Preparation method of solid tin-coated copper particles

Abstract

The invention relates to the technical field of electronic packaging, in particular to a preparation method of solid tin-coated copper particles, a phosphorus salt additive in a chemical plating solution is adsorbed on the surfaces of the copper particles to influence and control the replacement reaction speed between tin and copper and nucleation growth of tin on the surfaces of the copper particles, and then the performance of a coating layer is influenced and controlled; the problem of diffusion velocity imbalance of copper and tin in the replacement reaction process is solved, and then generation of Kirkendall cavities of a copper-tin interface is inhibited; the compactness of a tin coating layer generated on the surfaces of the copper particles is greatly improved through addition of the phosphor salt, then the prepared tin-coated copper particles have the advantage of better oxidation resistance, the welding material prepared by adopting the obtained copper particles as the raw material adopts the tin or tin-based alloy coated copper particles to replace traditional tin or silver, and the welding cost is reduced. Therefore, low-temperature interconnection and high-temperature service are realized, and the cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic packaging, and particularly relates to a preparation method of solid tin-coated copper particles. BACKGROUND

[0002] With the development of technology, new energy vehicles, 5G communication and high-speed rail traction systems and other key equipment are rapidly developing towards higher junction temperature, higher power density and longer service life, which puts unprecedentedly stringent requirements on the performance and reliability of core power devices. Traditional silicon-based power devices have been difficult to meet the above development needs due to their material physical limits, while wide-bandgap semiconductor materials (such as silicon carbide SiC and gallium nitride GaN) have become the first choice for the next generation of high-performance power modules due to their excellent electrical and thermal properties. However, the full play of device performance must rely on high-reliability packaging technology that can work stably at more than 250℃ for a long time. The widely used packaging interconnection materials, such as high-lead solder, gold-based / bismuth-based / zinc-based lead-free alloy and tin-based solder, generally have problems such as high toxicity, high cost, low melting point or remelting risk, and cannot meet the application requirements of wide-bandgap devices for high temperature and high reliability. Therefore, various alternative solutions have emerged to solve the above problems.

[0003] Among the many alternative solutions, transient liquid phase diffusion bonding materials and low-temperature sintering materials are considered as potential replacements for traditional solders. Among them, nano / micro silver sintering materials, as a kind of low-temperature sintering technology, have shown good application prospects in high-end packaging due to their excellent electrical conductivity and thermal conductivity. However, silver material itself has inherent disadvantages such as high sensitivity to electrochemical migration and high cost, which greatly limits its large-scale application.

[0004] Copper, with its electrical conductivity and thermal conductivity close to silver and a cost of only about 1 / 20 of silver, is considered to be the most potential alternative metal. However, copper particles are easily oxidized in air, and the dense copper oxide / copper oxide insulating layer formed on the surface can significantly reduce the sintering driving force and damage the interface connection reliability. The traditional hydrogen or formic acid reduction process can remove the oxide layer, but it also brings safety and environmental risks. To solve the sintering problem caused by copper oxidation, the core-shell structure of tin-coated copper has attracted widespread attention due to its unique "low-temperature melting and high-temperature stability" synergistic mechanism.

[0005] However, the core-shell structure of tin-coated copper has long been restricted by Kirkendall voids during its preparation and service process. This defect is caused by the significant asymmetric interdiffusion between copper and tin: the diffusion rate of copper atoms is much higher than that of tin, which causes a net vacancy flow from tin to copper at the interface, and finally forms a structural void on the copper side. This greatly limits the use of tin-coated copper as a soldering material in low-temperature interconnection and high-temperature service In summary, existing methods are insufficient to meet the requirements of wide-bandgap semiconductor power devices for low-temperature interconnection, high-temperature stable operation, high reliability, and low cost. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing solid tin-coated copper particles, which solves the technical problem in the prior art that it is difficult to meet the requirements of low-temperature interconnection, high-temperature stable operation, high reliability and low cost of wide bandgap semiconductor power devices.

