Kontron COMe Starterkit Eval T2 - Manual (Page 184)

Carrier Board PCB Layout Guidelines
6.5.3. USB 3.0 Trace Routing Guidelines
Table 63: USB 3.0 Trace Routing Guidelines
Parameter Trace Routing
Transfer rate / Port 5.0 GBit/s
Maximum signal line length
(coupled traces) 7.5 inches
Signal length used on COM Express Module (including the
COM Express connector) 3.0 inches
Signal length allowance for the COM Express Carrier
Board 4.5 inches
Differential Impedance 85 Ω +/-10%
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 pairs-to-pairs (inter-pair) (s) Min. 15mils
Spacing between differential pairs and high-speed periodic
signals Min. 15mils
Spacing between differential pairs and low-speed non
periodic signals Min. 20mils
Length matching between differential pairs
(intra-pair) Max. 5mils
Reference plane Ground
Spacing from edge of plane Min. 40mils
Via Usage Max. 3 vias per differential signal trace
6.5.4. PEG Trace Routing Guidelines
Please refer to Section 6.5.1. 'PCI Express Trace Routing Guidelines' on page 182
Note The COM Express specification does not define different trace routing rules for
PEG and PCI Express lanes. Newer chipsets feature low power modes for the
PEG signals. In order to ensure compatibility it's recommended to keep the
PEG signal lines as short as possible. A max of 5” to the carrier device down
and 4” to a carrier slot is advisable.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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