The Research Of Silver Powders Used For Conductive-paste Prepared By Liquid Chemical Reduction Method

In this experiment, the micron-size and sub-micron-sized silver powders used for conductive-paste were prepared by Liquid Chemical Reduction Method with silver nitrate as precursor. Silver powders are the most critical materials of preparing conductive-paste, its’ quality directly or indirectly affects the performance of the paste and eventually electronic component. The obtained powders were able to meet the requirements of the conductive-paste by optimizing the reaction conditions to control the silver particle’s morphology, size, size distribution, loose density, tap density and other properties. Scanning electronic microscope (SEM) was used to characterize the morphology of silver powders, the structure was analyzed by X-ray Diffraction(XRD), and the particle size distribution was analyzed by laser light scattering. In addition, the possible growth mechanism in the experimental system of the silver powders was also discussed.The experiment results indicated:it is easier to get high-purity, well dispersed, micron-sized or sub-micron-sized silver powders with ascorbic acid as reducer than glucose, formic acid, sulphurous acid, composite glucose and ascorbic acid, composite formic acid and ascorbic acid, composite sulphurous acid and ascorbic acid. Ascorbic acid being reducer, the morphology and the size of the silver particles were influenced a lot by the pH value of the solution. In the high pH circumstances, the silver crystal nucleus grew up mainly depending on gathering, and finally obtained the silver particles of sphere shape, little semidiameter, rough surface, and the low tap density. About pH≈4, there is a key change of the morphology and the growth mechanism of silver powders. When the pH was less than the point, silver particles grew up mainly depending on the crystallization; and the final particles appeared regular polyhedron; and the surface was relatively smooth, the density was relatively high. When the pH was greater than the point, silver particles grew up mainly depending on the coalescence; and the final particles appeared spherical; and the surface was relatively rough, the density was relatively low. It can make the uniform shape of silver particles by the symmetry way of dropping the fluid. Preparing with acacia gum as dispersant, the morphology of micron-size silver powders was the best when the mass ratio of acacia gum to silver nitrate is0.0178; The morphology of sub-micron-size silver powders was the best when the mass ratio of acacia gum to silver nitrate is0.039;The optimal parameter is that:reducing silver nitrate by ascorbic acid, silver nitrate concentration of1.0588mol/L, reducer concentration of0.625mol/L, pH value of the solution of1.0～1.5, gum Arabic as dispersant, mass ratio of gum Arabic to silver nitrate of0.0178, mixing through symmetrically dropping for30min, aging18h. It could be obtained the ultimate product of cubic silver, good crystallize, well dispersed, and the productivity would be over98%. Expanding test proved that the process was stable enough to be used for expanded production.