Emerson COM Express Carrier Design Manual page 28

 Differential pair to clock/high speed periodic signals: minimum 50 mils
 Differential pair to other signals spacing: minimum 20 mils
 Length matching between differential pairs (intra pair): 5 mils
 Ground reference if possible
 Spacing from differential pair to plane edge: minimum 40 mils, but if the space allowed is bigger, so
much the better
 For the differential pair trace width and spacing, refer the stack up structure and impedance table
from PCB vendor.
 Maximum number of vias is six on each differential signal
 TX+ and TX- signals should maintain symmetry when changing layers.
 No tight bend, use two 45° bends instead of 90° routing.
 Trace length compensation should be added to the short side after each bend.
Page 28 of 103 COM Express Carrier Type 2
Design Guide