Flux and solder paste

Abstract

To provide a flux capable of obtaining a solder paste excellent in viscosity stability even under a high-temperature environment, and a solder paste containing the flux.SOLUTION: The flux according to the present invention contains a polymer having a pyrrolidone ring in a side chain, a thixotropic agent, a solvent, and a rosin-based resin. Further, a solder paste according to the present invention includes the flux and a solder alloy powder containing tin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flux and a solder paste. [Background technology]

[0002] A solder paste containing a mixture of solder alloy powder and flux is used to bond electronic circuit boards, such as printed wiring boards, to bonding components. The solder paste is applied to the electrode portions on the surface of the board, and is heated (reflowed) while the electrode portions of the bonding components are in contact with the electrode portions. This melts the solder alloy powder to form a solder joint, resulting in a bonded structure in which the board and bonding components are bonded via the solder joint.

[0003] Known fluxes contained in solder pastes include resin-based fluxes containing natural or synthetic resins such as rosin, activators, solvents, thixotropic agents, etc. Furthermore, lead-free solder alloys, which do not contain lead, are widely used as solder alloys in solder pastes from the viewpoint of environmental impact. For example, Patent Document 1 discloses such a solder paste, which contains lead-free solder powder with an Sn content of more than 63 mass % and a flux containing a low-molecular-weight dibasic acid dialkyl ester compound, a resin component, an activator, a solvent, and a thixotropic agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4457070 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the solder alloy contains a large amount of tin, the solder paste will have poor viscosity stability. This problem is particularly pronounced in solder pastes that contain a halogen compound as a flux activator. For this reason, solder pastes are usually transported and stored at low temperatures of 0 to 10°C. However, if the temperature during transportation or storage of the solder paste rises to 25°C or higher due to the influence of the ambient temperature, the viscosity of the solder paste may become unstable. Therefore, there is a demand for solder pastes that have excellent viscosity stability even in high-temperature environments.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a flux that can provide a solder paste that has excellent viscosity stability even in a high-temperature environment, and a solder paste that contains the flux. [Means for solving the problem]

[0007] The flux according to the present invention contains a polymer having a pyrrolidone ring in a side chain, a thixotropic agent, a solvent, and a rosin-based resin.

[0008] The solder paste according to the present invention contains the flux and a solder alloy powder containing tin. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a flux that can produce a solder paste that has excellent viscosity stability even in a high-temperature environment, and a solder paste that contains the flux. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a flux and a solder paste according to an embodiment of the present invention will be described.

[0011] <Flux> The flux according to this embodiment contains a polymer having a pyrrolidone ring in a side chain, a thixotropic agent, a solvent, and a rosin-based resin.

[0012] (Polymer with pyrrolidone ring in the side chain) The polymer having a pyrrolidone ring in the side chain is preferably polyvinylpyrrolidone or polyvinylpolypyrrolidone.

[0013] The polymer may further have a substituent in the side chain, such as an alkyl group having from 1 to 30 carbon atoms, an ester group, a phenyl group, a carboxyl group, an amino group, an alkylamino group, an amide group, an alkylammonium group, an imidazole ring, or a hydroxyl group. From the viewpoint of stabilizing the viscosity of the solder paste, the substituent is preferably at least one selected from the group consisting of an alkyl group having from 1 to 30 carbon atoms, an ester group, a phenyl group, a carboxyl group, an amino group, an alkylamino group, an amide group, an alkylammonium group, an imidazole ring, and a hydroxyl group, and more preferably an alkyl group having from 1 to 30 carbon atoms or an ester group.

[0014] In one aspect of the flux according to the present embodiment, the polymer further has at least one substituent selected from the group consisting of an alkyl group having 1 to 30 carbon atoms, an ester group, a phenyl group, a carboxyl group, an amino group, an alkylamino group, an amide group, an alkylammonium group, an imidazole ring, and a hydroxyl group in a side chain.

