Flux and solder paste

Abstract

The flux according to the present invention is intended to be used for soldering, and comprises at least one carboxylic acid selected from the group consisting of a dicarboxylic acid having a cyclic structure and a tricarboxylic acid having a cyclic structure, at least one imidazole compound selected from the group consisting of an imidazole derivative having an alkyl chain having 1 to 11 carbon atoms inclusive and an imidazole derivative having a phenyl group, and at least one liquid polymerizable compound selected from the group consisting of a liquid resin and a liquid polymerizable fatty acid.

Description

Cross-reference to related applications

[0001] This application claims the priority of Japanese Patent Application No. 2022-151507 and is incorporated by reference into the description of this application specification.

Technical Field

[0002] The present invention relates to flux and solder paste.

Background Art

[0003] For joining an electronic circuit board such as a printed wiring board and a joining component, a solder paste in which solder alloy powder and flux are mixed is used. The solder paste is applied to the electrode portion on the surface of the substrate, and is heated (reflowed) in a state where the electrode portion of the joining component is brought into contact with the electrode portion. Thereby, the solder alloy powder melts to form a solder joint, and a joined structure in which the substrate and the joining component are joined through the solder joint can be obtained.

[0004] In such a joined structure, manufacturing defects are detected by performing various inspections. As one of the inspections, in order to find defects that cannot be detected by visual inspection and an appearance inspection device, an electrical inspection may be performed by bringing a probe into contact with the solder alloy formed by melting the solder alloy powder. For example, in an inspection called ICT (In-Circuit Test) for detecting manufacturing defects such as differences in component constants, a checker pin is brought into contact (pin contact) with the solder alloy, a measurement signal is applied, and voltage and current are measured.

[0005] In such an ICT inspection, from the viewpoint of improving measurement accuracy, it is required to reliably bring the checker pin into contact with the solder alloy. However, if a large amount of flux residue adheres to the solder alloy, the flux residue adheres to and accumulates on the checker pin, so that the checker pin cannot contact the solder alloy and a conduction failure occurs, and accurate inspection may not be possible.

[0006] To solve these problems, conventional methods involve replacing checker pins at regular intervals during inspection. However, if flux residue easily adheres to the checker pins, the inspection period for each checker pin becomes shorter. Since the number of points to be inspected using ICT can reach tens of thousands, a shorter inspection period necessitates replacing more checker pins, resulting in a longer work time per operation. There is also the problem of increased checker pin costs. Therefore, in recent years, methods have been proposed to use solder paste that reduces flux residue, or solder paste that leaves no flux residue at all (see, for example, Patent Document 1).

[0007] However, even with solder paste that reduces flux residue, as described in Patent Document 1, if the coverage rate of the flux residue on the solder alloy is high, the checker pins are more likely to come into contact with the flux residue, which may cause the flux residue to adhere to and accumulate on the checker pins. As a result, the checker pins may not be able to contact the solder alloy, leading to poor conductivity. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2004-25305 [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention has been made in view of the above circumstances, and aims to provide a flux and solder paste that can reduce the coverage rate of flux residue on a solder alloy. [Means for solving the problem]

[0010] The flux according to the present invention is a flux used for soldering and comprises at least one carboxylic acid selected from the group consisting of dicarboxylic acids having a cyclic structure and tricarboxylic acids having a cyclic structure, at least one imidazole compound selected from the group consisting of imidazole derivatives having an alkyl chain with 1 to 11 carbon atoms and imidazole derivatives having a phenyl group, and at least one liquid polymerization compound selected from the group consisting of a liquid resin and liquid polymerized fatty acids.

[0011] The solder paste according to the present invention comprises the flux and solder alloy powder. [Modes for carrying out the invention]

[0012] The flux and solder paste according to embodiments of the present invention will be described below.

