Flux, solder paste, and joint structure manufacturing method

Abstract

To provide a flux, solder paste and a joint structure manufacturing method which can reduce a reflowing process for achieving less residues.SOLUTION: A flux, which is used for soldering, contains at least one kind selected from a group consisting of aliphatic alcohol having one hydroxy group, which is solidified at 20°C and fatty acid ester which is solidified at 20°C, a liquid solvent having one or more and three or less of hydroxy groups, which is liquidized at 20°C, and a solid solvent having two or more and four or less of hydroxy groups, which is solidifies at 20°C, where the flux does not contain a thixotropic agent or contains 20.0 mass% or more of thixotropic agents with respect to the total of flux. The flux contains the fatty acid ester.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] A solder paste made by mixing a solder alloy powder and flux is used to bond an electronic circuit board such as a printed wiring board to a bonding component. The solder paste is applied to the electrode part on the surface of the board, and heated (reflowed) while the electrode part of the bonding component is in contact with the electrode part. This melts the solder alloy powder to form a solder joint, and a bonded structure can be obtained in which the board and the bonding component are bonded via the solder joint.

[0003] The flux contained in such solder paste is generally composed of a resin such as rosin, a solvent, a thixotropic agent, and an activator. However, when soldering is performed using a solder paste containing such a flux, flux residue may remain around the soldered portion. For this reason, attempts are made to reduce the flux residue by, for example, selecting a highly volatile material as the constituent component of the flux, or employing reduced pressure reflow or reduced pressure reduction reflow to sufficiently volatilize the flux in the reflow process.

[0004] For example, Patent Document 1 discloses a flux that does not contain resin such as rosin, which is difficult to volatilize. This flux uses a liquid solvent and a solid solvent in combination instead of resin such as rosin, thereby reducing flux residue.

[0005] Conventionally, solder foil has been widely used in the soldering of power device manufacturing. However, in recent years, solder paste has also been attracting attention in the field of power device manufacturing as an alternative material to solder foil. Solder paste can supply solder to a board in one go by printing. Furthermore, soldering using solder paste does not require a jig for fixing components to prevent components from shifting or falling during board transportation. This makes it easier to automate the manufacturing process of joint structures, so there have been active attempts to apply solder paste to soldering in power device manufacturing. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-38026

[0007] However, the soldering reflow process has a problem in that the reflow process time is long in order to reduce the flux residue after reflow. In particular, in the soldering of power devices, the flux residue can cause defects in the subsequent processes, so there is a need to further reduce the flux residue. Therefore, in the soldering of power devices, the reflow process time tends to be longer. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a flux, a solder paste, and a method for manufacturing a joint structure that can shorten the reflow process time to achieve low residue. [Means for solving the problem]

[0009] The flux according to the present invention is a flux used for soldering, which contains at least one selected from the group consisting of an aliphatic alcohol having one hydroxy group and being solid at 20°C, and a fatty acid ester that is solid at 20°C, a liquid solvent having one to three hydroxy groups and being liquid at 20°C, and a solid solvent having two to four hydroxy groups and being solid at 20°C, and which does not contain a thixotropic agent or contains 20.0 mass% or less of a thixotropic agent relative to the entire flux, and the flux contains the fatty acid ester.

[0010] The solder paste according to the present invention contains the flux and a solder alloy powder.

[0011] The method for manufacturing a joint structure according to the present invention uses a solder paste to join a substrate and a joining component. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a flux, a solder paste, and a method for manufacturing a joint structure according to an embodiment of the present invention will be described.

[0013] <Flux> The 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.

[0014] (Fatty alcohol) The aliphatic alcohol has one hydroxy group and is solid at 20° C. Examples of such aliphatic alcohol include 1-tetradecanol, 1-hexadecanol, 1-octadecanol, 1-eicosanol, 1-docosanol, 1-dodecanol, and 1-tetracosanol. Among these, 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.

[0015] 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, based on the total amount of the flux. 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, based on the total amount of the flux. When two or more types of aliphatic alcohol are included, the content is the total content.

[0016] (Fatty acid ester) 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 these, the fatty acid ester is preferably at least one selected from the group consisting of methyl stearate, ethyl stearate, and butyl stearate.

[0017] 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, based on the total mass of the flux. 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, based on the total mass of the flux. When two or more fatty acid esters are included, the above content is the total content.