[0015] When the polymer further has the substituent on a side chain, examples of the polymer include (vinylpyrrolidone / hexadecene) copolymer, (vinylpyrrolidone / eicosene) copolymer, vinyl acetate / vinylpyrrolidone copolymer, styrene / vinylpyrrolidone copolymer, (acrylates / vinylpyrrolidone) copolymer, (vinylpyrrolidone / DMAPA acrylic acid) copolymer, polyvinylpyrrolidone / dimethylaminomethyl / acrylic acid copolymer, (vinylpyrrolidone / methacrylamide / vinylimidazole) copolymer, and the like.

[0016] From the viewpoint of stabilizing the viscosity of the solder paste, the content of the structural units having a pyrrolidone ring among the structural units of the polymer is preferably 10 mol% or more and 100 mol% or less, and more preferably 50 mol% or more and 100 mol% or less, relative to the entire polymer.

[0017] From the viewpoint of stabilizing the viscosity of the solder paste, the molecular weight of the polymer is preferably 1,000 or more and 70,000 or less, and more preferably 5,000 or more and 55,000 or less. The molecular weight is a weight-average molecular weight. The weight-average molecular weight was measured by gel permeation chromatography (column: TSKgel GMHxL, TSKgel G4000HxL, or TSKgel G2000HxL (all manufactured by Tosoh Corporation); eluent: tetrahydrofuran; detector: differential refractometer) using polystyrene as a standard substance.

[0018] From the viewpoint of stabilizing the viscosity of the solder paste, the content of the polymer is preferably 0.1 mass % or more and 10.0 mass % or less, and more preferably 1.0 mass % or more and 7.0 mass % or less, based on the total mass of the flux.

[0019] The polymer may be a commercially available product. Examples of commercially available polyvinylpyrrolidone include PVP K-12, PVP K-15, PVP K-30, and PVP K-60 (all manufactured by Ashland Japan Co., Ltd.); Rubiscol K12, Rubiscol K17, and Rubiscol K30 (all manufactured by BASF); and Pitzcol K-17L, Pitzcol K-30L, Pitzcol K-30AL, and Pitzcol K-30 (all manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). Examples of commercially available vinylpyrrolidone / eicosene copolymers include Antaron® V-220F (manufactured by Ashland Japan Co., Ltd.) and UNIMER U-15 (manufactured by Matsumoto Trading Co., Ltd.). Commercially available vinyl acetate / vinylpyrrolidone copolymers include PVP / VA (registered trademark) S-630 (Ashland Japan Co., Ltd.), PVA-6450·Acorn M (Osaka Organic Chemical Industry Co., Ltd.), Rubiscol VA64P (Matsumoto Trading Co., Ltd.), PVP / VA64 Powder, PVP / VA64 E, PVP / VA64 W, PVP / VA64 I, PVP / VA55 E, PVP / VA37 E, PVP / VA37 I, PVP / 73 E, and PVP / VA73 W (all manufactured by JH Nanhang Life Sciences). Commercially available styrene / vinylpyrrolidone copolymers include ANTARA (registered trademark) 430 (Ashland Japan Co., Ltd.). Commercially available polyvinylpyrrolidone / dimethylaminomethyl / acrylic acid copolymers include Copolymer 845, Copolymer 937, and Copolymer 985 (all manufactured by Ashland Japan Co., Ltd.). Commercially available VP / methacrylamide / vinylimidazole copolymers include Luviset Clear (manufactured by BASF).

[0020] (thixotropic agent) The thixotropic agent is not particularly limited, and examples thereof include hardened castor oil, fatty acid amide, fatty acid bisamide, polyamide compound, kaolin, colloidal silica, organic bentonite, glass frit, etc. Among these, the thixotropic agent is preferably a fatty acid bisamide (fatty acid bisamide) or a polyamide compound from the viewpoint of improving heat resistance. The thixotropic agents may be used alone or in combination of two or more.

