Effect of Morphology and Hydrogen Evolution on Porosity of Electroplated Cobalt Hard Gold

Abstract

The impact of plating parameters on the porosity of cobalt hard gold electrodeposited from a cyanide bath is presented. Both constant current and pulsed current deposition were studied by electrochemical and microscopy methods. As observed previously, pores tend to decorate grain boundaries, defects, and other morphology features. Focused ion beam scanning electron microscopy indicates that perhaps only a small fraction of pores seen on the surface of the thick gold film extends to the electroplated Ni underlayer. The density of pores depends on morphology and current efficiency, both of which were found to vary significantly with plating conditions. Faceted surface features correlate with a higher pore density. For a similar morphology, the pore density increases with the hydrogen generation rate, estimated from current efficiency measurements. Pulse plating conditions, with relatively high peak current and frequency, result in deposits with lower porosity due to the capability of generating finer grains while influencing hydrogen evolution rates.