First of all, safety means reliability of the board during your system’s lifetime, many years, with an appropriate mission profile that considers the real usage of the board and it’s accessories, starting from the power supply. A 24/7 mission profile, is different than 8/5, and not just for the global working time that changes so much, but also from the number of bootstraps of the system that, not in a Novasom board for what I’m going to tell you, can compromise the functionality of the system itself.

Then there are the environmental stress factors, from the temperature to the EMC noise and spikes, that can easily break a power stage or GPIO not correctly protected.

A big problem with temperature range, is that most people don’t think , as we always do, to propose the conformal coating on the “outside temperature range “ board , and fail to consider on the datasheet the minus something indicated there.

The main problem is the humidity condensation that make short-circuits between test pad or components, especially 0201 often used for the stabilization of the DDR and USB3-Pci express bus.

Then, this condensation may freeze under at 0 (yes it is not necessary to go to -40, water becomes ice @ simply 0 Celsius), this increases the volume and cracks the BGA from inside the ball.