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.