And also there another myth that circulating around 
Some say that it is not the BGA solder itself that gone bad, is the bumpgate itself that is bad, bumpgate is the joints that connect the silicon die to the chip carrier. In the layer, the solder is ruined. That also can be reflow to get it fix temporally, and that also what explain why some laptop after a reball the exact same prob come back again. During the process of removing the chip from the board, the bumpgate are exposed to heat therefore being "fixed". Is the process that fix it, not the reball that fix it.