High-temperature-resistant and oxidation-resistant tin paste and preparation method thereof

Abstract

The application relates to the field of welding materials, and more particularly to a high-temperature-resistant and oxidation-resistant tin paste and a preparation method thereof. The raw materials of the high-temperature-resistant and oxidation-resistant tin paste include a tin-silver-copper alloy, a temperature-resistant copolymer resin, an antioxidant, a thixotropic agent, a corrosion inhibitor, a dispersing agent and a functional composite, etc. The tin paste material prepared finally not only has excellent high-temperature resistance and oxidation resistance, but also has good corrosion resistance, waterproofness and toughness, etc., so that the problems of the high-temperature resistance and oxidation resistance of the existing tin paste material are solved, the performance contradictions of the tin paste material are eliminated, the comprehensive performance requirements of the tin paste material in the existing electronic product field are met, and the tin paste material has wide application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of soldering materials, and more particularly to a high-temperature-resistant and oxidation-resistant solder paste and a preparation method thereof. BACKGROUND

[0002] Solder paste, also known as soldering paste, is an indispensable soldering material in modern electronic manufacturing industry. It is usually mixed by solder powder, flux and other additives, and is used for soldering of Printed Circuit Board (PCB) components in Surface Mount Technology (SMT). Solder paste has certain viscosity at room temperature, which can initially adhere electronic components to a designated position. During the reflow soldering process, as the temperature rises, the solvent and part of the additives volatilize, so that the soldered components and the pads on the PCB are permanently connected through the molten solder.

[0003] With the development of electronic products towards miniaturization and high-density packaging, the requirements for solder paste are becoming more and more stringent. Especially for some special application scenarios, such as working in high temperature environment or requiring extremely high long-term reliability, ordinary solder paste may not meet the requirements. In order to cope with these challenges, various improved solder paste products have appeared in the market, such as water-washing ultra-fine solder powder water-soluble lead-free high-temperature flux paste. This type of solder paste emphasizes its stability and oxidation resistance in high temperature conditions.

[0004] In recent years, there have been formulations 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 antioxidant, which is intended to prevent the oxidation of solder powder in the solder paste, thereby avoiding problems such as solder beads on the board after soldering. However, relying solely on the content of antioxidants to solve the above problems can easily affect the normal proportion of other raw materials of the solder paste, thereby affecting other properties.

[0005] Therefore, although the existing technology has made certain progress, it still faces many challenges in actual application, such as insufficient oxidation resistance. Although antioxidants are added, the solder paste may still oxidize under extreme conditions, such as high humidity, high temperature, cold and hot cycles, and long-term light exposure, which affects the quality of soldering. In addition, ordinary solder paste is prone to softening or flowing in high temperature environment, which leads to solder joint failure or changes in electrical properties, which is unacceptable for electronic products working in high temperature environment. Moreover, the corrosion resistance and water resistance of ordinary solder paste are in conflict with the above properties. SUMMARY

[0006] Therefore, in order to effectively solve the above problems and improve the comprehensive performance of the solder paste material, the application provides a high-temperature-resistant and oxidation-resistant solder paste and a preparation method thereof. The finally prepared solder paste material can not only have excellent high-temperature resistance and oxidation resistance, but also has good corrosion resistance, waterproofness and toughness, thereby solving the problems of the existing solder paste material in terms of high-temperature resistance and oxidation resistance, eliminating the performance contradictions of the solder paste material, meeting the comprehensive performance requirements of the existing electronic product field for the solder paste material, and having wide application potential.

[0007] The high-temperature-resistant and oxidation-resistant solder paste comprises, by mass fraction, 75-95 parts of a tin-silver-copper alloy, 8-12 parts of a temperature-resistant copolymer resin, 0.5-1.5 parts of an antioxidant, 1-3 parts of a thixotropic agent, 0.2-0.8 parts of a corrosion inhibitor, 0.2-0.6 parts of a dispersing agent, 0.5-1.2 parts of a coupling agent, 0.8-1.6 parts of a film-forming agent, 5-8 parts of a functional composite, and 5-15 parts of a solvent.

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

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

[0010] As a preferred embodiment, in the tin-silver-copper alloy, tin accounts for 95-96.5% by mass fraction, silver accounts for 2.5-3% by mass fraction, and the balance is copper.

