Flux, solder paste, and method for producing bonded structure

Abstract

The invention relates to a soldering flux which is used for soft soldering. The liquid solvent contains at least one component selected from the group consisting of an aliphatic alcohol that has one hydroxyl group and is solid at 20 DEG C and a fatty acid ester that is solid at 20 DEG C, a liquid solvent that has more than one and less than three hydroxyl groups and is liquid at 20 DEG C, and a solid solvent that has more than two and less than four hydroxyl groups and is solid at 20 DEG C. The flux does not contain a thixotropic agent or contains 20.0 mass% or less of a thixotropic agent relative to the entire flux.

Description

Technical Field

[0001] The present invention relates to a soldering flux, a solder paste and a method for producing a joint structure. Background Art

[0002] When joining electronic circuit substrates such as printed circuit boards and joining components, a solder paste made by mixing solder alloy powder and flux is used. The solder paste is applied to the electrode portion on the surface of the substrate and heated (reflow soldering) while the electrode portion is in contact with the electrode portion of the joining component. As a result, the solder alloy powder melts to form a solder joint portion, and a joint structure in which the substrate and the joining component are joined via the solder joint portion can be obtained.

[0003] As the flux contained in the above-mentioned solder paste, a flux composed of a resin such as rosin, a solvent, a thixotropic agent, an activator, etc. is generally used. However, when soldering is performed using a solder paste containing such a flux, flux residues may remain around the soldered portion. Therefore, the flux residues are reduced by, for example, a method of selecting the constituent components of the flux from highly volatile materials, a method of using reduced pressure reflow soldering or reduced pressure reduction reflow soldering to fully volatilize the flux during the reflow soldering process, and the like.

[0004] For example, a soldering flux that does not contain a resin such as rosin that is difficult to volatilize is disclosed in Patent Document 1. The soldering flux reduces the amount of flux residue by using a combination of a liquid solvent and a solid solvent instead of a resin such as rosin.

[0005] In the past, solder foil was widely used in the welding of power devices. However, in recent years, solder paste has also attracted much attention in the field of power device manufacturing as an alternative material to solder foil. Solder paste can supply soft solder to the substrate at one time by printing. In addition, when soldering is performed using solder paste, there is no need for a fixture to fix the components to prevent the movement and falling of the components during the transportation of the substrate. As a result, the manufacturing process of the joint structure is easy to automate, and therefore, attempts are being actively made to apply solder paste to welding in the manufacture of power devices.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-38026

[0009] However, the problem with the reflow process is that in order to reduce the flux residue after reflow, the reflow process time needs to be long. In particular, in the soldering of power devices, the flux residue will cause defects in the subsequent process, so it is necessary to further reduce the flux residue. Therefore, in the soldering of power devices, the reflow process time tends to become longer. Summary of the invention

[0010] Problem that the invention aims to solve

[0011] The present invention has been made in view of the above circumstances, and a technical object thereof is to provide a flux, a solder paste, and a method for manufacturing a joint structure that can shorten a reflow process time for achieving low residue.

[0012] Solutions for solving problems

[0013] The flux of the present invention is used for soldering, and contains: at least one selected from the group consisting of aliphatic alcohols having one hydroxyl group and being solid at 20°C and fatty acid esters being solid at 20°C, a liquid solvent having one or more and three or less hydroxyl groups and being liquid at 20°C, and a solid solvent having two or more and four or less hydroxyl groups and being solid at 20°C, wherein the flux does not contain a thixotropic agent or contains a thixotropic agent in an amount of 20.0 mass % or less relative to the entire flux.

[0014] The solder paste according to the present invention comprises the above-mentioned flux and solder alloy powder.

[0015] The method for manufacturing a joined structure according to the present invention joins a substrate and a joining member using solder paste. DETAILED DESCRIPTION

[0016] Hereinafter, a method for producing a flux, a solder paste, and a joint structure according to an embodiment of the present invention will be described.

