Current Carrying Capacity
Rev. 2.2

Continous current carrying capacity of a trace: (t>>10 sec.)

The model below calculates the relationship between current and temperature rise. It comes from UltraCAD, (Temperature Rise in PCB Traces Eq. 11). The origin of this model is presented in the article in Design News, Vol. 23, from the 6 December 1969. The article describes the experiments of leading current through copper traces in different sizes. The results were adapted to the mathematical functions, that are used here.

Give the known parameters below and push the Calculate button.

The trace is placed in an:

Increase of temperature: [°C]
Width of trace: [mm]
Thickness of trace:[um]
Current carrying capacity: [Ampere]

A trace with the length of cm will have a potential drop of V and a resistance of ohm.

Note: When producing a multilayer PCB the tolerances of the trace thickness are normally quite large in the outer layer. This implicates that it is difficult to get traces with exact resistances in the outer layer. On the other hand, leading current in an inner layer can entail cooling difficulties. (FR4-laminate transforms into electric conducting graphite at overheating. This can result in a short-circuit.)

Transient current carrying capacity of a trace: (t<10 sec.)

At transients the trace must be prevented to be as hot by the current as the metal melts.

Increase of temperature:[°C]
Width of trace: [mm]
Thickness of trace:[um]
Transient time: [sec]

Current carrying capacity: [Ampere]

Current carrying capacity of vias (t>>10 sek.):

Increase of temperature: [°C]
Board thickness: [mm]
Diameter of the via:[mm]

Current carrying capacity: [Ampere]

* Rule of thumb: A microvia corresponds at least a trace with the width 4mil=0.1mm, the thickness 13um and stands a current of 0.2A.

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Last uppdated: 2008-06-17
Sören Nilsson