1 2 First Previous 19 Replies Latest reply on Nov 2, 2009 3:16 AM by s.parker

    Do you use your Auto Router?

    steve_herbstman

      It's always a challange to get PCB designers to use an Auto-Router. In my experiance most look at it as an all or nothing approach while I think it's a combination of manual interaction and batch autorouting.

      If you have the software available today,

      1. What strategies do you employ when using an auto-router?

       

      2. If you don't use one today,why? (Ex. Setup time? Run Time? Look and feel of the results?) :_|

       

      3. What percentage of a typical design requires manual interaction?

       

      4. Where is your router software lacking? (No need to name names here)

       

      • Does it properly obey high speed rules?

      • Is the interface user friendly

      • Does it require too much cleanup after completion?

       

      Remember, this discussion thread is not limited to MGC PCB solutions. I'm not looking to pit one router against another,they all have pluses and minuses and can be effectively used with proper strategies.

        • 1. Re: Do you use your Auto Router?
          otto

           

          I use auto-router for sanity check. If it can do it, I can do it, probably, nicer.

           

           

          I also run it, when I'm stuck, to look for ideas.

           

           

          • 2. Re: Do you use your Auto Router?
            Kenneth_Wood

             

            I do not use the auto routers very much. They do not seem to adhere to the rules and make too many odd routing patterns.

             

             

            Ken

             

             

            _____________________________________

            Kenneth J. Wood

            President

            Saturn PCB Design, Inc.              sales@saturnpcb.com

            2737 Bishop Lane                        Phone: (407) 340-2668

            Deltona, Fl 32725                       Fax: (386) 789-2765

            www.saturnpcb.com

             

             

             

             

             

             

             

             

            • 3. Re: Do you use your Auto Router?
              carlos-m-monica

               

              Never used autorouter...there are lots of constraints for each signal and since every pcb today as 80% or more of those critical signals... there will be no way a autorouter properly route a board.

               

               

              Even if you put several rules in autorouter, and making it by step by steps...then it will be faster by hand..and you will use less layers, and defenitly better layout.

               

               

               

               

               

              Making a error is human...but messing all up, its software!

               

               

              Carlos

               

               

              • 4. Re: Do you use your Auto Router?
                jwalters

                 

                 

                 

                 

                I used PADS router on my last PCB design. It worked very well with only minimum changes needed. Of course this was a simple PCB interface board and you do have to spend some time going over the "rules" to make sure it does what you want.

                 

                 

                I don't know if I'd use it on a more complicated PCB but I will at least try on my next one to see if the results are good. It is a tool and will only be as good as the operator, plus it is software and I still don't trust software 100%

                 

                 

                 

                 

                 

                • 5. Re: Do you use your Auto Router?
                  mike.yetsko

                  I've only used autorouter once, and I have to say it was really neat. But I found I was constantly fighting what it wanted to do vs what I wanted to do. Then I realized it was real easy to do 'partials'. I let the autorouter run, then just went back and pulled up what I didn't like. Then run it again and so on.

                   

                  But I still had to go back and clean up a lot. I would set the layout software to select 'net' and then highlight each net one at a time and look for things I didn't like, and edit what I wanted to change. Being able to bounce back and forth from the layout to the router made it almost fun.

                   

                  But the fun ended. I have two boards I have to get out this week. I'm plagued by the software complaining that my security device is removed when it's not, segmentation faults (I always got those occasionally, even in the Logic program), and then yesterday when I finally got one design ready to route, it routes but the router says 'Fatal Error' and ends, loosing everything. I thought maybe it was something in my design, so I took a second design and when it got to the router, same error. All the logs show everything fine, and if I even click on the error to move it off the display I can see a completed route on my board. But it just won't save it.

                   

                  So today I have to fix that and hopefully still get the boards checked and out the door tomorrow.  If I can't get it fixed, I can snapshot the route to Paint and print it out, then manually try to recreate the route.  Oh well...