[0017] <Flux>

[0018] The soldering flux according to the present embodiment contains at least one selected from the group consisting of aliphatic alcohols and fatty acid esters, a liquid solvent, and a solid solvent.

[0019] (Aliphatic Alcohol)

[0020] The aliphatic alcohol has one hydroxyl group and is solid at 20° C. Examples of such aliphatic alcohols include 1-tetradecanol, 1-hexadecanol, 1-octadecanol, 1-eicosanol, 1-docosanol, 1-dodecanol, and 1-tetracosanol. Among them, the aliphatic alcohol is preferably at least one selected from the group consisting of 1-tetradecanol, 1-hexadecanol, 1-octadecanol, 1-eicosanol, and 1-docosanol.

[0021] The content of the aliphatic alcohol is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 5.0% by mass or more, relative to the entire flux. In addition, the content of the aliphatic alcohol is preferably 45.0% by mass or less, more preferably 30.0% by mass or less, and particularly preferably 20.0% by mass or less, relative to the entire flux. It should be noted that when two or more aliphatic alcohols are included, the content is the total content.

[0022] (Fatty acid esters)

[0023] The fatty acid ester is solid at 20° C. Examples of such fatty acid esters include methyl stearate, ethyl stearate, butyl stearate, methyl palmitate, ethyl palmitate, methyl arachidate, ethyl arachidate, methyl behenate, etc. Among them, the fatty acid ester is preferably at least one selected from the group consisting of methyl stearate, ethyl stearate, and butyl stearate.

[0024] The content of the fatty acid ester is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 3.0% by mass or more relative to the entire flux. In addition, the content of the fatty acid ester is preferably 45.0% by mass or less, more preferably 20.0% by mass or less, and particularly preferably 10.0% by mass or less relative to the entire flux. It should be noted that when two or more fatty acid esters are included, the content is the total content.

[0025] From the perspective of suppressing the separation of the soldering flux, the soldering flux involved in this embodiment preferably contains both the aliphatic alcohol and the fatty acid ester. The total content of the aliphatic alcohol and the fatty acid ester is preferably 1.0% by mass or more, more preferably 5.0% by mass or more, and particularly preferably 10.0% by mass or more relative to the entire soldering flux. In addition, the total content of the aliphatic alcohol and the fatty acid ester is preferably 45.0% by mass or less, more preferably 40.0% by mass or less, and particularly preferably 30.0% by mass or less relative to the entire soldering flux.

[0026] (Liquid Solvent)

[0027] The flux according to the present embodiment contains a liquid solvent having one or more and three or less hydroxyl groups and being liquid at 20° C. Examples of such a liquid solvent include 3-methyl-1,5-pentanediol, 1,4-butanediol, 2,5-hexanediol, 1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, hexyldecanol, isostearyl alcohol, 2-octyldodecanol, 2-decyltetradecanol, oleyl alcohol, 2-ethyl-1,3-hexanediol, 3-methyl-1,3-butanediol, and glycerol.

[0028] As for the liquid solvent, from the perspective of improving the volatility of the flux, it is preferred to use at least one, and from the perspective of improving the viscosity stability of the solder paste, it is more preferred to use two or more. When at least one of the liquid solvents is used, it is preferably at least one selected from the group consisting of 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,3-butanediol, 1,2,6-hexanetriol and 1,2,4-butanetriol.

[0029] The content of the liquid solvent is preferably 5.0% by mass or more, more preferably 20.0% by mass or more, relative to the total flux. In addition, the content of the liquid solvent is preferably 80.0% by mass or less, more preferably 60.0% by mass or less, relative to the total flux. It should be noted that when two or more liquid solvents are included, the content is the total content.

[0030] (Solid Solvent)

[0031] The flux according to the present embodiment contains a solid solvent having two or more and four or less hydroxyl groups and being solid at 20° C. Examples of such a solid solvent include 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-octanediol, 1,8-octanediol, 1,10-decanediol, 1,2-dodecanediol, 1,6-hexanediol, 1,9-nonanediol, trimethylolethane, trimethylolpropane, and erythritol. Among them, from the perspective of improving the printability of the solder paste, the solid solvent is preferably selected from at least 3 of the group consisting of 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-octanediol, 1,8-octanediol, 1,10-decanediol, 1,2-dodecanediol, 1,6-hexanediol, 1,9-nonanediol, trimethylolethane, trimethylolpropane and erythritol.

