Microstructure and Mechanical Properties of In-Doped Low-Temperature SnPb Solders

In this paper, In was introduced into SnPb eutectic solder to develop a new low-temperature solder for three-dimensional packaging technology. SnPbIn solders containing 5, 10, 13, 15 and 17 wt.% In were prepared through vacuum induction melting. The effect of the addition of In on the microstructure and thermal and mechanical properties of the SnPbIn solders was investigated. The results showed that the SnPb eutectic solder consisted of Sn(ss) and Pb(ss), but when the In content was higher than 5 wt.%, the SnPbIn solder included Sn(ss) and Pb(ss) and a new InSn4 phase. Solid dissolution of the In element into Sn(ss) and Pb(ss) preferentially occurred. The melting points of the SnPbIn solders gradually decreased with the increasing addition of the In element. The melting point of the Sn-Pb-13In solder decreased to 150.5 °C, which met the requirements of 2.5D packaging. But the cast Sn-Pb-5In solder reached the best tensile strength of 48.8 MPa and elongation of 27.3%. Super-plasticity occurred in the cold-rolled SnPbIn, while the 59.9Sn35.1 Pb5In solder achieved elongation of 382.0% and 408.6%, respectively, at deformation of 70% and 90%. The super-plasticity originated from the recrystallization behavior and soft orientation.