                   

                  I still love the software. When it works. I just wish it had better documentation, and tutorials that were up to date. It seems the tutorials are based on older software and the things they tell you aren't applicable. You have to figure out what they 'mean' as opposed to what they say. Oh, one thing I did notice, is that even when the tutorials are wrong or misleading, they sometimes put 'icons' on each section of the tutorial and a lot of times the icon matchs a button you can find on the screen. It's just frustrating, cause you KNOW tutorial wasn't run against shipping software by someone who didn't already know the system and was actually trying to learn it.

                   

                  That's my generic gripe for today I guess, against the software companies who insist on not having printed manuals. I understand the logic of it, that electronic manuals can be more 'up to date', but they never are....

                   

                  Mike Yetsko

                  • 6. Re: Do you use your Auto Router?
                    Jack

                    We have had the auto-router option for years, but I never seem to use it that much. Your question got me to wondering why, and here's all I can think of...

                     

                    Our boards have a lot of "mixed" technology, and I've noticed that I have fallen into a pattern of attacking each new design in a similar way. First, I sort the design into "clumps" of similar circuitry. Then I fine-tune each clump, paying attention to power distribution and decoupling, do via fanouts and route the short connections within the clump using the surface layers (short traces like <500mm). Then I route between clumps using internal horizontal/vertical layer pairs, starting with busses, forced order, control, etc. If I've done a decent job placing the clumps, the internal routing seems fairly easy and fun. If we have major digital sections with lots of "intra-clump" routing, I do the critical stuff by hand and let the router finish up. I've done that fairly successfully, but even at this point the router puts in strange loops that I have to clean up, so honestly, I love hand routing and prefer to go all the way myself.

                     

                    I admit, our boards are typically simple enough that I can manage the routing without stretching the schedule, but even on designs where I've had over 1400 differential pairs, I did every pair by hand. In fact, I can't imagine what the result would have been if I had let the router do those pairs. I would have been chaos, because I don't believe the router could have "seen" and followed the strategy we had developed to get the interconnections done. Lots of diagonal routing.

                     

                    In fact, if I had one wish it would be that the router would let the user set a "cost" for wrong-way routing. It seems the router is afraid to use vias, even if there is plenty of board space. I want to see more strict adherence to horizontal and vertical restrictions, because I have had better results in the long run. In fact, most of the strange loops the router puts in are because it put in a "wrong-way" segment that blocked channels, and then didn't see a need to correct it because the next route found a way around it. (which looks like crap)

                     

                    Anyway, I just HAD to comment about this post:

                     

                    otto wrote:

                    I use auto-router for sanity check. If it can do it, I can do it, probably, nicer.

                     

                    I also run it, when I'm stuck, to look for ideas.

                     

                    That is a fantastic idea. I can't believe I haven't been using it that way. Why not make a backup of the database and then run the router "just for fun" before I start my "real" routing? If I can watch where it chokes I would probably START there and work outwards. That is a great idea, THANKS!

                     

                    Jack

                    • 7. Re: Do you use your Auto Router?
                      Barry_Olney

                      Generally, designers don't like autorouters because they don't understand what they are capable of and prefer to complete all connections manually. This is just a waste of valuable time and can lead to other problems down the track.

                       

                      I do a lot of board level simulations and find that crosstalk is the main problem with boards that are manually routed. When we manually route we tend to use our artistic talent too much keeping everything nice and neat and couple traces close together (especially buses) mainly for aesthetics. This may be fine for analogue and low frequency designs but when we get into the high-speed domain, with rise times < 1nS, we can only run two traces in parallel for about an inch before we get excessive crosstalk.

                       

                       

                       

                       

                       

                      Of course we can spend hours setting up design rules to control the autorouter. But, I prefer to drive the autorouter from the schematic. When we draw a schematic we draw it by functionality and I believe that we should also place and router by functionality. Both Expedition and PADS Routers have the ability to crossprobe between the schematic and router. This is a fantastic feature that enables the designer to build up an extremely dense route, in a couple of hours, by controlling the router from the schematic.

