Solder paste and method of manufacturing electronic devices

Abstract

The solder paste of the present application is a solder paste including a flux composition and a solder powder, wherein the solder paste is configured such that, when a storage modulus at 100°C of a flux residue obtained from the solder paste according to a prescribed manufacturing procedure is determined using a rheometer based on prescribed determination conditions, G' 100 , a loss modulus is G" 100 , and G' 100 and G" 100 satisfy G' 100 > G" 100 .

Description

Technical Field

[0001] This invention relates to solder paste and methods for manufacturing electronic devices. Background Technology

[0002] Various developments have been made to solder paste to date. One such technology is described, for example, in Patent Document 1. Patent Document 1 describes a solder paste containing a rosin-based resin with a softening point of 90°C or lower.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent document 1: Japanese Patent Application Publication No. 2018-140429. Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, after research, the inventors have determined that there is room for improvement in the high-temperature migration of the solder paste described in the aforementioned Patent Document 1.

[0008] Methods for solving problems

[0009] In recent years, with the increasing output of equipment, the operating temperature of the equipment has reached high temperatures of over 100℃.

[0010] Based on the above development, the inventors conducted research and found that if the flux residue remaining after the solder paste has been reflowed is subjected to high-temperature heat generated during equipment operation for a long time, the tin ions dissolved in the flux residue will move towards the cathode and precipitate, resulting in high-temperature migration. As a result, poor insulation may occur.

[0011] Based on this understanding, further in-depth research was conducted, and it was found that by appropriately controlling the viscoelastic properties of flux residue in solder paste, high-temperature migration can be suppressed, thus completing this invention.

[0012] According to the present invention, a solder paste is provided, which comprises a flux composition and solder powder, wherein the solder paste is configured such that the storage modulus at 100°C, measured by a rheometer with respect to the flux residue obtained from the solder paste according to the following manufacturing steps, is set as G'. 100 The loss modulus is set to G. 100 At that time, G' 100 and G” 100 Satisfy G' 100 >G” 100 .

[0013] <Steps for preparing flux residue>

[0014] (1) Prepare two copper trays with a bottom surface of 45mm×45mm, a height of 5mm and a thickness of 0.3mm.

[0015] (2) Overlap one copper tray on the bottom surface of one copper tray with the opening of the other copper tray opposite the opening of one copper tray, and secure it with tape to prepare a copper box with a height of about 10 mm.

[0016] (3) Collect 5g of the solder paste as a sample and spread the sample out in such a way that it covers 80% of the area of ​​the bottom surface inside the copper tray.

[0017] (4) Using a reflow oven, under atmospheric conditions, the copper box containing the sample is subjected to reflow soldering treatment according to the following temperature profiles A to E.

[0018] (Temperature curves A to E)

[0019] A. Heating from room temperature (25°C) to 150°C at a heating rate of 1.9°C / second.

[0020] B. Maintain the temperature range of 150℃ to 180℃ for 80 seconds.

[0021] C. Heat to 220°C at a heating rate of 1.2°C / second.

[0022] D. Maintain a temperature above 220°C for 40 seconds, then heat to a peak temperature of 240°C.

[0023] E. Then, cool to room temperature (25°C).

[0024] (5) After reflow soldering, collect the flux residue remaining on the bottom surface of the inner side of one of the copper trays.

[0025] <Measurement Conditions>

[0026] Measuring apparatus: rheometer.

[0027] Measurement temperature: 20℃~180℃.

[0028] Upper geometry: 25mmφ, stainless steel, parallel plate.

[0029] Lower side panel: 60mmφ.

[0030] Mode: 5℃ / minute.

[0031] Strain: 1%.

[0032] Frequency: 10Hz.

[0033] Interval: 0.2mm.

[0034] In addition, according to the present invention, a method for manufacturing an electronic device is provided, wherein the method includes: a step of printing the above-mentioned solder paste on a soldering portion of an electronic circuit board; a step of mounting electronic components on the soldering portion; and a step of heating the soldering portion to a temperature at which the solder powder in the solder paste melts, thereby bonding the electronic components and the electronic circuit board, while a sealed structure exists around the soldering portion.

[0035] The effects of the invention

[0036] According to the present invention, a solder paste with excellent high-temperature migration resistance and a method for manufacturing an electronic device using the solder paste are provided. Attached Figure Description

[0037] Figure 1 This diagram illustrates the method for preparing flux residue.

[0038] Figure 2 This is a diagram used to illustrate a high-temperature migration test.

[0039] Figure 3 It is a standard reflow soldering curve diagram representing the flux residue during the preparation process. Detailed Implementation

[0040] Hereinafter, embodiments of the present invention will be described using the accompanying drawings. It should be noted that throughout the drawings, the same reference numerals are used to denote the same constituent elements, and descriptions are appropriately omitted. Furthermore, the drawings are schematic diagrams and do not conform to actual size ratios.

[0041] An overview of the solder paste of this embodiment will be provided.

[0042] The solder paste of this embodiment comprises a flux composition and solder powder, wherein the storage modulus at 100°C, measured by a rheometer using a rheometer under the following measurement conditions, is defined as G' for the flux residue obtained from the solder paste according to the following preparation steps. 100 The loss modulus is set to G. 100 At that time, G' 100 and G” 100 Satisfy G' 100 >G” 100 .

[0043] <Steps for preparing flux residue>

[0044] (1) Prepare two copper trays with a bottom surface of 43-45mm × 43-45mm, a height of 5-7mm, and a thickness of 0.2-0.4mm.

[0045] (2) Overlap one copper tray on the bottom of one copper tray with the opening of the other copper tray facing the opening of the first copper tray, and secure it with tape to prepare a copper box with a height of about 10 to 14 mm.

[0046] (3) Collect approximately 5g of the solder paste as a sample. Spread the sample out by covering approximately 80% of the bottom surface of the inner side of a copper tray.

[0047] (4) Using a reflow oven (Senju Metal Industries, Ltd., SNR-825), the copper box containing the sample was subjected to reflow soldering treatment with the temperature profiles A to E as described below under atmospheric conditions.

[0048] (Temperature curves A to E)

[0049] A. Heating from room temperature (25°C) to 150°C at a heating rate of 1.9°C / second.

[0050] B. Maintain the temperature range of 150℃ to 180℃ for 80 seconds.

[0051] C. Heat to 220°C at a heating rate of 1.2°C / second.

[0052] D. Maintain a temperature above 220°C for 40 seconds, then heat to a peak temperature of 240°C.

