AN 672: Transceiver Link Design Guidelines for High-Gbps Data Rate Transmission

ID 683624
Date 1/29/2020

1.4.3. Channel Design

  • For high-speed transceiver signals, use trace widths of 6mils or more to minimize conductor loss.
  • Limit use of 4-mil trace widths to the BGA breakout area and keep their trace length as short as possible.
  • Loosely coupled traces are easier to route and maintain impedance control but take up more routing area.
  • Tightly coupled traces saves routing space but can be difficult to control impedance.
  • Use stripline routing to avoid FEXT concerns.
  • Use stripline traces with 5H differential pair-to-pair separation to minimize NEXT to 1%.
  • If microstrip routing is required, used 6H-7H differential pair-to-pair separation to avoid NEXT and FEXT issues.
  • Cvia optimization techniques
    • Reduce the via capture pad size
    • Eliminate all non-functional pads (NFP)
    • Increase the via anti-pad size to 40 or 50 mils
  • Lvia optimization techniques:
    • Eliminate and / or reduce via stubs
    • Minimize via barrel length by routing near the stripline traces near the top surface layer and applying backdrilling
  • Add ground return vias within 35 mils of each signal via to further improve the insertion and return losses of the via.
  • Use manufacturer layout recommendations for connectors if available. In absence of any specific manufacturer recommendations, designers can apply the transparent via optimization and DC blocking capacitor compensation.