[0021] Examples of the fatty acid bisamide include methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, ethylene bisstearic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbehenic acid amide, hexamethylene bisstearic acid amide, hexamethylene bisbehenic acid amide, hexamethylene bis-12-hydroxystearic acid amide, N,N'-distearyl adipic acid amide, and N,N'-xylylene bis-12-hydroxystearyl amide.

[0022] Examples of the polyamide compound include aliphatic polyamide compounds and aromatic polyamide compounds (semi-aromatic polyamide compounds or fully aromatic polyamide compounds) containing cyclic compounds such as benzene rings or naphthalene rings in the main chain. Commercially available polyamide compounds may also be used. Among the commercially available polyamide compounds, examples of commercially available aliphatic polyamide compounds include Tallen VA-79, AMX-6096A, WH-215, and WH-255 (all manufactured by Kyoeisha Chemical Co., Ltd.); SP-10 and SP-500 (both manufactured by Toray Industries, Inc.); and Grilamid L20G and Grilamid TR55 (both manufactured by MSC Japan Co., Ltd.). Commercially available semi-aromatic polyamide compounds or fully aromatic polyamide compounds include JH-180 (manufactured by Ito Oil Mills, Ltd.).

[0023] From the viewpoint of stabilizing the viscosity of the solder paste, the content of the thixotropic agent is preferably 1.0 mass % or more and 10.0 mass % or less, and more preferably 2.0 mass % or more and 7.0 mass % or less, based on the total mass of the flux. When two or more types of thixotropic agents are contained, the content is the total content of the thixotropic agents.

[0024] (solvent) Examples of solvents that can be used include known solvents such as 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. These solvents may be used alone or in combination.

[0025] From the viewpoint of stabilizing the viscosity of the solder paste, the content of the solvent is preferably 20% by mass or more and 70% by mass or less, and more preferably 30% by mass or more and 60% by mass or less, based on the total weight of the flux. When two or more types of solvents are contained, the above content is the total content.

[0026] (rosin-based resin) The rosin-based resin is not particularly limited, and examples thereof include rosin and rosin derivatives (e.g., hydrogenated rosin, polymerized rosin, disproportionated rosin, acrylic acid-modified rosin, etc.) The rosin-based resins may be used alone or in combination of two or more.

[0027] From the viewpoint of improving solder melting property, the content of the rosin resin is preferably 20% by mass or more and 60% by mass or less, more preferably 30% by mass or more and 50% by mass or less, based on the total mass of the flux. When two or more types of rosin resins are contained, the above content is the total content.

[0028] (liquid resin) The flux according to this embodiment may contain a liquid resin in addition to the rosin-based resin. The liquid resin is not particularly limited, and examples thereof include dicarboxylic acids, dimer diols, hydrogenated polybutadiene having hydroxyl groups at both ends (hydroxyl-terminated hydrogenated polybutadiene), liquid polybutadiene having hydroxyl groups at both ends (hydroxyl-terminated liquid polybutadiene), liquid polyolefin having hydroxyl groups at both ends (hydroxyl-terminated liquid polyolefin), polybutene, acrylic resins, and polyester polyol resins. Among these, the liquid resin may be at least one selected from the group consisting of hydrogenated polybutadiene having hydroxyl groups at both ends, liquid polyolefin having hydroxyl groups at both ends, and polybutene. The liquid resins may be used alone or in combination.

