Sn/Pb共晶はんだ接合部における熱疲労き裂発生寿命の相成長による評価

概要

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Thermal fatigue damage of solder joint is considered to be closely related to microstructural phase growth. In order to evaluate the relation between the microstructural change and thermal fatigue crack initiation, thermal cycle tests were carried out by using fabricated PCB on which various chip capacitors were mounted. Following results were obtained through the microstructural observation. The phase growth is characterized by phase growth parameter S which is defined as average phase size to the 4th power d^4 and proceeds such that S increases proportional to the number of thermal cycles N. Furthermore, there exists simple relation between average number of cycles to thermai fatigue crack initiation N_i and average increase in parameter S_c per one cycle 〓S_c, where S_c is component of S, represents strain induced phase growth and corresponds to total equivalent creep strain approximately. That is, power law relation 〓S_c=CN^<-β>_i is found out. The relation enables us to evaluate the thermal crack initiation of solder joint based on the observation of microstructural evolution.
2000-09-25