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July 2000

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 21 Jul 2000 20:42:46 EDT
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This is a subject that has come up before...it has to do with the TI BGA's
with the metal heat sink incorporated into the top of the device. I have
x-ray but it doesn't have enough power to penetrate the heatsink. We've
recently aquired a Ersascope, I've been using that to inspect first article
placement to make sure that we're getting it on the pads...it's been fine.
But we still have had a problem with bridging.

Out of 50 or so boards, there's been maybe 5-6 boards that have bridged. The
bridges have all been in the corners. The balls all seem "squished" because
of the weight of the heatsink. I've been looking closely at everything,
making sure the print is good, placement is accurate, and that my reflow
profile is good too, but I still am seeing this bridging problem...

The last time I brought this subject up, I did get conflicting perspectives
on this problem with the T.I. parts with the heatsinks in them. One
experience shared was that they were having problems processing this part
without bridging, and another perspective was from someone that said they
built many, many boards with this part and didn't have a problem at all...

I'm really trying hard to make sure that everything is as it's supposed to
be, print definition and registration, placement accuracy, and reflow
profile, but I'm still experiencing this bridging problem, 5 or 6 boards out
of 50 isn't good at all...now that I have a Ersascope (because I can't x-ray)
it's painfully easy to see the bridges...and like I said, they're  mostly on
the corners..

Any ideas?

-Steve Gregory-

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