The interdiffusion coefficients and activation energies of Cu–Sn and Ni–Sn intermetallic formations were measured on flip-chip bumps with 40μm bond pad diameter. Also the morphology of the metallurgical reactions was described. Furthermore, the ideal case of a binary diffusion system was seldom present in real-life. In practice, the presence of additional alloying elements has an impact on the intermetallic stoichiometry and even on intermetallic growth and morphology. It was shown that small quantities of Cu in a Ni–Sn system could have a beneficial effect on the Ni consumption but larger quantities resulted in extreme scalloping of the intermetallic interface.

Solid State Diffusion in Cu–Sn and Ni–Sn Diffusion Couples with Flip-Chip Scale Dimensions. R.Labie, W.Ruythooren, J.Van Humbeeck: Intermetallics, 2007, 15[3], 396-403