Refer to the PDF data sheet for device specific package drawings
In case there is a need to use the outer layers for routing outside of shielded areas, it is recommended to route only static signals and ensure that these static signals do not carry any high-frequency components (due to parasitic coupling with other signals). In case of long traces, make provision for a bypass capacitor near the signal source.
Routing of high-frequency clock signals on outer layers, even for a short distance, is discouraged, because their emissions energy is concentrated at the discrete harmonics and can become significant even with poor radiators.
Coplanar shielding of traces on outer layers (placing ground near the sides of a track along its length) is effective only if the distance between the trace sides and the ground is smaller that the trace height above the ground reference plane. For modern multilayer PCBs this is often not possible, so coplanar shielding will not be effective. Do not route high-frequency traces near the periphery of the PCB, as the lack of a ground reference near the trace edges can increase EMI: see Section 188.8.131.52, Ground Guidelines.