ABSTRACT
Solders are high-temperature materials as their homologous temperatures at room temperature (TR/TM, where TR and TM are the room and melting temperatures, respectively, in Kelvin), are above 0.5. For example, the homologous temperature of Sn at room temperature is about 0.6. Tin-silver-, tin-zinc-, tin-indium-, and tin-bismuth-based solders have even lower homologous temperatures. Therefore, the mechanical properties at ambient and elevated temperatures are highly dependent on strain rate and dwell times. This impacts the design of solder interconnects in electronic devices for high reliability. The models for reliability prediction are based on the hightemperature behavior of solder. Thermally activated plastic flow (e.g., creep) dominates the stress-strain curve except at very low strains and very rapid strain rates. Elastic strains and plastic strains that are not thermally activated are very small compared to thermally activated plastic flow. Thermally activated plastic flow dominates both isothermal and thermomechanical fatigue (TMF).
