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PCB Trace Width vs. Current Table

A PCB trace width vs. current table helps you understand the relationship between PCB trace width and current carrying capacity so you can determine the required trace width for your printed circuit board design.

table for 1 oz. coppecurrent capacity

Relationship Trace Width and Current Carrying Capacity

The relationship between trace width and current carrying capacity in your printed circuit boards is fairly straightforward. Specifically, a cross-sectional area of trace and temperature rise determine your current carrying capacity, with your cross-section of trace directly proportional to copper thickness and trace width.

However, this does not necessarily mean that trace carrying capacity is directly proportional to cross-sectional area. Calculating the maximum current that a trace is able to hold based solely on trace width and temperature rise is not always a simple calculation, as you may already have found. Why should this be the case?

Elements Determining Maximum Current Carrying Capacity

The reason why it is not so easy to apply a direct formula to figure out the maximum current carrying capacity when you have the information about cross-sectional area and temperature rise is that there are other elements involved in determining maximum current capacity that you have not considered. Current carrying capacity can also be significantly affected by the number of vias, pads and components.

For example, if a high number of pads are distributed throughout the traces, you will find any tin-coated trace performing at a significantly higher capacity than other traces. If you do not compensate for this, you may end up putting too much solder on and creating a higher cross-sectional area without effectively modifying the trace, with the result that you get a huge transient surge or your trace could burn down entirely.

So how do you compensate for such a situation? The best solution is to increase the width of the trace. If this is not possible, you can always add solder mask to the traces that are in danger of burning down. Print the solder paste in your SMT procedure so that trace width will rise after reflow soldering, increasing your current carrying capacity.

The following table will definitely be useful to you in figuring out trace current carrying capacity, but you must also take into account other factors like contaminant pollution. During actual printed circuit board fabrication, debris can get into the PCB and create broken traces.

For this reason, even if you have calculated the current carrying capacity perfectly, you want to have a failsafe in case broken traces that go unnoticed allow overloading. You will also want to pay close attention to the turning traces because an acute angle in a trace could interfere with the smoothness of the transfer. If you are dealing with very slim current carrying margins, this could create a problem.

For more information about trace width and current carrying transfer on printed circuit boards, visit us online or call us now at 717-558-5975.