Nanosilver tin paste with high welding strength and preparation method thereof

Abstract

This application relates to the field of building materials, and more specifically to a nano-silver solder paste with high soldering strength and its preparation method. The raw materials for the high-soldering-strength nano-silver solder paste include nano-silver powder, nano-tin powder, composite resin, dispersant, activator, film-forming agent, thixotropic agent, silicon-titanium particles, and stabilizer. This application provides a nano-silver solder paste with high soldering strength and its preparation method, which not only achieves uniform dispersion of the internal system, thereby optimizing the soldering effect and performance, but also significantly improves oxidation resistance, greatly reducing the probability of easy oxidation and silver oxide formation due to the high surface energy of nano-silver. Furthermore, it balances the preparation process with the high strength of the silver solder paste, exhibiting excellent stability and mechanical strength, thus largely meeting the needs of high-reliability packaging in the existing technology field and possessing broad application potential.

Description

Technical Field

[0001] This application relates to the field of building materials, and more specifically to a nano-silver solder paste with high welding strength and its preparation method. Background Technology

[0002] As electronic devices evolve towards miniaturization, high density, and high frequency, the performance requirements for electronic packaging materials are becoming increasingly stringent. Soldering materials, as a key medium for electronic interconnection, must simultaneously meet requirements such as high conductivity, excellent mechanical strength, resistance to high-temperature aging, and compatibility with low-temperature processes. Traditional tin-lead solder has been gradually phased out due to environmental regulations, and lead-free solder has become the mainstream. However, lead-free solder often suffers from insufficient strength, interface brittleness, and thermal fatigue failure at high temperatures.

[0003] In recent years, nanomaterials have become a research hotspot in the field of high-reliability welding due to their unique surface effects and low-temperature sintering characteristics. Nanomaterials have high specific surface area and surface activity, and can form a dense metal bonding layer through solid-state sintering, significantly reducing thermal damage to heat-sensitive components.

[0004] Currently, nano-silver has been used to prepare various forms of solder paste, which contain mixtures of nano-silver powder and flux. These solder pastes can achieve effective soldering at relatively low temperatures and offer higher mechanical strength and better electrical properties than traditional solders. Furthermore, the soldering effect can be further optimized by controlling the size, shape, and distribution of nano-silver particles. However, despite the many advantages exhibited by nano-silver solder paste, it still faces many challenges in practical applications. These include the impact of system dispersion on soldering performance, the over-reliance of nano-silver on organic dispersants and its susceptibility to oxidation, which significantly reduces conductivity, and the challenge of balancing sintering processes with high strength, making it difficult to meet the high-reliability packaging requirements of current technological fields. Summary of the Invention

[0005] Therefore, in order to solve the above problems, this application provides a nano-silver solder paste with high soldering strength and its preparation method. It not only achieves uniform dispersion of the internal system, thereby optimizing the soldering effect and soldering performance, but also significantly improves the oxidation resistance, greatly reduces the probability of easy oxidation and formation of silver oxide due to the high surface energy of nano-silver, and further balances the balance between the preparation process and the high strength of silver solder paste. It has excellent stability and mechanical strength, thus meeting the needs of high reliability packaging in the existing technology field and has broad application potential.

[0006] A high-strength nano-silver solder paste, by mass percentage, comprises the following components: 40-50% nano-silver powder, 15-20% nano-tin powder, 10-15% composite resin, 0.8-1.2% dispersant, 0.5-0.8% activator, 1-1.5% film-forming agent, 1-2% thixotropic agent, 4-6% silicon-titanium particles, 0.2-0.4% stabilizer, 0.3-0.5% antioxidant, 0.2-0.4% wetting agent, and the remainder is solvent.

[0007] As a preferred embodiment, the nano-silver powder is spherical nano-silver powder with an average particle size of 30-50 nm.

[0008] As a preferred embodiment, the average particle size of the nano-tin powder is 50–90 nm.

