Steve,
What you are seeing is very likely copper migration. Color is hard to see unless you
have a high resolution and right lighting conditions. At my previous employer, I have
seen many examples of this mechanism.
Take a look at Figures 6.62 (a) through (d), page 223 for pictures of electromigartion,
Cu migration or dendrite growth. These figures show line-to-line, via to via and via to
plane copper migration examples both in raw board and assembled boards.  Source is
"Failure Modes and Mechanisms in Electronics Packages" (http:// www.wkap.nl)


You can also go to http://www.rampinc.com/cgi/librsrce.cgi and browse for Free Paper
Downloads.  and search for CAF (Conductive Anodic Filament) . These papers ( 5 -10)
have a bunch of technical data on copper migration with many examples.
"Stephen R. Gregory" wrote:

> Hi All!
>
> I've learned about electromigration, and fortunately have never had a real
> problem with (that I know about anyway). But recently, we've had some boards
> returned to us that have failed for a short from VCC to Ground, usually at
> the same area on the board.
>
> It's beneath a keyed header that is hand soldered on the board. The first
> couple of boards we got back, we couldn't find the problem. But we just got
> back 3 more and I did see something. In trouble shooting we remove the header
> (it's got a plastic body that has the plastic key molded into it) so we can
> see if anything beneath the plastic.
>
> Well, on one board today I think I saw something. There's traces that run
> between the header pins and on one trace, it looked like the mask was not
> adhered to the trace well. Then looking at it under higher magnification,
> there was what appeared to look like these copper fern like structures
> between the trace and the anular pad of the PTH on the laminate.
>
> Will the dendrites be copper colored? All the pictures I've seen they have a
> silvery gray to white appearance...I guess it would depend on which was the
> cathode and which was the Anode in the scheme of things as to what the
> dendrites would look like huh?
>
> Has anybody else ever seen this?
>
> Thanks ya'll!
>
> -Steve Gregory-
>
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--
____________________________________
Regards,
Pratap Singh

Tel./Fax: 512-255-6820,
e-mail: [log in to unmask] or [log in to unmask]

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