[0053] E. Then, cool to room temperature (25°C).

[0054] (5) After reflow soldering, collect the flux residue remaining on the bottom surface of the inner side of one of the copper trays.

[0055] <Measurement Conditions>

[0056] Measurement apparatus: rheometer (Made by Malvern Panalytical Ltd, KINEXUS1b+).

[0057] Measurement temperature: 20℃~180℃.

[0058] Geometry (top): 25mm φ, stainless steel, parallel plate.

[0059] Plate (bottom side): 60mmφ.

[0060] Mode: 5℃ / minute.

[0061] Strain: 1%.

[0062] Frequency: 10Hz.

[0063] Interval: 0.2mm.

[0064] In recent years, high-output devices have also experienced situations where the temperature around the heating element reaches over 100°C. Typically, since the humidity around a heating element exceeding 100°C is lower than normal, it is considered an environmental condition where ion migration is unlikely to occur. However, the inventors have confirmed that ion migration can still occur in high-output devices even in low-humidity environments.

[0065] However, typical ion migration tests are conducted at 85°C and 85% humidity, so it is difficult to say that they can cope with the above-mentioned realities.

[0066] Therefore, the inventors have newly developed a high-temperature migration test for evaluating the migration of metal ions at temperatures above 100°C. In this high-temperature migration test, environmental conditions such as low humidity (below 20%) and high humidity (above 85%) can be used.

[0067] According to the inventors' insights, it has been discovered that high-temperature migration can be suppressed by appropriately controlling the viscoelastic properties of flux residues in solder paste. Furthermore, it has been found that high-temperature migration can be suppressed even in harsher high-humidity environments.

[0068] For the flux residue obtained through the above manufacturing steps, the storage modulus at 100°C, measured by a rheometer under the above measurement conditions, is G'. 100 And the loss modulus is G” 100 This serves as an indicator, enabling a stable evaluation of the viscoelastic properties of flux residues. This is confirmed by the relationship between the viscoelastic properties of flux residues and the evaluation results of high-temperature migration tests using the same flux residues.

[0069] Furthermore, it was clarified that G' was obtained through flux residue. 100 and G” 100 Satisfy G' 100 >G” 100 The solder paste is made in a way that can suppress high-temperature migration.

[0070] The detailed mechanism is still uncertain, but it is believed that by making the storage modulus at 100°C greater than the loss modulus, it is possible to suppress deformation at high temperatures and achieve flux residues in a low-flow state. Therefore, it is possible to suppress the high-temperature migration of metal ions such as tin ions.

[0071] In the above steps for preparing flux residue, the temperature profiles used are those described above (temperature profiles A to E). Alternatively, they can be adjusted as needed. Figure 3 The standard reflow soldering profile is used for setting. The temperature in the temperature profile refers to the operating temperature.

[0072] Reflow soldering can also be performed using a heater to circulate hot air.

[0073] Furthermore, in the above-mentioned flux residue preparation steps, a sample size of approximately 5g is sufficient, with 4.5 to 5.5g being permissible. The area spread out on the copper tray can be approximately 80%, but if it is approximately 60% or more, a sufficient amount of collectable flux residue can be obtained.

[0074] It should be noted that copper trays can also be made by bending copper plates with a thickness of 0.2 to 0.4 mm.

[0075] The phase angle at 100°C, calculated from the storage modulus and loss modulus at 100°C using a rheometer based on the above measurement conditions, is denoted as δ. 100 The phase angle at 140℃, calculated based on the storage modulus and loss modulus, is set as δ. 140 .

[0076] δ 140 The lower limit is, for example, 1° or more, preferably 2° or more, and more preferably 3° or more.

[0077] On the other hand, δ 140 The upper limit is, for example, less than 45°, preferably less than 44°, and more preferably less than 30°. This improves the resistance to high-temperature migration in high-temperature working environments above 100°C.

[0078] It can also be configured as δ 140 and δ 100 Satisfying 0.1≤δ 140 / δ 100 ≤3.0.

[0079] δ 140 / δ 100 The lower limit is, for example, 0.1 or more, preferably 0.15 or more, and more preferably 0.2 or more.

[0080] On the other hand, δ 140 / δ 100 The upper limit is, for example, 3.0 or less, preferably 2.5 or less, and more preferably 2.0 or less.

[0081] By setting the values ​​within the range described above, the high-temperature migration resistance in high-temperature working environments above 100°C can be improved.

[0082] The viscosity of the solder paste at 25°C was measured using the rheometer described above, with a shear rate of 6 seconds. -1 The viscosity at that time is set to η1, and the shear rate is 1.8 seconds. -1 The viscosity at that time is set to η2, and the shear rate is set to 18 seconds. -1 The viscosity at that time is set to η3.

[0083] The lower limit of viscosity η1 is, for example, 5 Pa·s or more, preferably 20 Pa·s or more, and more preferably 50 Pa·s or more.

[0084] On the other hand, the upper limit of viscosity η1 is, for example, 400 Pa·s or less, preferably 300 Pa·s or less, and more preferably 280 Pa·s or less.

[0085] By setting the values ​​within the range described above, the printability of the solder paste can be improved.

[0086] The lower limit of the thixotropic ratio calculated by Log(η2 / η3) is, for example, 0.3 or more, preferably 0.4 or more, and more preferably 0.5 or more.

[0087] On the other hand, the upper limit of the aforementioned thixotropic ratio is, for example, 1.8 or less, preferably 1.5 or less, and more preferably 1.0 or less.

[0088] By setting the values ​​within the range described above, the printability of the solder paste can be improved.

[0089] In this embodiment, by appropriately selecting the types and amounts of each component contained in the solder paste, and the preparation method of the solder paste, the storage modulus, loss modulus, phase angle, viscosity η1, and thixotropic ratio at 100°C and 140°C can be controlled. Examples of factors for setting the storage modulus, loss modulus, phase angle, viscosity η1, and thixotropic ratio at 100°C and 140°C to the desired numerical range include, for example, using a first rosin-based resin with a high softening point, appropriately adjusting the content of the first rosin-based resin with a high softening point, not using a third rosin-based resin with a low softening point, and appropriately adjusting the content of solvent and / or activator.

[0090] The solder paste of this embodiment can be used to bond electronic circuit boards to electronic components, and in particular, it can also be used to bond them around a closed structure consisting of electronic circuit boards and electronic components. High-temperature migration can also be suppressed in the event of flux residue remaining in the closed structure.