[0009] As a preferred embodiment, the mass ratio of the nano-tin powder to the functional resin is (45-50):(18-20):(10-14).

[0010] As a preferred embodiment, the mass ratio of the nano-tin powder to the functional resin is 48:20:12.

[0011] As a preferred embodiment, the preparation method of the composite resin specifically includes the following steps: S1: Mixing acryloylmorpholine, vinyl trifluoroethyl ether and itaconic anhydride, adding a polymerization inhibitor, and preheating at 80-85°C to obtain a monomer mixture; S2: Under nitrogen protection, adding xylene to a reaction vessel and heating, then adding the monomer mixture dropwise, and after the dropwise addition is complete, adding azobisisobutyronitrile and maintaining the temperature for reaction; S3: After the reaction is complete, cooling the reaction solution, adding acetone to precipitate the polymer, and drying under vacuum to obtain the final product.

[0012] As a preferred embodiment, the preparation method of the composite resin specifically includes the following steps: S1: Acryloylmorpholine, vinyl trifluoroethyl ether and itaconic anhydride are mixed, and 0.1-0.15 wt% of hydroquinone is added. The mixture is preheated at 80-85°C to obtain a monomer mixture; S2: Under nitrogen protection, xylene is added to the reaction vessel and the temperature is raised to 85-90°C. Then, the monomer mixture is added dropwise at a rate of 1.5-2 mL / min. After the addition is complete, azobisisobutyronitrile is added and the reaction is maintained at this temperature for 7-8 h; S3: After the reaction is complete, the reaction solution is cooled to 35-40°C, acetone is added to precipitate the polymer, and the mixture is vacuum dried at 60-65°C for 20-24 h to obtain the final product.

[0013] As a preferred embodiment, the mass ratio of acryloylmorpholine, vinyl trifluoroethyl ether, and itaconic anhydride is (4-5):(2-3):(1-1.8).

[0014] As a preferred embodiment, the mass ratio of acryloylmorpholine, vinyl trifluoroethyl ether, and itaconic anhydride is (4.4–4.8):(2.5–3):(1.2–1.6).

[0015] By incorporating the aforementioned composite resin as the core binder phase of the nano-silver tin paste, its dispersion stability, film-forming effect, and welding mechanical strength can be significantly improved. Acryloylmorpholine can adsorb onto the oxide layer on the surface of nano-silver / tin through hydrogen and coordination bonds, thereby reducing the surface energy of the particles and inhibiting oxide layer thickening. On the other hand, itaconic anhydride, at high sintering temperatures, undergoes ring-opening to generate carboxylic acid groups, forming stable Ag-OOC covalent bonds with the nano-silver surface, significantly enhancing the resin-metal interface bonding energy. Furthermore, through internal reactions at high temperatures, a three-dimensional cross-linked network is formed, inhibiting the shrinkage and cracking of the nano-silver tin layer. Finally, the added vinyltrifluoroethyl ether-related groups form a low surface energy barrier, thereby blocking water and oxygen permeation, and inhibiting silver-tin oxidation by capturing free radicals through the strong electronegativity of the fluorocarbon chain.

[0016] As a preferred embodiment, the dispersant is at least one selected from polycarboxylate ammonium salts, phosphate esters, modified polyesters, and castor oil derivatives.

[0017] As a preferred embodiment, the dispersant is a modified polyester.

[0018] As a preferred embodiment, the activator is at least one selected from ammonium fluoroborate, ammonium fluorosilicate, triethyl citrate, aminosulfonic acid, and potassium sodium tartrate.

[0019] As a preferred embodiment, the activator is ammonium fluoroborate.

[0020] As a preferred embodiment, the film-forming agent is a combination of polyvinylpyrrolidone and polyvinyl alcohol.

[0021] As a preferred embodiment, the mass ratio of polyvinylpyrrolidone to polyvinyl alcohol is (3-5):(1-1.5).

[0022] As a preferred embodiment, the mass ratio of polyvinylpyrrolidone to polyvinyl alcohol is (4-4.5):(1.1-1.2).

