Soft gold electroplating from a non-cyanide bath for electronic applications

The electrodeposition of pure gold is an enabling technology for wafer bump and wire bonding interconnects applications. Most conventional pure gold electroplating processes used in the electronics industry are cyanide based. Due to the toxicity of the free cyanide formed during electrolysis, as well as cyanide´s incompatibility with positive photoresists, sulfite-based gold processes have been the traditional alternative for wafer applications. However, traditional sulfite-based processes have suffered from issues with solution stability and the necessity for annealing to achieve the desired deposit hardness. This paper describes a stable non-cyanide process that can be used for soft gold electroplating. Electrochemical characterization of two non-cyanide processes is presented to illustrate the electrochemical behaviour of gold in the presence of different complexing agents. The effects of operating parameters on process performance, including cathode efficiency, deposit purity, hardness, solderability and solution stability are presented. The thickness uniformity, surface morphology and topography of the electrodeposited gold bumps, as well as wire bonding performance, are also presented.