Non-ferrous solder for cryogenic brazing and application

Abstract

The application relates to the field of solder materials, and provides a non-ferrous metal solder for low-temperature brazing and application, which is composed of carbon-coated copper nanorods, tin-bismuth alloy-coated silver nanoparticles, 2-mercaptobenzimidazole, rosin resin, an organic active agent, a dispersing agent, an ionic liquid, hydroxyethyl cellulose, indium nitrate and citric acid. The silver particles adopt a core-shell structure, are coated with a tin-bismuth alloy layer, and form a continuous carbon layer on the surface of the copper nanorods, so that the conductivity and interface stability of the solder are effectively improved. Through a step-by-step mixing, hot-pressing and low-temperature heat treatment process, the non-ferrous metal solder with excellent conductivity, a low melting point and good wetting performance is prepared, and is suitable for electronic device packaging, power device connection and flexible circuit interconnection, and solves the deficiencies of existing solders in low-temperature welding and high-conductivity performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solder materials, in particular to a non-ferrous solder for low-temperature brazing and application. BACKGROUND

[0002] In the field of advanced manufacturing with high integration and high reliability requirements such as electronic packaging, power device interconnection and flexible circuit, brazing as a core connection means, its material performance directly affects the conductivity efficiency, thermal management capability and structural stability of the device. With the development of electronic components towards miniaturization and high density, the soldering interface is exposed to complex thermal and electrical stress environment, which puts forward higher functional requirements for the solder, especially in the low-temperature process window to realize efficient conductive connection, which is the key to improve packaging efficiency and system reliability. Low-temperature brazing technology has broad application prospects in the fields of flexible electronics, biosensors and thermal element packaging due to its small damage to the base material and strong environmental adaptability. Therefore, the solder material not only needs to have excellent low melting point characteristics to adapt to low-temperature welding process, but also should have high conductivity to ensure the stability of signal transmission and power conduction. The synergistic optimization of these two performances helps to significantly improve the comprehensive performance of the device, reduce the manufacturing cost, expand the application boundary of low-temperature welding technology in high-end electronic manufacturing, and thus promote the development of new generation of electronic interconnection technology, which has important significance for material design and process innovation.

[0003] The current non-ferrous solder developed for low-temperature brazing application still faces significant challenges in the synergistic realization of high conductivity and low-temperature welding performance. Although existing researches have tried to improve the performance of the solder by introducing metal nanostructures, composite flux or adjusting alloy composition, it is still difficult to meet the dual requirements of low-temperature processing and efficient conductivity in practical application. For example, a Chinese patent with publication number CN102873469B discloses a low-temperature aluminum thermal solder for welding metal and ceramic. Although it has made some progress in reducing the melting point, its conductive performance after welding is unstable, and the interface bonding layer resistance is high, which makes it difficult to meet the needs of high-performance device connection, and there is a problem of insufficient high conductivity and low-temperature welding performance. The reason is that the distribution of conductive phase in the traditional solder system is uneven, the interface structure lacks stability, the thermal decomposition of the flux component is not complete, and the microstructure regulation ability is limited. These problems jointly restrict the formation of continuous, dense and high-conductive welding connection of the solder at low temperature. Therefore, it is urgent to develop a non-ferrous solder that can efficiently melt, rapidly wet and form a high-conductive interface at low temperature, to meet the urgent needs of new generation of electronic packaging and interconnection technology for material performance. SUMMARY

[0004] (1) Technical problems solved

[0005] The application aims to provide a non-ferrous solder for low-temperature brazing and an application, and solve the problem of insufficient welding performance of current solder in high-conductivity and low-temperature welding.

[0006] (2) Technical scheme

[0007] In order to achieve the above-mentioned purpose, the application provides the following technical scheme:

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

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

[0010] The tin-bismuth alloy-coated silver nanoparticle is a core-shell structure particle, the core is a silver nanoparticle, and the shell is a tin-bismuth alloy layer coated on the outer surface thereof;

[0011] Further, the average diameter of the carbon-coated copper nanorod 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; and 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 nanoparticle is 20-80 nm.

[0014] Further, the preparation method of the carbon-coated copper nanorod is as follows: 1.0-1.5 parts of copper nanorod, 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 sequentially added into 3.0-5.0 parts of deionized water, mixed to form a homogeneous suspension under stirring at a speed of 300-600 rpm in an argon atmosphere, transferred into a polytetrafluoroethylene-lined high-pressure reaction kettle with a volume of 50-100 mL, sealed, heated to 160-200 °C at a rate of 2-5 °C / min, and subjected to hydrothermal reaction for 4-8 h. After the reaction, the liquid phase components are removed by centrifugal separation at a speed of 8000-12000 rpm, and the solid phase copper-glucose composite is retained. The unreacted glucose and dispersant are removed by washing with 3.0-5.0 parts of anhydrous ethanol for 3-5 times. The precursor is obtained by vacuum drying at 60-80 °C for 2-4 h. The precursor is uniformly 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 at a flow rate of 60-90 mL / min. The temperature is raised to 800-900 °C at a rate of 5-10 °C / min, and the glucose is pyrolyzed to form a carbon coating layer by carbonization treatment for 1-3 h. Subsequently, the temperature is lowered to 40-60 °C at a natural cooling rate, and then switched to an argon protective atmosphere. Finally, the carbon-coated copper nanorod is obtained.

[0015] Further, the preparation method of the copper nanorod is as follows: 1.0-1.5 parts of copper nitrate is dissolved in ethanol to prepare a 0.4-0.6 M copper nitrate ethanol solution. 8.0-12.0 parts of sodium hydroxide is 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 into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle. The mixture is subjected to hydrothermal reaction at 120-180 °C for 60-180 min. After the reaction, the mixture is naturally cooled to 25-30 °C. The solid phase product is retained by vacuum suction filtration through a polyether sulfone filter membrane with a pore size of 0.22-0.45 μm. The residual nitrate ions and sodium ions are removed by washing with deionized water for 3-5 times and anhydrous ethanol for 2-3 times. Subsequently, the copper oxide nanorod precursor is obtained by vacuum drying at 75-85 °C for 2.0-4.0 h. The copper oxide nanorod precursor is placed in a quartz boat with a length of 4.0-6.0 cm. 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 with a volume concentration of 3.5-4.5% carried by argon is introduced at a flow rate of 50-100 mL / min. The temperature is raised to 200-300 °C at a rate of 5-10 °C / min, and then kept constant for 50-70 min to complete the reduction reaction of the copper oxide nanorod to the copper nanorod. After the reduction is completed, the hydrogen flow rate is maintained, and the temperature is naturally cooled to 30-40 °C. Then, the atmosphere is switched to an argon protective atmosphere. Finally, the copper nanorod is obtained.

