Overview and Functional Characterization of Pb–Free Solders

Abstract

There are now new legislations emerging or being contemplated to restrict the use of Pb in electronic devices. This development has provided the impetus for the development of Pb- free solder alloys and efforts are now geared towards characterizing their operational and functional properties. The most common alloys being recommended and investigated are those primarily based on the Sn-Ag-Cu (SAC) system. These SAC alloys generally have higher melting points than conventional Pb-Sn alloy. Additionally they are susceptible to microstructural evolution of inter-metallic compounds that have been implicated in thermal fatigue life, mechanical strength and fracture toughness of the soldered joints. We have studied the Sn rich corner of the Sn-Ag-Cu system with minor additions aimed at minimizing detrimental microstructural development and improving the solderability and the mechanical strength of soldered joints. Some of the SAC alloys with minor additions showed some interesting properties. Their shear strength measured ranged from 30 – 60 MPa. The combined properties of strength and conductivity recorded compared favorably with that of traditional Pb-Sn solders.