A method for preparing micron-sized spherical silver-coated copper powder for the electronics industry

Abstract

This invention discloses a method for preparing micron-sized spherical silver-coated copper powder for the electronics industry, belonging to the field of conductive materials technology. The method includes: reacting copper sulfate solution and ethanol to obtain a first solution; adding ammonium oxalate solution to the first solution to obtain a slurry; adding silver nitrate solution and ammonium oxalate solution to the slurry, stirring, allowing to stand, and vacuum drying to obtain an oxalate precursor precipitate; mixing the oxalate precursor precipitate with stearic acid, performing a first vacuum kneading, adding fumed silica particles, and performing a second vacuum kneading to obtain powder; heating the powder under vacuum to 135–145°C, holding at that temperature for 1.5–2.5 hours, then further heating to 270–320°C, holding at that temperature for 1.5–2.5 hours, cooling to room temperature in the furnace, and then acid washing, filtration, washing, drying, and sieving. The micron-sized spherical silver-coated copper powder of this invention has strong oxidation resistance, a short process cycle, and a high yield.

Description

Technical Field

[0001] This invention belongs to the field of conductive materials technology, and particularly relates to a method for preparing micron-sized spherical silver-coated copper powder for the electronics industry. Background Technology

[0002] With the rising price of silver, the cost of traditional applications using micron-sized spherical and flake-shaped silver powder has increased. This is particularly true for shielding, conductive / antistatic applications such as electromagnetic shielding paints and films, where the environment is not extremely demanding. Silver-coated copper powder can be considered, overcoming the oxidation problem of copper powder while also addressing the high cost and migration issues of silver powder. In addition to using pure silver powder as a conductive and thermal interface material in high-reliability electronic components, silver-coated copper, silver-coated nickel, and silver-coated iron powder can be used as fillers for ordinary conductive materials (such as conductive adhesives). Since silver and copper belong to the same group of elements and both have a face-centered cubic crystal structure, their electrical and thermal conductivity are similar, except for a significant difference in their redox potentials. Therefore, copper-coated powder is currently the most researched and widely used filler to replace pure silver powder.

[0003] There are several methods for preparing silver-coated copper powder, including chemical displacement, chemical reduction, a combination of displacement and chemical deposition, and melt atomization. Chemical displacement utilizes the higher redox potential of silver compared to copper. Without adding a reducing agent, copper powder is directly added to a soluble silver salt. Copper ions on the surface of the powder continuously lose electrons and enter the solution, while silver ions in the solution gain electrons and are deposited on the copper powder surface, resulting in silver-coated copper powder. Chemical reduction uses external chemical reducing agents such as ascorbic acid or formaldehyde to reduce silver ions to silver atoms, which are then deposited on the copper powder surface to form a silver layer. The displacement-chemical deposition method combines the above two methods, involving both silver displacement of copper and the reduction of silver atoms by a reducing agent to form a silver coating layer. The atomization method disperses copper powder in a soluble silver salt, and after atomization, high-temperature decomposition thermally decomposes silver nitrate to obtain silver, which forms a coating layer on the original copper powder surface.

[0004] Traditional methods for preparing silver-coated copper powder first involve using a reducing agent to convert divalent copper to monovalent copper, then adjusting the reduction conditions to reduce the monovalent copper to obtain copper powder. Since copper powder is easily oxidized in air, the reduction process requires nitrogen protection, making it quite cumbersome. If a physical atomization method is used to prepare the precursor copper powder, the copper powder needs to be melted into a liquid, and then the molten copper is atomized and cooled through a high-speed nozzle to obtain the copper powder. Practical experience shows that this method produces copper powder with a wide particle size distribution, an overly smooth surface lacking active sites, resulting in poor silver plating effects and a long preparation cycle. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing micron-sized spherical silver-coated copper powder for the electronics industry. The micron-sized spherical silver-coated copper powder prepared by this method has strong antioxidant capacity, short process cycle, and high yield.

