Effects of anisotropy of tin on grain orientation evolution in Pb-free solder joints under thermomechanical stress

Abstract

In this paper, the grain orientation evolution of Pb-free solder joints during thermomechanical fatigue (TMF) was characterized quantitatively using in-situ electron backscattered diffraction (EBSD) observation, which was an effective way to clarify the mechanism of recrystallization. The results showed that the grain orientation evolution of solder joints was significantly affected by the anisotropy of β-tin grains. Recrystallization behavior of a solder joint during TMF was very sensitive to the location of grain boundaries and orientations in the joints. Substantial stress could build up at grain boundaries in real joints in micro-electronic applications under thermomechanical stress, leading to premature failures. Also, slip systems were clarified playing an important role in recrystallization and could be used to predict the subgrain and recrystallized grain formation. While it was conventional cognitive, tricrystals were less likely to develop cracks during TMF and had longer lifetime than single-crystal joints. However, for the tricrystal joint with particularly undesirable orientations, it was clarified that (1 0 1)[1 0 $\bar{1}$ ] and (1 0 1)[$\bar{1}$ 0 1] silp systems were activated in tricrystals and premature failures occurred with the internal stress caused by anisotropic thermomechanical responses.