EPD of Metallic Silver Particles: Problems and Solutions
Cerel has devoted the past several years to the development of prototype microcomponents for the electronics industry based on EPD processing. The present contribution summarizes some problems Cerel has experienced in the integration of EPD for metallic silver particles into a viable production process. In particular, the parameters that need to be controlled due to the metallic nature of the silver particles have been analyzed. Selection of a metallic silver powder suitable for EPD is the key factor. An appropriate particle size and shape, as well as a controlled size distribution, significantly improves the green density of the deposit. Metallic silver particles in a suspension tend to aggregate, especially when exposed to an electric field. This leads to premature sedimentation, as well as low green densities for the electrophoretic deposit. The following factors were found to contribute significantly to preventing premature sedimentation: • The replacement of pure silver by palladium-coated silver particles. • Dispersion preparation in a high viscosity medium of low dielectric constant. • The presence of steric, electrosteric and ceramic oxide additives in the siver powder dispersion. Finally, control of the solids loading and particle size distribution in the suspension, and the geometrical design of the EPD cell, including the counter-electrodes, were also shown to be important for the successful electrophoretic deposition of silver particles in the commercial production of micro-components by EPD.
A.R. Boccaccini, O. Van der Biest and R. Clasen
M. Zarbov et al., "EPD of Metallic Silver Particles: Problems and Solutions", Key Engineering Materials, Vol. 314, pp. 95-100, 2006