Re: Potting horror...
- From: makolber@xxxxxxxxx
- Date: Thu, 12 Feb 2009 17:41:46 -0800 (PST)
On Feb 12, 4:10 pm, n...@xxxxxxxxxxx (Nico Coesel) wrote:
A customer of mine has a problem with a PCB potted in polyurethane.
The circuit consists of some inputs (clamped & filtered), a
microcontroller with internal RAM / flash and some power electronics
to switch loads (up to 40V). 10 PCBs where produced and tested. All
worked fine. 4 of those PCBs where potted and they started to show
erratic behaviour like RAM corruption, software hang-ups. I already
milled one of the modules to expose the microcontroller to check
whether it is hot, but it stays cold. So its not a heat problem.
The polyurethane used is non-conductive and shouldn't shrink, the
potting was done by a company that specializes in potting electronics;
they know about ESD precautions.
Any ideas where to start looking?
--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
"If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------
did the boards work before potting
did you unpot one of the bad boards
did it start to work after unpotting
what speed is the uc
what is the dielectric constant of the potting
are there ANY hi impedance nodes anywhere in the system including
power supply, reset circuit, or anywhere else
what about the busses, do they go hi Z sometimes
was the potting fully cured and dry before powering up
let us know what you find
Mark
.
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- Potting horror...
- From: Nico Coesel
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