Investigation of void-free electroplating method on copper column based solder bump for flip-chip interconnections

A void-free copper electroplating method on copper column based solder bump for flip-chip interconnection enabling reduction of the copper column void defects in the solder bump was investigated. The surface energy of the resist mask surface, which affects the wettability of the electroplating solution, was investigated by applying a surface modification technique with ultraviolet (UV) radiation treatment and oxygen plasma treatment. Also, the surface tension of electroplating solution was evaluated by employing an interfacial activator. Both the UV radiation treatment and the oxygen plasma treatment were found to increase the wettability on the electroplating resist surfaces and decrease the number of bubbles causing void defects in the solder bump. In addition, the interfacial activator decreased the number of bubbles and prevented the copper column void defects completely.