We are a PCB design house/CM and we have found that if you elongate the QFN pads to the outside of the part by .025 to .030 you then have the opportunity of doing touch-up manually with a soldering iron should there be a voiding issue. This would have to be done at the CAD/Gerber level before PCB manufacturing.
Regards to all. JR
(http://www.smtnet.com/Forums/Index.cfm?CFApp=1&Message_ID=66125)