[0029] The liquid resin may be a commercially available product. Among the commercially available liquid resins, examples of commercially available dicarboxylic acids include Diacid 1550 (5 (or 6)-carboxy-4-hexylcyclohex-2-ene-1-octanoic acid: manufactured by Harima Chemicals Co., Ltd.). Examples of commercially available dimer diols include Pripol 2033 (manufactured by Croda Japan Co., Ltd.). Examples of commercially available hydroxyl-terminated hydrogenated polybutadiene products include GI-1000, GI-2000, and GI-3000 (all manufactured by Nippon Soda Co., Ltd.). Commercially available hydroxyl-terminated liquid polybutadienes include, for example, G-1000, G-2000, and G-3000 (all manufactured by Nippon Soda Co., Ltd.), Poly-bd R-15HT and Poly-bd R-45HT (all manufactured by Idemitsu Kosan Co., Ltd.), and Poly-ip (all manufactured by Idemitsu Kosan Co., Ltd.). Commercially available hydroxyl-terminated liquid polyolefins include, for example, EPOL (manufactured by Idemitsu Kosan Co., Ltd.). Commercially available polybutene products include NOF Polybutene O-15N, NOF Polybutene 3N, NOF Polybutene 10N, and 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, and Grade HV-300 (all manufactured by ENEOS Corporation). Commercially available acrylic resin products include Acrylic O (manufactured by Arakawa Chemical Industries, Ltd.); Actflow UMM-1001, UT-1001, CB-3060, and CBB-3098 (all manufactured by Soken Chemical Co., Ltd.).Commercially available polyester polyol resins include, for example, Priplast 1900, Priplast 1901, Priplast 1838, Priplast 3186, Priplast 3196, Priplast 3197, and Priplast 3199 (all manufactured by Croda Japan Co., Ltd.); 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, and P-2050 (all manufactured by Kuraray Co., Ltd.).

[0030] (Other resins) The flux according to this embodiment may contain other resins in addition to the rosin-based resin. The other resins are not particularly limited, and examples thereof include terpene phenol resin, phenol resin, polyvinyl acetate resin, ethylene-vinyl acetate copolymer, polylactic acid, and polystyrene.

[0031] (activator) The flux according to the present embodiment may contain an activator. Examples of activators include organic acids, amine compounds, amino acid compounds, and halogen compounds. Among these, the component contained in the activator is preferably a halogen compound from the viewpoint of improving the wettability of the solder. The flux according to the present embodiment may contain only one type of the activator, or may contain two or more types.

[0032] In one aspect, the flux according to the present embodiment contains an activator, and the activator is a halogen compound.

[0033] Examples of halogen compounds include organic halogen compounds, organic hydrohalides, amine halogen salts, etc. Among these, the halogen compound is preferably an organic halogen compound or an organic hydrohalide salt from the viewpoint of improving the wettability of the solder.

[0034] Examples of organic halogen compounds include organic fluorine compounds, organic chlorine compounds, organic bromine compounds, and organic iodine compounds. Among these, the organic halogen compounds are preferably organic bromine compounds or organic iodine compounds from the viewpoint of improving the wettability of solder. Specific examples of organic halogen compounds include 4-bromophenol, 2,4,6-tribromophenol, 3,5-dibromosalicylic acid, 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), 4,4'-diiodobiphenyl, 1,4-diiodobenzene, cyclohexyl iodide, and 1-tert-butyl ether. Examples of the iodoisopropyl tert-butyl ester include t-butoxycarbonyl-4-iodopiperidine, 4-iodophenol, 2,4,6-triiodophenol, ethyl 3-iodobenzoate, 4-iodobenzaldehyde, 4-iodoacetophenone, methyl 5-iodoanthranilate, iohexol, 2-bromo-5-iodo-3-methylpyridine, 2,4,5-triiodo-1H-imidazole, 5-iodofurfural, 5-iodofurfural, and 5,7-diiodo-8-hydroxyquinoline.