[0023] As a preferred embodiment, the thixotropic agent is at least one selected from fumed silica, hydrogenated castor oil, polyamide wax, and cellulose ether.

[0024] As a preferred embodiment, the thixotropic agent is hydrogenated castor oil.

[0025] As a preferred embodiment, the silicon-titanium particles are composite modified particles, and their preparation method specifically includes the following steps: S1: Silicon dioxide and titanium dioxide are mixed and added to ethanol, 3-aminopropyltrimethoxysilane is added and then added to tetrahydrofuran, 2-bromoisobutyryl bromide and triethylamine are added, and after the reaction is completed, the particles are washed and dried to obtain pretreated particles; S2: The pretreated particles are added to a mixed solvent of methanol and water, acrylic acid, cuprous bromide and 2,2'-bipyridine are added, and the reaction is sealed; S3: After the reaction is completed, the precipitate is removed by centrifugation, washed and dried to obtain the final product.

[0026] As a preferred embodiment, the silicon-titanium particles are composite modified particles, and their preparation method specifically includes the following steps: S1: Mix silicon dioxide and titanium dioxide and add them to ethanol, add 3-aminopropyltrimethoxysilane, stir and react at 60-70℃ for 5-6 hours, then filter and dry, and add to tetrahydrofuran, add 2-bromoisobutyryl bromide, add triethylamine under ice bath, stir at room temperature at 60-100 rpm for 16-20 hours, wash with methanol 2-3 times and dry to obtain pretreated particles; S2: Add the pretreated particles to a mixed solvent of methanol and water, ultrasonically disperse at 400-500W for 20-30 minutes, add acrylic acid, cuprous bromide and 2,2'-bipyridine, seal and stir at 50-55℃ at 300-500 rpm for 8-10 hours; S3: After the reaction is complete, centrifuge to remove the precipitate, wash with methanol and water 2-3 times in sequence, and vacuum dry at 70-75℃ for 10-12 hours to obtain the final product.

[0027] As a preferred embodiment, the mass ratio of silicon dioxide, titanium dioxide, 3-aminopropyltrimethoxysilane, and acrylic acid is (7-8):(2-3):(2-2.5):

[0028] (5-6).

[0029] As a preferred embodiment, the average particle size of the silicon dioxide is 20-30 nm, and the average particle size of the titanium dioxide is 50-70 nm.

[0030] As a preferred embodiment, the stabilizer is at least one selected from tricresyl phosphate, trinonylphenyl phosphite, epoxidized soybean oil, calcium stearate, and sodium thiosulfate.

[0031] As a preferred embodiment, the stabilizer is tricresyl phosphate or trinonylphenyl phosphite.

[0032] As a preferred embodiment, the antioxidant is at least one of antioxidant 1010, antioxidant 168, antioxidant 1076, antioxidant DLTP, and antioxidant TNP.

[0033] As a preferred embodiment, the antioxidant is antioxidant 168 or antioxidant DLTP.

[0034] As a preferred embodiment, the wetting agent is at least one of polyether-modified siloxane, acetylation diol derivative, and polydimethylsiloxane.

[0035] As a preferred embodiment, the wetting agent is a polyether-modified siloxane.

[0036] As a preferred embodiment, the solvent is diethylene glycol butyl ether acetate or propylene glycol monomethyl ether acetate.

[0037] As a preferred embodiment, the solvent is diethylene glycol butyl ether acetate.

[0038] A method for preparing a nano-silver solder paste with high welding strength includes the following steps: S1: After mixing the composite resin and solvent, stir in a water bath at 70-80℃ and 1000-1200rpm for 1-1.5h. Then, add nano-silver powder, nano-tin powder and dispersant, and grind with a three-roll mill at a roller gap of 1.5-2μm for 4-6 times to obtain a slurry with a fineness ≤0.3μm; S2: Add silicon-titanium particles and planetarily stir at -0.15--0.1MPa, 40-60rpm revolution and 1200-1500rpm rotation for 2.5-4h. Then, add the remaining raw materials and ultrasonically treat at 50-55℃ and 500-600W for 40-50min; S3: Adjust the viscosity to 18-22Pa·s, filter through a 500-600 mesh sieve at 25℃, and seal with nitrogen to obtain the final product.