[0011] As a preferred embodiment, the mass ratio of the tin-silver-copper alloy, the temperature-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 temperature-resistant copolymer resin and the functional composite is 85:10:6.5.

[0013] As a preferred embodiment, the preparation method of the temperature-resistant copolymer resin specifically comprises the following steps: S1: polyimide resin is added into an N-methylpyrrolidone solvent, and stirring is continuously performed at a constant temperature water bath of 60-70 ℃ and a stirring speed of 200-250 rpm for 2-3 h until the resin is completely dissolved into a transparent solution; S2: hexafluorobutyl acrylate, styrene and N-vinylpyrrolidone are sequentially added into the transparent solution, and azobisisobutyronitrile is added, and nitrogen is introduced for protection to exclude oxygen interference; S3: the temperature is increased to 80-85 ℃, and stirring is continuously performed at a nitrogen atmosphere and a stirring speed of 300-350 rpm for 6-7 h, and after the reaction is completed, the temperature is naturally cooled to room temperature, and the polymer is precipitated by slowly pouring into anhydrous ethanol while stirring, and then the precipitate is washed with deionized water and ethanol alternately for 3-4 times to remove unreacted monomers and solvents.

[0014] S4: The precipitate is placed in a vacuum drying oven and dried at 60-70℃ under a vacuum of-0.1MPa for 10-12h, then crushed and sieved 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):(1.2-1.4):(1.4-1.6).

[0016] 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):(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 temperature-resistant copolymer resin added in the present application can effectively improve the overall temperature resistance, oxidation resistance, corrosion resistance and waterproof performance of the tin paste material system. The main chain rigid skeleton contained in the temperature-resistant copolymer resin can provide high thermal stability, and can work together with the fluorocarbon side chain to impart hydrophobicity and greatly improve the dense molecular packing of the resin system, so that the tin paste material is significantly improved in waterproofness, mechanics and temperature resistance, etc.

[0019] On the other hand, the C-F bond in the fluorocarbon side chain has high energy in the resin system, can withstand more heat energy without breaking under high temperature environment, and can form a surface protection layer at the side chain position to slow down the oxidation reaction and reduce the migration efficiency of active molecules. In addition, the structure composed of aromatic ring and imide bond in the copolymer resin can also control heat energy transfer under high temperature environment, so that the molecular chain movement of the resin system under high temperature environment is limited, and the thermal activation and thermal decomposition are inhibited.

[0020] Finally, the fluorocarbon side chain in the copolymer resin forms a low-surface-energy hydrophobic layer on the surface of the resin, which hinders the penetration of oxygen and water, and greatly enhances the interfacial bonding force between the resin system and other raw materials by forming a coordination bond between the N and O atoms in the pyrrolidone ring and the metal surface. Whether it is resistance under external force or uniformity itself, it has been greatly improved, thereby comprehensively improving the heat resistance, oxidation resistance, waterproofness and corrosion resistance of the tin 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 20-50 nm.

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

[0025] As a preferred embodiment, the mass ratio of the fumed silica and the 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 and the 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 polycarboxylate, polyacrylate, alkylphenol polyoxyethylene ether, organosilane, and hyperbranched polyester.

[0030] As a more preferred embodiment, the dispersant is 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 combination of modified silicone resin and fluorocarbon resin.

[0034] As a preferred embodiment, the mass ratio of the modified silicone resin and 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 and the fluorocarbon resin is 3.2:1.8.

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

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

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

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

[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 application also includes a preparation method of the high-temperature-resistant and oxidation-resistant solder paste, which specifically comprises the following steps: S1: passing the tin-silver-copper alloy through a 400-500 mesh sieve to remove lumps and large particles, and placing the tin-silver-copper alloy in a vacuum drying box, drying at 80-85℃ for 2-3h, and controlling the water content to be <0.1wt%; then passing the temperature-resistant copolymer resin through a 200-300 mesh sieve and mixing with the solvent, stirring at 40℃ and a low speed of 40-60rpm for 30-40min 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, stirring at a constant temperature of 40-50℃, 300-400rpm revolution and 800-1000rpm rotation, and stirring at a high speed for 1.5-2h; then maintaining the vacuum degree at -0.08MPa to remove air bubbles; S3: adding the dried tin-silver-copper alloy obtained in S1 three times at intervals of 10-15min, increasing the rotation speed to 450-500rpm and the revolution speed to 1100-1200rpm, and continuously stirring for 1-2h; after completion, transferring the product to a vacuum defoaming machine, setting the vacuum degree at -0.1MPa and the temperature at 30-35℃, and defoaming for 20-30min until no air bubbles are generated on the surface of the paste, and the product is obtained.

