Flux and solder paste

Abstract

To provide flux capable of inhibiting the appearance of a void in a solder joint when used with a lead-free solder alloy and excellent in wettability of solder, and provide solder paste including the flux.SOLUTION: Flux according to the present invention, which is used with a lead-free solder alloy, contains a resin, an activator that includes a decarboxylation activator causing decarboxylation at a main heating temperature, a solvent, and a thixotropic agent.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a flux used for soldering and a solder paste containing the flux.

Background Art

[0002] For joining an electronic circuit board such as a printed wiring board and a joining component, a solder paste in which a solder alloy and a flux are mixed is used. The solder paste is applied to an electrode portion on the surface of the electronic circuit board and 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 melts to form a solder joint, and the substrate and the joining component are joined through the solder joint. As the flux contained in the solder paste, a resin-based flux containing a natural resin or a synthetic resin such as rosin, an activator, a solvent, a thixotropic agent, etc. is known.

[0003] In addition, as the solder alloy contained in the solder paste, from the viewpoint of environmental load, a lead-free solder alloy containing no lead is widely used. Since the surface tension at the time of solder melting is higher in the lead-free solder alloy than in the Sn-Pb-based solder alloy, there is a problem that voids generated in the solder joint at the time of reflow tend to remain. Further, since the solder paste containing the lead-free solder alloy is subjected to a reflow process at a high temperature for a long time as compared with the solder paste containing the Sn-Pb-based solder alloy, it is desirable that the flux used together with the lead-free solder alloy contains an activator that can exhibit activity at a high temperature and maintain that activity for a long time.

[0004] Conventionally, halogen compounds have been widely used as activators that can suppress the generation of voids in the solder joint and improve the wettability of the solder by removing the oxide film on the solder surface and reducing the surface tension of the solder (for example, Patent Documents 1 and 2). In particular, in Patent Document 2, it has been reported that the wettability of the solder is continuously improved by using a specific halogen compound as an activator.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-117737 [Patent Document 2] Japanese Patent Publication No. 2016-140915 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, halogen compounds may generate harmful substances such as dioxins when burned, so in recent years, there has been a trend towards halogen-free materials. Therefore, there is a need to develop activators that can suppress void formation in solder joints when used with lead-free solder alloys, even without using halogen compounds, and that also exhibit excellent solder wettability.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a flux that, when used with a lead-free solder alloy, can suppress the generation of voids in the solder joint and has excellent solder wettability, and a solder paste containing the flux. [Means for solving the problem]

[0008] The flux according to the present invention is used with a lead-free solder alloy and contains a resin, an activator including a decarboxylase activator that undergoes decarboxylation at the heating temperature, a solvent, and a thixotropic agent.

[0009] Because the flux is fluid, by including a decarboxylase activator that undergoes decarboxylation at the heating temperature, voids generated at the solder joint during reflow are pushed out by the carbon dioxide exhaust force. As a result, the flux can suppress the generation of voids at the solder joint. Furthermore, because the decarboxylase activator exhibits sustained activity during reflow, the flux exhibits excellent solder wettability when used with a lead-free solder alloy.

[0010] In the flux according to the present invention, it is preferable that the decarboxylase activator is an amino acid or a derivative thereof.

[0011] With this configuration, the flux can further suppress the generation of voids in the solder joint and has superior solder wettability.

[0012] The flux according to the present invention is used with medium-to-high temperature lead-free solder alloys, and it is preferable that the decarboxylase activator is at least one selected from L-glutamic acid, L-glutamine, L-carnitine, β-alanine, L-citrulline, and L-theanine.

[0013] L-glutamic acid, L-glutamine, L-carnitine, β-alanine, L-citrulline, and L-theanine undergo decarboxylation at the main heating temperature of medium-to-high temperature lead-free solder alloys. As a result, when the flux is used with medium-to-high temperature lead-free solder alloys, the generation of voids in the solder joint can be suppressed, and the solder wettability is excellent.

[0014] In the flux according to the present invention, it is preferable that the content of the decarboxylase activator is 0.5% by mass or more and 25% by mass or less of the total flux.

[0015] With this configuration, the flux can reduce flux residue after reflow. Furthermore, even with this configuration, the flux can suppress the generation of voids in the solder joint and has excellent solder wettability.

[0016] The solder paste according to the present invention contains the flux described above and a lead-free solder alloy.

