Thermal fatigue properties and grain boundary character distribution in Sn-xAg-o.5Cu (x=1, 1.2 and 3) lead free solder interconnects

Thermal fatigue properties of Sn-xAg-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, recrystalllsation 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.