Preparation process of silver-coated copper powder

Abstract

This invention provides a preparation process for silver-coated copper powder, relating to the field of metal powder technology. The preparation process of this invention involves acid-activated copper powder undergoing sequential acid pre-plating and alkaline thickening, followed by heat treatment after chemical plating, resulting in silver-coated copper powder with good adhesion and high density.

Description

Technical Field

[0001] This invention belongs to the field of metal powder technology and relates to a preparation process for silver-coated copper powder. Background Technology

[0002] Silver-coated copper powder is a substitute for silver powder and is used to prepare conductive pastes, which significantly reduces costs while maintaining the conductivity of the conductive paste. However, the following bottlenecks still exist when silver-coated copper powder is used to actually replace silver powder: (1) Incomplete coating structure: Conventional chemical silver plating process is difficult to achieve uniform coating, and there are pores in the silver layer, which leads to the oxidation of copper cores; (2) Uncontrollable replacement reaction rate: The silver layer grows in an island-like shape with large thickness deviation, which affects the continuity of the conductive network; (3) Insufficient oxidation resistance: Copper ion migration during storage causes the silver layer to crack, and existing passivation technology will sacrifice conductivity.

[0003] Chinese patent CN119387586A employs a two-step displacement-chemical reduction method. By precisely controlling the pH and combining it with the complexing agent EDTA, the dispersibility and antioxidant properties of silver-coated copper powder are significantly improved. However, in a strongly acidic environment, the silver layer that has already been formed is easily corroded, resulting in obvious silver layer defects on the surface of the prepared silver-coated copper powder. Furthermore, the silver utilization rate in this technology is not high enough, with a silver coating rate of only 20-28%, and excessive AgNO3 is wasted in the free silver particles.

[0004] Therefore, the existing preparation process for silver-coated copper powder needs further improvement. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a process for preparing silver-coated copper powder.

[0006] The technical solution of the present invention is as follows:

[0007] A process for preparing silver-coated copper powder includes the following steps: Acidic pre-plating: Acid-activated copper powder and dispersant are added to water, and the pH is adjusted to acidic to obtain a copper powder dispersion. A first silver salt solution is added to the copper powder dispersion, and a first reducing agent solution is added dropwise. After the dropwise addition, a first reaction is carried out to obtain a pre-plating dispersion. Alkaline thickening: The pH of the pre-plating dispersion is adjusted to alkaline, a second silver salt solution is added, and a second reducing agent solution is added dropwise. After the addition, a second reaction is carried out, followed by washing until neutral, drying, and heat treatment to obtain silver-coated copper powder. The concentration of the second silver salt solution is 2 to 10 times that of the first silver salt solution.

[0008] Preferably, the concentration of the first silver salt solution is 1-6 g / L, and the concentration of the second silver salt solution is 10-30 g / L; The weight ratio of the first silver salt to the acid-activated copper powder in the first silver salt solution is 0.01-0.03:1; The weight ratio of the second silver salt to the acid-activated copper powder in the second silver salt solution is 0.08-0.15:1.

[0009] Preferably, the first silver salt of the first silver salt solution and the second silver salt of the second silver salt solution are individually selected from one or both of silver nitrate and silver fluoride.

[0010] Preferably, the acid-activated copper powder is treated with a sulfuric acid solution with a concentration of 2-15 wt%. The pH value for adjusting the pH to acidity is 3-6; The pH value for adjusting the pH to alkaline is 9-11.

[0011] Preferably, the dispersant is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, gum arabic, and gelatin; The concentration of the dispersant in the copper powder dispersion is 1-10 g / L; The weight ratio of the copper powder to the dispersant is 100:0.3-15.

[0012] Preferably, the first reducing agent in the first reducing agent solution and the second reducing agent in the second reducing agent solution are individually selected from one or more of formic acid, glucose, L-ascorbic acid, vitamin C, citric acid, tartaric acid, sodium tartrate, and potassium tartrate. The concentration of the first reducing agent is 1-8 g / L, and the concentration of the second reducing agent is 10-40 g / L.

[0013] Preferably, the weight ratio of the first silver salt in the first silver salt solution to the first reducing agent in the first reducing agent solution is 1:0.7-1; The weight ratio of the second silver salt in the second silver salt solution to the second reducing agent in the second reducing agent solution is 1:1.2-2.

[0014] Preferably, the dropping rates of the first reducing agent solution and the second reducing agent solution are 1-30 mL / min each.

[0015] Preferably, the temperature of the first reaction is 20-50℃ and the time is 5-30 min; The temperature of the second reaction is 20-50℃, and the time is 30-90 min.

