Water-soluble flux and solder paste

Abstract

This water-soluble flux capable of further suppressing the occurrence of voids contains a keto acid having a melting point of 40°C or lower and a solvent having a boiling point of 240°C or lower.

Description

[Technical Field]

[0001] The present invention relates to a water-soluble flux and a solder paste. This application claims priority based on Japanese Patent Application No. 2021-183673, filed on November 10, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Fixing components to a board and electrically connecting the components to the board are generally performed by soldering, which uses flux, solder powder, and a solder paste made by mixing the flux and solder powder. Flux chemically removes metal oxides present in the solder and the metal surfaces of the objects being soldered, allowing the movement of metal elements at the interface between the two. Therefore, when soldering is performed using flux, an intermetallic compound is formed between the two, resulting in a strong bond.

[0003] In soldering using solder paste, the solder paste is first printed on a board, components are then mounted, and the board with the components mounted is heated in a heating furnace called a reflow furnace, which melts the solder powder contained in the solder paste and solders the components to the board.

[0004] Generally, flux contains resin components, solvents, activators, thixotropic agents, etc. To improve the reliability of the bond between the solder and the objects to be joined, excess flux is removed by cleaning after soldering. Flux remaining after cleaning is called flux residue.

[0005] Conventionally, rosin, which has excellent electrical insulation properties and moisture resistance, has been used as the resin component in flux. However, flux containing rosin requires an organic solvent for cleaning after soldering, which can cause safety and environmental problems. Therefore, there has been a demand for a water-soluble flux that can be easily cleaned with water after soldering. In contrast, Patent Document 1 describes a flux containing an organic acid polyglycerol ester, a thixotropic agent, and a solvent with a specific SP value. The flux described in Patent Document 1 is said to improve the cleanability with water after soldering. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-43398 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, miniaturized components such as QFN (Quad Flat Non-Leaded Package) have come into use. QFNs have no leads around the periphery of the package, but have the exposed surface of the lead frame and electrode terminals on the backside of the package. Therefore, when soldering a QFN, the backside of the QFN is joined to the surface of the substrate with solder paste.

[0008] When the exposed surface of the lead frame and electrode terminals on the back of a package such as a QFN are soldered to a substrate, flux residue tends to remain on the back of the package. The flux residue remaining on the back of the package can cause voids. In contrast, it is difficult to prevent voids from occurring with the solder paste using the flux described in Patent Document 1.

[0009] Therefore, an object of the present invention is to provide a flux and a solder paste that can further suppress the occurrence of voids. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention employs the following configuration. That is, a first aspect of the present invention is a water-soluble flux containing a keto acid having a melting point of 40°C or less and a solvent having a boiling point of 240°C or less.

[0011] In the water-soluble flux according to the first aspect, the keto acid preferably has a boiling point of 250° C. or less.

[0012] In the water-soluble flux according to the first aspect, the content of the keto acid is preferably 10 to 25 mass % relative to the total mass (100 mass %) of the water-soluble flux.

[0013] In the water-soluble flux according to the first aspect, the keto acid preferably includes an organic acid having one carboxy group in the molecule.

[0014] In the water-soluble flux according to the first aspect, the keto acid preferably includes levulinic acid.

[0015] In the water-soluble flux according to the first aspect, the ratio of the keto acid to the solvent is preferably 0.60 to 4.0 in terms of a mass ratio expressed as solvent / keto acid.

[0016] The water-soluble flux according to the first aspect preferably further contains a nonionic surfactant and an amine.

[0017] The water-soluble flux according to the first aspect preferably does not contain one or more resin components selected from the group consisting of rosin and thermosetting resin.

[0018] A second aspect of the present invention is a solder paste containing a solder alloy powder and the water-soluble flux according to the first aspect. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a flux and a solder paste that can further suppress the occurrence of voids. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 10 is a diagram showing a reflow profile in the evaluation of the void area ratio. DETAILED DESCRIPTION OF THE INVENTION

[0021] (Water-soluble flux) The water-soluble flux according to this embodiment contains a keto acid and a solvent. In this specification, the water-soluble flux refers to a flux whose flux residue can be removed by washing with water. Hereinafter, the water-soluble flux may be simply referred to as flux.

[0022] As used herein, boiling point refers to the temperature of a liquid when its saturated vapor pressure is equal to 1 atmosphere (ie, 1013 hPa). In this specification, the melting point means the temperature at which a solid melts and becomes a liquid. The melting point values ​​of compounds in this specification are mainly those listed in "Chemical Handbook, Basic Edition, Revised 5th Edition (Chemical Society of Japan, Maruzen Publishing)."

[0023] <Keto acid> <Specific keto acids> The water-soluble flux according to this embodiment contains, as the specific keto acid, a keto acid having a melting point of 40° C. or less. The keto acid is a compound containing a ketone group and a carboxy group. In the present invention, the specific keto acid may be, for example, a compound represented by the following general formula (1):

[0024] The melting point of the specific keto acid is preferably 38° C. or lower. The melting point of the specific keto acid is preferably 5° C. or higher, more preferably 10° C. or higher, even more preferably 15° C. or higher, particularly preferably 20° C. or higher, and most preferably 25° C. or higher. When the melting point of the specific keto acid is equal to or lower than the upper limit, the fluidity of the flux residue can be increased even at lower temperatures, which makes it easier to remove voids from the flux residue.

[0025] [ka] [In the formula, R 1 R is a hydrocarbon group which may have a substituent. 2 represents a hydrocarbon group which may have a substituent or a single bond.

[0026] R 1 Examples of the hydrocarbon group in the formula include a chain hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group having 3 to 20 carbon atoms, an aromatic hydrocarbon group, -OR 11 etc. R 1 When is a chain hydrocarbon group, the chain hydrocarbon group may be linear or branched. The chain hydrocarbon group is a saturated hydrocarbon group or an unsaturated hydrocarbon group, and is preferably a saturated hydrocarbon group. R 1 When is an alicyclic hydrocarbon group, the alicyclic hydrocarbon group may be a polycyclic group or a monocyclic group. As a monocyclic alicyclic hydrocarbon group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane is preferred. As a polycyclic alicyclic hydrocarbon group, a group in which one or more hydrogen atoms have been removed from a polycycloalkane is preferred. R 1 Examples of the substituent in R include a carbonyl group, a carboxy group, a hydroxy group, an amino group, and a halogen atom. 1 Examples of the halogen atom in the formula include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. R 1When R is an aromatic hydrocarbon group, the aromatic hydrocarbon group is a hydrocarbon group having at least one aromatic ring, and examples thereof include aromatic hydrocarbon rings such as benzene, naphthalene, anthracene, and phenanthrene, aromatic heterocycles in which some of the carbon atoms constituting the aromatic hydrocarbon ring are substituted with heteroatoms, and fused rings in which an aromatic hydrocarbon ring and an aromatic heterocycle are fused together. 1 When the aromatic hydrocarbon group in has a substituent, examples of the substituent include a hydrocarbon group having 1 to 20 carbon atoms, a carboxy group, a hydroxy group, an amino group, a halogen atom, etc. When the substituent is a hydrocarbon group, examples of the hydrocarbon group include, for example, R 1 The hydrocarbon groups are the same as those in the above. -OR 11 R in 11 As mentioned above, R 1 The hydrocarbon groups are the same as those in the above. R 1 is preferably a chain hydrocarbon group. The number of carbon atoms in the chain hydrocarbon group is preferably 1 to 10, more preferably 1 to 5, still more preferably 1 to 3, and particularly preferably 1. Examples of hydrocarbon groups having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group.

