SPRAAV1C May 2009 – March 2020 AM3703 , AM3715 , OMAP3503 , OMAP3515 , OMAP3525 , OMAP3530
When BGA packages are placed on the top and bottom layers, do not place one BGA package directly underneath another BGA package. The temperature cycle board level reliability degrades if overlap of package footprint occurs.
Several studies, including the one referenced here, show that temperature cycle board-level-reliability (BLR) performance degrades if there is an overlap of package footprints. A small BGA opposite a large BGA or QFP, with its footprint within the unpopulated I/O shadow of the larger package, has temperature cycle performance similar to that of a single-side board assembly.
For additional information on this concept, see section 5.4, Single-Sided Soldering and Double-Sided Soldering, of NEC’s, Semicondutor Device Mount Manual, http://www.necel.com/pkg/en/mount/ (this link is no longer good).