Non-ferrous metal solder for low-temperature brazing and application

Abstract

The invention relates to the field of solder materials, and provides a non-ferrous metal solder for low-temperature brazing and application, the solder is composed of carbon-coated copper nanorods, tin-bismuth alloy-coated silver nanoparticles, 2-mercaptobenzimidazole, rosin resin, an organic active agent, a dispersing agent, ionic liquid, hydroxyethyl cellulose, indium nitrate and citric acid. The silver particles are of a core-shell structure and are coated with tin-bismuth alloy layers, and continuous carbon layers are formed on the surfaces of the copper nanorods, so that the conductivity and the interface stability of the solder are effectively improved. The non-ferrous metal solder with excellent conductivity, low melting point and good wettability is prepared through step-by-step mixing, hot press molding and low-temperature heat treatment processes, and is suitable for electronic device packaging, power device connection and flexible circuit interconnection, and the defects of existing solder in the aspects of low-temperature welding and high conductivity are overcome.

Description

Technical Field

[0001] The present invention relates to the field of solder materials, and particularly to a non-ferrous metal solder for low-temperature brazing and its application. Background Art

[0002] In advanced manufacturing fields with high integration and high reliability requirements such as electronic packaging, power device interconnection, and flexible circuits, brazing, as the core connection method, its material properties directly affect the conductive efficiency, thermal management ability, and structural stability of devices. With the development of electronic components towards miniaturization and high density, the welding interface is exposed to complex thermal and electrical stress environments, posing higher functional requirements for solders. In particular, achieving efficient conductive connection under a low-temperature process window has become the key to improving packaging efficiency and system reliability. Due to its advantages such as less damage to the base material and strong environmental adaptability, low-temperature brazing technology shows broad application prospects in fields such as flexible electronics, biosensors, and thermal-sensitive component packaging. Therefore, solder materials not only need to have excellent low melting point characteristics to adapt to low-temperature welding processes but also should have high conductivity to ensure the stability of signal transmission and electrical energy conduction. Achieving the coordinated optimization of these two properties helps to significantly improve the comprehensive performance of devices, reduce manufacturing costs, expand the application boundaries of low-temperature welding technology in high-end electronic manufacturing, and thus promote the development of a new generation of electronic interconnection technology, which is of great significance for both material design and process innovation.

[0003] Currently, non-ferrous metal solders developed for low-temperature brazing applications still face significant challenges in achieving the coordination of high conductivity and low-temperature welding performance. Although existing research has attempted to improve solder performance by introducing metal nanostructures, composite fluxes, or adjusting alloy compositions, it is still difficult to simultaneously meet the dual requirements of low-temperature processing and high conductivity in practical applications. For example, a Chinese patent with the publication number CN102873469B discloses a low-temperature aluminothermic solder for welding metals and ceramics. Although certain progress has been made in reducing the melting point, its conductive performance after welding is unstable, and the interface bonding layer resistance is relatively high, making it difficult to meet the requirements of high-performance device connections, and there are problems of insufficient high conductivity and low-temperature welding performance. The main reasons are that the conductive phase distribution in traditional solder systems is uneven, the interface structure lacks stability, the thermal decomposition of flux components is incomplete, and the ability to control the microstructure is limited. These problems jointly limit the formation of continuous, dense, and highly conductive welding connections by solders at low temperatures. Therefore, there is an urgent need to develop a non-ferrous metal solder that can be efficiently melted, quickly wetted, and form a highly conductive interface under low-temperature conditions to meet the urgent material property requirements of the new generation of electronic packaging and interconnection technologies. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] The object of the present invention is to provide a non-ferrous metal solder for low-temperature brazing and its application, so as to solve the problems of insufficient high conductivity and low-temperature welding performance of the current solder.

[0006] (2) Technical solution

[0007] In order to achieve the above object, the present invention provides the following technical solution:

[0008] A non-ferrous metal solder for low-temperature brazing, comprising the following raw materials in parts by weight: 12.0 - 18.0 parts of carbon-coated copper nanorods, 60.0 - 90.0 parts of tin-bismuth alloy-coated silver nanoparticles, 1.5 - 2.5 parts of 2-mercaptobenzimidazole, 6.0 - 10.0 parts of rosin resin, 1.5 - 3.5 parts of organic activator, 2.0 - 4.5 parts of dispersant, 10.0 - 18.0 parts of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1.0 - 2.0 parts of hydroxyethyl cellulose, 0.5 - 1.5 parts of indium nitrate sintering aid, and 0.1 - 0.3 parts of citric acid.

[0009] The carbon-coated copper nanorods are composed of copper nanorods and a continuous carbon layer uniformly coated on the outer surface of the copper nanorods;

[0010] The tin-bismuth alloy-coated silver nanoparticles are core-shell structure particles, the core is silver nanoparticles, and the shell is a tin-bismuth alloy layer coated on its outer surface;

[0011] Further, the average diameter of the carbon-coated copper nanorods is 50 - 120 nm, the aspect ratio is 5 - 20, and the average thickness of the carbon layer is 4 - 10 nm;

[0012] Further, the average thickness of the tin-bismuth alloy layer is 11 - 30 nm; the mass ratio of tin to bismuth in the tin-bismuth alloy layer is (42 - 50):(50 - 58);

[0013] Further, the average diameter of the silver nanoparticles is 20 - 80 nm.

[0014] Further, the preparation method of the carbon-coated copper nanorods is as follows: by weight, 1.0 - 1.5 parts of copper nanorods, 0.5 - 1.5 parts of glucose, 0.2 - 0.8 parts of polyvinylpyrrolidone, and 0.1 - 0.3 parts of 50wt.% hydrochloric acid are successively added to 3.0 - 5.0 parts of deionized water. Under argon protection, a homogeneous suspension is formed by mixing at a stirring rate of 300 - 600 rpm, transferred to a polytetrafluoroethylene-lined high-pressure reactor with a volume of 50 - 100 mL and sealed. It is heated to 160 - 200 °C at a rate of 2 - 5 °C / min for hydrothermal reaction for 4 - 8 h. After the reaction terminates, the liquid-phase components are removed by centrifugal separation at a centrifugal rate of 8000 - 12000 rpm, and the solid-phase copper-glucose complex is retained. It is washed 3 - 5 times with 3.0 - 5.0 parts of absolute ethanol in sequence to remove unreacted glucose and dispersant, and vacuum dried at 60 - 80 °C for 2 - 4 h to obtain a precursor; the precursor is evenly spread in an alumina crucible and placed in the constant-temperature zone of a tube furnace. A hydrogen mixed gas with a volume fraction of 3.8 - 4.2% carried by argon is introduced with a flow rate of 60 - 90 mL / min. It is heated to 800 - 900 °C at a rate of 5 - 10 °C / min for carbonization treatment for 1 - 3 h to pyrolyze glucose to form a carbon coating layer. Subsequently, it is cooled to 40 - 60 °C at a natural cooling rate and then switched to argon protection, and finally carbon-coated copper nanorods are obtained.

[0015] Further, the preparation method of the copper nanorods is as follows: 1.0 - 1.5 parts of copper nitrate are dissolved in ethanol to prepare a 0.4 - 0.6 M copper nitrate ethanol solution, and 8.0 - 12.0 parts of sodium hydroxide are dissolved in deionized water to prepare a 4.0 - 6.0 M sodium hydroxide aqueous solution. The copper nitrate ethanol solution and the sodium hydroxide aqueous solution are mixed at a volume ratio of 1:8 - 1:12 and then transferred to a polytetrafluoroethylene-lined stainless-steel high-pressure reactor and sealed. Hydrothermal reaction is carried out at 120 - 180 °C for 60 - 180 min. After the reaction ends, it is naturally cooled to 25 - 30 °C. The solid-phase product is retained by vacuum filtration through a polyethersulfone membrane with a pore size of 0.22 - 0.45 μm. It is washed 3 - 5 times with deionized water and 2 - 3 times with absolute ethanol in sequence to remove residual nitrate ions and sodium ions. Subsequently, it is vacuum dried at 75 - 85 °C for 2.0 - 4.0 h to obtain a precursor of copper oxide nanorods; the precursor of copper oxide nanorods is placed in a quartz boat with a length of 4.0 - 6.0 cm, and the quartz boat is placed in the middle of a quartz tube reactor with an inner diameter of 1.0 - 1.5 cm. A hydrogen gas flow with a volume concentration of 3.5 - 4.5% carried by argon is introduced with a flow rate of 50 - 100 mL / min. It is heated to 200 - 300 °C at a heating rate of 5 - 10 °C / min and kept at a constant temperature for 50 - 70 min to complete the reduction reaction of copper oxide nanorods to copper nanorods. After the reduction ends, the hydrogen gas flow rate is maintained and it is naturally cooled to 30 - 40 °C and then switched to an argon protection atmosphere, and finally copper nanorods are obtained.

