The implementation of the Restriction of Hazardous Substances (RoHS) European Union (EU) Directive in 2005 resulted in greater use of pure tin as a surface finish for printed circuit boards and component terminations. The use of pure tin by electronics component fabricators is understandable as they are inexpensive, require simple plating systems to operate and have reasonable solderability characteristics. A drawback of pure tin surface finishes is the potential to form tin whiskers, which are a metallurgical phenomenon associated with tin rich/pure tin materials. Electronics used in high performance/harsh environment, such as avionics, typically have product life cycles that are measured in decades and therefore are much more susceptible to the potential long-term threat of tin whiskers. Including lead (Pb) is a well-accepted method for minimizing the risk of tin whiskers. The GEIA-STD-0005-2 “Standard for Mitigating the Effects of Tin Whiskers in Aerospace and High Performance Electronic Systems” established the definition of the term “Pb-free tin” as: pure tin or a tin alloy with <3% lead (Pb) content by weight. This investigation was conducted to assess the influence of 1% – 5% elemental Pb content in tin plating on tin whisker initiation and growth to determine if the acceptable minimum amount of Pb could be revised. Results indicate that the current definition of 3% Pb content should be maintained.
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Hillman et al. (2023) studied this question.
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