What are autorouters good for?

[Artlav]

A few years ago i started making my own PCBs, with Eagle.
It had an interesting-sounding button in there, called "auto", that was supposed to route the PCB automatically.
Great!

Except it wasn't.
The results are best described as chaotic, so i tried it a couple of times and wrote it off as a useless feature.

Since then i've heard many times that autorouters are useless for simple boards, complex tools, should not be used, etc, etc to the effect that "it's not worth using".
However, i was just listening to one of Dave's old rants and noticed the "complex tools" and "good when set up right" parts this time around.

Which raises the question - what autorouters are good for?
Where and how to use them?

[ElektroQuark]

They are for fast IC SMD to DIP adapters

[tom66]

I think they have applications on boards like these.
http://www.shopjimmy.com/media/catalog/product/cache/1/image/f8f28dc4a19c21aeb55ee5774693fb5d/s/h/shopjimmy-bn96-06760a-top.jpg

Lots of parallel buses, with length matching being non-critical.

[zapta]

I use the eagle autorouter on all of my boards. I first route manually the critical nets (~30%) and then unleash the router on the rest. I also use it during the placement as a quick evaluation of the routability of a specific placement. It's awesome and I don't care about aesthetics , just functionality.

[Dago]

The only autorouters that are good for anything require you to input so much data that it is almost easier to route them by hand...

But autorouters are good for large boards where there are massive amounts of traces in a confined space (like a PC motherboard) that need to be delay matched etc. This excludes basically all hobby level projects.

[zapta]

The only autorouters that are good for anything require you to input so much data that it is almost easier to route them by hand...

With the eagle router I typically need to change only one parameter, the grid size. The default value is to large.

[nctnico]

But autorouters are good for large boards where there are massive amounts of traces in a confined space (like a PC motherboard) that need to be delay matched etc. This excludes basically all hobby level projects.

I'm not sure an autorouter would be capable of routing such a board. I think that a PC motherboard is mostly hand work with lot's of pin swaps.

[Wilksey]

Depends on the autorouter.

For me, I use Eagle's auto router a lot, a few tweaks on sizes and run direction on different layers, it's functional in any case.

The only rule I have is power and high speed / RF traces are hand routed, everything else is auto routed and as far as I am concerned it does a good job.

Some people don't like them for various reasons, some people can't use them, it takes a small amount of time to set up the auto router, but the time spent saves me ages manually routing.

[AlfBaz]

Auto routers were handy back in the day where a lot of small logic IC's were used and signal integrity was pretty much a non issue.
Here's an old pdf written ages ago for the Electra shape based router. If memory serves, it was written by a guy who use to frequent the old Protel EDA mailing list many moons ago. It gives you an idea of what's involved in setting one up to get decent output

[Dago]

But autorouters are good for large boards where there are massive amounts of traces in a confined space (like a PC motherboard) that need to be delay matched etc. This excludes basically all hobby level projects.

I'm not sure an autorouter would be capable of routing such a board. I think that a PC motherboard is mostly hand work with lot's of pin swaps.

They are not fully routed with an autorouter of course. Just buses with a lot of hand work thrown in as well.

[Dago]

The only autorouters that are good for anything require you to input so much data that it is almost easier to route them by hand...

With the eagle router I typically need to change only one parameter, the grid size. The default value is to large.

And the result is totally useless, there you go

[zapta]

The only autorouters that are good for anything require you to input so much data that it is almost easier to route them by hand...

With the eagle router I typically need to change only one parameter, the grid size. The default value is to large.

And the result is totally useless, there you go

The boards work very well. No problem whatsoever.

[nctnico]

Depends on the autorouter.

For me, I use Eagle's auto router a lot, a few tweaks on sizes and run direction on different layers, it's functional in any case.

Some people don't like them for various reasons, some people can't use them, it takes a small amount of time to set up the auto router, but the time spent saves me ages manually routing.

Can you post a picture from an autorouted board?

[zapta]

Here is one (PDF):

https://github.com/zapta/linbus/blob/master/injector/eagle/injector_top.pdf?raw=true

~30% manual, then the rest is automatic.

[nctnico]

That is not a very good layout. I spot several traces which could have been on the top layer right away.

[zapta]

The boards work great and the ground plane has good connectivity. 

As I said, I am after functionality, not asthetics or perfection and the autorouter was very helpful.

[Precipice]

As I said, I am after functionality, not asthetics or perfection and the autorouter was very helpful.

Indeed, and on a board like that, the autorouter must have saved you two, maybe three minutes? Maybe a beer?
The design, and component placement, take the time, and you did that manually (and fine, imho). The routing, meh.

[zapta]

Indeed, and on a board like that, the autorouter must have saved you two, maybe three minutes? Maybe a beer?

I find auto router it to be very useful for me. Apparently you try to convince me for some reason not using it. Oh, well... 

[nctnico]

In my experience I spend 80% of my time on placing the components. Routing the traces is peanuts.

[miguelvp]

In my experience I spend 80% of my time on placing the components. Routing the traces is peanuts.

Because you spend 80% of your time placing it

[nctnico]

That is because I want my board to look nice. I have used autorouters in the past but usually the location of holes and connectors make placement a complex puzzle.

[Mattylad]

I recently used an autorouter to route the inner layers of an old design full of TTL etc. (4000+ pins)
Because I was reverse engineering the board the outer layers & holes\vias could not change - bu the inner layers I could route how I wanted to.
It did the job in minutes that would have taken me all day, then I just spent the rest of the day tidying it up lol 

I have always found that a human brain is far better at thinking how a route should go that an autorouter, these days we have to consdier EMI\RFI\DFT\DFM etc as well as getting the circuit right so by the time we have entered constraints to control the autorouter, setup the exact design rules on each net etc we might as well have done the job manually.

I prefer to use the autorouter tools on specific nets and usually the last few nets that will take me al day to get from one corner to the other, just autoroute them and go fix.