An autorouter is perfectly fine for whole classes of electronics. As a basic rule, if you'd happily assemble the circuit on a breadboard or with jumper cables and not worry about signal continuity, the autorouter will be fine.

It's only when you get to higher speed or higher currents that an autorouter won't have the context needed to effectively route the circuit.

But that's strange, isn't it? Higher currents basically just require wider traces, higher frequencies require very specific trace lengths.

That's nothing that can't be incorporated into an auto router.

I think I should have added the caveat "with the typical information we give it".

I suspect that if we made enough effort at the schematic stage to properly annotate all the nets and define the types of signals flowing around the board, an autorouter could do a superior job to a human (from an RF emissions and trace current sense).

I've never seen a schematic with that level of annotation though. So as long as the person doing the layout has to use external knowledge of what they're laying out, autorouters will struggle.

In theory you could make EDA software which incorporated a full circuit simulation which was then fed into the autorouter to provide a layout optimised for low-EMI and high efficiency. That would be nice!

Yea - I wish I had the time to write one which understands differential impedence, matched lengths etc.

Perhaps one exists, I don't know as I try to only use open source.

I am pretty sure that I saw some ads for a commercial PCB cad program that showed functionality for exactly that.

But yes ... probably not open source.

I didn’t get the sense the autorouter was used anywhere near as often as that.

I don't think it is ... and I think some it is some sort of "get of my lawn"-ism. I passed a degree in electrical engineering at some point (haven't used it too much after that), and "don't use the auto-router" is basically what is taught from day zero.

So ... while I can't say anything about PCB design in industry ... I can say that I tend to use a auto-router for my small DIY audio projects and it has never really failed me.

And ... if auto-routers are not used in the industry ... maybe that is something somebody on here should "disrupt" ... computers have become just too powerful not to be combative in solving some constraint path finding problems.

I tried using the auto-router in KiCAD on my last <simple hobbyist> design and realized that it had been removed from KiCAD.

There was some external package that could do it, but at that point “screw it, I can route this board faster than reading the docs on how to deal with the autorouter” took over, especially since I couldn’t be sure anything I learned for this project would still apply for my next project if KiCAD later re-added an autorouter.