Hello, KiCad newbie here trying to do a split power plane on a 4 layer board. I have layer 1 as signal, layer 2 as ground, layer 3 as power and layer 4 as mixed. On the power plane I have created two zones, one for +5V and one for -5V. I have a surface mount opamp that is power with +5V and -5V. I have a trace coming off the +5V zone that has a width of 0.25mm is that wide enough for a power trace?
KiCad has a calculator built in for current handling of copper tracks.
It is in the “main program selector” in the project manager.
A copper track of 0.25mm widht and 35um thick can still handle about 400mA (But it will have some resitance and therefore voltage drop. Copper on inner layers often is also thinner, 17um is a common thickness.
In general, the GND plane is used as a reference, for all voltages, and the power supply tracks just have to be fat enough to be able to handle the currents with a low enough voltage drop.
In general, you would not need power tracks wider then a few mm, unless you’re working with real high currents and bus bars.
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So far as I know, no pcb vendor refunds money for etched copper; so leaving plating on a board is basically free. With most pcbs (relatively low voltages and low to moderate voltage slew rates) pcb inductance is more of an issue than pcb capacitance. In my 45 year career I have had one situation where I know that capacitance between layers caused a problem. For reasons of low DCR, lower stray inductance, and better mechanical robustness I will generally use as much copper as I have space for. (OK on an inner layer I guess that mechanical robustness is less of an issue.) Of course a trace carrying 2 Amps should normally be wider than one carrying 20 mA. For my default (where there is enough space) I like to use 1 mm wide tracks for connecting to my 0603 chips which I hand solder onto a minimum sized 0805 footprint.
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