JP3449778B2 - Flux for soldering - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a soldering flux.

[0002]

2. Description of the Related Art Conventionally, most soldering fluxes are rosin or rosin-modified resin to which an activator composed of an organic acid or a hydrogen halide is added. However, these are judged to be defective because they remain on the board as a residue after the soldering work and cracks due to repeated cold and heat, or the contact needle does not stick in the in-circuit test performed by sticking the needle to the circuit of the printed circuit board. There was something. In addition, the residue often changed due to moisture absorption or temperature rise, which often caused corrosion of the base material and deterioration of electrical characteristics. Therefore, after the soldering work is completed, cleaning with chlorofluorocarbon or the like is performed for the purpose of removing the residue of the flux. Moreover, at present, the cleaning agent, Freon, is also strictly regulated with respect to environmental problems, making it difficult to carry out cleaning with Freon.

[0003]

SUMMARY OF THE INVENTION The present invention solves these problems, namely, it can withstand repeated cold and heat and in-circuit tests without cleaning and removing after soldering, and can corrode the base material due to increase in temperature and humidity. It is an object of the present invention to provide a soldering flux that is less likely to deteriorate electrical characteristics due to temperature rise, and that can comply with CFC regulations by eliminating cleaning.

[0004]

SUMMARY OF THE INVENTION The present invention is a soldering flux containing a bis (2-oxazoline) compound, a dithiol compound, an organic carboxylic acid compound and an activator. Bis (2-oxazoline) used in the present invention
The compound has the general formula

[Chemical 1] (However, R represents a carbon-carbon bond or a divalent hydrocarbon group,
R ₁ , R ₂ , R ₃ and R ₄ each represent hydrogen, an alkyl group or an aryl group. ), When R is a hydrocarbon group, an alkylene group, a cycloalkylene group, an arylene group or the like can be mentioned. When R is a carbon-carbon bond, 2,2'-
Bis (2-oxazoline), 2,2'-bis (4-methyl-2-oxazoline), 2,2'-bis (5-methyl-2-oxazoline), 2,2'-bis (5,5 ' -Dimethyl-2-oxazoline), 2,2'-bis (4,
4,4 ', 4'-tetramethyl-2-oxazoline) and the like. When R is a hydrocarbon group, 1,2-bis (2-oxazolin-2-yl) ethane, 1,4-bis (2-oxazolin-2-yl) butane, 1, as the one having the alkylene group 6-bis (2-oxazolin-2-yl) hexane, 1,8-bis (2-oxazolin-2-yl) octane and the like can be mentioned. As the one having the cycloalkylene group, 1,4-bis (2 -Oxazolin-2-yl) cyclohexane and the like, and those having the arylene group include 1,2-bis (2-oxazolin-2-yl) benzene and 1,3-bis (2-
Oxazolin-2-yl) benzene (hereinafter 1,3-PB
Abbreviated as O. ), 1,4-bis (2-oxazoline-2-
Yl) benzene, 1,2-bis (5-methyl-2-oxazolin-2-yl) benzene, 1,3-bis (5-methyl-2-oxazolin-2-yl) benzene, 1,4
Examples thereof include -bis (5-methyl-2-oxazolin-2-yl) benzene and 1,4-bis (4,4'-dimethyl-2-oxazolin-2-yl) benzene. Preferably 1,3-PBO is used. These may be used alone or in combination.

Examples of the dithiol compound used in the present invention include an aliphatic dithiol compound and an aromatic dithiol compound. Examples of the aliphatic dithiol compound include ethylene glycol bisthioglycolate and butylene glycol bisthioglycolate. Examples of the aromatic dithiol compound include aromatic hydrocarbon dithiol compounds and aromatic heterocyclic dithiol compounds. Examples of the aromatic hydrocarbon dithiol compound include 4,4′-
Examples thereof include thiobisbenzenethiol, bis (4-mercaptophenyl) ether (hereinafter abbreviated as MPS), and 3,4-dimercaptotoluene. As the aromatic heterocyclic dithiol compound, 6-dibutylamino-1,3,3
5-triazine-2,4-dithiol, 6-aminophenyl-1,3,5-triazine-2,4-dithiol,
2,5-dimercapto-1,2,4-thiadiazole and the like can be mentioned. Preferably, MPS, 6-dibutylamino-1,3,5-triazine-2,4-dithiol is used. Aromatic mercaptocarboxylic acids, such as thiosalicylic acid, can be used in place of the dithiol compound. These may be used alone or in combination.