[0043] The application has the following beneficial effects:

[0044] 1、The high-temperature-resistant and oxidation-resistant solder paste provided in the application not only has excellent high-temperature resistance and oxidation resistance, but also has good corrosion resistance, water resistance and toughness, thereby solving the problems of the existing solder paste materials in terms of high-temperature resistance and oxidation resistance, eliminating the performance contradictions of the solder paste materials, and meeting the comprehensive performance requirements of the solder paste materials in the field of electronic products, and has wide application potential.

[0045] 2、The high-temperature-resistant and oxidation-resistant solder paste provided in the application, the temperature-resistant copolymer resin added therein enhances the compact molecular packing property, the molecular chain movement restriction, and the interface bonding force of the resin system inside the solder paste through the interaction among the rigid main chain, the fluorocarbon side chain, and the polar group contained therein, thereby greatly improving the overall temperature resistance, oxidation resistance, corrosion resistance, waterproofness, and other properties of the solder paste material system.

[0046] 3、The high-temperature-resistant and oxidation-resistant solder paste provided in the application, the functional complex added therein can be crosslinked to form a continuous film through the interaction among the complexes, effectively blocking water vapor to improve the waterproof effect. On the other hand, the polar groups inside form hydrogen bonds, and the hydroxyl groups thereof chemically bond with the metal surface oxide layer, improving the mechanical properties of the interface. Moreover, the functional complex can form an interpenetrating network with the fluorocarbon chain segments in the copolymer resin added therein, improving the toughness while greatly limiting the penetration efficiency of corrosive molecules and increasing the barrier property, and finally forming a multiple protection mechanism of macroscopic barrier, microscopic passivation, and interface fixation, thereby assisting in improving the various properties of the solder paste material. DETAILED DESCRIPTION

[0047] In the detailed description, the content in the inventive content of the application will be more intuitively displayed and described through specific implementation cases.

[0048] Example 1

[0049] The high-temperature-resistant and oxidation-resistant solder paste comprises, by mass fraction, 85 parts of a tin-silver-copper alloy, 10 parts of a temperature-resistant copolymer resin, 0.8 parts of an antioxidant, 2.1 parts of a thixotropic agent, 0.4 parts of a corrosion inhibitor, 0.5 parts of a dispersing agent, 0.5 parts of a coupling agent, 1.2 parts of a film-forming agent, 6.5 parts of a functional complex, and 8.5 parts of a 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 the balance is copper.

[0051] The preparation method of the temperature-resistant copolymer resin comprises, by mass fraction, the following steps: S1: 50 parts of a polyimide resin are added to 160 parts of N-methylpyrrolidone solvent, and stirring is continuously performed at a constant temperature water bath of 65℃ and a stirring speed of 240 rpm for 2 h until the resin is completely dissolved into a transparent solution; S2: 21 parts of hexafluorobutyl acrylate, 13 parts of styrene, and 16 parts of N-vinylpyrrolidone are sequentially added to the transparent solution, 1.2 parts of azobisisobutyronitrile is added, and nitrogen is introduced for protection to exclude oxygen interference; S3: the temperature is increased to 80℃, and stirring is continuously performed at 320 rpm under a nitrogen atmosphere for 6 h. After the reaction is completed, the system is naturally cooled to room temperature, and 500 parts of anhydrous ethanol is slowly poured in while stirring to precipitate the polymer. Then, the precipitate is washed with deionized water and ethanol alternately for 3 times to remove unreacted monomers and solvents;

[0052] S4: Place the precipitate in a vacuum drying oven and dry it at 70℃ and a vacuum of -0.1MPa for 10 hours. After pulverizing, pass it through a 300-mesh sieve to obtain the final product.

[0053] The antioxidant is nano-cerium oxide with an average particle size of 35 nm.

