The electromigration of 6 different compositions of Sn-Pb solder, under a current density of 105/cm2 at about room temperature, was investigated by using thin-film strips. Among these compositions (0, 20, 30, 38 60 and 95at%Pb) the eutectic alloy (38at%Pb), with the lowest melting point and a high density of lamellar interfaces, was found to exhibit the most rapid hillock growth. As the composition approached the terminal phases, the hillock growth rate decreased. It increased again in pure Sn. The interfaces between Sn and Pb, which provided the most rapid paths for mass transport, were also sites of initiation of hillock and void formation.

Electromigration in Sn-Pb Solder Strips as a Function of Alloy Composition. C.Y.Liu, C.Chen, K.N.Tu: Journal of Applied Physics, 2000, 88[10], 5703-9