Silver-coated copper powder for high-frequency electronic components and method for producing the same

Abstract

The application relates to the technical field of silver-coated copper powder, in particular to silver-coated copper powder suitable for high-frequency electronic components and a preparation method thereof. The silver-coated copper powder comprises the following steps: copper powder treatment, chemical silver plating, cleaning and drying, surface finishing, silver layer deposition and passivation and material taking, the application utilizes the skin effect, and a surface silver layer formed through PVD is extremely dense and smooth, thus providing a nearly perfect transmission channel for high-frequency current, and the resistivity of the silver layer is close to that of a bulk silver single crystal. The reduction of surface roughness also reduces electron scattering; in a target high-frequency band, the conductive loss of the silver-coated copper powder is far higher than that of a pure chemical plating product and reaches the level of pure silver powder.

Description

Technical Field

[0001] This invention relates to the field of silver-coated copper powder technology, specifically to a silver-coated copper powder suitable for high-frequency electronic components and its preparation method. Background Technology

[0002] Heterojunction solar cells (HJT cells), due to their unique bifacial symmetrical structure and the excellent passivation effect of the amorphous silicon layer, possess significant performance advantages such as low-temperature manufacturing, fewer production steps, high conversion efficiency, high bifaciality, low degradation rate, and high stability. However, the use of silver paste as a conductive paste has been limited by the high cost of silver powder, necessitating its replacement by other powders.

[0003] Silver-coated copper powder combines the advantages of Ag and Cu, and is considered the most promising option, offering both oxidation resistance and high conductivity. However, obtaining a uniform and dense silver plating on copper surfaces typically requires a high silver content, thus increasing costs. To reduce costs, current methods focus on decreasing the silver content in the silver-coated copper powder.

[0004] For example, Chinese Patent No. CN118477998B discloses a method for confined preparation of low-silver-content nanoscale silver-coated copper powder, which includes the following steps: first, the copper powder is pretreated on the surface; then the pretreated copper powder is mixed with Schiff base solution and amino acid complexing agent to obtain copper powder precursor solution; silver salt solution is slowly added dropwise to copper powder precursor solution to carry out reaction; after reaction, a decrosslinking agent is added to carry out solid-liquid separation, and the obtained solid product is washed and dried to obtain low-silver-content nanoscale silver-coated copper powder.

[0005] This invention incorporates a Schiff base additive, which forms a cross-linked network in water that acts as both a dispersant and a complexing agent, while also confining copper spheres within the network to facilitate the exchange of silver ions. A one-step method is employed to prepare silver-coated copper powder; the process is simple, and the resulting powder has a low silver content, a uniform and dense silver coating, and exhibits high conductivity and antioxidant properties.

[0006] However, due to the reduced silver content, the silver coating on the surface of the copper powder is not continuous and uniform, and the silver layer is also thinner. When the current needs to penetrate the entire particle or requires close contact between particles, the thinner silver layer means that the proportion of copper in the current path increases. Combined with the contact resistance, the high-frequency conductivity and oxidation resistance of silver-coated copper powder with low silver content decrease, which has a significant impact on the final conductivity and aging resistance of the silver-coated copper powder.

[0007] To address the aforementioned problems, this invention provides a silver-coated copper powder suitable for high-frequency electronic components and its preparation method. Summary of the Invention

[0008] The purpose of this invention is to provide a silver-coated copper powder suitable for high-frequency electronic components and its preparation method, so as to solve the problems mentioned in the background art.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] A method for preparing silver-coated copper powder suitable for high-frequency electronic components includes the following steps:

[0011] S1, Copper powder treatment: Take a certain amount of copper powder, immerse it in sodium hydroxide solution, ultrasonically clean it for 10 minutes to remove surface grease and organic matter, and wash it thoroughly with deionized water until neutral; immerse the cleaned copper powder in an acidic solution for 3 minutes for acid washing, immerse the acid-washed copper powder in an acidic solution of stannous chloride and stir, rinse it with deionized water until neutral, and then vacuum dry it to obtain active copper powder;

[0012] S2, chemical silver plating: Take a certain amount of silver nitrate solution and complexing agent and heat to 55℃. Immerse active copper powder in silver nitrate solution, slowly add complexing agent and reducing agent, and stir with ultrasound for 45-60 minutes. During the stirring process, use sodium hydroxide to maintain the pH value between 11 and 12. Add stabilizer simultaneously during the drop addition. After the drop addition is completed, stir with ultrasound for another 10 minutes to obtain silver-plated copper powder.

