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SMART Group Webinar: Electronics in Harsh Environments

The webinar was brought to a close by Ian Fox from Aero Engine Controls, with a wrap-up presentation entitled Harsh Environment Electronics: Materials and Making it Work. Typical examples of harsh environment conditions were high or extremely low temperatures, high humidity, and corrosive atmospheres.

He first considered the effects of high temperatures on components: The maximum storage temperature for conventional semiconductors was 150ºC, although many would operate up to 175ºC with some possible degradation in performance and reduction in lifetime. To achieve useful life above 200ºC, devices based on silicon-on-insulator were required, and for temperatures above 300ºC there were very few options. One was to use devices based on silicon carbide but these were very expensive and of limited availability. For soldered assemblies, at operating temperatures above 150ºC, the properties of eutectic tin-lead were significantly degraded, the solder was extremely plastic and its fatigue resistance was low. Changing the alloy to tin-silver (SnAg4) or tin-antimony (SnSb5) gave satisfactory performance at temperatures up to 175ºC. Modern phenolic based FR4 printed circuit laminates with 180ºC glass transition temperature were acceptable for operation at 150ºC, but higher temperatures required the use of polyimide. For operating temperatures in the range 175-225ºC, high-lead solder alloys Pb95Sn5 and Pb93.5Sn5Ag1.5 were commonly used, although their wettability was limited, and 225ºC was considered the upper temperature limit for laminate-based PCB designs, and ceramic substrates offered a better option, with hermetic microelectronics approach considered the most robust solution.

This webinar gave a broad overview of issues associated with design and manufacture of electronics for operation in harsh environments, particularly at high temperatures. Anyone working in high-reliability electronics and interested in learning more can hear the full story and participate in interactive discussion at the SMART Group seminar at NPL July 2, which will also feature detailed presentations on laminates from Alun Morgan of Isola and conformal coatings from David Greenman of Humiseal. Full details can be found here.

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