Soldering flux, solder paste, and method for manufacturing a joining structure

Abstract

The flux according to the present application is a flux for soft soldering, which 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, 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, and does not contain a thixotropic agent or contains 20.0% by mass or less of a thixotropic agent relative to the entire flux.

Description

Technical Field

[0001] This invention relates to a method for manufacturing flux, solder paste, and joint structures. Background Technology

[0002] Solder paste, a mixture of solder alloy powder and flux, is used when bonding electronic circuit boards such as printed circuit boards and bonding components. The solder paste is applied to the electrode portion of the substrate surface and heated (reflow soldering) while the electrode portion is in contact with the electrode portion of the bonding component. As a result, the solder alloy powder melts to form a solder joint, and a bonding structure in which the substrate and the bonding component are bonded via the solder joint is obtained.

[0003] The flux contained in the aforementioned solder paste is typically composed of resins such as rosin, solvents, thixotropic agents, and activators. However, when soldering is performed using solder paste containing such flux, flux residue sometimes remains around the solder joint. Therefore, flux residue is reduced by methods such as selecting flux components from highly volatile materials, or by employing reduced-pressure reflow soldering or reduced-pressure reduction reflow soldering to ensure sufficient flux volatilization during the reflow soldering process.

[0004] For example, Patent Document 1 discloses a flux that does not contain resins such as rosin that are difficult to volatilize. This flux reduces flux residue by using a combination of liquid and solid solvents to replace resins such as rosin.

[0005] Previously, solder foil was widely used in the soldering of power devices. However, in recent years, solder paste has also attracted much attention as an alternative material in the field of power device manufacturing. Solder paste allows for the one-time application of soft solder onto the substrate through printing. Furthermore, when using solder paste for soldering, there is no need for component clamps to prevent component movement and drop during substrate transport. As a result, the manufacturing process of the bonding structure can be easily automated, and therefore, there is active exploration into the application of solder paste in the soldering of power device manufacturing.

[0006] Existing technical documents

[0007] Patent documents

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

[0009] However, a problem with reflow soldering is that a longer reflow time is required to reduce flux residue after reflow. This is especially true in the soldering of power devices, where flux residue can lead to defects in subsequent processes, necessitating further reduction of flux residue. Therefore, reflow soldering times tend to become longer in the soldering of power devices. Summary of the Invention

[0010] The problem the invention aims to solve

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

[0012] Solution for solving the problem

[0013] The flux of the present invention is used for soldering and contains: at least one of the following: an aliphatic alcohol having one hydroxyl group and being solid at 20°C and a fatty acid ester being solid at 20°C; a liquid solvent having one or more but less than three hydroxyl groups and being liquid at 20°C; and a solid solvent having two or more but less than four hydroxyl groups and being solid at 20°C. The flux contains 20.0% by mass or less of a thixotropic agent relative to the total flux content.

[0014] The solder paste of the present invention comprises the flux and soft solder alloy powder.

[0015] The method for manufacturing the bonding structure of the present invention uses solder paste to bond the substrate and the bonding components. Detailed Implementation

[0016] The following describes the manufacturing method of the flux, solder paste, and joint structure according to embodiments of the present invention.

[0017] <Fluoride>

[0018] The flux involved in this embodiment contains at least one of the following: selected from the group consisting of aliphatic alcohols and fatty acid esters, a liquid solvent, or a solid solvent.

[0019] (Aliphatic alcohols)

[0020] Aliphatic alcohols have one hydroxyl group and are solid at 20°C. Examples of such aliphatic alcohols include 1-tetradecaneol, 1-hexadecaneol, 1-octadecaneol, 1-eicosaneol, 1-docodecaneol, 1-dodecaneol, and 1-tetradecaneol. Preferably, the aliphatic alcohol is selected from at least one of the group consisting of 1-tetradecaneol, 1-hexadecaneol, 1-octadecaneol, 1-eicosaneol, and 1-docodecaneol.

[0021] The content of the aliphatic alcohol relative to the total flux 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. Furthermore, the content of the aliphatic alcohol relative to the total flux 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. It should be noted that when two or more of the aliphatic alcohols are included, the content refers to the total content.

[0022] (fatty acid esters)

[0023] Fatty acid esters are 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, and methyl behenate. Preferably, the fatty acid ester is at least one selected from the group consisting of methyl stearate, ethyl stearate, and butyl stearate.