[0035] Examples of organic hydrohalides include organic hydrofluorides, organic hydrochlorides, organic hydrobromides, and organic hydroiodides. Among these, the organic hydrohalides are preferably organic hydrobromides or organic hydroiodides from the viewpoint of improving the wettability of solder. Specific examples of organic hydrohalides include ethylamine hydrobromide, butylamine hydrobromide, hexylamine hydrobromide, 2-ethylhexyl hydrobromide, cyclohexylamine hydrobromide, aniline hydrobromide, benzylamine hydrobromide, diethylamine hydrobromide, dibutylamine hydrobromide, pyridine hydrobromide, 1-methylimidazole hydrobromide, morpholine hydrobromide, piperazine hydrobromide, and 1,3-diphenylguanidine hydrobromide. salts, ethylamine hydroiodide, butylamine hydroiodide, hexylamine hydroiodide, 2-ethylhexyl hydroiodide, cyclohexylamine hydroiodide, aniline hydroiodide, benzylamine hydroiodide, diethylamine hydroiodide, dibutylamine hydroiodide, pyridine hydroiodide, 1-methylimidazole hydroiodide, morpholine hydroiodide, piperazine hydroiodide, 1,3-diphenylguanidine hydroiodide, and the like.

[0036] Examples of the amine in the amine halogen salt include diethylamine, dibutylamine, tributylamine, diphenylguanidine, cyclohexylamine, etc. Examples of the halogen in the amine halogen salt include fluorine, chlorine, bromine, and iodine.

[0037] Examples of organic acids include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, pentadecylic acid, myristic acid, palmitic acid, margaric acid, stearic acid, tuberculostearic acid, arachidic acid, behenic acid, lignoceric acid, and glycolic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, methylsuccinic acid, phenylsuccinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, and diglycolic acid; tricarboxylic acids such as citric acid, tris(2-carboxyethyl)isocyanuric acid, and tris(2-carboxypropyl)isocyanuric acid; and other organic acids such as dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, and picolinic acid.

[0038] The amine compound is not particularly limited, and examples thereof include imidazole compounds and triazole compounds. Examples of the imidazole compounds include benzimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole (2E4MZ), 2-heptadecylimidazole, 2-undecylimidazole, 1-(4,6-diamino-s-triazin-2-yl)ethyl-2-undecylimidazole, 1-butylimidazole, 2-phenylimidazole, and 4-methyl-2-phenylimidazole. Examples of the triazole compounds include benzotriazole, 1H-benzotriazole-1-methanol, and 1-methyl-1H-benzotriazole. Examples of amine compounds other than the imidazole compounds and triazole compounds include cetylamine, erucic acid amide, 3-(dimethylamino)-1,2-propanediol, 3,5-dimethylpyrazole, dimethylurea, hexahydro-1,3,5-triphenyl-1,3,5-triazine, 2,4-diamino-6-(2'-undecyl-imidazolyl)-ethyl-s-triazine, pyrazinamide, N-phenylglycine, 3-methyl-5-pyrazolone, N-lauroylsarcosine, and 1,3-diphenylguanidine.

[0039] Examples of amino acids 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), and N-acetylphenylglycine (N-acetyl-N-phenylglycine, N-acetyl-L-phenylglycine, N-acetyl-DL-phenylglycine).

[0040] From the viewpoint of improving the wettability of the solder, the content of the activator is preferably 0.5% by mass to 10.0% by mass, more preferably 2.0% by mass to 5.0% by mass, based on the total mass of the flux. When two or more types of activators are contained, the content is the total content of the activators.

[0041] The flux according to this embodiment may contain other additives, such as a stabilizer, a surfactant, an antifoaming agent, and an antioxidant.

[0042] The flux according to this embodiment contains a polymer having a pyrrolidone ring in the side chain, a thixotropic agent, a solvent, and a rosin-based resin, and therefore can provide a solder paste with excellent viscosity stability even in high-temperature environments.

[0043] In the flux according to this embodiment, the molecular weight of the polymer is 1,000 or more and 70,000 or less, and therefore it is possible to obtain a solder paste with even better viscosity stability even in a high temperature environment.

