Development of transient liquid phase sintered (TLPS) Sn–Bi solider pastes

Thermal analysis of pure Sn and Bi powder mixtures indicates that a transient liquid phase affect can be induced in the presence of paste chemicals. Initially liquid forms with a eutectic composition (i.e. 140°C), followed by rapid re-solidification and secondary melting at temperatures above 180°C. Upon reheating, processed solders do not remelt until temperatures above 220°C. Solder consolidation below the liquidus depends critically on the amount of liquid phase formed which in turn depends on the paste ingredients. Sn-3 to 5 wt.% Bi pastes with densities in excess of 95%, which will not remelt when reheated to the same temperature have successfully been developed.