[0017] The aforementioned solder paste, by containing the flux described above, can suppress the generation of voids in the solder joint when used with a lead-free solder alloy, and also exhibits excellent solder wettability. [Effects of the Invention]

[0018] According to the present invention, when used with a lead-free solder alloy, it is possible to provide a flux that can suppress the generation of voids in the solder joint and has excellent solder wettability, as well as a solder paste containing the flux. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 shows the TG curve obtained when TG-DTA measurement was performed for L-glutamate. [Figure 2] Figure 2 shows the IR spectra obtained by FT-IR measurements of L-glutamate before and after weight loss. [Modes for carrying out the invention]

[0020] The flux and solder paste according to embodiments of the present invention will be described below.

[0021] <Flux> (Activating agent) The flux according to this embodiment contains a decarboxylation activator that undergoes decarboxylation at the heating temperature. Here, the heating temperature is the temperature at which the heating is performed in the reflow process, and specifically, it is a temperature within the range of the solidus temperature of the lead-free solder alloy used, from -40°C to +30°C. For example, when using a Sn-Ag-Cu alloy as the lead-free solder alloy, the solidus temperature is 217°C, so the heating temperature is 177°C to 247°C. Note that the decarboxylation activator does not need to undergo decarboxylation over the entire range of the heating temperature; it is sufficient if decarboxylation occurs within a portion of the heating temperature range. The solidus temperatures of each alloy are as described in JIS Z 3282;2017.

[0022] Decarboxylation occurring at this heating temperature means that carbon dioxide gas is generated at this heating temperature. The generation of carbon dioxide gas can be confirmed by thermogravimetric / differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR). Specifically, when a certain amount of weight loss occurs in the TG-DTA measurement, FT-IR measurements are performed on the compound before and after the weight loss. If the C=O double bond peak disappears or its intensity decreases in the spectrum after the weight loss, it can be said that carbon dioxide gas has been generated. For example, let's consider the case where the decarboxylase activator is L-glutamic acid. Figure 1 shows the TG curve when TG-DTA is performed on L-glutamic acid. As can be seen from Figure 1, weight loss occurs in L-glutamic acid between 207 and 217°C. Therefore, assuming that decarboxylation begins when the weight loss of L-glutamic acid starts (207°C), FT-IR measurements are performed on L-glutamic acid before weight loss and on L-glutamic acid at the temperature at which weight loss started + 10°C. Figure 2 shows the IR spectra obtained by FT-IR measurements of L-glutamic acid before and after weight loss. According to "Infrared Absorption Spectra of Glutamate-Related Compounds" (Journal of the Chemical Society of Japan, 1961, Vol. 82, No. 7, pp. 805-813), L-glutamic acid has an IR of 1663 cm⁻¹. -1 A peak originating from C=O stretching is detected in the vicinity. As can be seen from Figure 2, in the spectrum after weight reduction, 1663 cm⁻¹ is detected. -1 The peak in the vicinity has disappeared. This indicates that L-glutamic acid generates carbon dioxide at 207-217°C.

[0023] The decarboxylation activator is preferably an amino acid or its derivative. Examples of the amino acid include L-glutamic acid, L-glutamine, L-carnitine, β-alanine, L-citrulline, L-theanine, L-aspartic acid, L-arginine, L-cystine, N-(tert-butoxycarbonyl)-L-glutamic acid, and the like. Among these, when used with a high-temperature lead-free solder alloy, it is preferably at least one amino acid selected from L-aspartic acid, L-arginine, and L-cystine. When used with a medium-high temperature lead-free solder alloy, it is preferably at least one amino acid selected from L-glutamic acid, L-glutamine, L-carnitine, β-alanine, L-citrulline, and L-theanine, and more preferably L-glutamic acid or L-glutamine. When used with a medium-temperature lead-free solder alloy, it is preferably at least one amino acid selected from L-glutamic acid and L-theanine. When used with a medium-low temperature lead-free solder alloy, it is preferably at least one amino acid selected from L-glutamine and L-carnitine. When used with a low-temperature lead-free solder alloy, it is preferably N-(tert-butoxycarbonyl)-L-glutamic acid. The classification of high-temperature, medium-high temperature, medium-temperature, medium-low temperature, and low-temperature of the lead-free solder alloy is based on JIS Z 3282;2017. The decarboxylation activator may be used alone or in combination of two or more kinds.

[0024] The content of the decarboxylation activator is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, based on the total flux. Also, the content of the decarboxylation activator is preferably 25% by mass or less, more preferably 15% by mass or less, based on the total flux. When two or more kinds of decarboxylation activators are contained, the content is the total content of the decarboxylation activators.