[0032] The content of the solid solvent is preferably 5.0 mass % or more, more preferably 25.0 mass % or more, relative to the total flux. In addition, the content of the solid solvent is preferably 92.0 mass % or less, more preferably 65.0 mass % or less, relative to the total flux. It should be noted that when two or more solid solvents are included, the content is the total content.

[0033] (Thixotropic agent)

[0034] The soldering flux involved in the present embodiment does not contain a thixotropic agent or contains a thixotropic agent of less than 20.0 mass % relative to the entire soldering flux. As a thixotropic agent, for example, hydrogenated castor oil, fatty acid amide, fatty acid bisamide, polyamide compound, kaolin, colloidal silica, organic bentonite, glass powder, etc. can be listed. Among them, from the perspective of reducing the soldering flux residue, the thixotropic agent preferably contains fatty acid amide, and more preferably consists of fatty acid amide. As fatty acid amide, for example, stearic acid amide, lauric acid amide, palmitic acid amide, oleic acid amide, erucic acid amide, behenic acid amide, hydroxystearic acid amide, myristic acid amide, etc. can be listed. Among them, fatty acid amide is preferably stearic acid amide, lauric acid amide, palmitic acid amide, oleic acid amide, erucic acid amide, behenic acid amide. It should be noted that the thixotropic agent can be used alone or in combination of two or more.

[0035] From the perspective of increasing the volatility of the soldering flux, the content of the thixotropic agent is 20.0 mass % or less, preferably 15.0 mass % or less, and more preferably 10.0 mass % or less relative to the entire soldering flux. In addition, from the perspective of increasing the volatility of the soldering flux, the soldering flux involved in this embodiment preferably does not contain a thixotropic agent. It should be noted that when two or more thixotropic agents are included, the content is the total content.

[0036] (Active Agent)

[0037] The soldering flux involved in this embodiment may include an activator. The activator is not particularly limited, and examples thereof include organic acid-based activators, amine compounds, amino acids, amine halogen salts, halogen compounds, and other halogen-based activators. It should be noted that the activator may be used alone or in combination of two or more.

[0038] There are no particular limitations on the organic acid-based activators, and examples thereof include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, capric acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, tuberostearic 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 dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and picolinic acid.

[0039] The amine compound is not particularly limited, and examples thereof include imidazole compounds and triazole compounds. Examples of the imidazole compound 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, 2-phenylimidazole, and 4-methyl-2-phenylimidazole. Examples of the triazole compound include benzotriazole, 1H-benzotriazole-1-methanol, and 1-methyl-1H-benzotriazole. Examples of other amine compounds include cetylamine, 3-(dimethylamino)-1,2-propanediol, 3,5-dimethylpyrazole, dimethylurea, hexahydro-1,3,5-triphenyl-1,3,5-triazine, pyrazinamide, N-phenylglycine, 3-methyl-5-pyrazolone, N-lauroylsarcosine, and 1,3-diphenylguanidine.

[0040] The amino acid is not particularly limited, and examples thereof 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-acetyleucine (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).

[0041] The halogen-based activator is not particularly limited, and examples thereof include amine halogen salts and halogen compounds. Examples of amines of the amine halogen salts include diethylamine, dibutylamine, tributylamine, diphenylguanidine, and cyclohexylamine. Examples of halogens of the 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.

[0042] The content of the activator is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, relative to the total flux. In addition, the content of the activator is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, relative to the total flux. It should be noted that when two or more activators are included, the content of the activator is the total content.

[0043] The soldering flux according to the present embodiment may contain at least one selected from, for example, a stabilizer, a surfactant, a defoamer, and a corrosion inhibitor as other additives. The total content of other additives is not particularly limited, and may be, for example, 5.0 mass % or less relative to the entire soldering flux.

