PCB Trace Width and Calculations

What is a PCB Trace?

The point of a PCB trace is to connect any kind of electrical signal, whether it be analog, digital, or power, from one junction to another.

The junction can be the pin of a component, a branch off of a larger trace or plane, or an empty pad or test-point intended for probing.

Trace widths are often measured in mils or thousands of an inch.

The application will often drive the trace widths and types in a PCB design and at a certain point, there is usually a balance with regards to PCB fabrication cost, board density/size, and performance

Step 1: ​PCB Trace Width Clearance?

It is associated with two things: the space between two traces and the width of the traces.

the voltage difference between two tracks decides the spacing between them while how much current will they carry is based on the trace width.

After deciding the trace width, the cross-sectional area of the PCB can be evaluated, which helps to determine the resistance per unit length.

PCB Trace width calculators are helpful during such cumbersome calculations.

Step 2: Trace Routing

It is used to distribute power and ground to components on the PCB circuit. The traces must be large enough for the current they are carrying.

The Institute for Printed Circuits (IPC) has
prescribed some trace width clearance rules to define the minimum width for a given current requirement and PCB trace spacing clearance rules to determine the shortest path between two conductive traces. Trace width selection accounts for the following attributes:

How much current will flow through the track? The allowable spacing between the tracks Size and pitch of the pads associated with the track

Usually, manufacturers increase the trace width to improve its current carrying capacity, but it requires elaborative calculations:

Step 3: The Current Carrying Capacity of the PCB Track

It is the maximum amount of current it can handle before failure or overheating. Passing a high current may destroy the trace. Ideally, a trace has zero resistance, but this definitely not the case. All traces have resistance and it is very important to consider it.

Knowing the correct resistance value eventually helps to determine the exact amount of current a track will carry.

Step 4: PCB Fabrication Costs.

The costs become considerably higher due to tighter PCB tolerances and higher-end equipment needed to both manufacture and inspect or test the PCBs:

Trace widths narrower than 5 mils (0.005”) Trace spacing closer than 5 mils Via holes with a diameter smaller than 8 mils Trace thickness thinner or thicker than 1 ounce (which equates to 1.4 mils) Differential pairs and controlled lengths or trace impedance.

Step 5: Process of Calculations

The process of calculating for a certain trace width for a power signal delivering current from one power component to a peripheral. In this example, we’ll be calculating the minimum trace width for a power-path used for a DC motor. The power-path starts at a fuse, travels through an H-bridge (a component used to manage power delivery across a DC’s motor windings), and ends at the motor’s connector. The average continuous max current demanded by the DC motor will be around 2 Amps.

Now, a PCB trace acts as a resistor, and the longer and narrower the trace, the more resistance is added. If the trace isn’t properly defined, the high current could damage the trace and/or introduce a significant voltage drop to the motor (resulting in a slower speed). NetC21_2 shown in Figure 3 is about 0.8” long and needs to carry 2 Amps max. If we assume some general things like a 1-ounce copper pour and ambient room-temperature during normal operation, we have what we need to calculate both the minimum trace width and expected voltage drop at that width.

PCB Trace Width Calculator

Trace width is an important design parameter in PCB design. Adequate trace width is necessary to ensure the desired amount of current can be transported without overheating and damaging your board. You may use this online tool to calculate an estimate of the minimum trace width for a given current and copper weight. A higher current requires thicker traces while a thicker copper weight allows for thinner traces.