[0006] The initial oxidation temperature and the final oxidation temperature are 240–250℃ and 430–440℃, respectively, with a weight gain of 4.3%–4.8% and a high yield.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for preparing micron-sized spherical silver-coated copper powder for the electronics industry, the method comprising the following steps:

[0009] Step S1: Copper sulfate solution and ethanol are reacted at a temperature of 25-30°C to obtain a first solution; then ammonium oxalate solution is added to the first solution at a rate of 0.4-0.6 L / min to obtain a slurry containing white copper oxalate precipitate.

[0010] In step S1, the volume ratio of the copper sulfate solution, ethanol, and ammonium oxalate solution is 8-12:1:3-7.

[0011] Step S2: Add silver nitrate solution and ammonium oxalate solution to the slurry at a flow rate of 15-25 ml / min, stir for 25-35 min, and then let stand to obtain copper oxalate precipitate with silver oxalate coated on the surface. Then, vacuum dry at 50-60℃ for 10-14 hours to obtain oxalate precursor precipitate.

[0012] In step S2, the volume ratio of the silver nitrate solution, ammonium oxalate solution, and slurry is 1:1:2 to 5.

[0013] Step S3: After mixing the oxalate precursor precipitate and stearic acid, perform a first vacuum kneading for 1.8 to 2.8 hours, add fumed silica particles, and perform a second vacuum kneading for 1.8 to 2.8 hours to obtain powder.

[0014] In step S3, the mass ratio of the oxalate precursor precipitate, stearic acid, and fumed silica particles is 190–195:1:15–25.

[0015] Step S4: After the second vacuum mixing, the powder is placed in a graphite crucible and then placed in a vacuum heating furnace. Under vacuum, the temperature is increased to 135-145°C at a rate of 10-20°C / min and held for 1.5-2.5 hours. Then, the temperature is increased to 270-320°C at a rate of 10-20°C / min and held for 1.5-2.5 hours. After cooling to room temperature under vacuum, the powder is then subjected to acid washing, filtration, washing, drying, and sieving to obtain spherical silver-coated copper powder.

[0016] Furthermore, in step S1, the molar concentration of the copper sulfate solution is 0.6–0.8 mol / L; and the molar concentration of the ammonium oxalate solution is 0.7–0.9 mol / L.

[0017] Furthermore, in step S1, the reaction time is 30 to 100 minutes.

[0018] Furthermore, in step S2, the molar concentration of the silver nitrate solution is 0.4–0.6 mol / L; and the molar concentration of the ammonium oxalate solution is 0.23–0.29 mol / L.

[0019] Furthermore, in step S2, the settling time is 20 to 60 minutes;

[0020] In step S2, the vacuum degree of the vacuum drying is 0.015 to 0.03 MPa.

[0021] Furthermore, in step S3, the fumed silica is nanoscale silica particles; the particle size of the nanoscale silica particles is 1–100 nm.

[0022] Furthermore, in step S3, the vacuum degree of the first vacuum kneading is 0.015 to 0.03 MPa;

[0023] In step S3, the vacuum degree of the second vacuum kneading is 0.015 to 0.03 MPa.

[0024] Furthermore, in step S4, the pickling solution comprises polyvinylpyrrolidone and hydrofluoric acid; the mass concentration of the hydrofluoric acid is 10-20%.

[0025] Add 1.1 to 1.5 g of polyvinylpyrrolidone per liter of hydrofluoric acid.

[0026] Furthermore, in step S4, the vacuum degree of the vacuum state is 0.015 to 0.03 MPa;

[0027] In step S4, the drying temperature is 60-80°C and the drying time is 10-20 hours.

[0028] Furthermore, in step S4, the washing continues until the conductivity is less than 10 microsiemens.

