Silver-coated copper powder particles having uniform coating thickness and a method for producing the same

Abstract

The present application relates to the technical field of silver-coated copper powder, in particular to a silver-coated copper powder particle with uniform plating thickness and a preparation method thereof. The method comprises raw material pretreatment, plating solution preparation, plating, electroplating solution preparation, electroplating and post-treatment. First, the non-selective deposition characteristics of chemical plating are used to build a complete and non-porous thin silver layer on the surface of the copper powder, ensuring 100% conductive coverage. Then, the uniform conductive layer is used as a substrate to precisely thicken through a highly controllable electroplating process. The synergistic effect of electric field and fluid dynamics is used to achieve high uniformity and structural densification of the silver layer in the nanometer scale. Through the precise relay of "chemical plating bottoming" and "electroplating thickening", the inherent contradictions of traditional single methods in coverage, uniformity and plating quality are cooperatively overcome.

Description

Technical Field

[0001] This invention relates to the field of silver-coated copper powder technology, specifically to a silver-coated copper powder particle with uniform coating thickness and its preparation method. Background Technology

[0002] Silver-coated copper powder is a composite metal powder with copper powder as its core and a uniform silver coating on the surface. It combines the high conductivity of silver with the economic efficiency of copper, making it a cost-effective alternative to pure silver powder. It exhibits excellent conductivity, with a resistivity as low as 0.015–0.025 ohms / cm², and high chemical stability; the silver layer effectively prevents copper oxidation, maintaining long-term conductivity. Silver-coated copper powder comes in various shapes (such as spheres, flakes, and dendritic structures) and has a controllable particle size (D50 range 5–25 micrometers), making it suitable for different process requirements.

[0003] It is widely used in the electronics industry (conductive adhesives, conductive inks, MLCC electrodes, flexible circuits), electromagnetic shielding (5G equipment, aerospace components), photovoltaic industry (HJT low-temperature silver paste), and other fields. The preparation methods mainly include chemical plating (a mature process) and mechanical alloying (resulting in a dense silver layer, but with higher silver consumption).

[0004] Currently, Chinese patent CN120438614A discloses a silver-coated copper powder and its preparation method. Addressing the shortcomings of existing technologies, this invention innovatively proposes a combined chemical reduction and displacement method for preparing silver-coated copper powder. Specifically, copper powder is pretreated with acid and ammonia before being mixed with a reducing agent. This allows the reducing agent to be adsorbed onto the surface of the copper powder, confining the reduction reaction to the surface and facilitating the formation of a uniform, dense silver layer. Furthermore, during the displacement and reduction processes, an organic solvent is used as a dispersion medium for the copper powder, effectively preventing the presence of a large amount of reducing agent in the dispersion medium and thus avoiding the formation of pure silver particles through independent nucleation. The process of this invention is simple and easy to operate, and the overall performance of the prepared silver-coated copper powder is essentially equivalent to that of pure silver conductive paste.

[0005] However, in existing technologies, including the aforementioned patented technologies, the thickness of the silver-coated copper powder coating is not uniform due to improper control of process parameters or the particle size distribution characteristics of copper powder during the preparation process. This results in obstructed electron transport paths, decreased conductivity, and poor dispersion performance.

[0006] To address the above problems, this invention provides silver-coated copper powder particles with uniform coating thickness and a method for preparing the same. Summary of the Invention

[0007] The purpose of this invention is to provide silver-coated copper powder particles with uniform coating thickness and a method for preparing the same, so as to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing silver-coated copper powder particles with uniform coating thickness, comprising the following steps:

[0009] S1. Raw material pretreatment: Take spherical or near-spherical copper powder (D50=3μm), place the copper powder in an acidic solution, sonicate for 10 minutes to remove the surface oxide layer, and wash with deionized water until neutral; place the cleaned copper powder in a zinc chloride or palladium chloride solution and sonicate for 5 minutes to obtain sensitized copper powder; disperse the cleaned copper powder in a PVP aqueous solution, mechanically stir and sonicate for 30 minutes to form a stable suspension;