[0091] In addition, this solder paste is suitable for manufacturing equipment where the temperature of the joint between the electronic circuit board and the electronic component reaches 100°C or higher during operation.

[0092] The composition of the solder paste according to this embodiment will be described in detail below.

[0093] Solder paste contains a flux composition and solder powder.

[0094] Flux compositions may also be configured to contain one or more selected from the group consisting of activators, matrix resins, thixotropic agents and solvents.

[0095] (Active agent)

[0096] Flux compositions may also contain activators with the property of removing metal oxides.

[0097] By including activators, the wettability of solder during solder bonding processes can be improved.

[0098] Specific examples of surfactants include organic acids, amines, halogenated surfactants, and phosphorus-based surfactants. They can be used alone or in combination of two or more.

[0099] The detailed mechanism of these activators is not yet clear, but it is believed that by reducing metal oxides and forming salts with metals, they can remove the metal oxide film from the surface of the solder and the metal object being soldered.

[0100] The content of activator in 100% by weight of flux composition can be, for example, 0-30% by weight or 1-20% by weight.

[0101] It should be noted that, unless otherwise stated, in this specification, “~” indicates that there are upper and lower limits.

[0102] Examples of organic acids include monocarboxylic acids, dicarboxylic acids, anhydrides of dicarboxylic acids, and hydroxy acids. They can be used alone or in combination of two or more.

[0103] As specific examples of organic acids, for instance, glutaric acid, adipic acid, azelaic acid, eicosanoic acid, citric acid, glycolic acid, succinic acid, salicylic acid, diethylene glycolic acid, dipyridinecarboxylic acid, dibutylaniline diethylene glycolic acid, octanoic acid, sebacic acid, thioglycolic acid, terephthalic acid, dodecanoic acid, p-hydroxyphenylacetic acid, pyridinecarboxylic acid, phenylsuccinic acid, phthalic acid, fumaric acid, maleic acid, and malonic acid can be cited. Lauric acid, benzoic acid, tartaric acid, tris(2-carboxyethyl)isocyanurate, glycine, 1,3-cyclohexanedicarboxylic acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butyric acid, 2,3-dihydroxybenzoic acid, 2,4-diethylglutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, malic acid, p-anestic acid, stearic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, linolenic acid, etc.

[0104] From the perspective of low residue, organic acids can also include organic acids with 11 or fewer carbon atoms.

[0105] Examples of organic acids with 11 or fewer carbon atoms include glycolic acid (2 carbon atoms), thioglycolic acid (2 carbon atoms), glycine (2 carbon atoms), malonic acid (3 carbon atoms), fumaric acid (4 carbon atoms), maleic acid (4 carbon atoms), succinic acid (4 carbon atoms), diethylene glycol (4 carbon atoms), tartaric acid (4 carbon atoms), malic acid (4 carbon atoms), glutaric acid (5 carbon atoms), 2,2-bis(hydroxymethyl)propionic acid (5 carbon atoms), adipic acid (6 carbon atoms), citric acid (6 carbon atoms), pyridinecarboxylic acid (6 carbon atoms), benzoic acid (7 carbon atoms), 2,2-bis(hydroxymethyl)butyric acid (6 carbon atoms), and salicylic acid. Examples of carboxylic acids include: dipyridinecarboxylic acid (7 carbon atoms), 2,3-dihydroxybenzoic acid (7 carbon atoms), 3-hydroxybenzoic acid (7 carbon atoms), octanoic acid (8 carbon atoms), phthalic acid (8 carbon atoms), isophthalic acid (8 carbon atoms), terephthalic acid (8 carbon atoms), p-hydroxyphenylacetic acid (8 carbon atoms), 1,3-cyclohexanedicarboxylic acid (8 carbon atoms), p-anestic acid (8 carbon atoms), azelaic acid (9 carbon atoms), 2,4-diethylglutaric acid (9 carbon atoms), sebacic acid (10 carbon atoms), phenylsuccinic acid (10 carbon atoms), 2-quinolinecarboxylic acid (10 carbon atoms), and 4-tert-butylbenzoic acid (11 carbon atoms).

[0106] In addition, examples of organic acids include dimer acids, trimer acids, hydrides of dimer acids (hydrogenated dimer acids), and hydrides of trimer acids (hydrogenated trimer acids).

[0107] The content of organic acid in 100% by weight of the flux composition can be, for example, 0 to 25% by weight or 1 to 20% by weight. By setting it below the above upper limit, the viscoelastic properties of the flux residue can be made suitable.

[0108] Examples of amines include monoethanolamine, diphenylguanidine, ethylamine, triethylamine, ethylenediamine, triethylenetetramine, 2-methylimidazole, 2-undecylimidazole, 2-heptadecaylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole ontium trimellitate, 1-cyanoethyl-2-phenylimidazole ontium trimellitate, and 2,4-diamino-6-[2′-methylimidazole]. -(1′)]-ethyl-s-triazine, 2,4-diamino-6-[2′-undecylimidazolyl-(1′)]-ethyl-s-triazine, 2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-s-triazine, 2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine isocyanuric acid addition product, 2-phenylimidazolyl isocyanuric acid addition product, 2-phenyl-4,5-dihydroxymethylimidazolium, 2-phenyl-4-methyl-5-hydroxymethylimidazolium, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzyl chloride imidazolyl, 2-methylimidazoline, 2-phenylimidazoline, 2,4 -Diamino-6-vinyl-s-triazine, addition products of 2,4-diamino-6-vinyl-s-triazine isocyanuric acid, 2,4-diamino-6-methacryloyloxyethyl-s-triazine, addition products of epoxyimidazolium, 2-methylbenzimidazole, 2-octylbenzimidazole, 2-pentylbenzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-nonylbenzimidazole, 2-(4-thiazolyl)benzimidazole, benzimidazole, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole, 2-(2′-hydroxy-3′,5′-di-tert-pentylphenyl)benzotriazole, 2-(2′-hydroxy-5′-tert-octylphenyl)benzimidazole Benzotriazole, 2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol], 6-(2-benzotriazolyl)-4-tert-octyl-6′-tert-butyl-4′-methyl-2,2′-methylenebisphenol, 1,2,3-benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2′-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]diethanol, 1-(1′,2′-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-Bis[(1H-benzotriazol-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, 5-phenyltetrazole, etc.

[0109] The content of amines in 100% by weight of the flux composition can be, for example, 0 to 15% by weight or 0.1 to 10% by weight.

[0110] Examples of halogen-based activators include organic halogen compounds and amine hydrohalides.

