Hi Gabi,

I saw quite a few cases of molten C4s in a row with perfectly good one.

I think the easiest way to figure out what was going on in your case is
to check the intermetallic at the substrate/solder interface.
Electromigration shouldn't cause abnormal intermetallic growth, while
overheating the C4s (due to high current) will do just that.

Regards,

Vladimir

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gabriela
Sent: Thursday, August 21, 2008 1:17 PM
To: [log in to unmask]
Subject: [TN] Electromigration in solder bumps HELP!!

Dear Technetters!

I am sending these links because lately I performed cross sections with
very
similar results on a flip chip BGA which failed at our customer's site.

As stated by our customer, by applying force on the component, the
electrical results seemed to change, and the first supposition was that
the
solder joints between the BGA and the circuit had failed. X-ray results
can
not show cracks, but the re-reflow was not successful, and in the
meantime a
second identical component failed.

I was given the first one for analysis and checked it by x-ray,
separately,
so that I had a much better image of the inner solder bumps. I found
that
the bumps had random voids.

I started a very time consuming cross section of the bumps under the die
and
reached a region with voids under UBM and even melted bumps. The damaged
bumps were random, and on the same row there were perfectly good ones. 

Question:

Has anybody encountered such a problem?

 <http://www.jedec.org/download/search/JEP154.pdf>
http://www.jedec.org/download/search/JEP154.pdf


https://nscnt12.nsc.gov.tw/APPLYFORM/WRITINGS/L120452153/pb1-36.pdf


http://www.imec.be/ngfcs/13_Labie_EM_public.pdf




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