What is PCB Trace Width Clearance?

PCB trace width clearance is associated with two things: the space between two traces and width of the traces. In any PCB circuit, 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. The trace clearance is also important from a product safety point of view. It could be of any dimension as long as it meets the minimum feature size. 

The current carrying capacity of the PCB track 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. PCB Trace width calculators are helpful during such cumbersome calculations.

Trace routing 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: Let’s assume you have 1 oz of copper on your PCB, which gives a thickness of 1.38 mils (0.035 mm).

First of all, the area needs to be calculated.

Area [mils²] = (Current [Amp]/ (k x (Rise in Temp. [deg. C]) b))(1/c)

Where,

For IPC-2221 external layers, k = 0.048, b = 0.44, and c = 0.725

For IPC-2221 internal layers, k = 0.024, b = 0.44, and c = 0.725

After area, trace width can be calculated as:

Width [mils] = Area [mils²]/ (Thickness [oz] x 1.378 [mils/oz]) 

IPC-2221 are general PCB standards, which lists the minimum spacing between conductors for various conditions such as internal vs. external, coated vs. uncoated, high or low altitude, and traces vs. component leads. Determination of appropriate trace sizes based on current requirements is an important aspect of PCB development. Since copper is not a perfect conductor, it offers a certain amount of impedance against the current flowing through it, and some of the energy is lost in the form of heat.