High-temperature-resistant antioxidant solder paste and preparation method thereof

Abstract

The invention relates to the field of welding materials, in particular to high-temperature-resistant antioxidant solder paste and a preparation method thereof. The high-temperature-resistant antioxidant solder paste comprises the following raw materials: a tin-silver-copper alloy, temperature-resistant copolymer resin, an antioxidant, a thixotropic agent, a corrosion inhibitor, a dispersing agent, a functional compound and the like. The finally prepared solder paste material not only can maintain excellent high temperature resistance and oxidation resistance, but also can maintain good corrosion resistance, water resistance, toughness and the like at the same time, so that performance contradictions of the solder paste material are eliminated while the problems of temperature resistance and oxidation resistance of an existing solder paste material are solved, and the service life of the solder paste material is prolonged. Therefore, the solder paste meets the comprehensive performance requirements of existing electronic products and other fields on solder paste materials, and has wide application potential.

Description

Technical Field

[0001] The present application relates to the field of welding materials, and more specifically to a high temperature resistant and anti-oxidation solder paste and a preparation method thereof. Background Art

[0002] Solder paste, also known as solder paste, is an indispensable welding material in the modern electronic manufacturing industry. It is usually mixed with solder powder, flux and other additives, and is used for soldering printed circuit board (PCB) components in surface mount technology (SMT). Solder paste has a certain viscosity at room temperature, which can initially stick electronic components to a predetermined position. During the reflow soldering process, as the temperature rises, the solvent and some additives evaporate, so that the soldered components and the pads on the PCB are permanently connected through the molten solder.

[0003] As electronic products develop towards miniaturization and high-density packaging, the requirements for solder paste are becoming more and more stringent. In particular, for some special application scenarios, such as environments that need to work at higher temperatures, or occasions with extremely high requirements for long-term reliability, ordinary solder paste may not meet the needs. In order to meet these challenges, a variety of improved solder paste products have appeared on the market, such as water-washable ultra-fine tin powder water-soluble lead-free high-temperature flux paste. This type of solder paste particularly emphasizes its stability and anti-oxidation ability under high temperature conditions.

[0004] In recent years, there have been formulas specially designed to improve the strength, toughness, high temperature oxidation resistance and corrosion resistance of solder paste. This type of solder paste usually contains a certain amount of antioxidants to prevent the oxidation of tin powder in the solder paste, thereby avoiding problems such as tin beads on the board surface after welding. However, relying solely on the content of antioxidants to solve the above problems is likely to affect the normal proportion of other raw materials in the solder paste, thereby affecting other properties.

[0005] Therefore, although the existing technology has made certain progress, it still faces many challenges in practical applications, such as insufficient antioxidant performance. Although antioxidants are added, under extreme conditions, such as high humidity, high temperature, hot and cold cycles, and long-term light exposure, the solder paste may still oxidize, affecting the welding quality; in addition, ordinary solder paste is prone to softening or flowing in a high temperature environment, resulting in solder joint failure or changes in electrical properties, which is unacceptable for electronic products working in a high temperature environment, and the corrosion resistance, water resistance and other properties of ordinary solder paste are also inconsistent with the above properties. Summary of the invention

[0006] Therefore, in order to effectively solve the above-mentioned problems and improve the comprehensive performance of solder paste materials, the present application provides a high-temperature resistant and antioxidant solder paste and a preparation method thereof. The finally prepared solder paste material can not only maintain excellent high-temperature resistance and antioxidant properties, but also can simultaneously maintain good corrosion resistance, waterproofness and toughness and other properties, thereby solving the problems of heat resistance and antioxidant properties of existing solder paste materials while eliminating the performance contradictions of solder paste materials, thereby meeting the comprehensive performance requirements of solder paste materials in existing electronic products and other fields, and has broad application potential.

