Wednesday, April 20, 2005

Current carrying capacity of tracks

In the table the following are assumed

* 1oz/sq foot copper (0.035mm thickness).
* 10 degree C rise on outer layers, 20 degree C inner layers
* Groups of high current tracks will be de-rated
* Tracks are not near or over 'Heat Sink' areas

Imperial Width Metric Width Current Capacity

0.010" 0.25mm 0.8 Amps

0.015" 0.38mm 1.2 Amps

0.020" 0.50mm 1.5 Amps

0.050" 1.27mm 3.2 Amps

0.100" 2.5mm 6.0 Amps

For most purposes it will be easy to determine a practical width from the above. If you want to make more precise calculations (based, it must be noted, on empirical data) try the formula
I = 0.048 T0.44 A0.725
Where the units are

I Amps

T Temperature Rise in °C

A Cross sectional area in square mils (square THOU)

This formula is for outer layers, and needs to be de-rated to 50% for inner layers.
References to this formula can be found Here in the section PCB Data.

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