PCB Trace Resistance & IR Drop
DC resistance of a copper trace, the IR drop and power loss it costs at your current.
Why a "zero-ohm" trace isn't
Copper has resistance, and on a power or ground trace that resistance turns into a voltage drop the load never sees, plus heat the board has to shed. The DC resistance of a trace is:
where ρCu = 1.724×10⁻⁸ Ω·m, t is the copper thickness
(35 µm for 1 oz), and α ≈ 0.39 %/°C is copper's temperature coefficient — so a
trace that's fine on the bench gets ~30 % more resistive by 100 °C.
The drop matters most on low-voltage, high-current rails: 200 mV lost on a 1.2 V core rail is 17 % of the budget. The fixes are the usual ones — wider copper, more copper weight, shorter runs, or a plane instead of a trace. This tool is the DC half of power integrity; for the AC half see the PDN / decoupling calculator.