                       

                       

                      We don't need to do any routing ourselves to get a perfect route. I start by placing all the components by functionality, selecting the desired component on the schematic and dropping them where I want on the PCB. Similarly with routing, I select a chip on the schematic, the nets are highlighted on the PCB then I select ‘Fanout' on the router. Next select the critical nets on the schematic ‘Fanout' and ‘Route' in the router. I next use the move command to push and shove the traces to where I want. Then move on to the next group of nets and repeat.

                       

                       

                      When we drive the router from the schematic we can see what needs to be done without entering design rules and can manipulate the traces as if we hand routed them. Once all the critical nets are routed I ‘Fix' them then let the autorouter loose on the remainder of the nets to finish off the design. (Please see my blog on Autorouting - Is 98% the best it can do? for more ideas).

                       

                       

                      Cheers,

                       

                       

                      Barry

                      • 8. Re: Do you use your Auto Router?
                        yan_killy

                         

                        Auto Routers are Tools than can make PCB Designers more productive. It can be used for many varieties of tasks:

                         

                        • 1. Spot congestion of placement

                        • 2. Fan out rules

                        • 3. Identify if Design Rules are not to stringent

                        • 4. Quickly try different strategies

                         

                        Once the Placemat is optimized, Design Rules are set correctly and the Strategy is set for routing, Designers can use Auto Router more effectively in what I call Stage Routing.

                         

                         

                        Even though the name is 'Auto Router', staging helps you evaluate smaller portions of problems and came up with pointed solutions. It is like eating a good stake. If you try to swallow entire stake it will be not a good experience, yet smaller pieces of good stake are very enjoyable. Let's draw a parallel between good stake eating and Stage Auto Routing. For example:

                         

                        • After a Fan out, review if it is good and do some modifications and adjustments. Decide if you want to protect Fan out or Auto Router can moved them around during routing.

                        • Differential Pairs can be challenging, but Auto Router will do a good job if they are fist tobe routed before other traces. Again it is a good idea to review them and do appropriate modification interactively

                        • Clocks, Reset, Matched Length Group, etc..will also have much easier time and success rate of completion if they routed ahead of theregular traces and reviewed

                         

                        As you can see it just like eating good stake and not choking on it, Auto Routing can be very good experience and a tool than can help Designers to be more efficient if employed correctly. it is much easier to resolve smaller problems then entire design and declare that Auto Routers don't work.

                         

                         

                        Yan Killy, TME, Mentor Graphics

                         

                         

                        • 9. Re: Do you use your Auto Router?
                          Jack
                          Barry_Olney wrote:

                          Generally, designers don't like autorouters because they don't understand what they are capable of and prefer to complete all connections manually. This is just a waste of valuable time and can lead to other problems down the track.

                           

                          (snip)

                           

                           

                          We don't need to do any routing ourselves to get a perfect route. I start by placing all the components by functionality, selecting the desired component on the schematic and dropping them where I want on the PCB. Similarly with routing, I select a chip on the schematic, the nets are highlighted on the PCB then I select ‘Fanout' on the router. Next select the critical nets on the schematic ‘Fanout' and ‘Route' in the router. I next use the move command to push and shove the traces to where I want. Then move on to the next group of nets and repeat.

                           

                          I disagree with that statement.

                           

                           

                          The way you are describing use of the tool is more commonly referred to as "Interactive Routing", and everyone does that (at least the Veribest->Expedition->RE users I know).

