Low Voltage Arcing under SMD Components

-Edit. Woops, forgot references...Information shared by Bob Willis during a PCB Webinar hosted by Vision Engineering Eliminate Printed Circuit Board Problems & Failures

-Edit. And for the Slide-Show

Sounds like contamination and voltage tracking; as a function of the contamination and voltage potential, dendrites are forming. See attached.

If you are using the wrong kind of flux (eg. acid plumbing flux) this can happen.

Use only electronic grade solder and flux materials. Solder should be 60/40 or 63/37 Sn/Pb if lead-based and the flux should be something like RMA rosin.