[0024] The content of the fatty acid ester relative to the total flux 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. Furthermore, the content of the fatty acid ester relative to the total flux 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. It should be noted that when two or more of the fatty acid esters are included, the content refers to the total content.

[0025] From the perspective of suppressing flux separation, the flux involved in this embodiment preferably includes both the aliphatic alcohol and the fatty acid ester. The total content of the aliphatic alcohol and the fatty acid ester relative to the total flux 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. Furthermore, the total content of the aliphatic alcohol and the fatty acid ester relative to the total flux 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.

[0026] (Liquid solvent)

[0027] The flux described in this embodiment contains a liquid solvent having one or more but no more than three hydroxyl groups and being 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, hexyldecyl alcohol, isostearyl alcohol, 2-octyldodecyl alcohol, 2-decyltetradecyl alcohol, oleyl alcohol, 2-ethyl-1,3-hexanediol, 3-methyl-1,3-butanediol, and glycerol.

[0028] Regarding the liquid solvent, from the perspective of improving the volatility of the flux, it is preferable to use at least one, and from the perspective of improving the viscosity stability of the solder paste, it is more preferable to use two or more. When using at least one of the liquid solvents, it is preferably selected from at least one of 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 relative to the total flux is preferably 5.0% by mass or more, more preferably 20.0% by mass or more. Furthermore, the content of the liquid solvent relative to the total flux is preferably 80.0% by mass or less, more preferably 60.0% by mass or less. It should be noted that when two or more liquid solvents are included, the content refers to the total content.

[0030] (Solid solvent)

[0031] The flux described in this embodiment contains a solid solvent having two or more but less than four hydroxyl groups and being solid at 20°C. Examples of such solid solvents 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. From the perspective of improving the printability of solder paste, the solid solvent is preferably selected from at least three of the following groups: 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 relative to the total flux is preferably 5.0% by mass or more, more preferably 25.0% by mass or more. Furthermore, the content of the solid solvent relative to the total flux is preferably 92.0% by mass or less, more preferably 65.0% by mass or less. It should be noted that when two or more solid solvents are included, the content refers to the total content.

[0033] (Thixotropic agent)

[0034] The flux described in this embodiment contains 20.0% by mass or less of a thixotropic agent relative to the total flux volume. Examples of thixotropic agents include hydrogenated castor oil, fatty acid amides, fatty acid diamides, polyamide compounds, kaolin, colloidal silica, organobentonite, and glass powder. From the perspective of reducing flux residue, the thixotropic agent preferably contains a fatty acid amide, and more preferably is composed of a fatty acid amide. Examples of fatty acid amides include stearamide, lauryl amide, palmitamide, oleamide, erucamide, benzyl amide, hydroxystearamide, and myristamide. The fatty acid amides most preferably include stearamide, lauryl amide, palmitamide, oleamide, erucamide, and benzyl amide. It should be noted that a single thixotropic agent can be used alone, or two or more can be used in combination.

[0035] From the perspective of improving the volatility of the flux, the content of the thixotropic agent relative to the total flux is 20.0% by mass or less, preferably 15.0% by mass or less, and more preferably 10.0% by mass or less. Furthermore, from the perspective of improving the volatility of the flux, the flux according to this embodiment preferably does not contain a thixotropic agent. It should be noted that when two or more thixotropic agents are included, the content refers to the total content.

[0036] (Active agent)

[0037] The flux described in this embodiment may contain an activator. There are no particular limitations on the activator; examples include organic acid-based activators, amine compounds, amino acids, amine halides, or halogen compounds. It should be noted that one activator may be used alone, or two or more may be used in combination.

[0038] As an organic acid-based surfactant, there are no particular limitations. Examples include monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, decanoic acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nodular stearic acid, arachidic acid, benzyl acid, tetracosanoic acid, and glycolic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, and diethanolic acid; and other organic acids such as dimer acids, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and pyridinecarboxylic acid.