[0007] The high temperature resistant and antioxidant solder paste comprises the following raw materials, calculated by mass: 75-95 parts of tin-silver-copper alloy, 8-12 parts of heat-resistant copolymer resin, 0.5-1.5 parts of antioxidant, 1-3 parts of thixotropic agent, 0.2-0.8 parts of corrosion inhibitor, 0.2-0.6 parts of dispersant, 0.5-1.2 parts of coupling agent, 0.8-1.6 parts of film-forming agent, 5-8 parts of functional complex and 5-15 parts of solvent.

[0008] As a preferred embodiment, the average particle size of the tin-silver-copper alloy is 5 to 15 μm.

[0009] As a more preferred embodiment, the average particle size of the tin-silver-copper alloy is 7 to 12 μm.

[0010] As a preferred embodiment, the tin-silver-copper alloy contains, by mass percentage, 95-96.5% tin, 2.5-3% silver, and the balance made up by copper.

[0011] As a preferred embodiment, the mass ratio of the tin-silver-copper alloy, the heat-resistant copolymer resin and the functional composite is (80-88): (9-11): (6-7.5).

[0012] As a more preferred embodiment, the mass ratio of the tin-silver-copper alloy, the heat-resistant copolymer resin and the functional composite is 85:10:6.5.

[0013] As a preferred embodiment, the preparation method of the heat-resistant copolymer resin specifically includes the following steps: S1: adding polyimide resin to N-methylpyrrolidone solvent, stirring continuously for 2 to 3 hours at a stirring speed of 200 to 250 rpm in a constant temperature water bath at 60 to 70°C, until the resin is completely dissolved into a transparent solution; S2: adding hexafluorobutyl acrylate, styrene and N-vinylpyrrolidone to the transparent solution in sequence, and adding azobisisobutyronitrile, introducing nitrogen protection, and eliminating oxygen interference; S3: heating to 80 to 85°C, stirring continuously at 300 to 350 rpm for 6 to 7 hours in a nitrogen atmosphere, cooling naturally to room temperature after the reaction is completed, slowly pouring into anhydrous ethanol, stirring while pouring, so that the polymer is precipitated, and then washing the precipitate 3 to 4 times with deionized water and ethanol alternately to remove unreacted monomers and solvents;

[0014] S4: Place the precipitate in a vacuum drying oven, dry it at 60-70°C and vacuum degree -0.1MPa for 10-12h, grind it and pass it through a 300-400 mesh sieve to obtain the product.

[0015] As a preferred embodiment, the mass ratio of the polyimide resin, hexafluorobutyl acrylate, styrene and N-vinyl pyrrolidone is (4.5-5): (2-2.2):

[0016] (1.2~1.4):(1.4~1.6).

[0017] As a more preferred embodiment, the mass ratio of the polyimide resin, hexafluorobutyl acrylate, styrene and N-vinyl pyrrolidone is 5:2.1:1.3:1.6.

[0018] The heat-resistant copolymer resin added in the present application can effectively improve the overall heat resistance, oxidation resistance, corrosion resistance and water resistance of the solder paste material system. The main chain rigid skeleton contained in the heat-resistant copolymer resin can provide excessive thermal stability while working together with the fluorocarbon side chain to impart hydrophobicity and greatly improve the dense molecular stacking of the resin system, so that the solder paste material is significantly improved in terms of water resistance, mechanics and heat resistance.

[0019] On the other hand, the CF bond energy of the fluorocarbon side chain in the resin system is relatively high, and it can withstand more heat energy without breaking in a high temperature environment, and can form a surface protective layer under the side chain position, slowing down the oxidation reaction and weakening the migration efficiency of active molecules. In addition, the copolymer resin has more structures composed of aromatic rings and imide bonds, which can also control heat energy transfer in a high temperature environment, so that the movement of the molecular chains of the resin system in a high temperature environment is restricted, inhibiting thermal activation and thermal decomposition.

[0020] Finally, the fluorocarbon side chains in the copolymer resin form a low surface energy hydrophobic layer on the resin surface, which hinders the penetration of oxygen and moisture. The N and O atoms in the pyrrolidone ring form coordination bonds with the metal surface, which greatly enhances the interfacial bonding between the resin system and between the resin and other raw materials. Both the resistance to external forces and its own uniformity are greatly improved, thereby comprehensively improving the heat resistance, oxidation resistance, waterproofness and corrosion resistance of the solder paste material.

