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Can conformal coating affect performance?
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fx991ex:
So I have this very sensitive fully analog board - an EMG amplifier.

After I covered the board with urethane conformal coating the sensitivity of the amplifier plummeted. The amplifier still works but the signals that it outputs are much weaker.

I used the following conformal coating: https://uk.farnell.com/mg-chemicals/4223-55ml/chemical-coating-55ml/dp/2889756

The coating is fully died. It has been more than 24 hours since I coated the board.
EEEnthusiast:
If some of your pins of the ICs are too fine pitch (0.4 mm ) then the conformal coating can add additional capacitance between them. They will also add additional resistance, but once it dries up, the impact of resistance would be negligible.
What kind of circuits is it? If it is very low frequency, then there should be minimal impact to the design.
fx991ex:
Yeah, there are SOT23-8, MSOP-8 and 0402 components on the board. And the board is pretty densely populated. And the frequency is fairly high.



EEEnthusiast:
For high frequency circuits, conformal coatings are a bit tricky. The extra capacitance created by the coating layer dielectric, will cause frequency response changes. Circuits could oscillate and sometimes may loose bandwidth. There are specific chemicals made for RF boards, but I would still not use them without caution.

fx991ex:
Can you recommend me any product?

I intend to coat the board with conformal coating and then encapsulate it in polyurethane resin.
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