Rapid assessment of steady-state creep rates and stress dip effects in solder alloys

Abstract

Rapid comparisons of traditional and lead-free solders have been made using self stressing spirals. A novel extension of the technique has been used to create stress-dip effects during the steady-state regime. Reverse creep, incubation times, and changed post-dip creep rates have been observed which are free from the uncertainties of conventional stress-dip testing. The time to the re-establishment of forward creep has been used to determine the activation energy of the restoration processes. Re-established creep rates have been shown to be comparable to steady-state creep rates for modest stress dips. Larger stress reductions give higher post-dip creep rates that are closer to primary rates indicating that reverse yielding has disturbed the steady-state dislocation arrangements. Such events could occur in solder joints that are subjected to variable loading.