[0111] Examples of organohalogen compounds include, for example, trans-2,3-dibromo-1,4-butenediol, triallyl isocyanurate hexabromide, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, and 2,3-dibromo-2-butenediol.

[0112] Other examples of organohalogen compounds include, for instance, chlorinated alkanes, chlorinated fatty acid esters, chlorinated brittle acids, and chlorinated brittle anhydrides, which are organochlorine compounds. Additionally, examples of organofluorine compounds include fluorinated surfactants, surfactants with perfluoroalkyl groups, and polytetrafluoroethylene.

[0113] Examples of amine hydrohalides include salts of hydrohalic acids such as hydroiodic acid (HI), hydrobromic acid (HBr), hydrochloric acid (HCl), and hydrofluoric acid (HF) combined with amine compounds such as aniline, diphenylguanidine, diethylamine, and isopropylamine.

[0114] In addition, as an equivalent of amine hydrohalide salts, salts combining tetrafluoroboric acid (HBF4) and amine compounds can also be used.

[0115] Examples of amine hydrohalides include stearylamine hydrochloride, diethylaniline hydrochloride, diethanolamine hydrochloride, 2-ethylhexylamine hydrobromide, pyridine hydrobromide, isopropylamine hydrobromide, cyclohexylamine hydrobromide, diethylamine hydrobromide, monoethylamine hydrobromide, 1,3-diphenylguanidine hydrobromide, dimethylamine hydrobromide, dimethylamine hydrobromide, rosinamine hydrobromide, 2-ethylhexylamine hydrochloride, isopropylamine hydrobromide, cyclohexylamine hydrobromide, 2-methylpiperidine hydrobromide, 1,3-diphenylguanidine hydrobromide, dimethylbenzylamine hydrobromide, hydrazine hydrobromide, dimethylcyclohexylamine hydrobromide, trinonylamine hydrobromide, diethylaniline hydrobromide, 2-diethylaminoethanol hydrobromide, 2-diethylaminoethanol hydrobromide, ammonium chloride, diallylamine hydrochloride, diallylamine hydrobromide, monoethylamine hydrobromide, etc. Aminohydrochloride, monoethylamine hydrobromide, diethylamine hydrochloride, triethylamine hydrobromide, triethylamine hydrochloride, hydrazine monohydrochloride, hydrazine dihydrobromide, hydrazine monohydrobromide, hydrazine dihydrobromide, pyridine hydrochloride, aniline hydrobromide, butylamine hydrochloride, hexylamine hydrochloride, n-octylamine hydrochloride, dodecylamine hydrochloride, dimethylcyclohexylamine hydrobromide, ethylenediamine dihydrobromide, rosinamine hydrobromide, 2-phenylimidazolium hydrobromide, 4-benzylpyridine hydrobromide, L-glutamic acid hydrochloride, N-methylmorpholine hydrochloride, betaine hydrochloride, 2-methylpiperidine hydroiodide, cyclohexylamine hydroiodide, 1,3-diphenylguanidine hydrofluoride, diethylamine hydrofluoride, 2-ethylhexylamine hydrofluoride, cyclohexylamine hydrofluoride, ethylamine hydrofluoride, rosinamine hydrofluoride, cyclohexylamine tetrafluoroborate, and dicyclohexylamine tetrafluoroborate, etc.

[0116] The content of halogenated activator in 100% by weight of flux composition can be, for example, 0 to 10% by weight or 0.1 to 5% by weight.

[0117] The content of organohalogen compounds in 100% by weight of the flux composition may be, for example, 0 to 10% by weight, or 0.1 to 5% by weight.

[0118] The content of amine hydrohalates in 100% by weight of the flux composition can be, for example, 0-5% by weight or 0.1-3% by weight.

[0119] Examples of phosphorus-based activators include phosphonates, phenyl-substituted hypophosphonates, and phosphate esters.

[0120] Examples of phosphonates include, for example, 2-ethylhexyl (2-ethylhexyl) phosphonate, n-octyl (n-octyl) phosphonate, n-decyl (n-decyl) phosphonate and n-butyl (n-butyl) phosphonate.

[0121] Examples of phenyl-substituted phosphonic acids include, for example, phenylphosphonic acid and diphenylphosphonic acid.

[0122] The content of phosphorus-based activator in 100% by weight of flux composition can be, for example, 0-10% by weight or 0.1-5% by weight.

[0123] (Matrix resin)

[0124] Flux compositions may contain a base resin.

[0125] Examples of matrix resins include rosin-based resins, (meth)acrylic resins, polyurethane resins, polyester resins, phenoxy resins, vinyl ether resins, terpene resins, modified terpene resins (e.g., aromatic modified terpene resins, hydrogenated terpene resins, hydrogenated aromatic modified terpene resins, etc.), terpene phenol resins, modified terpene phenol resins (e.g., hydrogenated terpene phenol resins, etc.), styrene resins, modified styrene resins (e.g., styrene acrylic resins, styrene maleic resins, etc.), xylene resins, modified xylene resins (e.g., phenol-modified xylene resins, alkylphenol-modified xylene resins, phenol-modified methylphenolic xylene resins, polyol-modified xylene resins, polyoxyethylene addition xylene resins, etc.). These can be used alone or in combination of two or more.

[0126] It should be noted that in this specification, "(meth)acrylic resin" refers to the concept that includes both methacrylic resin and acrylic resin.

[0127] The matrix resin may contain rosin-based resins.

[0128] Examples of rosin-based resins include, for example, resin rosin, wood rosin, tall oil rosin, and other raw material rosins, as well as derivatives obtained from raw material rosins. Examples of derivatives include, for example, refined rosin, hydrogenated rosin, disproportionated rosin, polymerized rosin, and α,β-unsaturated carboxylic acid modified compounds (acrylated rosin), maleic acid-modified rosin, fumarate-modified rosin, etc.; as well as refined products, hydrides, and disproportionates of polymerized rosin; and refined products, hydrides, and disproportionates of α,β-unsaturated carboxylic acid modified compounds, etc. These rosin-based resins can be used alone or in combination of two or more.

[0129] The content of the matrix resin in 100% by weight of the flux composition can be, for example, 0-50% by weight, 10-49% by weight, or 15-48% by weight. By setting the content of the matrix resin to 15% by weight or more as described above, the viscoelastic properties of the flux residue can be made suitable.

[0130] The preferred flux composition contains a first rosin-based resin with a softening point of 135°C or higher. The softening point of the first rosin-based resin is preferably 138°C or higher, more preferably 140°C or higher.

