An investigation was made of the effect of electromigration upon interfacial reactions between Sn–Cu and Sn–Ag alloys on a Ni substrate. Sandwich-type reaction couples, consisting of Sn–0.7wt%Cu/Ni/Sn–0.7wt%Cu and Sn–3.5wt%Ag/Ni/Sn–3.5wt%Ag, were reacted at 160, 180 or 200C for various lengths of time; with and without an electric current. In the absence of a current, only one intermetallic compound (Sn4Ni3) - with some 7at%Cu solubility - was found at both interfaces of the Sn–0.7wt%Cu/Ni couples. Upon passing a current density of 500A/cm2, Cu6Sn5 formed at the alloy/Ni interface; next to the Sn4Ni3. As in the absence of a current, only Sn4Ni3 was found at the Ni/alloy interface. The directions of movement of electrons, Sn and Cu atoms were the same at the alloy/Ni interface, and the growth rates of the intermetallic layers were increased. At the Ni/alloy interface, the electrons flowed in the opposite direction to the Sn and Cu, and the growth rates of the intermetallic layers were slowed. Only Sn4Ni3 formed by Sn–3.5wt%Ag/Ni interfacial reaction; with and without a current. As in case of the Sn–0.7wt%Cu/Ni system, the movement of electrons increased or slowed the growth of intermetallic layers at the alloy/Ni and Ni/alloy interfaces, respectively. Calculations showed that the apparent effective charge decreased in magnitude with increasing temperature. This indicated that the electromigration effect became insignificant at higher temperatures.

Electromigration Effect upon the Sn–0.7wt%Cu/Ni and Sn–3.5wt%Ag/Ni Interfacial Reactions. C.Chen, S.Chen: Journal of Applied Physics, 2001, 90[3], 1208-14