Effect of grain boundary on failure behavior of SABI333 solder joints during creep

Sn_3.0Ag_3.0Bi_3.0In (SABI333) solder is easy to form solder joints with different crystal structures during solidification. Solder joints with different crystal structures can exhibit different failure behaviors during creep. Five kinds of SABI333 solder joints with different crystal structures were selected to study the effect of grain boundary on the failure behavior of creep. The scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were utilized to characterize the surface morphologies and crystal orientations of solder joints. When there were only low angle grain boundaries or twin boundaries in the solder joints, it was not easy to generate cracks inside the solder joints during creep but easy to generate cracks at the interfaces between the copper bars and solder matrices. However, when there were high angle grain boundaries greater than 70° in the solder joints, the cracks would propagate along such grain boundaries during creep. This phenomenon depends on the difference of grain boundary energy and the difference of deformation degrees of grains on both sides of grain boundaries during creep. The grain boundary energy of the high angle grain boundaries is relatively high and the deformation degrees of grains on both sides of high angle grain boundaries are quite different during creep. This research is conducive to further understand the creep failure behavior of SABI333 solder joints under the service environment.