Development of advanced AuSn alloy plating technology for semiconductor application

Comparing with solder preforms, pastes and wafer backside evaporation, electroplating is a cost effective alternative. Electroplating process for depositing AuSn alloys onto metallized ceramic and semiconductor substrates, from a single solution has been developed. The stability of electroplating solution along with the effect of current density was studied. In addition, deposition uniformity could be improved by solution circulation. In this paper, a range of methodologies including SEM-EDX, GD, XRD, Laser microscope, and DSC were used to characterize AuSn Morphology, composition, uniformity, crystal structure, roughness and melting point properties. Composition with Au80Sn20 corresponds to both Au5Sn and AuSn phase respectively, which resulted in the eutectic composition of AuSn alloy. Stability of AuSn as a backside metal (BSM) for eutectic die attach with respect to environmental test (temperature cycling) is presented.