Macro and micro-texture study for understanding whisker growth in Sn coatings

Abstract

The current work is aimed at analyzing the effects of crystallographic texture, both macro and microtexture, on whisker growth. The macro-texture of the Sn coatings deposited on brass substrate was systematically studied by varying the process parameters used for electro-deposition. The combination of process parameters, such as deposition temperature and current density, and the resulting macro-texture most prone to whisker growth were identified by monitoring the whisker growth in Sn coatings. The electron back-scatter diffraction (EBSD) technique was then used to identify the grains where whiskers actually grow. Both macro- and micro-texture of Sn coatings revealed that coatings with pre-dominant low Miller index grain orientations, such as (100), were highly susceptible for whisker growth. Whisker propensity decreased as the texture transitioned from low to high Miller index grain orientation. The microtexture mapping of the Sn coatings using EBSD technique confirmed that whisker grows from low Miller index grains with (100) or near (100) orientations, surrounded by grains of similar orientation followed by grains with high index plane grains, such as (211), (210) or (321). This particular double ring configuration along with local stress field can be used to predict the locations for whisker growth.