M. Mccormack et al., SIGNIFICANTLY IMPROVED MECHANICAL-PROPERTIES OF PB-FREE, SN-ZN-IN SOLDER ALLOY BY AG DOPING, Applied physics letters, 65(9), 1994, pp. 1100-1102
The 87%Sn-8%Zn-5%In alloy is a new Pb-free solder designed for possibl
e drop-in replacement of Pb-Sn solders. This Sn-Zn-In solder has a mel
ting point of approximately 188-degrees-C, which is comparable to that
of the widely used eutectic Pb-Sn solder. However, because of the rat
her coarse and nonuniform distribution of platelike, dendritic feature
s throughout the microstructure, the alloy exhibits a limited ductilit
y (tensile elongation of approximately 20%). In this letter, we show t
hat the addition of small amounts of Ag (as small as 0.1%) dramaticall
y improves the tensile ductility to approximately 40%. The observed im
provement in ductility is attributed to the elimination of the coarse
planar features and nonuniformities within the microstructure. The add
ition of Cu has a similar beneficial effect, although it is less prefe
rable to the Ag addition from the stand point of melting temperature.