I assumed (certainly don't *know*) that the specification is there because if the chip finishes too high above the PCB, then you didn't melt the balls enough and you may have cold joints, etc. and if the chips finishes too low/close to the PCB, then you've squished the balls too much and they may be in danger of shorting. At the least, it seems to me that if you meet the clearance specification, you're more likely to succeed at BGA soldering without expensive equipment to inspect the hidden solder balls. I could be wildly wrong though. I never carried through with my experimental ideas. Another thought is that if you use the feeler guage idea that I proposed, then you can heat the chip and board more thoroughly without the chip sinking any closer to the board. That should help to ensure good solder joints on the interior balls without allowing the chip to squish to close to the board. I think I was looking into it when the PPC750FX and later the PPC750GX came out and I really wanted to get them onto a ZIF module of the type that plugs into the Beige G3 model Macintosh. But Powerlogix came out with a couple of nice cards, so buying commercial became cheaper and more practicle than trying to do it myself. (Thank goodness!) Jeff Walther