BGAs are difficult to rework as they require a pretty deep knowledge of the original manufacturing process, knowledge of the chemistries involved in the original manufacturing process, the thermal profiles of the various processes as well as an experienced eye in terms of BGA inspection.
In terms of BGA inspection, while the IPC-A-610 standard indicates that the inspection of BGAs can be confirmed from a process standpoint via x-ray, it is imperative that the tools of visual inspection, endoscopic inspection, and x-ray be used for proper BGA inspection.