[0039] As amine compounds, there is no particular limitation, and examples include imidazole compounds, triazole compounds, etc. Examples of imidazole compounds include benzimidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-ethyl-4-methylimidazolium (2E4MZ), 2-heptadecylimidazolium, 2-undecylimidazolium, 1-(4,6-diamino-triazin-2-yl)ethyl-2-undecylimidazolium, 1-butylimidazolium, 2-phenylimidazolium, 4-methyl-2-phenylimidazolium, etc. Examples of triazole compounds include benzotriazole, 1H-benzotriazole-1-methanol, 1-methyl-1H-benzotriazole, etc. 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.

[0040] As an amino acid, there are no particular limitations. Examples 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), or N-acetylphenylglycine (N-acetyl-N-phenylglycine, N-acetyl-L-phenylglycine, N-acetyl-DL-phenylglycine), etc.

[0041] As halogen-based activators, there are no particular limitations; examples include amine halides and halogen compounds. Examples of amine halides include diethylamine, dibutylamine, tributylamine, diphenylguanidine, and cyclohexylamine. Examples of halogens that are amine halides include fluorine, chlorine, bromine, and iodine. Examples of halogen compounds include tris(2,3-dibromopropyl)isocyanurate, 2,3-dibromo-2-buten-1,4-diol, 2-bromo-3-iodo-2-buten-1,4-diol, TBA-bis(2,3-dibromopropyl ether), and 4,4'-diiodobiphenyl.

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

[0043] The flux described in this embodiment may contain at least one of, for example, stabilizers, surfactants, defoamers, and corrosion inhibitors as other additives. The total content of these other additives is not particularly limited; for example, it may be set to 5.0% by mass or less relative to the total flux content.

[0044] The flux involved in this embodiment comprises 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 the flux contains 20.0% by mass or less of a thixotropic agent relative to the total flux content. This allows for a reduction in the reflow soldering process time for achieving low residue.

[0045] According to the flux of this embodiment, it is preferable that the flux contains the aliphatic alcohol, and the content of the aliphatic alcohol is 0.5% by mass or more and 45.0% by mass or less relative to the total flux. This allows for a further reduction in the reflow soldering process time for achieving low residue. Furthermore, the increased viscosity of the flux ensures the viscosity of the solder paste.

[0046] According to the flux of this embodiment, it is preferable that the flux contains the fatty acid ester, and the content of the fatty acid ester is 0.5% by mass or more and 45.0% by mass or less relative to the total flux. This further shortens the reflow soldering process time for achieving low residue. In addition, the increased viscosity of the flux ensures the viscosity of the solder paste.

[0047] According to the 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-eicosanool, and 1-docodidecanol. This allows for a further reduction in the reflow soldering process time for achieving low residue.

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

[0049] Solder paste

[0050] The solder paste involved in this embodiment contains the aforementioned flux and solder alloy powder. Examples of solder alloys in the solder alloy powder include lead-free solder alloys and lead-containing eutectic solder alloys; from the perspective of reducing environmental impact, lead-free solder alloys are preferred. Examples of lead-free solder alloys include alloys containing tin, silver, copper, indium, zinc, bismuth, and antimony. More specifically, examples include Sn / Ag, Sn / Ag / Cu, Sn / Cu, Sn / Ag / Bi, Sn / Bi, Sn / Ag / Cu / Bi, Sn / Sb, Sn / Zn / Bi, Sn / Zn, Sn / Zn / Al, Sn / Ag / Bi / In, Sn / Ag / Cu / Sb, Sn / Ag / Sb, Sn / Ag / Cu / Bi, Sn / Ag / Cu / Bi / In / Sb, In / Ag, and Sn / In alloys. Furthermore, the alloy contains unavoidable impurities. Unavoidable impurities refer to components that are unavoidably mixed in during the manufacturing process, and are permissible to a extent that does not affect the effects of the present invention.

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

[0052] The solder paste described in this embodiment comprises the flux and solder alloy powder. This allows for a reduction in reflow soldering process time to achieve low residue.

[0053] <Manufacturing Method of Joint Structure>

[0054] The method for manufacturing the bonding structure according to this embodiment uses the solder paste to bond a substrate and bonding components. Specifically, in a reflow oven, the substrate and bonding components are heated while in contact via the solder paste, causing the soft solder alloy constituting the solder paste to melt. Then, the substrate and bonding components are bonded by cooling.

