In this work, the effects of extreme thermal fluctuations on the reliability of solder joints were investigated. For this purpose, the solder joints in insulated-gate bipolar transistor (IGBT) devices were exposed to the conventional thermal cycling and the thermal shock cycling (TSC) tests. The finite element method (FEM) simulation results indicated that the accumulated creep energy in solder layer is much higher under the TSC process. Moreover, the stress triaxiality, as the indicator of damage initiation, is more concentrated in the TSC-exposed sample. It is believed that the higher heating and cooling rates along with the higher peak temperatures lead to the damage susceptibility of solder joints under TSC process. The experimental results confirm that the void formation and growth significantly increases in the TSC-exposed sample, which is consistent with the simulation outcomes. Moreover, the shear test reveals that the ultimate strength of sample under the thermal shocking severely decreases which is due to the void growth and the intensified elemental heterogeneity. © 2011-2012 IEEE.