Cyclic deformation of (60)Sn--(40)Pb solder joints during thermomechanical fatigue.

摘要

Thermomechanical fatigue and isothermal fatigue tests were performed on (sup 60)Sn--(sup 40)Pb solder joints under a variety of strain ranges and rates. In isothermal fatigue deformation throughout the entire cycle occurs with the same mechanism. The mechanism at low temperatures is a dislocation process and at high temperatures it is a diffusional flow. In thermomechanical fatigue the deformation mechanism changes in each cycle from dislocation processes to diffusional flow which results in higher peak stresses at the high and low temperature portion of the cycle. This indicates thermomechanical fatigue behavior can not be accurately predicted using isothermal fatigue. It was also found that decrease in strain rate slowed the heterogeneous coarsening process in thermomechanical fatigue. This is due to the fact that the dislocation substructure recovers more quickly than it work hardens which tends to minimize recrystallization and growth in the solder microstructure. 13 refs., 14 figs., 2 tabs.