Nanomechanical characterization of Sn-Ag-Cu/Cu joints-Part 1: Young's modulus, hardness and deformation mechanisms as a function of temperature

Nanoindentation has been used at room and elevated temperature to measure the spatial distribution of mechanical properties within Pb-free solder ball joints. The hardness, Young's modulus and creep behaviour of the phases formed in a Sn-Ag-Cu/Cu solder joint have been characterized at temperatures from 25 to 175 °C. The hardness and Young's modulus of Cu6Sn5 and Cu3Sn had a weak dependence on temperature, while the hardness and modulus of primary β-Sn, eutectic regions and electroplated Cu were sensitive to temperature. Nanoindentation was able to detect both mechanical anisotropy in Cu6Sn5 and the sluggish η′ → η phase transformation at 150-175 °C. In a second part of this study, Pb-free solder creep behaviour has been investigated by nanoindentation and compared with Pb-free creep behaviour models from the literature. A two-dimensional finite-element analysis of solder nanoindentation creep has been used to compare creep measurement methods, and the insights from this analysis can be then implemented in commercial finite-element codes for creep behaviour prediction at the microscale in microelectronic solder joints.