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Layer 15 BOTTOM cannot be special supply $GND or poly GND?

autodeskguest

Searched for this among subjects in posts...I think I figured out that I

can't assign a plane (either $GND or a GND polygon) to bottom layer 16.

  I want four layers (signal-Vdd-signal-GND) with GND on the bottom and

Eagle seems to have significant difficulty autorouting vias to GND on

layer 16.  Is there some special requirement about layers 1 and 16

pertaining to signals?

 

Thanks.

 

Jon Fick

 

  • Jon Fick wrote:

    Searched for this among subjects in posts...I think I figured out that I

    can't assign a plane (either $GND or a GND polygon) to bottom layer 16.

    I want four layers (signal-Vdd-signal-GND) with GND on the bottom and

    Eagle seems to have significant difficulty autorouting vias to GND on

    layer 16.  Is there some special requirement about layers 1 and 16

    pertaining to signals?

     

    Thanks.

     

    Jon Fick

    Not sure about a power plane but adding a named polygon to any layer

    should work. Run ratsnest to fill polygons.

    I did a small 2 layer board with a ground polygon on the top and Vcc

    polygon on the bottom.

     

    Paul R.

     

  • Jon Fick wrote:

    Searched for this among subjects in posts...I think I figured out that I

    can't assign a plane (either $GND or a GND polygon) to bottom layer 16.

    I want four layers (signal-Vdd-signal-GND) with GND on the bottom and

    Eagle seems to have significant difficulty autorouting vias to GND on

    layer 16.  Is there some special requirement about layers 1 and 16

    pertaining to signals?

     

    Thanks.

     

    Jon Fick

     

    Only inner layers can be power planes, but as another poster noted just use

    a polygon.

     

    Personally I avoid using power planes at any time. Using polygons is far

    more flexible, allowing routing of the occasional track in the layer if

    required, obviously you can also have any shape with a polygon.

     

    Additioalaly when using power planes take care using the CAM processor, make

    sure pads are not active for any power plane layer, or you will end up with

    shorts

     

    cheers

     

    David