[0016] The design of the carbon-coated copper nanorods in the present invention is mainly used to enhance the comprehensive performance of electrical conductivity and oxidation resistance. The technical concept lies in constructing a nanoscale conductive framework with a regular structure and forming a dense and continuous carbon layer on its surface to achieve double optimization of the conductivity channel and interface stability. Copper nanorods can effectively construct a conductive network in the solder system due to their excellent intrinsic conductivity and the electron migration advantage brought by the one-dimensional structure, thus improving the overall conductivity of the solder joint. However, copper materials are prone to oxidation during heat treatment and welding processes, resulting in the interruption of the conduction path and an increase in interface resistance. Therefore, the carbon-coated copper nanorods prepared by the hydrothermal method and the atmosphere-controlled carbonization process in the present invention form a stable carbon layer structure. This carbon layer not only physically isolates and chemically passivates the copper nanorods, effectively inhibiting their oxidation behavior, but also has a certain electrical conductivity and can cooperate with the internal copper core to construct a multi-dimensional conductive network. In addition, the carbon layer can also enhance the interfacial binding between particles in the composite system, improving the wetting and spreading ability and bonding reliability of the solder under low-temperature conditions. By finely controlling the carbon layer thickness and the morphological parameters of the copper nanorods, while ensuring the continuity of the high-conductivity channel, it also has good thermal stability and electrochemical inertness, thus achieving stable and efficient electronic connection in a low-temperature welding environment. The introduction of the carbon-coated copper nanorods not only optimizes the performance at the single-component level, but also significantly improves the electrical conductivity and environmental adaptability of the overall material through the structural and interfacial synergistic effects between it and other components of the solder, providing an effective material basis and structural support for constructing high-performance, low-temperature processing non-ferrous metal solders.

[0017] Further, the preparation method of the tin-bismuth alloy-coated silver nanoparticles is as follows: calculated by weight, 1.0 - 3.0 parts of silver nanoparticles are dispersed in 8.0 - 15.0 parts of ethylene glycol to form a homogeneous dispersion system. Then, 0.8 - 2.5 parts of stannous chloride, 1.2 - 3.0 parts of bismuth nitrate, and 4.0 - 10.0 parts of polyvinylpyrrolidone are successively added thereto. After mixing evenly under the protection of argon at a stirring rate of 400 - 700 rpm, the temperature is raised to 60 - 90 °C at a rate of 2 - 5 °C / min and maintained at this temperature. Under the condition of pH 4.0 - 6.0, an ethylene glycol solution containing 0.5 - 2.0 parts of ascorbic acid or 0.1 - 0.3 parts of sodium borohydride is slowly added dropwise at a dropping rate of 0.5 - 2.0 mL / min. The reaction is carried out at a constant temperature for 30 - 60 min so that the tin-bismuth alloy layer is coated on the surface of the silver core in a co-reduction manner. After the reaction is completed, the supernatant is discarded by centrifugation at a centrifugation rate of 8000 - 12000 rpm, and the solid product is retained. It is successively ultrasonically washed 2 - 3 times with 6.0 - 10.0 parts of absolute ethanol to remove the residual unreacted chloride ions and nitrate ions, and then vacuum dried at 40 - 60 °C for 3 - 5 h to obtain the tin-bismuth alloy-coated silver nanoparticles.

[0018] Furthermore, the preparation method of the silver nanoparticles is as follows: by weight, 1.0 to 2.5 parts of silver nitrate are dissolved in a mixed solvent consisting of 30 to 50 parts of deionized water and 30 to 50 parts of ethanol, 10 to 30 parts of polyvinyl pyrrolidone are added as a surface stabilizer, the reaction system temperature is maintained at 0 to 10° C. under a stirring rate of 300 to 600 rpm, and 0.2 to 0.5 parts of an ethanol solution of sodium borohydride is added dropwise at a dropping rate of 0.5 to 2.0 mL / min. .0 to 10.0 parts of the raw material are used for reduction reaction, the reaction time is 10 to 30 minutes to reduce the silver ions to silver nanoparticles with a particle size of 20 to 80 nm. After the reaction is completed, the precipitate is retained by centrifugation at a centrifugal speed of 8000 to 12000 rpm and the supernatant containing unreacted ions and by-products is discarded. 20 to 40 parts of ethanol are used for 2 to 3 times of ultrasonic washing to remove residual nitrate ions and free surfactants. Finally, the silver nanoparticles are vacuum dried at 30 to 50° C. for 1 to 3 hours to obtain uniformly dispersed silver nanoparticles.

[0019] The design of the present invention using tin-bismuth alloy coated silver nanoparticles is mainly used to enhance the synergistic performance of conductivity and low-temperature welding. The core is to achieve functional complementarity between the high-conductivity metal core and the low-melting alloy shell by constructing composite nanoparticles with a core-shell structure, so as to take into account the dual needs of efficient electron transmission and low-temperature rapid melting during the welding process. Specifically, silver nanoparticles as the core can effectively construct a stable and dense conductive path by virtue of their intrinsic excellent conductive properties and high surface area at the nanoscale; while the outer coated tin-bismuth alloy shell has a lower melting characteristic, can participate in melting expansion at a lower temperature, and significantly improve the low-temperature wettability and interface bonding ability of the solder. The composition ratio of the tin-bismuth alloy is precisely controlled to have suitable phase change behavior and thermal stability, ensuring that it can be used as a molten carrier to promote inter-particle connection during the welding process without significantly sacrificing overall conductivity. The core-shell structure is coated by co-reduction deposition to form a continuous and uniform alloy shell layer, which further improves the compatibility and interface interaction between particles and avoids the problem of agglomeration or uncontrolled migration of single nanometal particles during the melting process. At the same time, the introduction of polyvinyl pyrrolidone effectively stabilizes the silver core and its alloy coating structure during the preparation process, ensuring the dispersion of particles and uniform film formation. The overall structural design not only combines the high conductivity advantages of the silver core with the low-temperature welding characteristics of the tin-bismuth alloy, but also improves the overall performance of the material during the welding process through the synergistic effect of structural levels and components, providing an effective solution for the performance optimization and process adaptability of low-temperature brazing materials.

[0020] Further, the organic active agent is azelaic acid or malic acid;

[0021] Furthermore, the dispersant is a mixture of PVP and polyethylene glycol with a mass ratio of 1:(1.0 - 2.0). Further, the preparation method of a non-ferrous metal solder for low-temperature soldering includes the following steps:

[0022] S1. Under a nitrogen protection atmosphere, add carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles into a mixing container according to a preset ratio, and use mechanical stirring at 200 - 400 rpm, a temperature of 20 - 40 °C, and a mixing time of 20 - 40 min. Subsequently, add 2-mercaptobenzimidazole, an organic activator, and a dispersant in sequence, and continue stirring at 300 - 600 rpm for 15 - 30 min to form a stable composite system;

[0023] S2. Add rosin resin, hydroxyethyl cellulose, and 1-ethyl-3-methylimidazolium tetrafluoroborate, with a mixing temperature of 30 - 60 °C, a mixing rate of 500 - 800 rpm, and a mixing time of 30 - 45 min. Subsequently, add indium nitrate and citric acid, and continue mixing for 10 - 20 min;

[0024] S3. Load the mixture into a hot press mold, control the pressing temperature within 40 - 60 °C, the pressure at 10 - 30 MPa, and keep the pressure for 1 - 3 min to form a strip-shaped solder;

[0025] S4. Conduct low-temperature heat treatment at 60 - 80 °C in an inert atmosphere, keep the temperature for 20 - 40 min, and perform cutting and vacuum packaging after cooling to obtain the final strip-shaped solder product.

[0026] The present invention also discloses the application of a non-ferrous metal solder for low-temperature soldering in electronic device packaging, heat dissipation connection of power devices, or metal interconnection of flexible circuits.

[0027] The present invention adopts a composite design strategy to synergistically introduce carbon-coated copper nanorods and silver nanoparticles coated with tin-bismuth alloy into the non-ferrous metal solder system for low-temperature soldering, aiming to achieve the organic unity of electrical conductivity and low-temperature welding performance, and improve the comprehensive adaptability of the solder in complex electronic connection environments through interface regulation and structure optimization among multiple components. As a high-conductivity structural unit, the internal copper core of the carbon-coated copper nanorod has excellent electrical conductivity characteristics, while the outer carbon shell effectively inhibits the oxidation behavior of copper during air exposure or heat treatment, stabilizing its conduction path and microstructure; the silver nanoparticles coated with tin-bismuth alloy combine the high electrical conductivity of silver and the low melting point characteristics of the tin-bismuth alloy to construct a composite conductive phase with both electron transport and low-temperature wetting functions. The combination of the two can form a multi-scale conductive network in the composite system, enhancing the overall conduction continuity and interface connection ability. The uniform compounding of the two types of core functional particles is achieved through mechanical stirring at medium temperature, and 2-mercaptobenzimidazole is introduced as an interface regulator to effectively improve the dispersion stability and wettability between metal particles. At the same time, organic activators such as azelaic acid or malic acid are used to regulate the surface activity and wetting behavior of the reaction system, and the dispersant composed of PVP and polyethylene glycol further enhances the uniformity and structural integrity of the system. On this basis, the addition of rosin resin, hydroxyethyl cellulose, and 1-ethyl-3-methylimidazolium tetrafluoroborate not only endows the solder with good bonding performance and film-forming ability but also improves its adaptability on flexible circuits and complex interfaces; the synergistic effect of indium nitrate and citric acid helps to regulate the interfacial electronic structure of the solder and the reaction activity between metals during welding. By controlling the hot pressing and low-temperature heat treatment conditions, the structural denseness and component distribution uniformity of the solder during the forming process are ensured, and finally, a strip-shaped solder product with excellent comprehensive performance is obtained. Through the synergistic construction of a variety of functional materials, this technical solution realizes the unified optimization of electrical conductivity, low-temperature weldability, dispersion stability, and interfacial activity, significantly enhancing the application potential of the solder in multiple scenarios such as electronic device packaging, heat dissipation connection of power devices, and metal interconnection of flexible circuits.

