Is This PCB Layer Stackup OK? Solid GND – Signal Layer – Split Planes ???

Why It Matters

Split or distant reference planes can turn a PCB into an unintended antenna, compromising high‑speed signal integrity and increasing EMI, which directly impacts product reliability and regulatory compliance.

Key Takeaways

• Split planes cause energy leakage into slot lines and increase crosstalk.
• Higher frequencies amplify unwanted radiation from plane gaps, degrading signal integrity.
• Proximity of reference plane strongly influences power flow and current distribution.
• Solid ground planes maintain localized fields, preserving transmission line mode.
• Asymmetric stackups shift power toward closer plane, reducing but not eliminating leakage.

Summary

The video examines how broken or split reference planes in a PCB stack‑up affect electromagnetic fields around high‑speed signal traces. Using Symbur simulations, the presenter compares a symmetric strip‑line with solid ground planes to configurations where one plane contains a slot or is asymmetrically spaced, observing the resulting field patterns and current distributions. Key findings show that a split plane diverts a portion of the signal’s power sideways into the slot, creating additional mode conversion and increasing crosstalk. At 1 GHz the leakage is modest, but raising the frequency to 10 GHz and beyond causes pronounced radiation and uncontrolled energy propagation, effectively turning the gap into an unintended antenna. The distance between the trace and each reference plane also matters: the nearer plane carries the majority of the power, while the farther plane contributes weaker currents, yet it never becomes negligible. The presenter highlights specific visualizations: power‑flow density maps that turn red near the trace for solid planes, and arrows that spill into the slot for split planes; surface‑current plots that reveal bell‑shaped distributions on both planes; and S‑parameter data confirming that most signal power still reaches the receiver despite the leakage. A quoted observation notes, “a small gap makes this an antenna unintentionally,” underscoring the EMI risk at multi‑gigabit data rates. For designers, the implication is clear: avoid gaps or splits in reference planes directly above or below high‑speed traces, keep reference planes as solid and as close as practical, and verify performance with full‑wave EM simulation, especially when operating above several gigahertz. These practices mitigate crosstalk, preserve signal integrity, and reduce unintended emissions.

Original Description

Watch what happens when PCB tracks are routed over split planes. Thank you very much Yuriy Shlepnev

Links:

- Yuriy's LinkedIn: https://www.linkedin.com/in/yuriy-shlepnev-7b39136/

- Yuriy's company: https://www.simberian.com/

- FEDEVEL courses: https://fedevel.com/courses

Chapters:

00:00 What is this video about

00:58 Setup

04:55 Example: Symmetrical - Solid ground planes on the top and bottom

11:14 Example: Symmetrical with a split on top plane

16:03 Example: Not-symmetrical - Solid ground planes on the top and bottom

20:29 Example: Not-symmetrical with a split plane far

23:53 Example: Gap with a bridge

27:13 Example: Partial cutout

35:52 Example: Crosstalk when routing over gap on far plane

38:22 Example: Crosstalk when routing over gap in near plane

40:15 Example: Crosstalk when routing differential pair over gap

49:33 AI in signal simulation software

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https://fedevel.com