High-reliability tin-silver-copper alloy and preparation method and application thereof

Abstract

The invention relates to a high-reliability tin-silver-copper alloy as well as a preparation method and application thereof. The alloy is prepared from the following raw materials in percentage by weight: 5 to 10 percent of Sn-In-Nd-graphene mixed material, 5 to 10 percent of Cu-Ag core-shell particles and the balance of Sn-Ag-Sb-Ni alloy, wherein the Sn-In-Nd-graphene mixed material is prepared from the following components in percentage by weight: 3 to 5 percent of In, 0.5 to 1 percent of Nd, 3 to 5 percent of graphene and the balance of Sn and inevitable impurities; the Sn-Ag-Sb-Ni alloy is prepared from the following components in percentage by weight: 4 to 7 percent of Ag, 0.1 to 0.5 percent of Sb, 0.1 to 0.5 percent of Ni and the balance of Sn and inevitable impurities. The alloy provided by the invention simultaneously meets the requirements of automotive electronics on high temperature resistance, vibration resistance and long service life, and becomes an ideal material for high-performance electronic packaging.

Description

Technical Field

[0001] The present invention relates to the technical field of tin-silver-copper alloys, and particularly relates to a high-reliability tin-silver-copper alloy and its preparation method and application. Background Art

[0002] Traditional tin-lead solders have occupied a wide range of applications in the electronics industry due to their excellent solderability, ductility, electrical conductivity, and corrosion resistance. However, the highly toxic and highly accumulative nature of lead poses a serious threat to the ecological environment and human health. Since the 1990s, a global wave of lead-free substitution has emerged, turning to seek alternatives to tin-lead solders. Currently, although lead-free systems such as pure Sn-Ag, Sn-Cu, Sn-Zn, Sn-Ag-Cu, etc. have received extensive attention, they have not been able to completely replace tin-lead solders. The main challenges faced by current lead-free solders are relatively high melting points and poor mechanical properties.

[0003] The modification strategies of lead-free solders mainly focus on two directions: alloying and the addition of a second phase. Although alloying can improve the solder properties to a certain extent, the effect is limited; while the addition of second-phase particles can not only refine the microstructure but also significantly improve the mechanical properties and wettability of the solder through the dispersion strengthening mechanism. Second-phase particles can be roughly divided into two categories: active particles (such as metal particles like Co, Ni, Cu, Al, etc.) and non-active particles (such as ceramic particles like Al2O3, ZrO2, etc., and carbon materials like graphene, carbon nanotubes, etc.). Active particles can chemically react with the matrix to form a good bond, but interdiffusion, dissolution, or coarsening may occur during long-term service, thereby affecting the stability of the solder properties. In contrast, non-active particles, with their high strength and good stability, effectively hinder grain growth and dislocation movement, but the bonding with the matrix is relatively weak. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a high-reliability tin-silver-copper alloy and its preparation method and application.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In the first aspect, the present invention provides a high-reliability tin-silver-copper alloy, including the following raw materials for preparation in weight percentages: 5-10% of Sn-In-Nd-graphene mixed material, 5-10% of Cu-Ag core-shell particles, and the balance being Sn-Ag-Sb-Ni alloy; Among them, the Sn-In-Nd-graphene mixed material includes the following components in weight percentages: 3-4% of In, 0.5-1% of Nd, and 3-5% of graphene, and the balance being Sn and inevitable impurities; The Sn-Ag-Sb-Ni alloy comprises the following components by weight percentage: Ag 4-7%, Sb 0.1-0.5% and Ni 0.1-0.5%, and the balance is Sn and inevitable impurities; The preparation method of the Sn-In-Nd-graphene hybrid material comprises the following steps: (1) Ultrasonically disperse graphene in absolute ethanol to obtain a graphene slurry; (2) Ultrasonically disperse Sn powder, In powder and Nd powder in absolute ethanol to obtain an alloy slurry; (3) Mix the graphene slurry and the alloy slurry, then carry out ball milling and vacuum drying to obtain a Sn-In-Nd-graphene precursor powder; (4) Sinter the Sn-In-Nd-graphene precursor powder at 600-700 °C for 2-3 h, then raise the temperature to 1500-1700 °C and continue sintering for 1-2 h, and keep the temperature for 5-10 min to obtain the Sn-In-Nd-graphene hybrid material.