[0028] (3) Beneficial technical effects

[0029] 1. The present invention constructs a stable conductive network through carbon-coated copper nanorods and improves the antioxidant property, achieving the synergistic enhancement of welding conduction continuity and interface stability, which is significantly superior to traditional copper-based solders and is suitable for application scenarios with strict requirements for low-temperature high conductivity such as flexible circuits.

[0030] 2. The present invention realizes the integration of high electrical conductivity and low-temperature welding functions through the synergistic design of silver cores and tin-bismuth alloy shells, significantly improving the welding efficiency and interface stability, solving the problems of molten out-of-control and insufficient electrical conductivity of existing nano-solders, and having excellent structural stability and application adaptability.

[0031] 3. The present invention synergistically constructs carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles, significantly optimizing electrical conductivity and low-temperature soldering performance, enhancing the stability and adaptability of the solder interface, being applicable to various electronic interconnection scenarios, and having the advantages of structural integrity and functional integration superior to single material systems. Description of the Drawings

[0032] Figure 1 It is the morphology diagram of the copper nanorods prepared in Example 1 of the present invention.

[0033] Figure 2 It is the XRD phase analysis diagram of the copper nanorods prepared in Example 1 of the present invention.

[0034] Figure 3 It is the morphology diagram of the carbon-coated copper nanorods prepared in Example 1 of the present invention.

[0035] Figure 4 It is the XRD phase analysis diagram of the carbon-coated copper nanorods prepared in Example 1 of the present invention.

[0036] Figure 5 It is the line-scan elemental distribution diagram of the tin-bismuth alloy-coated silver nanoparticles prepared in Example 1 of the present invention. Detailed Embodiments

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0038] Example 1

[0039] A non-ferrous metal solder for low-temperature brazing includes the following raw materials in parts by weight: 12.0 parts of carbon-coated copper nanorods, 60.0 parts of tin-bismuth alloy-coated silver nanoparticles, 1.5 parts of 2-mercaptobenzimidazole, 6.0 parts of rosin resin, 1.5 parts of organic activator, 2.0 parts of dispersant, 10.0 parts of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1.0 part of hydroxyethyl cellulose, 0.5 part of indium nitrate sintering aid, and 0.1 part of citric acid.

[0040] The carbon-coated copper nanorods are composed of copper nanorods with a continuous carbon layer uniformly coated on the outer surface of the copper nanorods; the tin-bismuth alloy-coated silver nanoparticles are core-shell structure particles, the core is silver nanoparticles, and the shell is a tin-bismuth alloy layer coated on its outer surface;

[0041] The average diameter of the carbon-coated copper nanorods is 50 nm, the aspect ratio is 4, and the average thickness of the carbon layer is 3.0 nm;

[0042] The preparation method of the carbon-coated copper nanorods in this embodiment is as follows: by weight, 1.0 part of copper nanorods, 0.5 part of glucose, 0.2 part of polyvinylpyrrolidone, and 0.1 part of 50 wt.% hydrochloric acid are sequentially added to 3.0 parts of deionized water, and mixed under argon protection at a stirring rate of 300 rpm to form a homogeneous suspension. The suspension is transferred to a polytetrafluoroethylene-lined autoclave with a volume of 50 mL and sealed. It is heated to 160 °C at a rate of 2 °C / min for a hydrothermal reaction for 4 h. After the reaction is terminated, the liquid-phase components are removed by centrifugation at a centrifugal rate of 8000 rpm, and the solid-phase copper-glucose complex is retained. It is washed 3 times with 3.0 parts of absolute ethanol to remove unreacted glucose and dispersant, and vacuum dried at 60 °C for 2 h to obtain a precursor; the precursor is evenly spread in an alumina crucible and placed in the constant-temperature zone of a tube furnace. A hydrogen mixed gas with a volume fraction of 3.8% carried by argon is introduced with a flow rate of 60 mL / min, and it is heated to 800 °C at a rate of 5 °C / min for carbonization treatment for 1 h to pyrolyze glucose to form a carbon coating layer. Subsequently, it is cooled to 40 °C at a natural cooling rate and then switched to argon protection, and finally carbon-coated copper nanorods are obtained.

[0043] The preparation method of the copper nanorods in this embodiment is as follows: 1.0 part of copper nitrate is dissolved in ethanol to prepare a 0.4 M copper nitrate ethanol solution, 8.0 parts of sodium hydroxide is dissolved in deionized water to prepare a 4.0 M sodium hydroxide aqueous solution. The copper nitrate ethanol solution and the sodium hydroxide aqueous solution are mixed at a volume ratio of 1:8 and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and sealed. A hydrothermal reaction is carried out at 120 °C for 60 min. After the reaction is completed, it is naturally cooled to 25 °C. The solid-phase product is retained by vacuum filtration through a polyethersulfone membrane with a pore size of 0.22 μm. It is washed 3 times with deionized water and 2 times with absolute ethanol to remove residual nitrate ions and sodium ions. Subsequently, it is vacuum dried at 75 °C for 2.0 h to obtain a precursor of copper oxide nanorods; the precursor of copper oxide nanorods is placed in a quartz boat with a length of 4.0 cm, and the quartz boat is placed in the middle of a quartz tube reactor with an inner diameter of 1.0 cm. A hydrogen gas flow with a volume concentration of 3.5% carried by argon is introduced with a flow rate of 50 mL / min. It is heated to 200 °C at a heating rate of 5 °C / min and kept at a constant temperature for 50 min to complete the reduction reaction of copper oxide nanorods to copper nanorods. After the reduction is completed, the hydrogen gas flow rate is maintained and it is naturally cooled to 30 °C and then switched to an argon protection atmosphere, and finally copper nanorods are obtained.

[0044] The average thickness of the tin-bismuth alloy layer in this embodiment is 17 nm; the mass ratio of tin to bismuth in the tin-bismuth alloy layer is 44:56; the average diameter of the silver nanoparticles is 38 nm.

[0045] The preparation method of the silver nanoparticles coated with tin-bismuth alloy in this embodiment is as follows: by weight, 1.6 parts of silver nanoparticles are dispersed in 10.1 parts of ethylene glycol to form a homogeneous dispersion system. Then, 1.3 parts of stannous chloride, 1.7 parts of bismuth nitrate and 5.8 parts of polyvinylpyrrolidone are added thereto in sequence. After being uniformly mixed under the protection of argon at a stirring rate of 490 rpm, the temperature is raised to 69 °C at a rate of 2.9 °C / min and this temperature is maintained. Under the condition of pH 4.6, a glycol solution containing 0.95 parts of ascorbic acid or 0.16 parts of sodium borohydride is slowly added at a dropping rate of 0.95 mL / min. The reaction is carried out at a constant temperature for 39 min so that the tin-bismuth alloy layer is coated on the surface of the silver core in a co-reduction manner. After the reaction is completed, centrifugal separation is carried out at a centrifugal rate of 9200 rpm to discard the supernatant and retain the solid-phase product. It is ultrasonically washed twice with 7.2 parts of absolute ethanol to remove the unreacted chloride ions and nitrate residues. Subsequently, it is vacuum-dried at 46 °C for 3.6 h to obtain the silver nanoparticles coated with tin-bismuth alloy.

[0046] The preparation method of the silver nanoparticles in this embodiment is as follows: by weight, 1.5 parts of silver nitrate is dissolved in a mixed solvent composed of 36 parts of deionized water and 36 parts of ethanol. 16 parts of polyvinylpyrrolidone is added as a surface stabilizer. Under the condition that the stirring rate is 390 rpm, the temperature of the reaction system is maintained at 3 °C. A glycol solution containing 0.29 parts of sodium borohydride in 6.5 parts is added dropwise at a dropping rate of 0.95 mL / min for a reduction reaction. The reaction time is 16 min to reduce silver ions to silver nanoparticles with a particle size of 38 nm. After the reaction is completed, centrifugal separation is carried out at a centrifugal rate of 9200 rpm to retain the precipitate and discard the supernatant containing unreacted ions and by-products. Ethanol in 26 parts is used for ultrasonic washing twice to remove the residual nitrate ions and free surfactants. Finally, it is vacuum-dried at 36 °C for 1.6 h to obtain uniformly dispersed silver nanoparticles.

