Interfacial Reaction between Lead-free Solder Ball and Au/Ni/Cu Pad during Laser Reflow Soldering

The interfacial reaction between Sn-Ag-Cu and Sn-Ag lead-free solder balls and Au/Ni/Cu pads in laser reflow process are presented in this paper. A continuous intermetallic compound layer and some needle-like AuSn4 were observed at the interface of solder and pad, their morphology and distribution were strongly dependent on the laser input energy. Some voids were observed at the interface of solder joints when using laser as the heating source and they weakened the joints. The formation of voids maybe caused by the unique properties of laser.