Just read this statement from a Boeing engineer:
"Sinnett, the 787?s chief project engineer, said that in each of the power-panel incidents electrical arcing inside a circuit board ? ?a low energy arc that lasted milliseconds, very small? ? had damaged the board and shut down some of the plane?s electrical power.
He said the small spark inside the circuit boards produced no safety hazard, only a loss of function that was handled by the plane?s multiple, redundant power systems.
In January, Boeing had not yet found the root cause, but Sinnett said the problems had been traced to a batch of faulty circuit boards inside the power-distribution panels, which are located, like the batteries, inside an electronics bay.".
Faulty because they use lead-free solder and the Humiseal didn't stop the growth of the tin whiskers.