Hi all...

We are placing a number of PBGA's onto 8 and 10 layer PCB's for a number of
years.  We have one paticular brand of PBGA, a 492 ball device that the
corners of the chip are warping upwards causing unsoldered connections near
the corners of the chips.
The parts are in proper dry pack from the manufacturer and we have even
tried baking these parts at 125 deg C for 24 hours just to make sure we are
not having a moisture problem with these devices.
We place other 492 ball devices on the same PCB with no problems and no
measurable warp.
We are not having much luck with the manufacturer of these parts, lastest
word from them is "they allow up to 8 mil warp" ... does not help me, I
only print solder paste with a 6 mil thick stencil.
This problem "comes and goes"... some reels of parts are fine, some are "so-
so", and some are terrible.

My question is, has anyone had a similar experience?  I'm reluctant to
mention the manufacturer of this part in the "open", however they are a
well known PC supplier.

Thanks in advance, Bill...

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