[0025] The flux according to this embodiment may contain other activators besides the decarboxylase activator. Examples of other activators include organic acid activators, amino acids, amine compounds, and complex salts thereof. The organic acid activators are not particularly limited and include, for example, monocarboxylic acids such as 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, 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 and tris(2-carboxyethyl) isocyanurate; and other organic acids such as dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and picolinic acid. Examples of the amino acids include N-acetyl-L-hydroxyproline and N-acetyl-L-tyrosine. The amine compound is preferably a compound having a cyclic structure. Examples of such amine compounds 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-triazine-2-yl)ethyl-2-undecylimidazole, 1-butylimidazole, and 2-phenylimidazole. Examples of the triazole compounds include benzotriazole, 1H-benzotriazole-1-methanol, and 1-methyl-1H-benzotriazole. Other amine compounds include, for example, cetylamine, erucic acid amide, 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, and N-lauroyl sarcosine.In addition, as for other activators, one kind may be used alone or two or more kinds may be used in combination.

[0026] Moreover, the flux according to this embodiment may contain halogen-based activators such as amine halide salts and halogen compounds within a range that does not impose an environmental burden as other activators. Examples of amines in amine halide salts include diethylamine, dibutylamine, tributylamine, diphenylguanidine, cyclohexylamine, etc. Examples of halogens in amine halide 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), etc. In addition, these halogen-based activators may be used alone or two or more kinds may be used in combination.

[0027] When the flux contains a halogen-based activator, its content is preferably 0.4% by mass or less, and more preferably 0.05% by mass or less. When two or more kinds of halogen-based activators are contained, the content is the total content of the halogen-based activators.

[0028] The content of the activator, that is, the total content of the decarboxylation activator and other activators, is preferably 1.0% by mass or more, and more preferably 3.0% by mass or more with respect to the entire flux. Also, the content of the activator is preferably 30% by mass or less, and more preferably 20% by mass or less with respect to the entire flux.

[0029] (Resin) The flux according to this embodiment includes a resin from the viewpoint of improving solder wettability. Examples of the resin include rosin-based resins and synthetic resins. As the rosin-based resin, for example, one or more rosin-based resins selected from rosin and rosin derivatives (e.g., hydrogenated rosin, polymerized rosin, disproportionated rosin, acrylic acid-modified rosin, rosin ester, etc.) can be used. As the synthetic resin, known synthetic resins can be used. From the viewpoint of improving fluidity and making it easier to discharge voids, it is preferable that the resin is one or more resins selected from rosin, rosin derivatives, terpene phenol resins, acrylic resins, polybutadiene resins, and polyester polyol resins. Note that the resin may be used alone or in combination of two or more types.

[0030] The resin 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 resin content is preferably 70.0% by mass or less, and more preferably 50.0% by mass or less, relative to the total flux. If two or more types of resin are included, the above content refers to the total content of the resins.

[0031] (solvent) The flux according to this embodiment contains a solvent. The solvent is not particularly limited, and known solvents can be used. Examples of solvents 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), and diethylene glycol monobutyl ether (butyl diglycol); 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. Note that one solvent may be used alone, or two or more solvents may be used in combination.

[0032] The solvent content is not particularly limited, but is preferably 10.0% by weight or more, and more preferably 20.0% by weight or more, relative to the total flux. It is also preferably 60.0% by weight or less, and more preferably 45.0% by weight or less. If two or more solvents are included, the content refers to the total content of the solvents.

[0033] (Tixotropic agent) The flux according to this embodiment contains a thixotropic agent. The thixotropic agent is not particularly limited and includes, for example, hydrogenated castor oil, amides, kaolin, colloidal silica, organic bentonite, glass frit, etc. The thixotropic agent may be used alone or in combination of two or more.

[0034] The thixotropic agent content is not particularly limited, but is preferably 3.0% by mass or more, and more preferably 5.0% by mass or more, relative to the total flux. Furthermore, the thixotropic agent content 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 refers to the total content of the thixotropic agents.

[0035] The flux according to this embodiment may also contain other additives, such as antioxidants, surfactants, defoamers, and corrosion inhibitors.

[0036] Because the flux according to this embodiment is fluid, by including a decarboxylase activator as an activator that undergoes decarboxylation at this heating temperature, voids generated at the solder joint during reflow are pushed out by the carbon dioxide exhaust force. As a result, the generation of voids at the solder joint can be suppressed. Furthermore, since the decarboxylase activator exhibits sustained activity during reflow, when used with a lead-free solder alloy, it provides excellent solder wettability.

[0037] The flux according to this embodiment, by using an amino acid or its derivative as the decarboxylase activator, can further suppress the generation of voids in the solder joint and has superior solder wettability.

