Silver-coated copper powder for conductive paste and preparation method and application of silver-coated copper powder

Abstract

The invention relates to silver-coated copper powder for conductive paste and a preparation method and application of the silver-coated copper powder. The preparation method comprises the steps that copper powder is soaked in an acid solution, and pretreated copper powder is obtained after washing; the pretreated copper powder is subjected to ultrasonic treatment in ethyl alcohol or isopropyl alcohol, and copper powder dispersion liquid is obtained; dissolving TGA in water, and adjusting the pH value to 8-9 to obtain a TGA solution; adding the copper powder dispersion liquid into a TGA solution, stirring, washing and drying to obtain TGA-coated copper powder; and adding the TGA-coated copper powder into a reduction solution of a silver nitrate and TGA aqueous solution, stirring for reaction, and carrying out post-treatment to obtain the silver-coated copper powder. According to the preparation method, TGA is adopted as a pre-protection layer of copper powder and a silver ion reduction accelerant, oxidation resistance is achieved through a bidentate coordination structure formed by sulfydryl and carboxyl in thioglycollic acid and copper, silver ions are complexed through carboxyl in thioglycollic acid, the silver ions are directly reduced into silver through sulfydryl, uniform deposition of silver is guided, and the copper powder is prepared. A silver coating layer in the obtained silver-coated copper is compact and uniform, and the conductivity is excellent.

Description

Technical Field

[0001] This invention belongs to the field of conductive paste technology, specifically relating to a silver-coated copper powder for conductive paste, its preparation method, and its application. Background Art

[0002] Currently, the use of silver powder in the electronics industry, especially in the field of conductive pastes, is constantly increasing. In order to reduce costs, people expect to develop a low-cost, high-conductivity conductive powder. Among them, silver-coated copper powder is considered an ideal alternative to silver powder. By wrapping a silver shell around a copper core, silver-coated copper can ensure the excellent conductivity of silver while using copper to reduce the overall material cost.

[0003] However, the silver shell layer of silver-coated copper powder in the existing technology inevitably has many coating defects, such as the silver coating layer not being dense or uniformly deposited, resulting in some of the inner copper powder surface being exposed to the air. The exposed copper powder is more prone to oxidation. These defects will also produce a "defect effect", further accelerating the oxidation rate of the copper core. In addition, the bond between silver and copper is not strong, which leads to the problem of detachment. As a result, the conductivity of silver-coated copper powder is poor.

[0004] Therefore, there is an urgent need for a method to prepare silver-coated copper powder for conductive pastes, which can avoid the problems of poor density, uniformity and conductivity of silver-coated copper nanoparticles in the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing silver-coated copper powder for conductive paste, wherein the silver coating layer in the prepared silver-coated copper is dense and uniform, and has excellent conductivity.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: a method for preparing silver-coated copper powder for conductive paste, comprising the following steps: (1) Soak copper powder in an acid solution for 10-20 minutes to remove surface oxides, and then wash with deionized water until neutral to obtain pretreated copper powder; (2) Disperse the pretreated copper powder in ethanol or isopropanol and sonicate for 10 to 20 minutes to obtain a copper powder dispersion; (3) Dissolve TGA in water and adjust the pH to 8-9 with NaOH to obtain a TGA solution; (4) Add the copper powder dispersion to the TGA solution, stir at room temperature, wash with water and ethanol alternately, and then dry to obtain TGA-coated copper powder; (5) Add the copper powder coated with TGA to the reducing solution and stir at 45-60°C for 20-40 minutes. After the reaction is complete, let it stand, filter, wash and dry to obtain silver-coated copper nanoparticles. The reducing solution is an aqueous solution of silver nitrate and TGA.

[0007] Preferably, the average particle size of the copper powder in step (1) is 0.5-2 μm, and the acid solution is a 0.1M hydrochloric acid aqueous solution or a 5% citric acid aqueous solution.

[0008] Preferably, the concentration of the copper powder dispersion in step (2) is 20-40 mg / mL.

[0009] Preferably, the concentration of the TGA solution in step (3) is 20-40 mM.

[0010] Preferably, the stirring time in step (4) is 30-60 min, and the mass ratio of the copper powder dispersion to the TGA solution is 50-20:0.1-0.5.

[0011] Preferably, the concentration of silver nitrate in the reducing solution in step (5) is 3-8 g / L and the concentration of TGA is 2-5 mM.

[0012] Preferably, the mass-to-volume ratio of the copper powder coated with TGA to the reducing solution in step (5) is 3-50 mg: 100-400 mL.