[0047] The organic active agent in this embodiment is azelaic acid;

[0048] The dispersant in this embodiment is a mixture of PVP and polyethylene glycol with a mass ratio of 1:1.3.

[0049] The preparation method of a non-ferrous metal solder for low-temperature soldering in this embodiment includes the following steps:

[0050] S1. Under the protection of a nitrogen atmosphere, carbon-coated copper nanorods and silver nanoparticles coated with tin-bismuth alloy are jointly added to a mixing container according to a preset ratio. Mechanical stirring is carried out at 260 rpm, the temperature is 26 °C, and the mixing time is 26 min. Then, 2-mercaptobenzimidazole, an organic active agent and a dispersant are added in sequence, and stirring is continued at 390 rpm for 20 min to form a stable composite system;

[0051] S2. Add rosin resin, hydroxyethyl cellulose, and 1-ethyl-3-methylimidazolium tetrafluoroborate. The mixing temperature is 39 °C, the mixing rate is 590 rpm, and the mixing time is 35 min. Then add indium nitrate and citric acid, and continue mixing for 13 min;

[0052] S3. Load the mixture into a hot pressing mold. Control the pressing temperature within 46 °C, the pressure is 16 MPa, and keep the pressure for 1.6 min to form a strip solder;

[0053] S4. Conduct low-temperature heat treatment at 66 °C in an inert atmosphere, keep the temperature for 26 min, and perform cutting and vacuum packaging after cooling to obtain the final strip solder product.

[0054] From Figure 1 It can be seen that the copper nanorods prepared in Example 1 exhibit a typical one-dimensional rod-like structure with uniform length, good dispersion, a high aspect ratio, and meet the structural requirements for constructing a conductive path; Figure 2 The XRD phase analysis shows that the copper nanorods have obvious diffraction peaks of metallic copper, indicating that their crystal structure is complete and there are no obvious impurity phases. Figure 3 Furthermore, it shows that after the carbon coating treatment, a uniform and continuous carbon layer coating structure is formed on the surface of the copper nanorods, and no agglomeration or breakage is observed, indicating that the coating process is stable and controllable, which helps to improve its antioxidant performance; Figure 4 The XRD analysis of the carbon-coated copper nanorods shows that in addition to retaining the crystal plane characteristics of metallic copper, weak carbon peak signals also appear, verifying the existence of the carbon layer and that it does not interfere with the crystal structure of copper. Figure 5 The line scan elemental distribution map of the tin-bismuth alloy-coated silver nanoparticles is shown. The results show that the silver core particles are uniformly coated with tin and bismuth elements on the outside, and no elemental segregation or stratification is observed, indicating that the alloy coating layer is continuous and dense, and the interface bonding is good. In summary, the copper nanorods prepared by the present invention have regular structures, uniform carbon coatings, and complete silver nanoparticle coatings. The structural and phase analysis results jointly verify the construction quality of the key components of the solder, providing a structural basis for subsequent excellent welding performance.

[0055] Example 2

[0056] A non-ferrous metal solder for low-temperature brazing, comprising the following raw materials in parts by weight: 14 parts of carbon-coated copper nanorods, 69 parts of tin-bismuth alloy-coated silver nanoparticles, 1.8 parts of 2-mercaptobenzimidazole, 7.2 parts of rosin resin, 2.1 parts of organic activator, 2.8 parts of dispersant, 12.4 parts of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1.3 parts of hydroxyethyl cellulose, 0.8 part of indium nitrate sintering aid, and 0.2 part of citric acid.

[0057] The carbon-coated copper nanorods are composed of copper nanorods with a continuous carbon layer uniformly coated on the outer surface thereof; the tin-bismuth alloy-coated silver nanoparticles are core-shell structure particles, the core is silver nanoparticles, and the shell is a tin-bismuth alloy layer coated on the outer surface thereof;

[0058] The average diameter of the carbon-coated copper nanorods is 71 nm, the aspect ratio is 6, and the average thickness of the carbon layer is 4.5 nm;

[0059] The preparation method of the carbon-coated copper nanorods in this example is as follows: by weight, 1.2 parts of copper nanorods, 0.8 parts of glucose, 0.4 parts of polyvinylpyrrolidone, and 0.2 parts of 50 wt.% hydrochloric acid are sequentially added to 3.6 parts of deionized water, and a homogeneous suspension is formed by stirring at a rate of 390 rpm under argon protection. It is transferred to a polytetrafluoroethylene-lined autoclave with a volume of 65 mL and sealed, heated to 172 °C at a rate of 3 °C / min for a hydrothermal reaction for 5 h. After the reaction is terminated, the liquid phase components are removed by centrifugation at a rate of 9200 rpm, and the solid-phase copper-glucose complex is retained. It is washed 4 times with 3.6 parts of absolute ethanol to remove unreacted glucose and dispersant, and vacuum dried at 66 °C for 3 h to obtain a precursor; the precursor is evenly spread in an alumina crucible and placed in the constant temperature zone of a tube furnace. A hydrogen mixed gas with a volume fraction of 3.9% carried by argon is introduced with a flow rate of 69 mL / min, heated to 830 °C at a rate of 6.5 °C / min for carbonization treatment for 1.6 h to pyrolyze glucose to form a carbon coating layer, and then cooled to 46 °C at a natural cooling rate and then switched to argon protection to finally obtain carbon-coated copper nanorods.

[0060] The preparation method of the copper nanorods in this example is as follows: Dissolve 1.2 parts of copper nitrate in ethanol to prepare a 0.5 M copper nitrate ethanol solution, dissolve 9.2 parts of sodium hydroxide in deionized water to prepare a 4.6 M sodium hydroxide aqueous solution. Mix the copper nitrate ethanol solution and the sodium hydroxide aqueous solution according to a volume ratio of 1:9.2, then transfer the mixture to a polytetrafluoroethylene-lined stainless steel autoclave and seal it. Carry out a hydrothermal reaction at 138 °C for 96 min. After the reaction is completed, naturally cool it to 26.5 °C. Vacuum filter through a polyethersulfone membrane with a pore size of 0.29 μm to retain the solid-phase product. Wash it 4 times with deionized water and 2 times with absolute ethanol in sequence to remove residual nitrate ions and sodium ions. Then, dry it in vacuum at 78 °C for 2.6 h to obtain a copper oxide nanorod precursor. Place the copper oxide nanorod precursor in a quartz boat with a length of 4.6 cm, place the quartz boat in the middle of a quartz tube reactor with an inner diameter of 1.2 cm, introduce a hydrogen gas flow with a volume concentration of 3.8% carried by argon at a flow rate of 65 mL / min, heat it to 230 °C at a heating rate of 6.5 °C / min and keep it at a constant temperature for 56 min to complete the reduction reaction of copper oxide nanorods to copper nanorods. After the reduction is completed, maintain the hydrogen gas flow rate and naturally cool it to 33 °C, then switch to an argon protection atmosphere to finally obtain copper nanorods.

[0061] The average thickness of the tin-bismuth alloy layer in this example is 11 nm; the mass ratio of tin to bismuth in the tin-bismuth alloy layer is 42:58; the average diameter of the silver nanoparticles is 20 nm.

[0062] The preparation method of the tin-bismuth alloy-coated silver nanoparticles in this example is as follows: By weight, disperse 1.0 part of silver nanoparticles in 8.0 parts of ethylene glycol to form a homogeneous dispersion system. Sequentially add 0.8 part of stannous chloride, 1.2 parts of bismuth nitrate, and 4.0 parts of polyvinylpyrrolidone thereto. After mixing evenly under argon protection at a stirring rate of 400 rpm, heat it to 60 °C at a rate of 2 °C / min and maintain this temperature. Under the condition of pH = 4.0, slowly add 0.5 part of ascorbic acid or 0.1 part of sodium borohydride in ethylene glycol solution dropwise at a dropping rate of 0.5 mL / min. React at a constant temperature for 30 min to coat the tin-bismuth alloy layer on the surface of the silver core in a co-reduction manner. After the reaction is completed, centrifuge and separate at a centrifugation rate of 8000 rpm, discard the supernatant, and retain the solid-phase product. Wash it ultrasonically 2 times with 6.0 parts of absolute ethanol in sequence to remove unreacted chloride ions and nitrate residues. Then, dry it in vacuum at 40 °C for 3 h to obtain tin-bismuth alloy-coated silver nanoparticles.

[0063] The preparation method of the silver nanoparticles in this embodiment is as follows: By weight, 1.0 part of silver nitrate is dissolved in a mixed solvent composed of 30 parts of deionized water and 30 parts of ethanol. 10 parts of polyvinylpyrrolidone is added as a surface stabilizer. The temperature of the reaction system is maintained at 0 °C under the condition that the stirring rate is 300 rpm. A 5.0 - part ethanol solution containing 0.2 part of sodium borohydride is added dropwise at a dropping rate of 0.5 mL / min for a reduction reaction. The reaction time is 10 min to reduce silver ions to silver nanoparticles with a particle size of 20 nm. After the reaction, centrifugal separation is carried out at a centrifugal rate of 8000 rpm to retain the precipitate and discard the supernatant containing unreacted ions and by - products. 20 parts of ethanol is used for ultrasonic washing in 2 times to remove residual nitrate ions and free surfactants. Finally, vacuum drying is carried out at 30 °C for 1 h to obtain uniformly dispersed silver nanoparticles.

