Evaluation of creep properties for Sn–Ag–Cu micro solder joint by multi-temperature stress relaxation test

The creep properties of a Sn–Ag–Cu micro solder joint with a solder ball with 500 μm were investigated by a multi-temperature stress relaxation test performed using a specimen at three temperatures (298, 348, and 398 K). The stress exponents in Norton’s law were 8 at 398 K, 8.8 at 348 K, and 9 at 298 K, and the activation energies were found to be 39 kJ/mol in the high-stress region and 80 kJ/mol in the low-stress region. The stress exponent in Norton’s law for a micro solder joint was lower than that for a large-scale specimen, which resulted in more coarsened intermetallics in the microstructure than in the large-scale specimen. The activation energies for the micro solder joint were almost equal to those for the large-scale specimen in the high- and low-stress regions. These results reflect the microstructure of the micro solder joint, and the creep constitutive equation for the Sn–Ag–Cu joint could be derived by the multi-temperature stress relaxation test proposed in this study.