[0021] As a preferred embodiment, the antioxidant is at least one of nano-cerium oxide, triphenyl phosphite, 2,6-di-tert-butyl-p-cresol, and triethyl phosphate.

[0022] As a more preferred embodiment, the antioxidant is nano cerium oxide.

[0023] As a more preferred embodiment, the average particle size of the nano-cerium oxide is 20 to 50 nm.

[0024] As a more preferred embodiment, the thixotropic agent is a composition of fumed silica and hydrogenated castor oil.

[0025] As a preferred embodiment, the mass ratio of the fumed silica to hydrogenated castor oil is (0.5-0.9):(1.2-1.8).

[0026] As a more preferred embodiment, the mass ratio of the fumed silica to hydrogenated castor oil is (0.6-0.7):(1.4-1.6).

[0027] As a preferred embodiment, the corrosion inhibitor is at least one of sodium molybdate, ammonium molybdate, benzotriazole, mercaptobenzothiazole and phytic acid.

[0028] As a more preferred embodiment, the corrosion inhibitor is sodium molybdate.

[0029] As a preferred embodiment, the dispersant is at least one of polycarboxylates, polyacrylates, alkylphenol polyoxyethylene ethers, organosilicones and hyperbranched polyesters.

[0030] As a more preferred embodiment, the dispersant is a polycarboxylate.

[0031] As a preferred embodiment, the coupling agent is a titanate coupling agent or a phosphate coupling agent.

[0032] As a more preferred embodiment, the coupling agent is a titanate coupling agent.

[0033] As a preferred embodiment, the film-forming agent is a composition of a modified silicone resin and a fluorocarbon resin.

[0034] As a preferred embodiment, the mass ratio of the modified silicone resin to the fluorocarbon resin is (3-3.3): (1.7-2.1).

[0035] As a more preferred embodiment, the mass ratio of the modified silicone resin to the fluorocarbon resin is 3.2:1.8.

[0036] As a preferred embodiment, the functional composite is a composition of polytetrafluoroethylene, polyvinyl butyral and polyaniline.

[0037] As a preferred embodiment, the mass ratio of polytetrafluoroethylene, polyvinyl butyral and polyaniline is (4-6): (2-4): (1-3).

[0038] As a more preferred embodiment, the mass ratio of polytetrafluoroethylene, polyvinyl butyral and polyaniline is (4.5-5.5):(2.5-3):(1.5-2).

[0039] As a preferred embodiment, polytetrafluoroethylene, polyvinyl butyral and polyaniline are mixed, added into a ball mill, zirconium oxide balls, ball-to-material ratio (5-6): 1 and ground for 2-3 hours, and then sieved through a 400-500 mesh sieve to ensure that the particle size is ≤10 μm to obtain a functional composite.

[0040] As a preferred embodiment, the solvent is at least one of propylene glycol methyl ether acetate, diethylene glycol butyl ether acetate, propylene glycol methyl ether propionate and isophorone.

[0041] As a more preferred embodiment, the solvent is propylene glycol methyl ether acetate.

[0042] The present application also includes a method for preparing a high temperature resistant and anti-oxidation solder paste, which specifically includes the following steps: S1: passing the tin-silver-copper alloy through a 400-500 mesh sieve to remove large agglomerated particles, and placing it in a vacuum drying oven, drying it at 80-85°C for 2-3 hours, and controlling the moisture content to be less than 0.1wt%; then passing the heat-resistant copolymer resin through a 200-300 mesh sieve and mixing it with a solvent, stirring it at 40°C at a low speed of 40-60rpm for 30-40min to obtain a resin premix; S2: adding the resin premix and other raw materials except the tin-silver-copper alloy into a planetary mixer in sequence, and stirring at a constant temperature of 40-50°C. Temperature, revolution at 300-400rpm, rotation at 800-1000rpm, high-speed stirring for 1.5-2h, then maintain the vacuum degree at -0.08MPa to eliminate bubbles; S3: add the dried tin-silver-copper alloy obtained in S1 three times, each time with an interval of 10-15min, increase the speed to 450-500rpm, revolution at 1100-1200rpm, and continue stirring for 1-2h. After completion, transfer the product to a vacuum degassing machine, set the vacuum degree to -0.1MPa, the temperature to 30-35℃, and degas for 20-30min until no bubbles are precipitated on the surface of the paste.