                           

                           

                          Most people think of "AutoRouting" as "pushing the button and letting the the tool go to completion". Not many people I know do that, unless they already have all the critical stuff done and are letting the tool finish all the junky routes. (as a disclaimer I'll admit I don't know too many people)

                           

                           

                          One more comment: Manual routing obeys the same rules as the router. Its not like you're going to make a mistake manually routing that the router will avoid. (I'm not talking about making the boards too pretty, just rules)

                           

                           

                          Jack (aka "the lonely guy")

                           

                           

                          • 10. Re: Do you use your Auto Router?
                            mike.yetsko

                            Ok, since the original question asked about where the router is lacking... I'll try here. Maybe this is something already built in, but I'm still such a newbie with this...

                             

                            I have a design (my first) that went to fab based upon my best available info. But, it turned out the guy that 'left me' with the PADs tools left them in a horrible state. For example... The CPU was only in the libraries as a TQFP. So, I looked at the spec sheet and the parts list and matched it. Boards came in and guess what? The only way you can get the CPU is in this QFP10x10 package. Oops! More than oops, I wanted the boards to work before I left on a 2 week vacation out of hte US. I did get a prototype built, with VERY careful use of wirewrap. But that wasn't all. He left ONLY custom transistors in the library that all had their B-E pins swapped. And LEDs in SOT23 packages that had the AK as the two pins across the top.

                             

                            Needless to say, it was a lot of work to get the PCB working. But I did, and in testing it shows a lot of promise.

                             

                            So, how do I fix it? First thing I did was go back to the schematic and change the parts so they now reflect what the correct footprint and pinout should be. OK, that's easy. I had to edit the library and create some custom parts in some cases, but that's done. My two new designs came right up prefectly. Well, as long as I realize how to get around the fatal errors in the router.

                             

                            But... I don't want to re-lay out the whole board. Is there an easy way to swap the part on the board and just relay out those parts? I did it with the CPU, which I though was the biggest pain, it it went surprisingly easy. The new footprint caused some problems, since there were vias under the chip and the new smaller footprint stepped on them. I just ripped up everything under the new footprint and redid it.

                             

                            But all the LEDs and trasistors are causing me problems. I can't seem to get the parts to change to the new pin designations. With the CPU, pin 1 was still pin 1 with the same function. With the LEDs and transistors, the actual pin numbers and functions change.

                             

                            So, is there an easy solution? Something like being able to select a part and break all nets to that part, Then put in the new correct part and have it pick up the net'/pin assignment?

                             

                            Or, even is there a way to blow away the whole design EXCEPT for parts placement. Erase all nets, and let it reroute. (Not that I'm looking forward to that, but if I have to...)

                             

                            You know what would be neat? If the layout/router would read in a netlist from a design, and any part that was on the pcb already leave it. Any net on the pcb that adhered to the netlist, leave it. But any part that wasn't on the netlist be placed off to the side like in the 'disperse components'. That way you could roll in a rework fairly easily. Is that do-able now and I just don't know how or is this something better left as wishware for now?

                             

                            Mike

                            • 11. Re: Do you use your Auto Router?
                              roger

                               

                              Mike,

                               

                               

                              You make an excellent point, it sure would be nice to be able to replace a component or even just change the decal after the part was routed.  I recently laid out a board with a QFN 64 part, then heard from the fabricator/assembly people that they would like a different via pattern under the part.

                               

                               

                              So how can this be done?   So far not easily, when I tried to replace the PCB Decal with a revised one, the PADS SW would not allow that because it had fewer "pins".   So instead it kept the old PCB decal and just left the three pins removed in the schematic level were just not connected.

                               

                               

                              If we could just take out one component, leaving the less of the routing alone that would be great.

                               

                               

                              Let me know if you get any answers on your questions.

                               

                               

                              I almost never use the autorouter, my designs are generally mixed signal and need individual attention, I spend as much time arranging the clumps of parts as I do routing.

                               

                               

                               

                               

                               

                              Roger

                               

                               

                               

                               

                               

                              • 12. Re: Do you use your Auto Router?
                                mike.yetsko

                                Hi Roger!

