SNLA426 june 2023 DS320PR1601 , DS320PR410
- 1
- Abstract
- Trademarks
- 1 Introduction
- 2 PCIe Gen3, Gen4, and Gen5 Loss Budget
- 3 Minimum Eye Width
- 4 Cross Talk Mitigation
- 5 Humidity and Temperature Insertion Loss
- 6 Critical Signals
- 7 General High-Speed Signal Routing
- 8 PCB Grain and Fiber Weave Selection
- 9 PCB Material Loss Budget
- 10High-Speed Signal Trace Impedance
- 11High-Speed Signal Trace Length Matching
- 12Differential Trace Routing Guidelines
- 13Differential-Inter-Pair Matching
- 14Intra-pair Length Matching
- 15Trace Bends
- 16Minimum Differential Trace-To-Trace Distance
- 17Serpentine Guidelines
- 18High-Speed Differential Signal Quick Rules
- 19High-Speed Differential Pair Reference Plane
- 20Via Staggering
- 21Via Stubs
- 22Via Pads
- 23Via Discontinuity Mitigation
- 24Back-Drill Stubs
- 25AC Coupling Capacitors Placement
- 26AC Coupling Capacitor Physical Placement
- 27Auxiliary Signal AC Match Termination
- 28Suggested PCB Stack-ups
- 29Summary
- 30References
22 Via Pads
When vias must be used, vias in pad are recommended versus vias in extended pads. Placing vias in an extended pad creates unwanted inductance which affects impedance. Via pads placed on unrouted layers must be removed otherwise via capacitance is reduced, which results in an impedance drop.
Figure 22-1 Via in Pad (Recommended)
Figure 22-2 Via in Extended Pad (Not Recommended)