Using nanoindentation to investigate the temperature cycling of Sn-37Pb solders

Abstract

Using nanoindentation and energy dispersive X-ray spectrometry (EDS), we have conducted an investigation into corner failures to elucidate not only the nanomechanical properties of Sn-37Pb solder balls but also the effects of temperature cycling tests (TCTs). We found that the hardness of Sn-37Pb solder balls was greater in central locations [1.18 +/- 0.05 GPa for room-temperature (RT) sample; 1.3 +/- 0.05 GPa for TCT sample], but had standard values in corner locations (>0.2 +/- 0.02 GPa). The modulus increased after the TCTs. Nevertheless, the mechanical properties were closely related to the average area of the alpha-Pb phase. The average area of the Pb-rich region was more stable after the TCTs than that of the RT sample, due to the enhanced mechanical properties of the Sn-37Pb solder, suggesting good reliability. From an analysis of average areas in the RT sample, it appears that the Pb-rich solid solution that formed led to weak Sn-Pb bonds near the corner locations. Electron back scattered diffraction measurements revealed that grains with grain boundaries formed as a result of accelerated TCT cycling. We conclude that Sn-Pb recrystallization was initiated and propagated after the TCTs, followed by propagation to the interfacial region. (C) 2017 Published by Elsevier Ltd.