[0064] The organic active agent in this embodiment is malic acid;

[0065] The dispersant in this embodiment is a mixture of PVP and polyethylene glycol with a mass ratio of 1:1.0.

[0066] The preparation method of a non - ferrous metal solder for low - temperature soldering in this embodiment includes the following steps:

[0067] S1. Under a nitrogen - protection atmosphere, carbon - coated copper nanorods and tin - bismuth alloy - coated silver nanoparticles are jointly added to a mixing container according to a preset ratio. Mechanical stirring is carried out at 200 rpm, the temperature is 20 °C, and the mixing time is 20 min. Subsequently, 2 - mercaptobenzimidazole, the organic active agent, and the dispersant are added in sequence, and stirring is continued at 300 rpm for 15 min to form a stable composite system;

[0068] S2. Rosin resin, hydroxyethyl cellulose, and 1 - ethyl - 3 - methylimidazolium tetrafluoroborate are added. The mixing temperature is 30 °C, the mixing rate is 500 rpm, and the mixing time is 30 min. Subsequently, indium nitrate and citric acid are added, and mixing is continued for 10 min;

[0069] S3. The mixture is filled into a hot - pressing mold. The pressing temperature is controlled within 40 °C, the pressure is 10 MPa, and the pressure is maintained for 1 min to form a strip - shaped solder;

[0070] S4. In an inert atmosphere, low - temperature heat treatment is carried out at 60 °C for 20 min of heat preservation. After cooling, cutting and vacuum packaging are carried out to obtain the final strip - shaped solder product.

[0071] Example 3

[0072] A non-ferrous metal solder for low-temperature brazing, comprising the following raw materials in parts by weight: 16 parts of carbon-coated copper nanorods, 78 parts of tin-bismuth alloy-coated silver nanoparticles, 2.1 parts of 2-mercaptobenzimidazole, 8.4 parts of rosin resin, 2.7 parts of organic activator, 3.5 parts of dispersant, 14.8 parts of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1.6 parts of hydroxyethyl cellulose, 1.1 parts of indium nitrate sintering aid, and 0.2 parts of citric acid.

[0073] The carbon-coated copper nanorods are composed of copper nanorods with a continuous carbon layer uniformly coated on the outer surface of the copper nanorods; the tin-bismuth alloy-coated silver nanoparticles are core-shell structure particles, the core is silver nanoparticles, and the shell is a tin-bismuth alloy layer coated on its outer surface;

[0074] The average diameter of the carbon-coated copper nanorods is 92 nm, the aspect ratio is 8, and the average thickness of the carbon layer is 6.0 nm;

[0075] The preparation method of the carbon-coated copper nanorods in this example is as follows: in parts by weight, 1.3 parts of copper nanorods, 1.1 parts of glucose, 0.6 parts of polyvinylpyrrolidone, and 0.2 parts of 50 wt.% hydrochloric acid are sequentially added to 4.2 parts of deionized water, and mixed under argon protection at a stirring rate of 480 rpm to form a homogeneous suspension. It is transferred to a polytetrafluoroethylene-lined autoclave with a volume of 80 mL and sealed, heated to 184 °C at a rate of 4 °C / min for hydrothermal reaction for 6 h. After the reaction is terminated, the liquid phase components are removed by centrifugation at a centrifugation rate of 10400 rpm, and the solid-phase copper-glucose complex is retained. It is washed 4 times with 4.2 parts of absolute ethanol to remove unreacted glucose and dispersant, and vacuum-dried at 72 °C for 3 h to obtain a precursor; the precursor is evenly spread in an alumina crucible and placed in the constant temperature zone of a tube furnace. A hydrogen mixed gas with a volume fraction of 4.0% carried by argon is introduced with a flow rate of 78 mL / min, heated to 860 °C at a rate of 8 °C / min for carbonization treatment for 2.2 h to pyrolyze glucose to form a carbon coating layer, and then cooled to 52 °C at a natural cooling rate and then switched to argon protection to finally obtain carbon-coated copper nanorods.

[0076] The preparation method of the copper nanorods in this embodiment is as follows: Dissolve 1.3 parts of copper nitrate in ethanol to prepare a 0.5 M copper nitrate ethanol solution, dissolve 10.4 parts of sodium hydroxide in deionized water to prepare a 5.2 M sodium hydroxide aqueous solution, mix the copper nitrate ethanol solution and the sodium hydroxide aqueous solution according to a volume ratio of 1:10.4, transfer the mixture to a polytetrafluoroethylene-lined stainless steel autoclave for sealing, carry out a hydrothermal reaction at 156 °C for 132 min, naturally cool to 28 °C after the reaction, vacuum filter through a polyethersulfone membrane with a pore size of 0.36 μm to retain the solid-phase product, wash with deionized water 4 times and anhydrous ethanol 3 times in sequence to remove residual nitrate ions and sodium ions, and then vacuum dry at 81 °C for 3.2 h to obtain a copper oxide nanorod precursor; Place the copper oxide nanorod precursor in a quartz boat with a length of 5.2 cm, place the quartz boat in the middle of a quartz tube reactor with an inner diameter of 1.3 cm, introduce a hydrogen gas stream with a volume concentration of 4.1% carried by argon at a flow rate of 80 mL / min, heat to 260 °C at a heating rate of 8 °C / min and keep it constant for 62 min to complete the reduction reaction of copper oxide nanorods to copper nanorods, maintain the hydrogen gas flow rate after the reduction and naturally cool to 36 °C, then switch to an argon protective atmosphere, and finally obtain copper nanorods.

[0077] The average thickness of the tin-bismuth alloy layer in this embodiment is 30 nm; the mass ratio of tin to bismuth in the tin-bismuth alloy layer is 50:50; the average diameter of the silver nanoparticles is 80 nm.

[0078] The preparation method of the tin-bismuth alloy-coated silver nanoparticles in this embodiment is as follows: By weight, disperse 3.0 parts of silver nanoparticles in 15.0 parts of ethylene glycol to form a homogeneous dispersion system, sequentially add 2.5 parts of stannous chloride, 3.0 parts of bismuth nitrate and 10.0 parts of polyvinylpyrrolidone thereto, mix evenly under argon protection at a stirring rate of 700 rpm, then heat to 90 °C at a rate of 5 °C / min and maintain this temperature, slowly add a 2.0 mL / min dropping rate of 2.0 parts of ascorbic acid or 0.3 part of sodium borohydride in an ethylene glycol solution at a pH of 6.0, react at a constant temperature for 60 min to coat the tin-bismuth alloy layer on the surface of the silver core in a co-reduction manner, after the reaction is completed, centrifuge at a centrifugation rate of 12,000 rpm to discard the supernatant and retain the solid-phase product, wash ultrasonically with 10.0 parts of anhydrous ethanol 3 times to remove unreacted chloride ions and residual nitrate, and then vacuum dry at 60 °C for 5 h to obtain tin-bismuth alloy-coated silver nanoparticles.

[0079] The preparation method of silver nanoparticles in this embodiment is as follows: By weight, 2.5 parts of silver nitrate are dissolved in a mixed solvent composed of 50 parts of deionized water and 50 parts of ethanol. 30 parts of polyvinylpyrrolidone are added as a surface stabilizer. While maintaining the reaction system temperature at 10 °C under the condition that the stirring rate is 600 rpm, a 10.0 - part ethanol solution of 0.5 part of sodium borohydride is added dropwise at a dropping rate of 2.0 mL / min for a reduction reaction. The reaction time is 30 min to reduce silver ions to silver nanoparticles with a particle size of 80 nm. After the reaction, centrifugal separation is carried out at a centrifugal rate of 12000 rpm to retain the precipitate and discard the supernatant containing unreacted ions and by - products. 40 parts of ethanol are used to wash ultrasonically 3 times to remove residual nitrate ions and free surfactants. Finally, vacuum drying is carried out at 50 °C for 3 h to obtain uniformly dispersed silver nanoparticles.

[0080] The organic active agent in this embodiment is azelaic acid;

[0081] The dispersant in this embodiment is a mixture of PVP and polyethylene glycol with a mass ratio of 1:2.0.