[0131] Depending on the requirements, the flux composition may also contain a second rosin-based resin with a softening point of 120°C or higher and less than 135°C.

[0132] It should be noted that the preferred flux composition does not contain third rosin-based resins with a softening point below 90°C.

[0133] By configuring the flux residue to contain a first rosin-based resin and / or a second rosin-based resin, or without a third rosin-based resin, the viscoelastic properties of the flux residue can be made suitable.

[0134] It should be noted that the softening point can be determined according to the softening point test method (ring and ball method) of JIS K 2207:1996.

[0135] The content of the first rosin-based resin in 100% by weight of the flux composition can be, for example, 1 to 50% by weight, 3 to 30% by weight, or 5 to 30% by weight. By setting it to the lower limit or above, the viscoelastic properties of the flux residue can be made suitable. By setting it to the upper limit or below, the reduction in the printability of the solder paste can be suppressed.

[0136] The content of the first rosin-based resin in 100% by weight of all rosin-based resins can be, for example, 3 to 100% by weight, 10 to 90% by weight, or 12 to 80% by weight. By setting it to a value above the lower limit mentioned above, the viscoelastic properties of the flux residue can be made suitable.

[0137] (solvent)

[0138] Flux compositions may contain solvents.

[0139] Solvents that are solid or liquid at 25°C can be used. They can be used alone or in combination of two or more.

[0140] As a solid solvent, for example, alcohol-based solid solvents, phenol-based solid solvents, etc. are used.

[0141] They can be used individually or in combination of two or more.

[0142] Any solid alcohol solvent can be a solid solvent with one or two or more hydroxyl groups in its molecule, preferably a polyol solid solvent with two or three or more hydroxyl groups.

[0143] Specific examples of polyol-based solid solvents include pentaerythritol, trimethylolpropane, 2,5-dimethyl-2,5-hexanediol, and neopentyl glycol.

[0144] As long as the phenolic solid solvent is a solid solvent with one or more phenol groups in the molecule, one or more hydroxyl groups can be attached to the benzene ring of the phenol group.

[0145] Liquid solvents include, for example, alcohol-based solvents, glycol ether-based solvents, terpineol, hydrocarbons, esters, water, etc. They can be used alone or in combination of two or more. Among them, at least one of alcohol-based solvents and glycol ether-based solvents can be used as liquid solvents.

[0146] Examples of alcohol-based solvents include isopropanol, 1,2-butanediol, isoborneol, 2,4-diethyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-3-hexyn-2,5-diol, 2,3-dimethyl-2,3-butanediol, 1,1,1-tris(hydroxymethyl)ethane, 2-ethyl-2-hydroxymethyl-1,3-propanediol, and 2,2'-oxybis(hydroxymethyl)ethane. Methyl)bis(2-ethyl-1,3-propanediol), 2,2-bis(hydroxymethyl)-1,3-propanediol, 1,2,6-trihydroxyhexane, bis[2,2,2-tri(hydroxymethyl)ethyl] ether, 1-ethyn-1-cyclohexanol, 1,4-cyclohexanediol, 1,4-cyclohexanediol, erythritol, threitol, guaiacol glycerol ether, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyn-4,7-diol, etc.

[0147] Examples of glycol ether solvents include, for example, diethylene glycol hexyl ether, diethylene glycol mono-2-ethylhexyl ether, ethylene glycol monophenyl ether, 2-methylpentane-2,4-diol, diethylene glycol monohexyl ether, diethylene glycol dibutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monomethyl ether.

[0148] The solvent content in 100% by weight of the flux composition can be, for example, 0-65% by weight, 1-50% by weight, or 5-40% by weight. By setting it to the upper limit mentioned above, the viscoelastic properties of the flux residue can be made suitable.

[0149] The content of liquid solvent in 100% by weight of the flux composition can be, for example, 0-65% by weight, 1-50% by weight, or 5-40% by weight.

[0150] (Thixotropic agent)

[0151] Flux compositions may contain thixotropic agents.

[0152] Examples of thixotropic agents include wax-based thixotropic agents, amide-based thixotropic agents, and sorbitol-based thixotropic agents.

[0153] Examples of wax-based thixotropic agents include, for instance, hardened castor oil.

[0154] Examples of amide-based thixotropic agents include monoamides, diamides, and polyamides. Examples include laurylamide, palmitamide, stearamide, behenamide, hydroxystearamide, saturated fatty acid amides, oleamide, erucamide, unsaturated fatty acid amides, p-toluenemethaneamide, aromatic amides, methylene bis-stearamide, ethylene bis-laurateamide, ethylene bis-hydroxystearamide, saturated fatty acid diamides, methylene bis-oleamide, unsaturated fatty acid diamides, isophthalic dimethyl bis-stearamide, aromatic diamides, aliphatic polyamides (saturated fatty acid polyamides, unsaturated fatty acid polyamides), aromatic polyamides, substituted amides, hydroxymethylstearamide, hydroxymethylamide, fatty acid ester amides, cyclic amide oligomers, and non-cyclic amide oligomers.

[0155] The content of thixotropic agent in 100% by weight of the flux composition can be, for example, 0-20% by weight or 1-15% by weight.

[0156] (additive)

[0157] The flux composition may also contain additives that are typically added to fluxes, provided that the effect of the invention is not compromised.

[0158] Examples of additives include antioxidants, rust inhibitors, defoamers, matting agents, surfactants, and colorants. They can be used alone or in combination of two or more.

[0159] For example, hindered phenolic antioxidants and phosphorus-based antioxidants can be cited as examples of antioxidants.

[0160] Solder powder can be composed of Sn monomers or Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Bi, Sn-In, etc., or solder powders with added Pb, Sb, Bi, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, P, etc.

[0161] Solder powder may have a specified particle size distribution as determined by a particle size distribution test according to JIS Z 3284:2014.

[0162] The solder powder may be configured such that the mass fraction of the powder with a particle size in the range of 2 to 150 μm is 80% or more, preferably the mass fraction of the powder with a particle size in the range of 5 to 75 μm is 80% or more, and more preferably the mass fraction of the powder with a particle size in the range of 5 to 45 μm is 80% or more.

[0163] According to JIS Z 3284:2017, solder powder can be classified into type 1 to type 8 based on particle size distribution through particle size distribution determination test.

[0164] In this embodiment, solder powder of type 2 to type 7 is preferred, and solder powder of type 3 to type 6 is more preferred.