[0006] The alloy matrix of the present invention is the Sn-Ag-Sb-Ni alloy. Sn forms an Ag3Sn strengthening phase with Ag, which can be distributed at the grain boundaries of the Sn matrix, hinder grain sliding and improve the high-temperature fatigue resistance; Sb acts as a grain refiner to inhibit the dendritic growth of the Sn matrix. At the same time, Sb is dissolved in the Sn matrix (SbSn phase) to enhance the tensile strength; Ni forms a Ni3Sn4 passivation film on the surface of the alloy, significantly improving the corrosion resistance of the alloy in sulfur- and chlorine-containing environments. Therefore, the Sn-Ag-Sb-Ni alloy as the matrix can provide good comprehensive properties (such as strength, conductivity, corrosion resistance, etc.), providing a basis for the high reliability of the whole alloy.

[0007] In the present invention, the main body Sn of the Sn-In-Nd-graphene hybrid material and the Sn in the alloy matrix belong to the same homologous component. Therefore, the hybrid material can reduce the interfacial energy in the Sn-based alloy matrix, improve the uniform distribution of the material, and enhance the bonding property. The graphene therein, as a two-dimensional nano-reinforcement, forms a three-dimensional network structure through ball milling and dispersion, which can significantly improve the strength and toughness of the alloy. The addition of In can reduce the melting point of the alloy and improve the wettability, making it easier for the alloy to form a dense structure during welding or sintering and reducing the porosity. As a rare earth element, Nd has a strong antioxidant property due to its 4f electron layer structure. It forms a dense Nd2O3 protective film at high temperatures. Meanwhile, Nd can purify the grain boundaries, reduce the segregation of impurities, and enhance the high-temperature stability of the alloy. During the preparation process of the hybrid material, staged sintering (pre-sintering at 600 - 700 °C + final sintering at 1500 - 1700 °C) realizes gradient densification: in the pre-sintering stage, a Sn-In-Nd intermetallic compound skeleton is formed through solid-state diffusion. High-temperature sintering (1500 - 1700 °C) promotes the formation of an alloying network of Sn, In, and Nd, forms a stable interfacial bond with graphene, avoids agglomeration, and ensures the uniform distribution of the strengthening phase. As the second-phase particles, the Sn-In-Nd-graphene hybrid material is uniformly distributed in the Sn-Ag-Sb-Ni alloy matrix, which can effectively improve the alloy's ability to resist plastic deformation, simultaneously inhibit grain coarsening at high temperatures, and enhance the dimensional stability.

[0008] The Cu-Ag core-shell particles of the present invention have Ag as the shell and Cu as the core. Ag forms a dense Ag2O film (melting point 430 °C) in the air, isolating the oxygen from contacting the Cu core and avoiding the high-temperature oxidation of Cu. The shell layer Ag can inhibit the excessive diffusion of the Sn matrix to Cu and avoid the excessive formation of brittle intermetallic compounds (such as Cu6Sn5). Meanwhile, the Ag shell layer in the Cu-Ag core-shell particles serves as a "transition layer" to relieve the difference in thermal expansion coefficients between the Cu core and the Sn matrix and reduce the interfacial stress in the thermal cycle.

[0009] In summary, the Sn-Ag-Sb-Ni alloy, the Sn-In-Nd-graphene hybrid material, and the Cu-Ag core-shell particles all have good compatibility. The three can be uniformly distributed in the alloy to form a stable organizational structure. This uniform and stable structure not only improves the overall performance of the alloy but also reduces the generation of local performance differences and defects, further enhancing the reliability and consistency of the alloy.

[0010] Preferably, in the preparation method of the Sn-In-Nd-graphene hybrid material, the addition amount of absolute ethanol in step (1) is 2 - 3 times the mass of graphene; the addition amount of absolute ethanol in step (2) is 2 - 3 times the total mass of Sn powder, In powder, and Nd powder.

[0011] Preferably, in the preparation method of the Sn-In-Nd-graphene hybrid material, the parameters of ultrasonic dispersion in step (1) are as follows: the power is 500 - 600 W, and the time is 10 - 20 min.

[0012] Preferably, in the preparation method of the Sn-In-Nd-graphene hybrid material, the parameters of ultrasonic dispersion in step (2) are as follows: the power is 500 - 600 W, and the time is 20 - 40 min.

[0013] Preferably, in the preparation method of the Sn-In-Nd-graphene hybrid material, the ball-to-material ratio of ball milling in step (3) is (4 - 5):1, and the ball milling time is 2 - 3 h.

