Damage storage measurement in Pb-Sn solder

Abstract

The effects of hold time, stress range, mean stress, and mechanical history were investigated in 37Pb-63Sn solder in the as-cast condition at 27 degrees C and 100 degrees C. Under some short-hold-time conditions at both temperatures, the anelastic strain storage prevents the storage of creep damage. This sets a limit on how much a hold time can be shortened because at short enough hold times, the damage storage rate of the test becomes slower while the object of shortening the hold time is to accelerate the test. The creep damage stored in solders can also be measured, at least under closely controlled conditions, by the volume of voids found on grain-boundary surfaces. These grain-boundary surfaces can be exposed for examination by the liquid-metal embrittlement of solders (from 98Pb-2Sn to 37Pb-63Sn) with gallium. The relationship between void volume at failure for a number of different creep-fatigue conditions in different solders (including thermally cycled packages) is being examined. >