Does anyone out there have any good guidelines (i.e., component temps, board
temps, solder joint temps, times) for reworking BGA's. The BGA I'm trying to
remove and replace is an ORCA (from Lucent) 432 perimeter PBGA that is on a
15X15 board that is 14 layers. I'm using a Pace Thermo-Flo unit with a
bottom side preheat. And I'm having a hard time getting a profile (plus I
don't have board to destroy). I am seeing bridging(via X-ray inspection) in
the corners of the component after reflow, or component and board warpage
during reflow, or if I keep the heat down opens in the circuit during test.
I know preheat is crucial but nothing I do seems to work. Help!!!

Thanks

I've been there and now being introduced to it again with new repair/rework equipment. One
thing you pointed to so rightly is the 14 layer MLB. Its construction no doubt has several
thermal/electrical planes that really amount to a huge thermal mass. As you've said bottom
side preheat is critical. This must be balanced with an effective profile.

Without test specimens, you have a problem as the board's termination areas,
notwithstanding its laminate integrity, will suffer significantly over several thermal
excursions of the type required to nail the profile. The only suggestion I could make
(others jump in any time - Steve) is to emulate the original reflow profile as closely as
possible. This is provided your machine is programmable to that extent - and I think it is.
Beyond that, I believe it's a crap shoot.

Very good luck on a very expensive experiment.

Earl Mooy

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