Development and characterization of Sn–1.3Ag–0.7Cu solder bearing Zn for electronic packaging

Abstract

The effect of small amounts of Zn on microstructure, thermal behavior and mechanical properties of low silver-content Sn–1.3Ag–0.7Cu (SAC137) solder was investigated. Microstructural investigations of SAC137 solder revealed that both the intermetallic compounds of rod-like Cu6Sn5 and needle-like Ag3Sn particles are dispersed in β-Sn matrix, which are gradually diminished with increasing Zn content in plain solder. Moreover, addition of 0.75 wt% Zn promotes the nucleation of β-Sn grains and leads to formation of new (Cu,Ag)5Zn8 IMC particles. Although the strength and Young’s modulus of plain solder are increased with increasing Zn content, the elongation was firstly increased with 0.75 wt% Zn addition and then decreased after adding 1.5 % Zn. The higher mechanical strength was contributed by the fine β-Sn grains and precipitations strengthen effects of new (Cu,Ag)5Zn8 IMC particles. The presence of Zn in SAC137–0.75 wt% Zn solder seems to result in a complete reduction of brittle pro-eutectic Ag3Sn phase to maintain the ductility at the highest level. The new (Cu,Ag)5Zn8 IMC developed in Zn added specimens was found to enviably affect the thermal properties according to DSC analyses.