Design007 Magazine

PCBD-Oct2016

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64 The PCB Design Magazine • October 2016 Last month, I started this series of columns on resins by going back to basics, questioning the core rationale for potting and encapsulation with resins, their fundamental chemistries and how each resin type differs one from the oth- er—indeed, how their individual properties can be exploited to maximise performance under a wide range of environmental conditions. I hope readers found this useful. Of course, when it comes to the choice and applications of resins, there's a great deal more to discuss, and over the following months I hope to provide some use- ful tips and design advice that will help you in your quest for reliable circuit protection. For this month's column, I'm placing a bit more emphasis on the critical points that arise when you embark on resin selection. We need to get down to the real nitty gritty here because it's important that circuit designers have an un- derstanding of some of the basic properties of resins before deciding which is the most suit- able for the task in hand. But let's not get too technical at this stage; instead, I'd like to simplify the selection criteria and try to make life a bit easier for those who have to make the decisions. So, picking up on my colleague Phil Kinner's format of providing a five-point guide in his previous articles on conformal coatings, let's take a look at five key resin properties that, if not taken carefully into consideration, could have serious implications for the performance of your application. Hardness Perhaps counterintuitively, bearing in mind that a resin is there to protect, the cured hard- ness of the resin is actually rather important as the higher the hardness, typically the stiffer the resin will be. For example, if cured too hard, the resin may place too much stress upon compo- nents, particularly those with fragile connec- tion legs. On the other hand, if too soft, then the resin will be easy to remove and it will pro- vide reduced protection against chemicals and by Alistair Little ELECTROLUBE Why are Resin Properties So Important? SENSIBLE DESIGN

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