Coupling of the intra-pair differential signals and increased spacing to neighboring signals help to minimize harmful crosstalk impacts and Electro-Magnetic Interference (EMI) effects. In the microstrip case, a differential trace should be 5 mils wide, with a 7 mil wide air gap spacing between the two traces of a pair. Any uncoupled sections whose intra-pair space exceeds 7 mils can be routed as a 7 mil wide trace, if the section is 100 mils or longer. In the stripline case, a differential trace should be 5 mils wide with a 5 mil wide gap between the two traces of a pair.
The spacing between pairs and to all non-PCI Express signals should be 20 mils or four times the dielectric height, whichever is greater. If the non-PCI Express signals have significantly higher voltage levels or edge rate than the PCI Express signal, the space should increase to 30 mils in order to avoid coupling.
Do you have any specifics for SAS controller, 6 GHz layout guidlines?
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