Signal Integrity - Guidelines

Stripline traces passing over a split plane should be at least four times farther from the signal than the reference plane. Source: Eric Bogatin




If a signal changes reference planes when passing through a via, add an adjacent ground via.

Source : Signal Consulting Inc. Dr. Johnson

Use a capacitor to AC couple the return path when reference planes are at different potentials. 

Source: TDK Outline of EMC Design Methods


This article compares the propagation delay (tpd) for serpentine, spiral, and straight traces.

The results show that a signal will travel faster in a microstrip serpentine trace compared to a straight trace of the same length. And the stripline serpentine trace will lag the straight trace. 

Source: A New Slant on Matched-Length Routing - Barry Olney


Serpentine Gaps should be 3 x height to nearest reference plane.

When a design requires equal-length traces between the source and multiple loads, you can bend some traces to match trace lengths (see Figure 11–20). However, improper trace bending affects signal integrity and propagation delay. 

To minimize crosstalk, ensure that S ≥ 3 × H, where S is the spacing between the parallel sections and H is the height of the signal trace above the reference ground plane.

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Differential Pairs

D = distance between two differential pair signals; W = width of a trace in a differential pair; S = distance between the traces in a differential pair; and H = dielectric height above the group plane.

• Ensure that D > 2S to minimize the crosstalk between the two differential pairs.
• Place the differential traces S = 3H as they leave the device to minimize reflection noise.
• Keep the length of the two differential traces the same to minimize the skew and phase difference.
• Avoid using multiple vias because they can cause impedance mismatch and inductance.

Source Altera: High-Speed Board Layout Guidelines.