Hi Steve,
I am not familiar with that device, but is the heatsink lifting at the
edge?  If not, it looks like the encapsulant they use has a bevel around
the corners when they mold.
Just a guess.  Maybe Altera would send you a picture of a part.


Kerry McMullen
Principal New Product Mfg. Engineer
LTX Corporation
50 Rosemont Road
Westwood, MA 02090-2306
(T) 781-467-5468



Stephen Gregory <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
07/27/2005 12:35 PM
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[TN] Strange Looking BGA Heatsink Gap...






Hi Everyone!

We just finished building 8-assemblies that used a 780-ball Altera Stratix
BGA on them. These BGA's have a pretty decent sized copper heatsink
in the top.

Everything went pretty good. But then I noticed something with the BGA
heatsink after we got them all built. In the corners, there seems to be
some
sort of gap beneath the heatsink and the top of the part that I didn't
notice
before. Go to: http://www.stevezeva.homestead.com  then click on Picture
Page 2, then look for "Heatsink Gap".

All the BGA's show this in all 4-corners. I don't have any more of these
BGA's
around that haven't been through reflow, so I can't do a before and after
reflow
comparison. The Altera package drawing doesn't show this gap either.

I'm thinking (hoping) that the parts are made like this, to somehow keep
the
whole part from warping during reflow because of a CTE mismatch between
the
substrate and the heatsink...it just looks strange though.

Anybody else out there familiar with these devices that can tell me this
is
normal?
(Please tell me this is normal!!)


Kind regards,

-Steve Gregory-
Senior Process Engineer
LaBarge Incorporated
Tulsa, Oklahoma
(918) 459-2285
(918) 459-2350 FAX
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