[0043] The beneficial effects of this application are:

[0044] 1. The high temperature resistant and antioxidant solder paste provided in the present application can not only maintain excellent high temperature resistance and antioxidant properties, but also maintain good corrosion resistance, waterproofness and toughness and other properties at the same time, thereby solving the problems of heat resistance and antioxidant properties of existing solder paste materials while eliminating the performance contradictions of solder paste materials, thereby meeting the comprehensive performance requirements of solder paste materials in existing electronic products and other fields, and has broad application potential.

[0045] 2. A high temperature resistant and antioxidant solder paste provided in the present application, wherein the added heat resistant copolymer resin enhances the dense molecular stacking, molecular chain motion restriction and interface bonding force of the resin system inside the solder paste through the interaction between the rigid main chain, fluorocarbon side chains and polar groups contained therein, thereby greatly improving the overall heat resistance, oxidation resistance, corrosion resistance and water resistance of the solder paste material system.

[0046] 3. A high temperature resistant and antioxidant solder paste provided in the present application has functional complexes added therein that can cross-link to form a continuous film through the interaction between the complexes, thereby effectively achieving water vapor barrier and improving the waterproof effect. On the other hand, the internal polar groups form hydrogen bonds while the hydroxyl groups chemically bond with the metal surface oxide layer to enhance the mechanical properties of the interface. In addition, the fluorocarbon segments in the added copolymer resin can form an interpenetrating network to enhance the toughness while greatly limiting the penetration efficiency of corrosion molecules and increasing the barrier properties, and ultimately forming a multi-protection mechanism of macroscopic barrier, microscopic passivation and interface fixation to help improve the various properties of the solder paste material. DETAILED DESCRIPTION

[0047] In the specific implementation manner, specific implementation cases will be used to more intuitively display and illustrate the contents of the invention content of this application.

[0048] Example 1

[0049] The high temperature resistant and antioxidant solder paste, calculated by mass, comprises the following raw materials: 85 parts of tin-silver-copper alloy, 10 parts of heat-resistant copolymer resin, 0.8 parts of antioxidant, 2.1 parts of thixotropic agent, 0.4 parts of corrosion inhibitor, 0.5 parts of dispersant, 0.5 parts of coupling agent, 1.2 parts of film-forming agent, 6.5 parts of functional complex and 8.5 parts of solvent.

[0050] The average particle size of the tin-silver-copper alloy is 10 μm; in the tin-silver-copper alloy, by mass percentage, tin is 96.5%, silver is 3%, and copper makes up the balance.

[0051] The preparation method of the heat-resistant copolymer resin specifically comprises the following steps, measured by mass: S1: adding 50 parts of polyimide resin to 160 parts of N-methylpyrrolidone solvent, stirring continuously for 2 hours at a stirring speed of 240 rpm in a constant temperature water bath at 65°C, until the resin is completely dissolved into a transparent solution; S2: adding 21 parts of hexafluorobutyl acrylate, 13 parts of styrene and 16 parts of N-vinylpyrrolidone to the transparent solution in sequence, and adding 1.2 parts of azobisisobutyronitrile, and introducing nitrogen protection to eliminate oxygen interference; S3: heating to 80°C, stirring continuously at 320 rpm for 6 hours under a nitrogen atmosphere, cooling naturally to room temperature after the reaction is completed, slowly pouring into 500 parts of anhydrous ethanol, stirring while pouring, so that the polymer is precipitated, and then washing the precipitate 3 times with deionized water and ethanol alternately to remove unreacted monomers and solvent;

[0052] S4: Place the precipitate in a vacuum drying oven, dry it at 70°C and vacuum degree -0.1MPa for 10 hours, grind it and pass it through a 300-mesh sieve to obtain the product.

