Weeeeell, putting aside lead free is supposed to be "stronger" and more resistant to board flex breaking the junction when done properly (and the higher eutectic point), Yes and No. Problem with ditching the lead free is heating the chip to get it off the board without lifting that last recalcitrant pad, cleaning the solder off the board and the underside of the chip, applying juuuuuust the right ammount of leaded paste to each and every pad whilst making damned sure it doesn't bridge across to an adjacent pin when you drop the chip back on it, re-aligning the chip to within a poofteenth of the right position and keeping it there whilst you heat it back up again. And you have to hit the device with lead-free soldering temps anyway to get the damned thing off in the first place - far friendlier to only cook the suspect thing once. If you've got access to a serious rework setup then yeah, worth the effort. Especially if you're being paid to do it as a career as well... Far easier to flood the underside of the BGA with good liquid No Clean flux then hit it with hot air or IR. And hope the bits on the underside of the board don't fall off either if you get too keen with the hot air... And I've got three 32- and 42-inch LCD/LED TVs here right now that I can show you that responded reliably to that second technique, plus a handful of other devices over time that even using my Yum Cha hot air station all behaved well afterwards to that method.