抄録
Thermal fatigue damage of solder joint is considered to be closely associated with microstructural phase growth. In order to relate the phase growth process to the damage quantitatively, thermal cyclic tests were carried out by using fabricated PCBs. Applying the phase growth parameter S_c which represents strain induced phase growth, to the experimental data, a new practical method is proposed for the evaluation of thermal fatigue crack initiation. The method is based on the relation ΔS_c=CN^<-β>_i, where N_i is average number of cycles to thermal fatigue crack initiation, ΔS_c is corresponding average increase in S_c per one cycle, and C and β are constants. It is very useful for the reliability of PCBs that the relation enables us to evaluate N_i by ΔS_c which is casily obtained by microstructural observation of solder joint.
