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How to connect vias to specific layers

tmd63

 I have a design which has 7 layers. The top layer has only short stubs.

There are two layers for traces but they are sensitive signals and there is a solid ground plane above and below these two layers. I have connected these two planes at one point near the incoming supply. I also have a single ground plane as layer 7 which is noisy.

How do I connect a number of ground signals from Layer 1 to Layer 7 WITHOUT connecting to the other two ground planes, which would inject noise onto these planes? 

When I try using the normal vias, they connect all planes from 1 to 7 and also 2 and 5, I just need layers 1 and 7 connected but they need to connect at the supply (one via connecting layers 1, 2, 5 and 7).

  • chads108

    You can do this one of two ways.

    First  method is to attach the no shape connect property to the individual vias you are working with and then manually connect them with clines to the layers you want them to connect to.

    Second method would be to void an area, or put a route keepout, around the vias on the layers you do not want them to connect to.

  • redwire

     Have you talked to your fabricator about a 7 layer design?  Most PCBs are fabricated with an even balance of copper layers for cost reasons.  I would suggest adding an 8th layer or making sure your design is at the proper cost target before doing an odd stackup count.

  • tmd63

    My design is not a standard Glass Fibre/Epoxy design and yes, it is standard for my design fabrication to use odd and even layer counts.

     #Chads108, Is there any way of adding the route keepout to a via (maybe give it a new name to separate the new via) instead of doing it for each via in the design?

  • ericchen
    and you can use the constain manager;
  • Khurram
     Now I think Cadence should introduce a property (something like “No_shape_Connet_exldue_layers”) which will allow shapes to connect vias on some particular layers while disconnect them on remaining because other methods are time consuming and not reliable.

    Thanks

    Khurram
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