[0013] <Flux> The flux according to this embodiment comprises at least one carboxylic acid selected from the group consisting of dicarboxylic acids having a cyclic structure and tricarboxylic acids having a cyclic structure, at least one imidazole compound selected from the group consisting of imidazole derivatives having an alkyl chain with 1 to 11 carbon atoms and imidazole derivatives having a phenyl group, and at least one liquid polymerization compound selected from the group consisting of a liquid resin and liquid polymerized fatty acids.

[0014] (Carboxylic acid) The carboxylic acid is at least one selected from the group consisting of dicarboxylic acids having a cyclic structure and tricarboxylic acids having a cyclic structure. Furthermore, from the viewpoint of improving solder meltability, it is preferable that the carboxylic acid has at least one cyclic structure selected from the group consisting of naphthalene structure, biphenyl structure, stilbene structure, biphenyl ether structure and isocyanuric acid structure.

[0015] Examples of dicarboxylic acids include 4,4'-dicarboxydiphenyl ether, 4,4-biphenyldicarboxylic acid, 4,4-stilbendicarboxylic acid, 2,6-naphthalenedicarboxylic acid, bis(2-carboxyethyl)isocyanuric acid, 3,3'-dicarboxydiphenyl ether, 2,2'-dicarboxydiphenyl ether, 3,3-biphenyldicarboxylic acid, 2,2-biphenyldicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, and decahydro-1,4-naphthalenedicarboxylic acid. Among these, from the viewpoint of improving solder meltability, it is preferable that the dicarboxylic acid is at least one selected from the group consisting of 4,4'-dicarboxydiphenyl ether and 2,6-naphthalenedicarboxylic acid. Note that the dicarboxylic acid may be used alone or in combination of two or more.

[0016] Examples of tricarboxylic acids include tris(2-carboxyethyl)isocyanuric acid, tris(2-carboxypropyl)isocyanuric acid, and 1,4,5-naphthalentricarboxylic acid. Among these, from the viewpoint of improving solder meltability, it is preferable that the tricarboxylic acid is at least one selected from the group consisting of tris(2-carboxyethyl)isocyanuric acid and tris(2-carboxypropyl)isocyanuric acid. Note that the tricarboxylic acid may be used alone or in combination of two or more types.

[0017] The content of the carboxylic acid is preferably 0.5% by mass or more, more preferably 1.5% by mass or more, and particularly preferably 4.0% by mass or more, relative to the total flux. Furthermore, the content of the carboxylic acid is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, and particularly preferably 6.0% by mass or less, relative to the total flux. If two or more types of carboxylic acids are present, the above content refers to the total content.

[0018] (Imidazole compounds) The imidazole compound is at least one selected from the group consisting of imidazole derivatives having an alkyl chain with 1 to 11 carbon atoms, and imidazole derivatives having a phenyl group. Furthermore, from the viewpoint of improving solder meltability, the imidazole compound is preferably an imidazole derivative having a phenyl group.

[0019] Examples of imidazole derivatives having an alkyl chain with 1 to 11 carbon atoms include 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-butylimidazole, 2-undecylimidazole, 2,4-diamino-6-(2-(2-methylimidazole-1-yl)ethyl)-1,3,5-triazine, 2,4-diamino-6-(2-(2-ethyl4-methylimidazole-1-yl)ethyl)-1,3,5-triazine, 2,4-diamino-6-(2'-undecylimidazolyl)-ethyl-s-triazine, and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct. Among these, the imidazole derivative having an alkyl chain with 1 to 11 carbon atoms may be at least one selected from the group consisting of 2-ethylimidazole, 2-undecylimidazole, 2,4-diamino-6-(2-(2-ethyl4-methylimidazole-1-yl)ethyl)-1,3,5-triazine, 2,4-diamino-6-(2'-undecylimidazolyl)-ethyl-s-triazine, and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct. Furthermore, the imidazole derivative having an alkyl chain with 1 to 11 carbon atoms may be used alone or in combination of two or more.

