Oxidation properties of Sn-Cu-Ni solders with minor alloying additions

Considering that solder surface may lose its brightness due to oxidation during the assembly and operation of electronic device, this study investigated the surface properties of Sn-Cu-Ni solders using UV-visible and X-ray photoelectron spectroscopies. The degree of discoloring could be evaluated by the reflectance of the sample surface in the visible light range. Two distinct absorption peaks respectively located at about 400 nm and between 250 and 300 nm were identified, which could be considered stemming from the formation of SnO and SnO₂ respectively. A minor addition of phosphorus can significantly reduce the discoloring of solders under both solid and semi-solid states. The formation of P₂O₅ and thus the suppression of SnO were also verified.