[0044] In the flux according to this embodiment, the polymer further has at least one substituent selected from the group consisting of an alkyl group having 1 to 30 carbon atoms, an ester group, a phenyl group, a carboxyl group, an amino group, an alkylamino group, an amide group, an alkylammonium group, an imidazole ring, and a hydroxyl group in the side chain, thereby making it possible to obtain a solder paste with even better viscosity stability even at high temperatures.

[0045] In the flux according to this embodiment, the polymer content is 0.1 mass % or more and 10.0 mass % or less relative to the total mass of the flux, and therefore it is possible to obtain a solder paste with even better viscosity stability even in high temperature environments.

[0046] The flux according to this embodiment further contains an activator, and since the activator is a halogen compound, a solder paste with excellent solder wettability can be obtained.

[0047] <Solder paste> The solder paste according to this embodiment contains the above-mentioned flux and solder alloy powder.

[0048] The alloy of the solder alloy powder is not particularly limited, and examples thereof include lead-free solder alloys and lead-containing eutectic solder alloys. From the viewpoint of reducing environmental impact, the alloy of the solder alloy powder is preferably a lead-free solder alloy. Examples of such alloys include alloys containing tin, silver, copper, indium, zinc, bismuth, antimony, etc. More specifically, examples of alloy compositions 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 composition is preferably Sn-Ag-Cu. Furthermore, Sn—Ag—Cu preferably further contains at least one element selected from the group consisting of In, Bi, Sb, and Ni. Such alloys contain unavoidable impurities. The term "unavoidable impurities" refers to components that are inevitably mixed in during the manufacturing process and are acceptable within a range that does not affect the effects of the present invention.

[0049] The solder alloy powder preferably contains tin, from the viewpoint of facilitating bonding by forming an intermetallic compound with copper contained in wiring or the like of a printed circuit board.

[0050] The tin content of the solder alloy powder is preferably 63.0% by mass or more, more preferably 80.0% by mass or more, from the viewpoint of achieving a melting point suitable for soldering, and is preferably 99.0% by mass or less, more preferably 97.0% by mass or less, from the viewpoint of adding other metal elements to impart various properties.

[0051] When the alloy has a composition of Sn-Ag-Cu and further contains at least one selected from In, Bi, Sb, and Ni, the content of at least one selected from In, Bi, Sb, and Ni contained in the alloy is preferably 0.01 mass% or more and 10.0 mass% or less, and more preferably 3.0 mass% or more and 8.0 mass% or less.

[0052] The solder paste according to this embodiment is obtained by, for example, mixing a flux with a solder alloy powder containing tin. The content of the flux is preferably 5% by mass or more and 20% by mass or less based on the total solder paste. The content of the solder alloy powder is preferably 80% by mass or more and 95% by mass or less based on the total solder paste.

[0053] The solder paste according to this embodiment contains the above-mentioned flux and a solder alloy powder containing tin, and the solder paste obtained thereby has excellent viscosity stability even in a high-temperature environment.

[0054] The flux and solder paste according to the present invention are not limited to the above-described embodiments, and various modifications are possible without departing from the spirit and scope of the present invention.

[0055] The present invention includes the following aspects. [1] A flux comprising a polymer having a pyrrolidone ring in a side chain, a thixotropic agent, a solvent, and a rosin-based resin. [2] The flux according to [1], wherein the molecular weight of the polymer is 1,000 or more and 70,000 or less. [3] The flux according to [1] or [2], wherein the polymer further has at least one substituent selected from the group consisting of an alkyl group having 1 to 30 carbon atoms, an ester group, a phenyl group, a carboxyl group, an amino group, an alkylamino group, an amide group, an alkylammonium group, an imidazole ring, and a hydroxyl group in a side chain. [4] The flux according to any one of [1] to [3], wherein the content of the polymer having a pyrrolidone ring in a side chain is 0.1% by mass or more and 10.0% by mass or less with respect to the entire flux. [5] The flux according to any one of [1] to [4], further comprising an activator, wherein the activator is a halogen compound. [6] A solder paste comprising the flux according to any one of [1] to [5] and a solder alloy powder containing tin. [Example]