[0027] R 2 Examples of the hydrocarbon group in R include a chain hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group having 3 to 20 carbon atoms, and an aromatic hydrocarbon group. 2 The substituents in 1 Examples of such examples include those mentioned above. R 2 When is a chain hydrocarbon group, the chain hydrocarbon group may be linear or branched. The chain hydrocarbon group is a saturated hydrocarbon group or an unsaturated hydrocarbon group, and is preferably a saturated hydrocarbon group. R 2The linear hydrocarbon group in is preferably a linear alkylene group, and specific examples thereof include a methylene group [-CH2-], an ethylene group [-(CH2)2-], a trimethylene group [-(CH2)3-], a tetramethylene group [-(CH2)4-], and a pentamethylene group [-(CH2)5-]. R 2 The branched hydrocarbon group in is preferably a branched alkylene group, and specific examples thereof include alkylmethylene groups such as -CH(CH3)-, -CH(CH2CH3)-, -C(CH3)2-, -C(CH3)(CH2CH3)-, -C(CH3)(CH2CH2CH3)-, and -C(CH2CH3)2-; alkylethylene groups such as -CH(CH3)CH2-, -CH(CH3)CH(CH3)-, -C(CH3)2CH2-, -CH(CH2CH3)CH2-, and -C(CH2CH3)2-CH2-; alkyltrimethylene groups such as -CH(CH3)CH2CH2- and -CH2CH(CH3)CH2-; and alkyltetramethylene groups such as -CH(CH3)CH2CH2CH2- and -CH2CH(CH3)CH2CH2-. R 2 is an alicyclic hydrocarbon group, the alicyclic hydrocarbon group is 1 Examples of the alicyclic hydrocarbon groups include those in which one hydrogen atom has been removed from the above-mentioned alicyclic hydrocarbon groups. R 2 is an aromatic hydrocarbon group, the aromatic hydrocarbon group is 1 Examples of the aromatic hydrocarbon groups include those in which one hydrogen atom has been removed from the aromatic hydrocarbon groups mentioned above. R 2 As the alkyl group, a chain hydrocarbon group is preferred, and a straight chain hydrocarbon group is more preferred. The number of carbon atoms in the chain hydrocarbon group is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3. The chain hydrocarbon group is preferably a methylene group, an ethylene group, or a trimethylene group.

[0028] Examples of specific keto acids include pyruvic acid (melting point: 13.6°C, boiling point: 165°C), levulinic acid (melting point: 37.2°C, boiling point: 245°C), 3-oxobutanoic acid (melting point: 36.5°C), 5-oxohexanoic acid (melting point: 13°C, boiling point: 274°C), 6-oxoheptanoic acid (melting point: 36°C, boiling point: 335°C), 7-oxooctanoic acid (melting point: 28°C, boiling point: 370°C), 2-oxobutanoic acid (melting point: 32°C, boiling point: 208°C), and 2-oxopentanoic acid (melting point: 7°C, boiling point: 230°C). The specific keto acids may be used alone or in combination of two or more.

[0029] The specific keto acid preferably contains an organic acid having one carboxy group in the molecule, which makes it easier to suppress the generation of voids. The specific keto acid preferably includes one or more selected from the group consisting of pyruvic acid and levulinic acid, and more preferably includes levulinic acid.

[0030] The boiling point (Tk) of the specific keto acid is preferably 150°C or higher, more preferably 200°C or higher, particularly preferably 220°C or higher, and most preferably 230°C or higher. When Tk is equal to or higher than the lower limit, complete volatilization of the specific keto acid during reflow is more easily suppressed. In addition, the specific solvent is more likely to volatilize before the specific keto acid. Therefore, during reflow, the specific keto acid volatilizes along with the solvent that has already begun to volatilize. As a result, during reflow, bubbles (voids) generated by the evaporation of the solvent and the specific keto acid merge with each other and grow larger, making it easier for the voids to be expelled from the solder paste. In other words, the generation of voids during reflow is more easily suppressed. Tk is preferably 280°C or less, more preferably 270°C or less, even more preferably 260°C or less, and particularly preferably 250°C or less. When Tk is equal to or less than the upper limit, the specific keto acid is more likely to volatilize together with the solvent during reflow. As a result, voids formed by the evaporation of the solvent and the specific keto acid during reflow merge with each other and become larger, making it easier for the voids to be expelled from the solder paste. In other words, the generation of voids during reflow is more easily suppressed. Tk is preferably 150°C or higher and 280°C or lower, more preferably 200°C or higher and 270°C or lower, even more preferably 220°C or higher and 260°C or lower, and particularly preferably 230°C or higher and 250°C or lower.

[0031] Other keto acids The water-soluble flux according to this embodiment may contain a keto acid having a melting point of more than 40° C. as the other keto acid. Other keto acids include, for example, oxaloacetic acid (melting point: 161°C), α-ketoglutaric acid (melting point: 113.5°C), acetonedicarboxylic acid (melting point: 138°C), α-ketoadipic acid (melting point: 127°C), and β-ketoadipic acid (melting point: 124-126°C). The other keto acids may be used singly or in combination of two or more.

[0032] The content of the specific keto acid in the flux is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, relative to the total amount (100% by mass) of the flux, and is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. For example, the content of the specific keto acid in the flux may be 10% by mass or more and 25% by mass or less, 15% by mass or more and 25% by mass or less, or 15% by mass or more and 20% by mass or less, relative to the total amount of the flux (100% by mass). The content of the specific keto acid in the flux is preferably 90% by mass or more, and more preferably 100% by mass, based on the total mass (100% by mass) of the keto acids. When the content of the specific keto acid is equal to or greater than the lower limit, the occurrence of voids can be more easily suppressed.When the content of the specific keto acid is equal to or less than the upper limit, the stability of the flux over time during storage can be improved.

[0033] <Solvent> <Specific solvent> The water-soluble flux according to this embodiment contains, as the specific solvent, a solvent (S1) having a boiling point of 240° C. or less. The lower limit of the boiling point of the specific solvent is not particularly limited, but may be, for example, 150° C. or more.