[0018] From the viewpoint of suppressing separation of the flux, the flux according to the present 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 mass% or more, more preferably 5.0 mass% or more, and particularly preferably 10.0 mass% or more, based on the entire flux. The total content of the aliphatic alcohol and the fatty acid ester is preferably 45.0 mass% or less, more preferably 40.0 mass% or less, and particularly preferably 30.0 mass% or less, based on the entire flux.

[0019] (liquid solvent) The flux according to this embodiment contains a liquid solvent that has one to three hydroxyl groups and is liquid at 20° C. Examples of such liquid solvents 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-decyltetradodecanol, oleyl alcohol, 2-ethyl-1,3-hexanediol, 3-methyl-1,3-butanediol, and glycerin.

[0020] From the viewpoint of increasing the volatility of the flux, it is preferable to use at least one of the liquid solvents, and from the viewpoint of increasing the viscosity stability of the solder paste, it is more preferable to use two or more of them. When at least one of the liquid solvents is used, it is preferable that the liquid solvent is 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.

[0021] The content of the liquid solvent is preferably 5.0 mass% or more, more preferably 20.0 mass% or more, based on the total amount of the flux. The content of the liquid solvent is preferably 80.0 mass% or less, more preferably 60.0 mass% or less, based on the total amount of the flux. When two or more liquid solvents are included, the content is the total content.

[0022] (Solid Solvent) The flux according to this embodiment contains a solid solvent that has two or more and four or less hydroxyl groups and is 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 these, from the viewpoint of improving the printability of the solder paste, the solid solvent is preferably at least three selected from 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.

[0023] The content of the solid solvent is preferably 5.0% by mass or more, more preferably 25.0% by mass or more, based on the total amount of the flux. The content of the solid solvent is preferably 92.0% by mass or less, more preferably 65.0% by mass or less, based on the total amount of the flux. When two or more solid solvents are included, the content is the total content.

[0024] (thixotropic agent) The flux according to the present embodiment does not contain a thixotropic agent, or contains a thixotropic agent in an amount of 20.0 mass% or less based on the entire flux. Examples of the thixotropic agent include castor hardened oil, fatty acid amide, fatty acid bisamide, polyamide compound, kaolin, colloidal silica, organic bentonite, glass frit, and the like. Among these, the thixotropic agent preferably contains a fatty acid amide, and more preferably consists of a fatty acid amide, from the viewpoint of reducing flux residue. Examples of the fatty acid amide include stearic acid amide, lauric acid amide, palmitic acid amide, oleic acid amide, erucic acid amide, behenic acid amide, hydroxystearic acid amide, myristic acid amide, and the like. Among these, the fatty acid amide is preferably stearic acid amide, lauric acid amide, palmitic acid amide, oleic acid amide, erucic acid amide, or behenic acid amide. The thixotropic agent may be used alone or in combination of two or more kinds.

[0025] 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, based on the total mass of the flux, from the viewpoint of increasing the volatility of the flux. Moreover, the flux according to the present embodiment preferably does not contain a thixotropic agent, from the viewpoint of increasing the volatility of the flux. Note that when two or more types of thixotropic agents are contained, the above content is the total content.

[0026] (Activator) The flux according to the present embodiment may contain an activator. The activator is not particularly limited, and examples thereof include organic acid activators, amine compounds, amino acids, and halogen activators such as amine halogen salts and halogen compounds. The activators may be used alone or in combination of two or more.

[0027] The organic acid surfactant is not particularly limited, and examples thereof include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecylic 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, 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.

[0028] The amine-based compound is not particularly limited, and examples thereof include imidazole-based compounds and triazole-based compounds. Examples of the imidazole-based 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-based compounds include benzotriazole, 1H-benzotriazole-1-methanol, and 1-methyl-1H-benzotriazole. Other amine compounds include, for example, 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.

[0029] 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-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).

[0030] The halogen-based activator is not particularly limited, and examples thereof include amine halogen salts and halogen compounds. Examples of the amines in the amine halogen salts include diethylamine, dibutylamine, tributylamine, diphenylguanidine, and cyclohexylamine. Examples of the halogens in the amine halogen salts include fluorine, chlorine, bromine, and iodine. Examples of the 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.

[0031] The content of the activator is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, based on the total amount of the flux. The content of the activator is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, based on the total amount of the flux. When two or more types of activators are included, the content of the activators is the total content.

[0032] The flux according to the present embodiment may contain at least one of the following other additives: a stabilizer, a surfactant, a defoamer, and a corrosion inhibitor. The total content of the other additives is not particularly limited, and may be, for example, 5.0 mass% or less with respect to the entire flux.

