Tin oxide coverage on tin whisker surfaces, measurements and implications for electronic circuits

Abstract

Purpose – This paper aims to evaluate the morphology and thickness of oxides that form on the surfaces of tin whiskers. The problems related to the growth of tin whiskers are stated, and the relevance of oxide layers adhering to whiskers is discussed. Design/methodology/approach – Modern laboratory methods including focused ion beam sectioning, energy dispersive spectroscopy and X-ray photoelectron spectroscopy have been used to characterise the composition of oxides present on the surfaces of 48-year-old whiskers. These very old whiskers had nucleated and grown on electronic equipment stored at ambient temperatures. They were compared to the oxide layers on newly grown 2-week-old whiskers. Findings – A dual oxide film, consisting of stannous and stannic oxides, was found present on both the old and the new whiskers. Measurements of oxide thickness were established for both generations of whiskers and these were noted to be similar to those films present on pure, cleaned bulk tin. Research limitations/implications – Only very new and very old whiskers, and their oxide films, were the focus of this investigation. However, sufficient data were gained to predict the effect both kinds of oxide films would have during whisker bridging between conductors and the risk of short circuits. Thick oxide films (order of 30 nm) may have a greater resistance to shorting, but they will be more difficult to remove during solder dipping (with respect to whisker mitigation). Practical implications – A knowledge of the oxide thickness on growing/gyrating tin whiskers will provide the electronics industry with data useful for establishing the risk of short circuits. It will also be useful during the forensic work associated with component and assembly failure analysis. Originality/value – The data resulting from this study are unique. They are of value to others who may require knowledge of the morphology, composition and thickness of oxides present on tin whiskers of different vintage.