From the fine SMTNet archives: http://www.smtnet.com/Forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=12824Message54659
There are a few other threads available, as well, by searchign on PCB Delamination.
Delamination post reflow is almost always caused by trapped moisture in the material explosively vaporizing during reflow. Storage temp/humidity have an enormous affect on the situation. If your boards have not been sealed and/or stored in an environmentally controlled manner, baking them pre-assembly is most likely called for.
To get the most information, work with your PCB vendor to cross-section the board. They ought to be able to determinet the root cause/corrective action.
cheers, ..rob
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