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I am thinking to encase my entire bluetooth PCB along and connected battery in an adhesive such as a soft urethane or silicone encapsulate. My board and battery are each about the size of two stacked quarters. Of course I will be avoiding getting the adhesive on any input ports and the on/off pairing button. I feel like this would give it good water resistance. Also it would hold my components together and to their enclosure and would especially protect a few soldered connections I made with the battery etc.

Has anyone tried this or can hazard a guess? I am concerned that the bluetooth reception will be significantly diminished. Should I also be concerned about the thing heating up and catching fire? I would use a non-flammable adhesive, and the battery for the bluetooth is only about 3V (and charges via usb).

What else might I be concerned about?

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  • \$\begingroup\$ Assembled PCBs often have a conformal coating applied. Unless the coating is really thick it should have negligible effect on the bluetooth (its wavelength is 12.5cm) - think of all the bluetooth devices encapsulated in plastic. \$\endgroup\$ Commented Mar 21, 2015 at 6:51
  • \$\begingroup\$ I understand @geometrikal however I am talking about an additional "thicker" coating to provide further protection and water resistance and also to make the whole thing adhere to an external enclosure. Also I am doing some soldering at several locations which need to be coated. Considering a glue called E6000. \$\endgroup\$
    – Jet59black
    Commented Mar 21, 2015 at 14:01

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If the Bluetooth antenna is inside the potting compound, it will certainly be detuned. It will quite likely cost you 10 dB of signal, or 3 x shorter range (to a phone... 10x between potted circuits). This applies whether the antenna is a track on the PCB or a bought item.

This effect can be solved by making a version of the board specially tuned for potting. This one won't work properly in air, but will work once potted.

The way you do this is simple: make a potted version that you can still open up to adjust. Coat the board with some release agent - spray 'n cook, light oil, and pot it halfway. Allow it to set. Then coat the surface of the potting, and add more compound until it's fully potted.

Now you have a PCB on which you can easily adjust the antenna and tuning network, but also test in the fully-potted environment.

The same effect happens when you out the circuit in a plastic case, but to a smaller extent, and it's easier to open up to adjust.

Don't worry about it heating up unless the circuit has a fan or heatsinks.
First of all, a small Bluetooth PCB probably lasts a long time on a single battery, so its heat output is tiny. Secondly, the potting compound will conduct the heat away better* than air will, so it will quite likely run cooler. (* this isn't true if you have heatsinks on chips, then air movement is better).

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