[0044] The soldering flux according to the present embodiment includes at least one selected from the group consisting of aliphatic alcohols having one hydroxyl group and being solid at 20° C. and fatty acid esters being solid at 20° C., and the soldering flux does not include a thixotropic agent or includes a thixotropic agent in an amount of 20.0 mass % or less relative to the entire soldering flux. Thus, the reflow process time for achieving low residue can be shortened.

[0045] According to the soldering flux involved in this embodiment, the soldering flux preferably contains the aliphatic alcohol, and the content of the aliphatic alcohol is 0.5 mass % or more and 45.0 mass % or less relative to the entire soldering flux. Thus, the reflow process time for achieving low residue can be further shortened. In addition, the viscosity of the soldering flux is increased, and the viscosity of the solder paste can be ensured.

[0046] According to the soldering flux involved in this embodiment, the soldering flux preferably contains the fatty acid ester, and the content of the fatty acid ester is 0.5 mass % or more and 45.0 mass % or less relative to the entire soldering flux. Thus, the reflow process time for achieving low residue can be further shortened. In addition, the viscosity of the soldering flux is increased, which can ensure the viscosity of the solder paste.

[0047] According to the soldering flux involved in this embodiment, the aliphatic alcohol is preferably at least one selected from the group consisting of 1-dodecanol, 1-tetradecanol, 1-hexadecanol, 1-octadecanol, 1-eicosanol and 1-docosanol. Thus, the reflow process time for achieving low residue can be further shortened.

[0048] According to the soldering flux of this embodiment, the fatty acid ester is preferably at least one selected from the group consisting of methyl stearate, ethyl stearate and butyl stearate. This can further shorten the reflow process time for achieving low residue.

[0049] <Solder paste>

[0050] The solder paste involved in the present embodiment contains the above-mentioned flux and solder alloy powder. As the solder alloy in the solder alloy powder, lead-free solder alloys and eutectic solder alloys containing lead can be listed. From the perspective of reducing environmental load, lead-free solder alloys are preferred. As lead-free solder alloys, for example, alloys containing tin, silver, copper, indium, zinc, bismuth, antimony, etc. can be listed. More specifically, alloys such as 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 / Sb, Sn / Ag / Sb, Sn / Ag / Cu / Bi, Sn / Ag / Cu / Bi / In / Sb, In / Ag, and Sn / In can be listed. In addition, the alloy contains inevitable impurities. Inevitable impurities refer to components that are inevitably mixed in during the production process and are allowed within a range that does not affect the effects of the present invention.

[0051] The content of the flux is preferably 5% by mass or more and 20% by mass or less relative to the entire solder paste. In addition, the content of the solder alloy powder is preferably 80% by mass or more and 95% by mass or less relative to the entire solder paste.

[0052] The solder paste according to the present embodiment includes the flux and solder alloy powder, thereby shortening the reflow process time for achieving low residue.

[0053] <Method for producing a bonded structure>

[0054] The manufacturing method of the joint structure involved in this embodiment uses the solder paste to join the substrate and the joining component. Specifically, in a reflow furnace, the substrate and the joining component are heated in a state of contacting each other via the solder paste to melt the solder alloy constituting the solder paste. Then, the substrate and the joining component are joined by cooling.

[0055] First, the solder paste is arranged on the surface of the substrate. The solder paste can be arranged by a known method such as printing with a solder printing device, transfer, coating with a dispenser, and mounting with a mounting machine. When the solder paste is printed with a solder printing device, the thickness of the coated solder paste can be made to be greater than 30 μm and less than 600 μm. In addition, the substrate is not particularly limited, and for example, a known substrate such as a printed circuit board, a DBC substrate, a base plate, a lead frame, a silicon wafer, etc. can be used.