[0033] The flux according to the present embodiment contains at least one selected from the group consisting of an aliphatic alcohol having one hydroxyl group and being solid at 20° C., and a fatty acid ester being solid at 20° C., and 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, and the flux contains the fatty acid ester, which allows the reflow process time for realizing low residue to be shortened.

[0034] According to the flux of this embodiment, the flux contains the aliphatic alcohol, and the content of the aliphatic alcohol is preferably 0.5% by mass or more and 45.0% by mass or less with respect to the entire flux. This makes it possible to further shorten the reflow process time required to achieve low residue. In addition, the viscosity of the flux increases, ensuring the viscosity of the solder paste.

[0035] According to the flux of the present embodiment, the flux contains the fatty acid ester, and the content of the fatty acid ester is preferably 0.5% by mass or more and 45.0% by mass or less with respect to the total flux. This allows the reflow process time required to achieve low residue to be further shortened. In addition, the viscosity of the flux is increased, ensuring the viscosity of the solder paste.

[0036] In the flux according to the present 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, which can further shorten the reflow process time to achieve low residue.

[0037] In the flux according to the present embodiment, the fatty acid ester is preferably at least one selected from the group consisting of methyl stearate, ethyl stearate, and butyl stearate, which can further shorten the reflow process time required to achieve low residue.

[0038] <Solder paste> The solder paste according to the present embodiment contains the above-mentioned flux and a solder alloy powder. The solder alloy in the solder alloy powder includes a lead-free solder alloy and a eutectic solder alloy containing lead, but from the viewpoint of reducing environmental load, a lead-free solder alloy is preferable. Examples of the lead-free solder alloy include alloys containing tin, silver, copper, indium, zinc, bismuth, antimony, etc. 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 mentioned. The alloy also contains unavoidable impurities, which are components that are inevitably mixed in during the manufacturing process and are acceptable to the extent that they do not affect the effects of the present invention.

[0039] The content of the flux is preferably 5% by mass to 20% by mass inclusive of the total amount of the solder paste, and the content of the solder alloy powder is preferably 80% by mass to 95% by mass inclusive of the total amount of the solder paste.

[0040] The solder paste according to the present embodiment contains the flux and a solder alloy powder, which makes it possible to shorten the reflow process time required to achieve low residue.

[0041] <Method of manufacturing bonded structure> In the method for manufacturing a joint structure according to the present embodiment, the substrate and the joint component are joined together using the solder paste. Specifically, the substrate and the joint component are heated in a reflow furnace while being in contact with each other via the solder paste, and the solder alloy constituting the solder paste is melted. The substrate and the joint component are then joined together by cooling.

[0042] First, the solder paste is placed on the surface of the substrate. The solder paste can be placed using a known method such as printing with a solder printing device, transfer printing, application with a dispenser, or mounting with a mounter. When the solder paste is printed using a solder printing device, the thickness of the applied solder paste can be 30 μm or more and 600 μm or less. The substrate is not particularly limited, and known substrates such as a printed circuit board, a DBC board, a base plate, a lead frame, and a silicon wafer can be used.

[0043] Next, the joining parts are arranged so as to contact the substrate via the solder paste. The joining parts are not particularly limited, and may be, for example, known joining parts such as chip parts (IC chips, etc.), resistors, diodes, capacitors, transistors, semiconductor chips (Si chips, etc.), and heat sinks.

[0044] Next, the substrate and the joining component are heated in a state of contact with each other via the solder paste. The heating temperature is not particularly limited and can be appropriately selected depending on the solder paste, and is in a range equal to or higher than the melting point of the solder paste. The heating step may be performed in an inert gas atmosphere using nitrogen gas or the like for the purpose of suppressing oxidation of the metal. In addition, the atmosphere may be reduced or evacuated using a vacuum pump for the purpose of promoting the release of gas. In addition, a preheating step may be performed before the heating step. The preheating temperature is not particularly limited and can be appropriately selected depending on the solder paste, and is in a range lower than the melting point of the solder paste. The preheating step may be performed in an inert gas atmosphere under reduced pressure or vacuum, or may be performed in a reducing atmosphere using hydrogen gas or formic acid gas.

[0045] Finally, the substrate and the joined components in contact with each other via the solder paste are cooled, for example, to a temperature drop rate of 120° C. / min to 5° C. / min to a temperature drop rate of 20° C. to 200° C.