[0039] The beneficial effects of this application are:

[0040] 1. The nano-silver solder paste with high soldering strength provided in this application not only achieves uniform dispersion of the internal system, thereby optimizing the soldering effect and soldering performance, but also significantly improves oxidation resistance, greatly reduces the probability of easy oxidation and formation of silver oxide due to the high surface energy of nano-silver, and further balances the balance between the preparation process and the high strength of silver solder paste. It has excellent stability and mechanical strength, thus meeting the needs of high reliability packaging in the existing technology field and has broad application potential.

[0041] 2. The nano-silver solder paste with high welding strength provided in this application incorporates a composite resin as the core binder phase, which significantly improves its dispersion stability, film-forming effect, and welding mechanical strength. Acryloylmorpholine can adsorb onto the oxide layer on the surface of nano-silver / tin through hydrogen bonds and coordination bonds, thereby reducing the surface energy of the particles and inhibiting oxide layer thickening. On the other hand, itaconic anhydride, at high sintering temperatures, opens its ring to generate carboxylic acid groups, forming stable Ag-OOC covalent bonds with the nano-silver surface, significantly enhancing the resin-metal interface bonding energy. Furthermore, through internal reactions at high temperatures, a three-dimensional cross-linked network is formed, inhibiting the shrinkage and cracking of the nano-silver-tin layer.

[0042] 3. The nano-silver solder paste with high welding strength provided in this application utilizes modified silicon-titanium particles. The polyacrylic acid graft layer contains carboxylic acid groups that ionize into -COO- in the solvent. Through electrostatic repulsion and steric hindrance, the nano-silver, tin powder, and modified particles themselves are prevented from agglomerating. Furthermore, the combined action with the composite resin can form good polar hydrogen bonds, thereby improving the interfacial bonding energy. On the other hand, the modified silicon-titanium particles in the paste can absorb energy through chain segment slip under external force, improving fracture toughness and preventing the propagation of microcracks under external force, thus ensuring the mechanical stability of the nano-silver solder paste. Detailed Implementation

[0043] Example 1

[0044] The nano silver solder paste with high soldering strength is composed of the following raw materials by weight percentage: 48% nano silver powder, 20% nano tin powder, 12% composite resin, 1.1% dispersant, 0.6% activator, 1.2% film-forming agent, 1.4% thixotropic agent, 5.6% silicon titanium particles, 0.3% stabilizer, 0.3% antioxidant, 0.2% wetting agent, and the balance being solvent.

[0045] The nano-silver powder is spherical with an average particle size of 40 nm; the nano-tin powder has an average particle size of 70 nm.

[0046] The preparation method of the composite resin, by weight, specifically includes the following steps: S1: Mix 4.6 parts of acryloylmorpholine, 2.8 parts of vinyl trifluoroethyl ether and 1.4 parts of itaconic anhydride, add 0.1 wt% of hydroquinone, and preheat at 80°C to obtain a monomer mixture; S2: Under nitrogen protection, add 150 parts of xylene to the reaction vessel and heat to 85°C, then add the monomer mixture dropwise at a rate of 1.5 mL / min. After the dropwise addition is complete, add 0.2 parts of azobisisobutyronitrile and keep the reaction at this temperature for 8 h; S3: After the reaction is complete, cool the reaction solution to 35°C, add 30 parts of acetone to precipitate the polymer, and vacuum dry at 60°C for 24 h to obtain the final product.

[0047] The dispersant is modified polyester BYK-111; the activator is ammonium fluoroborate.

[0048] A composition of film-forming agent polyvinylpyrrolidone K30 and polyvinyl alcohol PVA-1788 in a mass ratio of 4.3:1.2.