[0056] Next, the bonding component is configured so as to contact the substrate via the solder paste. The bonding component is not particularly limited, and for example, known bonding components such as chip components (IC chips, etc.), resistors, diodes, capacitors, transistors, semiconductor chips (Si chips, etc.), and heat sinks can be used.

[0057] Next, the substrate and the bonding component are heated in a state where they are in contact with each other via the solder paste. The heating temperature is not particularly limited and can be appropriately selected according to the solder paste, and its range is above the melting point of the solder paste. In order to suppress the oxidation of the metal, the heating process can be carried out in an inert gas atmosphere using nitrogen or the like. In addition, in order to promote the release of the gas, the atmosphere can be decompressed or vacuumed using a vacuum pump. In addition, a preheating process can be carried out before the heating process. The preheating temperature is not particularly limited and can be appropriately selected according to the solder paste, and its range is less than the melting point of the solder paste. The preheating process can be carried out in an inert gas atmosphere in a reduced pressure or vacuum, and can also be carried out in a reducing atmosphere using hydrogen or formic acid gas.

[0058] Finally, the substrate and the bonding member in contact with each other via the solder paste are cooled. In the cooling step, the substrate and the bonding member are cooled to 20° C. to 200° C. at a temperature drop rate of 120° C. / min to 5° C. / min, for example.

[0059] The method for manufacturing a bonded structure according to the present embodiment uses the solder paste to bond a substrate and a bonding member, thereby shortening the reflow process time for achieving low residue.

[0060] The present invention includes the following aspects.

[0061] [1] A flux for soldering,

[0062] The soldering flux contains:

[0063] at least one selected from the group consisting of aliphatic alcohols having one hydroxyl group and being solid at 20°C and fatty acid esters being solid at 20°C,

[0064] a liquid solvent having 1 or more and 3 or less hydroxyl groups and being liquid at 20°C, or a solid solvent having 2 or more and 4 or less hydroxyl groups and being solid at 20°C,

[0065] The soldering flux contains no thixotropic agent or contains 20.0 mass % or less of a thixotropic agent based on the entire soldering flux.

[0066] [2] The soldering flux according to [1], wherein the soldering flux contains the aliphatic alcohol, and a content of the aliphatic alcohol is 0.5 mass % or more and 45.0 mass % or less based on the entire soldering flux.

[0067] [3] The soldering flux according to [1] or [2], wherein the soldering flux contains the fatty acid ester, and a content of the fatty acid ester is 0.5 mass % or more and 45.0 mass % or less based on the entire soldering flux.

[0068] [4] The soldering flux according to any one of [1] to [3], wherein the aliphatic alcohol is at least one selected from the group consisting of 1-dodecanol, 1-tetradecanol, 1-hexadecanol, 1-octadecanol, 1-eicosanol, and 1-docosanol.

[0069] [5] The soldering flux according to any one of [1] to [4], wherein the fatty acid ester is at least one selected from the group consisting of methyl stearate, ethyl stearate, and butyl stearate.

[0070] [6] A solder paste comprising: the flux according to any one of [1] to [5] and a solder alloy powder.

[0071] [7] A method for manufacturing a joined structure, comprising joining a substrate and a joining member using the solder paste described in [6].

[0072] It should be noted that the manufacturing method of the flux, solder paste and joint structure involved in the present invention is not limited to the above-mentioned embodiment, and various changes can be made without departing from the main purpose of the present invention. In addition, the manufacturing method of the flux, solder paste and joint structure involved in the present invention is not limited to the effects of the above-mentioned embodiment. That is, the embodiments disclosed this time should be considered as exemplary rather than restrictive in all aspects. The scope of the present invention is indicated by the claims rather than the foregoing description. In addition, the scope of the present invention is intended to include all changes within the same meaning and scope as the claims.

[0073] Example

[0074] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0075] <Material of flux>

[0076] (Aliphatic Alcohol)

[0077] 1-Tetradecanol: Made by Tokyo Chemical Industry Co., Ltd.

[0078] 1-Hexadecanol: Made by Tokyo Chemical Industry Co., Ltd.