[0014] Preferably, the preparation method of the Cu-Ag core-shell particles includes the following steps: S1. Mix nano copper powder with deionized water, sodium citrate, and sodium hypophosphite to obtain solution A; wherein, the molar ratio of nano copper powder, sodium citrate, and sodium hypophosphite is 1:(0.5 - 1):(2 - 4), and the addition amount of deionized water is 1 - 2 times the total mass of nano copper powder, sodium citrate, and sodium hypophosphite; S2. Mix sodium citrate, silver sulfate, and deionized water to obtain solution B; wherein, the molar ratio of sodium citrate and silver sulfate is 1:(0.5 - 1), and the addition amount of deionized water is 1 - 2 times the total mass of sodium citrate and silver sulfate; S3. Drop solution B into solution A and react at 25 - 30 °C until the solution changes from red to purple and then to grayish brown; S4. Centrifuge the reacted solution, wash the precipitate, and dry it to obtain the Cu-Ag core-shell particles.

[0015] More preferably, the average particle size of the nano copper powder is 50 nm, but it is not limited to 50 nm.

[0016] Preferably, the preparation method of the Sn-Ag-Sb-Ni alloy includes the following steps: Under a nitrogen atmosphere, melt elemental Sn, elemental Ag, elemental Sb, and elemental Ni at 1000 - 1200 °C to obtain the Sn-Ag-Sb-Ni alloy.

[0017] During the alloy melting and casting process, metals such as Sn and Ag are prone to react with oxygen to form oxides such as SnO2 and Ag2O. By melting in a nitrogen atmosphere, oxygen contact can be isolated, and the formation of oxides can be reduced.

[0018] In a second aspect, the present invention provides the preparation method of the high-reliability tin-silver-copper-based alloy, including the following steps: Ball mill the Sn-In-Nd-graphene hybrid material and Cu-Ag core-shell particles to obtain a mixture; melt the mixture with the Sn-Ag-Sb-Ni alloy to obtain the high-reliability tin-silver-copper alloy system.

[0019] Preferably, the ball-to-material ratio is (2-3):1, and the ball milling time is 20-40 min.

[0020] Preferably, the melting temperature is 300-400 °C, and the melting time is 1-2 h.

[0021] In a third aspect, the present invention provides the application of the high-reliability tin-silver-copper alloy system in the preparation of high-reliability solder paste. After grinding the high-reliability tin-silver-copper alloy system into powder with a particle size of 15-40 μm, it is mixed with a flux to make solder paste.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The main components of the alloy in the present invention are the Sn-Ag-Sb-Ni alloy, the Sn-In-Nd-graphene hybrid material, and the Cu-Ag core-shell particles. Among them, the Sn-Ag-Sb-Ni alloy serves as the alloy matrix, which can absorb energy through plastic deformation to avoid brittle fracture. At the same time, the multiple components in the alloy can form a variety of stable precipitation phases, and the multiple precipitation phases contained therein can improve the high-temperature stability; the Sn-In-Nd-graphene hybrid material serves as the reinforcement phase, which bears the main mechanical load, disperses stress through nano-reinforcement and intermetallic compounds, and has good bonding with the alloy matrix due to the presence of Sn; the Cu-Ag core-shell particles serve as the stress buffer medium, coordinating the thermal expansion difference between the alloy matrix and the reinforcement phase, and suppressing the interfacial reaction through the Ag shell; the combined action of the three makes the stress distribution in the alloy more uniform under tensile, bending and other loads, avoiding local overload failure, and making the alloy have high reliability. The alloy of the present invention simultaneously meets the requirements of automotive electronics for high temperature resistance, vibration resistance, and long life, as well as the requirements of the AI field for ultra-high thermal conductivity, high-precision connection, and resistance to electromigration, and becomes an ideal material for high-performance electronic packaging. Detailed implementation manners

[0023] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0024] Other materials, reagents, etc. used in the examples and comparative examples can be obtained from commercial channels without special instructions.

