Calculate PCB Trace Width

There are two PCB trace width calculators available in the market — one based on graphs published by IPC 2221, and the other based on graphs published by the latest IPC 2152 standards.

The calculator (https://ninja-calc.mbedded.ninja/calculators/electronics/pcb-design/track-current-ipc2152) or (https://twcalculator.app.protoexpress.com/) based on the latest IPC 2152 standards is more accurate and requires more data input. However, for general purpose use, the calculator based on IPC 2221 is also helpful.

Both calculators find the minimum PCB track width for a specified continuous current and temperature rise. The calculations take into consideration the thickness of the copper track, its distance from planes, the entire thickness of the board, and the material the PCB uses.

IPC 2152 provides graphs, and the trace width calculator uses equations from the data extracted from these graphs. For this, the designers used the tool WebPlotDigitizer, with which they fitted suitable trend lines to the graphs.

The accuracy of the calculator based on the graphs provided by IPC 2152 is quite high, as long as the range of data lies within that provided by these graphs. Beyond this range, the equations tend to extrapolate, but the results can be inaccurate.

The calculator assumes the current to be DC and, hence, constant. However, it is also possible to use the RMS value for a pulsed current, provided the pulses are fast enough.

All PCB materials have a relative thermal index or RTI, and the designer must take care to never exceed the temperature of the PCB material beyond this RTI. The Underwriter Laboratories define this RTI as the temperature at which it is possible to retain at least 50% of the material properties of the material after 100,000 hours. However, this calculator will not take into account heat sources that are active nearby.

Details of Trace Width Calculator Based on IPC 2152

The calculator is basically a three-in-one calculator. The three parameters involved in the calculation are — trace width, maximum allowed temperature rise above the ambient, and maximum current capacity of the trace. Out the three, if the designer knows any two, the trace width calculator can calculate the third.

Additionally, the calculator also provides the DC resistance and the voltage drop across the trace for a given length. 

Expectations from the Trace Width Calculator

Trace width calculations are always critical for PCBs carrying high currents. Therefore, the designer must know the trace width that is just enough for carrying that high current. For instance, if the trace width is not adequate, the current flow may burn out the trace, and impact the functionality of the PCB.

With the trace width calculator, the designer can calculate only the trace width, but also the temperature rise and the amount of current the trace can handle. By altering any two of these parameters, the designer can find out the effect they have on the third parameter. 

As the calculator is based on the IPC 2152 graphs, the calculator provides the temperature rise in not only external traces (on the external surfaces of PCBs), but also in internal traces (buried in the internal layers of multi-layer PCBs).

For instance, the calculator shows that internal traces can also carry quite high currents similar to those external traces can carry. Convection air flow on external traces keep them cooler, and hence, they can carry higher currents. The trace width calculator allows change of units as necessary by the designer.

Using the Trace Width Calculator

While designing traces on a PCB, designers essentially consider four main parameters:

  • Trace Width (W)
  • Rise in temperature (ΔT)
  • Maximum Trace Current (Imax)
  • Trace Thickness (Th)

If the designer knows the Imax and ΔT, then the trace width calculator can provide the trace width for both internal and external traces.

The tool requires ambient temperature input and the trace length also. With these extra inputs, the tool can calculate additional parameters such as trace resistance at ambient and at elevated temperature, maximum voltage drop, and maximum power loss.

Conclusion

The trace width calculator based on IPC 2152 is a versatile tool for PCB designers. They can use it in multiple ways to calculate various parameters of a PCB trace under different operating conditions.