[0038] The flux according to this embodiment is used with a medium-to-high temperature lead-free solder alloy, and the decarboxylation activator is at least one selected from L-glutamic acid, L-glutamine, L-carnitine, β-alanine, L-citrulline, and L-theanine, so that decarboxylation occurs at the main heating temperature of the medium-to-high temperature lead-free solder alloy. As a result, when the flux is used with a medium-to-high temperature lead-free solder alloy, the generation of voids in the solder joint can be suppressed and the solder wettability is excellent.

[0039] The flux according to this embodiment has a decarboxylase activator content of 0.5% to 25% by mass relative to the total flux, thereby reducing flux residue after reflow soldering. Furthermore, even when the decarboxylase activator content is within the above range, the flux according to this embodiment can suppress the generation of voids in the solder joint and exhibits excellent solder wettability.

[0040] The flux according to this embodiment can be obtained, for example, by placing a resin, an activator, a solvent, a thixotropic agent, and other additives as needed into a heating container, heating to dissolve all the raw materials, and finally cooling to room temperature.

[0041] <Solda paste> The solder paste according to this embodiment contains the flux described above and a lead-free solder alloy. The lead-free solder alloy is not particularly limited and includes, for example, alloys containing tin, silver, copper, indium, zinc, bismuth, antimony, etc. More specifically, examples include high-temperature lead-free solder alloys such as Sn / Ag, Sn / Cu, and Sn / Sb; medium-to-high temperature lead-free solder alloys such as Sn / Ag / Cu, Sn / Ag / Bi / In, and Sn / Ag / Cu / Bi / In / Sb; medium-temperature lead-free solder alloys such as Sn / Ag / Cu / Bi; medium-to-low temperature lead-free solder alloys such as Sn / Zn / Bi, Sn / Zn, and Sn / Zn / Al; and low-temperature lead-free solder alloys such as Sn / Bi and Sn / Ag / Bi. The classification of lead-free solder alloys into high-temperature, medium-high-temperature, medium-temperature, medium-low-temperature, and low-temperature categories is based on JIS Z 3282;2017.

[0042] The solder paste according to this embodiment is obtained by mixing lead-free solder alloy powder with the flux described above. The flux content is preferably 5 to 20% by mass relative to the total solder paste. The lead-free solder alloy powder content is preferably 80 to 95% by mass relative to the total solder paste.

[0043] The solder paste according to this embodiment, by containing the flux described above, can suppress the generation of voids in the solder joint when used with a lead-free solder alloy, and also exhibits excellent solder wettability. [Examples]

[0044] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0045] [Measurement of decarboxylation temperature] First, TG-DTA measurements were performed on each activator shown in Table 1 using a differential thermal analyzer (Thermo plus TG 8120, Rigaku Corporation) to confirm that weight loss occurred. The TG-DTA measurement conditions were as follows. (Measurement conditions) Sample amount: 3mg Heating rate: 20℃ / min Atmosphere: Atmosphere Measurement temperature: room temperature ~ 350℃

[0046] Next, FT-IR measurements were performed on the compound before weight reduction and on the compound at the weight reduction initiation temperature + 10°C, using an FT-IR instrument (Frontier FT IR, PerkinElmer), confirming that the weight reduction was due to carbon dioxide generation.

[0047] Table 1 shows the decarboxylation temperatures obtained from TG-DTA and FT-IR measurements.

[0048] [Table 1]

[0049] Details of each ingredient shown in Table 1 are provided below. L-glutamic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. L-Glutamine: Manufactured by Tokyo Chemical Industry Co., Ltd. L-carnitine: Manufactured by Tokyo Chemical Industry Co., Ltd. β-Alanine: Manufactured by Tokyo Chemical Industry Co., Ltd. L-Citrulline: Manufactured by Tokyo Chemical Industry Co., Ltd. L-theanine: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0050] [Preparation of solder paste] The raw materials in the amounts shown in Tables 2 and 3 were placed in a heating container and heated to dissolve all the raw materials. Afterward, the mixture was cooled to room temperature to obtain a uniformly dispersed flux. Note that the amounts shown in Tables 2 and 3 are equal to the content of each component in the flux. Next, each flux was mixed at a concentration of 11.5% by mass, and solder powder (Sn-3.0wt%Ag-0.5wt%Cu) at a concentration of 88.5% by mass to obtain the solder paste for each example and comparative example. Note that in Tables 2 and 3, "other activators" are activators that do not cause decarboxylation.