[0025] Example 1 A high-reliability tin-silver-copper alloy system, comprising the following raw materials for preparation by weight percentage: 8% of the Sn-In-Nd-graphene hybrid material, 6% of the Cu-Ag core-shell particles, and the balance being the Sn-Ag-Sb-Ni alloy; Among them, the Sn-In-Nd-graphene hybrid material comprises the following components by weight percentage: In 3.5%, Nd 0.6% and graphene 4%, and the balance is Sn and inevitable impurities; The Sn-Ag-Sb-Ni alloy comprises the following components by weight percentage: Ag 5%, Sb 0.33% and Ni 0.3%, and the balance is Sn and inevitable impurities; The preparation method of the Sn-In-Nd-graphene hybrid material comprises the following steps: (1) Ultrasonically disperse graphene in absolute ethanol to obtain a graphene slurry; wherein, the addition amount of absolute ethanol is 2 times the mass of graphene, the ultrasonic power is 550 W, and the ultrasonic dispersion time is 15 min; (2) Ultrasonically disperse Sn powder, In powder and Nd powder in absolute ethanol to obtain an alloy slurry; wherein, the addition amount of absolute ethanol is 2 times the total mass of Sn powder, In powder and Nd powder, the ultrasonic power is 550 W, and the ultrasonic dispersion time is 30 min; (3) Mix the graphene slurry and the alloy slurry and then carry out ball milling and vacuum drying to obtain Sn-In-Nd-graphene precursor powder; wherein, the ball-to-material ratio of ball milling is 4:1, and the ball milling time is 3 h; (4) Sinter the Sn-In-Nd-graphene precursor powder at 650 °C for 2 h, then raise the temperature to 1600 °C and continue sintering for 1.5 h, and keep the temperature for 10 min to obtain the Sn-In-Nd-graphene hybrid material; The preparation method of the Cu-Ag core-shell particles comprises the following steps: S1. Mix nano copper powder with deionized water, sodium citrate and sodium hypophosphite to obtain solution A; wherein, the molar ratio of nano copper powder, sodium citrate and sodium hypophosphite is 1:0.8:3, and the addition amount of deionized water is 1.5 times the total mass of nano copper powder, sodium citrate and sodium hypophosphite; the average particle size of nano copper powder is 50 nm; S2. Mix sodium citrate, silver sulfate and deionized water to obtain solution B; wherein, the molar ratio of sodium citrate to silver sulfate is 1:0.6, and the addition amount of deionized water is 1.5 times the total mass of sodium citrate and silver sulfate; S3. Drop solution B into solution A and carry out the reaction at 25 °C until the solution changes from red to purple and then to grayish brown; S4. Centrifuge the reacted solution, wash the precipitate and dry it to obtain the Cu-Ag core-shell particles.

[0026] The preparation method of the Sn-Ag-Sb-Ni alloy comprises the following steps: Under a nitrogen atmosphere, Sn powder, Ag powder, Sb powder and Ni powder are melted at 1100 °C to obtain the Sn-Ag-Sb-Ni alloy; The method for preparing the high-reliability tin-silver-copper-based alloy includes the following steps: The Sn-In-Nd-graphene hybrid material and the Cu-Ag core-shell particles are ball-milled for 30 min under the condition that the ball-to-material ratio is 2.5:1 to obtain a mixture; the mixture and the Sn-Ag-Sb-Ni alloy are melted at 350 °C for 1.5 h to obtain the high-reliability tin-silver-copper-based alloy.

[0027] Example 2 A high-reliability tin-silver-copper-based alloy, comprising the following raw materials for preparation in weight percentages: 5% of Sn-In-Nd-graphene hybrid material, 5% of Cu-Ag core-shell particles, and the balance being Sn-Ag-Sb-Ni alloy; wherein, the Sn-In-Nd-graphene hybrid material comprises the following components in weight percentages: 3% of In, 0.5% of Nd, and 3% of graphene, and the balance being Sn and inevitable impurities; The Sn-Ag-Sb-Ni alloy comprises the following components in weight percentages: 4% of Ag, 0.1% of Sb, and 0.1% of Ni, and the balance being Sn and inevitable impurities; The method for preparing the Sn-In-Nd-graphene hybrid material includes the following steps: (1) Ultrasonically disperse graphene in absolute ethanol to obtain a graphene slurry; wherein, the addition amount of absolute ethanol is twice the mass of graphene, the ultrasonic power is 500 W, and the ultrasonic dispersion time is 20 min; (2) Ultrasonically disperse Sn powder, In powder and Nd powder in absolute ethanol to obtain an alloy slurry; wherein, the addition amount of absolute ethanol is twice the total mass of Sn powder, In powder and Nd powder, the ultrasonic power is 500 W, and the ultrasonic dispersion time is 40 min; (3) Mix the graphene slurry and the alloy slurry and then perform ball milling and vacuum drying to obtain Sn-In-Nd-graphene precursor powder; wherein, the ball-to-material ratio of the ball milling is 4:1, and the ball milling time is 3 h; (4) Sinter the Sn-In-Nd-graphene precursor powder at 600 °C for 3 h, raise the temperature to 1500 °C and continue sintering for 2 h, and keep the temperature for 10 min to obtain the Sn-In-Nd-graphene hybrid material; The method for preparing the Cu-Ag core-shell particles includes the following steps: S1. Mix nano copper powder with deionized water, sodium citrate, and sodium hypophosphite to obtain solution A. Among them, the molar ratio of nano copper powder, sodium citrate, and sodium hypophosphite is 1:0.5:2, and the addition amount of deionized water is 1 time the total mass of nano copper powder, sodium citrate, and sodium hypophosphite. The average particle size of the nano copper powder is 50 nm. S2. Mix sodium citrate, silver sulfate, and deionized water to obtain solution B. Among them, the molar ratio of sodium citrate to silver sulfate is 1:0.5, and the addition amount of deionized water is 1 time the total mass of sodium citrate and silver sulfate. S3. Drop solution B into solution A and react at 25 °C until the solution changes from red to purple and then to grayish brown. S4. Centrifuge the reacted solution, wash the precipitate, and dry it to obtain the Cu-Ag core-shell particles.

