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Placing components under mezzanine pcbs such as evaluation boards and modules?

drgdhorler

I want to create a pcb that can accept processor modules and breakout boards (daughter boards such as the ST Nucleo, arduino etc.)

These boards have a lot of space between the headers that I wish to populate, see picture where I want to populate resistor R0 under module M1.

I have created symbols and footprints for these module and they work, however if I try and place other components within the area of the footprint, DRC armgeddon ensues.

Is there an option to allow footprints within footprints while maintaining board drc rules?

 

I appreciate that I could layout the headers of the modules as discrete components, but this goes against the grain of "modularity".

As you can see this design as two modules and as a consequence a lot of board space is being wasted due to the default restricted access. Any suggestions? Many thanks

image

  • 0

    I won't be much help except to respond so you don't just hear the crickets.

     

    When I do this I just put down the connections as headers and not a full component module.  The reasons are that to use a module you probably need to work out rules for height clearances or set up special rules to allow the overlap.  CS rules are somewhat limited in comparison to AD so it seems to not be worth the time an effort to set that all up for the few times I have done hats, capes or shields.  However, in the past I have put in the 3D step models of some Arduino shields into the socket headers to check for height clearances manually.

     

    Also, another reason I can think of is that you may want the BOM to reflect the base board and so the parts installed are actually socket headers and not the module.  CS will then build the proper BOM.  Otherwise, you would have to manually remember to put in the socket headers or something.

     

    If I need to then I have made the 3D step models of the modules using CS.  Just make a bare board board outlines and add the pin headers and any taller parts with simple shapes.  That helps visualize the assembly.  Unless you can find someone that has the step models already.

     

    Last design I did for this used the Adafruit ESP32 Breakout module.

     

    If you do want to overlap footprints then handle it with rule exceptions to ignore the violations.

  • 0 in reply to tarribred61

    Thomas, thanks for the reply.

     

    You make some interesting and valid points. Looks like I need to read up on rule exceptions!

     

    Thanks again.