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Design007-Apr2019

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48 DESIGN007 MAGAZINE I APRIL 2019 In the second of my recent columns on res- in potting and encapsulation, I will expand on my previous Q&A guide on the subject with further advice on selection and application. Keeping to our tried and trusted five-point Q&A format, I am returning to the subject of potting and encapsulation with a few more pointers to help steer you in the di- rection of making appropriate resin choices—and, hopefully, away from problems that you are more than like- ly to encounter on the way. Ini- tially, here's a little primer to whet your appetite. There are a number of dif- ferent factors that influence the protection afforded by pot- ting compounds. The act of encapsulating a component or PCB means that it is sur- rounded by a layer of res- in, which completely seals a component or an entire PCB from the environ- ment in which it operates. When mixed, a two-part resin starts a chemical reaction, which results in the resin becoming fully poly- merised to provide a homogenous layer. The polymerisation reaction creates a three-di- mensional structure, which provides a barri- er against chemical attack and high humidity, physical shocks, and the potentially destruc- tive effects of thermal cycling. Now, let's refer to our questions. 1. What typical applications use epoxy resins? Epoxies are typically used where extremes of temperature and chemically aggressive en- vironments are encountered. Under-hood ap- plications are common, and epoxies are often used to protect the huge variety of sensors, digital electronics, and connectors that abound beneath the hood of a modern automobile not just from high temperatures but also from volatile fuels and lu- bricants. Even as we switch from the internal com- bustion engine to the electric motor, the chemical environment might change, but the requirements for chemi- cally resis- tant potting resins capa- ble of tolerat- ing a wide temperature range and resisting chemical attack will re- main. Their excellent adhesion to a wide range of substrates means that epoxies are used to ensure that the electronics are also very effectively sealed against the external environment and are perfectly adapted for use in equipment des- tined for deployment in ATEX and other haz- ardous areas. 2. What typical applications use silicones? Silicones are used where extremes of temper- atures are to be expected, or the components Five Tips to Further Improve Resin Encapsulant Performance Sensible Design by Alistair Little, ELECTROLUBE

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