[0016] Preferably, the drying temperature is 50-80°C; The heat treatment temperature is 180-300℃ and the time is 10-60min.

[0017] The beneficial effects of this invention are: (1) The present invention adopts a gradient chemical plating process. By stepwise adjusting the pH of the plating solution (acidic first and then alkaline), the silver salt content of the plating solution (low concentration first and then high concentration), and the distribution reduction, the structure of the silver layer "dense bottom layer + porous outer layer" is realized, thereby improving the uniformity of the silver coating. The silver-coated copper powder has a low resistivity.

[0018] (2) The present invention uses a low-temperature short-time heat treatment process to promote the densification of the silver layer and reduce the resistivity. Attached Figure Description

[0019] Figure 1 This is a SEM image of the silver-coated copper powder obtained in Example 1.

[0020] Figure 2 This is a SEM image of the silver-coated copper powder obtained in Comparative Example 4. Detailed Implementation

[0021] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0022] This invention proposes a preparation process for silver-coated copper powder, comprising the following steps: Acidic pre-plating: Acid-activated copper powder and dispersant are added to water, and the pH is adjusted to acidic to obtain a copper powder dispersion. A first silver salt solution is added to a copper powder dispersion, and a first reducing agent solution is added dropwise. After the dropwise addition, a first reaction is carried out to obtain a pre-plating dispersion. Alkaline thickening: The pH of the pre-plating dispersion is adjusted to alkaline, a second silver salt solution is added, and a second reducing agent solution is added dropwise. After the addition, a second reaction is carried out. The solution is washed until neutral, dried, and heat-treated to obtain silver-coated copper powder. The concentration of the second silver salt solution is 2 to 10 times that of the first silver salt solution.

[0023] This invention uses a gradient chemical plating method to prepare silver-coated copper powder. First, a low-concentration first silver salt solution is used under acidic conditions to form a dense bottom layer. Then, a high-concentration second silver salt solution is used under alkaline conditions to thicken the bottom layer, forming a porous outer layer. Finally, after heat treatment, silver-coated copper powder with relatively uniform thickness, good coating adhesion, and good density is obtained, achieving a lower resistivity.

[0024] For example, the concentration of the second silver salt solution is 2, 3, 4, 5, 6, 7, 8, 9, or 10 times that of the first silver salt solution. Furthermore, the concentration of the second silver salt solution can be 4-10 times that of the first silver salt solution.

[0025] There are no particular restrictions on the process for acid-activated copper powder. For example, commercially available copper powder (with an average particle size of 1-10 μm) can be pre-cleaned ultrasonically with anhydrous ethanol, then ultrasonically cleaned with deionized water, then immersed in a 2-15 wt% sulfuric acid solution for 0.5-1 hour, and finally rinsed with deionized water until neutral. Acid-activated copper powder has active groups on its surface, resulting in better adhesion to the silver plating layer. This can improve the density of the underlying layer and the adhesion between the silver plating layer and the copper powder.

[0026] The first and second silver salt solutions can be added dropwise at rates of 1-10 mL / min.

[0027] In some embodiments, the concentration of the first silver salt solution is 1-6 g / L, and the concentration of the second silver salt solution is 10-30 g / L; The weight ratio of the first silver salt to the acid-activated copper powder in the first silver salt solution is 0.01-0.03:1; The weight ratio of the second silver salt to the acid-activated copper powder in the second silver salt solution is 0.08-0.15:1.

[0028] For example, the concentration of the first silver salt solution can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, etc., and the concentration of the second silver salt solution can be 10 g / L, 12 g / L, 15 g / L, 18 g / L, 20 g / L, 22 g / L, 25 g / L, 30 g / L, etc. For example, the weight ratio of the first silver salt to the acid-activated copper powder in the first silver salt solution can be 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, etc. The first silver salt mainly serves as a base and its weight is relatively low compared to the copper powder. The second silver salt has a thickening effect and its weight is relatively higher than that of the copper powder. For example, the weight ratio of the second silver salt to the acid-activated copper powder in the second silver salt solution can be 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, etc.

[0029] In some embodiments, the first silver salt of the first silver salt solution and the second silver salt of the second silver salt solution are individually selected from one or both of silver nitrate and silver fluoride.

[0030] In some embodiments, the acid-activated copper powder is treated with a sulfuric acid solution with a concentration of 2-15 wt%. Adjust the pH to an acidic level of 3-6; The pH should be adjusted to be alkaline, with a range of 9-11.

[0031] To adjust the pH to acidic, citric acid, malic acid, tartaric acid, nitric acid, formic acid, acetic acid, etc., can be used. To adjust the pH to alkaline, ammonia, urea, triethylenetetramine, sodium carbonate, sodium hydroxide, etc., can be used.