[0056] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0057] <Preparing solder paste> The materials shown in Table 1 were placed in a heating vessel in the amounts shown in Table 3 and heated to 180°C until all materials were dissolved. The materials were then cooled to room temperature to obtain uniformly dispersed fluxes for each Example and Comparative Example. The amounts shown in Table 1 are equal to the contents of each component in the flux. The flux of Comparative Example 1 does not contain a polymer having a pyrrolidone ring in its side chain, and the flux of Comparative Example 2 contains laurylpyrrolidone, which is not a polymer.

[0058] Next, the flux obtained above was mixed with the solder alloy powder shown in Table 2 in the amounts shown in Table 3 to obtain the solder pastes of the examples and comparative examples.

[0059] [Table 1]

[0060] [Table 2]

[0061] [Table 3]

[0062] <Evaluation of Solder Paste Viscosity Stability> The viscosity increase rate was calculated from the viscosity value at the initial stage of production and the viscosity value after the viscosity stability accelerated test, and the viscosity stability of the solder paste was evaluated from the calculated viscosity increase rate value.

[0063] More specifically, after preparing the solder paste for each example and comparative example, the obtained solder paste was stored in a refrigerator for one day at a temperature of 0 to 10° C. After storing for one day, the solder paste was placed in a thermostatic water bath set at 25° C. to keep the temperature of the solder paste constant, and then the viscosity of the solder paste was measured according to the measurement conditions below, and the obtained value was taken as the viscosity value at the initial stage of preparation.

[0064] After preparing the solder pastes of each Example and Comparative Example, the resulting solder pastes were stored in a thermostatic bath at 40°C for two days. After storing the solder pastes for two days, they were placed in a thermostatic water bath set at 25°C to keep the temperature of the solder paste constant, and the viscosity of the solder paste was measured under the following measurement conditions. The obtained value was used as the viscosity value after the accelerated viscosity stability test. Measurement conditions Equipment used: Viscometer (manufactured by Malcom Co., Ltd.) Measurement temperature: 25℃ Measurement standard: JIS Z 3284-3:2014

[0065] The viscosity increase rate was calculated from the viscosity value at the initial stage of preparation and the viscosity value after the viscosity stability accelerated test according to the following formula (I).

[0066]

number

[0067] The thickening stability was determined based on the obtained thickening rate and the following evaluation. -Evaluation of viscosity A: Viscosity increase rate is 10.0% or less B: Viscosity increase rate is 10.1% or more and 20.0% or less C: Viscosity increase rate is 20.1% or more ·Determination of viscosity stability Pass: Thickening rate is rated A or B Fail: Thickening rate is C

[0068] As can be seen from the results in Table 3, the solder pastes containing the fluxes of the examples that satisfy all of the requirements of the present invention have excellent viscosity stability even in high-temperature environments.

Claims

1. A flux comprising a polymer having a pyrrolidone ring in a side chain, a thixotropic agent, a solvent, and a rosin-based resin.

2. 2. The flux according to claim 1, wherein the molecular weight of the polymer is 1,000 or more and 70,000 or less.

3. 2. The flux according to claim 1, wherein the polymer further has at least one substituent selected from the group consisting of an alkyl group having 1 to 30 carbon atoms, an ester group, a phenyl group, a carboxyl group, an amino group, an alkylamino group, an amide group, an alkylammonium group, an imidazole ring, and a hydroxyl group in a side chain.

4. 2. The flux according to claim 1, wherein the content of the polymer is 0.1 mass % or more and 10.0 mass % or less with respect to the total mass of the flux.

5. 10. The flux of claim 1, further comprising an activator, wherein the activator is a halogen compound.

6. A solder paste comprising the flux according to any one of claims 1 to 5 and a solder alloy powder containing tin.

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