[0054] The thixotropic agent was a composition of fumed silica and hydrogenated castor oil in a mass ratio of 0.7:1.5. The fumed silica was purchased from Evonik GmbH, Germany, as Aerosil R972; the hydrogenated castor oil was purchased from Haian Petrochemical Plant, Jiangsu Province, China, as polyoxyethylene (40) hydrogenated castor oil.

[0055] The corrosion inhibitor was sodium molybdate; the dispersant was polyacrylate, purchased from BASF (Sokalan PA30); and the coupling agent was titanate coupling agent, purchased from Dow Corning (KR-TTS).

[0056] The film-forming agent was a composition of modified silicone resin and fluorocarbon resin in a mass ratio of 3.2:1.8. The modified silicone resin was purchased from Evonik GmbH, Germany, as Silikopon EF; the fluorocarbon resin was purchased from Daikin Industries, Japan, as Zeffle GK-570.

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

[0058] Polytetrafluoroethylene (PTFE) was purchased from Shanghai Haosucheng New Materials Co., Ltd., China; polyvinyl butyral (PVB) was purchased from Jinan Shuangying Chemical Co., Ltd., China; and polyaniline was purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., China.

[0059] Polytetrafluoroethylene, polyvinyl butyral, and polyaniline were mixed and then added to a ball mill with zirconia balls at a ball-to-material ratio of 5:1. The mixture was ground for 2 hours, and then passed through a 400-mesh sieve to ensure the particle size distribution was correct.

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

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

[0062] The preparation method of high-temperature resistant and antioxidant solder paste specifically includes the following steps: S1: The tin-silver-copper alloy is passed through a 400-500 mesh sieve to remove large agglomerated particles, and then placed in a vacuum drying oven at 80-85℃ for 2-3 hours, with the moisture content controlled at <0.1wt%; then the heat-resistant copolymer resin is passed through a 200-300 mesh sieve and mixed with a solvent, and stirred at 40℃ and low speed (40-60 rpm) for 30-40 minutes to obtain a resin premix; S2: The resin premix and other raw materials except the tin-silver-copper alloy are added sequentially to a planetary mixer, and stirred at a constant temperature of 40-50℃ for 30 minutes. Stir at high speed for 1.5 to 2 hours with revolution at 0 to 400 rpm and rotation at 800 to 1000 rpm, then maintain a vacuum of -0.08 MPa to remove air bubbles; S3: Add the dried tin-silver-copper alloy obtained in S1 in three portions, with an interval of 10 to 15 minutes between each addition, increase the rotation speed to 450 to 500 rpm and rotation at 1100 to 1200 rpm for 1 to 2 hours. After completion, transfer the product to a vacuum degassing machine, set the vacuum to -0.1 MPa, the temperature to 30 to 35°C, and degas for 20 to 30 minutes until no air bubbles are precipitated on the surface of the paste.

[0063] Example 2

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

[0065] Example 3

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

[0067] Comparative Example 1

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

[0069] The thixotropic agent is a composition of fumed silica and hydrogenated castor oil in 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 high-temperature resistant and antioxidant solder paste, by weight, consists of the following raw materials: 95 parts tin-silver-copper alloy, 10 parts heat-resistant copolymer resin, 0.8 parts antioxidant, 2.1 parts thixotropic agent, 0.4 parts corrosion inhibitor, 0.5 parts dispersant, 0.5 parts coupling agent, 1.2 parts film-forming agent, 2.2 parts functional complex, and 8.5 parts solvent.

[0072] The film-forming agent is a composition of modified silicone resin and fluorocarbon resin in 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 compound is a composition of polytetrafluoroethylene, polyvinyl butyral, and polyaniline in a mass ratio of 2:5:0.2.

[0075] Comparative Example 4

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

[0077] Comparative Example 5

[0078] The only difference between this comparative example and Example 1 is the following: The preparation method of the heat-resistant copolymer resin, by mass, specifically includes the following steps: S1: 50 parts of polyimide resin are added to 160 parts of N-methylpyrrolidone solvent, and stirred continuously at 240 rpm for 2 hours in a constant temperature water bath at 65°C until the resin is completely dissolved into a transparent solution.

