Hi Mike:
        I might have a similar problem that I solved for small quantities. In the design lab, I sometimes help with uBGA field returns that have a substance that looks like black plastic between all the balls.

If it is still attached to the board, I turn the board at 45 degrees, with the BGA upside down, and GENTLY heat just the BGA with a narrow-nozzle heat gun. I use a very light tug with a tweezers or pointed tool to help it fall off onto the desk. (To protect other neighboring components, I cover them with masking tape. The tape provides an over-temperature warning by turning brown, and holds the parts more still to the board, and provides a partial shield from the heat.)
        Once the chip is cooled, turn the BGA upside-down and nest it in a piece of metal with a .020" deep square depression. This simply holds the chip from sliding horizontally while I do subsequent work. (I tried taping it to a board with double-sided tape, but heat loosens the tape.) At this stage there should be a wonderful mess of misshapen solder and black plastic (perhaps it is the paralyne you described.) Using a stereo microscope, I again use the heat gun, and use a  1-cm-wide chisel-blade X-Acto tool to gently shave off both messes simultaneously. Be very gentle, only removing the part that has sufficiently softened, eventually leaving the pads, traces, and soldermask that define the bottom of the BGA. (Scratched soldermask may later cause distorted balls at reattachment time.) You may have to shave it off in several stages. I don't think I had to use desoldering braid at all.
        Once the bottom of the BGA is done as well as this method allows, I think I used a solvent (it was probably isopropyl alcohol) with a paper towel to rub of remaining residue. I use a regular razor blade to mechanically scrape off any black substance from the four narrow sides of the package. These all come off easily. I then prepare the BGA for reballing. I use the solder preforms supplied by Winslow Automation (www.solderquik.com), then run the BGAs through a belt reflow oven. I peel off the paper, clean it, check it, and am done. The preform costs only about $3./BGA, and you don't need equipment (not even a microscope) to align the balls to the BGA! I usually am reballing .8 mm pitch balls. If someone plans to buy their reballing kit, I have some pre- & post-sales tips.
        The most challenging time was removing uBGAs from cell phones, where the BGA-BGA gap was about .075", with 0603 components between them, and black substance was everywhere. After the first try, I was able to remove a BGA from the midst of this mess without even disturbing the 0603 components! (But I am patient.)
        In summary, the materials cost of all this is about $3./BGA, the removal of all unwanted material takes about 15 minutes/BGA, and the reballing takes 3 minutes/BGA. Time to collect and later put away my tools was extra. I hope this helps. I did get 100% success.
Peter Casparius
Analog Devices, Inc.
ph. (781) 937-1464	
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