[0082] The preparation method of a non - ferrous metal solder for low - temperature soldering in this embodiment includes the following steps:

[0083] S1. Under a nitrogen - protected atmosphere, carbon - coated copper nanorods and tin - bismuth alloy - coated silver nanoparticles are jointly added to a mixing container according to a preset ratio. Mechanical stirring is carried out at 400 rpm, the temperature is 40 °C, and the mixing time is 40 min. Subsequently, 2 - mercaptobenzimidazole, the organic active agent, and the dispersant are added in sequence, and stirring is continued at 600 rpm for 30 min to form a stable composite system;

[0084] S2. Rosin resin, hydroxyethyl cellulose, and 1 - ethyl - 3 - methylimidazolium tetrafluoroborate are added. The mixing temperature is 60 °C, the mixing rate is 800 rpm, and the mixing time is 45 min. Subsequently, indium nitrate and citric acid are added, and mixing is continued for 20 min;

[0085] S3. The mixture is filled into a hot - pressing mold, the pressing temperature is controlled within 60 °C, the pressure is 30 MPa, and the pressure is maintained for 3 min to form a strip - shaped solder;

[0086] S4. In an inert atmosphere, low - temperature heat treatment is carried out at 80 °C for 40 min. After cooling, cutting and vacuum packaging are carried out to obtain the final strip - shaped solder product.

[0087] Example 4

[0088] A non-ferrous metal solder for low-temperature brazing, comprising the following raw materials in parts by weight: 18.0 parts of carbon-coated copper nanorods, 90.0 parts of tin-bismuth alloy-coated silver nanoparticles, 2.5 parts of 2-mercaptobenzimidazole, 10.0 parts of rosin resin, 3.5 parts of organic activator, 4.5 parts of dispersant, 18.0 parts of 1-ethyl-3-methylimidazolium tetrafluoroborate, 2.0 parts of hydroxyethyl cellulose, 1.5 parts of indium nitrate sintering aid, and 0.3 part of citric acid.

[0089] The carbon-coated copper nanorods are composed of copper nanorods with a continuous carbon layer uniformly coated on the outer surface of the copper nanorods; the tin-bismuth alloy-coated silver nanoparticles are core-shell structure particles, the core is silver nanoparticles, and the shell is a tin-bismuth alloy layer coated on its outer surface;

[0090] The average diameter of the carbon-coated copper nanorods is 120 nm, the aspect ratio is 10, and the average thickness of the carbon layer is 8.0 nm;

[0091] The preparation method of the carbon-coated copper nanorods in this example is as follows: in parts by weight, 1.5 parts of copper nanorods, 1.5 parts of glucose, 0.8 part of polyvinylpyrrolidone, and 0.3 part of 50 wt.% hydrochloric acid are sequentially added to 5.0 parts of deionized water, and mixed under argon protection at a stirring rate of 600 rpm to form a homogeneous suspension. The suspension is transferred to a polytetrafluoroethylene-lined autoclave with a volume of 100 mL and sealed, heated to 200 °C at a rate of 5 °C / min for hydrothermal reaction for 8 h. After the reaction is terminated, the liquid phase components are removed by centrifugation at a centrifugation rate of 12,000 rpm, and the solid-phase copper-glucose complex is retained. It is washed 5 times with 5.0 parts of absolute ethanol to remove unreacted glucose and dispersant, and vacuum-dried at 80 °C for 4 h to obtain a precursor; the precursor is evenly spread in an alumina crucible and placed in the constant temperature zone of a tube furnace. A hydrogen mixed gas with a volume fraction of 4.2% carried by argon is introduced with a flow rate of 90 mL / min, heated to 900 °C at a rate of 10 °C / min for carbonization treatment for 3 h to pyrolyze glucose to form a carbon coating layer, and then cooled to 60 °C at a natural cooling rate and switched to argon protection to finally obtain carbon-coated copper nanorods.

[0092] The preparation method of the copper nanorods in this embodiment is as follows: Dissolve 1.5 parts of copper nitrate in ethanol to prepare a 0.6 M copper nitrate ethanol solution, dissolve 12.0 parts of sodium hydroxide in deionized water to prepare a 6.0 M sodium hydroxide aqueous solution, mix the copper nitrate ethanol solution and the sodium hydroxide aqueous solution at a volume ratio of 1:12, transfer the mixture to a polytetrafluoroethylene-lined stainless steel autoclave for sealing, carry out a hydrothermal reaction at 180 °C for 180 min, naturally cool to 30 °C after the reaction, retain the solid-phase product by vacuum filtration through a polyethersulfone membrane with a pore size of 0.45 μm, wash with deionized water 5 times and anhydrous ethanol 3 times in sequence to remove residual nitrate ions and sodium ions, and then dry in vacuum at 85 °C for 4.0 h to obtain a copper oxide nanorod precursor; Place the copper oxide nanorod precursor in a quartz boat with a length of 6.0 cm, place the quartz boat in the middle of a quartz tube reactor with an inner diameter of 1.5 cm, introduce a hydrogen gas flow with a volume concentration of 4.5% carried by argon at a flow rate of 100 mL / min, heat to 300 °C at a heating rate of 10 °C / min and keep the temperature constant for 70 min to complete the reduction reaction of copper oxide nanorods to copper nanorods, maintain the hydrogen gas flow rate after the reduction and naturally cool to 40 °C, then switch to an argon protection atmosphere, and finally obtain copper nanorods.

[0093] The average thickness of the tin-bismuth alloy layer in this embodiment is 22 nm; the mass ratio of tin to bismuth in the tin-bismuth alloy layer is 47:53; the average diameter of the silver nanoparticles is 56 nm.

[0094] The preparation method of the tin-bismuth alloy-coated silver nanoparticles in this embodiment is as follows: By weight, disperse 2.2 parts of silver nanoparticles in 12.2 parts of ethylene glycol to form a homogeneous dispersion system, sequentially add 1.8 parts of stannous chloride, 2.3 parts of bismuth nitrate and 7.6 parts of polyvinylpyrrolidone thereto, mix evenly under argon protection at a stirring rate of 580 rpm, then heat to 78 °C at a rate of 3.8 °C / min and maintain this temperature, slowly add a 1.4 parts of ascorbic acid or 0.22 parts of sodium borohydride in ethylene glycol solution dropwise at a dropping rate of 1.4 mL / min under the condition of pH 5.2, carry out a constant-temperature reaction for 48 min to coat the tin-bismuth alloy layer on the surface of the silver core by a co-reduction method, after the reaction is completed, centrifuge and separate at a centrifugation rate of 10400 rpm, discard the supernatant and retain the solid-phase product, wash ultrasonically with 8.4 parts of anhydrous ethanol 3 times to remove unreacted chloride ions and nitrate residues, and then dry in vacuum at 52 °C for 4.2 h to obtain tin-bismuth alloy-coated silver nanoparticles.

[0095] The preparation method of the silver nanoparticles in this embodiment is as follows: By weight, 1.9 parts of silver nitrate are dissolved in a mixed solvent composed of 42 parts of deionized water and 42 parts of ethanol. 22 parts of polyvinylpyrrolidone are added as a surface stabilizer. The temperature of the reaction system is maintained at 6 °C under the condition that the stirring rate is 480 rpm. An ethanol solution of 8.0 parts containing 0.38 parts of sodium borohydride is added dropwise at a dropping rate of 1.4 mL / min for a reduction reaction. The reaction time is 22 min to reduce silver ions to silver nanoparticles with a particle size of 56 nm. After the reaction, centrifugal separation is carried out at a centrifugal rate of 10400 rpm to retain the precipitate and discard the supernatant containing unreacted ions and by-products. 32 parts of ethanol are used for ultrasonic washing in 3 times to remove residual nitrate ions and free surfactants. Finally, vacuum drying is carried out at 42 °C for 2.2 h to obtain uniformly dispersed silver nanoparticles.

[0096] The organic active agent in this embodiment is azelaic acid;

[0097] The dispersant in this embodiment is a mixture of PVP and polyethylene glycol with a mass ratio of 1:1.6.

[0098] The preparation method of a non-ferrous metal solder for low-temperature soldering in this embodiment includes the following steps:

[0099] S1. Under a nitrogen protection atmosphere, carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles are jointly added to a mixing container according to a preset ratio. Mechanical stirring is carried out at 320 rpm, a temperature of 32 °C, and a mixing time of 32 min. Subsequently, 2-mercaptobenzimidazole, an organic active agent, and a dispersant are added in sequence, and stirring is continued at 480 rpm for 24 min to form a stable composite system;

[0100] S2. Rosin resin, hydroxyethyl cellulose, and 1-ethyl-3-methylimidazolium tetrafluoroborate are added. The mixing temperature is 48 °C, the mixing rate is 680 rpm, and the mixing time is 39 min. Subsequently, indium nitrate and citric acid are added, and mixing is continued for 16 min;

[0101] S3. The mixture is filled into a hot pressing mold, the pressing temperature is controlled within 52 °C, the pressure is 22 MPa, and the pressure is maintained for 2.2 min to form a strip-shaped solder;

[0102] S4. In an inert atmosphere, low-temperature heat treatment is carried out at 72 °C, the heat preservation time is 32 min, and after cooling, cutting and vacuum packaging are carried out to obtain the final strip-shaped solder product.

[0103] Comparative Example 1

[0104] It is basically the same as Example 1, except that: the dosage of carbon-coated copper nanorods is adjusted to 10.0 parts.

[0105] Comparative Example 2

[0106] Basically the same as Example 1, except that the dosage of tin-bismuth alloy-coated silver nanoparticles is adjusted to 95.0 parts.