[0010] S2, prepare the plating solution by dissolving a certain amount of silver nitrate in water and slowly adding ammonia water dropwise while stirring until the precipitate is completely dissolved to obtain a transparent silver ammonia solution, i.e., solution A; dissolve a certain amount of reducing agent, dispersant, and stabilizer in deionized water to form solution B;

[0011] S3, plating: Heat the pretreated copper powder suspension to 42°C in a water bath. Add solution A and solution B slowly to the copper powder suspension at the same rate using two peristaltic pumps. At the same time, add a pH adjuster to stabilize the pH at 11.5. This process is carried out under nitrogen protection until the suspension turns a stable gray-black color. Immediately wash the suspension 3-5 times with deionized water and ethanol to remove residual ions and organic matter, and obtain wet powder.

[0012] S4, Electroplating solution preparation: Dissolve a measured amount of main complexing agent and auxiliary complexing agent in deionized water. Add the main salt while stirring at 55°C. After the main salt is completely dissolved, cool the electroplating solution to room temperature, add a pH adjuster, and continuously stir to precisely adjust the pH to 9.0. Take a measured amount of dithiocyanomethane powder, add anhydrous ethanol, and add 5% KOH solution dropwise while stirring. After stirring, dilute with deionized water to obtain dithiocyanomethane mother liquor. Add the dithiocyanomethane mother liquor to the electroplating solution with adjusted pH value, add brightener and conductive salt while stirring, and stir for 2 hours to obtain the electroplating solution.

[0013] S5. Take a quantitative amount of electroplating solution, mix the wet powder with the conductive adhesive to form a conductive slurry with a solid content of 40%, use a rotating cathode drum electroplating tank, load the conductive slurry into the rotating cathode drum, use a pulse power supply to carry out electroplating at a low current density, the electroplating time is 180-240 min, and the electroplating slurry is obtained.

[0014] S6, post-treatment: The electroplating slurry is repeatedly centrifuged and washed with deionized water and ethanol to completely remove the plating solution components. After vacuum drying, it is annealed at 200-300℃ under nitrogen protection for 60 minutes and cooled to room temperature to obtain silver-coated copper powder particles with uniform plating thickness.

[0015] In a more optimized manner, in step S1, the acidic solution is a 10% dilute sulfuric acid solution or a 5% citric acid solution; the concentration of the PVP solution is 0.3 g / L; and the solid content of the copper powder in it is controlled at 15-18%.

[0016] In a more optimized manner, in step S2, the concentration of ammonia is 25%, the reducing agent is glucose with a concentration of 15 g / L, the stabilizer is potassium sodium tartrate with a concentration of 4 g / L, and the dispersant is PVP with a concentration of 1 g / L.

[0017] Ideally, in step S3, the dropping rate of solution A and solution B is 1.5 mL / min.

[0018] In a more optimized manner, in step S4, the main salt is silver salicylate with a concentration of 35 g / L, the main complexing agent is 1,3-dibromo-5,5-dimethylhydantoin with a concentration of 100 g / L, and the auxiliary complexing agent is potassium pyrophosphate with a concentration of 80 g / L.

[0019] In a more optimized manner, in step S4, the conductive salt is potassium nitrate with a concentration of 15 g / L; the brightener is 2-mercaptobenzothiazole with a concentration of 0.2 g / L.

[0020] Ideally, the pH adjuster is a sodium hydroxide or potassium hydroxide solution; in step S5, the drum rotation speed is 15 rpm.

[0021] A more optimized approach is to use a low current density of 0.3 A / dm². 2 .

[0022] The present invention also provides a silver-coated copper powder particle with uniform coating thickness, which is prepared by any of the above-mentioned methods for preparing silver-coated copper powder particles with uniform coating thickness.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0024] (1) This invention fundamentally ensures the perfect coverage and ultra-high uniformity of the silver layer. Chemical plating, with its non-selective deposition characteristics, can coat all copper powder surfaces with a complete and continuous initial thin silver layer, solving the problem of "full coverage"; subsequently, electroplating is carried out on a conductive substrate, and its deposition process is precisely controlled by electric field and fluid dynamics, which can achieve a highly uniform thickening of the silver layer between particles and on the surface of individual particles, overcoming the difficulty of "uniformity".

