Without adequate board support, there may be board warping which may damage inner layers or cause the board to be badly deformed making placement of components difficult or have a reliability problem with respect to the solder joints. There are a variety of board support systems on the market with most higher end rework systems offering a flexible board mounting and support system design.
Not only is adequate board support required but proper bottom side heating of the boards will help ensure minimal differences in temperature across the board and a lesser propensity for board warpage. Modern BGA rework systems are equipped with sophisticated bottom side heaters. Advancements for making sure the process of reflow is optimized include multizone bottom side heaters.