Tutorial How To Design High Current PCB?

When it comes to PCB design, the limitations posed by the capacity of the PCB’s circuit current are critical. The current capacity of the wires on the PCB is determined by such factors as the width of the wires, the thickness of the wires, the maximum temperature rise required, whether the wires are inner or outer, whether they are covered with solder resistance, etc. In this article, we will discuss the following points:

What is PCB trace width?

PCB wiring or copper conductor on a PCB that transmits signals across the PCB surface. What is left after the etching is a narrow section of the copper foil, and the current flowing through the copper wire creates a lot of heat. Correctly calibrated PCB trace widths and thicknesses help minimize heat buildup on the board. The wider the wire width, the lower the resistance to the current, and the less heat is accumulated. PCB trace width is the horizontal size of the trace, while thickness is the vertical size of the trace.

PCB design always starts from the default route width. However, this default trace width is not always appropriate for the desired PCB. This is because you need to consider the current carrying capacity of the trace to determine the trace width. There are several factors to consider when determining the correct trace width:

1. Copper Layer Thickness — The copper layer thickness is the actual wire thickness on the PCB. The default copper thickness for high-current PCB is 1 ounce (35 microns) to 2 ounces (70 microns).
2. Cross-sectional Area of Wires — For a PCB to have higher power, a larger cross-sectional area is required for the wires, which is proportional to the wire width.
3. Position of trace — bottom or top or inner layer.

How to design high current PCB?

Digital circuits, RF circuits, and power circuits mainly process or transmit low power signals. The weight of copper in these circuits is 1-2oz and the current-carrying current is 1A or 2A. In some applications, such as motor control, up to 50A of current is required, which will require more copper on the PCB and greater wire width. The design approach for high current requirements is to widen the copper conductor and increase the thickness of the conductor to 2oz. This will increase the space on the board or increase the number of layers on the PCB board.

High current PCB layout criteria:

Reduces high current wire length

Longer wires have higher resistance values and also carry higher current, resulting in greater power loss. Because power loss generates heat, circuit board life is shortened.

Calculate the trace width when the temperature rise and fall is appropriate

The trace width is a function of variables such as the resistance and the current through it and the allowable temperature. In general, a temperature increase of 10℃ is allowed at ambient temperatures above 25℃. An increase of up to 20°C may be allowed if the material and design of the plates permit.

Isolate sensitive components from high-temperature environments

Some electronic components, such as voltage reference, analog-to-digital converters, and operational amplifiers, are sensitive to temperature changes. When these components are heated, their signals change. High current plates are known to heat up, so the above components need to be kept at a distance from high temperatures. You can do this by cutting holes in the board and providing a radiator.

Remove solder resistance layer

To increase the current flow capacity of the cable, remove the solder barrier and expose the copper underneath. Additional solders can then be added to the lead, which will increase the thickness of the lead and reduce the resistance value. This will allow more current to flow through the trace without increasing the width of the trace and without adding additional copper thickness.

Use the inner layer for high current routing

If the outer layer of the PCB does not have enough space for thicker wiring, the inner plate layer can be filled with wiring. Next, you can use a high current device connected to the outer layer through the hole.

Add copper strips for higher current

For electric vehicles and high-power inverters with currents over 100A, copper wiring may not be the best way to transmit power and signals. In this case, you can use copper bars that can be soldered to PCB pads. The copper bars are much thicker than the wires and can carry large currents as needed without any heating problems.

Use through-hole stitching to carry multiple wires across multiple layers that carry high current

When the wires cannot carry the required current in a single layer, they can be wired over multiple layers and treated by a stitching method that connects the layers together. This will increase current carrying capacity in cases where two layers are of the same thickness.

Conclusion

There are many complicating factors in determining the capacity of routing current. However, PCB designers can rely on the reliability of the thread-thickness calculator to help efficiently design their boards. When designing a reliable, high-performance PCB, the right wiring width and current carrying capacity can go a long way.