[0165] In Type 3, the mass fraction of powder with a particle size in the range of 25 to 45 μm is above 80%.

[0166] In type 4, the mass fraction of powder with a particle size in the range of 20 to 38 μm is above 80%.

[0167] In Type 5, the mass fraction of powder with a particle size in the range of 15–25 μm is above 80%.

[0168] In Type 6, the mass fraction of powder with a particle size in the range of 5 to 15 μm is above 80%.

[0169] The flux composition in 100% by weight of the solder paste comprising solder powder and flux composition is, for example, 7 to 30% by weight, preferably 8 to 25% by weight, and more preferably 10 to 20% by weight.

[0170] There are no limitations on the manufacturing method of the flux composition and solder paste; they can be manufactured by mixing the raw materials simultaneously or sequentially using any method.

[0171] As long as the flux composition is ultimately mixed with all its components, other components can be mixed sequentially in the solvent, or substances containing other components can be added to the solvent, or the solvent and all other components can be mixed simultaneously.

[0172] In addition, the manufacture of solder paste does not necessarily require the pre-preparation of flux composition and mixing it with solder powder. As long as all the components of the flux composition, solder powder, and additives to be added to the solder paste as needed are finally mixed, the order of mixing does not matter. The remaining components of the flux composition can be added after a portion of the components of the flux composition has been mixed with the solder powder.

[0173] As an example, the solder paste of this embodiment can be used in the manufacturing method of electronic devices such as semiconductor devices.

[0174] The manufacturing method of an electronic device may include: a process of applying the above-mentioned solder paste to electrodes, and a process of, for example, heating a substrate such as a lead frame or a printed wiring substrate and semiconductor components, and joining them together by molten solder.

[0175] An example of a method for manufacturing an electronic device may include: a step of printing the aforementioned solder paste onto a soldering portion of an electronic circuit board; a step of mounting electronic components onto the soldering portion; and a step of heating the soldering portion to a temperature at which the solder powder in the solder paste melts, thereby bonding the electronic components and the electronic circuit board, while the soldering portion is surrounded by a sealed structure.

[0176] Electronic components can use high-output devices such as power semiconductors.

[0177] Methods for printing solder paste include screen printing, film printing, and other methods besides jet dispensing.

[0178] The embodiments of the present invention have been described above, but these are merely examples, and various configurations other than those described above are possible. Furthermore, the present invention is not limited to the above embodiments, and modifications and alterations within the scope of achieving the objectives of the present invention are included in the present invention.

[0179] Below are examples of reference methods.

[0180] 1. A solder paste comprising a flux composition and solder powder, wherein the solder paste is configured such that the storage modulus at 100°C, measured by a rheometer with respect to the flux residue obtained from the solder paste according to the following manufacturing steps, is set as G'. 100 The loss modulus is set to G. 100 At that time, G' 100 and G” 100 Satisfy G' 100 >G” 100 .

[0181] <Steps for preparing flux residue>

[0182] (1) Prepare two copper trays with a bottom surface of 45mm×45mm, a height of 5mm and a thickness of 0.3mm.

[0183] (2) Overlap one copper tray on the bottom surface of one copper tray with the opening of the other copper tray opposite the opening of one copper tray, and secure it with tape to prepare a copper box with a height of about 10 mm.

[0184] (3) Collect 5g of the solder paste as a sample. Spread the sample out in such a way that it covers 80% of the area of ​​the bottom surface inside the copper tray.

[0185] (4) Using a reflow oven, under atmospheric conditions, the copper box containing the sample is subjected to reflow soldering treatment according to the following temperature profiles A to E.

[0186] (Temperature curves A to E)

[0187] A. Heating from room temperature (25°C) to 150°C at a heating rate of 1.9°C / second.

[0188] B. Maintain the temperature range of 150℃ to 180℃ for 80 seconds.

[0189] C. Heat to 220°C at a heating rate of 1.2°C / second.

[0190] D. Maintain a temperature above 220°C for 40 seconds, then heat to a peak temperature of 240°C.

[0191] E. Then, cool to room temperature (25°C).

[0192] (5) After reflow soldering, collect the flux residue remaining on the bottom surface of the inner side of one of the copper trays.

[0193] <Measurement Conditions>

[0194] Measuring apparatus: rheometer.

[0195] Measurement temperature: 20℃~180℃.

[0196] Geometry (top): 25mm φ, stainless steel, parallel plate.

[0197] Plate (bottom side): 60mmφ.

[0198] Mode: 5℃ / minute.

[0199] Strain: 1%.

[0200] Frequency: 10Hz.

[0201] Interval: 0.2mm.

[0202] 2. The solder paste as described in 1, wherein the phase angle at 140°C, obtained from the storage modulus and loss modulus measured using a rheometer based on the above-described measurement conditions, is set as δ. 140 At that time, δ 140 It is 1° or higher and less than 45°.

[0203] 3. The solder paste as described in 2, wherein the phase angle at 100°C, obtained by measuring the storage modulus and loss modulus at 100°C using a rheometer based on the above-described measurement conditions, is set as δ. 100 At that time, δ 140 and δ 100 Satisfying 0.1≤δ 140 / δ 100 ≤3.0.

[0204] 4. The solder paste according to any one of 1 to 3, wherein the flux composition comprises a rosin-based resin with a softening point of 135°C or higher.

[0205] 5. The solder paste according to any one of 1 to 4, wherein, in 100% by weight of the solder paste, the content of the flux composition is 7% by weight or more and 20% by weight or less.

[0206] 6. The solder paste as described in any one of 1 to 5, wherein, using the rheometer described above, at a shear rate of 6 seconds... -1 Furthermore, the viscosity η1 measured at 25℃ is above 5 Pa·s and below 400 Pa·s.

[0207] 7. The solder paste according to any one of 1 to 6, wherein the viscosity of the solder paste at 25°C is measured using the rheometer described above, and the shear rate is 1.8 seconds. -1 The viscosity at that time was set to η2 and the shear rate to 18 seconds. -1 When the viscosity is set to η3, the thixotropic ratio calculated from Log(η2 / η3) is above 0.3 and below 1.8.

[0208] 8. The solder paste as described in any one of 1 to 7, wherein the solder paste is used to bond electronic circuit boards and electronic components around a hermetically sealed structure.

[0209] 9. The solder paste as described in any one of 1 to 8, wherein the flux composition comprises one or more selected from the group consisting of an activator, a matrix resin, a thixotropic agent, and a solvent.

