Creep of dilute tin based lead free solder alloys as replacements of Sn–Pb solders

Abstract

The present paper reports behaviour of Sn–0˙7Cu, Sn–1Zn and Sn–0˙7Cu–1Zn tin based lead free solder alloys at the room temperature creep together with pure Sn and Sn–37Pb as the materials for comparison. Stress exponent values in the range 7˙8–9˙7, depending on the alloy type, determined by indentation and impression methods were in good agreement. All three tin based alloys showed creep resistances higher than pure Sn. The addition of 1%Zn to Sn resulted in the formation of fine Zn rich phase which increased both the hardness and creep resistance of the material, as indicated by the steady state creep rates. The same amount of Zn added to Sn–0˙7Cu deteriorated the creep resistance due to the fact that the formation of both Zn particles and Cu₆Sn₅ intermetallics was suppressed. Among the tested materials, Sn–1Zn which exhibited relatively high creep resistances could be considered as a suitable alternative for the Sn–37Pb solder alloy.