Abstract
Thermal fatigue properties of Sn–x Ag–0˙5Cu (x = 1, 1˙2 and 3, mass%) lead free solder interconnects were discussed from the viewpoints of both morphology and grain boundary character distribution. 3Ag showed the longer thermal fatigue life than 1Ag and 1˙2Ag. Both cracks, which were initiated by thermal strain, and grain boundary damage due to grain boundary sliding degraded the thermal fatigue lives. From a microstructural observation using orientation imaging microscopy, recrystallisation of tin grains was observed, and 3Ag suppressed coarsening of tin grains after further thermal fatigue as compared with 1Ag and 1˙2Ag. Moreover, 3Ag showed a larger amount of coincidence site lattice boundaries than 1Ag and 1˙2Ag. It is suggested that in 3Ag not only smaller tin grains but also larger amount of coincidence site lattice boundaries suppressed crack propagation and grain boundary sliding.
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