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Package to Package spacing

Lennie

My footprint's are created so the part outline is created on the PLACE_BOUND layer. We create this so the correct outline is used for  IDF file generation.

This layer is also used by the package to package DRC. I have not found a way to change the preset value from "0" package to package clearance. Since this places the footprints next to each other  then we cannot build the

board. Is there any way around that ?

  • I think you want to use DFA (design for assembly). We create our library parts to have a DFA shape that is the exact size of the component. The DFA shape is the same as the place bound if DFA shape isn't defined. Then use the DFA Constraints Dialog to set the Package to Package spacing. Here is a decent video describing how to use DFA

    www.youtube.com/watch

  • Thanks I have seen that but my current footprints have the DFA_BOUND created as a courtyard around the part. I was hoping to be able to set the package to package clearance to keep the packages 10 mils apart. I guess I need to rethink my footprint creation and the PLACE_BOUND, DFA_BOUND, layers.
  • Using DFA is the only one way to set the package to package spacing. If you have your DFA_BOUND defined as the size of the component its easy to accomplish a 10 mil package to package spacing.

    An easy way to think about DFA is dynamically changing the DFA_BOUND to be larger or smaller but at a PCB level, not a part level. I think you can accomplish what you are after using DFA.

  • I personally have a real issue with the courtyard approach (IPC standards) built into the footprints.  Every CM fab/assembly has different capability for density/spacing and with improvement in the pick/place equipment the spacing requirements will change.  If I put the clearances into the footprint it may cause excessive spacing when I need a high density design. Also as the pick/place equipment improves I'll need to go back and redo all the courtyards....  I've always thought these was a dumb approach by the IPC committee.

    The DFA Constraints spread sheet  built into the allegro tool on the other hand is a better approach.  I create place bound and the dfa bound geometries the same size as the physical body of the component.  The DFA constraint then shows errors for components too close.  I wish the courtyards would go the way of the dodo bird......

    My 2 Cents ......

  •  Lennie,

    You have mentioned you are using the IDF option to import into a mechanical 3D tool like Pro E. If this is the case, have your ME person create a mapping file to point your board parts to 3D models in their system. So, no matter how you have your place_bound set to it will not matter. Your 10 mil oversize around your parts is fine. All the parts mapped to a 3D model will be rendered. For the ones not mapped the place_bound size and z height will be used. The 3D models will be more actuate obviously. Now you can decide what parts need 3D models to observe interference in tight situations. The use of the Place_bound is really for DFA requirements not for 3D studies especially in tight situations in my opinion.

    Cheers  

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