Nano-silver solder paste with high welding strength and preparation method of nano-silver solder paste

Abstract

The invention relates to the field of building materials, in particular to nano-silver solder paste with high welding strength and a preparation method of the nano-silver solder paste. The nano-silver tin paste with high welding strength comprises the following raw materials: nano-silver powder, nano-tin powder, composite resin, a dispersing agent, an activating agent, a film-forming agent, a thixotropic agent, silicon-titanium particles, a stabilizing agent and the like. According to the nano-silver solder paste with the high welding strength and the preparation method thereof, uniform dispersion of an internal system is achieved, the welding effect and the welding performance are further optimized, the oxidation resistance can be greatly improved, the probability that high surface energy of nano-silver is prone to being oxidized to generate silver oxide is greatly reduced, and the welding quality of the nano-silver solder paste is improved. The silver solder paste prepared by the method further balances the balance between the preparation process and the high strength of the silver solder paste, and has excellent stability and mechanical strength, thereby meeting the requirements of high-reliability packaging in the prior art, and having wide application potential.

Description

Technical Field

[0001] The present application relates to the field of building materials, and more specifically to a nano silver solder paste with high welding strength and a preparation method thereof. Background Art

[0002] As electronic devices develop towards miniaturization, high density and high frequency, the performance requirements for electronic packaging materials are becoming increasingly stringent. As a key medium for electronic interconnection, welding materials must simultaneously meet the requirements of high conductivity, excellent mechanical strength, high temperature aging resistance and low temperature process compatibility. Traditional tin-lead solder has been gradually eliminated due to environmental regulations, and lead-free solder has become the mainstream, but its welding joints often have problems such as insufficient strength, interface brittleness and thermal fatigue failure at high temperatures.

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

[0004] At present, nanosilver has been used to prepare various forms of solder paste, which contains a mixture of nanosilver powder and flux. This type of solder paste can achieve effective welding at a relatively low temperature and can provide higher mechanical strength and better electrical properties than traditional solders. In addition, the welding effect can be further optimized by controlling the size, shape and distribution of nanosilver particles. However, although nanosilver solder paste has shown many advantages, it still faces many problems in practical applications, such as the influence of system dispersion effect on welding performance, nanosilver's excessive dependence on organic dispersants and easy oxidation, which greatly reduces conductivity, as well as the balance between sintering preparation process and high strength, which makes it difficult to meet the requirements of the prior art for high-reliability packaging. Summary of the invention

[0005] Therefore, in order to solve the above problems, the present application provides a nano silver solder paste with high welding strength and a preparation method thereof, which not only realizes uniform dispersion of the internal system, thereby optimizing the welding effect and welding performance, but also can greatly improve the oxidation resistance, greatly reduce the probability of easy oxidation to generate silver oxide due to the high surface energy of nano silver, and further balance the balance problem between the preparation process and the high strength of the silver solder paste, has excellent stability and mechanical strength, thereby limitedly meeting the needs of the existing technical field for high reliability packaging, and has broad application potential.

[0006] The invention discloses a nano silver solder paste with high welding strength. The raw materials are composed of the following components by mass percentage: 40-50% of nano silver powder, 15-20% of nano tin powder, 10-15% of composite resin, 0.8-1.2% of dispersant, 0.5-0.8% of activator, 1-1.5% of film former, 1-2% of thixotropic agent, 4-6% of silicon titanium particles, 0.2-0.4% of stabilizer, 0.3-0.5% of antioxidant, 0.2-0.4% of wetting agent and the remainder of solvent.

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

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

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

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

[0011] As a preferred embodiment, the preparation method of the composite resin specifically comprises the following steps: S1: mixing acryloylmorpholine, vinyl trifluoroethyl ether and itaconic anhydride, adding an inhibitor, and preheating at 80-85°C to obtain a monomer mixture; S2: under nitrogen protection, adding xylene to a reaction kettle and heating it, then dropwise adding the monomer mixture, and after the dropwise addition is completed, adding azobisisobutyronitrile and keeping the temperature for reaction; S3: after the reaction is completed, cooling the reaction liquid, adding acetone to precipitate the polymer, and vacuum drying to obtain the result.