[0046] In the method for manufacturing a joint structure according to the present embodiment, the solder paste is used to join a substrate and a joint component, thereby making it possible to shorten the reflow process time required to achieve low residue.

[0047] The present invention includes the following aspects. [1] A flux used in soldering, At least one selected from the group consisting of an aliphatic alcohol having one hydroxy group and being solid at 20° C., and a fatty acid ester being solid at 20° C.; a liquid solvent having one or more and three or less hydroxy groups and being liquid at 20°C; A solid solvent having 2 to 4 hydroxy groups and being solid at 20°C; Contains no thixotropic agent or contains 20.0 mass% or less of a thixotropic agent relative to the entire flux, The flux comprises the fatty acid ester. [2] The flux according to [1], wherein the content of the fatty acid ester is 0.5 mass % or more and 45.0 mass % or less with respect to the entire flux. [3] The flux according to [1] or [2], 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. [4] The flux according to any one of [1] to [3], wherein the fatty acid ester is at least one selected from the group consisting of methyl stearate, ethyl stearate, and butyl stearate. [5] A solder paste comprising the flux according to any one of [1] to [4] and a solder alloy powder. [6] A method for manufacturing a bonded structure, comprising bonding a substrate and a bonding component using the solder paste described in [5].

[0048] The flux, solder paste, and method for manufacturing a joint structure according to the present invention are not limited to the above-mentioned embodiment, and various modifications are possible within the scope of the present invention. Furthermore, the flux, solder paste, and method for manufacturing a joint structure according to the present invention are not limited by the effects of the above-mentioned embodiment. In other words, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the claims. EXAMPLES

[0049] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0050] <Flux materials> (Fatty alcohol) 1-Tetradecanol: Tokyo Chemical Industry Co., Ltd. 1-Hexadecanol: Tokyo Chemical Industry Co., Ltd. 1-Octadecanol: Tokyo Chemical Industry Co., Ltd. 1-Eicosanol: Tokyo Chemical Industry Co., Ltd. 1-Docosanol: manufactured by Tokyo Chemical Industry Co., Ltd. (Fatty acid ester) Methyl stearate: manufactured by Tokyo Chemical Industry Co., Ltd. Ethyl stearate: manufactured by Tokyo Chemical Industry Co., Ltd. Butyl stearate: Tokyo Chemical Industry Co., Ltd. (liquid solvent) 3-Methyl-1,5-pentanediol: Kuraray Co., Ltd. 1,4-Butanediol: Tokyo Chemical Industry Co., Ltd. 2,5-Hexanediol: Tokyo Chemical Industry Co., Ltd. 1,5-Pentanediol: Tokyo Chemical Industry Co., Ltd. 2,4-Diethyl-1,5-pentanediol: Tokyo Chemical Industry Co., Ltd. 1,2,6-Hexanetriol: Tokyo Chemical Industry Co., Ltd. 1,2,4-Butanetriol: Tokyo Chemical Industry Co., Ltd. Hexyldecanol: manufactured by Kokyu Alcohol Kogyo Co., Ltd. Isostearyl alcohol: manufactured by Koyu Alcohol Kogyo Co., Ltd. 2-Octyldodecanol: manufactured by Kokyu Alcohol Kogyo Co., Ltd. 2-Decyltetradodecanol: manufactured by Koyu Alcohol Kogyo Co., Ltd. Oleyl alcohol: manufactured by Koyu Alcohol Kogyo Co., Ltd. (Solid Solvent) 2,2-Dimethyl-1,3-propanediol: Mitsubishi Gas Chemical Company, Inc. 2,5-Dimethyl-2,5-hexanediol: Tokyo Chemical Industry Co., Ltd. 2,2,4-Trimethyl-1,3-pentanediol: Tokyo Chemical Industry Co., Ltd. 2-Butyl-2-ethyl-1,3-propanediol: Tokyo Chemical Industry Co., Ltd. 1,2-Octanediol: Tokyo Chemical Industry Co., Ltd. 1,8-Octanediol: Tokyo Chemical Industry Co., Ltd. 1,10-Decanediol: Tokyo Chemical Industry Co., Ltd. 1,2-Dodecanediol: Tokyo Chemical Industry Co., Ltd. 1,6-Hexanediol: Tokyo Chemical Industry Co., Ltd. 1,9-Nonanediol: Tokyo Chemical Industry Co., Ltd. Trimethylolethane: Mitsubishi Gas Chemical Company, Inc. Trimethylolpropane: Mitsubishi Gas Chemical Company, Inc. Erythritol: Tokyo Chemical Industry Co., Ltd. (thixotropic agent) Stearamide: Kao Corporation Lauric acid amide: Mitsubishi Chemical Corporation Palmitic acid amide: Mitsubishi Chemical Corporation Oleic acid amide: Kao Corporation Erucamide: Nippon Fine Chemical Co., Ltd. Behenamide: manufactured by Nippon Fine Chemicals Co., Ltd.

