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allegro17.2 How to Set Maximum Stacked Vias

Tyler U

In 17.2, is there a way to set the maximum amount of consecutive stacked vias in a design.

Here's the example,

L1 to L5 can have stacked uvias. We want to have the maximum amount of stacked vias at 4. We don't want any L1 to L5 vias but L3 to L5 vias are ok. Every other combination of stacked vias would be allowed.

Instead, we want L1 to L5 vias to go from L1-L3 and then dog-bone to L3-L5 uvia.

This is in response to IPC issuing a warning on reliability as it relates to stacked microvias (Source: https://epsnews.com/2019/03/06/ipc-issues-warning/)

  • Not sure about setting an automatic way, but here's my process. While going through my final checks (I have ~8 process steps I manage to quantify my designs) I'd turn on Layer 5, since that would have any transition that connects on Layer 5. Then I'd make the vias 'open' (not filled), and make sure the via spans are displayed. I'd hunt around the board and look for the L1-L5 spans. Hopefully you don't find any, or not too many. I'll assume you're hand-routing the board anyways, and you kept the L1-L5 issue in mind while routing. I've done this numerous times looking for overlapping via structures. Not too time consuming. Good day.

  • in reply to CadAce2K

    Thanks CadAce2K. Not the answer I was hoping for but thank you nonetheless.

  • in reply to Tyler U

    Try setting your min BBVia Stagger to a number that forces your vias apart for layers3-5.  This will be unique to your via size.  And set your stacked via layers1-3 to 0, with pad-pad connect set to all allowed.

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