Old app note from Weller on Surface mount rework. Link here(PDF!).
We know you can relate to the challenges presented by newer and more complex surface mount component packages. As systems continue to evolve, rework tasks can be increasingly difficult even for the most skilled rework technicians. The process of safely and efficiently removing and replacing components is more challenging than ever. The sheer mass, component density and cost per unit area of printed circuit board assemblies add to the complexity. Things can also get tricky when components need to be carefully removed and repurposed. The key is to select appropriate tools and proven techniques to tackle difficult rework issues.
Your specific application should dictate the tools and techniques used. Before final tool and process determinations can be made, a number of component, printed circuit board, tool, profile and process parameters and requirements should be considered.