Study On The Preparation Process And Performance Of Ultrafine Silver-coated Copper Powder For Conductive Paste

With the development of the electronics industry,the substitution of base metals for precious metals such as silver and palladium for the electronics industry has attracted increasing attention.Among them,copper is one of the ideal alternatives to silver,which has the advantages of low cost,low electrical resistivity,and low electro migration speed.As a kind of functional material,copper powder has excellent electrical conductivity,thermal conductivity and catalytic performance.It has important applications in electromagnetic shielding,chemical catalysts,conductive pastes,powder metallurgy and other fields.Due to the large specific surface area and active chemical properties of ultra-fine copper powder,dense Cu2O and CuO films can be easily formed on the surface,which can lead to a rapid decrease in electrical conductivity and even non-conductivity.This makes it difficult for conductive materials to maintain good electrical conductivity during prolonged use.Therefore,how to keep the copper powder from being oxidized during the sintering process and maintain its excellent electrical conductivity is a key issue in the application of the copper powder in the conductive paste.In this paper,the phosphate coating was coated on the surface of copper powder by chemical coating method.The influence of different phosphating conditions on the oxidation resistance of copper powder was studied,and the electro less silver plating process of the phosphatized copper powder was studied.Scanning electron microscopy,X-ray diffrac to metry,differential scanning calorimetry,and X-ray photoelectron spectroscopy were used to test the prepared powders.Electrochemical tests were used to characterize the electrochemical properties.Through single-factor tests,the effects of phosphoric acid,zinc phosphate,temperature and time on the oxidation resistance of copper powder were studied in detail.The best phosphating process was determined:zinc phosphate 7.7 g,zinc nitrate 5 g,zinc oxide 7.5 g,nitric acid 12ml,phosphoric acid 20 ml,water 1400 ml,reaction temperature 50℃,reaction time 30min.Under the optimal phosphating conditions,the copper powder’s oxidation resistance and electrical conductivity are significantly improved,which is in line with the requirements of the powder used in the conductive paste.Silver plating phosphatizing copper powder was prepared by liquid phase reduction method.The optimum conditions of silver plating were determined by studying the amount and type of dispersant,pH value of solution,and silver content.Under the optimal conditions of silver plating,the anti-Oxidation properties of the phosphating copper powder are significantly improved,and the silver plating cffect is excellent.The prepared silver-plated phosphatized copper powder was used as the conductive material.The cold pressing method was used to prepare the sample and the resistance of the electrode was measured by the four-probe method.The results showed that the silver content had an influence on the conductivity of the phosphatized copper powder and was low.The silver-containing silver phosphide powder has a higher resistance than the high ilver content,and the resistance gradually decreases as the silver content increases.Under the optimal conditions of silver plating,a continuous layer of uniform and densely coated silver layer is formed on the surface of the silver-plated phosphating copper powder,and the particle size of the silver-coated phosphating copper powder increases with the increase of the silver content,and along with The increase of the silver content of the surface of the phosphide powder is more uniform.In silver-plated phosphatized copper powder,silver is present in the form of metallic silver,and copper is present in the form of metallic copper and divalent copper,respectively.Silver-plated copper powder,silver-plated phosphatized copper powder and silver powder were used as the conductive phase to prepare conductive pastes.The migration and electrochemical behavior of different conductive phases were compared using the water droplet test method.The silver-plated phosphatized copper powder showed better resistance to migration,and the silver content was different,and the migration resistance of the conductive adhesive was also significantly different;the silver-coated phosphatized copper powder conductive adhesive electrode was better than the silver-coated copper powder,silver conductive adhesive electrode The corrosion resistance is good,the dissolution of the electrode is slower,and its tendency for electrochemical migration is smaller.