[0032] In some embodiments, the dispersant is selected from one or more of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG, such as PEG-2000, PEG-3000, etc.), polyvinyl alcohol (PVA, such as 85-90% degree of hydrolysis), gum arabic, and gelatin; The concentration of dispersant in the copper powder dispersion is 1-10 g / L; The weight ratio of copper powder to dispersant is 100:0.3-15.

[0033] For example, the concentration of the dispersant in the copper powder dispersion can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, etc.; the weight ratio of copper powder to dispersant can be 100:0.3, 100:1, 100:3, 100:5, 100:7, 100:10, 100:12, 100:15, etc. Further, the weight ratio of copper powder to dispersant can be 100:0.5-3.

[0034] In some embodiments, the first reducing agent in the first reducing agent solution and the second reducing agent in the second reducing agent solution are individually selected from one or more of formic acid, glucose, L-ascorbic acid, vitamin C, citric acid, tartaric acid, sodium tartrate, and potassium tartrate. The concentration of the first reducing agent is 1-8 g / L, and the concentration of the second reducing agent is 10-40 g / L.

[0035] The concentration of the first silver salt solution is relatively low, therefore the concentration of the first reducing agent is also relatively low; the concentration of the second silver salt solution is relatively high, therefore the concentration of the second reducing agent solution is also relatively high. For example, the concentration of the first reducing agent can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, etc., and further, the concentration of the first reducing agent can be 3-8 g / L. For example, the concentration of the second reducing agent can be 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, etc., and further, the concentration of the second reducing agent can be 10-20 g / L.

[0036] Furthermore, the first and second reducing agents are each composed of two reducing agents with different reducing properties. For example, the first and second reducing agents can be composed of formic acid and glucose, or glucose and L-ascorbic acid, respectively. The first and second reducing agents are composed of two reducing agents with different reducing abilities (the two reducing agents have different potentials E°; the lower the potential, the stronger the reducing power; the stronger the reducing agent is called a strong reducing agent, and the weaker the reducing agent is called a weak reducing agent). The reducing agent with high reducing power can quickly reduce silver salts and deposit a silver layer, while the reducing agent with low reducing power can reduce silver salts and deposit a silver layer more slowly. Together, they can form a dense silver plating layer with high bonding strength, which is beneficial for improving the conductivity of silver-coated copper powder and reducing resistivity. When the reducing agent is composed of a strong reducing agent and a weak reducing agent, the weight ratio of the strong reducing agent to the weak reducing agent can be 1:5 to 5:1.

[0037] In some embodiments, the weight ratio of the first silver salt in the first silver salt solution to the first reducing agent in the first reducing agent solution is 1:0.7-1; The weight ratio of the second silver salt in the second silver salt solution to the second reducing agent in the second reducing agent solution is 1:1.2-2.

[0038] For example, the weight ratio of the first silver salt to the first reducing agent can be 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, etc. The weight ratio of the second silver salt to the second reducing agent can be 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc.

[0039] In some embodiments, the dropping rates of the first reducing agent solution and the second reducing agent solution are individually 1-30 mL / min. For example, the individual dropping rates can be 1 mL / min, 2 mL / min, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, etc.

[0040] In some embodiments, the temperature of the first reaction is 20-50°C and the time is 5-30 min; The second reaction is carried out at a temperature of 20-50℃ for 30-90 minutes.

[0041] In this invention, both the acidic pre-plating and alkaline thickening reactions can be carried out under relatively mild conditions, such as room temperature or slight heating.

[0042] In some embodiments, the drying temperature is 50-80°C; The heat treatment temperature is 180-300℃, and the time is 10-60 minutes.

[0043] In this invention, because the underlying silver plating has high adhesion and good density, high-temperature heat treatment is not required. The heat treatment temperature can be relatively low and the treatment time short. For example, the heat treatment temperature can be 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc. Further, the heat treatment temperature can be 200-260℃.

[0044] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0045] Example 1 10g of copper powder was immersed in anhydrous ethanol and ultrasonically cleaned for 16 minutes. After filtration, it was washed three times with deionized water. Then, the copper powder was placed in 150mL of 8wt% sulfuric acid and stirred for 1 hour. After filtration, it was washed with deionized water until neutral to obtain activated copper powder.

