The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
Subject: Re: Side effects of potting compound !
Date: 31 Oct 2002 15:04:12 GMT
Organization: Concentric Internet Services
X-Mailer: Mozilla 4.79 [en] (Win95; U)
Why do they want them potted to begin with? Are they trying to cover up
everything so no one copies the design?
> We've just finished a small run of a project for a client. Everything
> completed. At the last minute the client said "can we have them potted please
> I replied that I saw no reason why not but would check a few to make sure.
> Potted 3 yesterday. Came to test them today. Calibration is miles out, by
> almost exactly the same error in each unit (it's a calibrate once only unit).
> Checked the compound.... fine, compound specs.. fine. I spent all this morning
> breaking open the compound to try to find out what had gone wrong. Had it
> affected some caps ? Had it formed some crazy dissimilar metal junction
> somewhere ? Had it absorbed moisture in the curing process ? Had it not cured
> completely and was slightly conductive ? Checked all sorts of ideas.
> There's a voltage reference feeding a resistor divider with a trimmer at the
> junction for fine trimming. A multi turn preset. Voltage at both sides of the
> trimmer are as they should be. Voltage at the wiper is now 6% higher (which is
> actually about 50% of the trimmer range). Overall resistance of trimmer is
> normal. Ratio has changed.
> Potting the PCB in the box using epoxy potting compound has actually moved the
> Anyone come across this before ? Anyone got any ideas how to prevent it ?
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup