Why should the QFN 148-pin package be used for thin PCB applications only?

Description

The QFN 148-pin package was is designed for use in thin PCB applications only (0.8 mm or 32 mils) and it should not be used with PCBs above 0.8-mm or 32-mils thick due to the differences in coefficients of thermal expansion between the PCB and the package. 

Long-term reliability of the solder joints on the QFN package may be reduced with thicker PCBs due to effects of thermal cycling