Gold plating for hybrid microcircuits

Electrochemical porosity tests and auger electron spectroscopy were used to evaluate three gold electroplating formulations (citrate, phosphonic acid, and phosphate) at varying current densities, deposition modes (ad, dc, and pulse), and thicknesses for eventual use on hybrid microcircuits. Electroplated films were shown to be less porous than evaporated or sputtered films by at least an order of magnitude. Plating current densities of 75.6 A/sq m produced deposits more porous than those obtained at 10.8 and 32.4 A/ sq m current or pulse plated deposits were typically less porous than ac deposits. Auger electron spectroscopy showed more chromium to be present on the surface of evaporated than on electroplated gold coated hybrid microcircuits after heating at 300 C for two hours. In the amount of chromium which diffused through the films, a comparison of the various methods of electrodeposition showed very little difference.