Efficient Tool Sizes High-Current PCB Traces

In this example, it’s easy enough to refute these guidelines on trace width. Most motherboard designs and VRM modules use much smaller traces due to the very short traces used. However, you will find that they never drop below the 30-CM/A guideline and they rely on the component masses, solder, heatsinks, etc., to pull heat out of the whole system, including the traces. It’s also noteworthy to mention that the output frequency will be 1.5 MHz into the capacitor bank. The depth of penetration in this trace will be roughly 2.4 mils, so the ripple currents will flow through most of the trace.

The table offers other features like resistance of the conductor (ohms per foot), via cross sections, temperature classifications, and equivalent square mil and square millimeter cross sections. This isn’t rare or obscure information, but rather a collective means to show well known guidelines and a handy tool.

I’ve heard that high-end PCB design and circuit-simulation tools actually have built-in programs to size PCB traces. Since I haven’t used these programs, I can’t comment on their effectiveness or correlate them to common-sense current-density values.

The PCB design world continues to push toward higher and higher power densities. Therefore, PCB traces carry more and more current per unit cross section. As a result, designers must have a reasonable understanding of a PCB’s current-carrying capabilities and, perhaps, follow a couple rules of thumb. Also, I have triangulated the fundamental cross-section values with numerous sources from the U.S. Navy to the NEC code book. I maintain the utmost confidence in the validity of the baseline data.

Reference

1. Fink, Donald G., and Beaty, H. Wayne, Standard Handbook For Electrical Engineers, 14th Edition; McGraw-Hill Professional, Oct. 1, 1999, ISBN 0-07-022005-0.