In this work, fatigue damage caused to solder joints in printed wiring assemblies due to the superposition of harmonic vibration and temperature is studied along with different damage superposition approaches. In this work, a non-linear interactive damage superposition method is used, with temperature-dependent vibration damage coefficients that are interpolated from isothermal vibration experiments at selected temperatures. The temperature range -40 °C to 125 °C was segmented into multiple sub-segments for this interpolation. By applying these measures, a new procedure for an improved incremental damage superposition approach (IDSA) was developed in this work. This new procedure was then used to superpose the vibration and temperature cycling loads to forecast the fatigue life of SAC105 solder joints for leadless chip resistors under simultaneous vibration and temperature cycling loads. Potential failure sites of the solder joint have been successfully investigated by utilizing this new procedure. Using the developed model, accelerated testing profiles are designed such that the vibration fatigue and temperature cycling fatigue damage are comparable and cause failure in approximately 250 temperature cycles.