[0049] The thixotropic agent was hydrogenated castor oil, a first-grade product purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd., China.

[0050] The silicon-titanium particles are composite modified particles. The preparation method, by mass, includes the following steps: S1: 7.6 parts of silicon dioxide and 2.4 parts of titanium dioxide are mixed and added to 200 parts of ethanol. 2.2 parts of 3-aminopropyltrimethoxysilane are added, and the mixture is stirred at 70°C for 6 hours. After filtration and drying, the mixture is added to 100 parts of tetrahydrofuran. 1.5 parts of 2-bromoisobutyryl bromide are added, and 1.2 parts of triethylamine are added under ice bath conditions. The mixture is stirred at 100 rpm for 18 hours at room temperature. After completion, the mixture is washed with methanol. S2: Add the pretreated particles to a mixed solvent of 100 parts methanol and water (methanol to water mass ratio of 1.5:1), ultrasonically disperse at 500W for 30min, add 5.8 parts acrylic acid, 0.3 parts cuprous bromide and 0.8 parts 2,2'-bipyridine, seal and stir at 55℃ and 400rpm for 10h; S3: After the reaction is complete, centrifuge to remove the precipitate, wash with methanol and water three times in sequence, and vacuum dry at 70℃ for 12h to obtain the final product.

[0051] The average particle size of silicon dioxide is 25 nm, and the average particle size of titanium dioxide is 60 nm.

[0052] The stabilizer is tricresyl phosphate; the antioxidant is antioxidant 168; the wetting agent is polyether-modified siloxane BYK-333; and the solvent is diethylene glycol butyl ether acetate.

[0053] A method for preparing a nano-silver solder paste with high welding strength includes the following steps: S1: After mixing the composite resin and solvent, stir at 1200 rpm in a water bath at 75°C for 1 hour. Then, add nano-silver powder, nano-tin powder and dispersant, and grind 4-6 times with a roller gap of 2 μm using a three-roll mill to obtain a slurry with a fineness of 0.2 μm; S2: Add silicon-titanium particles and planetarily stir at -0.1 MPa, 50 rpm revolution and 1300 rpm rotation for 3 hours. Then, add the remaining raw materials and ultrasonically treat at 55°C and 500W for 45 minutes; S3: Adjust the viscosity to 20 Pa·s, filter through a 500-mesh sieve at 25°C, and seal with nitrogen to obtain the final product.

[0054] Example 2

[0055] This embodiment differs from Embodiment 1 only in the following aspects: The nano-silver solder paste with high soldering strength is composed of the following raw materials by mass percentage: 50% nano-silver powder, 18% nano-tin powder, 10% composite resin, 1% dispersant, 0.6% activator, 1.1% film-forming agent, 1.2% thixotropic agent, 4.8% silicon-titanium particles, 0.3% stabilizer, 0.3% antioxidant, 0.2% wetting agent, and the remainder is solvent replenishment.

[0056] Example 3

[0057] This embodiment differs from Embodiment 1 only in the following aspects: The nano-silver solder paste with high soldering strength is composed of the following raw materials by mass percentage: 45% nano-silver powder, 20% nano-tin powder, 14% composite resin, 1.2% dispersant, 0.7% activator, 1.4% film-forming agent, 1.8% thixotropic agent, 5.1% silicon-titanium particles, 0.4% stabilizer, 0.3% antioxidant, 0.4% wetting agent, and the remainder is solvent replenishment.

[0058] Comparative Example 1

[0059] The only difference between this comparative example and Example 1 is as follows: the nano silver solder paste with high soldering strength is composed of the following raw materials by mass percentage: 52% nano silver powder, 24% nano tin powder, 4% composite resin, 1.1% dispersant, 0.6% activator, 1.2% film-forming agent, 1.4% thixotropic agent, 5.6% silicon titanium particles, 0.3% stabilizer, 0.3% antioxidant, 0.2% wetting agent, and the balance being solvent replenishment.

