Preparation Of Silver Palladium Alloy Powder By Liquid Chemical Reduction Method

The silver palladium alloy powder has good conductivity and stable chemical properties. The silver powder is with two defects, i.e. silver ions migration and bad resilience to soldering tin handle etching. The silver palladium alloy powder, overcoming the defects and making microelectronic devices more reliable, become the most compelling conductive electronic paste. In the international community, the preparation of monodispersed powder of silver and palladium is a fresh cutting-edge technology. However, the preparation of monodispersed Ag-Pd powder, on the basis that the two metals have different electrochemical reduction potential properties, is a difficult task.Critical indexes of the film of the paste, such as high conductivity and compactness, are directly decided by the properties of silver palladium alloy powders. And because of the properties mainly depending on the particle structure, morphology, size, size distribution and other factors, the preparation process of meeting the electronic paste for approximately spherical submicron particles, good dispersion and the relatively smooth surface of Ag-Pd powder is absolutely important. It is the key to the design and manufacture of electronic pastes and products with high quality. Therefore, it is the preparation technology of silver palladium alloy powder that is in our study.In this work, making silver nitrate and palladium nitrate as the oxidant and ascorbic acid as the reductant, the silver palladium alloy powder used for electronic paste is prepared by liquid chemical reduction method. By optimizing the reaction conditions, the preparation of particle morphology, size, size distribution, tap density and other properties is under control to meet the requirements of the electronic paste. Scanning electronic microscope(SEM), X-ray Diffraction (XRD), transmission electron microscope (TEM) and other testing methods were used in this work, for the characterization and analysis of the properties of silver palladium alloy powder. There is also an initial discussion in this paper over the nucleation and growth mechanism of the powder particle.The research of this preparation technology is conducted by taking factors such as dispersant dosage, reaction temperature, mixing condition, aging temperature and aging time into account. The results indicate that under the condition of mixing pouring as the method, Arabic gum as the dispersant dosage, ammonium citrate as the second phase, there is a notable effect on morphology and particle size of the Ag-Pd powder posed by reaction temperature and dispersant dosage.The optimum conditions for preparing the silver palladium alloy powder (Ag/Pd=9:1) were summed up as follows:the usage of double mixing method; a reactant concentration of 0.5mol/L; a mole ratio of 2:1 over reductant to oxidant; the usage of Gum and ammonium citrate as the dispersant; a mass ratio of 0.02:1 over Gum to oxidant; a mass ration of 0.10:1 over ammonium citrate to oxidant; an initial reaction temperature of 10℃; an 24-hour aging process at the temperature of 35℃. Under this optimum condition, excellent silver-palladium powder with sphere-like and smooth appearance, good dispersion, apparent density of 1.4g/cm3, a tap density of 1.68g/cm3 can be obtained, which basically meet the requirements of the electronic paste.