What are the common failure modes in ICs at low temp.?

[kamtar]

While working on a picoballoon and being curious about electronics at low temperatures I came over to information that the first thing to fail in an MCU would be flash and I could add robustness by executing the whole program from RAM.

So let's take an example where I have a battery (Li/FeS2) which is rated -40C but I can imagine that it can work for a while in -50C and more too. And then TPS61006 step-up, ARM and SX1276 LoRa module, everything else is expendable.

So what can be the main/most common failure mode at around -40/-50C?
From my uneducated guess, I'm worried mainly about radio module drifting too much, even sooner than -40C. But now I'm really curious about that flash thing and executing program from RAM; how beneficial it can be in this case.

[iMo]

Put the stuff into a small box (ie made of polystyrene foam) and it could stay above -40C..

[David Hess]

The common digital failure I have seen is an analog one.  Transistor transconductance drops with temperature which may cause crystal oscillator circuits to fail to start at low temperature if they were not designed with enough excess gain margin.

For other problems, two of the design steps I might take is to operate the logic at the higher end of its supply voltage range and at lower clock frequencies to give more timing margin.

[james_s]

The drifting crystal frequency is probably going to be significant, even at more normal temperatures it can affect those RF modules. Why don't you insulate the circuit to keep it warmer? If you have the power budget you could even ovenize it, it doesn't take much power if it's well insulated. Seems like it ought to be fairly easy to avoid most of the problems in the first place.

[kamtar]

Thanks, Yeah I really don't want to overdo it with stuff like heating. I treat it as a fun, fast and cheap project. Asking out of curiosity, and for the future.

[iMo]

You may calculate the thermal budget - the power dissipated off the electronics and the battery vs. outside temperature at certain altitude, considering, say, 20mm thick polystyrene foam.. Based on the temperature profile you may manipulate the actual duty cycles of the components

[james_s]

Heating doesn't have to be complicated, it can be something as simple as a resistor connected across the supply. You may be fine just having insulation and using what little heat is already produced by the electronics.