High-temperature oxidation behavior of cerium on the surface of Sn-Zn lead-free solders

The distribution and existing form of Ce on the surface of Sn-9Zn-0.15Ce and Sn-9Zn-0.002Al-0.2Ga-0.25Ag-0.15Ce solder are investigated by atomic emission spectrometry and X-ray photoelectron spectroscopy.Results indicate that Ce enriches on the surface of the Sn-9Zn-0.15Ce solder in the range of 0 to 40 nm.The concentration of Ce in the enriched zone is about 30 at.%,which is 250 times of that in the bulk solder,and the enriched Ce on the surface is mostly oxidized as CeO₂ and Ce₂O₃.With the multi-addition of Ga and Al in the Sn-9Zn-0.002Al-0.2Ga-0.25Ag-0.15Ce solder,Ga enriches in range of 0 to 6 nm on the surface,while Al enriches in range of 2 to 20 nm in oxidized form.The Ce-enriched layer is in the range of 2 to 60 nm on the surface covered by the Ga and Al enriched layers,and the oxidation of Ce is depressed significantly.