[0013] S3, cleaning and drying: the solution along with the silver-plated copper powder is poured into deionized water to quench the reaction, and then the silver-plated copper powder is obtained by centrifugation. After removing the residual solution by alternating cleaning with deionized water and anhydrous ethanol, it is vacuum dried to obtain primary silver-plated copper powder, which is then stored in an inert gas.

[0014] S4, Surface finishing: The primary silver-coated copper powder is transferred to a sealed PVD feed container in an inert gas environment. It is then loaded into a powder feeder equipped with a fluidized bed PVD sputtering chamber via a vacuum interconnection device, and the background vacuum is evacuated to ≤1.0×10⁻⁶. - 3 At the Pa level, high-purity argon gas is introduced to maintain the cavity pressure at 0.1-1 Pa. The radio frequency plasma power supply is turned on to generate argon plasma in the cavity. The fluidized bed is started to make the powder tumble in the cavity, ensuring that every surface of every powder particle is uniformly bombarded by the plasma. The cleaning process lasts for 12 minutes.

[0015] S5, deposit silver layer, stabilize the working pressure of argon gas at 0.5-2 Pa, turn on the silver target, and deposit a silver layer on the surface of the primary silver-coated copper powder after surface finishing at a sputtering power of 140W. The sputtering time is 3 minutes and the target deposition thickness is 27-32nm.

[0016] S6, passivation and material collection: After deposition, the powder is cooled in an inert atmosphere and a trace amount of silane or fluorocarbon gas is introduced for plasma-enhanced chemical vapor deposition. After cooling to room temperature, the chamber is filled with high-purity nitrogen to atmospheric pressure, and the final product is taken out under the protection of an inert atmosphere to obtain silver-coated copper powder.

[0017] In a more optimized manner, in step S1, the acidic solution includes dilute sulfuric acid or dilute hydrochloric acid with a concentration of 5-10%, and the acidic solution of stannous chloride has a concentration of 6%.

[0018] In a more optimized manner, in step S2, the concentration of silver nitrate solution is 3.5 g / L, the complexing agent is ammonia water with a concentration of 7.5%, and the reducing agent is glucose or ascorbic acid.

[0019] In a more optimized manner, in step S2, the pH adjuster is sodium hydroxide, and the stabilizer is sodium thiosulfate or an organic nitrogen-containing compound.

[0020] In a more optimized manner, in step S4, the cavity pressure is 0.8 Pa and the high-purity argon gas concentration is 99.999%.

[0021] In a more optimized manner, in step S5, the working pressure of argon gas is 1.4 Pa, and the target deposition thickness is 28 nm.

[0022] The optimal conditions for vacuum drying are 60℃ and -0.1MPa.

[0023] More preferably, the silane or fluorocarbon gas includes one of tetraethoxysilane, hexamethyldisilazane, tetramethylsilane, carbon tetrafluoride, hexafluoroethane, and octafluorocyclobutane.

[0024] The present invention also provides a silver-coated copper powder suitable for high-frequency electronic components, which is prepared by any of the above-mentioned methods for preparing silver-coated copper powder suitable for high-frequency electronic components.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0026] (1) This invention utilizes chemical plating to efficiently and economically construct the silver layer body, and then uses PVD technology to deposit an extremely pure and dense nano-silver layer on the outermost layer to "encapsulate" the chemical plating layer, make up for its microscopic defects, and achieve a leap in performance.

[0027] (2) The present invention uses high-energy silver atoms to penetrate into the micropores and grain boundaries of the chemical coating to achieve physical “blocking”, while the vacuum environment and slow deposition allow the atoms to be fully arranged to form a high-quality coating with large grains and few grain boundaries.

[0028] (3) The present invention can construct a continuous and dense monomolecular or nanoscale thin film (SiO2 or fluorocarbon polymer) on the outermost surface of the silver layer, which blocks corrosive media (H2O, O2, S) through steric hindrance effect. 2- When in contact with silver, the fluorocarbon film, in particular, prevents water molecules from spreading due to its extremely low surface energy (high hydrophobicity), thus fundamentally inhibiting the occurrence of electrochemical corrosion.

