微小SACはんだ試験片の疲労寿命に初晶Snの分布形態が及ぼす影響

抄録

Miniature specimens of Sn-3.0Ag-0.5Cu (SAC) solder show large variation in tensile strength even though they are under the same loading conditions. We have found that this phenomenon can be correlated to the difference in the distribution morphology of primary Tin crystals in the specimens. Such a different could affect the fatigue strength of the miniature specimen. Then, in this study, we carried out fatigue tests with cyclic tension-compression loading using the miniature SAC solder specimen to investigate the relationship between the fatigue life and the distribution morphology of primary Tin crystals. The results show that the stress amplitudes of the hysteresis loops under the same loading condition show large variations and the fatigue life becomes shorter with the increase in the stress amplitude. The specimens having a high-stress amplitude in their hysteresis loops contain a high proportion of the primary Tin crystals which grow in directions vertical to or parallel to the loading direction. Namely, the fatigue strength of the specimen containing a large number of such primary Tin crystals tends to become lower.