[0079] 1-Octadecanol: Made by Tokyo Chemical Industry Co., Ltd.

[0080] 1-Eicosanol: manufactured by Tokyo Chemical Industry Co., Ltd.

[0081] 1-Docosanol: manufactured by Tokyo Chemical Industry Co., Ltd.

[0082] (Fatty acid esters)

[0083] Methyl stearate: Made by Tokyo Chemical Industry Co., Ltd.

[0084] Ethyl stearate: Made by Tokyo Chemical Industry Co., Ltd.

[0085] Butyl stearate: Made by Tokyo Chemical Industry Co., Ltd.

[0086] (Liquid Solvent)

[0087] 3-Methyl-1,5-pentanediol: Made by Kuraray

[0088] 1,4-Butanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0089] 2,5-Hexanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0090] 1,5-Pentanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0091] 2,4-Diethyl-1,5-pentanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0092] 1,2,6-Hexanetriol: Made by Tokyo Chemical Industry Co., Ltd.

[0093] 1,2,4-Butanetriol: Made by Tokyo Chemical Industry Co., Ltd.

[0094] Hexyldecanol: Made by Advanced Alcohol Industries

[0095] Isostearyl alcohol: Made by Advanced Alcohol Industries

[0096] 2-Octyldodecanol: Made by Advanced Alcohol Industries, Ltd.

[0097] 2-Decyltetadecanol: Made by Advanced Alcohol Industries, Ltd.

[0098] Oleyl alcohol: Made by Advanced Alcohol Industries

[0099] (Solid Solvent)

[0100] 2,2-Dimethyl-1,3-propanediol: Made by Mitsubishi Gas Chemical Co., Ltd.

[0101] 2,5-Dimethyl-2,5-hexanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0102] 2,2,4-Trimethyl-1,3-pentanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0103] 2-Butyl-2-ethyl-1,3-propanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0104] 1,2-Octanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0105] 1,8-Octanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0106] 1,10-Decanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0107] 1,2-Dodecanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0108] 1,6-Hexanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0109] 1,9-Nonanediol: Made by Tokyo Chemical Industry Co., Ltd.

[0110] Trimethylolethane: Made by Mitsubishi Gas Chemical Co., Ltd.

[0111] Trimethylolpropane: Made by Mitsubishi Gas Chemical Co., Ltd.

[0112] Erythritol: Made by Tokyo Chemical Industry Co., Ltd.

[0113] (Thixotropic agent)

[0114] Stearamide: manufactured by Kao Co., Ltd.

[0115] Lauric acid amide: Made by Mitsubishi Chemical Corporation

[0116] Palmitic acid amide: Made by Mitsubishi Chemical Corporation

[0117] Oleic acid amide: Made by Kao Corporation

[0118] Erucamide: Made by Nippon Seika Co., Ltd.

[0119] Behenic acid amide: Made by Nippon Seika Co., Ltd.

[0120] <Preparation of flux>

[0121] The materials of the above-mentioned flux were put into a heating container according to the formulations shown in Tables 1 to 10, and heated to 120°C to dissolve all the materials. Then, the mixture was cooled to room temperature to obtain uniformly dispersed fluxes of each embodiment and each comparative example. It should be noted that the blending amounts shown in Tables 1 to 10 are the same as the contents of the components contained in the flux.

[0122] <Preparation of solder paste>

[0123] 9 mass % of the flux of each example and each comparative example and 91 mass % of solder alloy powder (96.5Sn / 3Ag / 0.5Cu, Type 3, manufactured by Honghui Co., Ltd.) were mixed to obtain solder paste of each example and each comparative example.