[0051] [Table 2]

[0052] [Table 3]

[0053] Details of each raw material shown in Tables 2 and 3 are provided below. The same amino acids as in Table 1 were used as the decarboxylase activators. KE-604: Product name "KE-604", acid-modified rosin, manufactured by Arakawa Chemical Industries, Ltd. S-145: Product name "YS Polystar S145", terpene phenol resin, manufactured by Yasuhara Chemical Co., Ltd. KE-359: Product name "KE-359", ultra-pale rosin ester, manufactured by Arakawa Chemical Industries, Ltd. EHDG: 2-Ethylhexyl diglycol, manufactured by Nippon Emulsifier Co., Ltd. HeDG: Hexyl diglycol, manufactured by Nippon Emulsifier Co., Ltd. VA-79: Product name "Tallen VA-79", high-grade fatty acid amide, manufactured by Kyoeisha Chemical Co., Ltd. N-acetyl-L-hydroxyproline: Manufactured by Kyowa Hakko Bio Co., Ltd. N-acetyl-L-tyrosine: Manufactured by Tokyo Chemical Industry Co., Ltd. 2-Phenylimidazole: Manufactured by Tokyo Chemical Industry Co., Ltd. Tris(2-carboxyethyl) isocyanurate: Manufactured by Tokyo Chemical Industry Co., Ltd. Adipic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. Maleic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. trans-2,3-dibromo-2-butene-1,4-diol: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0054] [Evaluation of Void Factor] <Fabrication of test boards> The solder paste obtained in each example and comparative example was printed onto a test printed circuit board. The printing thickness of the solder paste was adjusted using a 120 μm metal mask. After printing the solder paste, a 72-pin QFN (Quad Flat No-lead package) (10 mm × 10 mm, Sn-plated) was mounted in the designated position. Subsequently, the test circuit boards for each example and comparative example were fabricated by heating under the following temperature conditions. (Temperature conditions) Heating rate: 3.0°C / second Heating temperature: 220°C or higher for 30 seconds Peak temperature: 240℃

[0055] <Calculation of Void Factor> X-ray radiographs were taken at the component mounting locations of each test board. A TUX-3100 (manufactured by Maas Token Co., Ltd.) was used for imaging, with the following conditions: tube voltage: 75.0V, tube current: 100.0μA, filament current: 3.130A, and magnification: 10.9x. Next, the void ratio of the joint was calculated by binarizing the captured images. A void ratio of less than 25.0% was considered acceptable. The results are shown in Tables 2 and 3.

[0056] [Evaluation of solder wettability] <Fabrication of test boards> The solder paste obtained in each example and comparative example was printed onto a test printed circuit board. The printing thickness of the solder paste was adjusted using a 120 μm metal mask. After printing the solder paste, 0603 size (0.6 mm × 0.3 mm) chip resistors (Sn plated) were mounted in the designated positions. Subsequently, test circuit boards for each example and comparative example were fabricated by heating under the same temperature conditions as for evaluating the void ratio.

[0057] <Evaluation of solder wettability> The obtained test substrates were visually inspected, and a uniform metallic luster was observed in the fillet area if it was deemed acceptable (○). The results are shown in Tables 2 and 3.

[0058] As can be seen from the results in Tables 2 and 3, the solder pastes of each embodiment that satisfy all the requirements of the present invention contain a decarboxylase activator as an activator that undergoes decarboxylation at the heating temperature (177°C to 247°C in this embodiment), thereby suppressing the generation of voids in the solder joint and providing good solder wettability.

[0059] On the other hand, the solder pastes of Comparative Examples 1, 3 to 6, which do not contain decarboxylizing agents, generate many voids at the solder joints and have poor solder wettability. Furthermore, the solder paste of Comparative Example 2, which does not contain decarboxylizing agents but contains halogen compounds, suppresses the generation of voids at the solder joints, but has poor solder wettability due to the low content of halogen compounds.

Claims

1. 1. A flux for use with a lead-free solder alloy, comprising: A flux containing a resin, an activator containing a decarboxylation activator that undergoes decarboxylation at the heating temperature, a solvent, and a thixotropic agent.

2. 2. The flux according to claim 1, wherein the decarboxylation activator is an amino acid or a derivative thereof.

3. Used with medium- to high-temperature lead-free solder alloys, 3. The flux according to claim 2, wherein the decarboxylation activator is at least one selected from the group consisting of L-glutamic acid, L-glutamine, L-carnitine, β-alanine, L-citrulline, and L-theanine.

4. 4. The flux according to claim 1, wherein the content of the decarboxylation activator is 0.5 mass % or more and 25 mass % or less with respect to the total mass of the flux.

5. A solder paste comprising the flux according to any one of claims 1 to 4 and a lead-free solder alloy.

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