Au Microstructure and the Functional Properties of Ni/Au Finishes On Ceramic IC Packages

Ni/Au plated finishes used on thick-film metallized multilayer ceramic packages for integrated circuits must meet functional requirements such as bondability, sealability, and solderability. Their ability to do so is dependent, among other things, upon the ability of the Au deposit to inhibit the grain boundary diffusion and subsequent surface oxidation of Ni. In this study, the relationship between functional performance, Ni diffusion rate, and Au microstructure was examined. The extent of Ni diffusion during heating was determined by Auger Electron Spectroscopy (AES) for several electrolytic and electroless Ni/Au finishing processes. The results were correlated with differences in the Au microstructures determined by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-Ray Diffraction (XRD).