When reassembling your device, be sure the heat sink's rubber gasket is installed correctly. The nub on the gasket should mate with the hole cut into the logic board near the heat sink fins.

The tail of the gasket should fit into the notch in the heat sink, it should not end up underneath the heat sink tab that will rest on the logic board.

Make sure the antenna cables are inserted into their respective notches on the logic board, as highlighted in the last picture.