Examples of the organic carboxylic acid compound used in the present invention include organic monocarboxylic acids, dicarboxylic acids and polycarboxylic acids. They also act as activators. The organic carboxylic acid compound may have a hydroxyl group and a double bond in addition to the carboxyl group. As the organic monocarboxylic acid, an aliphatic group having 6 to 21 carbon atoms such as caproic acid, enanthic acid, capric acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid and behenic acid Monocarboxylic acid and benzoic acid, salicylic acid, anisic acid, anthranilic acid, p
-Aromatic monocarboxylic acids having 7 to 11 carbon atoms such as toluenesulfonic acid, 5-sulfosalicylic acid, 4-sulfophthalic acid, sulfanilic acid and naphthalenecarboxylic acid. Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid and eicosanedioic acid having 0 to 34 carbon atoms. Aliphatic dicarboxylic acid is mentioned. Examples of the aromatic dicarboxylic acid include those having 6 to 13 carbon atoms such as phthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl sulfone dicarboxylic acid and diphenylmethane dicarboxylic acid. These may be used alone or in combination. Examples of the polycarboxylic acid include trimellitic acid having 4 to 8 carbon atoms, trimesic acid, pyromellitic acid, butane-1,2,3,4.
-Tetracarboxylic acids. Examples of the organic carboxylic acid having a hydroxyl group also include hydroxycarboxylic acids having 3 to 18 carbon atoms such as lactic acid, citric acid, tartaric acid, levulinic acid, and 12-hydroxystearic acid. Organic carboxylic acids having a double bond are also included. Examples thereof include those having 2 to 36 carbon atoms such as acrylic acid, methacrylic acid, fumaric acid, maleic acid, oleic acid, linoleic acid, linolenic acid and dimer acid. These may be used alone or in combination.
Among the organic carboxylic acid compounds, the dicarboxylic acid compound is advantageously used because it gives a tough residual film.

Another activator used in the present invention is a hydrogen halide salt of various amine compounds.
As the amine compound, aliphatic primary monoamine, aliphatic secondary monoamine, aliphatic tertiary monoamine, aliphatic diamine, triamine, polyamine, alicyclic amine, aromatic amine, heterocyclic amine, amino alcohol, hydrazine, amino Examples include compounds. Examples of the aliphatic primary monoamines having 1 to 8 carbon atoms include, for example, methylamine, ethylamine, n-propylamine, n-butylamine, isobutylamine, sec-butylamine, t-butylamine, n-amylamine, sec-amylamine, 2-ethyl. Butylamine, n-heptylamine, 2-ethylhexylamine, n-octylamine, t-octylamine and the like can be mentioned. As the aliphatic secondary monoamine, dimethylamine having 2 to 16 carbon atoms, diethylamine, di-n-
Propylamine, isopropylamine, diisopropylamine, di-n-butylamine, diisobutylamine,
Diamylamine, dioctylamine and the like can be mentioned. Examples of the aliphatic tertiary monoamine include trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, triisobutylamine, tri-n-amylamine, tri-n-octylamine and the like having 3 to 24 carbon atoms. To be Aliphatic diamines, triamines and polyamines having 2 to 8 carbon atoms such as ethylenediamine, 1,2-propylenediamine, 1,3-diaminopropane, diethylenetriamine, methylaminopropylamine, dimethylaminopropylamine, triethylenetetramine, 1, 6-hexamethylenediamine, 3-
Diethylaminopropylamine, N-2-hydroxyethylenediamine, tetraethylenepentamine and the like can be mentioned. Examples of the alicyclic amine include cyclohexylamine having 6 to 12 carbon atoms and dicyclohexylamine. An aniline having 6 to 14 carbon atoms as the aromatic amine,
Methylaniline, dimethylaniline, diethylaniline, butylaniline, N, N-dibutylaniline, amylaniline, t-amylaniline, N, N-diamylaniline, N, N-di-t-amylaniline, o-toluidine, Diethylbenzylamine, benzylamine, o-
Examples include chloroaniline.

