How do i identify my pcb trace need how much depth?

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Lets break this down and keeping this KiCad centric.
cross-sectional area of a trace influences how much current it can carry, the length influences the voltage drop.

Fundamentally a track is just a resistor and thus also exhibits the same traits in as far as it will warm up and drop some voltage AND at some point fail … To choose the correct track characteristics you need three additional inputs

  1. What is the copper weight you will be asking your fabricator to build - 0.5oz, 1oz …
  2. How hot do you want this track to operate at - +5C, +10C…
  3. How much voltage drop across this track can you accomodate?

Since the current handling capability is associated with the cross sectional area once you know the copper weight of your PCB you know the depth (0.5oz ~ 18um) and thus the only other parameter you can influence is track width.

Under Board setup you can predefine track widths and under Net Classes you can assign certain widths to certain nets (following rules).

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So how wide should you use? Well KiCad also includes a calculator. NOTE: this follows the IPC-2221 definition which isn’t accurate and this does need to be updated to IPC-2152 …which is harsher (I have some code to submit :frowning: )

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So once the trackwidth is determined for a certain PCB copper thickness and for a certain temperature rise KiCad can be configured for this.
It is then the responsibility of the PCB design to track this from SOURCE to LOAD… the longer the track the higher the voltage drop this “resistor/track” will create which will reduce the voltage seen at the LOAD. You might have 15V at the SOURCE but could end up with 14V at the LOAD (if poorly designed) and if this isn’t acceptable then the voltage drop needs to be reduced and the only things that can be done are

  1. shorten the track
  2. widen then track
  3. increase the copper weight.

The other consideration is the FUSING … Onderdonk’s equation (again in KiCad calculator).

So for 20A and 100mm..
Additional design constrains could be

  1. Temprise <5C
  2. Voltage drop < 0.1V
  3. 18um (0.5oz) copper

The KiCad calculator (IPC-2221) advises:
External: 55mm wide track and 0.068V drop
Internal: 144mm wide track and 0.026V drop

An IPC-2152 calculator advises:
Calc: 180mm wide track and 0.02V drop

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