[0029] (4) This invention utilizes the skin effect to form an extremely dense and smooth surface silver layer through PVD, providing a near-perfect transmission channel for high-frequency current, with a resistivity close to that of bulk silver single crystal. The reduction in surface roughness also reduces electron scattering; in the target high-frequency range, its conductivity loss far exceeds that of pure chemical plating products, reaching the level of pure silver powder.

[0030] (5) The silver-coated copper powder prepared by the present invention has an extremely low resistance change rate under harsh environments such as high temperature and high humidity (e.g., 85℃ / 85%RH), high temperature storage, and sulfides. It has a strong ability to resist electrochemical migration, sulfidation and oxidation, and its service life is greatly extended. This is because the PVD silver layer blocks all the physical defect channels of the chemical plating layer, and the outermost PECVD film provides chemical passivation and hydrophobic barrier. Attached Figure Description

[0031] Figure 1 This is an electron microscope image of Example 1. Detailed Implementation

[0032] 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.

[0033] This invention provides a method for preparing silver-coated copper powder suitable for high-frequency electronic components, comprising the following steps:

[0034] S1, Copper powder treatment: Take a certain amount of copper powder, immerse it in sodium hydroxide solution, ultrasonically clean it for 10 minutes to remove surface grease and organic matter, and wash it thoroughly with deionized water until neutral; soak the cleaned copper powder in an acidic solution for 3 minutes for acid washing, immerse the acid-washed copper powder in an acidic solution of stannous chloride and stir, rinse it with deionized water until neutral, and then vacuum dry it to obtain active copper powder.

[0035] This step removes the natural oxide layer (Cu₂O / CuO) of copper, exposing the fresh metal surface. The reaction is: CuO + 2H₂O + → Cu 2++ H2O. Immerse the acid-washed copper powder in an acidic solution containing stannous chloride, Sn 2+ Ions adsorb onto the copper surface, forming a very thin reducing "catalytic layer" that provides active sites for subsequent silver ion reduction.

[0036] S2, chemical silver plating: A measured amount of silver nitrate solution and complexing agent are heated to 55°C. Active copper powder is immersed in the silver nitrate solution, and the complexing agent and reducing agent are slowly added dropwise. The mixture is ultrasonically stirred for 45-60 minutes. During stirring, sodium hydroxide is used to maintain the pH between 11 and 12. A stabilizer is added simultaneously during the dropwise addition. After the dropwise addition is complete, the mixture is ultrasonically stirred for another 10 minutes to obtain silver-plated copper powder. In this step, the concentration of the silver nitrate solution is 3.5 g / L, the complexing agent is ammonia water with a concentration of 7.5%, the reducing agent is glucose or ascorbic acid, the pH adjuster is sodium hydroxide, and the stabilizer is sodium thiosulfate or an organic nitrogen-containing compound.

[0037] In this step, silver nitrate provides silver ions, and the complexing agent forms a stable [Ag(NH3)2] with the silver ions. + Complexes prevent spontaneous decomposition of the solution, reducing agents ensure controllable deposition rates, and stabilizers prevent spontaneous decomposition of the plating solution.

[0038] S3, cleaning and drying: the solution along with the silver-plated copper powder is poured into deionized water to quench the reaction, and then the silver-plated copper powder is obtained by centrifugation. After removing the residual solution by alternating cleaning with deionized water and anhydrous ethanol, it is vacuum dried to obtain primary silver-plated copper powder, which is then stored in an inert gas.

[0039] The purpose of this step is to remove moisture in an extremely low temperature and vacuum environment, so as to avoid the silver layer reacting with water and oxygen at high temperatures, and also to prevent the silver layer from cracking due to surface tension contraction.

