Autoroute not repeatable

[mnauss]

As an experiement, I layed out a microcontroller with headers on each side. I connected the pin of the micro to the headers in such a way as it was a one to one connection. I then copied this header connection for all four sides of the micro. I used same dimensions in all four cases so autoroute should have been identicle. This was mot the case. I tried all sorts of autoroute settings but could never get all four sides to route. It was able to route two sides, but other 2 it failed. Why, this should have been identicle for all sides. See images.

Note: Unrouted image on top image. All sides mirrored images. Attempted routed signals in bottem image.

[stressed_user]

Just for your information,

I have been routing boards for over 20 years and I have never met anyone using an autorouter.

[lucaso3 · Accepted solution]

Hello mnauss,

Thank you very much for your question.

I would like to show you an article that mentions a reason why this might be happening. You might be able to find the document on the following link:

• Best Practices in PCB Design: Routing

http://www.ni.com/tutorial/6880/en/#toc7

As mentiones over here, the autorouting process is made by a mathematical routine that it might not be specificly what you need and that is why we do not recommend to use it on a critical route. We recommend to do the critical nets manually to avoid any errors, because this way we avoid having unacceptable routing on your board.

I really hope this information helps answering your question.

Regards,

Luis

[mnauss]

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@stressed_user wrote:

Just for your information,

I have been routing boards for over 20 years and I have never met anyone using an autorouter.

---

Well, unfortunatly I do not have the benefit of 20 years experience in PCB layout. In my last job I only designed the boards using schematic capture. After I completed the schematic design we had a CAD group that did the board layouts for all the hardware designers. We gave the layout guys a list of critical nets, special placement considerations, etc. so that is the extent of my knowledge using layout tools.

Oh back in the 80's I did some RF layouts by hand using black tape on clear mylar...

So if nobody uses autoroute, then why do they even bother having it?

[mnauss]

Thanks Luis for the link to the tech tip. What does not make sense to me and maybe you can explain this, Since all 4 sides are mirror images of each other, why if two side could be routed, then why could it not route the other two sides which are exacly the same? Just seems odd.

Thanks

[stressed_user]

Hi,

I think you should consider an autoraouter as if it were a GPS or SATNAV....

It takes you to the right place but there's many ways to reach that place....

Why having an autorouter? I guesss thatit was fashionable back in the nineties...

I was told that some specific industries such as computer main board designers use that for the digital routiings, but I never met anyone doing so...

The boards I design are usually:

-50% power

-25% analog

-25% digital

An autorouter , even with the best settings would probably make a mess...

I'v tried it a few times (just for fun) but an autorouter will never match the human brain...

[lucaso3]

Hello mnauss,

Regarding why we have the autorouter is a good tool for people that would like to have an idea on how to star routing the PCB, since is a quick tool to route some nets. I am not sure why is not routing equally all sides, because this is a mathematical algorithm that I am not aware on how is set up. This information might only be handled by our R&D Department. What I would recommend is using the manual routing, but if you still want to use the autorouter to speed up the process, you can use small pieces of the layout to be autorouted and try to fix any possible issue manually.

Regards,

Luis