[0034] Examples of specific solvents include water, glycol ether-based solvents with a boiling point of 240°C or less, terpineols with a boiling point of 240°C or less, alcohol-based solvents with a boiling point of 240°C or less, and ester-based solvents with a boiling point of 240°C or less.

[0035] Examples of glycol ether solvents with a temperature of 240°C or less include phenyl glycol (boiling point 237°C: ethylene glycol monophenyl ether), butyl carbitol (boiling point 231°C: diethylene glycol monobutyl ether), and hexylene glycol (boiling point 197°C: 2-methylpentane-2,4-diol).

[0036] Terpineols with a boiling point of 240°C or less include, for example, α-terpineol (boiling point 217°C).

[0037] Examples of alcohol-based solvents having a boiling point of 240°C or less include ethanol (boiling point 78°C), 1-propanol (boiling point 97°C), 2-propanol (boiling point 82°C), 1,2-butanediol (boiling point 192°C), 2,2-dimethyl-1,3-propanediol (boiling point 210°C), 2,5-dimethyl-2,5-hexanediol (boiling point 215°C), 2,5-dimethyl-3-hexyne-2,5-diol (boiling point 206°C), 2,3-dimethyl-2,3-butanediol (boiling point 174°C), 2-methylpentane-2,4-diol (boiling point 197°C), and 1-ethynyl-1-cyclohexanol (boiling point 180°C). The specific solvent may be used alone or in combination of two or more.

[0038] The specific solvent preferably includes one or more selected from the group consisting of glycol ether-based solvents with a boiling point of 240°C or less, terpineols with a boiling point of 240°C or less, alcohol-based solvents with a boiling point of 240°C or less, and ester-based solvents with a boiling point of 240°C or less, and more preferably includes one or more selected from the group consisting of glycol ether-based solvents with a boiling point of 240°C or less, and terpineols with a boiling point of 240°C or less. The specific solvent more preferably includes one or more selected from the group consisting of phenyl glycol, hexylene glycol, and α-terpineol, and even more preferably includes α-terpineol.

[0039] The boiling point (Ts) of the specific solvent is preferably 150° C. or higher, more preferably 180° C. or higher, even more preferably 190° C. or higher, particularly preferably 200° C. or higher, and most preferably 210° C. or higher. When Ts is equal to or higher than the lower limit, the generation of voids is more easily suppressed. Ts is equal to or lower than 240° C., preferably equal to or lower than 235° C., more preferably equal to or lower than 230° C., and even more preferably equal to or lower than 225° C. When Ts is equal to or lower than the upper limit, the generation of voids can be more easily suppressed. Ts is preferably 150°C or higher and 240°C or lower, more preferably 180°C or higher and 235°C or lower, still more preferably 200°C or higher and 230°C or lower, and particularly preferably 210°C or higher and 225°C or lower.

[0040] The absolute value of the temperature difference ΔT between Tk and Ts is preferably 0°C or higher, more preferably 3°C or higher, and still more preferably 5°C or higher. When ΔT is at or above the lower limit value, it becomes easier to further suppress the generation of voids. ΔT is preferably 70°C or lower, more preferably 60°C or lower, and still more preferably 55°C or lower. When ΔT is at or below the upper limit value, it becomes easier to further suppress the generation of voids.

[0041] Furthermore, it is preferable that Tk and Ts satisfy the relationship Ts < Tk. When Ts < Tk, ΔT is preferably 5°C or higher and 50°C or lower, more preferably 10°C or higher and 45°C or lower, still more preferably 15°C or higher and 40°C or lower, and particularly preferably 20°C or higher and 35°C or lower. When ΔT is within the above range, it becomes easier to further suppress the generation of voids.

[0042] ≪Other solvents≫ The water-soluble flux according to the present embodiment may contain other solvents (that is, solvents other than the specific solvent). Examples of other solvents include glycol ether solvents having a boiling point exceeding 240°C, alcohol solvents having a boiling point exceeding 240°C, ester solvents having a boiling point exceeding 240°C, and the like.

[0043] Examples of glycol ether solvents having a boiling point of more than 240°C include diethylene glycol monohexyl ether (boiling point 258°C), diethylene glycol mono-2-ethylhexyl ether (boiling point 272°C), diethylene glycol dibutyl ether (boiling point 256°C), triethylene glycol monobutyl ether (boiling point 278°C), triethylene glycol butyl methyl ether (boiling point 261°C), tetraethylene glycol dimethyl ether (boiling point 275°C), and tripropylene glycol monomethyl ether (boiling point 243°C).

[0044] Examples of alcohol-based solvents having a boiling point of over 240°C include 2,4-diethyl-1,5-pentanediol (boiling point 264°C), 2-ethyl-2-hydroxymethyl-1,3-propanediol (boiling point 292°C), 2,2'-oxybis(methylene)bis(2-ethyl-1,3-propanediol) (boiling point 448°C), 1,2,6-trihydroxyhexane (boiling point 386°C), 1,4-cyclohexanediol (boiling point 293°C), 1,4-cyclohexanedimethanol (boiling point 283°C), 2,4,7,9-tetramethyl-5-decyne-4,7-diol (boiling point 255°C), 2,2-bis(hydroxymethyl)-1,3-propanediol (boiling point 437°C), and isobornylcyclohexanol (boiling point 318°C).

[0045] Examples of ester solvents having a boiling point of more than 240°C include bis(2-ethylhexyl) sebacate (boiling point: 377°C). The other solvents may be used singly or in combination of two or more.

[0046] The content of the specific solvent in the flux is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 15% by mass or more and 50% by mass or less, relative to the total amount of the flux (100% by mass). The content of the specific solvent in the flux is preferably 90% by mass or more, and more preferably 100% by mass, relative to the total mass (100% by mass) of the solvent. When the content of the specific solvent is equal to or greater than the lower limit, the occurrence of voids can be more easily suppressed.

[0047] The mixing ratio of the specific keto acid to the specific solvent, expressed as the mass ratio of specific solvent / specific keto acid, i.e., the ratio of the content of the specific solvent to the content of the specific keto acid, is preferably 0.60 to 4.0, more preferably 0.60 to 3.0, and even more preferably 0.60 to 2.5. If the mixing ratio is within the above-mentioned preferred range, the occurrence of voids can be more easily suppressed.

[0048] <Other ingredients> The flux in this embodiment may contain other components in addition to the keto acid and the solvent, as necessary. Examples of other components include organic acids other than keto acids, other activators such as amines and halogen compounds, surfactants, metal deactivators, silane coupling agents, antioxidants, and colorants.