[0051] <Preparation of flux> The flux materials were placed in a heating vessel in the proportions shown in Tables 1 to 10, and all the materials were dissolved by heating to 120°C. Then, the materials were cooled to room temperature to obtain uniformly dispersed fluxes of each Example and Comparative Example. The proportions shown in Tables 1 to 10 are equal to the contents of each component in the flux.

[0052] <Preparation of solder paste> The flux of each Example and Comparative Example was mixed at 9 mass % with solder alloy powder (96.5Sn / 3Ag / 0.5Cu, Type 3, manufactured by Koki Co., Ltd.) at 91 mass % to obtain a solder paste of each Example and Comparative Example.

[0053] [Table 1]

[0054] [Table 2]

[0055] [Table 3]

[0056] [Table 4]

[0057] [Table 5]

[0058] [Table 6]

[0059] [Table 7]

[0060] [Table 8]

[0061] [Table 9]

[0062] [Table 10]

[0063] <Evaluation of flux volatility> First, the weight of the evaporating dish was measured, and the weight was designated as W1. Next, 0.3 to 0.303 g of flux of each Example and Comparative Example was weighed and placed in the evaporating dish, and the weight was designated as W2. Next, the evaporating dish with the weighed flux was placed on a hot plate heated to 350°C, and the time until all the flux was volatilized was measured by visual inspection, after which the evaporating dish was removed from the hot plate and cooled to room temperature. The maximum heating time was 240 seconds, and even if all the flux was not volatilized, the evaporating dish was removed from the hot plate and cooled to room temperature. The weight of the evaporating dish cooled to room temperature was measured, and the weight was designated as W3. The flux volatilization amount [%] of each Example and Comparative Example was calculated from the following formula (1). The results are shown in Tables 1 to 10.

[0064] Flux volatilization amount [%] = (W2-(W3-W1)) / W2 x 100 (1) In the formula, W1 is the weight of the evaporating dish, W2 is the weight of the evaporating dish in which the flux was measured, and W3 is the weight of the evaporating dish in which the flux was measured after it was heated and then cooled to room temperature.

[0065] The flux volatility was evaluated based on the following criteria. The results are shown in Tables 1 to 10. ◎: The flux volatilization amount [%] is 97% or more, and the time until the flux volatilizes is within 180 seconds 〇: The flux volatilization amount [%] is 97% or more, and the time until the flux volatilizes is within 240 seconds ×: Flux volatilization amount [%] is 97% or less

[0066] <Solder paste evaluation> The solder paste of each Example and Comparative Example was left in an environment of 20 to 30°C for 1 hour, and then the state of the solder paste was confirmed. The solder paste was evaluated based on the following criteria. The results are shown in Tables 1 to 10. Note that "separation of flux" refers to a 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 top. A: No change (flux and solder alloy powder are dispersed) B: The flux separates, and by stirring with a spatula it returns to state A. C: The solder paste is hard, but it returns to state A by stirring with a spatula.

[0067] As can be seen from the results in Tables 1 to 10, the flux of each embodiment that satisfies all the requirements of the present invention has a flux volatilization amount of 97% or more and a flux volatilization time of 240 seconds or less. Therefore, the flux according to the present invention can shorten the reflow process time to achieve low residue.

Claims

1. A flux used in soldering, At least one selected from the group consisting of an aliphatic alcohol having one hydroxy group and being solid at 20° C., and a fatty acid ester being solid at 20° C.; a liquid solvent having one to three hydroxy groups and being liquid at 20°C; A solid solvent having 2 to 4 hydroxy groups and being solid at 20° C., The flux does not contain a thixotropic agent or contains a thixotropic agent in an amount of 20.0 mass% or less based on the total amount of the flux, The flux comprises the fatty acid ester.

2. 2. The flux according to claim 1, wherein a content of the fatty acid ester is 0.5 mass % or more and 45.0 mass % or less with respect to the entire flux.

3. 2. The 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.

4. 2. The 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.

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

6. A method for manufacturing a joint structure, comprising the steps of: joining a substrate and a joining component using the solder paste according to claim 5.

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