Examples of the heterocyclic amine include pyridine having 5 to 9 carbon atoms, β-picoline, 2,6-lutidine, isoquinoline, quinoline, pyrazole, α-picoline, γ-picoline and 2,4-lutidine. . Examples of amino alcohols having 2 to 6 carbon atoms include monoethanolamine, diethanolamine, triethanolamine, monoethylethanolamine, mono-n-butylethanolamine, dimethylethanolamine, diethylethanolamine, ethyldiethanolamine, n-butyldiethanolamine, Examples thereof include di-n-butyl ethanolamine and triisopropanolamine. Examples of the hydrazine-based amino compound include those having 0 to 7 carbon atoms such as hydrazine, phenylhydrazine, β-acetylphenylhydrazine, 2-hydroxyethylhydrazine, and 1,1-dimethylhydrazine. Examples of the salt used as the hydrogen halide salt include hydrogen fluoride salt, hydrochloride and hydrobromide salt. Diethylamine, ethylamine, 2-ethylhexylamine hydrochloride and hydrobromide are preferably used. In the present invention, the usage ratio of each component is such that the molar ratio of the total amount of the dithiol compound and the organic carboxylic acid compound to the bis (2-oxazoline) compound is in the range of 0.5 to 1.5, preferably 0.95. ~ 1.0
Used in the range of 5. Further, the amount of the organic carboxylic acid compound is used in the range of 5 to 95 mol%, preferably 10 to 50 mol% based on the dithiol compound. The amount of activator is 0.05 to 50% by weight with respect to the flux solid content.
In the range of, preferably 5 to 30% by weight. Further, the hydrogen halide salt used in the activator is in the range of 10% by weight or less based on the solid content of the flux, preferably 0.1%.
It is used in the range of 5 to 5% by weight. When the flux is used in liquid form, an organic solvent may be added. Examples of the solvent include ketone solvents such as acetone and methyl ethyl ketone, methanol, ethanol, isopropanol, methyl cellosolve, ethyl cellosolve, butyl cellosolve,
Examples thereof include alcohol solvents such as 1-methoxy-2-propanol and aromatic solvents such as toluene and xylene. These may be used alone or in combination. The organic solvent is usually used in the range of 20-99.5% by weight. When the amount of the solvent is less than 20% by weight, the viscosity of the flux may be too high and the coating property may be deteriorated. When the amount of the solvent exceeds 99.5% by weight, the effective component of the flux is small,
The solderability may deteriorate even in a non-oxygen atmosphere.

The flux of the present invention may further contain a thermoplastic resin. Examples of the thermoplastic resin used in the present invention include rosin, rosin-modified resin, and synthetic resin. Examples of the rosin and rosin-modified resin include wood rosin, gum rosin, tall rosin, disproportionated rosin, hydrogenated rosin, polymerized rosin and modified rosin. As the synthetic resin, a resin containing a carboxyl group such as polyester resin, acrylic resin, styrene-maleic resin,
Alternatively, an epoxy resin, a resole-based resin, a novolac-based phenolic resin, or the like is used. These may be used alone or in combination. In the present invention, the amount of the thermoplastic resin used is
It is used in the range of 5 to 95% by weight, preferably 10 to 50% by weight, based on the flux solids. The flux of the present invention may further include an epoxy group-containing compound. Examples of the epoxy group-containing compound used in the present invention include phenol glycidyl type compounds and ester glycidyl type compounds. Examples of the phenol glycidyl type compound include bisphenol A glycidyl ether, bisphenol F glycidyl ether, and tetrabromobisphenol A glycidyl ether. Examples of the glycidyl ester type compound include phthalic acid glycidyl ester, tetrahydrophthalic acid glycidyl ester, dimer acid glycidyl ester, and 8,11-dimethyl-7,1.
1-octadecadiene-1,18-diglycidyl ester, n-ethyl octadecane diglycidyl ester and the like can be mentioned. These may be used alone or in combination.
In the present invention, a catalyst may be used in order to accelerate the reaction between the organic carboxylic acid compound and the epoxy group compound. Examples of such catalysts include quaternary ammonium salts such as triethylbenzylammonium chloride, trimethylbenzylammonium chloride, tetramethylammonium chloride, benzyldimethylamine, tributylamine,
Examples include tertiary amines such as tris (dimethylamino) methylphenol, and imidazole compounds such as 2-methyl-4-ethylimidazole and 2-methylimidazole. These can be used in an amount of 0.2-2% by weight based on the flux solid content.