[0053] The antioxidant is nano-cerium oxide, and the average particle size thereof is 35 nm.

[0054] The thixotropic agent is a composition of fumed silica and hydrogenated castor oil, with a mass ratio of 0.7:1.5. The fumed silica was purchased from the Aerosil R972 product sold by Evonik of Germany; the hydrogenated castor oil was purchased from the polyoxyethylene (40) hydrogenated castor oil product sold by Hai'an Petrochemical Plant of Jiangsu Province, China.

[0055] The corrosion inhibitor is sodium molybdate; the dispersant is polyacrylate, purchased from SokalanPA30 sold by BASF of Germany; the coupling agent is titanate coupling agent, purchased from KR-TTS sold by Dow Corning of the United States.

[0056] The film former is a composition of modified silicone resin and fluorocarbon resin, with a mass ratio of 3.2:1.8. The modified silicone resin is purchased from Silikopon EF sold by Evonik of Germany; the fluorocarbon resin is purchased from Zeffle GK-570 sold by Daikin Industries of Japan.

[0057] The functional composite material is a composition of polytetrafluoroethylene, polyvinyl butyral and polyaniline, with a mass ratio of 5:2.5:1.8.

[0058] Polytetrafluoroethylene was purchased from PTFE L206F sold by Shanghai Haosucheng New Materials Co., Ltd., China; polyvinyl butyral was purchased from industrial-grade products sold by Jinan Shuangying Chemical Co., Ltd., China; and polyaniline was purchased from intrinsic products sold by Hubei Biaoyue Biotechnology Development Co., Ltd., China.

[0059] After mixing polytetrafluoroethylene, polyvinyl butyral and polyaniline, add them into the ball mill, add zirconium oxide balls, and grind for 2 hours with a ball-to-material ratio of 5:1. After completion, pass through a 400-mesh sieve to ensure the particle size

[0060] ≤10μm, and a functional complex is obtained.

[0061] The solvent is propylene glycol methyl ether acetate.

[0062] The preparation method of high temperature resistant and anti-oxidation solder paste specifically comprises the following steps: S1: passing the tin-silver-copper alloy through a 400-500 mesh sieve to remove large agglomerated particles, and placing the tin-silver-copper alloy in a vacuum drying oven, drying at 80-85° C. for 2-3 hours, and controlling the moisture content to be less than 0.1wt%; then passing the heat resistant copolymer resin through a 200-300 mesh sieve and mixing it with a solvent, stirring at 40° C. and a low speed of 40-60 rpm for 30-40 minutes to obtain a resin premix; S2: sequentially adding the resin premix and other raw materials except the tin-silver-copper alloy into a planetary mixer, and stirring at a constant temperature of 40-50° C. for 30 0-400rpm revolution, 800-1000rpm autogenous stirring for 1.5-2h, then maintain the vacuum degree at -0.08MPa to eliminate bubbles; S3: add the dried tin-silver-copper alloy obtained in S1 three times, each time with an interval of 10-15min, increase the speed to 450-500rpm revolution, 1100-1200rpm autogenous stirring for 1-2h, after completion, transfer the product to a vacuum degassing machine, set the vacuum degree to -0.1MPa, the temperature to 30-35℃, and degas for 20-30min until no bubbles are precipitated on the surface of the paste.

[0063] Example 2

[0064] The only difference between this embodiment and Embodiment 1 is as follows: the raw materials of the high temperature resistant and antioxidant solder paste, in parts by mass, are: 88 parts of tin-silver-copper alloy, 9 parts of heat-resistant copolymer resin, 0.8 parts of antioxidant, 2.1 parts of thixotropic agent, 0.4 parts of corrosion inhibitor, 0.5 parts of dispersant, 0.5 parts of coupling agent, 1.2 parts of film-forming agent, 7.5 parts of functional composite, and 8.5 parts of solvent.