[0107] Comparative Example 3

[0108] Basically the same as Example 1, except that the carbon layer thickness of carbon-coated copper nanorods is adjusted to 2.0 nm, resulting in insufficient antioxidant ability and increased oxidation of copper nanorods at high temperatures.

[0109] Comparative Example 4

[0110] Basically the same as Example 1, except that the hydrothermal reaction temperature of carbon-coated copper nanorods is adjusted to 150 °C, resulting in a loose carbon layer structure.

[0111] Comparative Example 5

[0112] Basically the same as Example 1, except that the concentration of copper nitrate ethanol solution in the preparation of copper nanorods is adjusted to 0.3 M, and the aspect ratio of copper nanorods is <4, resulting in the failure of electrical conductivity anisotropy.

[0113] Comparative Example 6

[0114] Basically the same as Example 1, except that the mass ratio of tin to bismuth in tin-bismuth alloy-coated silver nanoparticles is adjusted to 40:60, resulting in an offset of the eutectic point and an increase in the melting temperature.

[0115] Comparative Example 7

[0116] Basically the same as Example 1, except that the dosage of sodium borohydride in the preparation of silver nanoparticles is adjusted to 0.1 part, resulting in insufficient reduction, silver particle size >80 nm, and uneven alloy coating layer.

[0117] Comparative Example 8

[0118] Basically the same as Example 1, except that the pH value of the tin-bismuth alloy coating process is adjusted to 3.0, resulting in too fast co-reduction rate of tin and bismuth and cracks in the alloy layer.

[0119] Comparative Example 9

[0120] Basically the same as Example 1, except that the organic active agent is replaced with citric acid, resulting in too strong acidity and premature decomposition of rosin resin, and abnormal increase in the viscosity of the solder.

[0121] Comparative Example 10

[0122] Basically the same as Example 1, except that the mass ratio of PVP to polyethylene glycol in the dispersant is adjusted to 1:3, resulting in deteriorated compatibility of the dispersant and increased agglomeration of nanoparticles.

[0123] Comparative Example 11

[0124] Basically the same as Example 1, except that: the solder pressing pressure is adjusted to 5 MPa, and the porosity inside the strip solder increases.

[0125] Comparative Example 12

[0126] Basically the same as Example 1, except that: the stirring rate in the mixing step S1 is adjusted to 100 rpm, the carbon-coated copper nanorods and silver particles are unevenly dispersed, and the conductivity decreases.

[0127] Comparative Example 13

[0128] Basically the same as Example 1, except that: the low-temperature heat treatment temperature is adjusted to 90 °C (higher than 60 - 80 °C in Claim 9), the hydroxyethyl cellulose thermally decomposes, and the toughness of the solder decreases.

[0129] Comparative Example 14

[0130] Basically the same as Example 1, except that the surface of the copper nanorods is not coated with a carbon layer.

[0131] Comparative Example 15

[0132] Basically the same as Example 1, except that the tin-bismuth layer is not prepared on the surface of the silver nanoparticles.

[0133] Performance Test:

[0134] Interface bonding strength of the solder joints: Referring to the IPC-SM-840 standard, solder (thickness 100 μm) is applied on a pretreated oxygen-free copper plate (size 10 mm × 10 mm), preheated at 50 °C for 60 seconds and then welded at 70 ± 5 °C for 90 seconds (nitrogen protection), and then a pressure of 15 MPa is applied and held for 2 minutes. Copper-copper lap specimens (3 mm × 3 mm) are prepared according to ASTM D1002, and loaded to fracture at 1 mm / min through a universal testing machine to test the interfacial metallurgical bonding strength.

[0135] Conductive performance after welding: The solder (thickness 100 μm) is coated on a nickel-plated flexible substrate by the drop method, preheated at 50 °C for 60 seconds and then welded at 70 ± 5 °C (nitrogen flow rate 0.5 L / min). A constant current of 10 mA is applied by the four-probe method to measure the resistivity of the solder joints, and the local temperature rise (ΔT ≤ 5 °C) is detected simultaneously using an infrared thermal imager, and the conductive stability is verified by combining the circuit on-off test.

[0136] Wettability and forming quality of the solder joints: The solder (thickness 100 μm) is scraped on an oxygen-free copper plate, heated at 70 ± 5 °C for 90 seconds, and then the spreading area and wetting angle are quantified by an optical profiler, the internal porosity is detected by X-ray flaw detection, and the surface roughness (Ra ≤ 0.5 μm) is analyzed by a laser confocal microscope to ensure the forming density of the low-temperature welding.

[0137] Solder Melting Point and Melting Behavior Test: The differential scanning calorimetry (DSC) was used to measure the initial melting temperature, peak temperature and heat of fusion of the solder, and analyze its low-temperature soldering ability.

[0138] Reliability Test after Soldering: The thermocompression soldering specimens (pressurized at 15 MPa for 2 minutes) were subjected to the JEDEC JESD22-A104 standard thermal cycle (-55 to 125 °C, 1000 cycles). The SAM detected that the interface delamination rate ≤ 5%, and a current density of 1×10 4 A / cm 2 was applied for 500 hours. The resistance change rate was measured, and the SEM was used to observe the microscopic void expansion trend to comprehensively evaluate the solder joint's ability to resist thermo-electro coupling failure.

[0139] The properties of the solders in Examples 1-4 and Comparative Examples 1-15 are summarized in Table 1.

[0140] Table 1 Summary of the Properties of the Solders in Examples 1-4 and Comparative Examples 1-15

[0141]

[0142]

[0143] As can be seen from Table 1, the solder properties are synergistically affected by the ratio of multiple raw materials and process parameters. Among them, the amount of carbon-coated copper nanorods plays an important role in the construction of the conductive network. Excessive amount (such as 10.0 parts) is easy to cause nanorod agglomeration, increase solder joint resistance and weaken interface bonding strength; if the ratio of tin-bismuth alloy coated silver nanoparticles is too high (such as 95.0 parts), it is beneficial to maintain conductivity, but it may dilute the enhancement effect of the copper rod network; insufficient carbon layer thickness (such as 2.0nm) or loose carbon layer structure (such as too high hydrothermal temperature) will weaken the copper nanorods. The oxidation resistance of the rods. Copper is easily oxidized during high-temperature welding, resulting in a significant decrease in conductivity and interface bonding. If the aspect ratio of the copper nanorods is too small (<4), its one-dimensional conductive properties will be destroyed, resulting in conductive anisotropy failure and a significant increase in solder joint resistance. If the tin-bismuth mass ratio deviates from the eutectic composition (such as 40:60), the melting point will increase, affecting the adaptability and reliability of low-temperature welding. If the silver particle size is too large or the coating is uneven (such as insufficient reduction), the wettability and interface formation will deteriorate. If the pH of the tin-bismuth coating process is too low (such as 3.0), the alloy layer will be quickly reduced. Cracks will appear, weakening the metallurgical bonding; if strong acidic substances such as citric acid are used as organic surfactants, the thermal decomposition of rosin resin will be accelerated, resulting in an abnormal increase in solder viscosity and affecting wetting and spreading; an imbalance in the ratio of PVP and polyethylene glycol in the dispersant will reduce the compatibility of the system, causing nanoparticles to agglomerate and form local conductive dead zones; insufficient solder pressing pressure (such as 5MPa) will easily form internal pores, reducing the density and strength of the solder joint; too low a stirring rate (such as 100rpm) will cause uneven dispersion of copper rods and silver particles, discontinuous conductivity paths, and overall reduced solder joint performance If the heat treatment temperature exceeds a reasonable range (such as 90°C), additives such as hydroxyethyl cellulose will decompose, affecting the toughness and forming stability of the solder. If the surface of the copper nanorods is not coated with a carbon layer, they are easily oxidized during welding, seriously damaging the conductivity and bonding strength. If the silver particles do not form a tin-bismuth alloy coating, the wettability and interface alloying ability are insufficient, the solder joint morphology is poor, and the reliability is significantly reduced. The above factors interact with each other to jointly determine the conductivity, interface bonding performance, wetting and forming ability, and long-term service reliability of the solder during low-temperature welding.

[0144] 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 it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that all equivalent structural changes made under the concept of the present invention and using the contents of the present invention specification and drawings should be covered within the scope of protection of the claims of the present invention.

Claims

1. A non-ferrous metal solder for low-temperature brazing, characterized in that, It comprises raw materials in the following parts by weight: 12.0 - 18.0 parts of carbon-coated copper nanorods, 60.0 - 90.0 parts of tin-bismuth alloy-coated silver nanoparticles, 1.5 - 2.5 parts of 2-mercaptobenzimidazole, 6.0 - 10.0 parts of rosin resin, 1.5 - 3.5 parts of organic activator, 2.0 - 4.5 parts of dispersant, 10.0 - 18.0 parts of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1.0 - 2.0 parts of hydroxyethyl cellulose, 0.5 - 1.5 parts of indium nitrate sintering aid, and 0.1 - 0.3 parts of citric acid; The carbon-coated copper nanorods are composed of copper nanorods with a continuous carbon layer uniformly coated on the outer surface of the copper nanorods; The tin-bismuth alloy-coated silver nanoparticles are core-shell structure particles, the core is silver nanoparticles, and the shell is a tin-bismuth alloy layer coated on its outer surface.