In the present invention, bis (2-oxazoline)
The amount ratio of the compound and the epoxy group-containing compound combined with the compound of the dithiol compound and the organic carboxylic acid compound is preferably in the range of 0.8 to 1.2 times the mole of the latter in terms of molar ratio. Is used in the range of 0.95 to 1.05 times by mole. The amount ratios of the bis (2-oxazoline) compound and the epoxy group-containing compound, and the dithiol compound and the dicarboxylic acid are 5 to 95 mol%, respectively. In the inspection process after soldering, a so-called matte type flux with the gloss of the solder is desired because it prevents the blurring of the eyes of the worker and prevents misjudgment by the optical inspection device. It is rare. In the present flux, in order to obtain this effect, rosin or a rosin-modified resin is partially or entirely used as the thermoplastic resin, and in addition, higher monosaturated or unsaturated fatty acid is used. The proportions of rosin, rosin-modified resin and mono-fatty acid used are in the ranges of 5-95% by weight and 2-30% by weight, respectively, with respect to the flux solid content.
Examples of higher saturated and unsaturated monocarboxylic acids used for matting include those having 8 to 21 carbon atoms such as caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, oleic acid and linoleic acid. , Linolenic acid and the like. In addition, the hydrogen halide salt used as an activator gives a stable covalent bond compound in part when it reacts with an oxazoline compound or an epoxy compound, but it is doubled in order to immobilize more hydrogen halide by the reaction. A carboxyl compound having a bond may be added. As compounds having these double bonds, higher unsaturated monocarboxylic acids such as oleic acid, linoleic acid, linolenic acid, etc., hydroxyethyl acrylate, hydroxyethyl methacrylate and acid anhydrides such as succinic anhydride,
Examples thereof include maleic anhydride, itaconic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and equimolar reaction products with trimellitic anhydride.
The amount used is 1 to 50% by weight with respect to the flux solid content.

[0011]

The flux of the present invention is a mixture of highly reactive compounds, and reacts upon heating during soldering to form a polymer having excellent heat resistance, moisture resistance and toughness. Therefore, the flux residue polymerized film after the soldering process does not crack with respect to the temperature shock of heating and cooling,
Furthermore, even in an in-circuit test in which a needle is placed upright on the flux-treated substrate, the needle easily comes into contact with the circuit at a low pressure.
In addition, organic carboxylic acids that cause corrosion and insulation deterioration are incorporated into the polymer, and the hydrogen halide generated from the hydrogen halide salt during heating reacts mostly with the bis (2-oxazoline) compound, The unreacted balance is fixed in the polymer. Therefore, even if the flux residue is not washed and removed, the reliability of the soldered portion can be secured without causing corrosion or deterioration of electrical characteristics. When the flux of the present invention contains a large amount of a thermoplastic resin, it is possible to improve the water resistance in the unreacted state, the wettability at the time of soldering heating, and the water resistance, toughness, heat resistance and the like.
When the epoxy group-containing compound is contained in the flux of the present invention, water resistance when unreacted and storage stability when an organic solvent is added are significantly improved. Further, the epoxy group-containing compound has a role of reacting with hydrogen halide generated from the hydrogen halide salt when heated, and capturing the hydrogen halide together with the bis (2-oxazoline) compound. When a higher saturated or unsaturated monocarboxylic acid is contained in the present invention, delustering of the solder can be performed to reduce the gloss. When the carboxylic acid compound having a double bond is contained in the present invention, the hydrogen halide compound used as the activator can be more reliably replaced with a stable compound by heating during soldering.

[0012]

EXAMPLES The effects of the soldering flux according to the present invention will be specifically described below with reference to Examples and Comparative Examples. The abbreviations used in Examples and Comparative Examples mean the following. 1,3-bis (2-oxazolin-2-yl) benzene 1,3-PBO 6-dibutylamino-1,3,5-triazine-2,4-DB dithiol (Dysnet (trade name) DB manufactured by Sankyo Kasei) ) Adipic acid AA Succinic acid SA Bisphenol A Glycidyl ether type epoxy compound EP-828 (Oilized shell epoxy, Epicoat (trade name) 828) Glycidyl ester type epoxy compound SB-20G (Okamura Oil, OS-resin SB-20G) ) Diethylamine hydrochloride DEA.HCl 1-methoxy-2-propanol MIPA isopropanol IPA acrylic resin A: high acid value acrylic resin acid value 110,
Molecular weight 9000Tg 50 ° C Acrylic resin B: High acid value acrylic resin Acid value 140,
Molecular weight 10000Tg 80 ° C Special rosin: Acid value 165-175, Softening point 80-87
℃, colorless and transparent TMBAC: trimethylbenzylammonium chloride acrylic carboxylic acid: equimolar reaction product of hydroxyethyl acrylate and hydrophthalic anhydride

