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.
- Moisture in PCB Layers that didn't get baked out?
- Uncured epoxy betweem layers?
- 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.