[0029] In summary, the solution proposed in this invention has the following technical effects:

[0030] This invention utilizes the fact that the particle size of nano-sized silica particles (i.e., fumed silica) is much smaller than that of oxalate precursor particles. Under the action of a kneader, the fumed silica particles adhere to the surface of the oily oxalate precursor, forming a coating barrier layer, thus preventing sintering after the formation of metallic silver in the later stages of thermal decomposition. Hydrofluoric acid is then used to effectively wash away the silica particles, yielding pure spherical silver-coated copper powder particles. The silver-coated copper powder particles of this invention have strong oxidation resistance, and the bonding between the silver and copper interfaces is a coherent / semi-coherent alloy contact, exhibiting strong oxidation resistance and mechanical strength. This invention does not... This invention employs traditional copper powder preparation and electroless silver plating methods, avoiding the traditional steps of acid washing, alkali washing, tin chloride sensitization, palladium nitrate activation, electroless silver plating, and localized defects caused by poor coating. The micron-sized spherical silver-coated copper powder for the electronics industry of this invention exhibits high oxidation resistance, requires no complex equipment or reagents, and can be prepared with a short process and controllable particle size. The initial oxidation temperature and final oxidation temperature of the micron-sized spherical silver-coated copper powder for the electronics industry of this invention are 240–250℃ and 430–440℃, respectively, with a weight gain of 4.3%–4.8% and a high yield. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] Step S1: Copper sulfate solution with a molar concentration of 0.7 mol / L and ethanol are reacted at 28°C for 65 min to obtain the first solution; then ammonium oxalate solution with a molar concentration of 0.8 mol / L is added to the first solution at a rate of 0.5 L / min to obtain a slurry containing white copper oxalate precipitate.

[0034] The volume ratio of copper sulfate solution, ethanol and ammonium oxalate solution is 10:1:5.

[0035] Step S2: Add a silver nitrate solution with a molar concentration of 0.5 mol / L and an ammonium oxalate solution with a molar concentration of 0.26 mol / L to the slurry at a flow rate of 20 ml / min. Stir for 30 min and then let stand for 40 min to obtain a copper oxalate precipitate coated with silver oxalate. Then dry at 55 °C under a vacuum of 0.025 MPa for 12 hours to obtain the oxalate precursor precipitate.

[0036] The volume ratio of silver nitrate solution, ammonium oxalate solution and slurry is 1:1:3.

[0037] Step S3: After mixing the oxalate precursor precipitate and stearic acid, perform a first vacuum kneading for 2.3 hours under a vacuum of 0.025 MPa. Then, add fumed silica particles with a particle size of 50 nm and perform a second vacuum kneading for 2.3 hours under a vacuum of 0.025 MPa to obtain powder.

[0038] The mass ratio of oxalate precursor precipitate, stearic acid, and fumed silica particles is 192:1:20.

[0039] Step S4: After the second vacuum mixing, the powder is placed in a graphite crucible and then placed in a vacuum heating furnace. Under vacuum, the temperature is increased to 140°C at a rate of 15°C / min and held for 2 hours. Then, the temperature is increased to 300°C at a rate of 15°C / min and held for 2 hours. Under vacuum of 0.025 MPa, the powder is cooled to room temperature in the furnace. Then, acid washing, filtration, washing, drying and sieving are performed in sequence to obtain spherical silver-coated copper powder.

[0040] The pickling solution includes polyvinylpyrrolidone (PVP) and hydrofluoric acid, with a hydrofluoric acid concentration of 15% by mass. 1.3 g of PPVP is added per liter of hydrofluoric acid. Washing continues until the conductivity reaches 8 μSiemens. Drying is performed at 70°C for 15 hours.

[0041] Example 2:

[0042] Step S1: Copper sulfate solution with a molar concentration of 0.6 mol / L and ethanol are reacted at 25°C for 30 min to obtain the first solution; then ammonium oxalate solution with a molar concentration of 0.7 mol / L is added to the first solution at a rate of 0.4 L / min to obtain a slurry containing white copper oxalate precipitate.

[0043] The volume ratio of copper sulfate solution, ethanol and ammonium oxalate solution is 8:1:3.