Example 1 1,3-PBO 0.507 g, DB 0.384 g,
SA 0.110 g and DEA-HCl 0.046 g
Then, 9.22 g of MIPA was added and well stirred to prepare a uniform flux solution. Various tests described below were performed on the adjusted flux. Examples 2 to 7 In the same manner as in Example 1, the flux was adjusted in the compositions shown in [Table 4], [Table 5], and [Table 6], and various tests were conducted. The results are shown in [Table 4], [Table 5] and [Table 6]. Comparative Examples 1 and 2 In the same manner as in Example 1, the flux was adjusted in the composition shown in [Table 6] and various tests were conducted. The results are shown in [Table 6].

Example 8 Acrylic resin B 2.4 g, special rosin 1.6 g, AA
0.4 g, DB 2.4 g, 1,3-PBO 1.7
8g, SB-20G 1.57g, DEA / HCl
0.5 g and TMBAC 0.05 g were weighed out, and then MIPA 90 g was added and stirred to prepare a uniform flux liquid. Various tests were conducted on the adjusted flux.

[Table 1] The flux was applied to a glass epoxy printed board with a soldering device, dried (100 ° C. × 35 seconds), and soldered (3 seconds). Since this flux has low viscosity and good flowability, it was applied thinly and uniformly and had good drying properties, and when soldering, no generation of bridges, fluffs, and solder balls was observed. Further, the residue obtained by heat-treating this flux and a commercial rosin-based flux for 30 minutes at 180 ° C. was left for 1 week under the condition of 50 ° C. × 95% RH, and then the increase in weight was examined. With respect to the amount of water absorption, when the rosin-based flux was 100, this flux was 76, showing a good low hygroscopicity.

Example 9 Acrylic resin B 2.0 g, special rosin 1.34 g, A
A 0.19g, DB1.47g, 1,3-PBO
2.45g, SB-20G 0.96g, DEA / HC
l 0.35 g, TMBAC 0.05 g, stearic acid 0.5 g, and little acid 0.5 g, and then MI
90 g of PA was added to prepare a uniform flux solution. Apply this flux to a glass epoxy printed circuit board,
After drying, soldering was performed in a solder bath at 245 ° C. for 3 seconds. The solder wettability was good and the solder fillet had a dull, glossy, matte appearance. Example 10 1,3-PBO 3.77 g, SB-20G 4.29
g, DB 4.42g, AA 1.27g, DEA · H
Cl 0.51 g, acrylic resin A 0.46 g, acrylic resin B 0.46 g and TMBAC 0.05 g were weighed out, and then MIPA 84.73 g was added to prepare a uniform flux liquid. Various tests were conducted on the adjusted flux.

[Table 2] This flux was applied to a paper phenol substrate and a glass epoxy substrate of approximately 10 cm x 15 cm, and soldering was performed, and a thermal shock was applied 200 times each at -40 ° C for 30 minutes and 80 ° C for 30 minutes while leaving a residue. In both cases, the residue of the substrate was not cracked or cracked, nor was it peeled from the substrate at all. The contact pressure is 15 in the in-circuit test in which a needle is attached to the circuit of the printed circuit board that has been soldered to make contact.
The needle easily penetrated the residual film with a force of 0 g or less, and no inspection failure occurred in the in-circuit test. Therefore, even if the substrate is not washed, it can be handled in the same manner as a substrate from which residues are washed and removed.