[0013] Another object of the present invention is to provide a silver-coated copper powder for conductive paste, wherein the silver-coated copper powder for conductive paste is prepared by the above-mentioned preparation method of silver-coated copper powder for conductive paste, and the average particle size of the silver-coated copper nanoparticles is 3-5 μm.

[0014] Another object of the present invention is to provide an application of the silver-coated copper powder prepared by the above method in a conductive paste, wherein the conductive paste comprises the following components by mass percentage: 50-82% silver-coated copper powder, 17-47% organic carrier, 2-8% inorganic binder, 0.5-1% dispersant and 0.5-2% sintering inhibitor.

[0015] Preferably, the organic carrier is composed of organic resin, organic solvent and defoamer in a mass percentage ratio of 10-40%: 60-85%: 0.2-1%, wherein the organic resin is epoxy resin, phenolic resin or urethane, the organic solvent is at least one of ethanol, diethylene glycol butyl ether, ethylene glycol, ethylene glycol butyl ether acetate, and the defoamer is tributyl phosphate.

[0016] Preferably, the inorganic binder is glass powder PbO-B2O3-SiO2, the dispersant is at least one of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone, and the sintering inhibitor is carbon black.

[0017] More preferably, the content of each component of the glass powder, in molar percentage, is as follows: PbO 15-65 wt.%, B2O3 10-35 wt.%, SiO2 5-18 wt.%.

[0018] Compared with the prior art, the advantages of the present invention are: In the preparation method of silver-coated copper powder of the present invention, mercaptoacetic acid (TGA) is used as a pre-protective layer for copper powder and a silver ion reduction promoter. The strong binding ability of the mercapto-SH and carboxyl-COOH groups in mercaptoacetic acid to form a bidentate coordination structure with copper achieves anti-oxidation. On the other hand, the carboxyl-COOH groups in mercaptoacetic acid complex silver ions, and the mercapto-SH groups directly reduce silver ions to silver, guiding the uniform deposition of silver. In the reduction process, mercaptoacetic acid also acts as a reducing agent and a dispersant, regulating the release rate of silver ions, preventing excessive growth of silver particles, and controlling the particle size of silver-coated copper powder. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the embodiments. Example 1

[0020] A method for preparing silver-coated copper powder for conductive paste includes the following steps: (1) Copper powder with an average particle size of 10 μm was soaked in 0.1 M hydrochloric acid aqueous solution for 15 minutes to remove surface oxides, and then washed with deionized water until neutral to obtain pretreated copper powder; (2) Disperse the pretreated copper powder in ethanol and sonicate for 20 minutes to obtain a copper powder dispersion with a concentration of 20 mg / mL. (3) Dissolve TGA in water and adjust the pH to 8 with NaOH to obtain a TGA solution with a concentration of 20 mM; (4) Add the copper powder dispersion to the TGA solution, stir at room temperature for 50 min, wash with water and ethanol three times alternately, and then dry to obtain TGA-coated copper powder, wherein the mass ratio of copper powder dispersion to TGA solution is 50:0.5; (5) Add the copper powder coated with TGA to the reducing solution, stir at 50°C for 40 minutes, and after the reaction is complete, let it stand, filter, wash with water and dry to obtain silver-coated copper powder with an average particle size of 3.2 μm; wherein the reducing solution is an aqueous solution of silver nitrate and TGA, the concentration of silver nitrate in the reducing solution is 5 g / L and the concentration of TGA is 3 mM.

[0021] An application of the silver-coated copper powder prepared by the above method in a conductive paste, wherein the conductive paste comprises the following components by mass percentage: 70% silver-coated copper powder, 23% organic carrier, 5.8% inorganic binder, 0.6% dispersant and 0.6% sintering inhibitor.

[0022] The organic carrier is composed of organic resin, organic solvent and defoamer in a mass percentage ratio of 30%:69.5%:0.5%, wherein the organic resin is epoxy resin E44, the organic solvent is diethylene glycol butyl ether, and the defoamer is tributyl phosphate.

