The sequential thermal-mechanical coupling analysis, which solves in turn the transient temperature field and subsequent thermomechanical deformations, was performed in this work to investigate thermal characteristics along with fatigue reliability of a thin-profile fine-pitch ball grid array chip-scale package subjected to power cycling. The numerical model was calibrated using steady-state and power cycling experiments. Following the calibrated numerical model, different power cycling durations on the thermal characteristics and fatigue reliability of the solder joints were examined. Numerical results indicate that, compared with thermal cycling, power cycling requires many more cycles to achieve a stabilized plasticity index between test cycles. The fatigue reliability would therefore be greatly underestimated if only such an index of the first several cycles is followed in the predictions.