[0020] Examples of imidazole derivatives having a phenyl group include 2-phenylimidazole, 1-benzyl-2-phenyl-1H-imidazole, 4-methyl-2-phenylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4,5-triphenylimidazole, and the like. Among these, from the viewpoint of improving solder melting property, the imidazole derivative having a phenyl group is preferably 2-phenyl-4-methyl-5-hydroxymethylimidazole. The imidazole derivative having a phenyl group may be used alone or in combination of two or more.

[0021] The content of the imidazole compound is preferably 0.5% by mass or more, more preferably 1.5% by mass or more, and particularly preferably 4.0% by mass or more with respect to the whole flux. Also, the content of the imidazole compound is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, and particularly preferably 6.0% by mass or less with respect to the whole flux. When two or more kinds of the imidazole compounds are contained, the content is the total content.

[0022] (Liquid polymer compound) The liquid polymer compound is at least one selected from the group consisting of a liquid resin and a liquid polymer fatty acid. Also, from the viewpoint of improving solder melting property, the liquid polymer compound is preferably a liquid polymer fatty acid.

[0023] Examples of the liquid resin include dimer ol, hydrogenated polybutadiene with hydroxyl groups at both ends (hydroxyl-terminated liquid polybutadiene), liquid polybutadiene with hydroxyl groups at both ends (hydroxyl-terminated liquid polybutadiene), liquid polyisoprene with hydroxyl groups at both ends (hydroxyl-terminated liquid polyisoprene), polybutene, acrylic resin, polyester polyol resin, and the like. Among these, the liquid resin may be at least one selected from the group consisting of hydrogenated polybutadiene with hydroxyl groups at both ends, liquid polyisoprene with hydroxyl groups at both ends, and polybutene. Examples of commercially available liquid resins include Prepol 2033 (manufactured by Croda Japan Co., Ltd.), GI-1000, GI-2000, GI-3000 (manufactured by Nippon Soda Co., Ltd.), G-1000, G-2000, G-3000 (manufactured by Nippon Soda Co., Ltd.), Poly-bd R-15HT, Poly-bd R-45HT (all manufactured by Idemitsu Kosan Co., Ltd.), Poly-ip (manufactured by Idemitsu Kosan Co., Ltd.), EPOL (manufactured by Idemitsu Kosan Co., Ltd.), NOF Polybutene O-15N, NOF Polybutene 3N, NOF Polybutene 10N, NOF Polybutene 30N (all manufactured by NOF Corporation), Nippon Oil Polybutene Grade LV-7, Grade LV-50, Grade LV-100, Grade HV-15, Grade 35, Grade HV-50, Grade HV-100, Grade HV-300 (all manufactured by ENEOS Corporation), Acrylic O (manufactured by Arakawa Chemical Industries, Ltd.), Outflow UMM-1001, UT-1001, CB-3060, CBB-3098 (all manufactured by NOF Corporation) Examples include: Preplast 1900, Preplast 1901, Preplast 1838, Preplast 3186, Preplast 3196, Preplast 3197, Preplast 3199 (all manufactured by Croda Japan), Kuraray Polyol P-510, P-1010, P-2010, P-3010, P-4010, P-5010, P-6010, F-510, F-1010, F-2010, F-3010, P-2011, P-520, P-1020, P-2020, P-1012, P-2012, P-530, P-2030, P-2050 (all manufactured by Kuraray Co., Ltd.). Note that the above liquid resins may be used individually or in combination of two or more types.

[0024] From the perspective of improving solder meltability, the acid value of the liquid polymerized fatty acid is preferably 150 mgKOH / g or more and 320 mgKOH / g or less, more preferably 250 mgKOH / g or more and 300 mgKOH / g or less. Here, the acid value represents the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of the sample, and can be measured in accordance with the potentiometric titration method of JIS K 2501:2003.

