Removing Voids in BGA Process

We have been told that the process described below, to remove voids in a BGA, is not reliable. We would like to know what the consequences are in doing this and what would make the process not reliable.

The process:
We place a small amount of liquid water soluble flux under the BGA. Using a hot air rework station we heat the board and BGA until the solder reaches a liquidus state then lift the BGA about .150" to .250" above the site and hold for 10 to 12 seconds. We then place it back down on the site and finish out the profile. The maximum temperature measured at a solder ball is 210 F.

We X-ray and the voids have been eliminated.