Xilinx is changing the material set for the PLCC and PQFP packages per PCN 2003-11 to make the package more environment-friendly. For more information, see the PCN at:
Select "See All Customer Notifications" and then search for PCN2003-11.
How does this affect the thermal resistance of these packages? The affected packages are the following:
PC 20 / 44
PC 68 / 84
TQ 100 / 144
VQ 44 / 64 / 100
Xilinx has run preliminary thermal simulations with the Green Material set incorporated in the package composition. Xilinx has found from the simulations that there is negligible difference in all thermal resistance values between the Green Material set and the older material set.
The reason for this is that the two material components that are changed are the mold compound and die-attach material (see PCN 2003-11 for more details); the conductivity for the die-attach material decreased while that of the mold compound increased in the newer materials. As a result, a very small net effect was found.