PCB Trace Width vs. Current Table: How To Balance The Two

We will compare PCB trace width vs. current table below to understand the best copper trace design practices. 

Copper is a good conductor of electricity and is the ideal metal for making PCB traces. Although it has a high melting point, you should keep the temperatures in these power rails low. 

Heat can damage sensitive PCB components. And if too thin, the line can act as a fuse, burning out when excessive current passes through. 

So design the trace width to handle the maximum current in that circuit section without overheating. Let’s look at how to calculate this width below.

What Is a PCBs Trace Width?

Circuit board traces are the wires that connect components in PCBs, and they can form continuous paths in multiple layers. 

Ohm’s law applies to the circuit as electricity runs through these transmission lines. 

So if a high current flows through the lines, they will generate heat because the resistance in thin wires is high.

You might notice a default trace width set on the CAD programs during design, but this parameter might not be the best for your circuit.

 Instead, consider the conductive lines’ required current carrying capacity to calculate the most appropriate track width.

And consider these factors, as well.

• Trace length
• Track layer in the stack (heat cannot escape easily from internal layers)
• Copper layer thickness

What Are Current Tables?

Current tables define the correlation between the track width and its current carrying capacity. 

This current carrying capacity is the highest current level the power trace can handle without exceeding the maximum temperature rise. 

PCBs have maximum operating currents, and you should not allow the traces to heat up and exceed this level.

Here’s the IPC recommended track width for 1oz. copper PCB with a 10°C maximum temperature rise.

Relationship Between Trace Width and Current Carrying Capacity

The relationship between these two variables is resistance. And resistance depends on the cross-sectional area of the wire (trace thickness and width).

But determining this width needs multiple calculations because several other factors determine the current-carrying capacity. Let’s look at these formulas.

How To Calculate Trace Width Using a Trace Width Calculator

A trace width calculator helps you determine multiple trace components using these formulas.

Maximum Current

You can calculate the maximum current using the formula below.

A = (T x W x 1.378 [mils/oz/ft²])

Where:

• A is the cross-section area
• T [mils2] is the PCB trace thickness
• W [oz/ft²] is the track width

Once you get the cross-sectional area, transfer it to this equation to calculate the max current.

I_MAX = (K x T_RISE^b) x A^C

Where:

• I_MAX is the maximum current
• [A] T_RISE is the maximum allowable temperature rise
• [°C] b, c, and k are constants

A circuit board with thick and narrow traces

Trace Temperature

The next critical variable to calculate is the trace temperature, which we calculate using this formula.

T_TEMP = T_RISE + T_AMB

Where:

• T_TEMP is the copper trace temperature
• T_RISE is the maximum temperature increase
• T_AMB is the ambient temperature

These values must be in °C.

Power Dissipation Calculation

Power dissipation or power loss is the energy wasted in the form of heat when the trace temperature increases.

You can calculate it using this formula.

P_LOSS = R x I²

Where:

• P_LOSS is the power dissipation (loss)
• R is the resistance
• I am the maximum current

Voltage Drop Calculation

Voltage drop defines the reduction in electrical potential as electrical current moves through the printed circuit board. Use this equation to calculate this drop.

V_DROP = I x R

Where:

• V_DROP is the decrease in electric potential
• I is the maximum current
• R is the PCB trace resistance

A voltage stabilizer with voltage drop

Trace Resistance Calculation

You first have to convert the cross-section area from mils² to cm² units. Use this formula for the conversion.

Area in cm² = Area in mils² x 2.54 x 2.54 x 10^-6

After that, use this trace resistance calculator formula.

R = (p x L/A) x (1 + a x (T_TEMP – 25°C))

Where:

• R is the trace resistance in mils
• p is the resistivity parameter in ohms
• L is the trace length in cm
• A is the area in cm² calculated above
• a is the resistivity temperature coefficient in cm
• T_TEMP is the trace temperature (1/°C)

Trace Width Calculator Limits

With these formulas, you can only calculate the variables up to the following limits.

• Trace width up to 400 mils
• 35 amps maximum current
• 10-100°C temperature rise
• 0.5-3oz. per square foot of copper thickness

PCB Trace Width vs. Trace Thickness

The copper thickness and width of a PCB trace determine its cross-section area. And we define the thickness using the amount of copper used to make the copper layer.

 Similarly, we determine the copper layer using its weight (the amount of copper that fills a square foot).

So 1oz. of copper poured evenly on an area covering one square foot will be 1.4 mils thick. And 3oz. will be 4.2 mils thick. 

Therefore, if you have a single layer with 0.5oz. of copper, the trace thickness will be 0.7 mils.

But the trace width is easier to determine because it is the distance across the cross-section area.

So with the trace thickness and the required operating current, you can calculate the trace width when creating the PCB layout.

Conductor tracing in a multilayer circuit board

High Current PCB Design Guidelines

Use these guidelines when designing high-current PCBs to avoid thermal incidents.

Design Short Traces

Long traces increase resistance. So it is better to keep them as short as possible if transmitting a high current. 

And since resistance generates heat, using long conductive lines will damage large PCB sections over time. So shortening them increases board durability and reliability.

Use Heavier Copper

The standard copper thickness in circuit boards is 1oz. per square inch (17.5 microns). Consider using heavy copper in high-current circuit boards to reduce resistance.

 The typical thickness should be 3-4oz. per square inch (35-50 microns) to handle at least ten amps.

Isolate Thermally Sensitive Components

High temperatures can alter the signal output of sensitive components like:

• ADC converters
• Voltage references
• Operational amplifiers
• Regulators

So separate them using cutouts and position them far from the high current power traces.

Mount Components Appropriately

High-power components have high thermals and can damage the board if placed near the edge due to uneven heat distribution. 

But positioning them in the middle distributes the heat in all directions. And if they are several, spread them evenly to eliminate heat spots.

A 3D illustration of a high thermal PCB component positioned inappropriately

Eliminate the Solder Mask

Removing the solder mask layer exposes the circuit traces, which you can support with additional solder to boost the thickness. 

This increase will allow more current through without incurring the costs of increasing the copper material.

Use Polygon Pours

Microprocessors and FPGAs come in LGA and BGA packages with a high current draw.

 You can place polygon pours under the chip and drop vias to connect them to enable the high current flow.

 After that, link the polygon pours to thick power planes or traces.

A microprocessor mounted on a PCB

Use Via Stitching, Thermal Vias, and Thermal Landing

Via stitching allows you to transmit high current levels using multiple traces in different layers

. So you’ll be able to maintain the same narrow trace width in the layers.

As for thermal vias, you can use them for heat transfer away from high current lines and sensitive components.

 This heat can go to the thermal landing, which functions like a heat sink.

Add Copper Bars

You cannot use copper traces to transmit high current levels that exceed 100A. The best option would be to solder copper bus bars to the PCB pads to link the components. 

These bars are thick enough to transmit such electrical currents without overheating.

Use Internal Layers for High Current Transmission

Design a solid internal copper layer if there isn’t enough space in the outer layers to have thick PCB traces. 

Couple this design with Vias to link the high-current devices to the power plane.

Wrap Up

The trace width property is critical in circuit boards because it determines the maximum current carrying capacity. 

And as you can see above, you need to do multiple calculations and consider several guidelines when designing these tracks. 

That’s it for this article. Contact us below if you need assistance laying out your board’s power lines. We’ll be in touch to help.