[0065] Example 3

[0066] The only difference between this embodiment and Embodiment 1 is as follows: the raw materials of the high temperature resistant and antioxidant solder paste, in parts by mass, are: 80 parts of tin-silver-copper alloy, 11 parts of heat-resistant copolymer resin, 0.8 parts of antioxidant, 2.1 parts of thixotropic agent, 0.4 parts of corrosion inhibitor, 0.5 parts of dispersant, 0.5 parts of coupling agent, 1.2 parts of film-forming agent, 6 parts of functional composite, and 8.5 parts of solvent.

[0067] Comparative Example 1

[0068] The only difference between this comparative example and Example 1 is as follows: the raw materials of the high temperature resistant and antioxidant solder paste, in parts by mass, are: 95 parts of tin-silver-copper alloy, 3.5 parts of heat-resistant copolymer resin, 0.8 parts of antioxidant, 2.1 parts of thixotropic agent, 0.4 parts of corrosion inhibitor, 0.5 parts of dispersant, 0.5 parts of coupling agent, 1.2 parts of film-forming agent, 7.5 parts of functional composite and 7.5 parts of solvent.

[0069] The thixotropic agent is a composition of fumed silica and hydrogenated castor oil, with a mass ratio of 1.5:0.3.

[0070] Comparative Example 2

[0071] The only difference between this comparative example and Example 1 is as follows: the raw materials of the high temperature resistant and antioxidant solder paste, in parts by mass, are: 95 parts of tin-silver-copper alloy, 10 parts of heat-resistant copolymer resin, 0.8 parts of antioxidant, 2.1 parts of thixotropic agent, 0.4 parts of corrosion inhibitor, 0.5 parts of dispersant, 0.5 parts of coupling agent, 1.2 parts of film-forming agent, 2.2 parts of functional composite, and 8.5 parts of solvent.

[0072] The film-forming agent is a composition of modified silicone resin and fluorocarbon resin, with a mass ratio of 1.2:3.5.

[0073] Comparative Example 3

[0074] The only difference between this comparative example and Example 1 is that the functional composite is a composition of polytetrafluoroethylene, polyvinyl butyral and polyaniline, and the mass ratio is 2:5:0.2.

[0075] Comparative Example 4

[0076] The only difference between this comparative example and Example 1 is that the functional composite is a composition of polytetrafluoroethylene, polyvinyl butyral and polyaniline, and the mass ratio is 8:1:0.5.

[0077] Comparative Example 5

[0078] This comparative example differs from Example 1 only in the following: The preparation method of the heat-resistant copolymer resin, in parts by mass, specifically comprises the following steps: S1: adding 50 parts of polyimide resin to 160 parts of N-methylpyrrolidone solvent, stirring continuously for 2 hours at a stirring speed of 240 rpm in a constant temperature water bath at 65°C, until the resin is completely dissolved into a transparent solution;

[0079] S2: add 10 parts of hexafluorobutyl acrylate, 6 parts of styrene and 5 parts of N-vinyl pyrrolidone to the transparent solution in sequence, and add 0.8 parts of azobisisobutyronitrile, and introduce nitrogen protection to eliminate oxygen interference; S3: heat to 80°C, and continue stirring at 320rpm for 6 hours under a nitrogen atmosphere. After the reaction is completed, naturally cool to room temperature, slowly pour into 500 parts of anhydrous ethanol, stirring while pouring to precipitate the polymer, and then wash the precipitate with deionized water and ethanol alternately for 3 times to remove unreacted monomers and solvents; S4: place the precipitate in a vacuum drying oven, dry it at 70°C and vacuum degree -0.1MPa for 10 hours, crush it and pass it through a 300-mesh sieve to obtain it.

