Presence of Anelastic Strains in High Lead Solders at Ambient and High Temperatures

We had reported last year that cyclically tested Pb/Sn solders of different compositions exhibited a complicating anelastic effect. The storage and recovery of anelastic strains suppresses damaging creep strain from being stored thus causing non-conservative life prediction estimates and results in complications with respect to accelerated testing. These complications were at that time believed to be characteristic of only eutectic solders at near ambient temperatures. We now find that said complications exist for high end Pb solders and at higher temperatures. Strain rate behavior of high lead solders indicate that a different failure mechanism might exist at temperatures where the material exists as a two phase and in regimes where it exists as a solid solution. Experiments conducted to determine the effect of grain size on accelerated cycling indicated that recrystallization of large grains occurs due to cycling at high temperatures. At ambient temperature, which is greater than half the absolute melting temperature of 90/10 Pb/Sn, it was observed that large grains suppress creep.