[0079] S2: Add 10 parts hexafluorobutyl acrylate, 6 parts styrene, and 5 parts N-vinylpyrrolidone sequentially to a transparent solution, and add 0.8 parts azobisisobutyronitrile. Purge with nitrogen gas to eliminate oxygen interference. S3: Heat to 80℃ and stir continuously at 320 rpm for 6 hours under a nitrogen atmosphere. After the reaction is complete, allow it to cool naturally to room temperature. Slowly pour the mixture into 500 parts anhydrous ethanol while stirring to precipitate the polymer. Then wash the precipitate three times with deionized water and ethanol alternately to remove unreacted monomers and solvent. S4: Place the precipitate in a vacuum drying oven and dry it at 70℃ and a vacuum of -0.1 MPa for 10 hours. After pulverizing, pass it through a 300-mesh sieve to obtain the final product.

[0080] Comparative Example 6

[0081] The only difference between this comparative example and Example 1 is the following: The preparation method of the heat-resistant copolymer resin, by mass, specifically includes the following steps: S1: 35 parts of polyimide resin are added to 160 parts of N-methylpyrrolidone solvent, and stirred continuously at 240 rpm for 2 hours in a constant temperature water bath at 65°C until the resin is completely dissolved into a transparent solution.

[0082] S2: Add 30 parts hexafluorobutyl acrylate, 3 parts styrene, and 25 parts N-vinylpyrrolidone sequentially to a transparent solution, and add 1.3 parts azobisisobutyronitrile. Purge with nitrogen gas to eliminate oxygen interference. S3: Heat to 80℃ and stir continuously at 320 rpm for 6 hours under a nitrogen atmosphere. After the reaction is complete, allow to cool naturally to room temperature. Slowly pour the mixture into 500 parts anhydrous ethanol while stirring to precipitate the polymer. Then wash the precipitate three times with deionized water and ethanol alternately to remove unreacted monomers and solvent. S4: Place the precipitate in a vacuum drying oven and dry it at 70℃ and a vacuum of -0.1 MPa for 10 hours. After pulverizing, pass the precipitate through a 300-mesh sieve to obtain the final product.

[0083] Performance Evaluation

[0084] 1. High temperature resistance: Solder paste was printed on a copper substrate (pad size 0.5mm × 0.5mm). The reflow soldering peak temperature was 280℃ for 60 seconds. The soldered sample was placed in a high temperature oven and treated at 300℃ for 30 minutes. Then it was allowed to cool naturally to room temperature. The shear strength of the solder joint was tested using a push-pull tester (Dage 4000) at a speed of 0.5mm / s. The shear strength was compared with the shear strength before the test. The shear strength retention rate % was calculated as follows: shear strength retention rate % = strength after test / strength before test × 100%. The average value of 10 tests was recorded in Table 1.

[0085] 2. Antioxidant test: Solder paste was applied to a copper plate (10mm×10mm) with a thickness of 50μm. After reflow soldering, a uniform solder film was formed. The sample was placed in a muffle furnace and heated in air at 280℃ for 30 minutes. After cooling, the percentage of the surface oxidation area was measured using an optical microscope. The results were the average of 10 tests and recorded in Table 1.

[0086] 3. Waterproofing test: Water contact angle test was conducted according to ASTM D7334-08, and the average of 10 tests was recorded in Table 1.

[0087] 4. Corrosion Resistance Test: Corrosion resistance tests were conducted 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℃) for 500 hours. The corrosion point results are recorded in Table 1.

[0088] Table 1 Performance Evaluation Results

[0089]

[0090]

[0091] Based on the final performance test results of the examples and comparative examples, comparative examples 1-6 achieved worse performance results compared to the examples. The examples, on the other hand, improved the various properties of the solder paste material by using the combined action of the copolymer resin with the best performance and the functional compound to form a surface protective film layer, enhance the internal density, and ultimately form a multi-protection mechanism of macroscopic barrier, microscopic passivation and interface fixation.

