Mechanisms behind the spontaneous growth of Tin whiskers on the Ti2SnC ceramics

Abstract

The spontaneous growth of Tin whiskers has been a reliability issue in electronic assemblies for around 70 years, but the underlying physics is still ambiguous. Herein, Sn whiskers formed on the Ti2SnC, a layered ternary carbide ceramic MAX phase, were studied to trace the atomic motion in whisker growth process. Free Sn source was found to be necessary for the formation of Sn whiskers, however, the interface microstructure suggests that Sn atoms feeding whiskers are diffusing through the Ti2SnC lattice. According to the simulation results on the formation and migration energies of vacancies in Ti2SnC, a low diffusion barrier is expected for Sn atoms to diffuse along the basal planes. When Sn atoms diffuse out of the substrate, Sn whiskers bounded by low-energy planes form to minimize the total energy. In contrast, the whiskers maintain the striated morphology inherited from the whisker root in the environment containing oxygen, which is mainly attributed to the confinement of the oxide film on whisker surface. The findings will also shed new light on understanding the general whiskering problems found in other materials.