[0046] The activated copper powder and 1g PVP were added to 200mL of deionized water, and citric acid was added to adjust the pH to 3. The mixture was then dispersed evenly to obtain a copper powder dispersion. 55mL of a 3g / L silver nitrate solution was added dropwise to the copper powder dispersion at a rate of 2mL / min. Then, a first reducing agent solution consisting of 15mL of a 2g / L formic acid solution and 25mL of a 5g / L glucose solution was added dropwise at a rate of 20mL / min. After the addition was complete, the mixture was stirred at 25℃ and 400rpm for 20min to obtain a pre-plating solution.

[0047] The pH of the pre-plating solution was adjusted to 10 with ammonia. 75 mL of a 20 g / L silver nitrate solution was added dropwise at a rate of 3 mL / min. Then, a second reducing agent solution consisting of 110 mL of a 10 g / L glucose solution and 55 mL of a 20 g / L L-ascorbic acid solution was added dropwise at a rate of 30 mL / min. After the addition was complete, the mixture was stirred at 45°C and 400 rpm for 1 hour. After the reaction, the solid was filtered out, washed with deionized water until neutral, and vacuum dried at 60°C for 8 hours. Finally, it was placed in a tube furnace under a N2 atmosphere and heat-treated at 250°C for 30 minutes to obtain silver-coated copper powder.

[0048] The SEM images of the silver-coated copper powder obtained in this embodiment are attached. Figure 1 As shown, the surface has good density.

[0049] Example 2 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the first reducing agent solution is replaced with 40 mL of glucose solution with a concentration of 4 g / L, and the second reducing agent solution is replaced with 165 mL of glucose solution with a concentration of 13 g / L. The remaining steps remain unchanged.

[0050] Example 3 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the first reducing agent solution is replaced with 40 mL of formic acid at a concentration of 4 g / L, and the second reducing agent solution is replaced with 165 mL of glucose at a concentration of 13 g / L. The remaining steps remain unchanged.

[0051] Example 4 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the first reducing agent solution is replaced with 40 mL of a 4 g / L glucose solution, and the second reducing agent solution is replaced with 165 mL of a 13 g / L L-ascorbic acid solution. The remaining steps remain unchanged.

[0052] Comparative Example 1 The difference between this comparative example and Example 1 is that in Example 1, the copper powder was not activated with sulfuric acid; instead, the copper powder was directly subjected to acidic pre-plating after ultrasonic cleaning with anhydrous ethanol and cleaning with deionized water. The remaining steps remained unchanged.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that in Example 1, citric acid was not added to the copper powder dispersion to adjust the pH, and the pH of the copper powder dispersion was 6.5. The remaining steps remained unchanged.

[0054] Comparative Example 3 The difference between this comparative example and Example 1 is that in Example 1, ammonia was not added to the pre-plating solution to adjust the pH to 10, and a silver nitrate solution with a concentration of 20 g / L was directly added to the pre-plating solution, i.e., the alkaline thickening step was changed to an acidic thickening step. The remaining steps remained unchanged.

[0055] Comparative Example 4 The difference between this comparative example and Example 1 is that in Example 1, the silver-coated copper powder obtained after vacuum drying was not subjected to heat treatment. The remaining steps remained unchanged.

[0056] The SEM images of the silver-coated copper powder obtained in this comparative example are attached. Figure 2 As shown, the surface density is not as good as that of the silver-coated copper powder obtained in Example 1.

[0057] Example 5 10g of copper powder was immersed in anhydrous ethanol and ultrasonically cleaned for 15 minutes. After filtration, it was washed three times with deionized water. Then, the copper powder was placed in 200mL of 5wt% sulfuric acid and stirred for 1 hour. After filtration, it was washed with deionized water until neutral to obtain activated copper powder.

[0058] The activated copper powder and 0.5 g of PEG-2000 were added to 200 mL of deionized water. Tartaric acid was added to adjust the pH to 5.5, and the mixture was dispersed evenly to obtain a copper powder dispersion. 100 mL of a 2 g / L silver nitrate solution was added dropwise to the copper powder dispersion at a rate of 2 mL / min. Then, a first reducing agent solution consisting of 25 mL of a 5 g / L formic acid solution and 15 mL of a 2 g / L glucose solution was added dropwise at a rate of 20 mL / min. After the addition was complete, the mixture was stirred at 25°C and 400 rpm for 20 min to obtain a pre-plating solution.

[0059] The pH of the pre-plating solution was adjusted to 9.5 with ammonia. Then, 50 mL of a 20 g / L silver nitrate solution was added dropwise at a rate of 2 mL / min. Following this, a second reducing agent solution consisting of 30 mL of a 10 g / L glucose solution and 100 mL of a 15 g / L L-ascorbic acid solution was added dropwise at a rate of 20 mL / min. After the addition was complete, the mixture was stirred at 30°C and 400 rpm for 90 min. After the reaction was complete, the solid was filtered out, washed with deionized water until neutral, and vacuum dried at 60°C for 8 h. Finally, it was placed in a tube furnace under a N2 atmosphere and heat-treated at 200°C for 60 min to obtain silver-coated copper powder.

