into areas where it shouldn't be and solidifying, resulting in an undesirable connection.

[0198] The following shows the evaluation criteria for solder leg size and various evaluations of bridging.

[0199] Evaluation criteria for weld leg size

[0200] Acceptable: Solder leg size is 1.400mm 3 above

[0201] Unacceptable: Weld leg size less than 1.400mm 3

[0202] Evaluation criteria in the evaluation of bridging

[0203] Pass: Bridging count is zero

[0204] Unacceptable: Bridging count is 1 or higher

[0205] [Table 1]

[0206]

[0207] (The amount of dicarboxylic acid and the evaluation results based on solder differences)

[0208] Comparison of Example 1 and Comparative Example 7 with Reference Examples 1 and 2

[0209] The flux of Example 1 contains rosin, an activator, and a solvent. The activator contains an imidazole compound and two dicarboxylic acids. 2-Undecylimidazolium is used as the imidazole compound, and succinic acid and malonic acid are used as the two dicarboxylic acids.

[0210] The flux of Comparative Example 7 contains rosin, an activator, and a solvent. The activator contains an imidazole compound and a dicarboxylic acid. 2-Undecylimidazolium is used as the imidazole compound, and malonic acid is used as the dicarboxylic acid.

[0211] The flux of Reference Example 1 has the same composition as the flux of Example 1.

[0212] The flux of Reference Example 2 has the same composition as the flux of Comparative Example 7.

[0213] Comparison of Example 1 and Comparative Example 7: (Sn-Bi based solder was used in the evaluation)

[0214] During flow soldering, in which Sn-Bi-based solder comes into contact with the pretreated substrate, it was confirmed that the solder lead size was larger when using the flux of Example 1 compared to the case where the flux of Comparative Example 7 was used.

[0215] Furthermore, it can be confirmed that using the flux of Example 1 can suppress the formation of bridging. Bridging occurred when using the flux of Comparative Example 7.

[0216] Refer to Examples 1 and 2: (Using Sn-Ag-Cu based solder in the evaluation)

[0217] During flow soldering, where Sn-Ag-Cu solder contacts a pretreated substrate, the solder pad size can be increased when using the flux of Example 1 and when using the flux of Comparative Example 7. However, bridging occurs in both cases.

[0218] The results shown in Table 1 confirm that during flow soldering where Sn-Bi-based flux contacts the pretreated substrate, the solder joint size can be increased and bridging can be suppressed only when the flux of Example 1 is used.

[0219] [Table 2]

[0220]

[0221] (Evaluation results based on solder variation)

[0222] Comparison of Example 2 and Reference Example 3

[0223] As shown in Table 2, the fluxes of Example 2 and Reference Example 3 both contain rosin, an activator, and a solvent. The activator contains an imidazole compound and two dicarboxylic acids; 2-undecylimidazolium is used as the imidazole compound, and adipic acid and malonic acid are used as the two dicarboxylic acids. That is, the flux of Example 2 and the flux of Reference Example 3 have the same composition.

[0224] In flow soldering where Sn-Ag-Cu solder comes into contact with a pretreated substrate, the solder lead size can be increased. However, bridging occurs (see Example 3).

[0225] In contrast, during flow soldering where Sn-Bi-based solder comes into contact with the pretreated substrate, it was found that the solder lead size could be increased and bridging was suppressed (Example 2).

[0226] Comparison of Example 3 and Reference Example 4

[0227] As shown in Table 2, the fluxes of Example 3 and Reference Example 4 both contain rosin, an activator, and a solvent. The activator contains an imidazole compound and two dicarboxylic acids. 2-Undecylimidazolium is used as the imidazole compound, and sebacic acid and malonic acid are used as the two dicarboxylic acids. That is, the flux of Example 3 and the flux of Reference Example 4 have the same composition.

