Activation energies of intermetallic growth of Sn-Ag eutectic solder on copper substrates
Intermetallic phases formed along a Sn-Ag eutectic solder/Cu interface during solid-state aging have been characterized and the activation energies of Cu3Sn and Cu6Sn5 growth have been calculated. Diffusion couples consisting of Cu/ 96.5Sn-3.5Ag/Cu were aged at 110 to 208°C for 0 to 32 days. After aging, the Cu/ solder interfaces were examined using scanning electron microscopy and energy dispersive x-ray spectroscopy. The growth rate constants for each intermetallic layer were calculated assuming a simple parabolic diffusion-controlled growth model. The activation energy for Cu3Sn growth is 0.73 eV/atom and the activa-tion energy for Cu6Sn5 growth is 1.11 eV/atom.