Crystallographic Texture and Whisker Growth in Electroplated Sn and Sn-Alloy Films

Tin whisker growth poses a continued reliability concern for Pb-free electronic systems. The fundamental mechanisms behind the spontaneous growth of these metallic filaments are not well understood and a greater understanding is required to develop mitigation strategies. Published data shows that variations of plating process parameters can produce electroplated films with clearly different crystallographic textures, and for electroplated Sn

and Sn-alloy films changes in crystallographic texture may lead to different rates of whisker growth.

In this work, the relationship between materials, processing parameters, crystallographic texture, and whisker propensity is examined. Four electrolyte compositions were used to electroplate Sn and Sn alloy films with different compositions and microstructures on phosphor bronze and pure Cu substrates. Pole figures and inverse pole figures created using x-ray diffraction were used to determine the quantitative crystallographic texture of films as a function of processing parameters such as current density. The tendency for these films to form whiskers or other surface defects was categorized by surface defect density and type. The relationship between film texture, film composition, and whisker formation is presented. These data suggest that while the optimal crystallographic texture is not yet known, it may be possible to use x-ray texture data as a guideline for controlling and monitoring plating

processes to reduce the tendency of films to form whiskers.