[0016] The carbon-coated copper nanorod design of the present application is mainly used for enhancing the comprehensive performance of conductivity and oxidation resistance, and the technical concept is to build a nanoscale conductive framework with regular structure, and form a dense and continuous carbon layer on the surface, so as to realize the double optimization of the conductive channel and the interface stability. The copper nanorod can effectively build a conductive network in the solder system due to its excellent intrinsic conductivity and the electronic migration advantage brought by the one-dimensional structure, thereby improving the overall conductivity of the solder joint. However, the copper material is easy to oxidize during heat treatment and welding, which leads to the interruption of the conductive path and the increase of the interface resistance. Therefore, the carbon-coated copper nanorod prepared by the hydrothermal method and atmosphere control carbonization process forms a stable carbon layer structure. The carbon layer not only plays a physical isolation and chemical passivation role for the copper nanorod, effectively inhibits the oxidation behavior, but also has a certain conductivity, which can cooperate with the internal copper core to build a multi-dimensional conductive network. In addition, the carbon layer can also enhance the interfacial bonding between the particles in the composite system, and improve the wetting and spreading ability and bonding reliability of the solder under low temperature conditions. By fine tuning the carbon layer thickness and copper nanorod morphology parameters, the carbon-coated copper nanorod can not only ensure the continuity of the high-conductive channel, but also has good thermal stability and electrochemical inertness, so as to realize stable and efficient electronic connection in the low-temperature welding environment. The introduction of the carbon-coated copper nanorod not only realizes the optimization of the performance at the single component level, but also significantly improves the overall conductivity and environmental adaptability of the material through the structure and interface synergy between the carbon-coated copper nanorod and other components of the solder, thereby providing an effective material basis and structural support for building high-performance and low-temperature processing non-ferrous metal solder.

[0017] Further, the preparation method of the tin-bismuth alloy-coated silver nanoparticles is as follows: 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, 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 sequentially added thereto, and then mixed uniformly under argon protection at a stirring speed of 400-700 rpm, and then heated to 60-90 DEG C at a temperature rising rate of 2-5 DEG C / min and maintained at this temperature, 0.5-2.0 parts of ascorbic acid or 0.1-0.3 parts of sodium borohydride in ethylene glycol is slowly added at a dropping rate of 0.5-2.0 mL / min under the condition of pH 4.0-6.0, and the reaction is carried out at 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, and then the supernatant is discarded by centrifugal separation at a centrifugal speed of 8000-12000 rpm, and the solid product is retained, and then the unreacted chloride ions and nitrate residues are removed by ultrasonic washing with 6.0-10.0 parts of anhydrous ethanol for 2-3 times, and then vacuum dried at 40-60 DEG C for 3-5 h to obtain the tin-bismuth alloy-coated silver nanoparticles.

[0018] Further, the preparation method of the silver nanoparticles is as follows: 1.0-2.5 parts of silver nitrate is dissolved in a mixed solvent composed of 30-50 parts of deionized water and 30-50 parts of ethanol, 10-30 parts of polyvinylpyrrolidone is added as a surface stabilizer, the reaction system temperature is maintained at 0-10 DEG C under the condition of a stirring rate of 300-600 rpm, 0.2-0.5 parts of sodium borohydride ethanol solution 5.0-10.0 parts is added dropwise at a dropping rate of 0.5-2.0 mL / min to carry out a reduction reaction, the reaction time is 10-30 min to reduce silver ions into silver nanoparticles with a particle size of 20-80 nm, after the reaction, the precipitate is reserved by centrifugal separation at a centrifugal rate of 8000-12000 rpm and the supernatant containing unreacted ions and by-products is discarded, 20-40 parts of ethanol is used for ultrasonic washing for 2-3 times to remove residual nitrate ions and free surfactants, and finally, vacuum drying at 30-50 DEG C for 1-3 h obtains uniformly dispersed silver nanoparticles.

[0019] The present application adopts the design of tin-bismuth alloy coated silver nanoparticles, which is mainly used for enhancing the synergistic performance of conductivity and low-temperature welding. The core is to realize the functional complementation between the high-conductivity metal core and the low-melting alloy shell by constructing composite nanoparticles with core-shell structure, so as to meet the dual requirements of efficient electron transmission and low-temperature rapid melting in the welding process. Specifically, the silver nanoparticles as the inner core can effectively construct stable and dense conductive paths due to their excellent intrinsic conductivity and high surface area at the nanoscale; and the outer tin-bismuth alloy shell has lower melting characteristics and can participate in melting and expansion at a lower temperature, which significantly improves the low-temperature wettability and interface bonding capacity of the solder. The composition ratio of tin-bismuth alloy is accurately controlled to make it have suitable phase change behavior and thermal stability, which ensures that it can act as a melting carrier to promote the connection between particles in the welding process, and will not significantly sacrifice the overall conductivity. The core-shell structure is realized by co-reduction deposition method to form a continuous and uniform alloy shell layer, which further improves the compatibility and interface interaction between particles, avoiding the problems of aggregation or uncontrolled migration of single nanometer metal particles in the melting process. At the same time, the introduction of polyvinylpyrrolidone effectively stabilizes the silver core and its alloy coated structure during preparation, ensuring the dispersity and film uniformity of the particles. The overall structural design not only combines the high conductivity advantage of silver core and the low-temperature welding characteristics of tin-bismuth alloy, but also improves the comprehensive performance of the material in the welding process through the synergistic effect of structure level 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] Further, the dispersant is a mixture of PVP and polyethylene glycol in a mass ratio of 1:(1.0-2.0).

[0022] S1. Under a nitrogen protective atmosphere, carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles are added into a mixing container according to a preset ratio, mechanical stirring is adopted at a speed of 200-400 rpm and a temperature of 20-40℃, and mixing is performed for 20-40 min, then 2-mercaptobenzimidazole, an organic active agent and a dispersant are sequentially added, stirring is continued at a speed of 300-600 rpm, and mixing is performed for 15-30 min to form a stable composite system;

[0023] S2. Rosin, hydroxyethyl cellulose and 1-ethyl-3-methylimidazole tetrafluoroborate are added, mixing is performed at a temperature of 30-60℃ and a speed of 500-800 rpm for 30-45 min, then indium nitrate and citric acid are added, and mixing is continued for 10-20 min;

[0024] S3. The mixture is loaded into a hot-pressing mold, the pressing temperature is controlled within 40-60℃, the pressure is 10-30 MPa, and the pressure is maintained for 1-3 min to form a strip-shaped solder;

[0025] S4. Low-temperature heat treatment is performed at 60-80℃ in an inert atmosphere, heat preservation is performed for 20-40 min, and after cooling, cutting and vacuum packaging are performed to obtain a final strip-shaped solder product.

[0026] The application further discloses an application of the non-ferrous metal solder for low-temperature brazing in electronic device packaging, power device heat dissipation connection or flexible circuit metal interconnection.

[0027] The present application adopts a composite design strategy to introduce carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles into a low-temperature soldering non-ferrous metal solder system in cooperation, aiming to realize the organic unity of electrical conductivity and low-temperature welding performance, and to improve the comprehensive adaptability of the solder in complex electronic connection environment through interface regulation and structure optimization among multiple components. The carbon-coated copper nanorods serve as high-conductivity structural units, with the copper core inside having excellent electrical conductivity, and the outer carbon shell effectively inhibiting the oxidation of copper in air or during heat treatment, stabilizing the electrical conductivity path and microstructure; the tin-bismuth alloy-coated silver nanoparticles combine the high electrical conductivity of silver with the low melting point characteristics of tin-bismuth alloy, forming a composite conductive phase with both electronic transport and low-temperature wetting functions, and the combination of the two in the composite system can form a multi-scale conductive network, improving the overall continuity and interface connection capability. Through mechanical stirring at medium temperature, the two types of core functional particles are uniformly compounded, and 2-mercaptobenzimidazole is introduced as an interface regulator to effectively improve the dispersion stability and wettability between metal particles, while n-dicarboxylic acid or malic acid and other organic active agents are used to adjust 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 gives the solder good adhesive properties and film-forming ability, but also improves its adaptability in flexible circuits and complex interfaces; the synergistic effect of indium nitrate and citric acid helps to adjust the interface electronic structure of the solder and the intermetallic reaction activity during welding. By controlling the hot pressing and low-temperature heat treatment conditions, the structural density and component distribution uniformity of the solder during the molding process are ensured, and finally a strip-shaped solder product with excellent comprehensive performance is obtained. This technical scheme realizes the unified optimization of electrical conductivity, low-temperature weldability, dispersion stability and interface activity through the synergistic construction of multiple functional materials, significantly improving the application potential of the solder in electronic device packaging, power device heat dissipation connection and flexible circuit metal interconnection, etc.