[0080] Comparative Example 6

[0081] This comparative example differs from Example 1 only in the following: The preparation method of the heat-resistant copolymer resin, in parts by mass, specifically comprises the following steps: S1: adding 35 parts of polyimide resin to 160 parts of N-methylpyrrolidone solvent, stirring continuously for 2 hours at a stirring speed of 240 rpm in a constant temperature water bath at 65°C, until the resin is completely dissolved into a transparent solution;

[0082] S2: add 30 parts of hexafluorobutyl acrylate, 3 parts of styrene and 25 parts of N-vinyl pyrrolidone to the transparent solution in sequence, and add 1.3 parts of azobisisobutyronitrile, introduce nitrogen protection to eliminate oxygen interference; S3: heat to 80°C, stir and react continuously at 320rpm for 6 hours under nitrogen atmosphere, cool naturally to room temperature after the reaction is completed, slowly pour into 500 parts of anhydrous ethanol, stir while pouring to precipitate the polymer, and then wash the precipitate with deionized water and ethanol alternately for 3 times to remove unreacted monomers and solvent; S4: place the precipitate in a vacuum drying oven, dry at 70°C and vacuum degree -0.1MPa for 10 hours, crush and pass through a 300-mesh sieve to obtain.

[0083] Performance Evaluation

[0084] 1. High temperature resistance: The solder paste was printed on a copper substrate (pad size 0.5 mm × 0.5 mm), the reflow peak temperature was 280 ° C, the duration was 60 seconds, the soldered sample was placed in a high temperature oven, and treated at a constant temperature of 300 ° C for 30 minutes, then naturally cooled to room temperature, and a push-pull force tester (Dage 4000) was used to test the shear strength of the solder joint at a speed of 0.5 mm / s, and compared with the shear strength before the test, the shear strength retention rate was obtained (%) = strength after test / strength before test × 100%, and the average value of 10 tests was recorded in Table 1.

[0085] 2. Anti-oxidation test: Apply solder paste to a copper plate (10mm×10mm) with a thickness of 50μm, and form a uniform solder film by reflow soldering. Place the sample in a muffle furnace and heat it in air at 280℃ for 30 minutes, then take it out and cool it. Use an optical microscope to measure the percentage of surface oxidation area. The results are recorded in Table 1 as the average of 10 tests.

[0086] 3. Waterproof test: Refer to ASTM D7334-08 for water contact angle test, and take the average value of 10 tests and record it in Table 1.

[0087] 4. Corrosion test: Corrosion test was carried out according to ASTM B117-19. The welded samples were placed in a salt spray chamber (5wt% NaCl solution, pH 6.5-7.2, temperature 35°C) for 500 hours. The corrosion point results were recorded in Table 1.

[0088] Table 1 Performance evaluation results

[0089]

[0090]

[0091] From the final performance test results of the embodiments and comparative examples, comparative examples 1 to 6 achieved worse performance results than the embodiments, while the embodiments formed a surface protection film layer, enhanced the internal density, and ultimately formed a multiple protection mechanism of macro-barrier, micro-passivation and interface fixation, thereby improving the various properties of the solder paste material.

Claims

1. A high temperature resistant and anti-oxidation solder paste, characterized in that: The raw materials are, by mass: 75-95 parts of tin-silver-copper alloy, 8-12 parts of heat-resistant copolymer resin, 0.5-1.5 parts of antioxidant, 1-3 parts of thixotropic agent, 0.2-0.8 parts of corrosion inhibitor, 0.2-0.6 parts of dispersant, 0.5-1.2 parts of coupling agent, 0.8-1.6 parts of film-forming agent, 5-8 parts of functional complex, and 5-15 parts of solvent; The average particle size of the tin-silver-copper alloy is 5 to 15 μm; The thixotropic agent is a composition of fumed silica and hydrogenated castor oil, with a mass ratio of (0.5-0.9): (1.2-1.8); The film-forming agent is a composition of modified silicone resin and fluorocarbon resin, with a mass ratio of (3-3.3): (1.7-2.1); The functional composite material is a composition of polytetrafluoroethylene, polyvinyl butyral and polyaniline, and the mass ratio is (4-6): (2-4): (1-3).

2. The high temperature resistant and anti-oxidation solder paste according to claim 1, characterized in that: The mass ratio of the tin-silver-copper alloy, the heat-resistant copolymer resin and the functional composite is (80-88): (9-11): (6-7.5).

