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Tracks routed at defined non-45 degree angles?

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  • Tracks routed at defined non-45 degree angles?

    In one of Robert's recent videos analysing a PC motherboard, he showed the way the parallel traces of the busses were routed as a series of shallow upwards and then downward zig-zags, so that they weren't aligned with the direction of the internal weave of the FR4's glass fibres, and thereby maintained good impedance matching for all the bus traces.
    (See attached image, taken from page 17 of this excellent paper from Intel on the subject, )

    What I want to know is how you would implement this in Altium Designer, as the routing styles seem to me to be either locked to 45/90 degrees, or they are "any angle", which means there is no defined routing angle, and therefore no way to get a complete bus routed with the same neat set of matching up and down angles.

    I also have a secondary reason for wanting to be able to select (say) 30-degrees for the routing angle, rather than just a choice between 45 and 90.
    I do a lot of boards that are hexagonal, or that have repeated circuit elements placed with rotational symmetry, and the ability to match the routing angle with the angle at which the components have been placed on the PCB would be very helpful.
    We can specify an arbitrary angle in the preferences for when rotating existing objects, so why are we limited to 45/90 whilst routing tracks and busses?
    Or have I simply missed where the relevant option setting is located?
    Last edited by NicholasLee; 02-03-2019, 03:23 PM.

  • #2
    To my knowledge that can't be done in Altium. You can cheat it in a way to some extent, by carefully drawing one track (by copy/paste of segments with known angle lets say), setting up a minimum clearance for the particular group and then drawings the next tracks as close as possible to the first one, so that they follow the same angle.

    Many times you don't really need fixed angles though. I've seen different boards from Nvidia for example, which use random angles. It might be using a bit more space, but it depends how much space for routing you have. Another thing is that you might not need to do this at all, unless you have very very tight impedance requirements or signal integrity requirements. So far I've never used this and never had problems with impedance/signal integrity.


    • #3
      Also, I know, some people do it the way, that they rotate the whole PCB in PANEL and then your horizontal and vertical lines will not be parallel with fibers.


      • #4
        Well, thank you for the tips, and for confirming that I hadn't simply missed where the setting is in Altium.
        I really hope they add this feature in a future version of Altium, as being restricted to 45/90 degree routing is really inconvenient when your components are placed angled at 15, 30,or 60 degrees around a polygonal PCB.


        • #5
          when in routing track mode pres shift - space.. it will sycle between different track modes.. one of them is unidirectional.. that can help maybe?


          • #6
            Dear Paul,
            Thanks, but this is called "any angle" routing, and it is only a partial solution as it doesn't help snap the routing to a particular desired angle. This free-hand routing is always going to be a bit "off" positionally, which makes it difficult to maintain track-gap spacings, (and it would mess with my OCD).
            The only way to do this precisely seems to be to draw a horizontal line of the correct length, then copy it to the clip board, and then paste it back after having rotated it by the desired angle, as set in "options->preferences->rotation step", before placing it.
            This will allow repeatable zig-zag angled traces to be created, but it's not a very convenient way to route tracks as you loose all the nice routing features like track-push etc.
            In fact any nearby track-push events will destroy any carefully layed-out "special-angle" tracks, by moving them and then re-snapping their angles to the nearest 45 degrees. So, after laying out any non-45 degree tracks, it is adviable to lock them to prevent this from happening.


            • #7
              the main reason for doing this is the FR4 material.. if you would go to FR408HR or other materials like Isola or megtron. you might just be cheaper off. also like robert mentioned. you can get manufacturing to rotate the board 10 degree in the panels..
              you could setup your grid accordingly, (so differtent Y spacing to X specing.,. aslo a cartesian gridto help with you hexagonal boards..

              again, i would rather go to other materials. then to draw this manuallyl.. i believe this is possible in allegro (but robert might know that)