This video was captured using technologies developed by Glenbrook Technologies and described in patent numbers: 6,009,145 and 7,426,258.
The video dramatically shows the BGA self-aligning during reflow.
The process begins as the solder heats up, melts, and then wicks from the bump to the pad.
The wicking action of the solder pulls the BGA into place.
After alignment the solder balls are uniform and round.