Emerson COM Express Carrier Design Manual page 95

 Do not route traces under crystals, crystal oscillators, clock synthesizers, magnetic devices or ICs
that use, and/or generate, clocks.
 Stubs on differential signals should be avoided due to the fact that stubs will cause signal reflections
and affect signal quality.
 Keep the length of high-speed clock and periodic signal traces that run parallel to high-speed signal
lines at a minimum to avoid crosstalk. Based on EMI testing experience, the minimum suggested
spacing to clock signals is 50mil.
 Use a minimum of 20mil spacing between the differential signal pairs and other signal traces for
optimal signal quality. This helps to prevent crosstalk.
 Route all traces over continuous planes (VCC or GND) with no interruptions. Avoid crossing over
anti-etch if at all possible. Crossing over anti-etch (split planes) increases inductance and radiation
levels by forcing a greater loop area.
Figure 41 Layout Considerations
In order to determine the necessary trace width, trace height and spacing needed to fulfill the
requirements of the interface specification, it's necessary to use an impedance calculator.
COM Express Carrier Type 2
Design Guide
Page 95 of 103