We have a board built in the thousands, and several have (apparently) short-circuited a plated through hole (PTH) to an adjacent pour (see photo, note the other thermal damage is probably due to thermal conduction of via internal trace running to the PTH).
The PTH to pour clearance is 7mil, and the PCB manufacturer and assembler is big name CM!
Any ideas about possible causes or lines of inquiry to pursue?
- This problem has occured in ~0.05% percent of the builds.
- the damaged PTH is where the short is suspected to an INTERNAL pour.
- I had assumed that 100% of these PCBs were electrically tested. perhaps I should not assume.
- the applied signals are from a <50V battery which is rated for ~20A, but if we assume ~3kv / mil dielectric withstand we are nowhere near a breakdown even with some voltage ringing given our 7mil clearance.
- Failures are found during sub assembly testing in a pretty organized / clean facility, and occurs upon connection of power, not during use.