Potting calibrated components

[markp]

Is there a micro involved? If so, use software calibration. If no
micro, then you need to find alternative methods of calibration after
potting.

Yes, there is a micro and I do use software calibration already, the problem
was drift. Funny enough, baking the unit for many hours at 100 deg C fixed
the problem, so I assume it was an interaction between the potting compound
and the PCB.

 

[Tony Williams]

Yes, there is a micro and I do use software calibration already,
the problem was drift. Funny enough, baking the unit for many
hours at 100 deg C fixed the problem, so I assume it was an
interaction between the potting compound and the PCB.

We used to temperature-cycle precision potted modules,
after curing, for at least 5x full cycles of the
operating temperature range. My theory was it relieved
the static stress on components that had been created
by the shrinkage of the potting compound when cured.

I also found that potting in small sections (of about
5 cu-inch per section) reduced the total stress. It
also gave a chance of tweaking the calibration after
early part-pots.

Room temperature potting compounds were the worst for
shrinkage (and resultant stress), even to the extent
of pulling electrolytic capacitors apart. We settled
on Emerson and Cummins 2651MM, which needed to be heated
to about 70C to start the cross-linking and send it off.

 

[Keith Williams]

Thought we were in alt.sex for a second there...

Nope, not at all! Rather, alt.sleeping_on_the_couch or perhaps
alt.law.divorce-court.