[0025] Examples of the liquid polymerized fatty acid include dimer acid, hydrogenated dimer acid, 5(or 6)-carboxy-4-hexylcyclohex-2-en-1-octanoic acid, trimer acid, etc. Among these, from the perspective of improving solder meltability, the liquid polymerized fatty acid is preferably 5(or 6)-carboxy-4-hexylcyclohex-2-en-1-octanoic acid. Examples of commercially available products of the liquid polymerized fatty acid include Tsunoda Dimer 205, Tsunoda Dimer 216, Tsunoda Dimer 228, Tsunoda Dimer 395 (all manufactured by Tsuno Food Industry Co., Ltd.), Privol 1004, Privol 1009, Privol 1006, Privol 1010, Privol 1013, Privol 1017, Privol 1025 (all manufactured by Croda Japan Co., Ltd.), Tsunoda Dimer 346 (manufactured by Tsuno Food Industry Co., Ltd.), Privol 1040 (manufactured by Croda Japan Co., Ltd.), Harima Dimer 200, Harima Dimer 250, Harima Dimer 300 (all manufactured by Harima Chemicals Group, Inc.), Diaacid 1550 (manufactured by Harima Chemicals Group, Inc.), etc. Note that the liquid polymerized fatty acid may be used alone or in combination of two or more.

[0026] From the viewpoint of improving solder meltability, the content of the liquid polymerization compound is preferably 2.0% by mass or more, more preferably 5.0% by mass or more, and particularly preferably 8.0% by mass or more, relative to the total flux. Furthermore, from the viewpoint of improving the viscosity stability of the solder paste, the content of the liquid polymerization compound is preferably 18.0% by mass or less, more preferably 12.0% by mass or less, and particularly preferably 10.0% by mass or less, relative to the total flux. Note that if two or more types of liquid polymerization compounds are included, the above content is the total content.

[0027] (Other resins) The flux according to this embodiment may contain resins other than the liquid resin. Examples of these other resins include rosin-based resins, terpene phenol resins, phenol resins, polyvinyl acetate resins, ethylene-vinyl acetate copolymers, polylactic acid, and polystyrene. Among these, it is preferable that the other resins include rosin-based resins from the viewpoint of improving solder meltability. The rosin-based resin is not particularly limited, and for example, one or more rosin-based resins selected from the group consisting of rosin and rosin derivatives (e.g., hydrogenated rosin, polymerized rosin, disproportionated rosin, acrylic acid-modified rosin, etc.) can be used. Note that the other resins may be used individually or in combination of two or more.

[0028] From the viewpoint of improving solder meltability, the content of the other resins is preferably 25.0% by mass or more, and more preferably 30.0% by mass or more, relative to the total flux. Furthermore, from the viewpoint of improving the viscosity stability of the solder paste, the content of the other resins is preferably 45.0% by mass or less, and more preferably 40.0% by mass or less, relative to the total flux. Note that if two or more types of other resins are included, the above content is the total content.

[0029] (solvent) The flux according to this embodiment may contain a solvent. Examples of the solvent include glycol ethers such as diethylene glycol monohexyl ether (hexyl diglycol), diethylene glycol dibutyl ether (dibutyl diglycol), diethylene glycol mono-2-ethylhexyl ether (2-ethylhexyl diglycol), diethylene glycol monobutyl ether (butyl diglycol), triethylene glycol monobutyl ether (butyl triglycol), polyethylene glycol dimethyl ether, and tripropylene glycol n-butyl ether; aliphatic compounds such as n-hexane, isohexane, and n-heptane; esters such as isopropyl acetate, methyl propionate, and ethyl propionate; ketones such as methyl ethyl ketone, methyl-n-propyl ketone, and diethyl ketone; and alcohols such as ethanol, n-propanol, isopropanol, and isobutanol. The solvent may be used individually or in combination of two or more.

[0030] The solvent content is preferably 30.0% by mass or more, and more preferably 40.0% by mass or more, relative to the total flux. Furthermore, the solvent content is preferably 60.0% by mass or less, and more preferably 50.0% by mass or less, relative to the total flux. If two or more solvents are present, the content refers to the total content.

[0031] (Tixotropic agent) The flux according to this embodiment may contain a thixotropic agent. Examples of thixotropic agents include hydrogenated castor oil, fatty acid amides, fatty acid bisamides, polyamide compounds, kaolin, colloidal silica, organic bentonite, and glass frit. Among these, from the viewpoint of improving heat resistance, the thixotropic agent is preferably a fatty acid bisamide (fatty acid bisamide) or a polyamide compound. Examples of fatty acid bisamides include methylenebisstearate, ethylenebiscaprate, ethylenebislaurate, ethylenebisstearate, ethylenebishydroxystearate, ethylenebisbehenamide, hexamethylenebisstearate, hexamethylenebisbehenamide, hexamethylenebis-12-hydroxystearate, N,N'-distearyladipamide, and N,N'-xylylenebis-12-hydroxystearylamide. Examples of polyamide compounds include aliphatic polyamide compounds such as Talen VA-79, AMX-6096A, WH-215, WH-255 (all manufactured by Kyoeisha Chemical Co., Ltd.), SP-10, SP-500 (both manufactured by Toray Industries, Inc.), Grilamid L20G, Grilamid TR55 (both manufactured by M-Chemistry Japan Co., Ltd.), and aromatic polyamide compounds (semi-aromatic polyamide compounds or fully aromatic polyamide compounds) containing cyclic compounds such as benzene rings and naphthalene rings in the main chain, such as JH-180 (manufactured by Ito Oil Co., Ltd.). The thixotropin may be used alone or in combination of two or more types.

[0032] The content of the thixotropic agent is preferably 1.0% by mass or more, and more preferably 3.0% by mass or more, relative to the total flux. Furthermore, the content of the thixotropic agent is preferably 10.0% by mass or less, and more preferably 8.0% by mass or less, relative to the total flux. If two or more thixotropic agents are included, the above content is the total content.

[0033] (Other activators) The flux according to this embodiment may contain the imidazole compound and other activators other than the dicarboxylic acid. The other activators are not particularly limited and include, for example, organic acid activators, amine compounds, amino acids, halogenated activators such as amine halogen salts and halogen compounds. The other activators may be used individually or in combination of two or more.

[0034] The aforementioned organic acid-based surfactants are not particularly limited and include, for example, monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecyl acid, palmitic acid, margaric acid, stearic acid, tubercurostearic acid, arachidic acid, behenic acid, lignoceric acid, and glycolic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, and diglycolic acid; and other organic acids such as levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and picolinic acid.

[0035] The amine compounds are not particularly limited, and examples include triazole compounds. Examples of triazole compounds include benzotriazole, 1H-benzotriazole-1-methanol, and 1-methyl-1H-benzotriazole. Examples of other amine compounds include cetylamine, erucamide, 3-(dimethylamino)-1,2-propanediol, 3,5-dimethylpyrazole, dimethylurea, hexahydro-1,3,5-triphenyl-1,3,5-triazine, pyrazineamide, N-phenylglycine, 3-methyl-5-pyrazolone, N-lauroyl sarcosine, and 1,3-diphenylguanidine.

[0036] The aforementioned amino acids are not particularly limited, and examples include N-acetylphenylalanine (N-acetyl-L-phenylalanine, N-acetyl-DL-phenylalanine, N-acetyl-D-phenylalanine), N-acetylglutamic acid (N-acetyl-L-glutamic acid), N-acetylglycine, N-acetylleucine (N-acetyl-L-leucine, N-acetyl-DL-leucine, N-acetyl-D-leucine), or N-acetylphenylglycine (N-acetyl-N-phenylglycine, N-acetyl-L-phenylglycine, N-acetyl-DL-phenylglycine).

