Oxidation behavior of rare-earth-containing Pb-free solders

Abstract

We have previously shown that small additions of the rare-earth (RE) element La to Sn-Ag-Cu alloys significantly increases their ductility, without significant loss in the overall strength. However, due to the high reactivity of La with oxygen, oxidation of the La-containing phases can affect the mechanical performance of the solder. In this work, we have investigated the effect of the addition of 2 wt.% Ce, La and Y on the oxidation behavior of Sn-3.9Ag-0.7Cu. Oxidation kinetics were established by heating samples in ambient air to 60°C, 95°C or 130°C for up to 250 h. Microstructural characterization of the samples, before and after oxidation, was conducted in order to determine the influence of RE-containing phases on the oxidation kinetics. The oxidation mechanism, including the phenomenon of Sn whiskering during oxidation, is also discussed. © 2008 TMS.