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FEBRUARY 2022 I DESIGN007 MAGAZINE 59 it ideally suited for EV battery protection. e thermal conductivity is 1 W/mK, mak- ing it suitable for use in applications where the operating temperature will be up to 200°C. Its good flow characteristics make it an excellent choice for extremely tight spaces or difficult geometries. What You Need to Know As a rule of thumb, silicone resins have the broadest temperature range (-50 to +250°C), are generally so resins, and are not as chemi- cally resistant as some of the other chemistires. Some polyurethanes have a low glass transition temperature and are suited to lower tempera- tures than silicones (-60°C). Epoxies are more designed for higher temperature applications (-40 to +200°C), but have excellent adhesion to a wide range of substrates and excellent chemical resistance. e majority of resins I use are two-part systems that, when mixed together in the cor- rect ratio, react to form polymeric materials. By careful formulation, the properties of the cured resin can be tailored to meet individual customer requirements. If you foresee any challenges with matching resin types to your production procedures, be sure to contact your supplier's technical support team for fur- ther advice. In my next column, I shall be tak- ing an in-depth look at some of the most fre- quently asked questions we get asked as resin experts and will be exploring various options in response to these enquiries. DESIGN007 Beth Turner is head of encapsu- lation resins at Electrolube. To read past columns from Electro- lube, click here. Download your free copy of Electrolube's book, The Printed Circuit Assembler's Guide to… Conformal Coatings for Harsh Environments, and watch the micro webinar series "Coatings Uncoated!" One of our newest polyurethane resins has successfully been deployed in a car park sen- sor application, where the resin requirement needed to avoid RF interference and provide a dielectric constant of between 3-4 at 50Hz. It has a low viscosity ensuring sufficient flow in small gaps, as well as a wide temperature range of -60 to +125°C and a low exotherm (<35°C). With a Shore hardness of A80, the resin is suitable for protecting delicate com- ponents whilst providing good impact resis- tance to the external environment. It is a high- demand resin for IoT applications, due to its proven capability of protecting RF transmit- ters, sensors, and circuitry from harsh envi- ronments, vibration, temperature extremes, and water ingress. It is much easier to tailor the cure speed with polyurethane systems, and the usable life and gel time of these can be adjusted to suit cus- tomer requirements, leading to faster process times and less work in progress. Polyurethanes show lower exotherm during cure than epox- ies, and the heat generated is not usually a problem, even for fast cure systems. Silicone Resin Chemistry ough not as popular as epoxy and polyure- thane resins, silicone resins do offer some dis- tinct advantages when used as an encapsulating resin because the cured products have a high degree of flexibility across a wide temperature range, excellent chemical, dust and moisture resistance, and good electrical insulating prop- erties. Silicone resins tend to be more expensive than epoxies or polyurethanes, but are ideally suited where high continuous operating tem- peratures (above 180°C) are required. More- over, the exothermic temperature when work- ing with silicone systems is very low indeed, ensuring compatibility with heat-sensitive components. One product I work with is a two-part sili- cone potting and encapsulating resin which was primarily developed for the protection of LED drivers, however, its properties make