c2007 Springer - The Delco process is a major flip chip under-bump metallurgy process and its contact is soldered with the Ni-7wt.%V substrate; there are, however, only a few studies on the interfacial reactions between solders and Ni-V alloys. This study examines the interfacial reactions of the Sn-0.7wt.%Cu alloy with the Ni-7wt.%V, Ni-5wt.%V, and Ni-3wt.%V substrates at 250 degrees C. It is found that the interfacial reactions between Sn-0.7wt.%Cu and Ni-V alloys are different from those between Sn-0.7wt.%Cu and pure Ni. In addition to the formation of the Cu6Sn5 phase, a new Sn-rich phase, denoted the Q phase, is found in the Ni-V substrate couples. Nucleation of the Ni3Sn4 phase is at a much earlier stage and the rates of consumption of Ni are much higher in Ni-V substrate couples than in Ni substrate couples. Knowledge of these different reactions is important for proper assessment of the flip chip products.