An Examination of the Tin Pest Phenomenon Over a 10-Year Period

Primarily in response to the implementation of the Restriction of Hazardous Substances (RoHS) European Directive, tin-rich solder alloys and pure tin component surface finishes have been introduced to printed circuit assembly processes. "Tin pest," a metallurgical phenomenon that can lead to mechanical and electrical degradation of solder, has been associated with tin-rich/pure tin materials. Historically, solder alloy element additions, such as lead or antimony, were used to prevent the formation of tin pest. However, the re-introduction of pure tin component surface finishes and high-percentage tin solder alloys, driven by the requirement to eliminate lead from electronics products, has allowed tin pest to re-emerge as a potential reliability threat. In this study, a pure tin printed circuit assembly test vehicle was created to assess the possible impact of the tin pest in an actual "real-world" process scenario. Some test vehicles were subjected to a static -40 degrees C temperature soak for a period of 10 years while other test vehicles were subjected to thermal shock. Subsequent to this testing, no indications of tin pest were observed in either set of test vehicles.