Effects of minute amounts of Mg and Al additives on the wettability of Sn-8Zn-1Bi Pb-free cream solder

Abstract

In order to improve the wettability and storage stability of Sn-Zn system Pb-free cream solders, minute amounts of Mg, Al, Cu, Pb, and Sb were added to the Sn-8Zn-1Bi Pb-free alloy, and its properties were evaluated. The results obtained are: - Mg and Al additions were effective in improving wettability, - the addition of Al increased the amount of unmelted solder, and - the addition of Mg caused degradation of storage stability due to an increase in solder viscosity. Addition of the other elements did not improve the wettability. The combination of Mg and Al additions was found to improve wettability and storage stability, leading to stable wettability. Results of AES surface analyses showed that the solder with Mg and Al additive forms an Mg-Al-composite oxide film in the surface layer, which suppresses Zn oxidation observed in non-added solders. The suppression of Zn oxidation and the formation of a thin Mg-Al-composite film contribute to the wettability and storage stability improvements.