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Problem connecting Power Pads to GND polygon

autodeskguest

I am designing a board that includes several kinds of ICs

with "Power Pads" under the IC package that need

to be grounded.  For some of the ICs, the GND polygon

connects to the Power Pad as it should.  For other

ICs, the GND polygon is not connecting to the Power Pad.

Examining the devices in the library, they appear to be

constructed and labeled the same way.  I can't see

a difference in labeling, pin declaration, or grounding

between the ones that connect to ground and the ones

that don't.

 

Can you suggest what might be different between the

ICs or the libraries to cause this?

 

Thank you,

--- Graham

 

==

 

Parents

  • Hi Gary:

     

    Eagle Help warns of setting the polygon width to a very low number,

    they indicate it should be set to about the width of the

    smallest feature or trace, because the solid fills are actually

    a raster scan at the polygon width, and the number of scans and

    the associated Gerber file get extremely large for very small widths.

     

    A few experiments with this parameter indicate that it is not the

    problem.  Setting it very low does not cure the problem.

     

    It is really not a thermal problem in this case, as much as

    enabling a very low impedance RF ground.  There will also be

    vias in the power pad, but I want the lowest possible impedance

    ground, and that would be helped by connecting the ground pins

    to the well grounded very nearby power pad.

     

    Thank you for your thoughts and interest.

    --- Graham

     

    ==

     

    Gary Gofstein wrote:

    Is the polygon width set to a low number, like zero, to help it get into

    the spaces?

     

    also, maybe it should just be connected with a via( or as many vias as

    will fit in the pad) rather than trying to get in between the pads, it

    sounds like a thermal connection that needs a lot of copper to work

    properly.

     

Reply

  • Hi Gary:

     

    Eagle Help warns of setting the polygon width to a very low number,

    they indicate it should be set to about the width of the

    smallest feature or trace, because the solid fills are actually

    a raster scan at the polygon width, and the number of scans and

    the associated Gerber file get extremely large for very small widths.

     

    A few experiments with this parameter indicate that it is not the

    problem.  Setting it very low does not cure the problem.

     

    It is really not a thermal problem in this case, as much as

    enabling a very low impedance RF ground.  There will also be

    vias in the power pad, but I want the lowest possible impedance

    ground, and that would be helped by connecting the ground pins

    to the well grounded very nearby power pad.

     

    Thank you for your thoughts and interest.

    --- Graham

     

    ==

     

    Gary Gofstein wrote:

    Is the polygon width set to a low number, like zero, to help it get into

    the spaces?

     

    also, maybe it should just be connected with a via( or as many vias as

    will fit in the pad) rather than trying to get in between the pads, it

    sounds like a thermal connection that needs a lot of copper to work

    properly.

     

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