Peter's 2nd 🧠

    High-Speed PCB Design

    Via Stitching / Fencing

    Uniform Ground Potential

    Ground plane has resistance

    Vias (or ground pins) etc. helps to keep ground potential as uniform as possible under current flow.

    Thermal Dissipation

    Vias are much better heat dissipators than FR4.

    Return Path

    Return currents follow path of least impedance.

    At low frequencies / DC, return current is shortest path between trace start and end in ground plane (least resistance). At high frequencies, return current follows trace in reference plane (least inductance by minimizing loop area). current_return_path.png

    Higher Current Flow

    Stitch multiple track layers to increase current capacity

    Perimeter Via Fencing

    Faraday Cage (λ/10 spacing)

    Reduces received and emitted EM radiation. Do this together with the 3H copper pour pullback guideline.

    Crossing Layers

    Ground via when changing reference plane

    Or else the return current will spread out in a nasty matter across the original reference plane to find the nearest via.

    References

    • https://electronics.stackexchange.com/questions/371559/why-try-to-maximize-number-of-grounding-vias-in-rf-pcbs
    • https://www.emcs.org/acstrial/newsletters/fall08/tips.pdf
    • https://rushpcbinc.com/what-is-via-stitching-and-why-it-is-useful/
    • https://www.ndsu.edu/pubweb/~braaten/EMC_2016_1.pdf
    • https://incompliancemag.com/article/alternative-paths-of-the-return-current/
    • https://www.youtube.com/watch?v=nPx2iqmVAHY
    • https://www.youtube.com/watch?v=S6PNYKxJsdk
    • https://circuitdigest.com/article/here-is-why-you-should-use-via-stitching-for-your-next-pcb-design

    Routing Directions

    Goal: reduce cross talk

    Configure your board layers so that two adjacent signal layers will have preferred routing directions that cross each other instead of running parallel to each other. If layer two is running “north to south,” then make sure that layer three is running “east to west.” In this way you can minimize the possibility of broadside coupling.

    Other

    • Avoid return path discontinuity (i.e. ensure full ground polygon adjacent to high speed traces)
    • Impedance Matching (simple transmisson line stuff, reduce loss)
    • Termination (reduce reflection)

    Concepts

    • Every circuit is a loop (hence inductance), capacitance comes from dielectric
    • Conductors carry current, non-conductors carry EM waves
    • Multiple decoupling capacitors are needed because of inductance (so they block different frequencies as that are not just a simple RC)

    To-Read

    • https://www.protoexpress.com/blog/effects-high-speed-signals-pcb-design/
    • https://www.microwavejournal.com/blogs/1-rog-blog/post/24374-comparing-microstrip-and-grounded-coplanar-waveguide
    • https://www.electronics-notes.com/articles/basic_concepts/inductance/inductance-of-straight-wire-coils.php