The evolution of plastic deformation of Sn3.5Ag-based lead-free solders

Abstract

Small amount of additives, namely, 0.2Co + 0.1Ni, were doped into the Sn3.5Ag solder matrix which has been considered as one of the most promising candidates to replace the conventional Sn-Pb solders. The mechanical properties of the lead-free solders were assessed from the force-penetration curves measured by nanoindentation testing. These mechanical properties were then used as the input parameters in the simulation based on the Dao's method. In the meantime, the rate sensitivity value in the constitutive model, say sigma = Amiddotepsivdotm for the lead-free solders were also determined by the variable tensile speed methodology. The creep deformation of both solders is the function of the loading rate. The creep deformation behavior during nanoindentation testing at dwell time for Sn3.5Ag0.2Co0.1Ni solder seemed more severe than that for Sn3.5Ag solder. The pile-up phenomenon was more remarkable for Sn3.5Ag0.2Co0.1Ni solder. The simulated plastic deformation under indentation showed that the greatest plastic deformation was beneath the indentation tips for both of the solders. And the plastic deformation zone for Sn3.5Ag was slightly greater