Anisotropic mechanical properties of Cu6Sn5 and (Cu,Ni)6Sn5

The mechanical reliability of solder joints is influenced by a layer of Cu6Sn5 intermetallics (IMC) present at the interface of tin-based solders/Cu substrates. We have discovered that the mechanical properties of hexagonal Cu6Sn5 are strongly related to the crystal orientation, using Electron Back Scattered Diffraction (EBSD) and nanoindentation on unidirectionally solidified Sn–4 wt% Cu with/without 0.05 wt% Ni. This fundamental discovery on the anisotropic mechanical properties of Cu6Sn5 may find practical applications in designing soldering processes to obtain preferred IMC orientations.

► The relationship between crystal orientation and mechanical properties of Cu6Sn5 and (Cu,Ni)6Sn5 was investigated.
► A strong anisotropy in elastic modulus and hardness of Cu6Sn5 was found.
► Addition of Ni in Cu6Sn5 increased both elastic modulus and hardness on all crystal planes.
► Minimal anisotropy in the hardness of the Ni containing Cu6Sn5 in comparison to the Ni-free Cu6Sn5 suggested that different deformation mechanism prevailed.