Abstract
Prior strain rate history during stress relaxation (SR) behavior is one of the fundamental issues adapting the design of solder joints. In this paper, the SR tests were performed on Sn–1.7Ag–0.7Cu (SAC177) solder with Te and Co addition at the elastic region. The SR of SAC177 solders occurred at high prior deformation history could induce unexpected relaxation resistance depending on the qualified proportions of Te and Co microalloying. The global strain rate \(\varepsilon^{\cdot}_{\text{p}}\) of three solders was found to follow the power-law with stress-sensitivity n of 5.8–7.6. The activation energies Q of 58.15–78.23 kJ mol−1 were achieved from SR results at initial stress σo of 10 MPa. An evolved SR model based on logarithmic single barrier model is intended in the present study to predict and confirms the SR mechanism. Microstructure assessment shows that the SR behaviors are controlled by pipe diffusion assisted with dislocation climb. According to the proposed relaxation model, the extent of SR and SR rate of SAC177 solder were found to be decreased markedly with increasing prior strain rate, Q value and Te/Co addition. Moreover, significant enrichment in the elastic compliance of SAC177 solders was noticed after Te/Co addition due to increasing the ductility, which has good predictions for electronics applications.
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