Abstract
In the present paper, in order to evaluate the creep properties of Co/Ni-bearing SAC305 lead-free alloys, the strain rate change tensile (SRCT) test was conducted. Two parameters, m0 and k, obtained from the SRCT test could be applied to estimate the thermal fatigue resistance and the creep properties for lead-free solder alloys. The m0 value implied the material’s creep resistance, and the k value revealed the stability of the creep resistance during the whole tensile test process. The Co/Ni-bearing SAC305 solder alloys showed much lower m0 and k values than the conventional Sn37Pb solders which indicated that the Co/Ni-bearing SAC305 solder alloys possessed of excellent thermal fatigue resistance and higher creep resistance. For the lead free solder alloys, high temperature aging led to microstructural coarsening. After aging, the m0 value increased meanwhile the k value decreased for the Co/Ni-bearing SAC305 solders. Furthermore, the two parameters showed a converse change tendency between the conventional Sn37Pb and Co/Ni-bearing SAC305 solders after high temperature aging, which implied that they have different creep mechanism. It can be deduced that, for the conventional Sn37Pb solder, the grain boundary slide is the dominant creep mechanism, whereas the Co/Ni-bearing SAC305 solders showed a dislocation glide/climb creep mode.
