Effect of Ni addition on the wettability and microstructure of Sn2.5Ag0.7Cu0.1RE solder alloy

In order to study the effect of Ni addition on the wettability and microstructure of Sn2.5Ag0.7CuO.1RE solder alloy, samples of 7compositions were prepared with Ni content ranging from 0 to 0.5% and contents of other alloying elements (Ag, Cu and RE) being kept the same. Results obtained have shown that the wettability of Sn2.5Ag0.7Cu0.1RE can be largely improved by adding 0.1%Ni in the alloy, and Sn2.5Ag0.7Cu0.1RE0.1Ni exhibits a better wettability than the commercially used Sn3.8Ag0.7Cu alloy. The wetting angle measured on Cu substrate is clearly larger than that measured on Cu wire, which is considering the static and dynamic natures of the two testing procedures. In addition, Ni has been found to be able to reduce the volume fraction of primary Sn, increase the ratio of eutectic structure and form a much finer eutectic microstructure from a three-dimensional view of the microstructure after deep-etching. Moreover, Ni shows a clear impact on the interface between Cu substrate and solder alloy. Compared to the solder alloy without Ni, adding 0.1% Ni leads to a relative flatter and thinner interface. For the solder alloy with 0.5% Ni, micro-cracks are observed at the interface. (C) 2017 Elsevier Ltd. All rights reserved.