Mechanical properties evolution of Sn-3.5Ag based lead-free solders by nanoindentation

The mechanical properties of some promising Sn-3.5Ag based lead-free solders, such as hardness and Young's modulus, were explored by instrumented nano-indentation. It was found that the hardness was dependent on the loading rate significantly, while the Young's modulus value was almost independent on the loading rate. Higher loading rate caused larger creep deformation at dwell time, as well as larger hardness value. For the casting alloys, the additives, namely Ni and Co into Sn-3.5Ag solder, could lead to an increase of Young's modulus, however, this difference tended to be unremarkable after reflow process. Based on the concept of “work of indentation” at the dwell time portion, the rate sensitivity n of the solders before and after reflow process was also determined. The results revealed that the additives Ni and Co in Sn-3.5Ag solder resulted in the slight increase of rate sensitivity value n. After reflow process, for both of these solders alloys, the rate sensitivity n was elevated.