[0025] (2) This invention demonstrates superior controllability in coating quality and performance. Electroplated coatings are known for their dense crystals and high purity, effectively sealing microscopic defects that may exist in chemical plating, thereby significantly improving the conductivity, oxidation resistance, and sintering activity of the final powder in the final slurry. By precisely controlling the current, time, and fluid environment of the electroplating, the thickness, morphology, and performance of the silver layer can be precisely controlled with high repeatability.

[0026] (3) In this invention, chemical plating only serves as the base layer, with a thin silver layer, mild reaction, and relatively small waste liquid treatment volume; while the main thickness is increased by electroplating, which has higher efficiency and faster deposition rate. Its silver utilization rate is high and the waste liquid is easy to recover silver through electrolysis and other methods, thereby reducing the overall manufacturing cost and precious metal loss while ensuring high performance.

[0027] (4) This invention conforms to the trend of environmental protection and safety upgrades. The salicylic acid system and other cyanide-free electroplating solutions recommended in the solution fundamentally avoid the use of highly toxic cyanide, greatly reduce the safety risks and environmental pressure of production and waste liquid treatment, and make the manufacturing process of high-performance silver-coated copper powder greener and more sustainable.

[0028] (5) This invention first utilizes the non-selective deposition characteristics of chemical plating to construct a complete and non-porous thin silver layer on the surface of copper powder to ensure 100% conductive coverage; then, using this uniform conductive layer as a base, it is precisely thickened through a highly controllable electroplating process. By utilizing the synergistic effect of electric field and fluid dynamics, the silver layer thickness is highly uniform and the structure is compacted at the nanoscale. Through the precise relay of "chemical plating base" and "electroplating thickening", the inherent contradictions of traditional single methods in terms of coverage, uniformity and plating quality are overcome. Attached Figure Description

[0029] Figure 1 The image shown is an electron microscope image of an example. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0031] This invention provides a method for preparing silver-coated copper powder particles with uniform coating thickness, comprising the following steps:

[0032] S1. Raw material pretreatment: Take spherical or near-spherical copper powder, place it in an acidic solution, and sonicate for 10 minutes to remove the surface oxide layer. Wash with deionized water until neutral. Place the cleaned copper powder in a zinc chloride or palladium chloride solution and sonicate for 5 minutes to obtain sensitized copper powder. Disperse the cleaned copper powder in a PVP aqueous solution, mechanically stir and sonicate for 30 minutes to form a stable suspension. In this step, the acidic solution is a 10% dilute sulfuric acid or 5% citric acid solution; the PVP solution concentration is 0.3 g / L, and the solid content of the copper powder in it is controlled at 15-18%.

[0033] S2, Prepare the plating solution: Dissolve a measured amount of silver nitrate in water, and slowly add ammonia water dropwise while stirring until the precipitate is completely dissolved to obtain a transparent silver ammonia solution, i.e., solution A; Dissolve a measured amount of reducing agent, dispersant, and stabilizer in deionized water to form solution B; In this step, the concentration of ammonia water is 25%, the reducing agent is glucose with a concentration of 15 g / L, the stabilizer is potassium sodium tartrate with a concentration of 4 g / L, and the dispersant is PVP with a concentration of 1 g / L.

[0034] S3, Plating: Heat the pretreated copper powder suspension to 42°C in a water bath. Slowly add solutions A and B to the copper powder suspension at the same rate using two peristaltic pumps. Simultaneously, add a pH adjuster to stabilize the pH at 11.5. This process is carried out under nitrogen protection until the suspension turns a stable gray-black color. Immediately wash the suspension 3-5 times with deionized water and ethanol to remove residual ions and organic matter, obtaining wet powder. In this step, the dropping rate of solutions A and B is 1.5 mL / min.

