Characterization of the ternary phase at the Sn/Ni–V joint

Ni–7 wt% V diffusion barrier is commonly used in flip chip technology, and Sn is the primary element of all commercial electronic solders. Different from the interfacial reactions in the Sn/Ni couples, a ternary T phase is formed in the Sn/Ni–7 wt% V couples reacted at temperatures lower than 350 °C. The T phase is a mixture of an amorphous phase and the Ni₃Sn₄ phase with grains about 50 nm in size. The amorphous phase is composed mainly of Sn and V atoms, and it is formed due to the fast diffusion of Sn and relative immobility of V. Activation energy of the T phase formation is 16.5 kJ/mol, which is approximately 50% of that of the Ni₃Sn₄ phase determined from the Sn/Ni interfacial reactions. The T phase is no longer formed and the reaction product is the Ni₃Sn₄ phase in the Sn/Ni–7 wt% V couples reacted at temperatures higher than 350 °C.