Altium Designer Documentation

Convert Tracks to Chamfered Path

Created: August 1, 2018 | Updated: August 1, 2018


Selected tracks will be chamfered by the specified amount at each right-angle corner.

Summary

The chamfering of 90 degree routing corners is a technique used to reduce reflections caused by the corner in a microwave frequency route. Arcs can be used but should have a radius of at least 3x the route width. Chamfering (also called mitering) is an alternative where the outer point of the corner is sliced off. Because Altium Designer's track objects have rounded ends, they cannot be used to create a chamfered corner. To create the chamfered corner, the selected track segments are replaced with region objects.

Access

First, select all the track segments to be chamfered. To do this, select a single segment then press Tab to extend that selection to all connected segments on the same layer. Press Tab a second time to select all net objects on all layer then press Tab a third time to return to your original selection.

Then, select Tools » Convert » Convert Selected Tracks to Chamfered Path from the main menus.

Options/Controls

  • Chamfer - amount of the outside corner that is to be sliced off, or chamfered, as a percentage of the existing diagonal corner distance.
  • Inside Chamfer - amount of material to be added to the inside corner as a percentage of the existing diagonal corner distance.

The percentage mitre is the cut-away fraction of the diagonal between the inner and outer corners of the un-mitred bend. 

The optimum mitre for a wide range of microstrip geometries has been determined experimentally by Douville and James. They find that a good fit for the optimum percentage mitre is given by

Subject to  and with the substrate dielectric constant .

This formula is entirely independent of . The actual range of parameters for which Douville and James present evidence is  and . They report a VSWR of better than 1.1 (i.e. a return better than −26 dB) for any percentage mitre within 4% (of the original ) of that given by the formula. At the minimum  of 0.25, the percentage mitre is 98.4%, so that the strip is very nearly cut through.

The process of chamfering converts multiple track segments into a single region object. This is a one-way process; once the tracks have been converted to a region, they cannot be converted back. For this reason chamfering should only be performed once all routing is complete. If you are unsure, save off a copy of the board before chamfering.

 

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