[0037] The halogenated activators are not particularly limited and include amine halogen salts, halogen compounds, etc. Examples of amines in amine halogen salts include diethylamine, dibutylamine, tributylamine, diphenylguanidine, and cyclohexylamine. Examples of halogens in amine halogen salts include fluorine, chlorine, bromine, and iodine. Examples of halogen compounds include tris(2,3-dibromopropyl) isocyanurate, 2,3-dibromo-2-butene-1,4-diol, 2-bromo-3-iodo-2-butene-1,4-diol, TBA-bis(2,3-dibromopropyl ether), and 4,4'-diiodobiphenyl.

[0038] From the viewpoint of improving solder meltability, the content of the aforementioned other activators is preferably 0.5% by mass or more, and more preferably 3.0% by mass or more, relative to the total flux. Furthermore, from the viewpoint of improving the viscosity stability of the solder paste, the content of the aforementioned other activators is preferably 20.0% by mass or less, and more preferably 10.0% by mass or less, relative to the total flux. Note that if two or more of the aforementioned other activators are included, the above content is the total content.

[0039] The flux according to this embodiment may also contain, as other additives, at least one selected from the group consisting of stabilizers, surfactants, defoamers, and antioxidants. The total content of the other additives is not particularly limited and can be, for example, 5.0% by mass or less of the total flux.

[0040] The flux according to this embodiment is useful for visual inspection using cameras, such as ICT inspection and automated optical inspection (AOI), and can be suitably used for such applications.

[0041] The flux according to this embodiment includes at least one carboxylic acid selected from the group consisting of cyclic dicarboxylic acids and cyclic tricarboxylic acids, at least one imidazole compound selected from the group consisting of imidazole derivatives having an alkyl chain with 1 to 11 carbon atoms and imidazole derivatives having a phenyl group, and at least one liquid polymerization compound selected from the group consisting of a liquid resin and liquid polymerized fatty acids, thereby reducing the coverage rate of the flux residue on the solder alloy.

[0042] Furthermore, the flux according to this embodiment can suppress the adhesion of flux residue to the checker pins by reducing the coverage rate of flux residue on the solder alloy. As a result, the inspection period for a single checker pin is extended, and the work time per step can be shortened.

[0043] In this embodiment, the flux can further reduce the coverage rate of the flux residue on the solder alloy by having the carboxylic acid have at least one cyclic structure selected from the group consisting of a naphthalene structure, a biphenyl structure, a stilbene structure, a biphenyl ether structure, and an isocyanuric acid structure.

[0044] In this embodiment, the flux has a carboxylic acid content of 0.5% by mass or more and 10.0% by mass or less relative to the total flux, which further reduces the coverage rate of flux residue on the solder alloy.

[0045] In this embodiment, the flux contains 0.5% by mass or more and 10.0% by mass or less of the imidazole compound relative to the total flux, thereby further reducing the coverage rate of flux residue on the solder alloy.

[0046] In this embodiment, the flux has an acid value of 150 mg KOH / g or more and 320 mg KOH / g or less for the liquid polymerized fatty acid, which further reduces the coverage rate of the flux residue on the solder alloy.

[0047] In this embodiment, the flux contains 2.0% by mass or more and 18.0% by mass or less of the liquid polymerization compound relative to the total flux, thereby further reducing the coverage rate of flux residue on the solder alloy.

[0048] <Solda paste> The solder paste according to this embodiment contains the flux described above and solder alloy powder. The solder paste is obtained by mixing the flux and the solder alloy powder. The flux content is preferably 5.0% by mass or more and 20.0% by mass or less of the total solder paste. The solder alloy powder content is preferably 80.0% by mass or more and 95.0% by mass or less of the total solder paste.

