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I'm designing a 4 layer GPS tracker PCB with the 2nd layer as ground and 3rd as Vcc. Is this a good practice? I know a gnd layer is good but I'm not sure how to distribute the positive of the supply on the 3rd layer. Should I cover the whole layer with the supply even underneath the antennas? Or just pour Vcc underneath the Vcc pins?

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    \$\begingroup\$ I think it depends to power plane noise. If your power plane is not too noisy and not carrying high current voltage on that plane, you may cover whole layer with Vcc. Also using gnd-Vcc planes on consecutive layers is a good thing. It generates capacitance between layers and acts like decoupling capacitor. \$\endgroup\$ – Koray Jan 9 at 7:35
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    \$\begingroup\$ Probably it will depend mostly on what you connect Vcc to. If you get noise backwards from the circuit into the Vcc plane, you'd probably want that noise to go towards the Vcc regulator and not towards other circuits. Consider for example if you have 5V layer, from which you connect a 3.3V switch regulator but also 5V logic. If the 3.3V regulator is noisy, you don't want that noise to get passed to the 5V logic circuits. Though of course the proper solution to that is to address the root of the problem where the noise originates from (and in addition decouple each IC supply). \$\endgroup\$ – Lundin Jan 9 at 8:46
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Planes are often used to ensure that RETURN paths are available for fast edges, to constraint radiation (for EMI control), to achieve clean waveforms.

If your fast edges are from logic UP edges, then the logic VDD is providing high currents that will demand return paths.

You can use local and tiny ceramic capacitors from the VDD pin of the IC, to the GROUND plane. No need for that plane IMHO.

But you'll have to do a bit of thinking. And sketching the return paths. In exchange for this effort, you free up that "VDD plane" for many other valuable uses.

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