Calorimetric study of the energetics and kinetics of interdiffusion in Cu/Cu₆Sn₅ thin-film diffusion couples

Differential scanning calorimetry was used to characterize the energetics and kinetics of interdiffusion in solder/metal diffusion couples. The heat of formation of Cu₃Sn from Cu₆Sn₅ and Cu thin films was found to be ΔH_r=-4.3±0.3kJ/mol, similar to the results of previous measurements on bulk samples. We have seen that the nucleation of Cu₃Sn begins at temperatures near 360 K, but that the nucleation and initial growth of Cu₃Sn is not a well-defined Arrhenius process in these diffusion couples. Later portions of our differential scanning calorimetry scans were identified with diffusion-limited growth of Cu₃Sn. From these calorimetry data we have estimated the averaged interdiffusion coefficient, D̃(cm²/s)=D₀ exp (-E/k_bT), where k_b is Boltzmann's constant and D ₀=3.2×10^-2cm²/s and E=0.87 eV/atom.