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Hi I am new to PCB design and Im still learning. I am wondering what is the reason behind copper fills? I searched online but I could not find an good explanation of the reason of using the copper fills.

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3 Answers 3

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It can be used to create a ground or power plane to where all your components ground and power pins can connect to usings vias and there is no need for traces.

It also works as noise innmunity and also a a thermal dissipator

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  • \$\begingroup\$ So how does it work as noise immunity? I can understand the thermal dissipation. \$\endgroup\$
    – Tea
    Commented Jul 29, 2020 at 9:53
  • \$\begingroup\$ It reduces the inductance of the signal return path \$\endgroup\$
    – SolarTec
    Commented Jul 29, 2020 at 9:56
  • \$\begingroup\$ I also read online that copper fills reduce the cost. Is it true? \$\endgroup\$
    – Tea
    Commented Jul 29, 2020 at 9:58
  • \$\begingroup\$ That's possible too. If you keep more copper on finished product, you spend less money on chemicals needed to remove the "unused" copper when manufacturing it. \$\endgroup\$
    – akwky
    Commented Jul 29, 2020 at 10:09
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If a single region of copper fill happens to overlap both a noisy region/trace and a sensitive region/trace, the capacitive coupling will upset the sensitive region.

Thus casually allowing copper_fill can be bad. On a purely digital PCB, should be OK.

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On large PCB, the board can warp if there is a lot of copper on one side and not on the other. The different temperature coefficients of expansion between the copper and the fiberglass cause mechanical stress and strain. The effect is worse with thinner board material.

I once had a business-card sized board (demonstration for a thin, PCMCIA power supply solution) which was on half-thickness (0.031inch or 0.8mm) material. The corporate applications engineer wanted a surface-mount prototyping area on the back of the board, so we ended up with lots of copper on the back and very little on the top. Even though the board was small, the thin material together with the copper layer imbalance caused the boards to warp very noticeably, by about 2-3mm...

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