Microbump Formation by Noncyanide Gold Electroplating

Formation of gold microbumps by electrodeposition using gold sulfite as a metal source was investigated. Gold bumps 20-80 μm wide and 20 μm high were fabricated by either direct or pulse current plating. It was found that selection of additives in the plating bath is important for the formation of gold bumps having smooth surface without nodules. Soft and uniform gold bumps can be obtained by adding 1-10 ppm of cerium ions in the plating bath. Removal of dissolved air in the plating solution is effective to avoid the skip plating and bubble pinholes on the bumps. Furthermore, higher speed bump formation can be achieved by optimizing the pulse conditions, and the plating rate can be doubled compared with direct current plating.