[0060] Comparative Example 2

[0061] The only difference between this comparative example and Example 1 is as follows: the nano silver solder paste with high soldering strength is composed of the following raw materials by mass percentage: 48% nano silver powder, 20% nano tin powder, 12% composite resin, 1.1% dispersant, 0.6% activator, 1.2% film-forming agent, 1.4% thixotropic agent, 2.2% silicon titanium particles, 0.3% stabilizer, 0.3% antioxidant, 0.2% wetting agent, and the balance being solvent replenishment.

[0062] Comparative Example 3

[0063] The only difference between this comparative example and Example 1 is the following: The preparation method of the composite resin, by mass, specifically includes the following steps: S1: Mix 8.5 parts of acryloylmorpholine, 1.2 parts of vinyl trifluoroethyl ether and 2.5 parts of itaconic anhydride, add 0.1 wt% of hydroquinone, and preheat at 80°C to obtain a monomer mixture; S2: Under nitrogen protection, add 150 parts of xylene to the reaction vessel and heat to 85°C, then add the monomer mixture dropwise at a rate of 1.5 mL / min. After the dropwise addition is complete, add 0.2 parts of azobisisobutyronitrile and keep the reaction at this temperature for 8 hours; S3: After the reaction is complete, cool the reaction solution to 35°C, add 30 parts of acetone to precipitate the polymer, and vacuum dry at 60°C for 24 hours to obtain the final product.

[0064] Comparative Example 4

[0065] The only difference between this comparative example and Example 1 is as follows: The preparation method of the composite resin, by mass, specifically includes the following steps: S1: Mix 2.5 parts of acryloylmorpholine, 4.5 parts of vinyl trifluoroethyl ether and 0.6 parts of itaconic anhydride, add 0.1 wt% of hydroquinone, and preheat at 80°C to obtain a monomer mixture; S2: Under nitrogen protection, add 150 parts of xylene to the reaction vessel and heat to 85°C, then add the monomer mixture dropwise at a rate of 1.5 mL / min. After the dropwise addition is complete, add 0.2 parts of azobisisobutyronitrile and keep the reaction at this temperature for 8 hours; S3: After the reaction is complete, cool the reaction solution to 35°C, add 30 parts of acetone to precipitate the polymer, and vacuum dry at 60°C for 24 hours to obtain the final product.

[0066] Comparative Example 5

[0067] The only difference between this comparative example and Example 1 is the following: the silicon-titanium particles are composite modified particles, and their preparation method specifically includes the following steps: S1: 10 parts of silicon dioxide and 0.8 parts of titanium dioxide are mixed and added to 200 parts of ethanol, 2.2 parts of 3-aminopropyltrimethoxysilane are added, and the mixture is stirred at 70°C for 6 hours. After filtration and drying, the mixture is added to 100 parts of tetrahydrofuran, 1.2 parts of 2-bromoisobutyryl bromide are added, and 0.4 parts of triethylamine are added under ice bath conditions. The mixture is stirred at 100 rpm at room temperature for 18 hours. After completion, the particles were washed three times with methanol and dried to obtain pretreated particles; S2: The pretreated particles were added to a mixed solvent of 100 parts methanol and water (methanol to water mass ratio of 1.5:1), ultrasonically dispersed at 500W for 30min, and 5.8 parts acrylic acid, 0.3 parts cuprous bromide and 0.8 parts 2,2'-bipyridine were added. After sealing, the mixture was stirred at 55℃ and 400rpm for 10h; S3: After the reaction was completed, the precipitate was removed by centrifugation, washed three times with methanol and water, and vacuum dried at 70℃ for 12h to obtain the final product.

