How to Route High Speed Signals on PCB: Best Practices

To route high speed signals on a PCB, use controlled impedance traces with consistent width and spacing, keep traces short and direct, and separate them from noisy signals to reduce interference. Also, use proper ground planes and layer stacking to maintain signal integrity.

Syntax

Routing high speed signals involves these key steps:

• Controlled impedance traces: Define trace width and spacing to match the required impedance.
• Short and direct routing: Keep traces as short as possible to reduce delay and signal loss.
• Ground planes: Use continuous ground planes under signal layers for return paths.
• Layer stacking: Arrange signal and ground layers to minimize noise and crosstalk.
• Separation: Keep high speed signals away from noisy or switching signals.

pseudo

TraceWidth = CalculateImpedance(DesiredImpedance, DielectricConstant, TraceHeight)
RouteTrace(StartPoint, EndPoint, TraceWidth)
PlaceGroundPlane(BelowSignalLayer)
KeepTraceLengthMinimized()
SeparateFromNoisySignals(MinDistance)

Example

This example shows how to route a 50-ohm controlled impedance trace on a 4-layer PCB with a ground plane below the signal layer.

steps

1. Calculate trace width for 50 ohms impedance using PCB stackup parameters.
2. Draw the trace from component A to component B keeping width constant.
3. Ensure the trace length is as short and straight as possible.
4. Place a continuous ground plane on the layer below the signal trace.
5. Keep at least 3 times the trace width distance from other high speed signals to reduce crosstalk.

Output

A 50-ohm impedance controlled trace routed directly with a ground plane below and proper spacing from other signals.

Common Pitfalls

Common mistakes when routing high speed signals include:

• Using inconsistent trace widths causing impedance mismatch.
• Routing traces too close to noisy signals causing crosstalk.
• Breaking ground planes under high speed traces, disrupting return paths.
• Making traces too long or with unnecessary bends increasing signal delay and reflections.

Always verify impedance with your PCB manufacturer and use simulation tools if possible.

pseudo

Wrong:
RouteTrace(Start, End, VariableWidth)
BreakGroundPlane(UnderTrace)

Right:
RouteTrace(Start, End, ConstantWidth)
MaintainContinuousGroundPlane()

Quick Reference

Tip	Description
Controlled Impedance	Keep trace width and spacing consistent to match impedance.
Ground Plane	Use continuous ground planes under signal layers for return paths.
Trace Length	Keep traces short and direct to reduce delay and loss.
Separation	Keep high speed signals away from noisy or switching signals.
Layer Stackup	Arrange layers to minimize crosstalk and noise coupling.

Key Takeaways

Use controlled impedance traces with consistent width for signal integrity.

Keep high speed traces short, direct, and away from noisy signals.

Maintain continuous ground planes under signal layers for proper return paths.

Avoid breaks in ground planes and unnecessary bends in traces.

Plan layer stacking to reduce crosstalk and electromagnetic interference.