[0228] During flow soldering, where Sn-Ag-Cu based solder is brought into contact with a pretreated substrate, although the solder lead size can be increased, bridging occurs (see Example 4). In contrast, during flow soldering, where Sn-Bi based solder is brought into contact with a pretreated substrate, it was found that the solder lead size can be increased and bridging is suppressed (Example 3).

[0229] Comparison of Example 13 and Reference Example 5

[0230] As shown in Table 2, the fluxes of Example 13 and Reference Example 5 both 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 octanoic acid are used as the two dicarboxylic acids. That is, the flux of Example 13 and the flux of Reference Example 5 have the same composition.

[0231] During flow soldering, where Sn-Ag-Cu based solder is brought into contact with a pretreated substrate, although the solder lead size can be increased, bridging occurs (see Example 5). In contrast, during flow soldering, where Sn-Bi based solder is brought into contact with a pretreated substrate, it was found that the solder lead size can be increased and bridging is suppressed (Example 13).

[0232] Comparison of Example 14 and Reference Example 6

[0233] As shown in Table 2, the fluxes of Example 14 and Reference Example 6 both contain rosin, an activator, and a solvent. The activator contains an imidazole compound and two dicarboxylic acids. 2-Undecylimidazolium is used as the imidazole compound, and succinic acid and methylsuccinic acid are used as the two dicarboxylic acids. That is, the flux of Example 14 and the flux of Reference Example 6 have the same composition.

[0234] During flow soldering, where Sn-Ag-Cu based solder is brought into contact with a pretreated substrate, although the solder lead size can be increased, bridging occurs (see Example 6). In contrast, during flow soldering, where Sn-Bi based solder is brought into contact with a pretreated substrate, it was found that the solder lead size can be increased and bridging is suppressed (Example 14).

[0235] Comparison of Example 15 and Reference Example 7

[0236] As shown in Table 2, the fluxes of Example 15 and Reference Example 7 both 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 as the two dicarboxylic acids. That is, the flux of Example 15 and the flux of Reference Example 7 have the same composition.

[0237] During flow soldering, where Sn-Ag-Cu based solder is brought into contact with a pretreated substrate, although the solder lead size can be increased, bridging occurs (see Example 7). In contrast, during flow soldering, where Sn-Bi based solder is brought into contact with a pretreated substrate, it was found that the solder lead size can be increased and bridging is suppressed (Example 15).

[0238] As can be seen from the results shown in Tables 1 and 2, the effect of using the flux of the embodiments of the present invention is significant when using Sn-Bi-based solder.

[0239] [Table 3]

[0240]

[0241] (Evaluation results of the flux of the first embodiment: Examples 1-12)

[0242] As shown in Table 3, the fluxes of Examples 1 to 12 all contain rosin, activator and solvent. The activator contains an imidazole compound and two dicarboxylic acids. 2-Undecylimidazolium is used as the imidazole compound. The two dicarboxylic acids are selected from one of succinic acid, adipic acid and sebacic acid and malonic acid (equivalent to the flux of the first embodiment).

[0243] The results shown in Table 3 confirm that, in flow soldering where Sn-Bi-based flux contacts the pretreated substrate, the fluxes of Examples 1 to 12 can increase the solder lead size and suppress bridging.

[0244] [Table 4]

[0245]

[0246] (Evaluation results of the flux in the second embodiment: Examples 1, 4-6, 12-16)

[0247] As shown in Table 4, 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 dicarboxylic acids. 2-Undecylimidazolium is used as the imidazole compound, and the two dicarboxylic acids are selected from one of octanoic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid, along with succinic acid (equivalent to the flux of the second embodiment).

[0248] The results shown in Table 4 confirm that, during flow soldering where Sn-Bi-based flux contacts the pretreated substrate, the fluxes of Examples 1, 13, 4, 5, 14, 15, 16, 6, and 12 can increase the solder lead size and suppress bridging.