[0044] Step S2: Add a silver nitrate solution with a molar concentration of 0.4 mol / L and an ammonium oxalate solution with a molar concentration of 0.23 mol / L to the slurry at a flow rate of 15 ml / min. Stir for 25 min and then let stand for 20 min to obtain a copper oxalate precipitate coated with silver oxalate. Then dry it at 50 °C under a vacuum of 0.015 MPa for 10 hours to obtain the oxalate precursor precipitate.

[0045] The volume ratio of silver nitrate solution, ammonium oxalate solution and slurry is 1:1:2.

[0046] Step S3: After mixing the oxalate precursor precipitate and stearic acid, perform a first vacuum kneading for 1.8 hours under a vacuum of 0.015 MPa. Then, add fumed silica particles with a particle size of 1 nm and perform a second vacuum kneading for 1.8 hours under a vacuum of 0.015 MPa to obtain powder.

[0047] The mass ratio of oxalate precursor precipitate, stearic acid and fumed silica particles is 190:1:15.

[0048] Step S4: After the second vacuum mixing, the powder is placed in a graphite crucible and then placed in a vacuum heating furnace. Under vacuum, the temperature is increased to 135°C at a rate of 10°C / min and held for 1.5 hours. Then, the temperature is increased to 270°C at a rate of 10°C / min and held for 1.5 hours. Under vacuum of 0.015 MPa, the powder is cooled to room temperature in the furnace. Then, the powder is acid washed, filtered, washed, dried, and sieved in sequence to obtain spherical silver-coated copper powder.

[0049] The pickling solution includes polyvinylpyrrolidone (PVP) and hydrofluoric acid, with a hydrofluoric acid concentration of 10% by mass. 1.1 g of PPVP is added per liter of hydrofluoric acid. Washing continues until the conductivity reaches 9 μSiemens. Drying is performed at 60°C for 10 hours.

[0050] Example 3:

[0051] Step S1: Copper sulfate solution with a molar concentration of 0.8 mol / L and ethanol are reacted at 30°C for 100 min to obtain the first solution; then ammonium oxalate solution with a molar concentration of 0.9 mol / L is added to the first solution at a rate of 0.6 L / min to obtain a slurry containing white copper oxalate precipitate.

[0052] The volume ratio of copper sulfate solution, ethanol and ammonium oxalate solution is 12:1:7.

[0053] Step S2: Add a silver nitrate solution with a molar concentration of 0.6 mol / L and an ammonium oxalate solution with a molar concentration of 0.29 mol / L to the slurry at a flow rate of 25 ml / min. Stir for 35 min and then let stand for 60 min to obtain a copper oxalate precipitate coated with silver oxalate. Then dry at 60 °C under a vacuum of 0.03 MPa for 14 hours to obtain the oxalate precursor precipitate.

[0054] The volume ratio of silver nitrate solution, ammonium oxalate solution and slurry is 1:1:5.

[0055] Step S3: After mixing the oxalate precursor precipitate and stearic acid, perform a first vacuum kneading for 2.8 hours under a vacuum of 0.03 MPa. Then, add fumed silica particles with a particle size of 100 nm and perform a second vacuum kneading for 2.8 hours under a vacuum of 0.03 MPa to obtain powder.

[0056] The mass ratio of oxalate precursor precipitate, stearic acid, and fumed silica particles is 195:1:25.

[0057] Step S4: After the second vacuum mixing, the powder is placed in a graphite crucible and then placed in a vacuum heating furnace. Under vacuum, the temperature is increased to 145°C at a rate of 20°C / min and held for 2.5 hours. Then, the temperature is increased to 320°C at a rate of 20°C / min and held for 2.5 hours. Under vacuum of 0.03 MPa, the powder is cooled to room temperature in the furnace. Then, acid washing, filtration, washing, drying and sieving are performed in sequence to obtain spherical silver-coated copper powder.

[0058] The pickling solution includes polyvinylpyrrolidone (PVP) and hydrofluoric acid, with a hydrofluoric acid concentration of 20% by mass. 1.5 g of PPVP is added per liter of hydrofluoric acid. Washing continues until the conductivity reaches 7 μSiemens. Drying is performed at 80°C for 20 hours.

