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

摘要

Tin whisker growth poses a continued reliability concern for Pb-free electronic systems. The fundamentalrnmechanisms behind the spontaneous growth of these metallic filaments are not well understood and a greaterrnunderstanding is required to develop mitigation strategies. Published data shows that variations of plating processrnparameters can produce electroplated films with clearly different crystallographic textures, and for electroplated Snrnand Sn-alloy films changes in crystallographic texture may lead to different rates of whisker growth.rnIn this work, the relationship between materials, processing parameters, crystallographic texture, andrnwhisker propensity is examined. Four electrolyte compositions were used to electroplate Sn and Sn alloy films withrndifferent compositions and microstructures on phosphor bronze and pure Cu substrates. Pole figures and inversernpole figures created using x-ray diffraction were used to determine the quantitative crystallographic texture of filmsrnas a function of processing parameters such as current density. The tendency for these films to form whiskers orrnother surface defects was categorized by surface defect density and type. The relationship between film texture, filmrncomposition, and whisker formation is presented. These data suggest that while the optimal crystallographic texturernis not yet known, it may be possible to use x-ray texture data as a guideline for controlling and monitoring platingrnprocesses to reduce the tendency of films to form whiskers.