[0055] First, the solder paste is applied to the surface of the substrate. The solder paste can be applied using known methods such as printing with a solder printing apparatus, transfer printing, application using a dispenser, or mounting using a mounting machine. When printing the solder paste using a solder printing apparatus, the thickness of the applied solder paste can be 30 μm or more and 600 μm or less. Furthermore, the substrate is not particularly limited; for example, known substrates such as printed circuit boards, DBC substrates, base plates, lead frames, and silicon wafers can be used.

[0056] Next, the bonding component is configured to contact the substrate via the solder paste. The bonding component is not particularly limited; 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, heating is performed while the substrate and the bonding component are in contact via the solder paste. The heating temperature is not particularly limited and can be appropriately selected based on the solder paste, ensuring it is above the melting point of the solder paste. To suppress metal oxidation, the heating process can be performed in an atmosphere of inert gas such as nitrogen. Furthermore, to promote gas release, a vacuum pump can be used to reduce the pressure of the atmosphere or to create a vacuum. Additionally, a preheating process can be performed before the heating process. The preheating temperature is not particularly limited and can be appropriately selected based on the solder paste, ensuring it is below the melting point of the solder paste. The preheating process can be performed under reduced pressure or a vacuum in an inert gas atmosphere; alternatively, hydrogen or formic acid gas can be used in a reducing atmosphere.

[0058] Finally, the substrate and bonding components that have been in contact with the solder paste are cooled. In the cooling process, for example, the temperature is cooled to 20°C or higher and 200°C or lower at a cooling rate of 120°C / min or higher and 5°C / min or lower.

[0059] The method for manufacturing the bonding structure according to this embodiment uses the solder paste to bond the substrate and the bonding components. This reduces the reflow soldering process time required to achieve low residue.

[0060] The present invention includes the following methods.

[0061] [1] A flux used for soldering,

[0062] The flux contains:

[0063] Selected from at least one aliphatic alcohol having one hydroxyl group and being solid at 20°C and fatty acid esters being solid at 20°C.

[0064] Liquid solvents having one or more but three or fewer hydroxyl groups and being liquid at 20°C; solid solvents having two or more but four or fewer hydroxyl groups and being solid at 20°C.

[0065] The flux contains less than 20.0% by mass of thixotropic agent relative to the total flux.

[0066] [2] The flux according to [1], wherein the flux contains the aliphatic alcohol, the content of the aliphatic alcohol being more than 0.5% by mass and less than 45.0% by mass relative to the total flux.

[0067] [3] The flux according to [1] or [2], wherein the flux contains the fatty acid ester, the content of the fatty acid ester being more than 0.5% by mass and less than 45.0% by mass relative to the total flux.

[0068] [4] The 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-eicosanool and 1-docosahexadecanol.

[0069] [5] The 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: any one of [1] to [5] flux and solder alloy powder.

[0071] [7] A method for manufacturing a bonding structure, wherein a substrate and a bonding component are bonded using the solder paste described in [6].

[0072] It should be noted that the manufacturing methods of flux, solder paste, and bonding structures involved in this invention are not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, the manufacturing methods of flux, solder paste, and bonding structures involved in this invention are not limited to the effects of the above-described embodiments. That is, the embodiments disclosed herein should be considered exemplary rather than restrictive in all respects. The scope of this invention is defined by the claims rather than the foregoing description. Additionally, the scope of this invention is intended to include all modifications with the same meaning and scope as the claims.

[0073] Example

[0074] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0075] <Materials of Flux>

[0076] (Aliphatic alcohols)

[0077] 1-Tetradecaneol: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0078] 1-Hexadecaneol: Manufactured by Tokyo Chemical Industry Co., Ltd.

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

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

[0081] 1-Chocosanol: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0082] (fatty acid esters)

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

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

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

[0086] (Liquid solvent)

[0087] 3-Methyl-1,5-pentanediol: Manufactured by Kuraray Co., Ltd.

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

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

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

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

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

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

[0094] Hexyldecyl alcohol: Produced by Higher Alcohols Industrial Company

[0095] Isostearyl alcohol: manufactured by Higher Alcohols Industrial Company

[0096] 2-Octyldodecanol: Produced by Higher Alcohols Industrial Company

[0097] 2-Decyltetradecanool: Produced by Higher Alcohols Industrial Company

[0098] Oil alcohol: Produced by Higher Alcohols Industrial Company

[0099] (Solid solvent)

[0100] 2,2-Dimethyl-1,3-propanediol: Manufactured by Mitsubishi Gas Chemical Company

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

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

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

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

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

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

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

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

[0109] 1,9-Nonadiol: Produced by Tokyo Chemical Industry Co., Ltd.