[0028] The preparation method of the Sn-Ag-Sb-Ni alloy includes the following steps: Under a nitrogen atmosphere, melt Sn powder, Ag powder, Sb powder, and Ni powder at 1000 °C to obtain the Sn-Ag-Sb-Ni alloy. The preparation method of the high-reliability tin-silver-copper-based alloy includes the following steps: Ball-mill the Sn-In-Nd-graphene hybrid material and the Cu-Ag core-shell particles for 40 min under the condition of a ball-to-material ratio of 2:1 to obtain a mixture. Melt the mixture with the Sn-Ag-Sb-Ni alloy at 300 °C for 2 h to obtain the high-reliability tin-silver-copper-based alloy.

[0029] Example 3 A high-reliability tin-silver-copper-based alloy includes the following raw materials for preparation by weight percentage: 10% of the Sn-In-Nd-graphene hybrid material, 10% of the Cu-Ag core-shell particles, and the balance is the Sn-Ag-Sb-Ni alloy. Among them, the Sn-In-Nd-graphene hybrid material includes the following components by weight percentage: 4% of In, 1% of Nd, and 5% of graphene, and the balance is Sn and inevitable impurities. The Sn-Ag-Sb-Ni alloy includes the following components by weight percentage: 7% of Ag, 0.5% of Sb, and 0.5% of Ni, and the balance is Sn and inevitable impurities. The preparation method of the Sn-In-Nd-graphene hybrid material includes the following steps: (1) Ultrasonically disperse graphene in absolute ethanol to obtain a graphene slurry. Among them, the addition amount of absolute ethanol is 3 times the mass of graphene, the ultrasonic power is 600 W, and the ultrasonic dispersion time is 10 min. (2) Ultrasonically disperse Sn powder, In powder, and Nd powder in absolute ethanol to obtain an alloy slurry; wherein, the addition amount of absolute ethanol is 3 times the total mass of Sn powder, In powder, and Nd powder, the ultrasonic power is 600 W, and the ultrasonic dispersion time is 20 min; (3) Mix the graphene slurry and the alloy slurry and then perform ball milling and vacuum drying to obtain the Sn-In-Nd-graphene precursor powder; wherein, the ball-to-material ratio of ball milling is 5:1, and the ball milling time is 2 h; (4) Sinter the Sn-In-Nd-graphene precursor powder at 700 °C for 2 h, then raise the temperature to 1700 °C and continue sintering for 1 h, and hold for 5 min to obtain the Sn-In-Nd-graphene composite material.

[0030] The preparation method of the Cu-Ag core-shell particles includes the following steps: S1. Mix nano copper powder with deionized water, sodium citrate, and sodium hypophosphite to obtain solution A; wherein, the molar ratio of nano copper powder, sodium citrate, and sodium hypophosphite is 1:1:4, and the addition amount of deionized water is 2 times the total mass of nano copper powder, sodium citrate, and sodium hypophosphite; the average particle size of nano copper powder is 50 nm; S2. Mix sodium citrate, silver sulfate, and deionized water to obtain solution B; wherein, the molar ratio of sodium citrate to silver sulfate is 1:1, and the addition amount of deionized water is 2 times the total mass of sodium citrate and silver sulfate; S3. Drop solution B into solution A and react at 30 °C until the solution changes from red to purple and then to grayish brown; S4. Centrifuge the reacted solution, wash the precipitate, and dry it to obtain the Cu-Ag core-shell particles.

[0031] The preparation method of the Sn-Ag-Sb-Ni alloy includes the following steps: Under a nitrogen atmosphere, melt Sn powder, Ag powder, Sb powder, and Ni powder at 1200 °C to obtain the Sn-Ag-Sb-Ni alloy; The preparation method of the high-reliability tin-silver-copper-based alloy includes the following steps: Ball mill the Sn-In-Nd-graphene composite material and the Cu-Ag core-shell particles for 20 min under the condition of a ball-to-material ratio of 3:1 to obtain a mixture; melt the mixture and the Sn-Ag-Sb-Ni alloy at 400 °C for 1 - 2 h to obtain the high-reliability tin-silver-copper-based alloy.

