Steve,
As mentioned yesterday, yes I have seen this many times, both in test qualifications on
test vehicles and as well as actual product. Depending upon the contaminants available,
color of the adjacent materials ( substrate, mask etc), your resolution, lighting type
etc. you can see copper color. If you look into the figures that were referenced in my
previous memo, photoes show two types of growth - a fern like structure, and a single
strand type growth.
If the migration is occuring on surface, growth is more fern type, if it is internal
growth along glass fiber for example via to plane, it is a single strand type. When I
locate my color file collection, a copy will be emailed to you of both examples.
Greenish mess has been seen only when there was corrosion due to the presence of
chloride ions/sulpher molecules which formed copper chloride or copper sulphate.
Personally I have not seen green color during migration failure studies.
"Stephen R. Gregory" wrote:
> Hi ya'll!
>
> After all the replies that were sent to me, I think what I have is
> electrochemical migration. I wish I had a microscope where I could take a
> picture to show you, but I'll describe things again.
>
> There is a 6-pin header that is hand-soldered on this board. The board failed
> due to a short from VCC to Ground. We removed the header to see if we could
> spot anything beneath the plastic of the header because we didn't see
> anything on the other side of the board. This header location has traces that
> run between some of the pins, and what I discovered that is if the mask isn't
> perfectly registered, the clearance area around each of the holes for the
> header will expose an area on the traces that are running between them.
>
> On one of the boards that I looked at yesterday, I observed a "fern-like"
> stucture of copper that appeared to be growing from the anular pad of the
> header pins to the exposed area of the trace. I seen this at two places at
> the header locations...
>
> I also discovered (to my dismay) that one or two of the operators have just
> been hand cleaning after soldering in this header. That since has ceased
> (dammit!)...
>
> Again, I just want to ask, has anybody else ever seen actual copper filaments
> grow like that? From the replies I got back yesterday, most were telling me
> that I should be seeing a black, or maybe greenish mess there, and that it
> would be really tough to tell if it was copper. But I swear, it clearly has a
> copper color to it..
>
> Thanks again!
>
> -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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