[SI-LIST] Re: Potting/encapsulation/conformal coating and SI
- From: "Andrew Ingraham" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 5 Oct 2004 08:35:13 -0400
You also would want to choose a potting material that doesn't exhibit
undesirable characteristics (i.e., loss) at the frequencies of interest.
I know zilch (nothing) about the electrical characteristics of potting
materials, so I don't know whether there are lossy compounds that you need
to avoid. Certainly anything that is even slightly conductive, or sprinkled
with fine metal particles, would be bad. This sounds like something where
the electrical engineer should help specify the potting material and make
sure someone can't change the formula later, not realizing the electrical
impact it could have.
I have seen L-C circuits that were potted. Because it's in such close
proximity to the coil's windings, it probably affects their self-capacitance
as well, so final tuning should take that into account.
Regards,
Andy
> Be sure to evaluate what the coating will do to the impedance of your
> PCB traces. If you intend to coat the board, design to account for that
> effect. Adding conformal coating to a properly operating board _may_
> cause improper operation of the circuitry if you are depending on a
> particular impedance.
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