[0028] (3)Beneficial technical effects

[0029] 1. The present application realizes the synergistic enhancement of welding continuity and interface stability by constructing a stable conductive network and improving the oxidation resistance of carbon-coated copper nanorods, which is significantly better than traditional copper-based solders and is suitable for flexible circuits and other applications that require low-temperature high-conductivity.

[0030] 2. The present application realizes the fusion of high electrical conductivity and low-temperature welding function through the synergistic design of silver core and tin-bismuth alloy shell, significantly improves the welding efficiency and interface stability, solves the problems of melting out of control and insufficient electrical conductivity of existing nanoscale solders, and has excellent structural stability and application adaptability.

[0031] 3.The present application is constructed by the synergy of carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles, which significantly optimizes the conductivity and low-temperature soldering performance, improves the solder interface stability and adaptability, is suitable for various electronic interconnection scenarios, and has the advantages of structural integrity and functional integration over single material system. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Morphology diagram of copper nanorods prepared for the present application embodiment 1.

[0033] Figure 2 XRD phase analysis diagram of copper nanorods prepared for the present application embodiment 1.

[0034] Figure 3 Morphology diagram of carbon-coated copper nanorods prepared for the present application embodiment 1.

[0035] Figure 4 XRD phase analysis diagram of carbon-coated copper nanorods prepared for the present application embodiment 1.

[0036] Figure 5 Line scanning element distribution diagram of tin-bismuth alloy-coated silver nanoparticles prepared for the present application embodiment 1. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present application embodiment clearer, the technical scheme of the present application embodiment will be described clearly and completely below in combination with the drawings in the present application embodiment.

[0038] Embodiment 1

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

[0040] 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; 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;

[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 nanorod of the present embodiment is as follows: 1.0 part of copper nanorod, 0.5 part of glucose, 0.2 part of polyvinylpyrrolidone, and 0.1 part of 50 wt.% hydrochloric acid are sequentially added into 3.0 parts of deionized water, mixed to form a homogeneous suspension under the protection of argon at a stirring speed of 300 rpm, transferred into a polytetrafluoroethylene-lined high-pressure reaction kettle with a volume of 50 mL, sealed, and subjected to hydrothermal reaction at 160 ℃ with a temperature increase rate of 2 ℃ / min for 4 h. After the reaction is completed, the liquid phase components are removed by centrifugal separation at a centrifugal speed of 8000 rpm, and the solid phase copper-glucose composite is retained. The unreacted glucose and dispersant are removed by washing the solid phase copper-glucose composite with 3.0 parts of anhydrous ethanol for 3 times. The precursor is obtained by vacuum drying at 60 ℃ for 2 h. The precursor is uniformly spread in an alumina crucible and placed in the constant temperature zone of a tube furnace. Argon-carrying hydrogen mixed gas with a volume fraction of 3.8% and a flow rate of 60 mL / min is introduced. The glucose is pyrolyzed to form a carbon coating layer by carbonization treatment at 800 ℃ with a temperature increase rate of 5 ℃ / min for 1 h. Subsequently, the temperature is decreased to 40 ℃ at a natural cooling rate, and then switched to an argon protection atmosphere. Finally, the carbon-coated copper nanorod is obtained.

[0043] The preparation method of the copper nanorod of the present 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 into a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle. The mixture is subjected to hydrothermal reaction at 120 ℃ for 60 min. After the reaction is completed, the mixture is naturally cooled to 25 ℃. The solid phase product is retained by vacuum suction filtration through a polyether sulfone filter membrane with a pore size of 0.22 μm. The residual nitrate ions and sodium ions are removed by washing the solid phase product with deionized water for 3 times and anhydrous ethanol for 2 times, respectively. Subsequently, the copper oxide nanorod precursor is obtained by vacuum drying at 75 ℃ for 2.0 h. The copper oxide nanorod precursor is placed in a quartz boat with a length of 4.0 cm. The quartz boat is placed in the middle of a quartz tube reactor with an inner diameter of 1.0 cm. Argon-carrying hydrogen gas with a volume concentration of 3.5% and a flow rate of 50 mL / min is introduced. The reduction reaction of the copper oxide nanorod to the copper nanorod is completed by heating to 200 ℃ at a temperature increase rate of 5 ℃ / min and maintaining the temperature for 50 min. After the reduction is completed, the hydrogen flow rate is maintained, and the quartz boat is naturally cooled to 30 ℃. Then, the protection atmosphere is switched to argon. Finally, the copper nanorod is obtained.

[0044] The average thickness of the tin-bismuth alloy layer of the present 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 tin-bismuth alloy coated silver nanoparticles in this embodiment is as follows: 1.6 parts of silver nanoparticles are dispersed in 10.1 parts of ethylene glycol to form a homogeneous dispersion system, and then 1.3 parts of stannous chloride, 1.7 parts of bismuth nitrate and 5.8 parts of polyvinylpyrrolidone are sequentially added thereto. After mixing uniformly under argon protection at a stirring speed of 490 rpm, the temperature is increased to 69℃ at a rate of 2.9℃ / min and maintained at this temperature. A solution of 0.95 parts of ascorbic acid or 0.16 parts of sodium borohydride in ethylene glycol is slowly added at a rate of 0.95 mL / min at a pH of 4.6. The tin-bismuth alloy layer is coated on the surface of the silver core in a coreduction manner after constant temperature reaction for 39 min. After the reaction is completed, the supernatant is discarded by centrifugal separation at a centrifugal speed of 9200 rpm, and the solid phase product is retained. The unreacted chloride ions and nitrate residues are removed by ultrasonic washing twice with 7.2 parts of anhydrous ethanol, followed by vacuum drying at 46℃ for 3.6 h to obtain tin-bismuth alloy coated silver nanoparticles.

[0046] The preparation method of the silver nanoparticles in this embodiment is as follows: 1.5 parts of silver nitrate is dissolved in a mixed solvent composed of 36 parts of deionized water and 36 parts of ethanol, and 16 parts of polyvinylpyrrolidone is added as a surface stabilizer. The reaction system temperature is maintained at 3℃ under stirring at a speed of 390 rpm. A solution of 0.29 parts of sodium borohydride in 6.5 parts of ethanol is added dropwise at a rate of 0.95 mL / min to carry out 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, the precipitate is retained by centrifugal separation at a centrifugal speed of 9200 rpm, and the supernatant containing unreacted ions and byproducts is discarded. The residual nitrate ions and free surfactant are removed by ultrasonic washing twice with 26 parts of ethanol. Finally, the uniformly dispersed silver nanoparticles are obtained by vacuum drying at 36℃ for 1.6 h.

