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I have an electronic assembly that is heat sensitive. Due to the incorporation of a CR3032 coin cell battery, it can survive being heated to a maximum of 60 degrees C.

I want to coat this assembly in a biocompatible, waterproof plastic. This layer will be the ultimate barrier to moisture between my device and a biological environment.

At the moment I am using parylene-C, which performs admirably, but is very expensive.

Various species of thermoplastic promise to perform just as well, at dramatically lower cost, but I don't know how I'd apply them without damaging my battery.

My question to you is, how could I coat my circuit in a thermoplastic without thermally damaging it, and without spending more than a few dollars per unit?

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    $\begingroup$ Have you considered chemically cured silicons instead? $\endgroup$ – SF. Jun 11 '18 at 0:02
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    $\begingroup$ Can you clarify what you mean by biocompatible? If this is to be implanted, you should probably stick with parylene-c. $\endgroup$ – Eric S Jul 11 '18 at 1:32
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here are two alternatives.

first, you can conformally coat the assembly with a sprayed-on and heat-cured waterproofing compound, commonly know as "paint".

second, you can immerse the circuit assembly in a liquid which will cure into a solid. substances like this are known as "potting compounds" and there are dozens of different varieties which are not particularly expensive.

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Use wax the kind people use to pull hair it is durable and doesn't crack unlike candle wax and has a lower melting point. I us this on match sticks to water proof them. It doesn't burn the skin so it should be cold enough not harm your battery. The down side it is hard to get off once one. You can also use rubber cement since it has a 0 reactivity but is flammable in the liquid state and does not dry as hard as the wax, but is easier to get off. I have not tried to mix the to together. I know you where looking for an out of the box solution and hope this helps. Please let me know.

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