[0007] To achieve the above objectives, the present invention provides a method for preparing solid tin-coated copper particles, comprising the following: The surface of the copper particles is pretreated to remove oxides and impurities. Pretreated copper particles are placed in a plating solution containing phosphate salts, thiourea, hydroquinone, disodium ethylenediaminetetraacetate dihydrate, ethylene glycol, ascorbic acid, and sodium dodecylbenzenesulfonate. Tin salt solution is added to the Cu particle plating solution to carry out an ion exchange reaction. After filtration, washing and drying, tin-coated copper particles are obtained.

[0008] In the step of "pre-treating the surface of copper particles to remove oxides and impurities", the pre-treatment is washing with a dilute hydrochloric acid aqueous solution.

[0009] In the step of "pre-treating the surface of copper particles to remove oxides and impurities from the surface of copper particles", the copper particles are micron-sized copper particles.

[0010] The phosphate salt is any one or more combinations of sodium phosphite, sodium hypophosphite, potassium phosphite, and ammonium phosphite.

[0011] The plating solution contains 0.4-1 mol / L thiourea, 0.001-0.01 mol / L hydroquinone, 0.0001-0.001 mol / L EDTA-2Na, 0.002-0.01 mol / L ascorbic acid, 12 ml / L ethylene glycol, 0.2-1 mol / L sodium hypophosphite monohydrate, and 0.001-0.01 mol / L sodium dodecylbenzenesulfonate.

[0012] In the step of "placing pretreated copper particles in a plating solution containing phosphate salts, thiourea, hydroquinone, disodium ethylenediaminetetraacetate dihydrate, ethylene glycol, ascorbic acid, and sodium dodecylbenzenesulfonate", tin salts are dissolved in hydrochloric acid and slowly added dropwise to the plating solution.

[0013] In the step of "placing the pretreated copper particles in the plating solution containing phosphate salts, thiourea, hydroquinone, disodium ethylenediaminetetraacetate dihydrate, ethylene glycol, ascorbic acid, and sodium dodecylbenzenesulfonate", the temperature is room temperature and the stirring time is 30-120 min.

[0014] This invention discloses a method for preparing solid tin-coated copper particles. The phosphate salt additive in the plating solution of this invention influences and controls the displacement reaction rate between tin and copper and the nucleation and growth of tin on the copper particle surface through adsorption, thereby affecting and controlling the performance of the coating layer. It solves the imbalance in the diffusion rate of copper and tin during the displacement reaction, thus inhibiting the formation of Kirkendal voids at the copper-tin interface. The addition of phosphate salts significantly improves the density of the tin coating layer formed on the copper particle surface, resulting in better oxidation resistance in the prepared tin-coated copper particles. Welding materials prepared using the copper particles obtained by this invention, which use tin or tin-based alloy-coated copper particles instead of traditional tin or silver, achieve high-temperature operation in low-temperature interconnects, significantly reducing costs. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0016] Figure 1 This is a schematic diagram showing the change in weight of tin-coated copper particles compared to uncoated copper particles as temperature increases, according to Embodiment 1 of the present invention.

[0017] Figure 2 These are cross-sectional views of the tin-coated copper particles prepared in Example 1 of the present invention and the tin-coated copper particles in Comparative Example 1. Detailed Implementation

[0018] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0019] Please see Figure 1 and Figure 2 , Figure 1 This is a schematic diagram showing the change in weight of tin-coated copper particles compared to uncoated copper particles as temperature increases, according to Embodiment 1 of the present invention. Figure 2 These are cross-sectional views of the tin-coated copper particles prepared in Example 1 of the present invention and the tin-coated copper particles in Comparative Example 1.

[0020] This invention provides a method for preparing solid tin-coated copper particles, comprising the following: S1. Pre-treat the surface of the copper particles to remove oxides and impurities from the surface of the copper particles; In this specific embodiment, the copper powder used as the starting material is not limited, and the particle size of the electronic solder is 1-10 micrometers. The copper particles used in this invention are self-made copper particles with a particle size of about 1-3 micrometers. The copper particles used as the substrate are prepared by a chemical reduction method and have a near-spherical morphology. Copper particles are easily oxidized in air to form oxides on their surface, and the oxides or other impurities on the surface are generally removed by washing with hydrochloric acid aqueous solution.

