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I'm currently working on a PCB design project which will be a four layer board. The inner two layers will be ground and the top and bottom will be signal. The board doesn't have any high-speed signals. I've only ever designed two layer boards and I've always included a ground pour on both the top and bottom layers. On this new four layer board with internal ground planes, should I also include ground pours on the top and bottom with stitching vias?

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  • \$\begingroup\$ Very few downsides to doing that. If not for high speed or immunity, it eases the PCB manufacturing. \$\endgroup\$
    – winny
    Commented Jan 18, 2023 at 21:04

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I'm currently working on a PCB design project which will be a four layer board. The inner two layers will be ground and the top and bottom will be signal.

Good! The signal-ground-ground-signal stackup is optimal, and your signal traces will be referenced to the adjacent ground plane, providing a low impedance path for return currents.

The board doesn't have any high-speed signals.

Be careful here. The frequency of the signals on a digital board is usually set by the rise/fall time of the signal, not the clock rate. ICs produced with modern small die processes have very fast short rise/fall times. It's far from unusual to have frequencies in the hundreds of MHz propagating through your traces during signal transitions, even if you're only using microcontrollers clocked at hundreds of kHz or a couple of MHz.

On this new four layer board with internal ground planes, should I also include ground pours on the top and bottom with stitching vias?

You generally don't need to include a ground pour on the outer layers, but there are some advantages. It makes manufacturing a little easier due to not needing to etch off so much copper, and it may also offer thermal dissipation advantages.

If you're already including vias to inner planes near all your ground connections, and you're not doing anything particularly high frequency, you also don't necessarily need to add additional stitching vias. It won't hurt either, though, as long as you don't add so many that your manufacturer increases costs. Another thing you might want to consider is including ground return vias nearby signal and power vias when you change layers, to ensure that the signals travelling through those vias have a reference "plane" in the vertical axis.

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  • \$\begingroup\$ This is a great response, thank you! That's really interesting about how the rise-fall time is important like that. \$\endgroup\$
    – Vera Fodor
    Commented Jan 18, 2023 at 21:30
  • \$\begingroup\$ No problem! That insight is one of my favourite points from this talk. \$\endgroup\$
    – Polynomial
    Commented Jan 18, 2023 at 22:14

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