Claims

1. A high temperature resistant antioxidant solder paste, characterized in that: Raw materials are tin-silver-copper alloy 75-95 parts by mass, temperature-resistant copolymer resin 8-12 parts by mass, antioxidant 0.5-1.5 parts by mass, thixotropic agent 1-3 parts by mass, corrosion inhibitor 0.2-0.8 parts by mass, dispersant 0.2-0.6 parts by mass, coupling agent 0.5-1.2 parts by mass, film-forming agent 0.8-1.6 parts by mass, functional complex 5-8 parts by mass, and solvent 5-15 parts by mass; In the tin-silver-copper alloy, tin accounts for 95-96.5% by mass, silver accounts for 2.5-3% by mass, and the balance is copper; The preparation method of the temperature-resistant copolymer resin comprises the following steps: S1: polyimide resin is added to N-methyl pyrrolidone solvent, and stirred at a constant temperature of 60-70℃ in a water bath at a stirring speed of 200-250 rpm for 2-3 hours until the resin is completely dissolved into a transparent solution; S2: hexafluorobutyl acrylate, styrene and N-vinyl pyrrolidone are sequentially added to the transparent solution, and azobisisobutyronitrile is added, and nitrogen is introduced for protection to exclude oxygen interference; S3: the temperature is raised to 80-85℃, and stirring is continuously carried out at 300-350 rpm under a nitrogen atmosphere for 6-7 hours, and after the reaction is completed, the solution is naturally cooled to room temperature, and is slowly poured into anhydrous ethanol while stirring, so that the polymer is precipitated and separated out, and then the precipitate is washed with deionized water and ethanol alternately for 3-4 times to remove unreacted monomers and solvents; S4: the precipitate is placed in a vacuum drying oven and dried at 60-70℃ under a vacuum degree of -0.1 MPa for 10-12 hours, and after being crushed, it is sieved through a 300-400 mesh sieve to obtain the product; 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); The average particle size of the tin-silver-copper alloy is 5-15 μm; The thixotropic agent is a combination of fumed silica and hydrogenated castor oil, and the mass ratio is (0.5-0.9):(1.2-1.8); The film-forming agent is a combination of modified silicone resin and fluorocarbon resin, and the mass ratio is (3-3.3):(1.7-2.1); The functional complex is a combination of polytetrafluoroethylene, polyvinyl butyral and polyaniline, and the mass ratio is (4-6):(2-4):(1-3). The mass ratio of the tin-silver-copper alloy, temperature-resistant copolymer resin and functional complex is (80-88):(9-11):(6-7.5).

2. The high-temperature resistant antioxidant solder paste according to claim 1, 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.

3. The high-temperature resistant antioxidant solder paste according to claim 2, wherein: The corrosion inhibitor is at least one of sodium molybdate, ammonium molybdate, benzotriazole, mercaptobenzothiazole and phytic acid.

4. The high-temperature resistant antioxidant solder paste according to claim 3, characterized in that: The coupling agent is a titanate coupling agent or a phosphate coupling agent.

5. The high-temperature resistant antioxidant solder paste according to claim 4, wherein: The dispersant is at least one of polycarboxylate, polyacrylate, alkylphenol polyoxyethylene ether, organosilane and hyperbranched polyester.

6. The high-temperature-resistant antioxidant solder paste according to claim 5, 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.

7. The high-temperature-resistant antioxidant solder paste according to claim 6, characterized in that: The preparation method comprises the following steps:

8. A method for preparing the high-temperature-resistant and oxidation-resistant solder paste according to any one of claims 1-7, characterized in that: ​ S1: tin-silver-copper alloy is passed through a 400-500 mesh sieve to remove large particles of agglomerates, and is placed in a vacuum drying oven, dried at 80-85°C for 2-3h, and the moisture content is controlled to be <0.1wt%; then the temperature-resistant copolymer resin is passed through a 200-300 mesh sieve and mixed with a solvent, stirred at 40°C at a low speed of 40-60rpm for 30-40min to obtain a resin premix; S2: the resin premix and other raw materials except tin-silver-copper alloy are sequentially added to a planetary mixer, stirred at a constant temperature of 40-50°C, at a revolution speed of 300-400rpm and a rotation speed of 800-1000rpm for 1.5-2h, and then the vacuum degree is maintained at -0.08MPa to remove air bubbles; S3: the dried tin-silver-copper alloy obtained in S1 is added in three portions, each interval is 10-15min, the revolution speed is increased to 450-500rpm, and the rotation speed is 1100-1200rpm, and the stirring is continued for 1-2h, then the product is transferred to a vacuum degassing machine, the vacuum degree is set to -0.1MPa, the temperature is 30-35°C, and the degassing is carried out for 20-30min until no air bubbles are precipitated on the surface of the paste, and the product is obtained.

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