It is important to evaluate the thermal fatigue crack initiation lifetime of Sn-3.0Ag-0.5Cu solder joints in order to improve the reliability of electronic devices. In this paper, in order to clear the phase growth process in the solder joint which has a strain concentration in the end of the joint, the detail finite element analysis of the mini-lap joint type specimen was performed and the strain around the corner of the joint was examined. Consequently, it is clear that the crack initiation life time can be evaluated by using the increment of phase growth parameter at the strain concentration occurring zone as same as PCB specimen.