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I don't have much experience with designing PCBs and when doing so I had to make a surprising number of decisions concerning the copper fill.

Assume a simple analog or digital circuit, 2-layer PCB. No RF, no switching regulators, transmission lines, differential pairs or anything like that. Maybe an ADC.

Do I use copper fill on both sides? Both connected to GND? Do I route GND manually first or do I leave the ratsnest and let the copper fill do the job? (If KiCad can do this.) Do I route on top and only use bottom for crossings or do I sort my signals into top and bottom beforehand?

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  • \$\begingroup\$ Both sides. To gnd. Let copper fill do its job. Do whatever you want for crossings. \$\endgroup\$
    – DKNguyen
    Oct 21, 2021 at 1:39
  • \$\begingroup\$ Since the cost of 2 vs 4 layer for prototyping is nearly the same, rather than try to route mixed digital/analog components without a proper ground plane, I would strongly consider using a 4 layer board with a ground plane. Even if you don't strictly need 4 layers, it will take you less time and will probably give you a better performing device. \$\endgroup\$ Oct 21, 2021 at 1:40
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    \$\begingroup\$ @user1850479 I was trying not to ask about specific market situations, but JLCPCB 60x40 2-layer USD 2, 4-layer USD 8, that's 4 times the price, not really what I'd call "nearly the same". Granted, the PCB costs are probably the smallest part of a project. \$\endgroup\$
    – AndreKR
    Oct 21, 2021 at 1:45
  • \$\begingroup\$ Though personally, on 2 layers i would copper fill one side as gnd and the other as power. Then the plane on the other side is always nearby. \$\endgroup\$
    – DKNguyen
    Oct 21, 2021 at 1:51
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    \$\begingroup\$ On a 2 layer board without a solid ground plane, definitely route ground first. That will force you to look at the current return paths and hopefully catch any that are extremely ugly in time to fix them. Then fill with copper on top of them (KiCAD can easily do this with the "Add Filled Zone" button). If you have a solid copper plane, routing the ground connections doesn't make sense. \$\endgroup\$ Oct 21, 2021 at 1:54

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Use as much as GND copper as possible on every layer. That's good for EMI performance of your board. Connect all the GND copper areas on different layers by vias.

They are called stiching vias.

Since you are going to have a lot of stiching vias, I suggest you to have a hole diameter of 0.4/0.5 mm in order for the PCB manufacturer to use standard drill tools.

In a 2-layer board GND copper should fill the entire board except for those areas needed by signals for completing the routing.

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