[0021] S2. Place the pretreated copper particles in the plating solution, which contains phosphate salts, thiourea, hydroquinone, disodium ethylenediaminetetraacetate dihydrate, ethylene glycol, ascorbic acid, and sodium dodecylbenzenesulfonate. In this specific embodiment, the plating solution contains phosphate salt additives and thiourea; during the chemical displacement process, the copper particles are kept in a dispersed state. S3. Add tin salt solution to Cu particle plating solution to carry out ion exchange reaction. After filtration, washing and drying, tin-coated copper particles are obtained.

[0022] In this specific embodiment, the present invention is a chemical plating process that forms tin-coated copper particles through a displacement reaction between tin and copper. During chemical plating, one of the plating solutions, either thiourea or a urea derivative, is used as a ligand to effectively lower the copper electrode potential below that of the tin electrode. Magnetic stirring can be used during the displacement reaction to prevent the copper particles from sticking together. Simultaneously, other methods can be selected to keep the plating solution and copper particles in a dynamic state, thereby preventing the copper particles from sticking together.

[0023] The choice of plating bath, especially the selection of additives within it, plays a crucial role in the quality of the electroless plating layer and the performance of the resulting coated copper particles. The electroless plating process prepares tin-coated copper particles through a displacement reaction between tin and copper, where tin nucleates and diffuses on the surface of the copper particles. Reducing agents that can be used in the plating bath include glucose, ascorbic acid, potassium borohydride, potassium sodium tartrate, hydrazine hydrate, and formaldehyde. Phosphate salt additives in the plating bath, by forming a mediating layer on the copper particles and their surface, control the displacement and diffusion rates between tin and copper, thereby influencing and controlling tin nucleation and growth, and ultimately affecting and controlling the performance of the coating layer.

[0024] Extensive experiments revealed that phosphate salts, as additives, can form a mediating layer on the copper surface. This results in tin-coated copper particles with a complete core-shell structure, and the tin-coated copper interface does not exhibit Kirkendal voids. Tin-coated copper also demonstrates superior oxidation resistance. The phosphate salts are any one or more of sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite. Example

[0025] Take 0.3g of copper particles and place them in a dilute hydrochloric acid aqueous solution and stir to remove oxides and other impurities from the surface of the copper particles; Pickled copper particles are added to the plating solution. The plating solution contains 0.4-1 mol / L thiourea, 0.001-0.01 mol / L hydroquinone, 0.0001-0.001 mol / L EDTA-2Na, 0.002-0.01 mol / L ascorbic acid, 12 ml / L ethylene glycol, 0.2-1 mol / L sodium hypophosphite monohydrate, and 0.001-0.01 mol / L sodium dodecylbenzenesulfonate. The temperature is 10-70℃. 0.1-0.5 mol / L stannous chloride is dissolved in hydrochloric acid aqueous solution and then slowly added dropwise to the above plating solution. Electroplating is performed for 30-120 minutes, with the solution kept stirred during the process to prevent copper particles from sticking together. After electroplating, the solution is washed three or more times alternately with water and ethanol, and then dried under vacuum at 50-60℃ to obtain tin-coated copper particles.

[0026] Comparative Example 1: Take 0.3g of copper particles and place them in a dilute hydrochloric acid aqueous solution and stir to remove oxides and other impurities from the surface of the copper particles; Pickled copper particles are added to the plating solution. The plating solution contains 0.4-1 mol / L thiourea, 0.001-0.01 mol / L hydroquinone, 0.0001-0.001 mol / L EDTA-2Na, 0.002-0.01 mol / L ascorbic acid, 12 ml / L ethylene glycol, and 0.001-0.01 mol / L sodium dodecylbenzenesulfonate. The temperature is 10-70℃. 0.1-0.5 mol / L stannous chloride is dissolved in hydrochloric acid aqueous solution and then slowly added dropwise to the above plating solution. Electroplating is performed for 30-120 minutes, with the solution kept stirred during the process to prevent copper particles from sticking together. After electroplating, the solution is washed three or more times alternately with water and ethanol, and then dried under vacuum at 50-60℃ to obtain tin-coated copper particles.

