Preparation Of Silver Palladium Alloy Powders For Electronic Pastes

The silver palladium alloy powder has stable chemical properties and good conductivity. The powder overcomes the two defects of silver powder as electric conductive materials in microelectronics industry, i.e. silver ions migration and bad resilience to soldering tin handle etching. Therefore, the silver palladium alloy powders become the most compelling conductive extenders of electronic pastes. The preparation of monodispersed powders of silver and palladium has been the advanced technology in recent years, since the two metals have different oxidation reduction properties.The properties of silver palladium alloy powders can directly determine the critical indexes of the film of pastes, such as high conductivity and compactness. The properties mainly depend on the particle structure, morphology, size, and size distribution and so on. The preparation process of the powders is the key to the design and manufacture of high-quality electronic products and pastes. Thus, the main purpose of this work is to study the preparation technology of silver palladium alloy powders.In this work, the silver palladium alloy powder used for electronic pastes was prepared by liquid chemical reduction method with silver nitrate and palladium nitrate as the oxidant and ascorbic acid as the reductant. The obtained powders were able to meet the requirements of the electronic pastes by optimizing the reaction conditions to control the particle morphology, particle size, size distribution, tap density and other properties. Scanning electronic microscope (SEM) and X-ray Diffraction (XRD) and other testing methods were used to characterize and analyze the properties of the silver palladium alloy powders. The nucleation and growth mechanism of the powder particles was also discussed.In this experiment, the preparation technology of silver palladium alloy powder was investigated from different aspects, such as mixing condition, concentration of the reactants and dispersant, reaction temperature, pH value of the solution, and heat treatment temperature and time. The results indicate that reaction temperature and dispersant dosage affects significantly the morphology and particle size of the Ag-Pd powder under the condition of pouring mixing. The optimum conditions for preparing the silver palladium alloy powder (Ag/Pd=7:3), were summed up as follows:the reactant concentration is0.5mol/L, the mole ratio of reductant to oxidant is2:1, the mass ratio of Gum to oxidant is0.01:1, pH value of the oxidation solution is adjusted to2.0by sodium hydroxide, the temperature of reaction is20℃, and the heat treatment is at450℃for4hours. The Silver-palladium powder prepared by the optimum condition is sphere-like and well dispersed, with particle size ranging from0.6μm to1.0μm, a tap tensity of2.8g/cm3, an average particle size of0.75μm, and a production yield of91.43%. The powder can basically meet the requirements of the electronic pastes.