[0012] 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 0.1 to 0.15 wt% of hydroquinone in total mass, and preheating at 80 to 85°C to obtain a monomer mixture; S2: under nitrogen protection, adding xylene to the reactor and heating to 85 to 90°C, then dripping the monomer mixture at a rate of 1.5 to 2 mL / min, adding azobisisobutyronitrile after the dripping is completed, and keeping the reaction temperature for 7 to 8 hours; S3: after the reaction is completed, cooling the reaction solution to 35 to 40°C, adding acetone to precipitate the polymer, and vacuum drying at 60 to 65°C for 20 to 24 hours to obtain the obtained 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 adding the above-mentioned composite resin as the core bonding phase of nano silver solder paste, its dispersion stability, film-forming effect and welding mechanical strength can be greatly improved. Among them, acryloyl morpholine can be adsorbed on the surface oxide layer of nano silver / tin through hydrogen bonds and coordination bonds, thereby reducing the surface energy of the particles and inhibiting the thickening of the oxide layer. On the other hand, itaconic anhydride forms a stable Ag-OOC covalent bond with the surface of nano silver by ring opening at high sintering temperature, which greatly improves the resin-metal interface binding energy, and forms a three-dimensional cross-linked network through internal mutual reaction at high temperature to inhibit the shrinkage and cracking of the nano silver tin layer. Finally, the added vinyl trifluoroethyl ether related groups can form a low surface energy barrier, thereby blocking the penetration of water and oxygen, and inhibiting the oxidation of silver tin by capturing free radicals through the strong electronegativity of the fluorocarbon chain.

[0016] As a preferred embodiment, the dispersant is at least one of polycarboxylic acid ammonium salts, phosphates, modified polyesters and castor oil derivatives.

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

[0018] As a preferred embodiment, the activator is at least one of 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 composition of polyvinyl pyrrolidone and polyvinyl alcohol.

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

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

[0023] As a preferred embodiment, the thixotropic agent is at least one of 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 the preparation method thereof specifically includes the following steps: S1: adding a mixture of silicon dioxide and titanium dioxide to ethanol, adding 3-aminopropyltrimethoxysilane and then adding 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: after the reaction is completed, centrifuging to remove the precipitate, washing and drying to obtain.

[0026] As a preferred embodiment, the silicon-titanium particles are composite modified particles, and their preparation method specifically includes the following steps: S1: adding silicon dioxide and titanium dioxide to ethanol, adding 3-aminopropyltrimethoxysilane, stirring and reacting at 60-70°C for 5-6h, then filtering and drying, adding to tetrahydrofuran, adding 2-bromoisobutyryl bromide, adding triethylamine in an ice bath, stirring at 60-100rpm at room temperature for 16-20h, washing with methanol 2-3 times after completion and drying to obtain pretreated particles; S2: adding the pretreated particles to a mixed solvent of methanol and water, ultrasonically dispersing at 400-500W for 20-30min, adding acrylic acid, cuprous bromide and 2,2'-bipyridine, sealing, stirring and reacting at 50-55°C, 300-500rpm for 8-10h; S3: after the reaction is completed, centrifuging to remove the precipitate, washing it with methanol and water for 2-3 times in turn, and vacuum drying at 70-75°C for 10-12h to obtain the obtained particles.

[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 solution, the average particle size of the silicon dioxide is 20 to 30 nm, and the average particle size of the titanium dioxide is 50 to 70 nm.

[0030] As a preferred embodiment, the stabilizer is at least one of 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 solution, the wetting agent is at least one of polyether-modified siloxane, acetylene glycol derivatives and polydimethylsiloxane.

[0035] As a preferred solution, the wetting agent is 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 preparation method of nano silver solder paste with high welding strength specifically comprises the following steps: S1: mixing a composite resin and a solvent, stirring them in a water bath at 70-80°C at 1000-1200 rpm for 1-1.5 hours, then adding nano silver powder, nano tin powder and a dispersant, grinding them 4-6 times with a roller gap of 1.5-2 μm on a three-roll grinder to obtain a slurry fineness of ≤0.3 μm; S2: adding silicon titanium particles, and planetary stirring at -0.15--0.1 MPa, 40-60 rpm for revolution and 1200-1500 rpm for rotation for 2.5-4 hours, then adding the remaining raw materials, and ultrasonically treating them at 50-55°C and 500-600W for 40-50 minutes; S3: adjusting the viscosity to 18-22 Pa·s, 25°C, filtering through a 500-600 mesh screen, and then filling with nitrogen and sealing to obtain the paste.

[0039] The beneficial effects of this application are:

[0040] 1. The nano silver solder paste with high welding strength provided in the present application not only realizes uniform dispersion of the internal system, thereby optimizing the welding effect and welding performance, but also can greatly improve the oxidation resistance, greatly reduce the probability of easy oxidation to generate silver oxide due to the high surface energy of nano silver, and further balance the balance problem between the preparation process and the high strength of the silver solder paste, and has excellent stability and mechanical strength, thereby limitedly meeting the needs of the existing technical field for high reliability packaging, and has broad application potential.