[0124] Table 1

[0125]

[0126] Table 2

[0127]

[0128] Table 3

[0129]

[0130] Table 4

[0131]

[0132] Table 5

[0133]

[0134] Table 6

[0135]

[0136] Table 7

[0137]

[0138] Table 8

[0139]

[0140] Table 9

[0141]

[0142] Table 10

[0143]

[0144] <Evaluation of Flux Volatility>

[0145] First, measure the weight of the evaporating dish, and set its weight as W1. Next, weigh 0.3 to 0.303 g of the flux of each embodiment and each comparative example on the above evaporating dish, and set its weight as W2. Next, put the evaporating dish with the flux on a hot plate heated to 350°C, visually observe the time until the flux is completely volatilized, then remove the evaporating dish from the hot plate and cool it to room temperature. Set the maximum heating time to 240 seconds. Even if the flux is not completely volatilized, remove the evaporating dish from the hot plate and cool it to room temperature. Measure the weight of the evaporating dish cooled to room temperature, and set its weight as W3. Calculate the flux volatilization amount [%] of each embodiment and each comparative example according to the following formula (1). The results are shown in Tables 1 to 10.

[0146] Flux volatilization amount [%] = (W2-(W3-W1)) / W2×100(1)

[0147] In the formula, W1 represents the weight of the evaporating dish, W2 represents the weight of the evaporating dish with the flux weighed, and W3 represents the weight of the evaporating dish when the evaporating dish with the flux weighed is heated and then cooled to room temperature.

[0148] The volatility of the flux was evaluated according to the following criteria. The results are shown in Tables 1 to 10.

[0149] ◎: The flux volatilization amount [%] is 97% or more and the time until the flux volatilizes is within 180 seconds

[0150] ○: The flux volatilization amount [%] is 97% or more and the time until the flux volatilizes is within 240 seconds

[0151] ×: Flux volatilization amount [%] is 97% or less

[0152] <Evaluation of solder paste>

[0153] After the solder paste of each embodiment and each comparative example was placed in an environment of 20 to 30°C for 1 hour, the state of the solder paste was confirmed. The solder paste was evaluated according to the following criteria. The results are shown in Tables 1 to 10. It should be noted that "separation of flux" refers to the state in which the solder alloy powder in the solder paste settles due to the difference in specific gravity between the solder alloy powder and the flux, and the flux accumulates on the upper part.

[0154] A: No change (dispersion state of flux and solder alloy powder)

[0155] B: There is flux separation, and it returns to state A after stirring with a scraper

[0156] C: The solder paste is harder, but after stirring with a scraper, it returns to the state of A.

[0157] From the results of Tables 1 to 10, it can be seen that in the fluxes of the embodiments that meet all the characteristics of the present invention, the volatilization amount of the flux is 97% or more and the time until the flux volatilizes is within 240 seconds. Therefore, the flux according to the present invention can shorten the reflow process time for achieving low residue.

Claims

1. A flux for soldering, The soldering flux contains: at least one selected from the group consisting of aliphatic alcohols having one hydroxyl group and being solid at 20°C and fatty acid esters being solid at 20°C, A liquid solvent having one or more and three or less hydroxyl groups and being liquid at 20°C, A solid solvent having 2 or more and 4 or less hydroxyl groups and being solid at 20° C., The soldering flux contains no thixotropic agent or contains 20.0 mass % or less of a thixotropic agent based on the entire soldering flux.

2. The soldering flux according to claim 1, wherein The soldering flux comprises the aliphatic alcohol, The content of the aliphatic alcohol is 0.5 mass % or more and 45.0 mass % or less based on the entire flux.

3. The soldering flux according to claim 1, wherein The soldering flux comprises the fatty acid ester, The content of the fatty acid ester is 0.5 mass % or more and 45.0 mass % or less based on the entire flux.

4. The soldering flux according to claim 1, wherein The aliphatic alcohol is at least one selected from the group consisting of 1-dodecanol, 1-tetradecanol, 1-hexadecanol, 1-octadecanol, 1-eicosanol, and 1-docosanol.

5. The soldering flux according to claim 1, wherein The fatty acid ester is at least one selected from the group consisting of methyl stearate, ethyl stearate, and butyl stearate.

6. A solder paste comprising: the flux according to claim 1 and solder alloy powder. 7 . A method for producing a joined structure, comprising joining a substrate and a joining member using the solder paste according to claim 6 .

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