PCB layout auto routing problem

Discussion in 'General Electronics Chat' started by legolas11, Jan 31, 2014.

  1. legolas11

    Thread Starter Member

    Feb 26, 2013
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    Hi,
    I am trying to autoroute a layout using ultiboard. But don know why it is taking ages. I changed the cost factor and all other factors to minimum. And changed the mode into Gridless. But still it does not finish. I tried doing overnight yet it keeps on doing auto routing. Please tell what i am doing wrong. Is there any specific settings or so that i need to change.


    Thanks
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Autorouting does not always finish. For tight boards with little room for traces an autorouter may find the last few nets impossible to route. Then they either hit the max attempts and stop, or just keep trying over and over.

    People are smarter then autorouters and can usually find ways to get the last 7 of 700 traces to fit.
     
  3. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I agree with ErnieM. I never trust autorouters , they generally only lead you down the wrong path. Your best bet would be to learn how to do it by hand.

    As with every post I come across asking why the autorouter isn't working, I post this video for your information and entertainment:

    http://www.youtube.com/watch?v=6JYG49zgEio
     
  4. John P

    AAC Fanatic!

    Oct 14, 2008
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    Ultiboard seems to be a proprietary setup with National Instruments, and unless someone here has used it, you probably won't get any specific help. The general answer is to let the autorouter do what it can, then finish off by hand. That's assuming that the router will have done a useful amount of work before you take over.

    In general I think the kind of project built by people on Allaboutcircuits isn't very sensitive to layout issues, and you can use an autorouter without worries. You certainly have to be able to run a few traces yourself, though!
     
  5. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    The problem with that is that if the autorouter can't finish, you probably won't be able to lay just the last few traces by hand. When the router can't finish, it means there are no direct paths. You'll need to completely redo what the autorouter has already done, find a layout that allows all of the traces to be laid without crossing over each other, etc. If you have to rip up all the auto-routed traces just to lay the correct ones, what's the point in using he autorouter at all? Like I said, it'll only lead you down the wrong path and you'll have to redo most of it anyway.
     
  6. bluebrakes

    Active Member

    Oct 17, 2009
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    I use Ultiboard. It takes ages when it can't find a route for all of the tracks.... and often never finishes, just keeps whirring away.

    I find you either need to move components about to find a more optimum position for all of the traces, adjust some of the rules for the groups, such as whether you're using double sided boards/trace width/etc or stop the autoroute on the best cause and add some link wires in.
     
    Last edited: Jan 31, 2014
  7. MrChips

    Moderator

    Oct 2, 2009
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    I do not use autorouting for the same reasons that others have already stated.

    The autorouting works for simple layouts which you can do manually in any case.

    For a more complex layout the autorouter fails to route the last two traces and leaves that for you to do, which happens to be the most difficult traces anyway. It would be nice if the autorouter can do the reverse, i.e. do the difficult traces and leave the easy stuff to you.

    My human eyes and brain can visualize what the final layout should look like better than the autorouter can.
     
    DerStrom8 likes this.
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I never said that. I use autorouters as much as possible to handle the grunt work of simple signal connections. Anything complex, such as power routing, special signals, 4 point (kelvin) connections, I do these manually before handing the job to an autorouter.

    If the autorouter hands me back a small portion of unrouted signals it's usually possible to find a way to make these connect. People can just do that, computers can't.

    If I get a high percentage of unrouted things I look to change my footprint array or board size to accommodate more things.

    Oh, and when the autorouter is dome and I'm done then I run a design rules check, and while THAT I trust I still give the gerbers a good look over.
     
  9. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Sorry, I should have said that better. What I was trying to say is that I agree with you that people are smarter than autorouters. Then, as a separate comment (completely my own), I was saying I do not trust them.

    I apologize for the confusion :p

    Matt
     
  10. John P

    AAC Fanatic!

    Oct 14, 2008
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    What ErnieM said.

    I wish there were some way to have a manual-versus-autorouter contest! It might work if someone who doesn't use an autorouter could post a netlist for a PCB, and then other people could run it through an autorouter and we could compare the results, including how much of a person's time was involved. Of course then there would be the arguments over what's "good enough" as an output.

    It probably isn't workable the other way round, with someone taking a netlist from someone else who had autorouted it, and manually routing it. That would leave that person routing a design (which would need to be reasonably complex if it was going to demonstrate anything) without ever expecting the board to be used, and certainly without hope of earning anything.
     
  11. nigelwright7557

    Senior Member

    May 10, 2008
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    An autorouter is a last resort.
    An autorouter doesn't usually understand star grounding.

    Also you need to get the component placement right first.
    My CAD software has a component swap autoplacer which swaps the positions of two components if it gives a shorter net length. It does this with the whole pcb. This gives an autorouter half a chance at a decent layout.
    However I still go in afterwards and sort out the star grounding.
     
  12. redplaya

    Member

    Jan 26, 2014
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    I always route every wire manually and then AutoRoute at the end to fix any miswires (EAGLE). If auto routing was any good, all of the PCB layout engineers I know would be out of a job
     
  13. crutschow

    Expert

    Mar 14, 2008
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    If you can view the layout connections in a "ratsnest" format before routing you can often see how to change the layout/orientation of the parts to minimize connection lengths and cross-overs which helps the autorouter do a better job. Autorouters certainly aren't perfect but they can reduce a lot of the grunt work on a board with a large number of parts and interconnects.
     
  14. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    All of the currently employed PCB engineers I know of ALL use autorouters to keep their jobs.
     
  15. redplaya

    Member

    Jan 26, 2014
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    Well they must not be dealing with anything complex or any high frequency signals because as far as I know, AutoRoute wont lay out the proper impedance matching for mixed signal designs. What company do you know AutoRoute's everything? Ill make sure to keep a distance of their products
     
  16. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    It would be preferable to actually read my posts before you comment on what I have said.

    Then perhaps what you say may have a bit of relevance to advance the conversation.
     
  17. redplaya

    Member

    Jan 26, 2014
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    So you're agreeing with me that PCB engineers you know don't do anything complex since your other posts coincides with my last post. I was merely reinforcing that any REAL pcb layout engineer does not rely on the computer doing their work and I would never tell the PO something I wouldn't tell myself. I guess I have never done an easy enough project where any trace AutoRoute provided was acceptable (or had a better solution).

    To this end I am telling the PO to just run them himself and learn something in the process, which in fact DOES add value to the conversation.
     
  18. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Sorry ErnieM, but I read your post the same way redplaya did, and I'd have to agree. Autorouters especially cannot be relied upon when dealing with circuits sensitive to stray impedance/capacitance, etc. Much better to do it all by hand (like most of the professionals I know do).
     
  19. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    I use the one in Eagle all the time.

    But not for a final layout.

    The auto-router will attempt to make the connections. I look it over and decide on a layout change. then I run the auto-router again. Again I look it over and make further tweaks to the layout.

    When I get a good idea of how the layout needs to be, to avoid excessively long trace runs and open up bottlenecks where to many traces need to pass. I then hand connect all the components. The auto-router is something I find useful as a quick method of ruling out BAD layouts and finding problem areas. Once you have those eliminated routing is simple and easy to do by hand.
     
    kubeek likes this.
  20. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    If your experience with autorouting ends with packages such as Eagle or Kicad then you are playing in the bush leagues using amateur tools.

    The professionals I know of use tools such as Mentor Graphics' Pads, which allows design rules for some very sophisticated concepts such as path length matching, controlled impedance, and can roll the PCB layout back into the simulation model to recheck the integrity of any and all crucial signal.
     
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