[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 in a mass ratio of 1:1.3.

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

[0050] S1. Under a nitrogen protective atmosphere, carbon-coated copper nanorods and tin-bismuth alloy coated silver nanoparticles are added to a mixing container according to a predetermined ratio. Mechanical stirring is used at a speed of 260 rpm and a temperature of 26℃ for 26 min. Then 2-mercaptobenzimidazole, an organic active agent and a dispersant are sequentially added. The stirring speed is increased to 390 rpm and the mixing time is 20 min to form a stable composite system.

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

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

[0053] S4. Perform low-temperature heat treatment at 66°C in an inert atmosphere for 26 minutes. After cooling, cut and vacuum package the final solder strip product.

[0054] Depend on 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, and a high aspect ratio, which meets the structural requirements for constructing a conductive path; Figure 2 XRD phase analysis showed that the copper nanorods had obvious metallic copper diffraction peaks, indicating that their crystal structure was complete and there was no obvious impurity phase. Figure 3 It was further shown that after carbon coating, a uniform and continuous carbon layer coating structure was formed on the surface of the copper nanorods, without agglomeration or breakage, indicating that the coating process was stable and controllable, which helped to improve their antioxidant properties. Figure 4 XRD analysis of the carbon-coated copper nanorods showed that in addition to retaining the crystal plane characteristics of metallic copper, a weak carbon peak signal also appeared, verifying the existence of the carbon layer and that it did not interfere with the crystal structure of copper. Figure 5 The line scan elemental distribution of tin-bismuth alloy-coated silver nanoparticles is shown. The results show that the outer surface of the silver core particles is uniformly coated with tin and bismuth elements, with no observed elemental segregation or delamination, indicating a continuous and dense alloy coating with good interfacial bonding. In summary, the copper nanorods produced by this invention have a regular structure, uniform carbon coating, and complete silver nanoparticle coating. The structural and phase analysis results jointly verify the quality of the solder's key components, providing the structural foundation for subsequent excellent soldering performance.

[0055] Example 2

[0056] A non-ferrous metal solder for low-temperature brazing comprises 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 active agent, 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 nanorod is composed of a copper nanorod and a continuous carbon layer uniformly coated on the outer surface of the copper nanorod; and the tin-bismuth alloy-coated silver nanoparticle is a core-shell structure particle, wherein the core is a silver nanoparticle, and the shell is a tin-bismuth alloy layer coated on the outer surface of the core.

[0058] The average diameter of the carbon-coated copper nanorod 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 nanorod of the embodiment is as follows: 1.2 parts by weight of copper nanorods, 0.8 parts by weight of glucose, 0.4 parts by weight of polyvinylpyrrolidone, and 0.2 parts by weight of 50 wt.% hydrochloric acid are sequentially added to 3.6 parts by weight of deionized water, and a homogeneous suspension is formed by mixing under the protection of argon gas at a stirring speed of 390 rpm. The homogeneous suspension is transferred to a polytetrafluoroethylene-lined high-pressure reaction kettle with a volume of 65 mL and sealed. The temperature is raised to 172℃ at a rate of 3℃ / min, and the hydrothermal reaction is carried out for 5 h. After the reaction is completed, the liquid phase components are removed by centrifugal separation at a centrifugal speed of 9200 rpm, and the solid copper-glucose composite is retained. The unreacted glucose and dispersant are removed by washing the solid copper-glucose composite with 3.6 parts by weight of anhydrous ethanol for 4 times. The precursor is obtained by vacuum drying at 66℃ for 3 h. The precursor is uniformly 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 gas is introduced at a flow rate of 69 mL / min. The temperature is raised to 830℃ at a rate of 6.5℃ / min, and the glucose is pyrolyzed to form a carbon coating layer by carbonization treatment for 1.6 h. Then, the temperature is lowered to 46℃ at a natural cooling rate, and the protection of argon gas is switched. Finally, the carbon-coated copper nanorod is obtained.

[0060] The preparation method of the copper nanorod of the embodiment is as follows: 1.2 parts of copper nitrate is dissolved in ethanol to prepare a 0.5M copper nitrate ethanol solution, 9.2 parts of sodium hydroxide is dissolved in deionized water to prepare a 4.6M sodium hydroxide aqueous solution, the copper nitrate ethanol solution and the sodium hydroxide aqueous solution are mixed at a volume ratio of 1:9.2, then transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, sealed, and subjected to hydrothermal reaction at 138°C for 96 min, then naturally cooled to 26.5°C, and the solid phase product is retained by vacuum suction filtration through a polyether sulfone filter membrane with a pore size of 0.29μm, washed with deionized water for 4 times and anhydrous ethanol for 2 times to remove residual nitrate ions and sodium ions, then vacuum dried at 78°C for 2.6h to obtain copper oxide nanorod precursor; the copper oxide nanorod precursor is placed in a quartz boat with a length of 4.6cm, the quartz boat is placed in the middle of a quartz tube reactor with an inner diameter of 1.2cm, argon gas is introduced at a flow rate of 65mL / min, the temperature is raised to 230°C at a rate of 6.5°C / min and kept constant for 56min to complete the reduction reaction of copper oxide nanorod to copper nanorod, then the hydrogen flow rate is maintained and the temperature is naturally cooled to 33°C, then the atmosphere is switched to argon protection, and finally the copper nanorod is obtained.

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

[0062] The preparation method of the tin-bismuth alloy coated silver nanoparticles of the embodiment is as follows: 1.0 parts of silver nanoparticles is dispersed in 8.0 parts of ethylene glycol to form a homogeneous dispersion system, 0.8 parts of stannous chloride, 1.2 parts of bismuth nitrate and 4.0 parts of polyvinylpyrrolidone are sequentially added thereto, and the mixture is uniformly mixed under argon protection at a stirring rate of 400rpm, then the temperature is raised to 60°C at a rate of 2°C / min and kept constant, 0.5 parts of ascorbic acid or 0.1 parts of sodium borohydride in ethylene glycol is slowly added at a rate of 0.5mL / min under the condition of pH 4.0, and the tin-bismuth alloy layer is coated on the surface of the silver core in a co-reduction manner after constant temperature reaction for 30min, then the supernatant is discarded by centrifugal separation at a centrifugal speed of 8000rpm and the solid phase product is retained, the unreacted chloride ions and nitrate residues are removed by ultrasonic washing with 6.0 parts of anhydrous ethanol for 2 times, and then the tin-bismuth alloy coated silver nanoparticles are obtained by vacuum drying at 40°C for 3h.

[0063] The preparation method of the silver nanoparticles of the present embodiment is as follows: 1.0 parts 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 reaction system temperature is maintained at 0°C under the condition of a stirring rate of 300 rpm, 5.0 parts of 0.2 parts of sodium borohydride ethanol solution is added dropwise at a dropping rate of 0.5 mL / min to carry out a reduction reaction, the reaction time is 10 min to reduce silver ions into silver nanoparticles with a particle size of 20 nm, after the reaction, the supernatant containing unreacted ions and by-products is discarded by centrifugal separation at a centrifugal rate of 8000 rpm, 20 parts of ethanol is used for ultrasonic washing twice to remove residual nitrate ions and free surfactants, and finally, uniformly dispersed silver nanoparticles are obtained by vacuum drying at 30°C for 1 h.