[0049] Examples of alloys for the solder alloy powder include lead-free solder alloys and lead-containing eutectic solder alloys, but from the viewpoint of reducing environmental impact, lead-free solder alloys are preferred. Examples of lead-free solder alloys include alloys containing tin, silver, copper, indium, zinc, bismuth, antimony, etc. More specifically, examples of alloys include Sn / Ag, Sn / Ag / Cu, Sn / Cu, Sn / Ag / Bi, Sn / Bi, Sn / Ag / Cu / Bi, Sn / Sb, Sn / Zn / Bi, Sn / Zn, Sn / Zn / Al, Sn / Ag / Bi / In, Sn / Ag / Cu / Bi / In / Sb, and In / Ag. Among these, the alloy for the solder alloy powder is preferably a Sn / Ag / Cu alloy. Furthermore, it is more preferable that the Sn / Ag / Cu alloy contains at least one selected from the group consisting of In, Bi, Sb, and Ni. Furthermore, the alloy contains unavoidable impurities. Unavoidable impurities refer to components that are inevitably mixed in during the manufacturing process and are acceptable to the extent that they do not affect the effects of the present invention.

[0050] The particle size of the solder alloy powder is preferably 5 μm or more and 45 μm or less, and more preferably 15 μm or more and 39 μm or less.

[0051] The solder paste according to this embodiment contains the flux described above and solder alloy powder. This makes it possible to reduce the coverage rate of flux residue on the solder alloy.

[0052] The present invention includes the following embodiments. [1] A flux used for soldering, A carboxylic acid selected from the group consisting of dicarboxylic acids having a cyclic structure and tricarboxylic acids having a cyclic structure, At least one imidazole compound selected from the group consisting of imidazole derivatives having an alkyl chain with 1 to 11 carbon atoms, and imidazole derivatives having a phenyl group, A flux comprising a liquid resin and at least one liquid polymerization compound selected from the group consisting of liquid polymerized fatty acids. [2] The flux according to [1], wherein the carboxylic acid has at least one cyclic structure selected from the group consisting of a naphthalene structure, a biphenyl structure, a stilbene structure, a biphenyl ether structure, and an isocyanuric acid structure. [3] The flux according to [1] or [2], wherein the content of the carboxylic acid is 0.5% by mass or more and 10.0% by mass or less with respect to the entire flux. [4] The flux according to any one of [1] to [3], wherein the content of the imidazole compound is 0.5% by mass or more and 10.0% by mass or less of the total flux. [5] The flux according to any one of [1] to [4], wherein the acid value of the liquid polymerized fatty acid is 150 mg KOH / g or more and 320 mg KOH / g or less. [6] The flux according to any one of [1] to [5], wherein the content of the liquid polymerization compound is 2.0% by mass or more and 18.0% by mass or less with respect to the entire flux. A solder paste comprising the flux described in any one of [7][1] to [6] and solder alloy powder.

[0053] Furthermore, the flux and solder paste according to the present invention are not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. Also, the flux and solder paste according to the present invention are not limited by the effects of the embodiments described above. That is, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, not by the above description. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope of the claims. [Examples]

[0054] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0055] <Preparation of flux> The materials in the amounts shown in Tables 1 to 4 were placed in a heating container and heated to 180°C to dissolve all the materials. Afterward, the mixture was cooled to room temperature to obtain uniformly dispersed fluxes for each example and comparative example. Note that the amounts shown in Tables 1 to 4 are equivalent to the content of each component in the flux.

[0056] <Preparation of Solder Paste> Solder pastes for each example and comparative example were obtained by mixing the flux of each example and comparative example at a concentration of 11.0% by mass with the solder alloy powders shown in Tables 1 to 4 at a concentration of 89.0% by mass.

[0057] [Table 1]

[0058] [Table 2]

[0059] [Table 3]

[0060] [Table 4]

[0061] Table 5 shows the details of each material contained in the fluxes shown in Tables 1 to 4. Table 6 also shows the details of the solder alloys shown in Tables 1 to 4.

