SIGNIFICANTLY IMPROVED MECHANICAL-PROPERTIES OF PB-FREE, SN-ZN-IN SOLDER ALLOY BY AG DOPING

The 87%Sn-8%Zn-5%In alloy is a new Pb-free solder designed for possible drop-in replacement of Pb-Sn solders. This Sn-Zn-In solder has a melting point of approximately 188-degrees-C, which is comparable to that of the widely used eutectic Pb-Sn solder. However, because of the rather coarse and nonuniform distribution of platelike, dendritic features throughout the microstructure, the alloy exhibits a limited ductility (tensile elongation of approximately 20%). In this letter, we show that the addition of small amounts of Ag (as small as 0.1%) dramatically improves the tensile ductility to approximately 40%. The observed improvement in ductility is attributed to the elimination of the coarse planar features and nonuniformities within the microstructure. The addition of Cu has a similar beneficial effect, although it is less preferable to the Ag addition from the stand point of melting temperature.