[0064] The organic active agent of the present embodiment is malic acid.

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

[0066] The preparation method of the non-ferrous solder for low-temperature brazing of the present embodiment comprises the following steps:

[0067] S1. Under the protection of a nitrogen atmosphere, carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles are added into a mixing container according to a predetermined proportion, mechanical stirring is adopted at a rate of 200 rpm and a temperature of 20°C, and the mixing time is 20 min, then 2-mercaptobenzimidazole, an organic active agent, and a dispersant are sequentially added, the stirring rate is increased to 300 rpm, and the mixing time is 15 min to form a stable composite system;

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

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

[0070] S4. Low-temperature heat treatment is carried out at 60°C in an inert atmosphere, the holding time is 20 min, after cooling, cutting and vacuum packaging are carried out to obtain the final strip-shaped solder product.

[0071] Example 3

[0072] The low-temperature brazing non-ferrous filler metal comprises the following raw materials in parts by weight: carbon-coated copper nanorods 16 parts, tin-bismuth alloy-coated silver nanoparticles 78 parts, 2-mercaptobenzimidazole 2.1 parts, rosin resin 8.4 parts, organic active agent 2.7 parts, dispersing agent 3.5 parts, 1-ethyl-3-methylimidazole tetrafluoroborate 14.8 parts, hydroxyethyl cellulose 1.6 parts, indium nitrate sintering aid 1.1 parts, and citric acid 0.2 parts.

[0073] 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; 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;

[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 of the embodiment is as follows: in parts by weight, copper nanorods 1.3 parts, glucose 1.1 parts, polyvinylpyrrolidone 0.6 parts, and 50 wt.% hydrochloric acid 0.2 parts are sequentially added to deionized water 4.2 parts, mixed to form a homogeneous suspension under argon protection at a stirring speed of 480 rpm, transferred to a polytetrafluoroethylene-lined high-pressure reaction kettle with a volume of 80 mL, sealed, heated to 184℃ at a rate of 4℃ / min, and hydrothermally reacted for 6h. After the reaction is terminated, the liquid phase components are removed by centrifugal separation at a centrifugal speed of 10400 rpm, and the solid phase copper-glucose composite is retained. The unreacted glucose and dispersing agent are removed by washing with anhydrous ethanol 4.2 parts for 4 times, and the precursor is obtained by vacuum drying at 72℃ for 3h. The precursor is uniformly spread in an alumina crucible and placed in the constant temperature zone of a tube furnace, and the argon-carrying hydrogen mixed gas with a volume fraction of 4.0% and a flow rate of 78mL / min is introduced. The temperature is raised to 860℃ at a rate of 8℃ / min, and the glucose is pyrolyzed to form a carbon coating layer by carbonization treatment for 2.2h. Then, the temperature is lowered to 52℃ at a natural cooling rate, and the argon protection is switched. Finally, the carbon-coated copper nanorods are obtained.

[0076] The preparation method of the copper nanorod of the embodiment is as follows: 1.3 parts of copper nitrate is dissolved in ethanol to prepare a 0.5M copper nitrate ethanol solution, 10.4 parts of sodium hydroxide is dissolved in deionized water to prepare a 5.2M sodium hydroxide aqueous solution, the copper nitrate ethanol solution and the sodium hydroxide aqueous solution are mixed at a volume ratio of 1:10.4, then transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, sealed, and subjected to hydrothermal reaction at 156°C for 132 min, then naturally cooled to 28°C, and the solid phase product is retained by vacuum suction filtration through a polyether sulfone filter membrane with a pore size of 0.36 μm, washed with deionized water for 4 times and anhydrous ethanol for 3 times to remove residual nitrate ions and sodium ions, then vacuum dried at 81°C for 3.2 h to obtain a copper oxide nanorod precursor; the copper oxide nanorod precursor is placed in a quartz boat with a length of 5.2 cm, the quartz boat is placed in the middle of a quartz tube reactor with an inner diameter of 1.3 cm, argon gas is introduced at a flow rate of 80 mL / min, the volume concentration of hydrogen gas is 4.1%, the temperature is increased to 260°C at a rate of 8°C / min and kept constant for 62 min to complete the reduction reaction of the copper oxide nanorod to the copper nanorod, after the reduction is completed, the hydrogen flow rate is maintained and the temperature is naturally cooled to 36°C, then the atmosphere is switched to argon protection, and finally the copper nanorod is obtained.

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

[0078] The preparation method of the tin-bismuth alloy-coated silver nanoparticles of the embodiment is as follows: 3.0 parts of silver nanoparticles is dispersed in 15.0 parts of ethylene glycol to form a homogeneous dispersion system, 2.5 parts of stannous chloride, 3.0 parts of bismuth nitrate, and 10.0 parts of polyvinylpyrrolidone are sequentially added thereto, and the mixture is uniformly mixed under argon protection at a stirring rate of 700 rpm, then heated to 90°C at a rate of 5°C / min and kept at this temperature, 2.0 parts of ascorbic acid or 0.3 parts of sodium borohydride in ethylene glycol is slowly added at a rate of 2.0 mL / min under the condition of pH 6.0, and the tin-bismuth alloy layer is coated on the surface of the silver core in a co-reduction manner after constant temperature reaction for 60 min, the supernatant is discarded by centrifugal separation at a speed of 12000 rpm after the reaction is completed, and the solid phase product is retained, then washed with 10.0 parts of anhydrous ethanol for 3 times by ultrasonic to remove unreacted chloride ions and nitrate residues, and then vacuum dried at 60°C for 5 h to obtain tin-bismuth alloy-coated silver nanoparticles.

[0079] The preparation method of the silver nanoparticles of the present embodiment is as follows: 2.5 parts of silver nitrate is dissolved in a mixed solvent composed of 50 parts of deionized water and 50 parts of ethanol, 30 parts of polyvinylpyrrolidone is added as a surface stabilizer, the reaction system temperature is maintained at 10°C at a stirring rate of 600 rpm, 10.0 parts of 0.5 parts of sodium borohydride ethanol solution is added dropwise at a dropping rate of 2.0 mL / min to carry out 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 is used for ultrasonic washing for 3 times to remove residual nitrate ions and free surfactants, and finally vacuum drying at 50°C for 3 h to obtain uniformly dispersed silver nanoparticles.

[0080] The organic active agent of the present embodiment is azelaic acid.

[0081] The dispersant of the present 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 solder for low-temperature brazing of the present embodiment comprises the following steps:

[0083] S1. Under a nitrogen protective atmosphere, carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles are added into a mixing container according to a predetermined proportion, mechanical stirring is adopted at a speed of 400 rpm and a temperature of 40°C, and the mixing time is 40 min, then 2-mercaptobenzimidazole, an organic active agent and a dispersant are sequentially added, the stirring speed is increased to 600 rpm, and the mixing time is 30 min to form a stable composite system;

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

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

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

[0087] Example 4

[0088] The low-temperature brazing non-ferrous filler metal comprises the following raw materials in parts by weight: carbon-coated copper nanorods 18.0 parts, tin-bismuth alloy-coated silver nanoparticles 90.0 parts, 2-mercaptobenzimidazole 2.5 parts, rosin resin 10.0 parts, organic active agent 3.5 parts, dispersing agent 4.5 parts, 1-ethyl-3-methylimidazole tetrafluoroborate 18.0 parts, hydroxyethyl cellulose 2.0 parts, indium nitrate sintering aid 1.5 parts, and citric acid 0.3 parts.

