Interfacial reactions in the Sn-(Ag)/(Ni,V) couples and phase equilibria of the Sn-Ni-V system at the Sn-Rich corner

Ni-7wt.%V is commonly used as the barrier layer material in the under-bump metallurgy in the microelectronic industry. Although interfacial reactions between various solders with the nickel substrate have been investigated intensively, the effects of vanadium addition upon the solder/(Ni,V) interfacial reactions have not been studied. Sn/(Ni,V) and Sn-Ag/(Ni,V) interfacial reactions at 250°C were investigated in this study using the reaction couple technique. The vanadium contents of the (Ni,V) substrates examined in this study are 3 wt.%, 5 wt.%, 7 wt.%, and 12 wt.% and the reaction time is 12 h. The results indicate that when the vanadium contents in the (Ni,V) substrate are 5 wt.% and higher, the Sn/(Ni,V) and Sn-Ag/(Ni,V) interfacial reactions are different from those in the solder/Ni couples. Besides the Ni₃Sn₄ phase as commonly formed in the reaction with Ni substrate, a new ternary T phase has been found, and the reaction path is L/Ni₃Sn₄/T/(Ni,V). A 250°C Sn-Ni-V isothermal section is proposed based on the three constituent binary systems and limited experimental results obtained in this study. The reaction path is illustrated with the proposed Sn-Ni-V isothermal section. No stable ternary Sn-Ni-V phase is found from the phase equilibria study, and the new T phase is likely a metastable phase.