[0068] Comparative Example 6

[0069] The only difference between this comparative example and Example 1 is the following: the silicon-titanium particles are composite modified particles, and their preparation method, by mass, specifically includes the following steps: S1: 5 parts of silicon dioxide and 5 parts of titanium dioxide are mixed and added to 200 parts of ethanol, 2.2 parts of 3-aminopropyltrimethoxysilane are added, and the mixture is stirred at 70°C for 6 hours. After filtration and drying, the mixture is added to 100 parts of tetrahydrofuran, 1.9 parts of 2-bromoisobutyryl bromide are added, and 1.4 parts of triethylamine are added under ice bath conditions. The mixture is stirred at 100 rpm at room temperature for 18 hours to complete the process. The pretreated particles were washed three times with methanol and dried to obtain pretreated particles. S2: The pretreated particles were added to a mixed solvent of 100 parts methanol and water (methanol to water mass ratio of 1.5:1), ultrasonically dispersed at 500W for 30 min, and then 2.1 parts acrylic acid, 0.1 parts cuprous bromide and 0.3 parts 2,2'-bipyridine were added. After sealing, the mixture was stirred at 55℃ and 400rpm for 10 h. S3: After the reaction was completed, the precipitate was removed by centrifugation, washed three times with methanol and water, and vacuum dried at 70℃ for 12 h to obtain the final product.

[0070] Performance testing

[0071] 1. The silver solder paste prepared in the examples and comparative examples was subjected to shear strength test. The silver solder paste was printed on a copper substrate (size 10×10mm, thickness 0.5mm) with an overlap area of ​​5×5mm. It was sintered in a nitrogen-protected reflow oven at 210℃ for 20 minutes with a heating rate of 3℃ / s. The test was conducted using a universal testing machine with a shear rate of 0.5mm / min. The shear strength was recorded, and the average value of 10 tests was recorded in Table 1.

[0072] 2. Conductivity tests were conducted on the silver-tin paste prepared in the examples and comparative examples. The silver-tin paste was coated on a glass substrate (25×25mm) with a thickness of 50±5μm, sintered at 210℃, cut into 10×10mm squares, and the surface was polished to a roughness Ra≤0.1μm. The test was conducted using a four-probe resistance meter with a current of 1A and a voltage range of 0.1mV~10V. The average value of 5 points was taken, and the resistance values ​​were recorded in Table 1.

[0073] 3. The silver solder paste prepared in the examples and comparative examples was subjected to a damp heat aging test. The test conditions were 85℃±2℃ and 85%±3% RH for 1000h. Samples were taken every 200h to test resistivity and shear strength according to the performance test 1 scheme. The shear strength retention rate after 1000h was recorded. The average value of 10 tests was recorded in Table 1.

[0074] 4. The wettability of the silver-tin paste prepared in the examples and comparative examples was tested. After the copper substrate was immersed in the silver-tin paste, the temperature was increased to 210°C at 3°C / s and held for 60s. The test was conducted using a wetting balance tester with an immersion speed of 2mm / s and an immersion depth of 2mm. The wetting force results were recorded and the average value of 10 tests was included in Table 1.

[0075] Table 1 Performance Test Results

[0076]

[0077] From the final performance test results of the examples and comparative examples, comparative examples 1 to 6 achieved worse performance results compared to the examples. The examples, on the other hand, prepared composite resins and modified particles with superior performance by adopting better technical solutions defined in this application. Through the combined effect of the two, good polar hydrogen bonding can be formed, improving the interfacial bonding energy. On the other hand, the modified silicon-titanium particles in the paste can absorb energy through chain segment slip under external force, improve fracture toughness, and prevent the propagation of microcracks under external force, thereby ensuring the overall comprehensive performance of the nano-silver solder paste.