[0059] Table 1. Antioxidant properties of micron-sized spherical silver-coated copper powder for electronic industry (Examples 1-3)

[0060] category Initial oxidation temperature, ℃ End of oxidation temperature (°C) Weight gain, % Example 1 249.3 439.6 4.7 Example 2 242.5 432.4 4.4 Example 3 247.7 434.6 4.8

[0061] The yields of micron-sized spherical silver-coated copper powder for the electronics industry in Examples 1, 2, and 3 were 99.5%, 99.6%, and 99.7%, respectively.

[0062] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing micron-sized spherical silver-coated copper powder for the electronics industry, characterized in that, The preparation method includes the following steps: Step S1: Copper sulfate solution and ethanol are reacted at a temperature of 25-30°C to obtain a first solution; then ammonium oxalate solution is added to the first solution at a rate of 0.4-0.6 L / min to obtain a slurry containing white copper oxalate precipitate. In step S1, the volume ratio of the copper sulfate solution, ethanol, and ammonium oxalate solution is 8-12:1:3-7. Step S2: Add silver nitrate solution and ammonium oxalate solution to the slurry at a flow rate of 15-25 ml / min, stir for 25-35 min, and then let stand to obtain copper oxalate precipitate with silver oxalate coated on the surface. Then, vacuum dry at 50-60℃ for 10-14 hours to obtain oxalate precursor precipitate. In step S2, the volume ratio of the silver nitrate solution, ammonium oxalate solution, and slurry is 1:1:2 to 5. Step S3: After mixing the oxalate precursor precipitate and stearic acid, perform a first vacuum kneading for 1.8 to 2.8 hours, add fumed silica particles, and perform a second vacuum kneading for 1.8 to 2.8 hours to obtain powder. In step S3, the mass ratio of the oxalate precursor precipitate, stearic acid, and fumed silica particles is 190–195:1:15–25. Step S4: After the second vacuum kneading, the powder is placed in a graphite crucible and then placed in a vacuum heating furnace. Under vacuum, the temperature is increased to 135-145°C at a rate of 10-20°C / min and held for 1.5-2.5 hours. Then, the temperature is increased to 270-320°C at a rate of 10-20°C / min and held for 1.5-2.5 hours. After cooling to room temperature under vacuum, the powder is then subjected to acid washing, filtration, washing, drying, and sieving to obtain spherical silver-coated copper powder. In step S4, the pickling solution comprises polyvinylpyrrolidone and hydrofluoric acid; the mass concentration of the hydrofluoric acid is 10-20%. Add 1.1 to 1.5 g of polyvinylpyrrolidone per liter of hydrofluoric acid.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar concentration of the copper sulfate solution is 0.6–0.8 mol / L; the molar concentration of the ammonium oxalate solution is 0.7–0.9 mol / L.

3. The preparation method according to claim 2, characterized in that, In step S1, the reaction time is 30 to 100 minutes.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S2, the molar concentration of the silver nitrate solution is 0.4–0.6 mol / L; the molar concentration of the ammonium oxalate solution is 0.23–0.29 mol / L.

5. The preparation method according to claim 4, characterized in that, In step S2, the settling time is 20 to 60 minutes; In step S2, the vacuum degree of the vacuum drying is 0.015 to 0.03 MPa.

6. The preparation method according to claim 5, characterized in that, In step S3, the fumed silica is nanoscale silica particles; the particle size of the nanoscale silica particles is 1 to 100 nm.

7. The preparation method according to claim 6, characterized in that, In step S3, the vacuum degree of the first vacuum kneading is 0.015 to 0.03 MPa; In step S3, the vacuum degree of the second vacuum kneading is 0.015 to 0.03 MPa.

8. The preparation method according to claim 7, characterized in that, In step S4, the vacuum degree of the vacuum state is 0.015 to 0.03 MPa; In step S4, the drying temperature is 60-80°C and the time is 10-20 hours.

9. The preparation method according to claim 8, characterized in that, In step S4, the washing continues until the conductivity is less than 10 microsiemens.