[0032] Comparative Example 1 The difference from Example 1 is that the Sn-In-Nd-graphene composite material is not added, and the missing amount is supplemented with Cu-Ag core-shell particles and Sn-Ag-Sb-Ni alloy with a mass ratio of 6:86.

[0033] Comparative Example 2 The difference from Example 1 is that no Cu-Ag core-shell particles are added, and the Sn-In-Nd-graphene hybrid material and Sn-Ag-Sb-Ni alloy with a mass ratio of 8:86 are used to make up the missing amount.

[0034] Comparative Example 3 The difference from Example 1 is that the addition amount of the Sn-In-Nd-graphene hybrid material remains unchanged, and the Sn-In-Nd-graphene hybrid material comprises the following components by weight percentage: 0.6% In, 3.5% Nd, and 4% graphene, and the balance is Sn and unavoidable impurities.

[0035] Comparative Example 4 The difference from Example 1 is that the addition amount of the Sn-In-Nd-graphene hybrid material remains unchanged, and the Sn-In-Nd-graphene hybrid material comprises the following components by weight percentage: 3.5% In, 4% Nd, and 0.6% graphene, and the balance is Sn and unavoidable impurities.

[0036] Comparative Example 5 The difference from Example 1 is that In in the Sn-In-Nd-graphene hybrid material is moved to the Sn-Ag-Sb-Ni alloy to obtain a Sn-Ag-Sb-Ni-In alloy.

[0037] Performance Test 1. Mechanical Property Test of the Alloy The hardness of the alloys of Examples 1-3 and Comparative Examples 1-5 was tested respectively by the standard method of GB / T 231.1-2018 "Metallic materials - Brinell hardness test - Part 1: Test method", and the elongation and tensile strength were tested by GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The specific data are shown in Table 1.

[0038] 2. Test of High Stability of the Solder Paste The alloys of each group were ground into powders with a particle size of 15-40 μm, and the alloy powders were made into solder paste. The specific steps are as follows: 84 wt% of the alloy powder and 16 wt% of the water-soluble lead-free soldering flux were placed in a disperser and stirred at a stirring speed of 20 r / min for 10 min, then evacuated to 0.06 Mpa for 10 min, and stirring continued during evacuation. As a result, a solder paste with a viscosity of 50 Pa·s was obtained. Among them, the raw materials and preparation method of the water-soluble lead-free soldering flux refer to Example 1 of CN112589318B.

[0039] The prepared solder paste was subjected to the following tests: GB / T 31474-2015 was used to test the surface insulation resistance, IPC-TM-650 2.5.5.9 was used to test the dielectric loss (1MHz), IPC-TM-650 2.6.15 was used to test the corrosion resistance, and IPC-TM-650 2.4.35 was used to test the expansion rate, as shown in Table 2.

[0040] Table 1 Mechanical properties test results of each group of alloy samples Group Hardness / HB Elongation / % Tensile Strength / MPa Example 1 32.7 23.3 122.1 Example 2 30.4 20.8 112.2 Example 3 31.8 21.6 121.5 Comparative Example 1 16.0 12.7 71.9 Comparative Example 2 18.3 14.4 73.7 Comparative Example 3 26.2 16.1 81.6 Comparative Example 4 26.0 15.2 85.3 Comparative Example 5 28.2 17.7 86.3 As shown in Table 1, combined with the data of Examples 1-3 and Comparative Examples 1-2, it can be seen that in Comparative Example 1, no Sn-In-Nd-graphene mixed material is added, and its mechanical properties are significantly reduced compared with Example 1. This may be because after the lack of Sn-In-Nd-graphene mixed material, the stress cannot be effectively dispersed through the graphene skeleton, resulting in a significant decrease in the mechanical strength of the alloy. At the same time, the lack of In leads to a decrease in the porosity of the alloy, and the lack of Nd causes the alloy to be unable to form a dense Nd2O3 protective film at high temperatures, and the high-temperature stability of the alloy is reduced. In Comparative Example 2, no Cu-Ag core-shell particles are added, and its mechanical properties are significantly reduced compared with Example 1. This may be because the Cu-Ag core-shell particles can coordinate the deformation of the soft / hard areas through the core-shell structure, while maintaining plasticity while improving strength, and the lack of Cu-Ag core-shell particles may destroy the strength-ductility balance, and plasticity may be reduced due to the simplification of the strengthening mechanism. Therefore, the Sn-In-Nd-graphene hybrid material, Cu-Ag core-shell particles and Sn-Ag-Sb-Ni alloy have synergistic alloy mechanical properties.