Claims

1. A nano-silver solder paste with high soldering strength, characterized in that: By mass percentage, the raw materials include: 40-50% nano silver powder, 15-20% nano tin powder, 10-15% composite resin, and the remainder is solvent. The preparation method of the composite resin includes: S1: mixing acryloylmorpholine, vinyl trifluoroethyl ether and itaconic anhydride, adding a polymerization inhibitor, and preheating to obtain a monomer mixture; S2: Under nitrogen protection, xylene is added to the reactor and the temperature is raised. Then, the monomer mixture is added dropwise, followed by the addition of azobisisobutyronitrile (AIBN) and the reaction is maintained at this temperature. S3: After the reaction is complete, the reaction solution is cooled, acetone is added to precipitate the polymer, and the product is dried. The mass ratio of the acryloylmorpholine, vinyl trifluoroethyl ether and itaconic anhydride is (4-5):(2-3):(1-1.8).

2. The nano-silver solder paste with high welding strength according to claim 1, characterized in that: The nano-tin powder and the functional resin have a mass ratio of (45-50):(18-20):(10-14).

3. The nano-silver solder paste with high welding strength according to claim 2, characterized in that: By weight percentage, the raw materials also include: dispersant 0.8-1.2%, activator 0.5-0.8%, film-forming agent 1-1.5%, thixotropic agent 1-2%, silicon-titanium particles 4-6%, stabilizer 0.2-0.4%, antioxidant 0.3-0.5%, and wetting agent 0.2-0.4%.

4. The nano-silver solder paste with high welding strength according to claim 3, characterized in that: The dispersant is at least one of ammonium polycarboxylate, phosphate esters, modified polyesters, and castor oil derivatives; the activator is at least one of ammonium fluoroborate, ammonium fluorosilicate, triethyl citrate, aminosulfonic acid, and potassium sodium tartrate.

5. The nano-silver solder paste with high welding strength according to claim 4, characterized in that: The film-forming agent is a composition of polyvinylpyrrolidone and polyvinyl alcohol in a mass ratio of (3-5):(1-1.5).

6. The nano-silver solder paste with high welding strength according to claim 5, characterized in that: The silicon-titanium particles are composite modified particles, and the preparation method includes: S1: adding silicon dioxide and titanium dioxide to ethanol, adding 3-aminopropyltrimethoxysilane and then to tetrahydrofuran, adding 2-bromoisobutyryl bromide and triethylamine, washing and drying after the reaction is completed to obtain pretreated particles; S2: adding the pretreated particles to a mixed solvent of methanol and water, adding acrylic acid, cuprous bromide and 2,2'-bipyridine, and sealing the reaction; S3: centrifuging to remove the precipitate after the reaction is completed, washing and drying to obtain the final product.

7. The nano-silver solder paste with high welding strength according to claim 6, characterized in that: The mass ratio of silicon dioxide, titanium dioxide, 3-aminopropyltrimethoxysilane and acrylic acid is (7-8):(2-3):(2-2.5):(5-6).

8. The nano-silver solder paste with high welding strength according to claim 7, characterized in that: The average particle size of the silicon dioxide is 20-30 nm, and the average particle size of the titanium dioxide is 50-70 nm.

9. The nano-silver solder paste with high welding strength according to claim 8, characterized in that: The stabilizer is at least one of tricresyl phosphate, trinonylphenyl phosphite, epoxidized soybean oil, calcium stearate, and sodium thiosulfate.

10. A method for preparing nano-silver solder paste with high soldering strength according to any one of claims 1 to 9, characterized in that: Specifically, the following steps are included: S1: Mix the composite resin and solvent, then stir in a water bath at 70-80℃ for 1000-1200 rpm for 1-1.5 hours. Next, add nano-silver powder, nano-tin powder, and dispersant. Grind the mixture 4-6 times using a three-roll mill with a roller gap of 1.5-2 μm to obtain a slurry with a fineness ≤0.3 μm. S2: Add silicon-titanium particles and planetarily stir at -0.15-0.1 MPa, 40-60 rpm revolution, and 1200-1500 rpm rotation for 2.5-4 hours. Then add the remaining raw materials and ultrasonically treat at 50-55℃ and 500-600W for 40-50 minutes. S3: Adjust the viscosity to 18-22 Pa·s, filter through a 500-600 mesh sieve at 25℃, and seal with nitrogen to obtain the final product.

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