The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. In our prior work, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during elevated temperature aging were unexpectedly large and universally detrimental to reliability. Solder joints in electronic assemblies are typically subjected to thermal cycling, either in actual application or in accelerated life testing used for qualification. Mismatches in the thermal expansion coefficients of the assembly materials leads to the solder joints being subjected to cyclic (positive/negative) mechanical strains and stresses. This cyclic loading leads to thermomechanical fatigue damage that involves damage accumulation, crack initiation, crack propagation, and failure. While the effects of aging on solder constitutive behavior (stress-strain and creep) have been recently examined in some detail, there have been no prior studies on the effects of aging on solder failure and fatigue behavior.