[0210] 10. The solder paste as described in 9, wherein the activator comprises one or more selected from the group consisting of organic acids, amines, halogenated activators and phosphorus-based activators.

[0211] 11. The solder paste according to any one of 1 to 10, wherein the mass fraction of the solder powder having a particle size in the range of 2 to 150 μm is 80% or more.

[0212] 12. A method for manufacturing an electronic device, wherein the method comprises: a step of printing solder paste as described in any one of 1 to 11 onto a soldering portion of an electronic circuit board; a step of mounting an electronic component onto the soldering portion; and a step of heating the soldering portion to a temperature at which the solder powder in the solder paste melts, thereby bonding the electronic component and the electronic circuit board, while a sealed structure exists around the soldering portion.

[0213] Example

[0214] The present invention will now be described in detail with reference to the embodiments, but the present invention is not limited to the description of these embodiments at all.

[0215] The following table shows the information on the raw material composition.

[0216] (Matrix resin)

[0217] Rosin-based resin 1: Acrylic acid modified hydrogenated rosin (softening point: 131℃, manufactured by Arakawa Chemical Industry Co., Ltd., KE-604).

[0218] Rosin-based resin 2: Hydrogenated rosin (softening point: 74°C, manufactured by Eastman Chemical Company, FORAL AX-E).

[0219] Rosin-based resin 3: Polymerized rosin (softening point: 141℃, manufactured by Arakawa Chemical Industry Co., Ltd., KR-140).

[0220] It should be noted that the softening point of rosin-based resins was determined according to the softening point test method (ring and ball method) of JIS K 2207:1996, and the result was the average of two measurements (rounding the first decimal place).

[0221] Acrylic resin 1: Acrylic resin.

[0222] (Active agent)

[0223] Organic acid 1: dimer acid.

[0224] Organic acid 2: adipic acid.

[0225] Organic acid 3: Azelaic acid.

[0226] Amine 1: 2-Phenyle-4-methylimidazole (abbreviation: 2P4MZ).

[0227] Aminohydric halides 1: Diphenylguanidine hydrobromide.

[0228] Organohalogen compound 1: 2,3-dibromo-2-butene-1,4-diol.

[0229] (solvent)

[0230] Solvent 1: Diethanol ether solvent (diethylene glycol monohexyl ether).

[0231] (Thixotropic agent)

[0232] Thixotropic agent 1: Polyamide.

[0233] (additive)

[0234] Antioxidant 1: Hindered phenolic antioxidants.

[0235] (Solder powder)

[0236] Solder powder 1: Solder powder (SEC305: Sn-3.0Ag-0.5Cu, Type 4, manufactured by Senju Metal Industries, Ltd.).

[0237] <Preparation of solder paste>

[0238] The raw material components are mixed according to the proportions shown in Table 1 below to obtain a flux composition.

[0239] Then, 11.5% by weight of the obtained flux composition and 88.5% by weight of solder powder are mixed to obtain solder paste.

[0240]

[0241] The obtained solder paste was evaluated for the following criteria.

[0242] <Determination of Energy Storage Modulus and Loss Modulus>

[0243] Collect flux residue from solder paste according to the following production steps.

[0244] (Steps for preparing flux residue)

[0245] (1) As Figure 1 As shown, prepare two copper trays 12 and 14 with a bottom surface of 45mm×45mm, a height of 5mm, and a thickness of 0.3mm.

[0246] (2) Overlap one copper tray 14 on the bottom surface of one copper tray 12 with the opening of the other copper tray 14 opposite to the opening of one copper tray 12, and secure it with tape to prepare a copper box 10 with a height of about 10 mm.

[0247] (3) Collect 5g of the obtained solder paste as a sample. Spread the sample out in such a way that it covers 80% of the bottom surface of the inner side of a copper tray 12.

[0248] (4) Using a reflow oven (Senju Metal Industries, Ltd., SNR-825), the copper box 10 containing the sample was subjected to reflow soldering treatment with the following temperature profiles A to E under atmospheric conditions.

[0249] (Temperature curves A to E)

[0250] A. Heating from room temperature (25°C) to 150°C at a heating rate of 1.9°C / second.

[0251] B. Maintain the temperature range of 150℃ to 180℃ for 80 seconds.

[0252] C. Heat to 220°C at a heating rate of 1.2°C / second.

[0253] D. Maintain a temperature above 220°C for 40 seconds, then heat to a peak temperature of 240°C.

[0254] E. Then, cool to room temperature (25°C).

[0255] (5) After reflow soldering, collect the flux residue remaining on the bottom surface of the inner side of a copper tray 12.

[0256] For the obtained flux residue, the storage modulus at 25℃~180℃ was determined using a rheometer based on the following measurement conditions.

[0257] (Measurement conditions)

[0258] Measurement apparatus: rheometer (Made by Malvern Panalytical Ltd, KINEXUS1b+).

[0259] Measurement temperature: 20℃~180℃.

[0260] Geometry (top): 25mm φ, stainless steel, parallel plate.

[0261] Plate (bottom side): 60mmφ.

[0262] Mode: 5℃ / minute.

[0263] Strain: 1%.

[0264] Frequency: 10Hz.

[0265] Interval: 0.2mm.

[0266] Let the storage modulus at 100℃, measured using the aforementioned rheometer, be denoted as G'. 100 The loss modulus is set to G. 100 Let the energy storage modulus at 140℃ be G' 140 The loss modulus is set to G. 140 .

[0267] Based on the relationship tanδ=G' / G”, according to G' 100 and G” 100 Let the phase angle at 100℃ be δ. 100 According to G' 140 and G” 140 Let the phase angle at 140℃ be δ 140 The results are shown in Table 1.

[0268] <Viscosity Measurement>

[0269] The viscosity of the solder paste at 25°C was measured using the rheometer described above, with a shear rate of 6 seconds. -1 The viscosity at that time is set to η1, and the shear rate is 1.8 seconds. -1 The viscosity at that time is set to η2, and the shear rate is set to 18 seconds. -1 Let the viscosity at time η3 be denoted as η1, η2, and η3. Additionally, calculate the thixotropic ratio using Log(η2 / η3). The results are shown in Table 1.

[0270] <High Temperature Migration Test>

[0271] The obtained solder paste was used to simulate the actual process, printed onto the copper electrodes 30 on the printed circuit board, and then reflow soldering was performed at 240°C to bond the solder 50 to the copper electrodes 30. Then, flux residue remaining around the printed area was washed and removed. This process completes the fabrication of... Figure 2 The evaluation device shown is a structure consisting of a printed circuit board, copper electrode 30, and solder 50.