[0023] The inorganic binder is glass powder PbO-B2O3-SiO2, and the content of each component of the glass powder by molar percentage is as follows: PbO 60 wt.%, B2O3 30 wt.%, SiO2 10 wt.%, the dispersant is polyethylene glycol, and the sintering inhibitor is carbon black. Example 2

[0024] A method for preparing silver-coated copper powder for conductive paste includes the following steps: (1) Copper powder with an average particle size of 0.8 μm was soaked in a 5% citric acid aqueous solution for 15 minutes to remove surface oxides, and then washed with deionized water until neutral to obtain pretreated copper powder. (2) Disperse the pretreated copper powder in isopropanol and sonicate for 20 minutes to obtain a copper powder dispersion with a concentration of 40 mg / mL. (3) Dissolve TGA in water and adjust the pH to 9 with NaOH to obtain a TGA solution with a concentration of 40 mM; (4) Add the copper powder dispersion to the TGA solution. The mass ratio of the copper powder dispersion to the TGA solution is 30:0.2. Stir at room temperature for 60 min. Wash with water and ethanol three times alternately and then dry to obtain TGA-coated copper powder. (5) Add the copper powder coated with TGA to the reducing solution, stir at 60°C for 40 minutes, and after the reaction is complete, let it stand, filter, wash and dry to obtain silver-coated copper powder with an average particle size of 4μm; wherein the reducing solution is an aqueous solution of silver nitrate and TGA, the concentration of silver nitrate is 8g / L and the concentration of TGA is 5mM.

[0025] An application of the silver-coated copper powder prepared by the above method in a conductive paste, wherein the conductive paste comprises the following components by mass percentage: 65% silver-coated copper powder, 28% organic carrier, 5.2% inorganic binder, 0.8% dispersant and 0.8% sintering inhibitor.

[0026] The organic carrier is composed of organic resin, organic solvent and defoamer in a mass percentage ratio of 20%:79.2%:0.8%, wherein the organic resin is epoxy resin E44, the organic solvent is ethanol and the defoamer is tributyl phosphate.

[0027] The inorganic binder is glass powder PbO-B2O3-SiO2, and the content of each component of the glass powder by molar percentage is as follows: PbO 60 wt.%, B2O3 30 wt.%, SiO2 10 wt.%. The dispersant is polyvinyl alcohol, and the sintering inhibitor is carbon black. Example 3

[0028] A method for preparing silver-coated copper powder for conductive paste includes the following steps: (1) Copper powder with an average particle size of 1 μm was soaked in 0.1 M hydrochloric acid aqueous solution for 20 minutes to remove surface oxides, and then washed with deionized water until neutral to obtain pretreated copper powder; (2) Disperse the pretreated copper powder in ethanol and sonicate for 20 minutes to obtain a copper powder dispersion with a concentration of 30 mg / mL. (3) Dissolve TGA in water and adjust the pH to 9 with NaOH to obtain a TGA solution with a concentration of 30 mM; (4) Add the copper powder dispersion to the TGA solution. The mass ratio of the copper powder dispersion to the TGA solution is 40:0.2. Stir at room temperature for 50 min. Wash with water and ethanol three times alternately and then dry to obtain TGA-coated copper powder. (5) Add the TGA-coated copper powder to the reducing solution and stir at 60°C for 30 minutes. After the reaction is complete, let it stand, filter, wash and dry to obtain silver-coated copper powder with an average particle size of 4 μm. The reducing solution is an aqueous solution of silver nitrate and TGA, with a silver nitrate concentration of 3 g / L and a TGA concentration of 2 mM.

[0029] An application of the silver-coated copper powder prepared by the above method in a conductive paste, wherein the conductive paste comprises the following components by mass percentage: 75% silver-coated copper powder, 20% organic carrier, 3% inorganic binder, 1% dispersant and 1% sintering inhibitor.

[0030] The organic carrier is composed of organic resin, organic solvent and defoamer in a mass percentage ratio of 18%:81.6%:0.4%, wherein the organic resin is epoxy resin E44, the organic solvent is ethylene glycol butyl ether acetate, and the defoamer is tributyl phosphate.

[0031] The inorganic binder is glass powder PbO-B2O3-SiO2, and the content of each component of the glass powder by molar percentage is as follows: PbO 60 wt.%, B2O3 30 wt.%, SiO2 10 wt.%. The dispersant is polyvinylpyrrolidone, and the sintering inhibitor is carbon black.

[0032] Comparative Example 1 The only difference from Example 1 is that commercially available silver-coated copper powder is used. The silver-coated copper powder is product model YF-1705 from Guangzhou Yinfeng Metal Technology Co., Ltd. (China), and its particle size is 5μm spherical silver-coated copper powder.

[0033] The resistivity of the conductive pastes from Examples 1-3 and Comparative Example 1 was tested using a four-probe tester after sintering and curing. The conductive pastes from Examples 1-3 and Comparative Example 1, after sintering and curing, were placed in a high-temperature environment of 100°C and a humid environment of 100% relative humidity for 48 hours, and the changes in their resistivity before and after were tested.

