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I would like to embed a PCB in epoxy to protect it. There are certain areas that should remain accessible/epoxy-free (e.g. USB socket, buttons).

I am looking for a chemical that I can apply to the PCB in the appropriate areas before casting. After the epoxy has cured, I want to remove the chemical with as little residue as possible by treating it with a solvent (ethanol, isopropanol, aceton, H2O) or heat (<= 100°C).

What kind of chemicals are suitable for this? What experience have you had?

Edit

I have some SMDs and LEDs. It should be a thick layer which replaces a case (like potting).

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    \$\begingroup\$ Have you looked into conformal coating sprays? They are used to provide environmental protection and can be fairly easily masked off. Plus they don't have the hassles of epoxy potting - making a mold form, overheating parts, days of curing time, shrinkage issues, toxic chemicals (mgchemicals.com/downloads/msds/01%20English%20Can-USA%20SDS/…), etc. They can also be scraped off and the circuit reworked if necessary. \$\endgroup\$
    – vir
    Commented Jan 11, 2023 at 20:37
  • \$\begingroup\$ @vir OP is asking for the masking actually :) \$\endgroup\$
    – datenheim
    Commented Jan 11, 2023 at 21:26
  • \$\begingroup\$ @Molitoris do you want to mask the component side, the bottom side or both? What type of components are in the areas that should not be protected (SMD or THT, Connectors)? Should protection be a thin coating, or do we speak about potting? A photo would be helpful. \$\endgroup\$
    – datenheim
    Commented Jan 11, 2023 at 21:30
  • \$\begingroup\$ Can you just use masking tape? \$\endgroup\$
    – Kyle B
    Commented Jan 11, 2023 at 21:49
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    \$\begingroup\$ Generally your mold should keep epoxy from the places you don’t want it \$\endgroup\$
    – Bryan
    Commented Jan 12, 2023 at 0:43

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I usually print a mold out of plastic (resin 3D-printer for details etc.). You can buy one of these cheaply these days. You also can buy printed parts for a small dollar these days.

If buying is not an option, or time is limited, I sometimes build a mold out of scrap PCBs/cardboard/whatever and tape/glue - not that pretty and a little fiddly, but works as well.

If even this option is not viable, I use sealing compound (for engines and mechanics and stuff) and apply it to the areas not to be epoxy coated. It is a little messy and clean-up is required.

Before pouring I spray the mold - regardless which type - with a release agent. If I am out of stock on this, I use regular olive oil... not in production of course, but works okay for hobby projects and prototypes.

Works like a charm!

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