Copper Electroless Bonding of Dome-Shaped Pillars for Chip-to-Package Interconnect

Abstract

Electroless plating was used to achieve compliant bonding between two components with electroplated copper pillars for chip-to-package interconnects. The geometry of the pillars was modified from flat-topped to round, dome-shaped structures by addition of a leveler to the electroplating bath used to form the pillars. The effect of the dome-shaped structure on the electroless joining process was studied using different electroless plating baths. The baths contained a surfactant and used forced convection during electroplating. Void trapping was observed in the electroless region between the domed, electroplated pillars, however, the size of the voids is smaller than previously reported with flat-topped pillars. The surfactant, Triton X-100 was found to decrease void formation at the electroless joint.