2. The non-ferrous metal solder for cryogenic brazing according to claim 1, characterized in that, The average diameter of the carbon-coated copper nanorods is 50 - 120 nm, the aspect ratio is 4 - 10, and the average thickness of the carbon layer is 3.0 - 8.0 nm.

3. A non-ferrous metal solder for low-temperature brazing according to claim 1, characterized in that, The average thickness of the tin-bismuth alloy layer is 11 - 30 nm; the mass ratio of tin to bismuth in the tin-bismuth alloy layer is (42 - 50):(50 - 58); The average diameter of the silver nanoparticles is 20 - 80 nm.

4. A non-ferrous metal solder for low-temperature brazing according to claim 1, characterized in that, The preparation method of the carbon-coated copper nanorods is as follows: calculated by parts by weight, 1.0 - 1.5 parts of copper nanorods, 0.5 - 1.5 parts of glucose, 0.2 - 0.8 parts of polyvinylpyrrolidone, and 0.1 - 0.3 parts of 50 wt.% hydrochloric acid are successively added to 3.0 - 5.0 parts of deionized water, and a homogeneous suspension is formed by mixing at a stirring rate of 300 - 600 rpm under argon protection. Then it is transferred to a polytetrafluoroethylene-lined autoclave with a volume of 50 - 100 mL and sealed, and heated to 160 - 200 °C at a rate of 2 - 5 °C / min for hydrothermal reaction for 4 - 8 h. After the reaction is terminated, the liquid phase components are removed by centrifugation at a centrifugation rate of 8000 - 12000 rpm, and the solid-phase copper-glucose complex is retained. It is washed 3 - 5 times with 3.0 - 5.0 parts of absolute ethanol to remove unreacted glucose and dispersant, and vacuum dried at 60 - 80 °C for 2 - 4 h to obtain a precursor; the precursor is evenly spread in an alumina crucible and placed in the constant temperature zone of a tube furnace. A hydrogen mixed gas with a volume fraction of 3.8 - 4.2% carried by argon is introduced with a flow rate of 60 - 90 mL / min, and it is heated to 800 - 900 °C at a rate of 5 - 10 °C / min for carbonization treatment for 1 - 3 h to pyrolyze glucose to form a carbon coating layer. Then it is cooled to 40 - 60 °C at a natural cooling rate and then switched to argon protection to finally obtain carbon-coated copper nanorods.

5. A non-ferrous metal solder for low-temperature brazing according to claim 4, characterized in that, The preparation method of the copper nanorods is as follows: Dissolve 1.0 - 1.5 parts of copper nitrate in ethanol to prepare a 0.4 - 0.6 M copper nitrate ethanol solution, dissolve 8.0 - 12.0 parts of sodium hydroxide in deionized water to prepare a 4.0 - 6.0 M sodium hydroxide aqueous solution. Mix the copper nitrate ethanol solution and the sodium hydroxide aqueous solution according to a volume ratio of 1:8 - 1:12, then transfer the mixture to a stainless-steel autoclave with a polytetrafluoroethylene liner and seal it. Carry out a hydrothermal reaction at 120 - 180 °C for 60 - 180 min. After the reaction is completed, naturally cool it to 25 - 30 °C. Vacuum filter through a polyethersulfone membrane with a pore size of 0.22 - 0.45 μm to retain the solid-phase product. Wash it with deionized water 3 - 5 times and anhydrous ethanol 2 - 3 times in sequence to remove residual nitrate ions and sodium ions. Then vacuum dry it at 75 - 85 °C for 2.0 - 4.0 h to obtain a copper oxide nanorod precursor. Place the copper oxide nanorod precursor in a quartz boat with a length of 4.0 - 6.0 cm, place the quartz boat in the middle of a quartz tube reactor with an inner diameter of 1.0 - 1.5 cm, introduce a hydrogen gas flow with a volume concentration of 3.5 - 4.5% carried by argon at a flow rate of 50 - 100 mL / min, heat it to 200 - 300 °C at a heating rate of 5 - 10 °C / min and keep it at a constant temperature for 50 - 70 min to complete the reduction reaction of copper oxide nanorods to copper nanorods. After the reduction is completed, maintain the hydrogen gas flow rate and naturally cool it to 30 - 40 °C, then switch to an argon protection atmosphere to finally obtain copper nanorods.

6. The non-ferrous metal solder for cryogenic brazing according to claim 1, characterized in that The preparation method of the tin-bismuth alloy-coated silver nanoparticles is as follows: By weight, disperse 1.0 - 3.0 parts of silver nanoparticles in 8.0 - 15.0 parts of ethylene glycol to form a homogeneous dispersion system. Sequentially add 0.8 - 2.5 parts of stannous chloride, 1.2 - 3.0 parts of bismuth nitrate, and 4.0 - 10.0 parts of polyvinylpyrrolidone thereto. Under argon protection, mix them evenly at a stirring rate of 400 - 700 rpm, then heat it to 60 - 90 °C at a rate of 2 - 5 °C / min and maintain this temperature. Slowly add 0.5 - 2.0 parts of ascorbic acid or 0.1 - 0.3 parts of sodium borohydride in ethylene glycol solution dropwise at a dropping rate of 0.5 - 2.0 mL / min under the condition of pH 4.0 - 6.

0. React at a constant temperature for 30 - 60 min to coat the tin-bismuth alloy layer on the surface of the silver core in a co-reduction manner. After the reaction is completed, centrifuge and separate at a centrifugation rate of 8000 - 12000 rpm, discard the supernatant, and retain the solid-phase product. Wash it ultrasonically with 6.0 - 10.0 parts of anhydrous ethanol 2 - 3 times to remove unreacted chloride ions and nitrate residues. Then vacuum dry it at 40 - 60 °C for 3 - 5 h to obtain tin-bismuth alloy-coated silver nanoparticles.

7. The method for preparing the silver nanoparticles as described in claim 1 is as follows: by weight, 1.0 - 2.5 parts of silver nitrate are dissolved in a mixed solvent composed of 30 - 50 parts of deionized water and 30 - 50 parts of ethanol. 10 - 30 parts of polyvinylpyrrolidone are added as a surface stabilizer. While maintaining the temperature of the reaction system at 0 - 10 °C under the condition that the stirring rate is 300 - 600 rpm, a 5.0 - 10.0 - part ethanol solution of 0.2 - 0.5 parts of sodium borohydride is added dropwise at a dropping rate of 0.5 - 2.0 mL / min for a reduction reaction. The reaction time is 10 - 30 min to reduce silver ions to silver nanoparticles with a particle size of 20 - 80 nm. After the reaction, centrifugal separation is carried out at a centrifugal rate of 8000 - 12000 rpm to retain the precipitate and discard the supernatant containing unreacted ions and by - products. 20 - 40 parts of ethanol are used to wash the residue by ultrasonic wave in 2 - 3 times to remove residual nitrate ions and free surfactants. Finally, vacuum drying is carried out at 30 - 50 °C for 1 - 3 h to obtain uniformly dispersed silver nanoparticles.

8. A non-ferrous metal solder for low-temperature brazing according to claim 1, characterized in that, The organic active agent is azelaic acid or malic acid; The dispersant is a mixture of PVP and polyethylene glycol with a mass ratio of 1:(1.0 - 2.0).

9. The preparation method of a non-ferrous metal solder for low-temperature brazing according to claim 1, characterized in that, It includes the following steps: S1. Under a nitrogen - protected atmosphere, the carbon - coated copper nanorods and the tin - bismuth - alloy - coated silver nanoparticles are jointly added to a mixing container according to a preset ratio. Mechanical stirring is carried out at 200 - 400 rpm, the temperature is 20 - 40 °C, and the mixing time is 20 - 40 min. Subsequently, 2 - mercaptobenzimidazole, the organic active agent, and the dispersant are added in sequence, and stirring is continued at 300 - 600 rpm for 15 - 30 min to form a stable composite system; S2. Rosin resin, hydroxyethyl cellulose, and 1 - ethyl - 3 - methylimidazolium tetrafluoroborate are added. The mixing temperature is 30 - 60 °C, the mixing rate is 500 - 800 rpm, and the mixing time is 30 - 45 min. Subsequently, indium nitrate and citric acid are added, and mixing is continued for 10 - 20 min; S3. The mixture is filled into a hot - pressing mold. The pressing temperature is controlled within 40 - 60 °C, the pressure is 10 - 30 MPa, and the pressure is maintained for 1 - 3 min to form a strip - shaped solder; S4. In an inert atmosphere, low - temperature heat treatment is carried out at 60 - 80 °C, the heat preservation time is 20 - 40 min, and after cooling, cutting and vacuum packaging are carried out to obtain the final strip - shaped solder product.

10. The application of a non - ferrous metal solder for low - temperature soldering as described in claim 1 in the encapsulation of electronic devices, the heat - dissipation connection of power devices, or the metal interconnection of flexible circuits.

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