Is it possible that electromigration cause a short circuit in a PCB? Theoretically due to chemical potential difference between gold and nickel (1.68 V) it's known that metal ions can penetrate into the isolation and form a bridge. Is that really a practical threat and such a process is really causing short circuit in PCB devices? Is that process occurring only when the device is turned off? Could that make a short circuit between two close pads of a component for example a smd capacitor 0603?