Growth kinetics of the intermetallic phase in diffusion-soldered (Cu–5 at.%Ni)/Sn/(Cu–5 at.%Ni) interconnections

•Fast growth of (Cu1−xNix)6Sn5 phase in the Cu–5at%Ni/Sn/Cu–5at%Ni joint.•The (Cu1−xNix)6Sn5 phase occurs almost simultaneously in the whole reaction area.•The n parameter was found to be 0.27–0.15 in the temperature range 240–260 °C.•The n value indicates grain boundary diffusion during soldering.

A stereological analysis was carried out in order to obtain the kinetics parameters of the (Cu1−xNix)6Sn5 growth in the diffusion soldered (Cu–5 at.%Ni)/Sn/(Cu–5 at.%Ni) interconnections where previously anomalous fast growth of this phase was described. The n-parameter in the equation x = ktn was found to be 0.27–0.15 in the temperature range 240–260 °C, respectively. This is far away from the volume control process (n = 1 if total surface of forming phase is the reference). The TEM/EDX microanalysis made across the (Cu1−xNix)6Sn5/Sn – solder showed sudden change of Sn and Cu content typical for the grain boundary diffusion as the rate controlling mechanism.