A STUDY OF INTERMETALLIC COMPOUND FORMATION IN A COPPER-TIN BIMETALLIC COUPLE

The formation of intermetallics in copper-tin bimetallic couples has been studied from room temperature to 183 °C by measuring the evolution of contact resistance and composite electrical resistance with time and temperature in order to assess the kinetic behavior of the system. X-ray diffractogram (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies have also been performed on the samples. As regards bulk diffusion, copper diffuses interstitially into tin rapidly at room temperature with the formation of η'-Cu6Sn5 intermetallic compound. Further diffusion through this phase as evaluated by composite electrical resistivity measurements is given by 0.40 eV, assuming a model of defect-assisted diffusion into the grains. The grain-boundary diffusion is found to occur with an activation energy of 0.78 eV as estimated from contact resistivity measurements. SEM confirms the presence of grain-boundary diffusion of tin in copper, whereas XRD and TEM measurements indicate the growth of η' intermetallics at room temperature which exists up to 90 °C when it transforms to the ε-Cu3Sn phase. The presence of tin whiskers on the tin surface has also been occasionally observed.