[0041] 2. The present application provides a nano silver solder paste with high welding strength, wherein the added composite resin is used as the core bonding phase of the nano silver solder paste, which can greatly improve its dispersion stability, film-forming effect and welding mechanical strength. Acryloyl morpholine can be adsorbed on the surface oxide layer of nano silver / tin through hydrogen bonds and coordination bonds, thereby reducing the surface energy of the particles and inhibiting the thickening of the oxide layer. On the other hand, itaconic anhydride forms a stable Ag-OOC covalent bond with the surface of nano silver by ring opening at high sintering temperatures, thereby greatly improving the resin-metal interface binding energy, and forms a three-dimensional cross-linked network through internal mutual reactions at high temperatures to inhibit the shrinkage and cracking of the nano silver tin layer.

[0042] 3. The nano silver solder paste with high welding strength provided in the present application has a polyacrylic acid graft layer containing carboxylic acid groups which are ionized into -COO- in the solvent through the action of modified silicon titanium particles, and the electrostatic repulsion effect and steric hindrance effect are used to prevent the nano silver, tin powder and modified particles from agglomerating themselves, and the combined action with the composite resin can form a good polar hydrogen bond to improve the interface binding energy; on the other hand, the modified silicon titanium particles in the paste can absorb energy through segment slip under external force, improve the fracture toughness, and prevent the expansion of micro cracks when external force acts, thereby ensuring the mechanical stability of the nano silver solder paste. DETAILED DESCRIPTION

[0043] Example 1

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

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

[0046] The preparation method of the composite resin, calculated by mass, specifically includes the following steps: S1: 4.6 parts of acryloylmorpholine, 2.8 parts of vinyl trifluoroethyl ether and 1.4 parts of itaconic anhydride are mixed, 0.1wt% of the total mass of hydroquinone is added, and the mixture is preheated at 80°C to obtain a monomer mixture; S2: Under nitrogen protection, 150 parts of xylene are added to the reactor and the temperature is raised to 85°C, and then the monomer mixture is added dropwise at a rate of 1.5mL / min, and after the addition is completed, 0.2 parts of azobisisobutyronitrile are added and the mixture is kept warm for reaction for 8h; S3: After the reaction is completed, the reaction solution is cooled to 35°C, 30 parts of acetone are added to precipitate the polymer, and the polymer is dried in vacuo at 60°C for 24h to obtain the obtained product.

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

[0048] The composition of film-forming agent polyvinyl pyrrolidone K30 and polyvinyl alcohol PVA-1788 has a mass ratio of 4.3:1.2.

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

[0050] The silicon-titanium particles are composite modified particles, and the preparation method thereof specifically includes the following steps, calculated by mass: 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, stirred and reacted at 70°C for 6 hours, then filtered and dried, and then added to 100 parts of tetrahydrofuran, 1.5 parts of 2-bromoisobutyryl bromide are added, 1.2 parts of triethylamine are added under ice bath, stirred at room temperature at 100rpm for 18 hours, and washed with methanol after completion. 3 times and dried to obtain pretreated particles; S2: add the pretreated particles to a mixed solvent of 100 parts of methanol and water (the mass ratio of methanol to water is 1.5:1), ultrasonically disperse at 500W for 30 minutes, add 5.8 parts of acrylic acid, 0.3 parts of cuprous bromide and 0.8 parts of 2,2'-bipyridine, seal and react at 55°C, 400rpm for 10 hours; S3: after the reaction is completed, centrifuge to remove the precipitate, wash it with methanol and water for 3 times in turn, and vacuum dry it at 70°C for 12 hours to obtain the obtained particles.

[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 preparation method of nano silver solder paste with high welding strength specifically comprises the following steps: S1: after mixing a composite resin and a solvent, stir them in a water bath at 75°C and 1200 rpm for 1 hour, then add nano silver powder, nano tin powder and a dispersant, grind them 4 to 6 times with a roller gap of 2 μm on a three-roll grinder to obtain a slurry with a fineness of 0.2 μm; S2: add silicon titanium particles, and planetary stir them at -0.1 MPa, 50 rpm for revolution and 1300 rpm for rotation for 3 hours, then add the remaining raw materials, and ultrasonically treat them at 55°C and 500W for 45 minutes; S3: adjust the viscosity to 20 Pa·s, 25°C, filter through a 500-mesh screen, and then fill with nitrogen and seal to obtain the paste.