[0035] S4, Electroplating solution preparation: Dissolve a measured amount of main complexing agent and auxiliary complexing agent in deionized water. Add the main salt while stirring at 55°C. After the main salt is completely dissolved, cool the electroplating solution to room temperature, add a pH adjuster, and continuously stir to precisely adjust the pH to 9.0. Take a measured amount of dithiocyanomethane powder, add anhydrous ethanol, and add 5% KOH solution dropwise while stirring. After stirring, dilute with deionized water to obtain dithiocyanomethane mother liquor. Add the dithiocyanomethane mother liquor to the electroplating solution with adjusted pH value, add brightener and conductive salt while stirring, and stir for 2 hours to obtain the electroplating solution.

[0036] In this step, the main salt is silver salicylate with a concentration of 35 g / L, the main complexing agent is 1,3-dibromo-5,5-dimethylhydantoin with a concentration of 100 g / L, and the auxiliary complexing agent is potassium pyrophosphate with a concentration of 80 g / L. The conductive salt is potassium nitrate with a concentration of 15 g / L; and the brightening agent is 2-mercaptobenzothiazole with a concentration of 0.2 g / L.

[0037] In the above steps, the pH adjuster is either sodium hydroxide or potassium hydroxide solution.

[0038] S5. Take a measured amount of electroplating solution, mix the wet powder with conductive adhesive to form a conductive slurry with a solid content of 40%. Use a rotating cathode drum electroplating tank, load the conductive slurry into the rotating cathode drum, the drum rotation speed is 15 rpm, and electroplating is carried out using a pulse power supply at a low current density for 180-240 minutes to obtain the electroplating slurry; the low current density is 0.3 A / dm³. 2 .

[0039] S6, post-treatment: The electroplating slurry is repeatedly centrifuged and washed with deionized water and ethanol to completely remove the plating solution components. After vacuum drying, it is annealed at 200-300°C under nitrogen protection for 60 minutes and cooled to room temperature to obtain silver-coated copper powder particles with uniform plating thickness.

[0040] The advantages of the present invention are verified through several embodiments and comparative examples.

[0041] Comparative Example 1

[0042] The traditional direct chemical plating process is adopted. Using raw copper powder of the same quality and from the same supplier, after acid washing and activation, it is directly put into the chemical silver plating reactor. The same total amount of silver salt and reducing agent is used. The reaction is started by adding the reducing agent in one go, and finally silver-coated copper powder with the same silver content is obtained.

[0043] Example 1

[0044] Using the method of this invention, after chemical silver plating as a base, electroplating silver is performed, followed by heat treatment and vacuum drying to finally obtain silver-coated copper powder (total silver content 70wt%).

[0045] The results of comparing Comparative Example 1 and Example 1 are shown in Table 1.

[0046] Table 1. Detection results of silver-coated copper powder prepared in Comparative Example 1 and Example 1

[0047]

[0048] It can be seen that Example 1 has an absolute advantage in morphology and dispersibility, proving that the seed method effectively avoids the self-nucleation and particle agglomeration of silver.

[0049] The conductive pastes of Example 1 and Comparative Example 1 were prepared using the same formulation and process, and printed into standard test patterns for electrical performance testing. The test results are shown in Table 2.

[0050] Table 2. Test results of slurry performance in Example 1 and Comparative Example 1

[0051]

[0052] As can be seen from the data in Table 2, thanks to the excellent continuity and thickness uniformity of the coating, the present invention has achieved orders of magnitude or multiple-fold improvements in key application indicators such as sheet resistance, stability and sintering density in conductive pastes, and its comprehensive performance meets the requirements of high-end applications.

[0053] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing silver-coated copper powder particles with uniform coating thickness, characterized in that, Includes the following steps: S1. Raw material pretreatment: Take spherical or near-spherical copper powder (D50=3μm), place the copper powder in an acidic solution, sonicate for 10 minutes to remove the surface oxide layer, and wash with deionized water until neutral; place the cleaned copper powder in a zinc chloride or palladium chloride solution and sonicate for 5 minutes to obtain sensitized copper powder; disperse the cleaned copper powder in a PVP aqueous solution, mechanically stir and sonicate for 30 minutes to form a stable suspension; S2, prepare the plating solution by dissolving a certain amount of silver nitrate in water and slowly adding ammonia water dropwise while stirring until the precipitate is completely dissolved to obtain a transparent silver ammonia solution, i.e., solution A; dissolve a certain amount of reducing agent, dispersant, and stabilizer in deionized water to form solution B; S3, plating: Heat the pretreated copper powder suspension to 42°C in a water bath. Add solutions A and B slowly to the copper powder suspension at the same rate using two peristaltic pumps. At the same time, add a pH adjuster to stabilize the pH at 11.