[0041] It can be seen from the data of Example 1 and Comparative Examples 3-4 that in the Sn-In-Nd-graphene mixed material, if the addition amount of graphene is less than 3%, the mechanical properties of the alloy are significantly reduced. This may be because the graphene content is too low to form an effective three-dimensional reinforcement network, the load transfer efficiency is reduced, and the inhibition of graphene on grain boundary slip is weakened, and the plasticity is reduced. Similarly, if the In addition amount is less than 3%, it is difficult for the alloy to form a dense structure during welding or sintering, and the porosity is increased, thereby reducing the alloy performance. When the Nd content is higher than 1%, excessive Nd may form more coarse Nd compounds in the alloy, and these coarse compounds will split the matrix and destroy the continuity of the alloy, thereby affecting the mechanical properties of the alloy. Therefore, when the Sn-In-Nd-graphene mixed material includes the following weight percentage components: In 3-4%, Nd 0.5-1% and graphene 3-5%, and the balance is Sn and unavoidable impurities, the performance of its alloy is at a better level.

[0042] Combined with the data of Example 1 and Comparative Example 5, it can be seen that the mechanical properties of the alloy in Comparative Example 5 are significantly lower than those in Example 1. This may be because In and Nd in the graphene hybrid material Sn-In-Nd system can form nanoscale InNd intermetallic compounds (IMCs), which pin the grain boundaries and inhibit grain coarsening. However, when In migrates, Nd in the Sn-In-Nd system cannot effectively form IMCs, resulting in grain coarsening and reducing the mechanical properties of the alloy. When the Sn-Ag-Sb-Ni-In alloy is formed, In forms a brittle NiIn3 phase with Ni, further reducing the mechanical properties of the alloy. Therefore, it shows that the addition position of In is also an important parameter affecting the mechanical properties such as the hardness, elongation, and tensile strength of the alloy.

[0043] Table 2 Reliability test data of each group of solder pastes Group Surface Insulation Impedance Dielectric Loss (1MHz) Corrosion Resistance Expansion Rate / % Example 1 <![CDATA[2.8×10 12 > 0.0115 No Penetration 92.6 Example 2 <![CDATA[2.1×10 12 > 0.0130 No Penetration 88.1 Example 3 <![CDATA[2.6×10 12 > 0.0118 No Penetration 91.3 Comparative Example 1 <![CDATA[2.7×10 10 > 0.0857 Partial Penetration 75.0 Comparative Example 2 <![CDATA[3.2×10 10 > 0.0816 Partial Penetration 74.3 Comparative Example 3 <![CDATA[6.2×10 11 > 0.0408 Partial Penetration 85.6 Comparative Example 4 <![CDATA[6.9×10 11 > 0.0369 No Penetration 86.0 Comparative Example 5 <![CDATA[6.5×10 11 > 0.0611 Partial Penetration 88.4 As can be seen from Table 2, combined with the data of Example 1 and Comparative Examples 1-2, the reliability test data of Example 1 are significantly better than those of Comparative Examples 1-2. This may be because the synergistic strengthening and antioxidant effects of the Sn-In-Nd-graphene hybrid material are missing, resulting in significant deterioration in thermomechanical reliability, drop resistance, and long-term stability. The wetting regulation and mechanical strengthening effects of the Cu-Ag core-shell particles are missing, resulting in obvious shortcomings in welding quality, interface stability, and electromigration resistance. Therefore, the absence of any component of the alloy of the present invention will lead to a sharp increase in interface defects and cannot meet the stringent requirements for high-reliability solder pastes in new energy vehicle electronics and AI chip packaging.

[0044] Combined with the data of Example 1 and Comparative Examples 3-4, it can be seen that in the Sn-In-Nd-graphene hybrid material, the mass ratio of each component is also an important parameter affecting the reliability of the solder paste. If the components are too much or too little, it will be difficult to form a uniform graphene / metal interface bond in the hybrid material, and the oxidation of the Sn matrix surface not covered by graphene will be aggravated, thereby reducing the reliability of the solder paste.

[0045] Combined with Example 1 and Comparative Example 5, it can be seen that the position of In will affect the reliability of the solder paste. This may be because In does not play the role of refining grains and improving wettability in the Sn-In-Nd-graphene hybrid material, resulting in coarse alloy structure, affecting the fluidity and wettability of the solder paste, reducing the spread rate, and affecting the welding quality. Therefore, in the present invention, In is arranged in the graphene hybrid material system to ensure its synergistic effects on graphene dispersion, grain refinement, and interface strengthening, and to avoid reliability deterioration caused by improper distribution or abnormal content.