[0054] Example 2

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

[0056] Example 3

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

[0058] Comparative Example 1

[0059] The only difference between this comparative example and Example 1 is that the nano silver solder paste with high welding strength consists of the following ingredients, measured by mass percentage: 52% nano silver powder, 24% nano tin powder, 4% composite resin, 1.1% dispersant, 0.6% activator, 1.2% film former, 1.4% thixotropic agent, 5.6% silicon titanium particles, 0.3% stabilizer, 0.3% antioxidant, 0.2% wetting agent, and the remainder is made up of solvent.

[0060] Comparative Example 2

[0061] The only difference between this comparative example and Example 1 is that the nano silver solder paste with high welding strength consists of the following ingredients, measured by mass percentage: 48% nano silver powder, 20% nano tin powder, 12% composite resin, 1.1% dispersant, 0.6% activator, 1.2% film former, 1.4% thixotropic agent, 2.2% silicon titanium particles, 0.3% stabilizer, 0.3% antioxidant, 0.2% wetting agent, and the remainder is made up of solvent.

[0062] Comparative Example 3

[0063] The only difference between this comparative example and Example 1 is as follows: the preparation method of the composite resin, calculated by mass, specifically comprises the following steps: S1: 8.5 parts of acryloylmorpholine, 1.2 parts of vinyl trifluoroethyl ether and 2.5 parts of itaconic anhydride are mixed, 0.1wt% of the total mass of hydroquinone is added, and the mixture is preheated at 80°C to obtain a monomer mixture; S2: under nitrogen protection, 150 parts of xylene are added to the reactor and the temperature is raised to 85°C, and then the monomer mixture is added dropwise at a rate of 1.5mL / min, and after the addition is completed, 0.2 parts of azobisisobutyronitrile are added and the mixture is kept warm for reaction for 8h; S3: after the reaction is completed, the reaction solution is cooled to 35°C, 30 parts of acetone are added to precipitate the polymer, and the polymer is dried in vacuo at 60°C for 24h to obtain the obtained 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, calculated by mass, specifically comprises the following steps: S1: 2.5 parts of acryloylmorpholine, 4.5 parts of vinyl trifluoroethyl ether and 0.6 parts of itaconic anhydride are mixed, 0.1wt% of the total mass of hydroquinone is added, and the mixture is preheated at 80°C to obtain a monomer mixture; S2: under nitrogen protection, 150 parts of xylene are added to the reactor and the temperature is raised to 85°C, and then the monomer mixture is added dropwise at a rate of 1.5mL / min, and after the addition is completed, 0.2 parts of azobisisobutyronitrile are added and the mixture is kept warm for reaction for 8h; S3: after the reaction is completed, the reaction solution is cooled to 35°C, 30 parts of acetone are added to precipitate the polymer, and the polymer is dried in vacuo at 60°C for 24h to obtain the obtained product.

[0066] Comparative Example 5

[0067] The only difference between this comparative example and Example 1 is that the silicon-titanium particles are composite modified particles, and the preparation method thereof specifically comprises the following steps, calculated by mass: 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, stirred and reacted at 70°C for 6 hours, then filtered and dried, and then added to 100 parts of tetrahydrofuran, 1.2 parts of 2-bromoisobutyryl bromide are added, 0.4 parts of triethylamine are added under ice bath, and stirred at room temperature at 100 rpm for 18 hours, After completion, wash with methanol for 3 times and dry to obtain pretreated particles; S2: add the pretreated particles to a mixed solvent of 100 parts of methanol and water (the mass ratio of methanol to water is 1.5:1), ultrasonically disperse at 500W for 30 minutes, add 5.8 parts of acrylic acid, 0.3 parts of cuprous bromide and 0.8 parts of 2,2'-bipyridine, seal and react at 55°C, 400rpm for 10 hours; S3: after the reaction is completed, centrifuge to remove the precipitate, wash it with methanol and water for 3 times in turn, and vacuum dry it at 70°C for 12 hours.