[0249] [Table 5]

[0250]

[0251] (Evaluation results of flux in comparative examples)

[0252] As shown in Table 5, the fluxes of Comparative Examples 1 to 3 and 8 all contain two dicarboxylic acids in combinations different from the combination (1) or combination (2) of the two dicarboxylic acids, and are fluxes outside the scope of the present invention.

[0253] The flux of Comparative Example 4 contains three dicarboxylic acids, which are outside the scope of this invention.

[0254] The flux of Comparative Example 5 does not contain dicarboxylic acid and is outside the scope of this invention.

[0255] The fluxes in Comparative Examples 6, 7, and 12 all contain only one type of dicarboxylic acid, which is outside the scope of this invention.

[0256] The flux of Comparative Example 9 does not contain imidazole compounds and is outside the scope of this invention.

[0257] The fluxes of Comparative Examples 10 and 11 both contain amine compounds that are different from imidazole compounds, and are fluxes outside the scope of this invention.

[0258] As shown in Table 5, when the Sn-Bi flux is brought into contact with the pretreated substrate during flow soldering, when using the fluxes of Comparative Examples 1 to 12, either or both of the evaluation of solder lead size and the evaluation of bridging are poor results.

[0259] The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications to the structure are possible without departing from the spirit of the present invention. The present invention is not limited by the foregoing description, but only by the scope of the appended claims.

Claims

1. A flux for soldering Sn-Bi based solder, comprising rosin, an activator, and a solvent. The active agent contains an imidazole compound and two dicarboxylic acids. The two dicarboxylic acids are composed of a combination of dicarboxylic acid (1c) and malonic acid. The dicarboxylic acid (1c) is selected from succinic acid, adipic acid, and sebacic acid. The rosin content, relative to the total mass of flux (100% by mass), is 3% by mass or more and 25% by mass or less. The content of the imidazole compound relative to the total mass of the flux (100% by mass) is 0.1% by mass or more and 1.5% by mass or less. The total content of the two dicarboxylic acids relative to the total mass of the flux (100% by mass) is 0.5% by mass or more and 6% by mass or less. The mass ratio of the dicarboxylic acid (IC) to malonic acid, expressed as a dicarboxylic acid (IC) / malonic acid mass ratio, is 10 / 90 or more and 90 / 10 or less. Furthermore, the flux excludes fluxes containing three or more dicarboxylic acids.

2. The flux according to claim 1, wherein, The mass ratio expressed as dicarboxylic acid (1c) / malonic acid is 40 / 60 or more and 75 / 25 or less.

3. A flux for soldering Sn-Bi based solder, comprising rosin, an activator, and a solvent. The active agent contains an imidazole compound and two dicarboxylic acids. The two dicarboxylic acids are composed of a combination of dicarboxylic acid (2c) and succinic acid. The dicarboxylic acid (2c) is selected from one of octanoic acid, sebacic acid, methylsuccinic acid, malic acid, and malonic acid. The rosin content, relative to the total mass of flux (100% by mass), is 3% by mass or more and 25% by mass or less. The content of the imidazole compound relative to the total mass of the flux (100% by mass) is 0.1% by mass or more and 1.5% by mass or less. The total content of the two dicarboxylic acids relative to the total mass of the flux (100% by mass) is 0.5% by mass or more and 6% by mass or less. The mass ratio of the dicarboxylic acid (2c) to succinic acid, expressed as a dicarboxylic acid (2c) / succinic acid mass ratio, is 10 / 90 or more and 90 / 10 or less. Furthermore, the flux excludes fluxes containing three or more dicarboxylic acids.

4. The flux according to claim 3, wherein, The mass ratio expressed as dicarboxylic acid (2c) / succinic acid is 10 / 90 or more and 60 / 40 or less.

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

6. A method for preparing a bonding body, comprising the step of obtaining the bonding body by welding a solder alloy onto the surface of a substrate treated with the flux according to any one of claims 1 to 4, wherein the solder alloy is composed of an alloy containing Sn and Bi.

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