[0046] In summary, through the combined action of the Sn-In-Nd-graphene hybrid material, Cu-Ag core-shell particles, and the Sn-Ag-Sb-Ni alloy, the stress distribution of the alloy of the present invention under loads such as tension and bending is more uniform, avoiding local overload failure and making the alloy highly reliable.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A high reliability tin-silver-copper alloy, characterized in that: The preparation raw materials include the following weight percentages: 5-10% of Sn-In-Nd-graphene mixed material, 5-10% of Cu-Ag core-shell particles, and the balance is Sn-Ag-Sb-Ni alloy; Wherein, the Sn-In-Nd-graphene mixed material comprises the following components in weight percentage: 3-4% In, 0.5-1% Nd and 3-5% graphene, and the balance is Sn and unavoidable impurities; The Sn-Ag-Sb-Ni alloy comprises the following components in weight percentage: Ag 4-7%, Sb 0.1-0.5% and Ni 0.1-0.5%, with the balance being Sn and unavoidable impurities; The method for preparing the Sn-In-Nd-graphene mixed material comprises the following steps: (1) ultrasonically dispersing graphene in anhydrous ethanol to obtain a graphene slurry; (2) Ultrasonic dispersion of Sn powder, In powder and Nd powder in anhydrous ethanol to obtain alloy slurry; (3) mixing the graphene slurry and the alloy slurry, ball milling, and vacuum drying to obtain Sn-In-Nd-graphene precursor powder; (4) The Sn-In-Nd-graphene precursor powder is first sintered at 600-700°C for 2-3 hours, then heated to 1500-1700°C and further sintered for 1-2 hours, and kept warm for 5-10 minutes to obtain the Sn-In-Nd-graphene mixed material.

2. The high reliability Sn-Ag-Cu alloy according to claim 1, characterized in that: The amount of anhydrous ethanol added in step (1) is 2-3 times the mass of graphene; the amount of anhydrous ethanol added in step (2) is 2-3 times the total mass of Sn powder, In powder and Nd powder.

3. The high reliability Sn-Ag-Cu alloy according to claim 1, characterized in that: The ball-to-material ratio in the ball milling in step (3) is (4-5):1, and the ball milling time is 2-3 hours.

4. The high reliability Sn-Ag-Cu alloy according to claim 1, characterized in that: The method for preparing the Cu-Ag core-shell particles comprises the following steps: S1. Mixing nano copper powder with deionized water, sodium citrate and sodium hypophosphite to obtain solution A; wherein the molar ratio of nano copper powder, sodium citrate and sodium hypophosphite is 1:(0.5-1):(2-4), and the amount of deionized water added is 1-2 times the total mass of the nano copper powder, sodium citrate and sodium hypophosphite; S2, mixing sodium citrate, silver sulfate and deionized water to obtain solution B; wherein the molar ratio of sodium citrate to silver sulfate is 1:(0.5-1), and the amount of deionized water added is 1-2 times the total mass of sodium citrate and silver sulfate; S3, adding solution B dropwise to solution A, and reacting at 25-30°C until the solution changes from red to purple and then to gray-brown; S4, centrifuging the solution after the reaction, washing the precipitate, and drying to obtain the Cu-Ag core-shell particles.

5. The high reliability Sn-Ag-Cu alloy according to claim 4, characterized in that: The average particle size of the nano copper powder is 50 nm.

6. The high reliability Sn-Ag-Cu alloy according to claim 1, characterized in that: The preparation method of the Sn-Ag-Sb-Ni alloy comprises the following steps: In a nitrogen atmosphere, Sn powder, Ag powder, Sb powder and Ni powder are melted at 1000-1200° C. to obtain a Sn—Ag—Sb—Ni alloy.

7. The method for preparing a high reliability Sn-Ag-Cu alloy according to any one of claims 1 to 6, characterized in that: The following steps are involved: The Sn-In-Nd-graphene mixed material and the Cu-Ag core-shell particles are ball-milled to obtain a mixture; the mixture is smelted with a Sn-Ag-Sb-Ni alloy to obtain the high-reliability tin-silver-copper alloy.

8. The method for preparing a high-reliability Sn-Ag-Cu alloy according to claim 7, characterized in that: The ball-to-material ratio is (2-3): 1, the ball milling time is 20-40 minutes; and / or, the smelting temperature is 300-400°C, and the smelting time is 1-2 hours.

9. Use of the high reliability tin-silver-copper alloy according to any one of claims 1 to 8 in preparing solder paste.