Melting KiCad – making curved traces

KiCad has improved a lot, but one of the features it’s really lacking is the ability to do smooth, rounded traces with teardrops (fillets on pads and vias).

A lot of early, hand drawn PCBs had this look, where every connection is smooth and slightly melted.

When people first switched to using computers to design circuit boards, the routing options were very limited and traces were forced to have sharp corners. Some people forget that our tendency to restrict traces to 45° angles is mainly a holdover from before there were any other options.

Some of the benefits of teardrops and smooth traces are controversial, but the following can generally be agreed upon:

  • Smooth corners are potentially less prone to errors in the etching process
  • In the case of drill/pad misalignment, teardrops reduce the chance of a breakout
  • For flexible PCBs, sharp corners are stress concentrators, so removing them reduces the chance of cracking
  • Denser routing is possible when arbitrary angles are permitted
  • There may be some electromagnetic compliance (EMC) benefits, since sharp transitions represent a sudden change in impedance

Curved traces are apparently on the roadmap for KiCad 6, which hopefully isn’t too far in the future, but I’m not holding my breath.

Another way to add functionality is via “action plugins” – Python scripts. This is in many ways more limited, but has the massive benefit of not needing to recompile the KiCad source code.

See the details in the post here.

The improvements to the teardrop plugin have been submitted and merged into Niluje’s kicad_scripts repo. The plugin can be found here.


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