Kontron COMe Starterkit Eval T2 - Manual (Page 188)

Carrier Board PCB Layout Guidelines
6.5.8. Serial ATA Trace Routing Guidelines
Table 67: Serial ATA Trace Routing Guidelines
Parameter Trace Routing
Transfer Rate Up to 6.0 GBit/s
Maximum signal line length
(coupled traces) 5.0 inches on PCB (COM Express Module and Carrier Board. The
length of the SATA cable is specified between 0 and 40 inches)
Signal length used on COM Express Module
(including the COM Express Carrier Board connector) 2 inches
Signal length available for the COM Express Carrier
Board 3 inches, a redriver may be necessary for GEN3 signaling rates
Differential Impedance 85 Ω +/-20%
Single-ended Impedance 50 Ω +/-15%
Trace width (W) PCB stack-up dependent
Spacing between differential pairs (intra-pair) (S) PCB stack-up dependent
Spacing between RX and TX pairs (inter-pair) (s) Min. 20mils
Spacing between differential pairs and high-speed
periodic signals Min. 50mils
Spacing between differential pairs and low-speed non
periodic signals Min. 20mils
Length matching between differential pairs (intra-pair) Max. 5mils
Length matching between RX and TX pairs (inter-pair) No strict length-matching requirements. Route the signals as
directly as possible.
Spacing from edge of plane Min. 40mils
Via Usage A maximum of 2 vias is recommended.
AC Coupling capacitors The AC coupling capacitors for the TX and RX lines are
incorporated on the COM Express Module.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
188/218