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Autodesk EAGLE
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Autodesk EAGLE
Forum Large SMT pad, heatsink pad how, non rectangle SMT pad?
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Large SMT pad, heatsink pad how, non rectangle SMT pad?

simpsonron
simpsonron over 14 years ago
I am using a heatsink Aavid 7109.  It needs a SMT pad that is 0.66x0.8 inches which is too big.  So my first try was to over lay 6 pads.  It works but many DRC errors!
My second try uses 'Stop' (layer 29) to allow copper to show in the ground plane.  When the heatsink is not connected to ground then the ground plane shorts to the heatsink.
Then I tried adding copper fill to the part but could not find a way of connecting the fill to a net or pin.
How can I connect a .66 by .8 inch exposed area to a net and have a ground or power plane flow around it.
thanks
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  • Richard_H
    0 Richard_H over 14 years ago

    Hi,

     

    currently SMD pad size is limited at about 0.5 x 0.5 inch. So you have to use a smaller SMD for connecting the signal and use a polygon over the SMD for the whole copper area. Or you can combine several SMDs as you already tried to. Currently I don't have better solution. I'ld prefer to have some SMDs and live with the DRC errors which you can approve in the layout.

    I am pretty sure that this issue will be solved in future. Probably with the XML based data structure in EAGLE.

     

    Regards,

    Richard

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  • simpsonron
    0 simpsonron over 14 years ago in reply to Richard_H

    For a very large SMD pad, this time, I am using layer 29 Tstop to define an area where there will be no solder mask (defined in the part).

     

    In the board editor, turn on layer 29, then "polygon gnd" and draw a polygon over the Tstop area uner the part.  (where gnd is the net to solder the part to)  You will want to turn off layer 29 before you do a DRC or you will get many errors as many parts will have layer 29 over laying pads.

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