> Is it really just the PCB itself initiating the burn? In my experience it=
 is always a component failure that initiates a burn - but having said that=
 I have had a backplane PCB that had an intermittent short in it, on a mini=
computer. But that short caused something else to give up, not the backplan=
e.


I've not seen any cases where the PCB itself failed, it was always
initiated by a component failure.
The thing is that surprisingly low energy levels (<0.5W average) can
cause the component package to degrade, then to arc, and once that
happens, the arc easily transfers to the PCB.

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