[0068] Comparative Example 6

[0069] The only difference between this comparative example and Example 1 is that the silicon-titanium particles are composite modified particles, and the preparation method thereof specifically comprises the following steps, calculated by mass: 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, stirred and reacted at 70°C for 6 hours, then filtered and dried, and then added to 100 parts of tetrahydrofuran, 1.9 parts of 2-bromoisobutyryl bromide are added, 1.4 parts of triethylamine are added under ice bath, and stirred at room temperature at 100 rpm for 18 hours to complete. The particles were then washed with methanol for three times and dried to obtain pretreated particles; S2: the pretreated particles were added to a mixed solvent of 100 parts of methanol and water (the mass ratio of methanol to water was 1.5:1), ultrasonically dispersed at 500W for 30 minutes, 2.1 parts of acrylic acid, 0.1 parts of cuprous bromide and 0.3 parts of 2,2'-bipyridine were added, and the mixture was sealed and stirred at 55°C and 400rpm for 10 hours; S3: after the reaction was completed, the precipitate was taken out by centrifugation, washed with methanol and water for three times in turn, and vacuum dried at 70°C for 12 hours to obtain the particles.

[0070] Performance Testing

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

[0072] 2. The conductivity of the silver solder paste prepared in the embodiment and the comparative example was tested. The silver solder paste was coated on a glass substrate (25×25 mm) with a thickness of 50±5 μm, sintered at 210°C, cut into 10×10 mm squares, and the surface was polished to a roughness Ra≤0.1 μm. The test was performed using a four-probe resistance tester with a current of 1 A and a voltage range of 0.1 mV to 10 V. The average value of 5 points was taken and the resistance value results were recorded in Table 1.

[0073] 3. The silver solder pastes prepared in the embodiments and comparative examples were subjected to a moisture and heat aging resistance test. The test conditions were a temperature of 85°C ± 2°C and a humidity of 85% ± 3% RH for 1000 h. Samples were taken every 200 h to detect resistivity and shear strength using the method of performance test 1. The shear strength retention rate after 1000 h was recorded. The results were averaged over 10 tests and recorded in Table 1.

[0074] 4. The silver solder paste prepared in the embodiment and the comparative example was subjected to a wettability test. After the copper substrate was immersed in the silver solder paste, the temperature was raised to 210°C at a rate of 3°C / s and maintained for 60s. The test was performed 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 recorded in Table 1.

[0075] Table 1 Performance test results

[0076]

[0077] 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 prepared composite resins and modified particles with better performance by adopting the better technical solutions defined in the present application, and through the joint action of the two, good polar hydrogen bonding can be formed to improve the interface binding energy; on the other hand, the modified silicon-titanium particles in the paste can absorb energy through segment slip under external force, improve fracture toughness, and prevent the expansion of microcracks when external force acts, thereby ensuring the overall comprehensive performance of the nano silver solder paste.

Claims

1. A nano silver solder paste with high welding strength, characterized in that: The raw materials include, by mass percentage: 40-50% of nano silver powder, 15-20% of nano tin powder, 10-15% of composite resin, and the remainder of solvent; The preparation method of the composite resin comprises: 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, and azobisisobutyronitrile is added and the temperature is kept for reaction; S3: after the reaction is completed, the reaction solution is cooled, acetone is added to precipitate the polymer, and the polymer is dried to obtain the polymer; The mass ratio of 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 mass ratio of the nano tin powder, the nano tin powder and the functional resin is (45-50): (18-20): (10-14).

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

4. The nano silver solder paste with high welding strength according to claim 3, characterized in that: The dispersant is at least one of polycarboxylic acid ammonium salt, phosphate ester, modified polyester and castor oil derivative; 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 polyvinyl pyrrolidone and polyvinyl alcohol, and the mass ratio is (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 comprises: S1: adding silicon dioxide and titanium dioxide to ethanol, adding 3-aminopropyltrimethoxysilane and then adding 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: after the reaction is completed, centrifuging to remove the precipitate, washing and drying to obtain the particles.

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 to 30 nm, and the average particle size of the titanium dioxide is 50 to 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 a nano silver solder paste with high welding strength according to any one of claims 1 to 9, characterized in that: The specific steps include: S1: After mixing the composite resin and the solvent, stir them in a water bath at 70-80°C at 1000-1200 rpm for 1-1.5 hours, then add nano silver powder, nano tin powder and dispersant, grind them on a three-roll grinder with a roller gap of 1.5-2 μm for 4-6 times to obtain a slurry fineness of ≤0.3 μm; S2: Add silicon titanium particles, and planetary stir them at -0.15--0.1 MPa, 40-60 rpm for revolution and 1200-1500 rpm for rotation for 2.5-4 hours, then add the remaining raw materials, and ultrasonically treat them at 50-55°C and 500-600W for 40-50 minutes; S3: Adjust the viscosity to 18-22 Pa·s, 25°C, filter through a 500-600 mesh sieve, and seal with nitrogen to obtain the product.

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