[0034] Stability test of slurry: Take 20 ml of the conductive slurry from Examples 1-3 and Comparative Example 1, and observe the changes after standing in the air at room temperature for 60 days.

[0035] The test results are shown in Table 1: Table 1. Test results of the conductive pastes in Examples 1-3 and Comparative Example 1

[0036] As can be seen from the table above, compared with Comparative Example 1, the resistivity of Example 1 is lower, indicating that the silver-coated copper powder prepared in this invention has better conductivity. Moreover, after being placed in a humid and hot environment, the resistivity of Example 1 changes less than that before placement compared with Comparative Example 1. It can be seen that the conductive paste of this invention uses mercaptoacetic acid as a pre-protective layer for copper powder and a silver ion reduction promoter, which can effectively prevent the oxidation of copper powder while guiding the uniform deposition of silver, making the silver-coated copper powder more dense and uniform, resulting in a lower resistivity.

[0037] In Comparative Example 1, a small number of green spots appeared on the surface of the conductive paste because, even with the silver coating, some bare copper that was not effectively coated by the silver was oxidized and dissolved. The pastes used in Example 1 remained unchanged, demonstrating that thioglycolic acid, as a pre-protective layer for copper powder, can prevent the oxidation of bare copper.

[0038] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing silver-coated copper powder for conductive paste, characterized in that: The following steps are involved: (1) Soak copper powder in an acid solution for 10-20 minutes to remove surface oxides, and then wash with deionized water until neutral to obtain pretreated copper powder; (2) Disperse the pretreated copper powder in ethanol or isopropanol and sonicate for 10 to 20 minutes to obtain a copper powder dispersion; (3) Dissolve TGA in water and adjust the pH to 8-9 with NaOH to obtain a TGA solution; (4) Add the copper powder dispersion to the TGA solution, stir at room temperature, wash with water and ethanol alternately, and then dry to obtain TGA-coated copper powder; (5) Add the copper powder coated with TGA to the reducing solution and stir at 45-60°C for 20-40 minutes. After the reaction is complete, let it stand, filter, wash and dry to obtain silver-coated copper nanoparticles. The reducing solution is an aqueous solution of silver nitrate and TGA.

2. The method for preparing silver-coated copper powder for conductive paste according to claim 1, characterized in that: The average particle size of the copper powder in step (1) is 0.5-2 μm, and the acid solution is a 0.1M hydrochloric acid aqueous solution or a 5% citric acid aqueous solution.

3. The method for preparing silver-coated copper powder for conductive paste according to claim 1, characterized in that: The concentration of the copper powder dispersion in step (2) is 20-40 mg / mL.

4. The method for preparing silver-coated copper powder for conductive paste according to claim 1, characterized in that: The concentration of the TGA solution in step (3) is 20-40 mM.

5. The method for preparing silver-coated copper powder for conductive paste according to claim 1, characterized in that: The stirring time in step (4) is 30-60 min, and the mass ratio of the copper powder dispersion to the TGA solution is 50-20:0.1-0.

5.

6. The method for preparing silver-coated copper powder for conductive paste according to claim 1, characterized in that: The silver nitrate concentration in the reducing solution in step (5) is 3-8 g / L, and the TGA concentration is 2-5 mM.

7. A silver-coated copper powder for conductive paste, characterized in that: The conductive paste silver-coated copper powder is prepared by any one of the preparation methods of conductive paste silver-coated copper powder according to claims 1-6, and the average particle size of the silver-coated copper powder is 3-5 μm.

8. The application of silver-coated copper powder prepared according to any one of claims 1-6 in conductive paste, characterized in that: The conductive paste comprises, by weight percentage, the following components: 50-82% silver-coated copper powder, 17-47% organic carrier, 2-8% inorganic binder, 0.5-1% dispersant, and 0.5-2% sintering inhibitor.

9. The application of the silver-coated copper powder according to claim 8 in conductive paste, characterized in that: The organic carrier is composed of organic resin, organic solvent, and defoamer in a mass percentage ratio of 10-40% : 60-85%. The composition is 0.2-1%, wherein the organic resin is epoxy resin, phenolic resin or urethane, the organic solvent is at least one of ethanol, diethylene glycol butyl ether, ethylene glycol, and ethylene glycol butyl ether acetate, and the defoamer is tributyl phosphate.

10. The application of the silver-coated copper powder according to claim 8 in conductive paste, characterized in that: The inorganic binder is glass powder PbO-B2O3-SiO2, the dispersant is at least one of polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone, and the sintering inhibitor is carbon black.

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