[0089] 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; 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;

[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 the embodiment is as follows: in parts by weight, copper nanorods 1.5 parts, glucose 1.5 parts, polyvinylpyrrolidone 0.8 parts, and 50 wt.% hydrochloric acid 0.3 parts are sequentially added into deionized water 5.0 parts, mixed to form a homogeneous suspension under the protection of argon at a stirring speed of 600 rpm, transferred into a polytetrafluoroethylene-lined high-pressure reaction kettle with a volume of 100 mL, sealed, heated to 200℃ at a rate of 5℃ / min, and hydrothermally reacted for 8 h; after the reaction is terminated, the liquid phase components are removed by centrifugal separation at a centrifugal speed of 12000 rpm, and the solid phase copper-glucose composite is retained; the unreacted glucose and dispersing agent are removed by washing with anhydrous ethanol 5.0 parts for 5 times; the precursor is obtained by vacuum drying at 80℃ for 4 h; the precursor is uniformly laid in an alumina crucible and placed in the constant temperature zone of a tube furnace; argon-carrying hydrogen mixed gas with a volume fraction of 4.2% is introduced at a flow rate of 90 mL / min; the temperature is raised to 900℃ at a rate of 10℃ / min; the glucose is pyrolyzed to form a carbon coating layer by carbonization treatment for 3 h; then the temperature is lowered to 60℃ at a natural cooling rate, and the protection of argon is switched; and finally, the carbon-coated copper nanorods are obtained.

[0092] The preparation method of the copper nanorod of the embodiment is as follows: 1.5 parts of copper nitrate is dissolved in ethanol to prepare a 0.6M copper nitrate ethanol solution, 12.0 parts of sodium hydroxide is dissolved in deionized water to prepare a 6.0M sodium hydroxide aqueous solution, the copper nitrate ethanol solution and the sodium hydroxide aqueous solution are mixed at a volume ratio of 1:12, then transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reaction kettle, sealed, and subjected to hydrothermal reaction at 180°C for 180 min. After the reaction is completed, it is naturally cooled to 30°C, and the solid phase product is retained by vacuum suction filtration through a polyether sulfone filter membrane with a pore size of 0.45 μm. The solid phase product is washed with deionized water for 5 times and anhydrous ethanol for 3 times to remove residual nitrate ions and sodium ions, and then vacuum dried at 85°C for 4.0 h to obtain a copper oxide nanorod precursor. The copper oxide nanorod precursor is placed in a quartz boat with a length of 6.0 cm, the quartz boat is placed in the middle of a quartz tube reactor with an inner diameter of 1.5 cm, argon gas is introduced at a flow rate of 100 mL / min, the temperature is raised to 300°C at a rate of 10°C / min, and the temperature is kept constant for 70 min to complete the reduction reaction of the copper oxide nanorod to the copper nanorod. After the reduction is completed, the hydrogen flow rate is maintained and the temperature is naturally cooled to 40°C, and then the atmosphere is switched to argon protection. Finally, the copper nanorod is obtained.

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

[0094] The preparation method of the tin-bismuth alloy-coated silver nanoparticles of the embodiment is as follows: 2.2 parts of silver nanoparticles is dispersed in 12.2 parts of ethylene glycol to form a homogeneous dispersion system, 1.8 parts of stannous chloride, 2.3 parts of bismuth nitrate, and 7.6 parts of polyvinylpyrrolidone are sequentially added thereto, and the mixture is uniformly mixed under argon protection at a stirring rate of 580 rpm, then heated to 78°C at a rate of 3.8°C / min and kept at this temperature, 1.4 parts of ascorbic acid or 0.22 parts of sodium borohydride in ethylene glycol is slowly added at a rate of 1.4 mL / min at a pH of 5.2, and the tin-bismuth alloy layer is coated on the surface of the silver core in a co-reduction manner after constant temperature reaction for 48 min. After the reaction is completed, the supernatant is discarded by centrifugal separation at a centrifugal speed of 10400 rpm, and the solid phase product is retained. The unreacted chloride ions and nitrate residues are removed by ultrasonic washing with 8.4 parts of anhydrous ethanol for 3 times, and then vacuum dried at 52°C for 4.2 h to obtain the tin-bismuth alloy-coated silver nanoparticles.

[0095] The preparation method of the silver nanoparticles of this embodiment is as follows: 1.9 parts of silver nitrate, by weight, is dissolved in a mixed solvent consisting of 42 parts of deionized water and 42 parts of ethanol, 22 parts of polyvinyl pyrrolidone is added as a surface stabilizer, and the reaction system temperature is maintained at 6°C under a stirring rate of 480 rpm. 8.0 parts of an ethanol solution of 0.38 parts of sodium borohydride is added dropwise at a dropwise rate of 1.4 mL / min to carry out a reduction reaction. The reaction time is 22 minutes to reduce the silver ions to silver nanoparticles with a particle size of 56 nm. After the reaction is completed, the precipitate is retained by centrifugation at a centrifugal speed of 10400 rpm, and the supernatant containing unreacted ions and by-products is discarded. The residual nitrate ions and free surfactant are removed by ultrasonic washing with 32 parts of ethanol three times. Finally, the mixture is vacuum dried at 42°C for 2.2 hours 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 in a mass ratio of 1:1.6.

[0098] The method for preparing a non-ferrous metal solder for low-temperature brazing of this embodiment comprises the following steps:

[0099] S1. Under a nitrogen atmosphere, carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles were added to a mixing vessel in a predetermined ratio. The mixture was mechanically stirred at 320 rpm, 32°C, and mixed for 32 minutes. 2-Mercaptobenzimidazole, an organic surfactant, and a dispersant were then added in sequence. Stirring was continued at 480 rpm for 24 minutes to form a stable composite system.

[0100] S2. Rosin resin, hydroxyethyl cellulose and 1-ethyl-3-methylimidazolium tetrafluoroborate were added at a mixing temperature of 48 ° C, a mixing rate of 680 rpm, and a mixing time of 39 min. Indium nitrate and citric acid were then added and mixing 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 22MPa, and the pressure is maintained for 2.2min to form a strip solder;

[0102] S4. Perform low-temperature heat treatment at 72°C in an inert atmosphere for 32 minutes. After cooling, cut and vacuum package the final solder strip product.

[0103] Comparative Example 1

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

[0105] Comparative Example 2

[0106] The same as example 1, the difference is that the amount of tin-bismuth alloy coated silver nanoparticles is adjusted to 95.0 parts.

[0107] Comparative example 3

[0108] The same as example 1, the difference is that the thickness of the carbon layer of the carbon-coated copper nanorod is adjusted to 2.0 nm, and the oxidation of the copper nanorod is intensified at high temperature due to insufficient oxidation resistance.

[0109] Comparative example 4

[0110] The same as example 1, the difference is that the hydrothermal reaction temperature of the carbon-coated copper nanorod is adjusted to 150°C, resulting in a loose carbon layer structure.