[0110] Trimethylolethane: Manufactured by Mitsubishi Gas Chemical Company

[0111] Trimethylolpropane: Manufactured by Mitsubishi Gas Chemical Company

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

[0113] (Thixotropic agent)

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

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

[0116] Palmitamide: Manufactured by Mitsubishi Chemical Corporation

[0117] Oleamide: Manufactured by Kao Corporation

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

[0119] Succinamide: Manufactured by Nippon Seika Co., Ltd.

[0120] <Fluoride Preparation>

[0121] The flux materials described above were added to 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 for each example and comparative example. It should be noted that the mixing amounts shown in Tables 1 to 10 are the same as the content of each component contained in the flux.

[0122] <Solder paste preparation>

[0123] The flux of each embodiment and the comparative example were mixed with 9% by mass and 91% by mass of soft solder alloy powder (96.5Sn / 3Ag / 0.5Cu, Type 3, manufactured by Honghui Company) to obtain the solder paste of each embodiment and the 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, the weight of the evaporating dish was measured and designated as W1. Next, 0.3 to 0.303 g of flux from each embodiment and comparative example was weighed onto the evaporating dish and designated as W2. Then, the evaporating dish containing the flux was placed on a hot plate heated to 350°C, and the time until all the flux evaporated was visually observed. The evaporating dish was then removed from the hot plate and cooled to room temperature. The maximum heating time was set to 240 seconds. Even if the flux did not evaporate completely, 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 designated as W3. The flux evaporation rate [%] for each embodiment and comparative example was calculated according to the following formula (1). The results are shown in Tables 1 to 10.

[0146] Flux evaporation [%] = (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 flux added, and W3 represents the weight of the evaporating dish after heating with flux added and then cooling to room temperature.

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

[0149] ◎: Flux evaporation rate [%] is 97% or higher and the time until flux evaporation is within 180 seconds.

[0150] 〇: The flux evaporation rate [%] is 97% or higher and the time until flux evaporation is within 240 seconds.

[0151] ×: Flux volatility [%] is below 97%

[0152] <Evaluation of solder paste>

[0153] The solder pastes of each embodiment and comparative example were placed at 20–30°C for 1 hour, and the state of the solder paste was checked. The evaluation of the solder paste was carried out according to the following criteria. The results are shown in Tables 1 to 10. It should be noted that "flux separation" refers to the state in which the solder alloy powder in the solder paste settles and the flux accumulates on the top due to the difference in specific gravity between the solder alloy powder and the flux.

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

[0155] B: Flux separation occurred. Stirring with a scraper will restore the state to that of A.

[0156] C: The solder paste is relatively hard, but it returns to the state of A after being stirred with a spatula.

[0157] As shown in Tables 1 to 10, in the fluxes of each embodiment that satisfy all the features of the present invention, the flux evaporation rate is 97% or higher and the time until flux evaporation is less than 240 seconds. Therefore, the flux of the present invention can shorten the reflow soldering process time for achieving low residue.

Claims

1. A flux for use in soldering, The flux contains: Fatty acid esters that are solid at 20°C, or aliphatic alcohols having one hydroxyl group and being solid at 20°C, and fatty acid esters that are solid at 20°C. Liquid solvents having one or more but no more than three hydroxyl groups and being liquid at 20°C A solid solvent having two or more but fewer than four hydroxyl groups and being solid at 20°C. The flux contains less than 20.0% by mass of thixotropic agent relative to the total flux content. The flux contains the fatty acid ester. The content of the fatty acid ester is more than 0.5% by mass and less than 45.0% by mass relative to the total flux.

2. The flux according to claim 1, wherein, The aliphatic alcohol is selected from at least one of the group consisting of 1-dodecanol, 1-tetradecanol, 1-hexadecanol, 1-octadecanol, 1-eicosanool and 1-docosahexadecanol.

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

4. A solder paste comprising: the flux of claim 1 and solder alloy powder.

5. A method for manufacturing a bonding structure, wherein a substrate and a bonding component are bonded using the solder paste of claim 4.

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