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Design007-Aug2022

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62 DESIGN007 MAGAZINE I AUGUST 2022 in the electronics industry, given the distinct performance advantages they provide in harsh environments, underwater applications, and hot and humid operating environments. Resin Cost Comparing the cost of resins can potentially cause confusion because resins are oen priced in kilograms but used in litres as the unit to be potted is of a fixed volume—which means den- sity can have a big effect on the actual cost per potted unit. If we consider two resins which have the same apparent cost per kg, but resin A is 1 kg/L (typical for an unfilled resin) and resin B is 2 kg/L (a highly filled resin), it will cost twice as much to pot a unit of fixed volume X using the denser resin vs. the lighter one. e differ- ence in densities is not usually this extreme as other requirements which are influenced by filler content, such as thermal conductivity and flame retardance, mean it's unlikely for both a completely unfilled and a heavily filled resin to be in the running for the same application. However it can still be an important consider- ation when choosing a resin for a cost-critical end-use. Mixing Not all mixers are created equally, both in terms of manual operators when using the resin bi-packs for prototyping, and also when using a mix-and-dispense machine for larger production runs. An improperly mixed resin will not cure properly, leaving voids and a sticky or uneven finish. Even if there are no visible defects, it is highly likely the mate- rial will not have the final cured properties expected, which could lead to unit failures later on and will certainly not allow a fair compari- son between materials at the approval stage. It's important to have a good resin pack mix- ing technique. ere are several videos avail- able on our website and our YouTube channel that give a good grounding in the best way to use our resin packs. If using a machine, it's important to work with your resin provider and your machine manufacturer to identify a static mixer with the correct attachment for your machine, the correct shape and mixing style, and with suf- ficient elements, diameter, and length to give the resin a good mix. e resin chemistry, den- sities, and viscosity difference of parts A and B, as well as the mix ratio, desired flow rate, and shot size, will all influence the amount of mix- ing required and consequently the selection of the mixer. Depending on whether the resin is filled, heating, stirring, and recirculation may also need to be considered on the machine's storage tanks as well. Not all resin manufacturers offer the same level of customer service or technical support, so do ask them what level of support you can expect to receive before embarking on your project with them. I hope you have enjoyed this month's column and picked up some top tips on comparing resin systems. I cannot stress enough how looking at bio-based resin systems could be of significant benefit when considering a resin system for your next appli- cation. DESIGN007 Beth Massey is head of encap- sulation resins at Electrolube. To read past columns from Electrolube, 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!" An improperly mixed resin will not cure properly, leaving voids and a sticky or uneven finish.

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