[0111] Comparative example 5

[0112] The same as example 1, the difference is that the concentration of copper nitrate ethanol solution in the preparation of copper nanorods is adjusted to 0.3M, and the aspect ratio of copper nanorods is <4, resulting in the failure of conductive anisotropy.

[0113] Comparative example 6

[0114] The same as example 1, the difference is that the mass ratio of tin to bismuth in the tin-bismuth alloy coated silver nanoparticles is adjusted to 40:60, and the eutectic point shift leads to an increase in melting temperature.

[0115] Comparative example 7

[0116] The same as example 1, the difference is that the amount of sodium borohydride in the preparation of silver nanoparticles is adjusted to 0.1 parts, and the reduction is insufficient, resulting in silver particles with a particle size >80 nm and an uneven alloy coating layer.

[0117] Comparative example 8

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

[0119] Comparative example 9

[0120] The same as example 1, the difference is that the organic active agent is replaced with citric acid, and the excessive acidity leads to premature decomposition of the rosin resin, resulting in an abnormal increase in the viscosity of the solder.

[0121] Comparative example 10

[0122] The same as example 1, the difference is that the mass ratio of PVP to polyethylene glycol in the dispersant is adjusted to 1:3, and the compatibility of the dispersant is deteriorated, resulting in an increase in nanoparticle agglomeration.

[0123] Comparative example 11

[0124] The same as Example 1, except that the solder pressing pressure is adjusted to 5 MPa, and the internal porosity of the strip-shaped solder is increased.

[0125] Comparative Example 12

[0126] The same as Example 1, except that the stirring rate of the mixing step S1 is adjusted to 100 rpm, and the carbon-coated copper nanorods and silver particles are not uniformly dispersed, and the conductivity is decreased.

[0127] Comparative Example 13

[0128] The same as Example 1, except that the low-temperature heat treatment temperature is adjusted to 90°C (higher than 60-80°C of claim 9), and the hydroxyethyl cellulose is thermally decomposed, and the solder toughness is decreased.

[0129] Comparative Example 14

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

[0131] Comparative Example 15

[0132] The same as Example 1, except that the surface of the silver nanoparticle is not prepared with a tin-bismuth layer.

[0133] Performance test:

[0134] Interface bonding strength of the solder joint: according to the IPC-SM-840 standard, the solder (thickness 100 μm) is applied on the pretreated oxygen-free copper plate (size 10 mm x 10 mm), and after preheating at 50°C for 60 seconds, it is welded at 70±5°C for 90 seconds (nitrogen protection), and then a pressure of 15 MPa is applied for 2 minutes. According to ASTM D1002, copper-copper lap joint samples (3 mm x 3 mm) are prepared, and a universal testing machine is used to load to break at 1 mm / min, and the interface metallurgical bonding strength is tested.

[0135] Conductive performance after welding: the solder (thickness 100 μm) is applied on the nickel-plated flexible substrate by drop method, and after preheating at 50°C for 60 seconds, the welding is completed at 70±5°C (nitrogen flow 0.5 L / min). A constant current of 10 mA is applied by four-probe method, and the resistance of the solder joint is tested, and an infrared thermal imager is used to detect the local temperature rise (ΔT≤5°C) at the same time, and the circuit on-off test is used to verify the stability of the conductivity.

[0136] Wettability and forming quality of the solder joint: the solder (thickness 100 μm) is applied on the oxygen-free copper plate by scraping, and after heating at 70±5°C for 90 seconds, the spreading area and wetting angle are quantified by optical profilometer, and the internal porosity is detected by X-ray flaw detection, and the surface roughness (Ra≤0.5 μm) is analyzed by laser confocal microscope, to ensure the forming density of the low-temperature soldering.

[0137] Solder melting point and melting behavior test: the melting onset temperature, peak temperature and melting heat of the solder were determined by differential scanning calorimetry (DSC) to analyze the low-temperature soldering capability.

[0138] Reliability test after soldering: the hot-press soldering sample (15 MPa for 2 minutes) was subjected to JEDEC JESD22-A104 standard thermal cycle (-55-125℃, 1000 times), the interface delamination rate was less than 5% detected by SAM, and the 1×10 4 A / cm 2 The current density was 500 hours, the resistance change rate was measured, the micro cavity expansion trend was observed by SEM, and the thermal-electric coupling failure resistance of the solder joint was comprehensively evaluated.

[0139] The performance of the solders of examples 1-4 and comparative examples 1-15 is summarized in table 1.

[0140] Table 1 Performance of solders of examples 1-4 and comparative examples 1-15

[0141]

[0142]

[0143] From Table 1, it can be seen that the solder performance is affected by the synergistic effect of the ratio of various raw materials and process parameters. 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) can easily lead to nanorod agglomeration, increase the solder joint resistance and weaken the 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 the conductivity, but it may dilute the enhancement effect of the copper rod network. Insufficient carbon layer thickness (such as 2.0 nm) or loose carbon layer structure (such as too high hydrothermal temperature) can weaken the oxidation resistance of copper nanorods. During high-temperature welding, copper is easily oxidized, which leads to a significant decrease in conductivity and interface bonding. If the aspect ratio of copper nanorods is too small (<4), it will destroy its one-dimensional conductive characteristics, causing the failure of the anisotropy of electrical conductivity, and the solder joint resistance increases significantly. If the mass ratio of tin-bismuth deviates from the eutectic composition (such as 40:60), the melting point increases, which affects the adaptability and reliability of low-temperature welding. If the particle size of silver particles is too large or the coating is uneven (such as insufficient reduction), it will lead to the deterioration of wettability and interface formation. If the pH is too low (such as 3.0) during the tin-bismuth coating process, the alloy layer will be rapidly reduced and cracks will occur, which will weaken the metallurgical bonding. If strong acidic substances such as citric acid are used as organic active agents, it will accelerate the pyrolysis of rosin resin, leading to an abnormal increase in the viscosity of the solder, which affects the wetting and spreading. If the ratio of PVP and polyethylene glycol in the dispersant is unbalanced, it will reduce the compatibility of the system, cause the agglomeration of nanoparticles, and form local conductive dead zones. If the pressing pressure of the solder is insufficient (such as 5 MPa), it is easy to form internal pores, which reduces the density and strength of the solder joint. If the stirring rate is too low (such as 100 rpm), the dispersion of copper rods and silver particles will be uneven, the electrical conductivity path will be discontinuous, and the overall performance of the solder joint will decrease. If the heat treatment temperature exceeds the reasonable range (such as 90℃), it will cause the decomposition of additives such as hydroxyethyl cellulose, which affects the toughness and forming stability of the solder. If the surface of the copper nanorods is not coated with a carbon layer, it will be easily oxidized during welding, which will seriously damage the conductivity and bonding strength. If the silver particles are not coated with a tin-bismuth alloy layer, the wettability and interface alloying ability will be insufficient, the solder joint appearance will be poor, and the reliability will decrease significantly. The above factors interact with each other to 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 examples are only used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that any equivalent structural transformation made within the concept of the present application, using the contents of the present application specification and drawings, should be covered within the protection scope of the claims of the present application.

Claims

1. A non-ferrous metal solder for low-temperature brazing, characterized in that: The invention comprises 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 active agent, 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 and 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, wherein the core is a silver nanoparticle and the shell is a tin-bismuth alloy layer coated on the outer surface of the core. The average thickness of the tin-bismuth alloy layer is 11-30 nm; wherein 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.