[0060] Example 6 The difference between this embodiment and Embodiment 5 is that in Embodiment 5, the first reducing agent solution was adjusted to consist of 16 mL of formic acid with a concentration of 5 g / L and 15 mL of glucose solution with a concentration of 5 g / L. The remaining steps remain unchanged.

[0061] Example 7 The difference between this embodiment and Embodiment 5 is that in Embodiment 5, the second reducing agent solution was adjusted to consist of 30 mL of formic acid with a concentration of 10 g / L and 100 mL of L-ascorbic acid with a concentration of 15 g / L. The remaining steps remain unchanged.

[0062] Performance testing Detection of silver content and D in silver-coated copper powder. 50 Particle size, volume resistivity, and oxidation resistance.

[0063] Antioxidant properties were characterized by the oxidation weight gain ratio of the silver-coated copper powder in hot air. The lower the oxidation weight gain ratio, the better the antioxidant properties and the higher the density of the silver plating. The specific test was as follows: 50 mg of silver-coated copper powder was heated at 200 °C for 2 hours in air using a thermogravimetric analyzer, and the oxidation weight gain ratio of the silver-coated copper powder was measured.

[0064] The performance results are shown in Table 1 below.

[0065] Table 1

[0066] As can be seen from the results in Table 1 above, when the first reducing agent and the second reducing agent are composed of two different reducing agents and when acidic pre-plating and alkaline thickening are used, the reduction and electroless plating effects are better, and the obtained silver-coated copper powder has low volume resistivity, good oxidation resistance, and high density of silver plating.

[0067] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A preparation process for silver-coated copper powder, characterized in that, Includes the following steps: Acidic pre-plating: Acid-activated copper powder and dispersant are added to water, and the pH is adjusted to acidic to obtain a copper powder dispersion. A first silver salt solution is added to the copper powder dispersion, and a first reducing agent solution is added dropwise. After the dropwise addition, a first reaction is carried out to obtain a pre-plating dispersion. Alkaline thickening: The pH of the pre-plating dispersion is adjusted to alkaline, a second silver salt solution is added, and a second reducing agent solution is added dropwise. After the addition, a second reaction is carried out, followed by washing until neutral, drying, and heat treatment to obtain silver-coated copper powder. The concentration of the second silver salt solution is 2 to 10 times that of the first silver salt solution.

2. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The concentration of the first silver salt solution is 1-6 g / L, and the concentration of the second silver salt solution is 10-30 g / L; The weight ratio of the first silver salt to the acid-activated copper powder in the first silver salt solution is 0.01-0.03:1; The weight ratio of the second silver salt to the acid-activated copper powder in the second silver salt solution is 0.08-0.15:

1.

3. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The first silver salt of the first silver salt solution and the second silver salt of the second silver salt solution are individually selected from one or both of silver nitrate and silver fluoride.

4. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The acid-activated copper powder is treated with a sulfuric acid solution with a concentration of 2-15 wt%. The pH value for adjusting the pH to acidity is 3-6; The pH value for adjusting the pH to alkaline is 9-11.

5. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The dispersant is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, gum arabic, and gelatin; The concentration of the dispersant in the copper powder dispersion is 1-10 g / L; The weight ratio of the copper powder to the dispersant is 100:0.3-15.

6. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The first reducing agent in the first reducing agent solution and the second reducing agent in the second reducing agent solution are individually selected from one or more of formic acid, glucose, L-ascorbic acid, vitamin C, citric acid, tartaric acid, sodium tartrate and potassium tartrate; The concentration of the first reducing agent is 1-8 g / L, and the concentration of the second reducing agent is 10-40 g / L.

7. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The weight ratio of the first silver salt in the first silver salt solution to the first reducing agent in the first reducing agent solution is 1:0.7-1; The weight ratio of the second silver salt in the second silver salt solution to the second reducing agent in the second reducing agent solution is 1:1.2-2.

8. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The dropping rates of the first reducing agent solution and the second reducing agent solution are 1-30 mL / min each.

9. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The temperature of the first reaction is 20-50℃, and the time is 5-30 min; The temperature of the second reaction is 20-50℃, and the time is 30-90 min.

10. The preparation process of silver-coated copper powder according to claim 1, characterized in that, The drying temperature is 50-80℃; The heat treatment temperature is 180-300℃ and the time is 10-60min.

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