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Differential pair constraint region problem

KSielewicz

Hello,

I have a problem with routing the differential pair out of the constraint region (under a big BGA package). Single ended tracks change the width on the border of the constraint region and this works fine. The problem is with the differential pairs as they don't resize directly on the constraint region border but they resize in random place (the point where I click the mouse) later.

Here I have some screens:

1) This presents that single-ended track resizing works OK. On the constraint region border the track resizes correctly.

2) Here is the actual problem. When I am in the routing mode (F3) and when I move the diff-pair out of the constraint region it doesn't resize automatically.

and then I click the left mouse button outside of the constraint region and the diff-pair is resized directly in that point:

The license I am using is "Allegro PCB Designer (was Performance L)". The Allegro version is 16.6 S050 (v16-6-112DX).

Do I have to configure anything else to get it working?

Best regards and thank you in advance for your help,

Krzysztof

Parents
  • csagan

    Hello,

    I am having a similar problem. I am using OrCAD PCB Designer Professional 17.2-2016 S049.

    This issue just started to happen when I changed around the constraints to match a stack-up I just received. I am not sure which specific constraints might be causing this, but when I do lay down trace in the way you described (not automatically changing when in F3 and crossing into or out of the region), needing to click inside/outside the region once to see the change. Also, once I finish routing the net, I have no DRCs, so it is hard to pin point what constraint is the issue. Anyone have any thoughts on this?

Reply
  • csagan

    Hello,

    I am having a similar problem. I am using OrCAD PCB Designer Professional 17.2-2016 S049.

    This issue just started to happen when I changed around the constraints to match a stack-up I just received. I am not sure which specific constraints might be causing this, but when I do lay down trace in the way you described (not automatically changing when in F3 and crossing into or out of the region), needing to click inside/outside the region once to see the change. Also, once I finish routing the net, I have no DRCs, so it is hard to pin point what constraint is the issue. Anyone have any thoughts on this?

Children
  • steve
    in reply to csagan

    Use the command Check - Constraints (or Display - Constraints) then either pick the cline or draw a window to encompass both halves of the diff pair. This will then tell you which rule (constraint) is being applied and you can then find out what is wrong. 

  • csagan
    in reply to steve

    Very helpful tool, thank you! However, this does not solve my problem. Like I said, I am able to route the net and there are no DRCs. Normally, as I am routing a net over a constraint region boundary, the geometry of the traces will automatically change at the boundary, based on the constraint, before I ever "click down" any trace. For some reason it is now not doing that, I have to click down trace beyond the boundary first, and then the geometry changes. This is more of an inconvenience than anything else, but weird behavior nonetheless.

    The pictures that Krzysztof provided show this behavior perfectly.

  • steve
    in reply to csagan

    This is working for me as expected so make sure that you have set your diff pair correctly (physical coupling not electrical). There is an app note which walks you through this orcad.co.uk/.../diffpairs_definition.pdf

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