Abstract
In microstructures such as whiskers, their surface free energy is supposed to determine the criterion on whether the whisker growth can take place ; then a critical dimension for the whisker growth should exist, depending on the degree of the excessive energy that drives the whisker growth. In this respect, the excessive energy included in matt Sn deposits plated on Cu substrates has been estimated to be approximately 1×10− 22 J atom−1 in terms of chemical potential.
Furthermore the contribution of grain-boundary free energy and strain energy to the excessive energy has been estimated. It has been shown that the grain-boundary free energy seems not to contribute to the excessive energy. On the other hand, it has been found that the strain energy sufficient for the whisker growth requires far more stress (ca. +400 or −400 MPa) than we usually observe (ca. −10 MPa). From these, it has been suggested that such a high stress can be attributed to the extremely large distortion of crystal lattice in an atomic level instead of macro-strains. The source of the distortion is supposed to be produced by the excessive Sn atoms generated by imbalanced diffusion between Sn and Cu.