Example 11

[Table 3] Weigh out each of a and b in Table 3 and use MIPA 90
g was added and stirred to prepare a uniform flux liquid. The solder wettability of this flux was a flux of 4.06 seconds and b flux of 2.08 seconds. Apply this flux to a 10cm x 15cm glass epoxy printed circuit board,
After heating for 1 minute to evaporate the solvent, it was soldered for 3 seconds in a solder bath at 240 to 245 ° C. The soldering-treated printed circuit board was immersed in acetone and left for 1 day to dissolve the residual film. When the immersion liquid was dried under reduced pressure and heating, the solid content was 0.244 g of a flux and 0.191 g of b flux. To this was added 50 ml of water and the mixture was boiled under reflux for 3 hours.
After cooling the boiling liquid, it was filtered. The chloride ion content of this filtrate was measured by an ion chromatography method, and the residual amount with respect to chlorine ions contained in the initial flux was determined from this value. a flux is 59%, b flux is 58%
Met. . In this way, chlorine ions, which lead to corrosion of the base material and deterioration of electrical characteristics due to moisture absorption, are greatly reduced.

[0017]

[Table 4]

[0018]

[Table 5]

[0019]

[Table 6] Test method / dryness Drop a drop of flux on the copper plate, 230 ℃
Heat on the hot plate for 5 seconds, and touch the stickiness after cooling. -Spread rate According to JIS-Z-3197 6.10. -Insulation resistance According to JIS-Z-3197 6.8.
Uses 2 comb electrodes. -Corrosion According to JIS-Z-3197 6.6.1.・ Test copper plate (dimension 7mm width x 0.3mm thickness) oxidized by solder wetting for 1 hour at 150 ° C is dipped and applied on the flux for 24
Time until the surface of the solder becomes horizontal again when it is placed in a solder bath (solder H63A) whose temperature is controlled to 5 ± 2 ° C (meniscograph method) ・ Peelability Flux residue peelability when the test piece is bent

[0020]

EFFECT OF THE INVENTION The flux of the present invention gives a residual film which is rich in heat resistance, low hygroscopicity and flexibility due to addition polymerization reaction caused by heating during soldering. Therefore, cracking does not occur due to repeated heating and cooling or stress from the outside, and even in an in-circuit test using a check pin, the film easily penetrates, so that no contact failure occurs. Furthermore, the organic carboxylic acid and hydrogen halide salts, which lead to corrosion and deterioration of electrical characteristics due to the polymerization reaction due to heating, become stable compounds and are fixed in a stable state against the external atmosphere. Does not need Not only can the cost be reduced by omitting the process, but it can also comply with CFC regulations. The flux of the present invention is in a dull lusterless matte state by using rosin and higher fatty acid in combination. This prevents the eyestrain of the operator in the inspection process and prevents the optical inspection device from making an erroneous determination. Further, in the present invention, the reactivity of the bis (2-oxazoline) compound with the dithiol compound and the reactivity of the bis (2-oxazoline) compound with the dicarboxylic acid is larger in the former than in the latter,
Also, the reactivity of the epoxy group-containing compound with the dithiol compound and the reactivity of the epoxy group-containing compound with the dicarboxylic acid are larger than those of the latter, so the reactivity can be controlled by changing the amount ratio of these four types. It is possible. For example, when it is required to react in a few seconds like dip soldering of a printed circuit board which is made into liquid flux in a solder bath, or when reflow soldering of a surface mounting board is performed in a reflow furnace mixed with solder powder. It can be used for a wide range of purposes because it can be used properly when it is required to react in several minutes.

Claims (9)

(57) [Claims] 1. A soldering flux comprising a bis (2-oxazoline) compound, a dithiol compound, an organic carboxylic acid compound and an activator. 2. The soldering flux according to claim 1, further comprising an organic solvent. 3. The soldering flux according to claim 1, further comprising a thermoplastic resin. 4. The soldering flux according to claim 1, further comprising an epoxy group-containing compound. 5. The soldering flux according to claim 1, wherein the dithiol compound is an aromatic dithiol compound. 6. The organic carboxylic acid compound is an aliphatic monocarboxylic acid, dicarboxylic acid or polycarboxylic acid.
Flux for soldering described. 7. The molar ratio of the total amount of the dithiol compound and the dicarboxylic acid to the bis (2-oxazoline) compound is 0.5 to 1.5, and the ratio of the dicarboxylic acid to the dithiol compound is 5 to 95 mol%. The soldering flux according to claim 1. 8. The soldering flux according to claim 1, which contains 0.05 to 50% by weight of an activator. 9. The soldering flux according to claim 4, wherein the ratio of the epoxy group-containing compound to the bis (2-oxazoline) compound is 5 to 95 mol%.