                                 

                                Well, I'm about to redo the whole thing. At least it's not THAT critical for parts placement.

                                 

                                It's too bad the software doesn't allow for a 'placement table' of parts. I mean, it would be a great too for the layout software to read the old 'physical' parameters of a board and read them in for preset definitions. That way complex board outlines and parts placement would 'match' previous board versions.

                                 

                                And it's not just a 'pretty' feature. I can see where it can get real critical with parts alignment for boards that may have custom heat-sinks, connectors, displays, LEDs, switches, and other issues that could depend on a precision parts placement. It's just too easy to screw up when re-doing the board.

                                 

                                And actually from the 'pretty feature' it would be nice if a new revision of a schematic taken to a board would at least 'look like' the old board automatically, rather than having to make a tedious effort each time you do a board spin.  I seem to remember Tango allowed that, but it was so long ago I may be mistaken.  If so, how did we ever allow a feature like that to get lost?

                                 

                                Mike

                                • 13. Re: Do you use your Auto Router?
                                  steve_hughes

                                  Mike, All,

                                   

                                  There are al ot of great ideas here for optimizimg the Auto Router & good arguements for & against using them.

                                   

                                  But then I see the conversation took a side track & started to discuss many things other than the Auto Router, this is where I want to chime in. 

                                   

                                  So without trying to be a Help Desk here...

                                   

                                  First of all Mike's comment:

                                   

                                  "It's too bad the software doesn't allow for a 'placement table' of parts. I mean, it would be a great too for the layout software to read the old 'physical' parameters of a board and read them in for preset definitions. That way complex board outlines and parts placement would 'match' previous board versions."

                                   

                                  I'm not sure what PCB tool you are using? But for sure Expedition PCB can address both of these requests.

                                   

                                  Firstly, Expedition PCB uses a concept of Template Designs, where anything & everything may be included ready to "seed" a new design.  So if you want the exact board dimesions, pre-placed, connectors.mounting holes etc, you can build it al linto the Template design.

                                   

                                  When you create a new  Expedition PCB design, use the Job Wizard to create it from that Template.

                                   

                                  Secondly, Expedition PCB supports a very robust "Circuit Move & Copy Circuit" command.  This allows yuo to copy circuitry between the active design and another host design.

                                   

                                  The details are to verbose to document here.

                                   

                                  Thirdly, there is a Key-in command that supports readign in a pre-placed compoment list. You coudl simply write this out from a known good layout & then read it back inot the new design.

                                   

                                  Here's the syntax from the Help files & it does work 

                                   

                                  pr -file= { fix | lock }  - one line for each part to be placed.

                                   

                                  Comment lines are prefixed with a '!'. The cellname need only be supplied if it's different than the default part entry for that part.

                                   

                                  The '-x' argument (if supplied) will export the current placement information into the named file; the file contents will be overwritten.

                                   

                                  If you are importing the file from the main directory, no directory needs to be specified, however, if you are importing a file that resides in the config directory, you must specify that directory. For example: default file is config\xyplace.dat. Created log file is logfiles\xyplace.log

                                   

                                  Hope that helps.

                                   

                                  Regards,

                                   

                                  Steve

                                  • 14. Re: Do you use your Auto Router?
                                    Irina_Pisman

                                     

                                    I actually use Auto Routers since Mentor offered CCT and did not have there own.

                                     

                                     

                                    The AutoActive RE allows plenty of options. If you set all the possible rules properly, Auto Router gives quite a good results.

                                     

                                     

                                    I use to run it a few times, overseeing results for each class separately. It still needs some cleanup, but by limiting via per net and number of layers used in each iteration

                                     

                                     

                                    I usually get very good results for data/address busses, PCI bus etc.

                                     

                                     

                                    The designer job slightly changed at last years, I would say. Amount of rules and requirements needles to be checked brings us to a different level of design work. If you choose a correct algorithm how to rule the tool, it works for you.

                                     

                                     

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