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Current Carrying Capacity of PCB tracks
The current carrying capacity of a PCB track is fundamentally
determined by two parameters:
The first parameter (Track resistance) can be easily calculated and compensated for by increasing copper thickness and track thickness.
The second parameter is more complex as a number of elements come into play. These include air moisture, mechanical orientation (which affects convection airflows), cumulative heating affects from adjacent tracks and components, and copper distribution adjacent to the track and on other parallel layers to the track..
For this reason calculating the exact current carrying capacity for a copper track, given a limiting temperature rise for the track, is complex.
The "Track Width Calculator" is based on data from IPC temperature charts. This calculator should only be used as a guide in determining track thickness for a given current load.
The calculator has a number of shortfalls which need to be understood by PCB designers in order to use this tool.
Copper thickness: The "track width calculator"
uses the input parameter of "Copper thickness" to determine
the cross section area of the copper track. PCB manufactures can produce
a given thickness by electro-plating onto a base copper foil (for
example a 2oz copper track may consist of a 1oz copper foil with 1oz
of electro plated copper on top of the foil), or they may use a straight
2oz base foil without plating. The current carrying characteristic
of the two are significantly different.
Thermal conductance of copper tracks: As mentioned
above, the current carrying capacity of a track is related to the
ability of the track to dissipate heat. If a track is connected to
a large copper area (plane), or even a via or pad, heat will be conducted
away from the track to the particular copper mass. This will increase
the track's ability to dissipate heat and hence increase the current
that the track can conduct, given the acceptable temperature rise
of the track.
Cumulative temperature rise: The "track width
calculator" uses the input parameter of "Ambient temperature"
to determine the copper track resistance for a given temperature rise
above this ambient.
Copyright © 2004 The PCB Company Pty Ltd All rights reserved - Last modified: Jan 18th 2016
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