[0049] [Organic acids other than keto acids] Examples of organic acids other than keto acids include carboxylic acids and organic sulfonic acids. Examples of the carboxylic acid include an aliphatic carboxylic acid and an aromatic carboxylic acid. Examples of carboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, eicosane diacid, salicylic acid, dipicolinic acid, dibutylaniline diglycolic acid, suberic acid, sebacic acid, terephthalic acid, dodecanedioic acid, parahydroxyphenylacetic acid, picolinic acid, phenylsuccinic acid, phthalic acid, lauric acid, benzoic acid, tartaric acid, tris(2-carboxyethyl) isocyanurate, 1,3-cyclohexanedicarboxylic acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butanoic acid, 2,3-dihydroxybenzoic acid, 2,4-diethylglutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, p-anisic acid, stearic acid, 12-hydroxystearic acid, oleic acid, hydroxybenzo ... Examples of the hydroxybenzoates include hydroxybenzoates, ...

[0050] Examples of dimer acids and trimer acids include dimer acids which are reaction products of oleic acid and linoleic acid, trimer acids which are reaction products of oleic acid and linoleic acid, dimer acids which are reaction products of acrylic acid, trimer acids which are reaction products of acrylic acid, dimer acids which are reaction products of methacrylic acid, trimer acids which are reaction products of methacrylic acid, dimer acids which are reaction products of acrylic acid and methacrylic acid, trimer acids which are reaction products of acrylic acid and methacrylic acid, dimer acids which are reaction products of oleic acid, trimer acids which are reaction products of oleic acid, dimer acids which are reaction products of linoleic acid, trimer acids which are reaction products of linolenic acid, trimer acids which are reaction products of linolenic acid, dimer acids which are reaction products of acrylic acid and oleic acid, trimer acids which are reaction products of acrylic acid and oleic acid, dimer acids which are reaction products of acrylic acid and linoleic acid, acrylic Examples of the dimer acid include a trimer acid which is a reaction product of acrylic acid and linoleic acid, a dimer acid which is a reaction product of acrylic acid and linoleic acid, a dimer acid which is a reaction product of methacrylic acid and oleic acid, a trimer acid which is a reaction product of methacrylic acid and linoleic acid, a dimer acid which is a reaction product of methacrylic acid and linoleic acid, a dimer acid which is a reaction product of methacrylic acid and linoleic acid, a dimer acid which is a reaction product of methacrylic acid and linoleic acid, a dimer acid which is a reaction product of methacrylic acid and linoleic acid, a dimer acid which is a reaction product of oleic acid and linolenic acid, a dimer acid which is a reaction product of linoleic acid and linolenic acid, a trimer acid which is a reaction product of linoleic acid and linolenic acid, a hydrogenated dimer acid which is a hydrogenated product of each of the above dimer acids, and a hydrogenated trimer acid which is a hydrogenated product of each of the above trimer acids. For example, dimer acid, a reaction product of oleic acid and linoleic acid, is a dimer with 36 carbon atoms. Also, trimer acid, a reaction product of oleic acid and linoleic acid, is a trimer with 54 carbon atoms.

[0051] Examples of organic sulfonic acids include aliphatic sulfonic acids, aromatic sulfonic acids, etc. Examples of aliphatic sulfonic acids include alkanesulfonic acids, alkanolsulfonic acids, etc.

[0052] Examples of alkanesulfonic acids include methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, decanesulfonic acid, and dodecanesulfonic acid. Examples of alkanol sulfonic acids include 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid, 1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid, 4-hydroxybutane-1-sulfonic acid, 2-hydroxyhexane-1-sulfonic acid, 2-hydroxydecane-1-sulfonic acid, and 2-hydroxydodecane-1-sulfonic acid. 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.

[0053] The organic acids other than keto acids may be used singly or in combination of two or more. The organic acid other than keto acid preferably includes one or more selected from the group consisting of carboxylic acids and organic sulfonic acids. The carboxylic acid preferably includes an aliphatic dicarboxylic acid, more preferably glutaric acid. The organic sulfonic acid preferably includes an aromatic sulfonic acid, more preferably p-toluenesulfonic acid. The content of the organic acid other than keto acid in the flux is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 6% by mass or less, relative to the total mass (100% by mass) of the flux.

[0054] The content of the specific keto acid in the flux is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, based on the total mass (100% by mass) of the organic acids. The upper limit of the content of the specific keto acid is not particularly limited, but may be 100% by mass. When the content of the specific keto acid is equal to or greater than the lower limit, the occurrence of voids can be more easily suppressed.

[0055] [Amine] Examples of the amine include azoles, guanidines, alkylamine compounds, aminoalcohol compounds, and amine polyoxyalkylene adducts.

[0056] Examples of azoles include 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, and 1-cyanoethyl-2-ethylimidazole. 1-cyanoethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl- s-Triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, 2-phenylimidazo Phosphorus, 2,4-diamino-6-vinyl-s-triazine, 2,4-diamino-6-vinyl-s-triazine isocyanuric acid adduct, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, epoxy-imidazole adduct, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-nonylbenzimidazole, 2-(4-thiazolyl)benzimidazole, benzimidazole, 1,2,4-Triazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol], 6-(2-benzotriazolyl)-4-tert-octyl-6'-tert-butyl-4'-methyl-2,2'-methylenebisphenol, 1,2,3-benzotriazolyl Examples of the benzotriazole include 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, 1-(1',2'-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-bis[(1H-benzotriazol-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, and 5-phenyltetrazole.

[0057] Examples of guanidines include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, 1,3-di-o-cumenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine.

[0058] Examples of alkylamine compounds include ethylamine, triethylamine, ethylenediamine, triethylenetetramine, cyclohexylamine, hexadecylamine, and stearylamine.

[0059] The amino alcohol compound may, for example, be monoisopropanolamine.

[0060] Examples of the amine polyoxyalkylene adducts include terminal diamine polyalkylene glycols, aliphatic amine polyoxyalkylene adducts, aromatic amine polyoxyalkylene adducts, and polyvalent amine polyoxyalkylene adducts. Examples of alkylene oxides from which the amine polyoxyalkylene adducts are derived include ethylene oxide, propylene oxide, and butylene oxide.

[0061] The diamine-terminated polyalkylene glycol is a compound in which both terminals of a polyalkylene glycol are aminated. Examples of diamine-terminated polyalkylene glycols include diamine-terminated polyethylene glycol, diamine-terminated polypropylene glycol, and diamine-terminated polyethylene glycol-polypropylene glycol copolymers. Examples of diamine-terminated polyethylene glycol-polypropylene glycol copolymers include polyethylene glycol-polypropylene glycol copolymer bis(2-aminopropyl) ether and polyethylene glycol-polypropylene glycol copolymer bis(2-aminoethyl) ether.

[0062] The aliphatic amine polyoxyalkylene adduct, aromatic amine polyoxyalkylene adduct, and polyvalent amine polyoxyalkylene adduct are compounds in which a polyoxyalkylene group is bonded to a nitrogen atom of an amine. Examples of the amine include ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, hexamethylenediamine, laurylamine, stearylamine, oleylamine, tallow amine, hardened tallow amine, tallow propyldiamine, m-xylenediamine, diethylenetriamine, metaxylenediamine, tolylenediamine, paraxylenediamine, phenylenediamine, isophoronediamine, 1,10-decanediamine, 1,12-dodecanediamine, 4,4-diaminodicyclohexylmethane, 4,4-diaminodiphenylmethane, butane-1,1,4,4-tetraamine, and pyrimidine-2,4,5,6-tetraamine. Examples of the aliphatic amine polyoxyalkylene adduct include polyoxyalkylene alkylamines. Examples of polyoxyalkylene alkylamines include polyoxyalkylene ethylenediamines. Polyoxyalkylene ethylenediamines are compounds in which at least one polyoxyalkylene group is bonded to any of the nitrogen atoms of ethylenediamine. Examples of polyoxyalkylene ethylenediamines include polyoxyethylene ethylenediamine, polyoxypropylene ethylenediamine, and polyoxyethylene polyoxypropylene ethylenediamine. Polyoxyethylene ethylenediamine is compounds in which one or more polyoxyethylene groups are bonded to any of the nitrogen atoms of ethylenediamine, and polyoxypropylene ethylenediamine is compounds in which one or more polyoxypropylene groups are bonded to any of the nitrogen atoms of ethylenediamine. Polyoxyethylene polyoxypropylene ethylenediamine is compounds in which at least one polyoxypropylene group or polyoxyethylene group is bonded to any of the nitrogen atoms of ethylenediamine. Examples of polyoxyalkyleneethylenediamines include N-polyoxypropyleneethylenediamine, N-polyoxyethyleneethylenediamine, N-polyoxyethylenepolyoxypropyleneethylenediamine, N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, and N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine.

[0063] The amines may be used alone or in combination of two or more. The amine preferably includes at least one selected from the group consisting of azoles, alkylamine compounds, and amine polyoxyalkylene adducts. The azoles preferably include 2-ethylimidazole. Preferably, the alkylamine compound comprises triethylenetetramine. The amine polyoxyalkylene adduct preferably comprises a terminal diamine polyalkylene glycol and / or an aliphatic amine polyoxyalkylene adduct. The aliphatic amine polyoxyalkylene adduct preferably contains polyoxyalkylene ethylenediamine, and more preferably contains N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine. The diamine-terminated polyalkylene glycol preferably includes a diamine-terminated polyethylene glycol-polypropylene glycol copolymer.

[0064] The total content of azoles and alkylamine compounds 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. The content of the aliphatic amine polyoxyalkylene adduct is preferably 10% by mass or more and 40% by mass or less, and more preferably 15% by mass or more and 30% by mass or less, relative to the total mass (100% by mass) of the flux.

[0065] [Halogen compounds] Examples of halogen compounds include amine hydrohalides and organic halogen compounds other than amine hydrohalides.

[0066] Amine hydrohalides are compounds obtained by reacting an amine with hydrogen halide. The amines include aliphatic amines, azoles, guanidines, etc. The hydrogen halides include, for example, chlorine, bromine, and iodine hydrides. Examples of the aliphatic amine include ethylamine, diethylamine, triethylamine, ethylenediamine, etc. Examples of the guanidines and azoles include those described above for the amines.

[0067] More specifically, examples of amine hydrohalides include cyclohexylamine hydrobromide, hexadecylamine hydrobromide, stearylamine hydrobromide, ethylamine hydrobromide, diphenylguanidine hydrobromide, ethylamine hydrochloride, stearylamine hydrochloride, diethylaniline hydrochloride, diethanolamine hydrochloride, 2-ethylhexylamine hydrobromide, pyridine hydrobromide, isopropylamine hydrobromide, diethylamine hydrobromide, dimethylamine hydrobromide, and dimethylamine hydrobromide. Hydrochloride, Rosinamine Hydrobromide, 2-Ethylhexylamine Hydrochloride, Isopropylamine Hydrochloride, Cyclohexylamine Hydrochloride, 2-Pipecoline Hydrobromide, 1,3-Diphenylguanidine Hydrochloride, Dimethylbenzylamine Hydrochloride, Hydrazine Hydrate Hydrobromide, Dimethylcyclohexylamine Hydrochloride, Trinonylamine Hydrobromide, Diethylaniline Hydrobromide, 2-Diethylaminoethanol Hydrobromide, 2-Diethylaminoethanol Hydrochloride, Ammonium Chloride, Diallylamine Hydrochloride, Diallylamine Aminomethylamine hydrobromide, diethylamine hydrochloride, triethylamine hydrobromide, triethylamine hydrochloride, hydrazine monohydrochloride, hydrazine dihydrochloride, hydrazine monohydrobromide, hydrazine dihydrobromide, pyridine hydrochloride, aniline hydrobromide, butylamine hydrochloride, hexylamine hydrochloride, n-octylamine hydrochloride, dodecylamine hydrochloride, dimethylcyclohexylamine hydrobromide, ethylenediamine dihydrobromide, rosinamine hydrobromide, 2-phenylimidazole hydrobromide, 4-benzyl Examples of the fluoride include pyridine hydrobromide, L-glutamic acid hydrochloride, N-methylmorpholine hydrochloride, betaine hydrochloride, 2-pipecoline hydroiodide, cyclohexylamine hydroiodide, 1,3-diphenylguanidine hydrofluoride, diethylamine hydrofluoride, 2-ethylhexylamine hydrofluoride, cyclohexylamine hydrofluoride, ethylamine hydrofluoride, rosinamine hydrofluoride, cyclohexylamine tetrafluoroborate, and dicyclohexylamine tetrafluoroborate.

[0068] Furthermore, examples of halogen compounds that can be used include salts obtained by reacting amines with tetrafluoroboric acid (HBF4) and complexes obtained by reacting amines with boron trifluoride (BF3). Examples of the complex include boron trifluoride piperidine.

[0069] Examples of organic halogen compounds other than amine hydrohalides include halogenated aliphatic compounds. A halogenated aliphatic hydrocarbon group is an aliphatic hydrocarbon group in which some or all of the hydrogen atoms constituting the aliphatic hydrocarbon group have been substituted with halogen atoms. Examples of the halogenated aliphatic compounds include halogenated aliphatic alcohols and halogenated heterocyclic compounds.

[0070] 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, 1,4-dibromo-2-butanol, and trans-2,3-dibromo-2-butene-1,4-diol.

[0071] Examples of the halogenated heterocyclic compound include compounds represented by the following general formula (2).

