Sn-whiskers: truths and myths

Whisker growth from the solid state has been documented in the public domain for more than 60 years. Unfortunately, a basic understanding upon which a quantitative model, one which would provide a means for predicting whisker growth and risk and ultimate prevention strategies, remains elusive. This paper is an attempt to critically review (hopefully with minimal bias) the state of Sn-whisker growth and mitigation. This is done by: (i) examining the existing experimental data and the limitations of collecting such data, (ii) analyzing the proposed driving forces, mechanism and models for whisker growth, and (iii) carefully evaluating the proposed mitigation strategies and how subsequent assembly processes and device applications may or may not impact these strategies. In each area, the validity of the model and mitigation strategy is examined by comparing it to existing experimental data. Areas where the experimental data is insufficient to adequately test the theory or predict risk are identified. In addition, the areas where experimental difficulties are found that could potentially negatively impact data collection and analysis are reviewed. The authors hope that at a minimum this review will provide a starting point for discussion between the users of the final products, the producers of the final products and the electronic components used in the final products on the topic of Sn-whisker growth, and its mitigation and risk management. In the best case scenario it could provide directions for the advancement of both experimental work and theoretical understanding of Sn-whisker growth and mitigation.