[0040] S4, Surface finishing: The primary silver-coated copper powder is transferred to a sealed PVD feed container in an inert gas environment. It is then loaded into a powder feeder equipped with a fluidized bed in a PVD sputtering chamber via a vacuum interconnection device, and the base vacuum is evacuated to ≤ 1.0 × 10⁻⁶. -3 At the Pa level, high-purity argon gas is introduced to maintain the cavity pressure at 0.1-1 Pa, with a cavity pressure of 0.8 Pa and a high-purity argon gas concentration of 99.999%. The radio frequency plasma power supply is turned on to generate argon plasma in the cavity. The fluidized bed is started to make the powder tumble in the cavity, ensuring that every surface of every powder particle is uniformly bombarded by the plasma. The cleaning process lasts for 12 minutes.

[0041] S5, depositing a silver layer: stabilize the argon working pressure at 0.5-2 Pa, preferably 1.4 Pa; turn on the silver target; deposit a silver layer on the surface of the primary silver-coated copper powder after surface finishing at a sputtering power of 140 W; sputtering time is 3 min; target deposition thickness is 27-32 nm, preferably 28 nm.

[0042] High-energy particle impacts energize surface silver atoms, causing them to rearrange and migrate, filling some defects and placing the surface lattice in a metastable state, making it easier for them to form strong chemical bonds with foreign deposited atoms. The sputtered silver atoms have high kinetic energy and still have enough energy to migrate on the surface after reaching the substrate, finding the lowest energy position (lattice site) to settle down, thereby achieving epitaxial growth or forming a dense columnar crystal structure.

[0043] S6, passivation and material collection: After deposition, the powder is cooled under an inert atmosphere, and a trace amount of silane or fluorocarbon gas is introduced for plasma-enhanced chemical vapor deposition. After cooling to room temperature, the chamber is filled with high-purity nitrogen to atmospheric pressure, and the final product is removed under inert atmosphere protection, yielding silver-coated copper powder. In this step, the silane or fluorocarbon gas includes one of tetraethoxysilane, hexamethyldisilazane, tetramethylsilane, carbon tetrafluoride, hexafluoroethane, and octafluorocyclobutane.

[0044] A continuous, dense monomolecular or nanoscale thin film (SiO2 or fluorocarbon polymer) is constructed on the outermost surface of the silver layer. This film blocks corrosive media (H2O, O2, S) through steric hindrance. 2- When in contact with silver, the fluorocarbon film, in particular, prevents water molecules from spreading due to its extremely low surface energy (high hydrophobicity), thus fundamentally inhibiting the occurrence of electrochemical corrosion.

[0045] This invention prepares different silver-coated copper powders using several embodiments and comparative examples to verify the performance of the products.

[0046] Comparative Example 1 is a simple chemically plated silver-coated copper powder with a silver content of 12wt%. The thickness of the silver layer was measured to be approximately 80nm using FIB-SEM cross-sectional imaging.

[0047] Comparative Example 2 is pure silver powder with a silver content of 100 wt%.

[0048] The example is the chemical plating + PVD surface finishing silver-coated copper powder prepared according to the present invention, with a silver content of 12.5 wt%, and the silver layer thickness was measured to be approximately 85 nm using FIB-SEM cross-sectional imaging.

[0049] First, electrical performance and high-frequency performance tests were conducted. The specific test methods and results are shown in Table 1.

[0050] Table 1. Test results of electrical and high-frequency performance in the examples and comparative examples.

[0051]

[0052] As shown in Table 1, the high-frequency conductivity of the embodiment is improved by more than 60% compared with Comparative Example 1, which is close to the level of pure silver powder. This proves that the PVD finishing layer provides a near-ideal high-frequency current channel and the signal attenuation is greatly reduced.

[0053] Environmental reliability testing was then conducted, and the results are shown in Table 2.

[0054] Table 2 Environmental Reliability Test Results

[0055]

[0056] As can be seen from Tables 1 and 2, this invention achieves a leap in product performance from "usable" to "excellent" and reliability from "risky" to "comparable to pure silver" with a negligible increase in silver content (0.5 wt%) and a raw material cost increase of about 5%, making it the most valuable technical path.