[0072] R 21 -(R 22 ) n (2) [In the formula, R 21 represents an n-valent heterocyclic group. 22 represents a halogenated aliphatic hydrocarbon group.

[0073] R 21In the above, the heterocyclic ring of the n-valent heterocyclic group may be a ring structure in which some of the carbon atoms constituting an aliphatic hydrocarbon or aromatic hydrocarbon ring are substituted with heteroatoms. Examples of heteroatoms in this heterocyclic ring include oxygen atoms, sulfur atoms, and nitrogen atoms. This heterocyclic ring is preferably a 3- to 10-membered ring, and more preferably a 5- to 7-membered ring. Examples of this heterocyclic ring include an isocyanurate ring. R 22 The halogenated aliphatic hydrocarbon group in R preferably has 1 to 10 carbon atoms, more preferably has 2 to 6 carbon atoms, and even more preferably has 3 to 5 carbon atoms. 22 is preferably a brominated aliphatic hydrocarbon group or a chlorinated aliphatic hydrocarbon group, more preferably a brominated aliphatic hydrocarbon group, and even more preferably a brominated saturated aliphatic hydrocarbon group. Examples of halogenated heterocyclic compounds include tris-(2,3-dibromopropyl)isocyanurate.

[0074] Furthermore, examples of organic halogen compounds other than amine hydrohalides include halogenated carboxyl compounds such as iodinated carboxyl compounds, such as 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, and 5-iodoanthranilic acid; chlorinated carboxyl compounds, such as 2-chlorobenzoic acid and 3-chloropropionic acid; and brominated carboxyl compounds, such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid, and 2-bromobenzoic acid. The halogen compounds may be used alone or in combination of two or more.

[0075] <Surfactants> The surfactant may be, for example, a nonionic surfactant. Examples of nonionic surfactants include polyalkylene glycols. Examples of alkylene oxides from which polyalkylene glycols are derived include ethylene oxide, propylene oxide, and butylene oxide. Examples of polyalkylene glycols include polyethylene glycol, ethylene oxide-resorcinol copolymers, polyoxyalkylene acetylene glycols, polyoxyalkylene glyceryl ethers, polyoxyalkylene alkyl ethers, polyoxyalkylene esters, and polyoxyalkylene alkylamides. Alternatively, the nonionic surfactant may be a polyoxyalkylene adduct of an alcohol, such as an aliphatic alcohol, an aromatic alcohol, or a polyhydric alcohol. The surfactant may be used alone or in combination of two or more.

[0076] The water-soluble flux according to this embodiment preferably contains a surfactant. The surfactant preferably includes a nonionic surfactant, and more preferably includes one or more selected from the group consisting of ethylene oxide-resorcinol copolymers and aliphatic alcohol polyoxyalkylene adducts. The content of the surfactant is preferably 5% by mass or more and 75% by mass or less, more preferably 5% by mass or more and 65% by mass or less, and even more preferably 5% by mass or more and 30% by mass or less, relative to the total mass (100% by mass) of the flux.

[0077] ≪Metal deactivator≫ Examples of the metal deactivator include hindered phenol compounds and nitrogen compounds. The term "metal deactivator" as used herein refers to a compound that has the ability to prevent metals from deteriorating when in contact with certain compounds.

[0078] The hindered phenol compound refers to a phenol compound having a bulky substituent (for example, a branched or cyclic alkyl group such as a t-butyl group) at least on one of the ortho positions of the phenol. The hindered phenol compound is not particularly limited, and examples thereof include bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid][ethylenebis(oxyethylene)], N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-methylenebis[6-( 1-methylcyclohexyl)-p-cresol], 2,2'-methylenebis(6-tert-butyl-p-cresol), 2,2'-methylenebis(6-tert-butyl-4-ethylphenol), triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,4-bis-(n-octyl thio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine, pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-hexamethylenebis(3 ,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 3,5-di-tert-butyl-4-hydroxybenzylphosphonate-diethyl ester, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, N,N'-bis[2-[2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethylcarbonyloxy]ethyl]oxamide, and compounds represented by the following general formula (3):

[0079] [ka] (wherein Z is an optionally substituted alkylene group. R 101 and R102 R is each independently an optionally substituted alkyl group, aralkyl group, aryl group, heteroaryl group, cycloalkyl group, or heterocycloalkyl group. 103 and R 104 are each independently an optionally substituted alkyl group.

[0080] Examples of the nitrogen compound in the metal deactivator include hydrazide-based nitrogen compounds, amide-based nitrogen compounds, triazole-based nitrogen compounds, and melamine-based nitrogen compounds.

[0081] The hydrazide nitrogen compound may be any nitrogen compound having a hydrazide skeleton, and examples thereof include dodecanedioic acid bis[N2-(2-hydroxybenzoyl)hydrazide], N,N'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, decanedicarboxylic acid disalicyloylhydrazide, N-salicylidene-N'-salicylhydrazide, m-nitrobenzhydrazide, 3-aminophthalhydrazide, phthalic acid dihydrazide, adipic acid hydrazide, oxalobis(2-hydroxy-5-octylbenzylidenehydrazide), N'-benzoylpyrrolidonecarboxylic acid hydrazide, and N,N'-bis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hydrazine.

[0082] The amide nitrogen compound may be any nitrogen compound having an amide skeleton, and examples thereof include N,N'-bis{2-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyl]ethyl}oxamide.

[0083] The triazole-based nitrogen compound may be any nitrogen compound having a triazole skeleton, and examples thereof include N-(2H-1,2,4-triazol-5-yl)salicylamide, 3-amino-1,2,4-triazole, and 3-(N-salicyloyl)amino-1,2,4-triazole.

[0084] The melamine-based nitrogen compound may be any nitrogen compound having a melamine skeleton, such as melamine, melamine derivatives, etc. More specific examples include trisaminotriazine, alkylated trisaminotriazine, alkoxyalkylated trisaminotriazine, melamine, alkylated melamine, alkoxyalkylated melamine, N2-butylmelamine, N2,N2-diethylmelamine, N,N,N',N',N'',N''-hexakis(methoxymethyl)melamine, etc. The metal deactivators may be used alone or in combination of two or more.

[0085] The flux according to this embodiment preferably does not contain a resin component. In this specification, examples of the resin component include rosin and resins other than rosin.

[0086] As used herein, "rosin" includes natural resins containing abietic acid as the main component, mixtures of abietic acid and its isomers, and chemically modified natural resins (sometimes referred to as rosin derivatives).

[0087] The content of abietic acid in the natural resin is, for example, 40% by mass or more and 80% by mass or less relative to the natural resin. In this specification, the term "main component" refers to a component that is contained in a compound in an amount of 40 mass % or more.

[0088] Representative isomers of abietic acid include neoabietic acid, palustric acid, levopimaric acid, etc. The structure of abietic acid is shown below.

