RobustPCBWhere Robust Design Starts
CalculatorsالعربيةUpgradeSign inSign up

What's new

Full changelogEngine 1.18.3

Trace Resistance & IR Drop

PCB & Copper

Resistance, voltage drop and loss of a copper run, at its operating temperature.

Inputs

Board profile

Fills Copper weight and Copper temperature from your board profile.

A
°C
V
Untick if the return is an identical trace; the drop doubles

Results

1 passed
Trace resistance R

Not judged: a resistance has no pass or fail. Compare the drop below with your budget.

121 mΩ at 25 °C, 0.0 % higher hot
121.2mΩ
Drop as % of rail
1.84%
Power dissipated
30.31mW
All results (4)
Squares

length ÷ width
240
Sheet resistance

1 oz at 25 °C
505µΩ/sq
Voltage drop Vdrop

signal path only
60.62mV
Copper volume
2.09mm³
Plane return: the return current flows under the trace and adds almost no resistance.

Accuracy

Verified against

1 independent case. See the working.

This is a design aid. The engineer remains responsible for the design and for checking the standard itself.

Parameter sweep

Vary one input over a range and see the answer and verdict at each step, as a table and a curve.Pro

Worst-case corners

Put a tolerance on each input and get the worst-case band around the answer.Pro

Geometry

The principle

Every trace is a resistor. On low-voltage, high-current rails its IR drop is often the largest error in the supply.

Resistivity with temperature
ρ(T)=ρ20[1+α(T−20)]\rho(T) = \rho_{20}\left[1 + \alpha (T - 20)\right]
ρ₂₀ = 1.724 × 10⁻⁸ Ω·m (IACS annealed copper), α = 0.00393 /°C.
Trace resistance
R=ρ lw tR = \frac{\rho\,l}{w\,t}
Squares form
R=R□⋅lw,R□=ρtR = R_{\square}\cdot\frac{l}{w}, \qquad R_{\square} = \frac{\rho}{t}
About 0.49 mΩ/sq for 1 oz at 20 °C. ½ oz doubles it; 2 oz halves it.
Drop and loss
Vdrop=IRP=I2RV_{drop} = I R \qquad P = I^{2} R
Skin depth (for AC)
δ=ρπfμ≈66f[Hz]  mm\delta = \sqrt{\frac{\rho}{\pi f \mu}} \approx \frac{66}{\sqrt{f_{[\t{Hz}]}}}\;\t{mm}
At 1 MHz δ ≈ 66 µm, about the thickness of 2 oz copper. Above a few MHz the DC value is optimistic.
  • R□R_{\square}sheet resistance, ohms per square
  • l/wl/wnumber of squares along the path
  • α\alphatemperature coefficient of copper, 0.00393 /°C
  • δ\deltaskin depth: at high frequency the current flows in this layer
More detail

Where drop matters most

  • Low-voltage cores. 50 mV on a 1.0 V rail is 5 %, more than the whole regulation budget. Use remote sense.
  • Sense and feedback paths. Drop in a shared ground adds directly to the measurement. Take feedback from the load side, and use a Kelvin connection at a shunt.
Budget the loop, not the trace. Current that goes out must come back. Unless the return is a solid plane directly beneath, count it twice.

Evaluate the drop hot: at 100 °C copper has about a third more resistance than at 20 °C. Check the narrowest point, such as a pad neck or thermal relief, not the average width.

Related: Trace Width for the IPC-2221 thermal limit, Via Current & Resistance for layer transitions.

Engine version ⁨1.18.3⁩