5. This process is carried out under nitrogen protection until the suspension turns a stable gray-black color. Immediately wash the suspension 3-5 times with deionized water and ethanol to remove residual ions and organic matter, and obtain wet powder. S4, Electroplating Solution Preparation: Dissolve a measured amount of the main complexing agent and auxiliary complexing agent in deionized water. Add the main salt while stirring at 55°C. After the main salt is completely dissolved, cool the electroplating solution to room temperature, add a pH adjuster, and continuously stir to precisely adjust the pH to 9.

0. Take a measured amount of dithiocyanomethane powder, add anhydrous ethanol, and add 5% KOH solution dropwise while stirring. After stirring, dilute with deionized water to obtain dithiocyanomethane mother liquor. Add the dithiocyanomethane mother liquor to the electroplating solution with adjusted pH, add a brightener and conductive salt while stirring, and stir for 2 hours to obtain the electroplating solution. S5. Take a quantitative amount of electroplating solution, mix the wet powder with the conductive adhesive to form a conductive slurry with a solid content of 40%, use a rotating cathode drum electroplating tank, load the conductive slurry into the rotating cathode drum, use a pulse power supply to carry out electroplating at a low current density, the electroplating time is 180-240 min, and the electroplating slurry is obtained. S6, post-treatment: The electroplating slurry is repeatedly centrifuged and washed with deionized water and ethanol to completely remove the plating solution components. After vacuum drying, it is annealed at 200-300°C under nitrogen protection for 60 minutes and cooled to room temperature to obtain silver-coated copper powder particles with uniform plating thickness.

2. The method for preparing silver-coated copper powder particles with uniform coating thickness according to claim 1, characterized in that: In step S1, the acidic solution is a 10% dilute sulfuric acid or a 5% citric acid solution; the concentration of the PVP solution is 0.3 g / L, and the solid content of the copper powder in it is controlled at 15-18%.

3. The method for preparing silver-coated copper powder particles with uniform coating thickness according to claim 1, characterized in that: In step S2, the ammonia concentration is 25%, the reducing agent is glucose with a concentration of 15 g / L, the stabilizer is potassium sodium tartrate with a concentration of 4 g / L, and the dispersant is PVP with a concentration of 1 g / L.

4. The method for preparing silver-coated copper powder particles with uniform coating thickness according to claim 1, characterized in that: In step S3, the dropping rate of solution A and solution B is 1.5 mL / min.

5. The method for preparing silver-coated copper powder particles with uniform coating thickness according to claim 1, characterized in that: In step S4, the main salt is silver salicylate with a concentration of 35 g / L, the main complexing agent is 1,3-dibromo-5,5-dimethylhydantoin with a concentration of 100 g / L, and the auxiliary complexing agent is potassium pyrophosphate with a concentration of 80 g / L.

6. The method for preparing silver-coated copper powder particles with uniform coating thickness according to claim 1, characterized in that: In step S4, the conductive salt is potassium nitrate with a concentration of 15 g / L; the brightener is 2-mercaptobenzothiazole with a concentration of 0.2 g / L.

7. The method for preparing silver-coated copper powder particles with uniform coating thickness according to claim 1, characterized in that: The pH adjuster is a sodium hydroxide or potassium hydroxide solution; in step S5, the drum rotation speed is 15 rpm.

8. The method for preparing silver-coated copper powder particles with uniform coating thickness according to claim 1, characterized in that: The low current density is 0.3 A / dm. 2 .

9. A type of silver-coated copper powder particles with uniform coating thickness, characterized in that: It is prepared by any of the methods described in claims 1-8 for preparing silver-coated copper powder particles with uniform coating thickness.

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