[0062] [Table 5]

[0063] [Table 6]

[0064] <Fabrication of test boards> Test substrates for each example and comparative example were prepared by printing the solder paste of each example and comparative example onto a standard Koki test substrate (material: FR-4) with a copper pad (circular shape with a diameter of 1.5 mm) on the surface of a substrate measuring 100 mm x 100 mm and a thickness of 1.6 mm, under the printing conditions described below. Subsequently, the substrate was heated under the temperature conditions described below to melt the solder alloy powder. For solder paste printing, 300 g of solder paste was placed on a metal mask set up in a printing press (YSP YAMAHA Motor, manufactured by YAMAHA Motor Co., Ltd.), and the solder paste was rolled four times to adhere to the metal mask. After dry cleaning the back of the metal mask plate, printing was performed once under the printing conditions described below. The substrate was preheated under the temperature conditions (i) below, and then heated under the temperature conditions (ii) below.

[0065] (Printing conditions) Printing environment: Temperature 24-26°C, humidity 50-60%RH Printing squeegee: Metal squeegee Squeegee angle: 60° Metal mask thickness: 150 μm Printing speed: 40mm / sec Pad shape and size: Circular, 1.5mm in diameter Pad material: OSP treated copper

[0066] (Temperature conditions) (i) During preheating Heating rate: 1.0~3.0℃ / second Preheat temperature: 150-190°C / 60-100 seconds Heating environment: atmospheric atmosphere (ii) When the solder melts Heating rate: 1.0~2.0℃ / second Melting temperature: 219°C or higher for 30 seconds or more Peak temperature: 230~250℃

[0067] <Measurement of Acid Value> The acid value of liquid polymerized fatty acids was measured by potentiometric titration according to JIS K 2501:2003. The measurement results are shown in Table 5.

[0068] <Evaluation of solder coverage> Using a scanning electron microscope (JSM-IT300LV, manufactured by JEOL Ltd.), images of the soldered areas (i.e., the areas where the solder alloy powder melted and became one) on the test substrates of each example and comparative example were acquired under the conditions of an acceleration voltage of 15.0 kV, an irradiation current of 60.0 μA, and a vacuum of 30 Pa. The acquired images were subjected to two-tone colorization, with areas where the solder alloy was visible displayed in white and other areas (i.e., areas where flux residue was visible) displayed in black, and the number of pixels in the white areas was determined. Subsequently, the flux residue on each test substrate was removed by washing, and the number of pixels in the white areas after flux residue removal was determined, and the solder coverage rate was calculated using the following formula (1).

[0069] Solder coverage [%] = (Number of pixels in white areas after flux residue removal - Number of pixels in white areas) / (Number of pixels in white areas after flux residue removal) × 100 (1)

[0070] The solder coverage rate was evaluated as follows: "Excellent" if the solder coverage rate was 0% or more and less than 35%, "Good" if the solder coverage rate was 35% or more and less than 55%, and "Poor" if the solder coverage rate was 55% or more. "Excellent" and "Good" were judged as "Pass," and "Poor" was judged as "Fail." The solder coverage rates and evaluation results are shown in Tables 1 to 4.

[0071] As can be seen from the results in Tables 1 to 4, the fluxes of each embodiment that satisfy all the requirements of the present invention can reduce the coverage rate of flux residue on the solder alloy.

Claims

1. A flux used for soldering, A dicarboxylic acid having at least one cyclic structure selected from the group consisting of a naphthalene structure, a biphenyl structure, a stilbene structure, and a biphenyl ether structure, At least one imidazole compound selected from the group consisting of imidazole derivatives having an alkyl chain with 1 to 11 carbon atoms, and imidazole derivatives having a phenyl group, It comprises a liquid resin and at least one liquid polymerization compound selected from the group consisting of liquid polymerized fatty acids, The content of the dicarboxylic acid is 0.5% by mass or more and 10.0% by mass or less relative to the total flux. The content of the imidazole compound is 0.5% by mass or more and 10.0% by mass or less relative to the total flux. A flux in which the content of the liquid polymerization compound is 8.0% by mass or more and 18.0% by mass or less of the total flux.

2. The flux according to claim 1, wherein the acid value of the liquid polymerized fatty acid is 150 mg KOH / g or more and 320 mg KOH / g or less.

3. A solder paste comprising the flux described in claim 1 and solder alloy powder.

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