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I have a mysterious component covered with yellow "glue" or something. It has very hard surface, but it seems its been poured into the plastic "cage". The shiny cover on the top is some kind of paper, I can rip it off.

Any idea how to remove this goo from the PCB? (Without damaging the components underneath)

enter image description here enter image description here

csadam
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3 Answers3

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That's a potted circuit. The shiny paper on top likely forms some sort of EMI shield to reduce interference it may cause or receive.

Potting is usually an epoxy, which usually cannot be removed either chemically (dissolution) or thermally (melting it), so you are left with mechanical (chip away at it). Some are soft, and while they stick fairly well, with a bit of time can be removed. If it's a hard variant, it may well be impossible, and if you really want to figure out what's under there, using an X-ray inspection machine would be a good idea.

Some rare epoxies are susceptible to attack by extremely aggressive organic solvents (dichloromethane, xylene, etc.), but you may well destroy the board in attempt to remove it. If you have access to some chemicals and can chip off small samples of the epoxy, you could give it a whirl.

Nick T
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    If you really want to know what's under there, asking the manufacturer would probably be a better idea. They might even be able to send you one without the potting compound so you can do your testing or whatever you need to do. – Kevin Vermeer Jan 28 '11 at 19:09
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    That top is only an EMI shield if it's grounded, and it needs to be grounded around all the edges to get the higher frequencies. Since it doesn't look like that, my bet is that it may be a thermal gap-fill pad and/or a mold release. – Mike DeSimone Apr 02 '12 at 13:05
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I don't know what that glue is, but I would try:

  • Acetone (nail polish remover)
  • Pliers (pull/chip it off)
  • Hot air (melt it)
  • Alcohol

Here are some suggestions from another thread: http://science.niuz.biz/solvent-t45294.html

Toby Jaffey
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Red fuming nitric acid is used to dissolve the epoxy resin used in chip packaging, and might work. It's dangerous stuff, though, and will probably dissolve the epoxy used in the PCB.

Leon Heller
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    Jeez...and I thought DCM was "bad"...RFNA can certainly oxidize almost anything, but I'd be worried that the only thing it would leave would be the more resistant plastics, glass, and maybe silicon die (and lead wires if they're made out of gold). Copper will disappear, and I don't even know if the soldermask would survive, so you couldn't even tell what traces were where. – Nick T Jan 25 '11 at 02:52