Cursitor Doom wrote:


I can't find any pictures that resemble these things on the web.
Following a closer look with a stereoscope, there are outbreaks of these
growths in at *least* a dozen places on this board. Here's two more
sharper pictures with the problem areas outlined:

https://www.flickr.com/photos/128859...in/dateposted-
public/

https://www.flickr.com/photos/128859...in/dateposted-
public/

All the pictures I've seen on the net show whiskers as silver in colour
but these are dark, metallic plum. They typically spring from vias in a
kind of branching, fern-like formation and certainly reach out to touch
other traces on the board.

Anyone seen anything like this before? Ideas on how to proceed?

These do NOT look like the whiskers I have encountered before. But, they
could be some sort of conductive stuff that has grown between nets on the
board. One possibility is they are fibers from a brush that either cleaned
the board or applied the conformal coat. But, they could still be trouble,
maybe they start out non-conductive but become conductive when moisture is
absorbed. Since you say the sprout from vias, maybe the board had some
contaminant left in the vias that slowly creeps out under heat and
electrical field. Anyway, not much to lose by trying to remove the
conformal coat at these spots and see if the EMU comes back to life.
If it does, then you need to get some new conformal coat and re-seal those
spots.

Jon