2. The non-ferrous metal solder for low-temperature 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. The non-ferrous metal solder for low-temperature brazing according to claim 1, characterized in that: The carbon-coated copper nanorods are prepared by adding 1.0-1.5 parts of copper nanorods, 0.5-1.5 parts of glucose, 0.2-0.8 parts of polyvinyl pyrrolidone, and 0.1-0.3 parts of 50 wt.% hydrochloric acid to 3.0-5.0 parts of deionized water in sequence, mixing the mixture at a stirring rate of 300-600 rpm under argon protection to form a homogeneous suspension, transferring the mixture to a polytetrafluoroethylene-lined autoclave with a volume of 50-100 mL and sealing the autoclave. The mixture is heated to 160-200° C. at a rate of 2-5° C. / min and subjected to a hydrothermal reaction for 4-8 h. After the reaction is terminated, the liquid phase components are removed by centrifugation at a centrifugal rate of 8000-12000 rpm, and a solid phase copper-glucose complex is retained. The solid phase copper-glucose complex is washed 3-5 times with 3.0-5.0 parts of anhydrous ethanol to remove unreacted glucose and dispersant, and then dried in vacuo at 60-80° C. for 2-4 h. h to obtain a precursor; the precursor was evenly spread in an alumina crucible and placed in the constant temperature zone of a tube furnace, and a hydrogen mixture with a volume fraction of 3.8~4.2% carried by argon was introduced at a flow rate of 60~90 mL / min, and the temperature was raised to 800~900°C at a rate of 5~10°C / min and carbonized for 1~3 h to thermally decompose glucose to form a carbon coating layer, and then the temperature was naturally cooled to 40~60°C and then switched to argon protection to finally obtain carbon-coated copper nanorods.

4. The non-ferrous metal solder for low-temperature brazing according to claim 3, characterized in that: The preparation method of the copper nanorods is as follows: 1.0-1.5 parts of copper nitrate is dissolved in ethanol to prepare a 0.4-0.6 M copper nitrate ethanol solution, 8.0-12.0 parts of sodium hydroxide is 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 in a volume ratio of 1:8-1:12, and then transferred to a polytetrafluoroethylene-lined stainless steel autoclave and sealed, and a hydrothermal reaction is carried out at 120-180°C for 60-180 min. After the reaction is completed, it is naturally cooled to 25-30°C, and a solid phase product is retained by vacuum filtration through a polyethersulfone filter membrane with a pore size of 0.22-0.45 μm, and then washed with deionized water 3-5 times and anhydrous ethanol 2-3 times to remove residual nitrate ions and sodium ions, and then vacuum dried at 75-85°C for 2.0-4.0 h to obtain a copper oxide nanorod precursor; the copper oxide nanorod precursor is placed in a quartz boat with a length of 4.0~6.0 cm, the quartz boat is placed in the middle of a quartz tube reactor with an inner diameter of 1.0~1.5 cm, and hydrogen with a volume concentration of 3.5~4.5% carried by argon is introduced at a flow rate of 50~100 mL / min, and is heated to 200~300°C at a heating rate of 5~10°C / min and maintained at a constant temperature for 50~70 min to complete the reduction reaction of the copper oxide nanorods to copper nanorods. After the reduction is completed, the hydrogen flow rate is maintained and the temperature is naturally cooled to 30~40°C, and then switched to an argon protective atmosphere to finally obtain copper nanorods.

5. The non-ferrous metal solder for low-temperature brazing according to claim 1, characterized in that: The preparation method of the tin-bismuth alloy-coated silver nanoparticles is as follows: 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, 0.8-2.5 parts of stannous chloride, 1.2-3.0 parts of bismuth nitrate, and 4.0-10.0 parts of polyvinyl pyrrolidone are sequentially added thereto, and the mixture is stirred at a rate of 400-700 rpm under argon protection to mix uniformly, and then the temperature is raised to 60-90°C at a rate of 2-5°C / min and maintained at this temperature, and an ethylene glycol solution of 0.5-2.0 parts of ascorbic acid or 0.1-0.3 parts of sodium borohydride is slowly added at a drop rate of 0.5-2.0 mL / min at a pH of 4.0-6.0, and the reaction is carried out at a constant temperature for 30-60 minutes to coat the tin-bismuth alloy layer on the surface of the silver core in a co-reduction manner. After the reaction is completed, the mixture is centrifuged at a rate of 8000-12000 The supernatant was discarded by centrifugation at rpm and the solid phase product was retained. The solid phase product was ultrasonically washed 2-3 times with 6.0-10.0 parts of anhydrous ethanol to remove unreacted chloride ions and residual nitrate. The product was then vacuum dried at 40-60°C for 3-5 h to obtain tin-bismuth alloy-coated silver nanoparticles.

6. The non-ferrous metal solder for low-temperature brazing according to claim 1, characterized in that: The preparation method of the silver nanoparticles is as follows: 1.0-2.5 parts of silver nitrate are dissolved in a mixed solvent consisting of 30-50 parts of deionized water and 30-50 parts of ethanol, 10-30 parts of polyvinyl pyrrolidone is added as a surface stabilizer, the reaction system temperature is maintained at 0-10°C under a stirring rate of 300-600 rpm, 5.0-10.0 parts of 0.2-0.5 parts of an ethanol solution of sodium borohydride are added dropwise at a drop rate of 0.5-2.0 mL / min to carry out a reduction reaction, and the reaction time is 10-30 minutes to reduce the silver ions to silver nanoparticles with a particle size of 20-80 nm. After the reaction is completed, the precipitate is retained by centrifugation at a centrifugal speed of 8000-12000 rpm and the supernatant containing unreacted ions and by-products is discarded. The residual nitrate ions and free surfactant are removed by ultrasonic washing with 20-40 parts of ethanol for 2-3 times, and finally, the precipitate is vacuum dried at 30-50°C for 1-3 minutes. h Obtain uniformly dispersed silver nanoparticles.

7. The 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 in a mass ratio of 1: (1.0-2.0).

8. The method for preparing a non-ferrous metal solder for low-temperature brazing according to claim 1, wherein: The following steps are involved: S1. Under a nitrogen atmosphere, carbon-coated copper nanorods and tin-bismuth alloy-coated silver nanoparticles were added to a mixing container in a predetermined ratio. The mixture was mechanically stirred at 200-400 rpm, a temperature of 20-40°C, and a mixing time of 20-40 min. 2-Mercaptobenzimidazole, an organic surfactant, and a dispersant were then added in sequence. Stirring was continued at 300-600 rpm for 15-30 min to form a stable composite system. S2. Add rosin resin, hydroxyethyl cellulose and 1-ethyl-3-methylimidazolium tetrafluoroborate, mixing temperature 30~60 ° C, mixing rate 500~800 rpm, mixing time 30~45 min, then add indium nitrate and citric acid, and continue mixing for 10~20min; 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 solder; S4. Perform low-temperature heat treatment at 60-80°C in an inert atmosphere for 20-40 minutes. After cooling, cut and vacuum package the final solder strip product.

9. Use of the non-ferrous metal solder for low-temperature brazing according to claim 1 in electronic device packaging, power device heat dissipation connection, or flexible circuit metal interconnection.

Images