[0272] Then, use Figure 2 The evaluation apparatus shown is used to conduct high-temperature migration tests.

[0273] Figure 2 The evaluation apparatus shown includes a substrate, a copper electrode 30 disposed on the substrate, and a solder 50 containing tin disposed on the copper electrode 30.

[0274] Using 0.002 to 0.005 g of flux residue 22 collected through the above-described (flux residue preparation steps), the separation portion of the copper electrodes 30 arranged at fine intervals is filled without gaps, and the glass cover plate 60 is arranged in such a way that the filled flux residue 22 is sealed by the substrate and solder 50.

[0275] A constant voltage of 10V was applied between the copper electrodes 30, and the evaluation device was stored in a temperature environment of 105°C.

[0276] Then, metal migration was observed on the flux residue 22 in the separation section of the copper electrode 30 (high temperature migration test).

[0277] When gray dendritic precipitation can be identified in the flux residue 22 in the separation section, it is determined that the tin contained in the solder has migrated.

[0278] Three high-temperature migration tests were conducted to confirm whether any precipitation occurred in each test.

[0279] In Table 1, cases where no precipitation was confirmed in all three out of three attempts are marked as "excellent", cases where precipitation was confirmed once out of three attempts are marked as "good", and cases where precipitation was confirmed more than twice out of three attempts are marked as "cannot".

[0280] Compared with the solder pastes of the comparative examples, the solder pastes of the embodiments suppressed precipitation in the high-temperature migration test, thus showing excellent high-temperature migration resistance.

[0281] This application claims priority based on Japanese Patent Application No. 2021-105629, filed on June 25, 2021, the entire contents of which are included herein.

[0282] Explanation of reference numerals in the attached figures

[0283] 10: Copper box.

[0284] 12: Copper tray.

[0285] 14: Copper tray.

[0286] 20: Solder paste.

[0287] 22: Flux residue.

[0288] 30: Copper electrode.

[0289] 50: Solder.

[0290] 60: Glass cover plate.

Claims

1. A solder paste comprising a flux composition and solder powder, wherein, The flux composition comprises a base resin, an activator, a solvent, and a thixotropic agent. The matrix resin comprises a rosin-based resin. The solder paste is configured such that the storage modulus at 100°C, measured by a rheometer under the following measurement conditions, for the flux residue obtained from the solder paste according to the following manufacturing steps, is set as G'. 100 The loss modulus is set to G'' 100 At that time, G' 100 and G'' 100 Satisfy G' 100 >G'' 100 , The steps for preparing flux residue are as follows: (1) Prepare two copper trays with a bottom surface of 45mm×45mm, a height of 5mm and a thickness of 0.3mm; (2) Overlap one copper tray on the bottom surface of one copper tray with the opening of the other copper tray facing the opening of one copper tray, and secure it with tape to prepare a copper box with a height of about 10mm. (3) Collect 5g of the solder paste as a sample and unfold the sample in such a way that it covers 80% of the area of ​​the bottom surface inside the copper tray. (4) Using a reflow oven, under atmospheric conditions, the copper box containing the sample is subjected to reflow soldering treatment according to the following temperature profiles A to E; Temperature curves A through E are as follows: A. Heating from room temperature (25°C) to 150°C at a heating rate of 1.9°C / second. B. Maintain a temperature range of 150℃ to 180℃ for 80 seconds. C. Heat to 220°C at a heating rate of 1.2°C / second. D. Maintain a temperature above 220°C for 40 seconds, then heat to a peak temperature of 240°C. E. Then, cool to room temperature (25°C). (5) After reflow soldering, collect the flux residue remaining on the bottom inner side of one of the copper trays. The measurement conditions are as follows: Measuring apparatus: rheometer; Measurement temperature: 20℃~180℃; Upper geometry: 25mmΦ, stainless steel, parallel plate; Bottom panel: 60mmΦ; Mode: 5℃ / minute; Strain: 1%; Frequency: 10Hz; Interval: 0.2mm.

2. The solder paste as described in claim 1, wherein, The phase angle at 140°C, calculated from the storage modulus and loss modulus of the flux residue obtained from the solder paste according to the above-described preparation steps using a rheometer under the above-described measurement conditions, is denoted as δ. 140 At that time, δ 140 It is 1° or higher and less than 45°.

3. The solder paste as described in claim 2, wherein, The phase angle at 100°C, calculated from the storage modulus and loss modulus of the flux residue obtained from the solder paste according to the above-described manufacturing steps using a rheometer under the above-described measurement conditions, is denoted as δ. 100 At that time, δ 140 and δ 100 Satisfying 0.1≤δ 140 / δ 100 ≤3.

0.

4. The solder paste as described in claim 1, wherein, The flux composition comprises a rosin-based resin with a softening point of 135°C or higher.

5. The solder paste as described in claim 1, wherein, In the solder paste, the content of the flux composition is 7% or more and 20% or less per 100% by weight.

6. The solder paste according to any one of claims 1 to 5, wherein, Using the rheometer described above, at a shear rate of 6 seconds... -1 Furthermore, the viscosity η1 of this solder paste was measured at 25℃ to be 5 Pa. s or more and 400Pa Below s.

7. The solder paste according to any one of claims 1 to 5, wherein, Using the rheometer described above, the viscosity of the solder paste at 25°C was measured with a shear rate of 1.8 seconds. -1 The viscosity at that time was set to η2 and the shear rate to 18 seconds. -1 When the viscosity is set to η3, the thixotropic ratio calculated from Log(η2 / η3) is above 0.3 and below 1.

8.

8. The solder paste according to any one of claims 1 to 5, wherein, The solder paste is used to bond electronic circuit boards and electronic components around a sealed structure.

9. The solder paste according to any one of claims 1 to 5, wherein, The surfactant comprises one or more selected from the group consisting of organic acids, amines, halogenated surfactants and phosphorus-based surfactants.

10. The solder paste according to any one of claims 1 to 5, wherein, The solder powder contains more than 80% by mass of powder with a particle size ranging from 2 to 150 μm.

11. A method for manufacturing an electronic device, wherein, The method for manufacturing the electronic device includes: The process of printing solder paste according to any one of claims 1 to 5 onto the soldering portion of an electronic circuit board; The process of installing electronic components at the welding site; and The process of bonding the electronic component and the electronic circuit board by heating the welding area to the temperature at which the solder powder in the solder paste melts, while the welding area is in a closed structure.

Images