Microstructure and creep behavior of antimony containing high silver solder alloy Sn-3.9Ag-0.6Cu-3.0Sb

Antimony containing Sn-3.9Ag-0.6Cu-3.0Sb (SAC 396 + ) is a high reliability solder alloy but its microstructure and creep behavior is not sufficiently investigated yet. In this paper the correlation between microstructure, using SEM, TEM, and XRD, and compression creep properties was investigated. Furthermore, a comparison in creep performance between SAC 396 + and Sn-3.8Ag-0.7Cu (SAC 387) was drawn, and the long-term microstructure evolution until 1500 h at 125 °C was compared. For SAC 396+, microstructure investigations of pre-aged (24 h at 125 °C) bulk samples revealed that Sb is mainly dissolved in β-Sn (Sb 2 Sn 23 , tetragonal, I41/amd), whereas some fine SbSn precipitates (Sb 0.49 Sn 0.51 , rhombohedral, R-3 m) were found in β-Sn. Compression creep tests were performed at temperatures between 35 °C and 125 °C with stresses between 7.5 MPa and 32.5 MPa. Stress exponents were in the range of 7.4 to 7.5 at 100 °C or below, and 4.8 at 125 °C and activation energies were in the range between 84.7 kJ/mol and 99.6 kJ/mol, indicating dislocation creep, controlled by pipe diffusion or by lattice diffusion. Overall, Sb hardened SAC 396 + showed better creep performance at all tested temperatures, as well as after isothermal ageing at 125 °C for 24 h, 500 h, or 1500 h.