Investigating the mechanical properties, creep and crack pattern of Cu6Sn5 and (Cu,Ni)6Sn5 on diverse crystal planes

Cu6Sn5 is an important intermetallic compound (IMC) commonly formed during lead-free soldering. It is known that Cu6Sn5 exhibits significantly different thermo-mechanical deformation behaviour compared to both bulk solder alloys and their substrates. In high-density 3-D electrical packages individual solder joints may contain only a few grains of Cu6Sn5. The knowledge of the mechanical properties, creep and crack behaviour of Cu6Sn5 on different crystal planes is therefore essential to understanding the deformation of lead-free solder joints in service. In this research, the mechanical properties, creep and crack patterns on diverse crystal planes of hexagonal Cu6Sn5 and (Cu,Ni)6Sn5 were investigated using electron back scattered diffraction (EBSD), scanning electron microscopy (SEM) and nanoindentation. It was found that the mechanical properties, creep and crack patterns of hexagonal Cu6Sn5 were strongly related to the crystal orientation. The addition of Ni was found to reduce the anisotropy in hardness and the creep of Cu6Sn5 and had a significant effect on the crack patterns of Cu6Sn5.