Re: PIC24EP256GP206 Package Question (TQFP64)
As far as I can understand, the thermal resistance data in Table 30-3,
48.3 C/W is for 64 pin TQFP package without a thermal pad in the package,
and do not require a thermal pad or thermal vias in the board.
The 64 pin TQFP package is still better than 28 pin SPDIP or SOIC packages that may mount the same chip with the same temperature limitations.
64 pin TQFP package with thermal pad, mounted on a board with thermal vias, should have thermal resistance from Chip to Ambient around 25 C/W.
With temperature limits and other data given in Table 30-2, there should be sufficient data available, for you to do your own calculations.