Nihon Superior’s Keith Sweatman to Present at SMTA International 2011

In recent times, the rising price of silver has prompted an increasing interest in the electronics industry in low- or no-Ag lead-free solders. One of the factors that is considered to have an effect on the reliability of solder joints – particularly at high strain rates such that occur in drop impact – is the intermetallic that forms between the solder and the substrate. The morphology and stability of this interfacial layer of intermetallic is, in turn, affected by the composition of the solder used to make the joint.

In this presentation, Mr. Sweatman will report on a study of the thickness morphology and growth of intermetallics formed on a copper substrate by eight alloys that are representative of the range of low- and no-Ag formulations currently used or proposed as Pb-free solders for electronic assembly. In addition to the basic constituents of Sn, Cu and Ag, these alloys included additions of Ni, Bi, Ce, Ge and P. Cross-sections were examined by SEM, and the thickness and growth at 130°, 140° and 150°C of both the Cu6Sn5 and Cu3Sn phases was monitored. While Ni was found to have a strong effect on all aspects of the interfacial intermetallics, any effects of Bi were more subtle.