Individual Phase Mechanical Properties at Different Temperatures of Sn–Ag–Cu Lead-Free Solders Incorporating Special Pileup Effects Using Nanoindentation

Abstract

Sn–Ag–Cu (SAC) alloys are considered as good replacements of Sn–Pb alloys which are banned due to the toxic nature of Pb. But, SAC alloys have a coarse microstructure that consists of β-Sn rich and eutectic phases. Nanoindentation is a useful technique to evaluate the mechanical properties at very small length scale. In this work, continuous stiffness measurement (CSM) nanoindentation setup (CSM Instruments SA, Peseux, Switzerland) is used to determine the individual phase mechanical properties like Young's modulus and hardness at high temperatures. It is demonstrated that these properties are a function of temperature for both β-Sn rich and eutectic phases. Loadings starting from 500 μN up to 5000 μN are used with 500 μN steps and average values are presented for Young's modulus and hardness. The loading rates applied are twice that of the loadings. High temperatures result in a higher creep deformation and therefore, to avoid it, different dwell times are used at peak loads. The special pileup effect, which is more significant at elevated temperatures, is determined and incorporated into the results. A better agreement is found with the previous studies.