For a 4-layer design, the maximum
track length on the top and bottom layers that are outside the Faraday cage can not
be longer than 8mm since the majority of the routing can be done on the third
layer.
Note: For a 2-layer design, the maximum track length
recommendation of 8mm can be difficult to follow since the main routing is done
mainly on the top layer. If the tracks on the top layer exceed 8mm in length, then
these tracks must have a GND directly underneath on the bottom layer to minimize the
unwanted radiation of the long tracks that exceed 8mm.