Diffusion Creep of Realistic SnAgCu Solder Joints at Times and Stresses of Relevance to Thermal Fatigue

A minimum requirement of constitutive relations for the modeling of the behavior of realistic SnAgCu is that they predict creep rates under constant stresses in the range of interest. Preliminary results have, however, shown common constitutive relations to not do so even at the relatively high stresses of relevance to life in accelerated thermal cycling or vibration. Focusing on times of relevance to thermal fatigue, as opposed to the much longer times required to reach steady state, this is shown to be a result of the inelastic deformation of realistic Sn3.0Ag0.5Cu solder joints being dominated by diffusion, rather than by the motion of dislocations as commonly assumed.