[0027] See Figure 1 , Figure 1 The changes in weight of the tin-coated copper particles of Example 1 compared to the uncoated copper particles as temperature increases are shown. It can be seen that the tin-coated copper particles prepared in Example 1 have better oxidation resistance.

[0028] See Figure 2 , Figure 2The cross-sectional views of the tin-coated copper particles prepared in Example 1 and Comparative Example 1 are shown. It can be seen that the cross-section of Comparative Example 1 has a hollow structure, while the cross-section of Example 1 has a solid core-shell structure. This result shows that surface phosphate salts, as additives, can control the diffusion rate between copper and tin, thereby forming solid tin-coated copper particles.

[0029] Using the method for preparing solid tin-coated copper particles according to this embodiment, the phosphate salt additive in the plating solution of this invention affects and controls the displacement reaction rate between tin and copper and the nucleation and growth of tin on the surface of the copper particles by adsorption, thereby influencing and controlling the performance of the coating layer. It solves the imbalance in the diffusion rate of copper and tin during the displacement reaction process, thus inhibiting the formation of Kirkendal voids at the copper-tin interface. The addition of phosphate salts greatly improves the density of the tin coating layer formed on the surface of the copper particles, thus giving the prepared tin-coated copper particles better oxidation resistance. Welding materials prepared using the copper particles obtained by this invention as raw materials, using tin or tin-based alloy coated copper particles instead of traditionally used tin or silver, achieve high-temperature service in low-temperature interconnection, greatly reducing costs.

[0030] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A method for preparing solid tin-coated copper particles, characterized in that, Including the following: The surface of the copper particles is pretreated to remove oxides and impurities. Pretreated copper particles are placed in a plating solution containing phosphate salts, thiourea, hydroquinone, disodium ethylenediaminetetraacetate dihydrate, ethylene glycol, ascorbic acid, and sodium dodecylbenzenesulfonate. Tin salt solution is added to the Cu particle plating solution to carry out an ion exchange reaction. After filtration, washing and drying, tin-coated copper particles are obtained.

2. The method for preparing solid tin-coated copper particles as described in claim 1, characterized in that, In the step "Pre-treatment of the copper particle surface to remove oxides and impurities", the pre-treatment is washing with a dilute hydrochloric acid aqueous solution.

3. The method for preparing solid tin-coated copper particles as described in claim 2, characterized in that, In the step "pre-treating the surface of copper particles to remove oxides and impurities", the copper particles are micron-sized copper particles.

4. The method for preparing solid tin-coated copper particles as described in claim 3, characterized in that, The phosphate salt is any one or more combinations of sodium phosphite, sodium hypophosphite, potassium phosphite, and ammonium phosphite.

5. The method for preparing solid tin-coated copper particles as described in claim 4, characterized in that, The plating solution contains 0.4-1 mol / L thiourea, 0.001-0.01 mol / L hydroquinone, 0.0001-0.001 mol / L EDTA-2Na, 0.002-0.01 mol / L ascorbic acid, 12 ml / L ethylene glycol, 0.2-1 mol / L sodium hypophosphite monohydrate, and 0.001-0.01 mol / L sodium dodecylbenzenesulfonate.

6. The method for preparing solid tin-coated copper particles as described in claim 5, characterized in that, In the step of "placing the pretreated copper particles in the plating solution containing phosphate salts, thiourea, hydroquinone, disodium ethylenediaminetetraacetate dihydrate, ethylene glycol, ascorbic acid, and sodium dodecylbenzenesulfonate", tin salts are dissolved in hydrochloric acid and slowly added dropwise to the plating solution.

7. The method for preparing solid tin-coated copper particles as described in claim 6, characterized in that, In the step of "placing the pretreated copper particles in the plating solution containing phosphate salts, thiourea, hydroquinone, disodium ethylenediaminetetraacetate dihydrate, ethylene glycol, ascorbic acid, and sodium dodecylbenzenesulfonate", the temperature is room temperature and the stirring time is 30-120 min.

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