3. The high temperature resistant and anti-oxidation solder paste according to claim 2, characterized in that: The preparation method of the heat-resistant copolymer resin specifically comprises the following steps: S1: adding polyimide resin to N-methylpyrrolidone solvent, stirring continuously for 2 to 3 hours at a stirring speed of 200 to 250 rpm in a constant temperature water bath at 60 to 70°C, until the resin is completely dissolved into a transparent solution; S2: adding hexafluorobutyl acrylate, styrene and N-vinylpyrrolidone to the transparent solution in sequence, and adding azobisisobutyronitrile, introducing nitrogen protection to eliminate oxygen interference; S3: heating to 80 ~85℃, stir and react at 300-350rpm for 6-7h in a nitrogen atmosphere, cool naturally to room temperature after the reaction is completed, slowly pour into anhydrous ethanol, stir while pouring to precipitate the polymer, and then wash the precipitate with deionized water and ethanol alternately for 3-4 times to remove unreacted monomers and solvent; S4: place the precipitate in a vacuum drying oven, dry it at 60-70℃ and vacuum degree -0.1MPa for 10-12h, crush it and pass it through a 300-400 mesh sieve to obtain.

4. The high temperature resistant and anti-oxidation solder paste according to claim 3, characterized in that: The mass ratio of the polyimide resin, hexafluorobutyl acrylate, styrene and N-vinyl pyrrolidone is (4.5-5): (2-2.2): (1.2-1.4): (1.4-1.6).

5. The high temperature resistant and anti-oxidation solder paste according to claim 4, characterized in that: The antioxidant is at least one of nano cerium oxide, triphenyl phosphite, 2,6-di-tert-butyl-p-cresol and triethyl phosphate.

6. The high temperature resistant and anti-oxidation solder paste according to claim 5, characterized in that: The corrosion inhibitor is at least one of sodium molybdate, ammonium molybdate, benzotriazole, mercaptobenzothiazole and phytic acid.

7. The high temperature resistant and anti-oxidation solder paste according to claim 6, characterized in that: The coupling agent is a titanate coupling agent or a phosphate coupling agent.

8. The high temperature resistant and anti-oxidation solder paste according to claim 7, characterized in that: The dispersant is at least one of polycarboxylate, polyacrylate, alkylphenol polyoxyethylene ether, organic silane and hyperbranched polyester.

9. The high temperature resistant and anti-oxidation solder paste according to claim 8, characterized in that: The solvent is at least one of propylene glycol methyl ether acetate, diethylene glycol butyl ether acetate, propylene glycol methyl ether propionate and isophorone.

10. A method for preparing a high temperature resistant and anti-oxidation solder paste according to any one of claims 1 to 9, characterized in that: The specific steps include: S1: passing the tin-silver-copper alloy through a 400-500 mesh sieve to remove large agglomerated particles, and placing the alloy in a vacuum drying oven, drying it at 80-85° C. for 2-3 hours, with the moisture content controlled at <0.1wt%; then passing the heat-resistant copolymer resin through a 200-300 mesh sieve, mixing the resin with the solvent, and stirring at 40° C. at a low speed of 40-60 rpm for 30-40 minutes to obtain a resin premix; S2: Add the resin premix and other raw materials except the tin-silver-copper alloy into a planetary mixer in sequence, keep the temperature at 40-50°C, rotate at 300-400rpm, and rotate at 800-1000rpm for 1.5-2h, then maintain the vacuum degree at -0.08MPa to eliminate bubbles; S3: Add the dried tin-silver-copper alloy obtained in S1 three times, each time with an interval of 10-15min, increase the speed to 450-500rpm for revolution, and rotate at 1100-1200rpm for continuous stirring for 1-2h. After completion, transfer the product to a vacuum degassing machine, set the vacuum degree to -0.1MPa, the temperature to 30-35°C, and degas for 20-30min until no bubbles are precipitated on the surface of the paste.

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