On Thu, 17 Mar 2016 17:24:00 -0000 (UTC), 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?

Early technet response suggests chemical contamination in vias, but
would require SEM EDX to confirm. This contamination could difuse in
the conformal coating cure stress lines (ie the pucker).

I don't see vias involved in every instance - some sites seem to
develop at pure surface mount pad sites.

There's an image of copper dendrites on Steve Zeva's gallery

http://stevezeva.homestead.com/

http://stevezeva.homestead.com/Dendrite_1.jpg

These tend to be inter-node rather than centrally expanding.

A close examination of tin whiskers should reveal a characteristic
three dimensional spike/thread detail. Not likely here.

RL