Nanoindentation of rare earth-Sn intermetallics in Pb-free solders

Incorporating rare earth (RE) elements into Sn-rich solder often results in the formation of RE-Sn intermetallics, which affect the deformation behavior of the solder. Little information is available on these constituent phases, and even less on their mechanical properties. In this paper, we report on Young's modulus and hardness of LaSn₃, CeSn₃ and YSn₃ intermetallic compounds formed in a Sn-Ag-Cu-2RE alloy, determined using nanoindentation. Nanoindentation on pure Sn was also performed for comparison. The Continuous Stiffness Method (CSM) was used during indentation to obtain the instantaneous Young's modulus as a function of depth. Scanning electron microscopy (SEM) was used to analyze the indentations after testing. The measured values of Young's modulus for LaSn₃, CeSn₃ and YSn₃ were 64 ± 3, 69 ± 3 and 98 ± 4 GPa, respectively. Values of hardness for LaSn₃, CeSn₃ and YSn₃ were 1.04 ± 0.16, 1.03 ± 0.03 and 3.47 ± 0.27, respectively. Comparison of these values with limited data in the literature was conducted and is discussed.