Development of Sn-Zn-Cu lead free solder

Sn-Zn based lead free solder is one type of promising candidate to replace Sn-Pb eutectic solder due to its low cost and melt temperature which near to Sn-Pb eutectic solder. The Sn-Zn-Cu lead free solder was developed by alloying Sn with Zn and Cu in this paper. The effect of Zn and Cu content on the wettability of solder to Cu substrate has been investigated by spread test. The microstructure and composition at interface between solder and Cu substrate were analyzed through optical microscope (OM) and electron probe microanalysis (EPMA). Results show that Sn-4Zn solder has best wettability among Sn-Zn solders. Adding Cu to Sn-4Zn solder can improve the wettability of Sn-4Zn solder for Cu can combine with Zn to produce Cu-Zn alloy and prevent Zn riched phase from existing in the surface of solder. Prior to Sn, Zn combined with Cu dissolved from substrate to produce Cu-Zn intermetallic compounds at the interface of solder and substrate. The formation of continuous Cu-Zn intermetallic compounds layer at the interface between solder and Cu substrate has depressed the forming of Sn-Cu inter metallic compounds layer.