Repost ---> PCBs and Moisture?

From: EdV <ed_vogel@xxxxxxxxxxx>
Date: Mon, 7 Apr 2008 07:16:49 -0700 (PDT)

sorry to repost but I thought mine may have got lost in the sea of
spam:

We got a batch of boards built and two of them show a curious
tendency(consitent) to shut down the crystal oscillator at -20 C. We
also notice that the capacitance of the xtal caps changes more on the
"bad" PCBs at -20C than the "good" boards.

1. Moisture in PCB Layers that didn't get baked out?
2. Uncured epoxy betweem layers?
3. Residual flux?

#3 I could address with vapor degreasing or other cleaning. #1 and 2
would mean baking at 100C or so which I guess is ok to see if it has
an effect.

Any thoughts, insights or expereinces as always are welcome.

Ed V.

.

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