[0089] [ka]

[0090] Examples of the "natural resin" include gum rosin, wood rosin, and tall oil rosin.

[0091] 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.

[0092] 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 (acrylic acid-modified rosin, maleic acid-modified rosin, fumaric acid-modified rosin, etc.), as well as purified products, hydrogenated products, and disproportionated products of the polymerized rosins, 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, and acid-modified rosin soap.

[0093] Examples of rosin amines include dehydroabietylamine and dihydroabietylamine. Rosin amine refers to so-called disproportionated rosin amine. The structures of dehydroabietylamine and dihydroabietylamine are shown below.

[0094] [ka]

[0095] Examples of resins other than rosin include terpene resins, modified terpene resins, terpene phenol resins, modified terpene phenol resins, styrene resins, modified styrene resins, xylene resins, modified xylene resins, acrylic resins, polyethylene resins, acrylic-polyethylene copolymer resins, and other thermosetting resins. Examples of modified terpene resins include aromatic modified terpene resins, hydrogenated terpene resins, and hydrogenated aromatic modified terpene resins. Examples of modified terpene phenolic resins include hydrogenated terpene phenolic resins. Examples of modified styrene resins include styrene acrylic resins and styrene maleic acid resins. Examples of modified xylene resins include phenol-modified xylene resins, alkylphenol-modified xylene resins, phenol-modified resol-type xylene resins, polyol-modified xylene resins, and polyoxyethylene-added xylene resins.

[0096] Other examples of thermosetting resins include epoxy resins. Examples of epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, glycidylamine type resins, alicyclic epoxy resins, aminopropane type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, anthracene type epoxy resins, triazine type epoxy resins, dicyclopentadiene type epoxy resins, triphenylmethane type epoxy resins, fluorene type epoxy resins, phenol aralkyl type epoxy resins, and novolac type epoxy resins. The flux according to this embodiment does not contain at least one resin component selected from the group consisting of rosin and thermosetting resin, making it more suitable as a water-soluble flux.

[0097] The water-soluble flux according to the present embodiment described above contains a combination of a keto acid having a melting point of 40°C or less and a solvent having a boiling point of 240°C or less, and thereby can further suppress the generation of voids during reflow (reflow temperature is, for example, 180 to 300°C). The reason why such an effect is obtained is not clear, but is presumed to be as follows. Organic acids such as dicarboxylic acids, which are commonly used as activators, typically have a melting point of around 100°C or higher. In contrast, the specific keto acid in the water-soluble flux according to this embodiment has a melting point of 40°C or lower. By containing the specific keto acid, the water-soluble flux according to this embodiment further enhances the fluidity of the solder paste during reflow. Furthermore, since the boiling point of the specific solvent in the water-soluble flux according to this embodiment is 240°C or lower, it is likely to volatilize during reflow, generating bubbles (voids). It is presumed that these synergistic effects cause voids generated in the solder paste to fuse together and become larger, making it easier for the voids to be expelled from the solder paste. Furthermore, it is presumed that when the boiling point of the specific keto acid is 250° C. or lower, the specific keto acid volatilizes together with the solvent, making it easier for voids to be expelled from the solder paste.

[0098] (solder paste) The solder paste of this embodiment contains a solder alloy powder and the above-described flux.

[0099] The solder alloy powder may be composed of a powder of solder containing only Sn, or a powder of a solder alloy such as Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Bi, or Sn-In, or an alloy of these to which Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, or P has been added. The solder alloy powder may be composed of a powder of a solder alloy of Sn-Pb system or a Sn-Pb system to which Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, P, etc. have been added. The solder alloy powder is preferably a Pb-free solder. The solder alloy powder that can be used has a melting temperature of 150 to 250°C, for example.

[0100] Flux Content: The content of the flux in the solder paste is preferably 5 to 30 mass % relative to the total mass of the solder paste, and more preferably 5 to 15 mass %.

[0101] The solder paste according to this embodiment contains a flux containing a keto acid with a melting point of 40° C. or less and a solvent with a boiling point of 240° C. or less, thereby making it possible to further suppress the occurrence of voids.

[0102] As described above, it is presumed that in the solder paste according to this embodiment, the volatilization of the specific keto acid and the specific solvent during reflow facilitates the elimination of voids from the solder paste. Examples of the flux composition that facilitates the elimination of voids from the solder paste include the following. That is, the flux contains a specific keto acid and a specific solvent, and it is preferable that the boiling point (Tk) of the specific keto acid and the boiling point (Ts) of the specific solvent satisfy the following conditions. Tk is preferably 150°C or higher and 280°C or lower, more preferably 200°C or higher and 270°C or lower, even more preferably 220°C or higher and 260°C or lower, and particularly preferably 230°C or higher and 250°C or lower. Ts is preferably 150°C or more and 240°C or less, more preferably 180°C or more and 235°C or less, even more preferably 200°C or more and 230°C or less, and particularly preferably 210°C or more and 225°C or less.

[0103] The absolute value of the temperature difference ΔT between Tk and Ts is preferably 0°C or more, more preferably 3°C or more, and even more preferably 5°C or more. When ΔT is equal to or greater than the lower limit, the occurrence of voids can be more easily suppressed. ΔT is preferably 70° C. or less, more preferably 60° C. or less, and even more preferably 55° C. or less. When ΔT is equal to or less than the upper limit, the occurrence of voids can be more easily suppressed.

[0104] The content of the specific keto acid in the flux may be 10% by mass or more and 25% by mass or less, may be 15% by mass or more and 25% by mass or less, or may be 15% by mass or more and 20% by mass or less with respect to the total amount (100% by mass) of the flux. The content of the specific solvent in the flux is preferably 10% by mass or more and 70% by mass or less, and more preferably 15% by mass or more and 60% by mass or less with respect to the total amount (100% by mass) of the flux.

[0105] Furthermore, it is preferable that Tk and Ts satisfy the relationship Ts < Tk. When such a relationship is satisfied, when the reflow temperature reaches the solder melting temperature, the specific keto acid volatilizes together with the specific solvent that has already started to volatilize. As a result, voids are more easily discharged from the solder paste. When Ts < Tk, ΔT is preferably 5°C or more and 50°C or less, more preferably 10°C or more and 45°C or less, still more preferably 15°C or more and 40°C or less, and particularly preferably 20°C or more and 35°C or less. When ΔT is within the above range, it becomes easier to suppress the generation of voids.

Examples

[0106] Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to the following examples.

[0107] <Preparation of Flux> (Examples 1 to 9, Comparative Examples 1 to 4) The fluxes of the examples and comparative examples were prepared with the compositions shown in Tables 1 to 2. The raw materials used are shown below. The melting point values of the compounds used in the examples are the values described in "Chemical Handbook, Basic Edition, Revised 5th Edition (Chemical Society of Japan, Maruzen Publishing)". The boiling point values of the compounds used in the examples are the values obtained by measuring the temperature of the liquid when the saturated vapor pressure of the target liquid becomes equal to 1 atmosphere (i.e., 1013 hPa).

[0108] Specific keto acids: Levulinic acid (melting point: 37.2°C, boiling point: 245°C), pyruvic acid (melting point: 13.6°C, boiling point: 165°C), Other keto acids: Acetone dicarboxylic acid (melting point: 138°C, boiling point: 408.4°C) Other organic acids: Glutaric acid, p-toluenesulfonic acid

[0109] Amine: 2-Ethylimidazole, Triethylenetetramine N,N,N',N'-Tetrakis(2-hydroxypropyl)ethylenediamine Diamine-terminated polyethylene glycol-polypropylene glycol copolymer (weight average molecular weight 600)

[0110] Specific solvent: α-Terpineol (boiling point: 217°C), ethylene glycol monophenyl ether (boiling point: 237°C), hexylene glycol (boiling point: 197°C) Other solvents: Diethylene glycol monohexyl ether (boiling point: 258°C), diethylene glycol mono-2-ethylhexyl ether (boiling point: 272°C)

[0111] Surfactants: Polyoxyethylene resorcinol (weight average molecular weight 1136) Polyoxyethylene behenyl ether (average number of ethylene oxide moles added: 30 mol)

[0112] <Preparation of solder paste> The flux of each example was mixed with the solder alloy powder shown below to prepare a solder paste. Each of the prepared solder pastes contained 11 mass % of flux and 89 mass % of solder alloy powder.

[0113] The solder alloy powder in the solder paste is a powder made of a solder alloy containing 3 mass % Ag, 0.5 mass % Cu, and the remainder Sn. This solder alloy has a solidus temperature of 217°C and a liquidus temperature of 219°C. The solder alloy powder has a size (particle size distribution) that satisfies symbol 4 in the powder size classification (Table 2) in JIS Z 3284-1:2014.

[0114] <Evaluation of void area ratio> How to verify: Using a metal mask (the size of the opening was the same as the size of the electrode, and the mask thickness was 80 μm), solder paste was printed on the Ni / Au plated electrodes. Next, a QFN (4 mm on one side, 1.7 mm on the bottom electrode) was mounted on the electrodes on which the solder paste was printed. Next, reflow soldering was performed. Figure 1 shows the reflow profile, which was preheated by holding the temperature at 150 to 180°C for 70 seconds, then held at 220°C or higher for 60 seconds, with a peak temperature of 245°C. The soldered joint was irradiated with X-rays perpendicular to the substrate, and the void area was measured by analyzing the transmitted X-rays. An XD7600NT Diamond X-ray inspection system (manufactured by Nordson DAGE) was used for the measurements. When measuring the void area, if the X-rays passed through at least one void, it was determined that a void existed. Voids with a diameter of 0.1 μm or more were detected. The ratio of the total area of ​​the voids to the total area of ​​the lower electrodes was then calculated to obtain the void area ratio (%).

[0115] [Table 1]

[0116] [Table 2]

[0117] When the fluxes of Comparative Examples 1 and 2, which did not contain the specific solvent, were used, the occurrence of voids could not be sufficiently suppressed. Moreover, the fluxes of Comparative Examples 3 and 4, which did not contain the specific keto acid, were unable to sufficiently suppress the occurrence of voids. When the fluxes of Examples 1 to 9 containing the specific keto acid and the specific solvent were used, the occurrence of voids was more effectively suppressed than when the fluxes of Comparative Examples were used.

[0118] The flux of Example 1 containing levulinic acid (boiling point 245°C) and α-terpineol (boiling point 217°C) was able to suppress the generation of voids more effectively than the flux of Example 4 containing pyruvic acid (boiling point 165°C) and α-terpineol (boiling point 217°C). In Example 1, when the reflow temperature reaches the solder melting temperature, levulinic acid (specific keto acid) volatilizes along with α-terpineol, which has already begun to volatilize. On the other hand, in Example 4, the volatilization of pyruvic acid (specific keto acid) has already progressed before the reflow temperature reaches the solder melting temperature, and then α-terpineol volatilizes. It is believed that this difference makes it easier for the flux of Example 1 to remove voids from the solder paste than the flux of Example 4. [Industrial Applicability]

[0119] According to the present invention, it is possible to provide a flux and a solder paste that can further suppress the occurrence of voids. This flux and solder paste are suitable for soldering QFN and other packages that do not have leads around the periphery of the package.

Claims

1. A water-soluble flux containing a keto acid having a melting point of 40°C or less and a solvent having a boiling point of 240°C or less, The content of the keto acid is 10% by mass or more and 25% by mass or less with respect to the total amount (100% by mass) of the water-soluble flux, The content of the solvent is 10% by mass or more and 70% by mass or less with respect to the total amount (100% by mass) of the water-soluble flux, the ratio of the keto acid to the solvent is 0.60 to 4.0 in terms of a mass ratio expressed as solvent / keto acid; The solvent is a water-soluble flux containing at least one solvent selected from the group consisting of phenyl glycol, hexylene glycol, and α-terpineol.

2. The water-soluble flux according to claim 1 , wherein the keto acid further has a boiling point of 250° C. or less.

3. The water-soluble flux according to claim 1 , wherein the keto acid includes an organic acid having one carboxy group in the molecule.

4. The water soluble flux of claim 3 , wherein the keto acid comprises levulinic acid.

5. The water-soluble flux according to claim 1, further comprising a nonionic surfactant and an amine.

6. A water-soluble flux as described in claim 5, wherein the content of the nonionic surfactant is 5 mass% or more and 75 mass% or less relative to the total amount (100 mass%) of the water-soluble flux.

7. The water-soluble flux described in claim 5, wherein the amine comprises one or more selected from the group consisting of azoles, triethylenetetramine, terminal diamine polyalkylene glycols, and aliphatic amine polyoxyalkylene adducts.

8. A water-soluble flux as described in claim 7, wherein the content of the aliphatic amine polyoxyalkylene adduct is 10 mass% or more and 40 mass% or less relative to the total mass of the flux.

9. A water-soluble flux as described in claim 7, wherein the total content of the azoles and triethylenetetramine is 0.5 mass% or more and 6 mass% or less relative to the total mass of the flux.

10. Further comprising one or more organic acids selected from the group consisting of carboxylic acids and organic sulfonic acids, 2. The water-soluble flux according to claim 1, wherein the content of the organic acid is 1% by mass or more and 10% by mass or less with respect to the total mass of the flux.

11. 2. The water-soluble flux according to claim 1, which does not contain one or more resin components selected from the group consisting of rosin and thermosetting resin.

12. A solder paste comprising a solder alloy powder and the water-soluble flux according to any one of claims 1 to 11.

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