[0057] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for preparing silver-coated copper powder suitable for high-frequency electronic components, characterized in that, Includes the following steps: S1, Copper powder treatment: Take a certain amount of copper powder, immerse it in sodium hydroxide solution, ultrasonically clean it for 10 minutes to remove surface grease and organic matter, and wash it thoroughly with deionized water until neutral; immerse the cleaned copper powder in an acidic solution for 3 minutes for acid washing, immerse the acid-washed copper powder in an acidic solution of stannous chloride and stir, rinse it with deionized water until neutral, and then vacuum dry it to obtain active copper powder; S2, chemical silver plating: Take a certain amount of silver nitrate solution and complexing agent and heat to 55℃. Immerse active copper powder in silver nitrate solution, slowly add complexing agent and reducing agent, and stir with ultrasound for 45-60 minutes. During the stirring process, use sodium hydroxide to maintain the pH value between 11 and 12. Add stabilizer simultaneously during the drop addition. After the drop addition is completed, stir with ultrasound for another 10 minutes to obtain silver-plated copper powder. S3, cleaning and drying: the solution along with the silver-plated copper powder is poured into deionized water to quench the reaction, and then the silver-plated copper powder is obtained by centrifugation. After removing the residual solution by alternating cleaning with deionized water and anhydrous ethanol, it is vacuum dried to obtain primary silver-plated copper powder, which is then stored in an inert gas. S4, Surface finishing: The primary silver-coated copper powder is transferred to a sealed PVD feed container in an inert gas environment. It is then loaded into a powder feeder equipped with a fluidized bed PVD sputtering chamber via a vacuum interconnection device, and the background vacuum is evacuated to ≤ 1.0 × 10⁻⁶. - 3 At the Pa level, high-purity argon gas is introduced to maintain the cavity pressure at 0.1-1 Pa. The radio frequency plasma power supply is turned on to generate argon plasma in the cavity. The fluidized bed is started to make the powder tumble in the cavity, ensuring that each surface of each powder particle is uniformly bombarded by the plasma. The cleaning process lasts for 12 minutes. S5, deposit silver layer, stabilize the working pressure of argon gas at 0.5-2 Pa, turn on the silver target, and deposit a silver layer on the surface of the primary silver-coated copper powder after surface finishing at a sputtering power of 140W. The sputtering time is 3 minutes and the target deposition thickness is 27-32nm. S6, passivation and material collection: After deposition, the powder is cooled in an inert atmosphere and a trace amount of silane or fluorocarbon gas is introduced for plasma-enhanced chemical vapor deposition. After cooling to room temperature, the chamber is filled with high-purity nitrogen to atmospheric pressure, and the final product is taken out under the protection of an inert atmosphere to obtain silver-coated copper powder.

2. The method for preparing silver-coated copper powder suitable for high-frequency electronic components according to claim 1, characterized in that: In step S1, the acidic solution includes dilute sulfuric acid or dilute hydrochloric acid with a concentration of 5-10%, and the acidic solution of stannous chloride has a concentration of 6%.

3. The method for preparing silver-coated copper powder suitable for high-frequency electronic components according to claim 1, characterized in that: In step S2, the concentration of silver nitrate solution is 3.5 g / L, the complexing agent is ammonia water with a concentration of 7.5%, and the reducing agent is glucose or ascorbic acid.

4. The method for preparing silver-coated copper powder suitable for high-frequency electronic components according to claim 1, characterized in that: In step S2, the pH adjuster is sodium hydroxide, and the stabilizer is sodium thiosulfate or an organic nitrogen-containing compound.

5. The method for preparing silver-coated copper powder suitable for high-frequency electronic components according to claim 1, characterized in that: In step S4, the cavity pressure is 0.8 Pa and the concentration of high-purity argon gas is 99.999%.

6. The method for preparing silver-coated copper powder suitable for high-frequency electronic components according to claim 1, characterized in that: In step S5, the working pressure of argon gas is 1.4 Pa, and the target deposition thickness is 28 nm.

7. The method for preparing silver-coated copper powder suitable for high-frequency electronic components according to claim 1, characterized in that: The vacuum drying conditions are all 60℃ and -0.1MPa.

8. The method for preparing silver-coated copper powder suitable for high-frequency electronic components according to claim 1, characterized in that: The silane or fluorocarbon gas includes one of tetraethoxysilane, hexamethyldisilazane, tetramethylsilane, carbon tetrafluoride, hexafluoroethane, and octafluorocyclobutane.

9. A silver-coated copper powder suitable for high-frequency electronic components, characterized in that: It is prepared by any one of the methods described in claims 1-8 for preparing silver-coated copper powder suitable for high-frequency electronic components.

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