Feature: Avionics
High Density PCB
The cause and effect of tin whiskers in electronic systems deployed in space
By Daniel Theis, Technical Manager, Rhopoint Components T
he removal of lead from electronic components has been an ongoing process since the late 1990s, driven by environmental and health concerns. Subsequently
regulations formalising the process were introduced, such as the Restriction of Hazardous Substances Directive (RoHS), which restricted the use of six hazardous substances, including lead, in electrical and electronic equipment sold in the EU, and the WEEE Directive which covers waste management and recycling of electronic devices.
Te electronics industry has largely moved
to using lead-free solder alloys, such as tin-silver-copper (SAC), bismuth-tin or tin- copper and coating materials such as nickel- gold or palladium. Manufacturing processes have had to be changed to accommodate lead-free materials as lead-free solders have higher melting points. Lead-free soldering is now commonplace
but does introduce some reliability issues, such as increased brittleness and risk of tin whiskers. Tin whiskers are hair-like metallic filaments that grow from tin-rich surfaces, creating risks including short-circuits,
12 April 2025
www.electronicsworld.co.uk
leading to equipment failure. While not seen as a particular problem for earth-bound commercial and industrial applications, where they can grow at rates of 0.03–9 mm per year depending on stress and environmental conditions, in space studies suggest whiskers may grow faster in a vacuum under the influence of radiation-induced stress and thermal cycling. Tin whiskers are a very real issue in high-
reliability systems such as aerospace, medical and defence electronics causing equipment failures as the result of intermittent or permanent short-circuits between contacts or PCB tracks. Te growth of Tin Whiskers can be
reduced by improving the plating process or annealing the final assembly to reduce internal stress, introducing alloying additives to the solder or application of a conformal coating to block whisker growth. None of these procedures can completely overcome the risk of tin whiskers and sensitive, high-reliability equipment requires special attention during manufacturing. Te long history and demonstrated reliability
of lead solder means it is still used in critical electronic systems such as those to be deployed in space, as well as defence and medical
equipment, where environmental concerns are mitigated. Lead solder suppresses the formation of tin whiskers, can deal with extreme temperature fluctuations, is less sensitive to radiation-induced degradation, has low outgassing properties in a vacuum, is less prone to stress fractures and has less risk of cracking. Lead solder is likely to remain the choice for critical equipment while development of lead- free alternatives is ongoing. Te exponential growth of Low Earth
Orbit (LEO) satellites is being fuelled by advancements in technology, reducing launch costs and increasing demand for global connectivity, this is increasing the demand for high-reliability electronic systems. Projects such as SpaceX's Starlink, anticipating the launch of some 42,000 satellites, demonstrates the growth of the LEO satellite market. Secure, reliable hardware is essential as
clearly there is no opportunity to service or repair a satellite once launched and failure or loss is very costly, both financially and in terms of lost service. System components which are qualified for use in space are essential and for the medium-term lead-solder will continue to be used to maximise system reliability, while a reliable alternative is sought. Te low volume of the current market for space electronics is a
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