Might need to be warmer, read of at least one person using a tea candle holder with burning alcohol to heat the solder on an ibook with a loose gpu problem.. You might try more heat and maybe trying to find a way to apply constant, steady pressure from the time it's hot enough to help til it's cooled completely. Being able to view the chip while doing this (if you can't?) might help you get a sense of what's actually going on.