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Preferred way to put a ground pad under an SMD device

autodeskguest

My design has an smd that needs a ground pad under it as a heatsink.

What is the preferred way to do this?

--

John Bachman, W1JGB

AnaTek Corporation

 

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  • On 03/15/2010 02:38 PM, John Bachman wrote:

    My design has an smd that needs a ground pad under it as a heatsink.

    What is the preferred way to do this?

     

    John,

     

    Two ways that I can think of...

     

    Tried and true:

    Add a polygon under the IC and name it GND.  Then add another one on the

    opposite side of the board, also named GND.  Connect the two with lots

    and lots of vias (12 - 15 mil drill size).  Be sure to name all the vias

    GND as well.  The more copper you have in the vias, the more heat will

    be drawn to the opposite side of the board.  To make sure you have

    minimal thermal resistance, you can also add a polygon on the MASK

    layers (both sides).  If the ground pad needs to be soldered, also add a

    polygon or square on the component side PASTE layer.

     

    This amounts to a lot of different features all associated with one

    part, so you may consider the next method.

     

    Theoretically possible:

    The other method is to copy and modify the part itself.  I added an SMD

    pad to the top and bottom layers of the package as well as an array of

    through-hole pads.  I also added prolific GND pins to the symbol, one

    for each of the PTH pads and one for each of the SMD pads.

     

    Enjoy,

        - Chuck

     

Reply

  • On 03/15/2010 02:38 PM, John Bachman wrote:

    My design has an smd that needs a ground pad under it as a heatsink.

    What is the preferred way to do this?

     

    John,

     

    Two ways that I can think of...

     

    Tried and true:

    Add a polygon under the IC and name it GND.  Then add another one on the

    opposite side of the board, also named GND.  Connect the two with lots

    and lots of vias (12 - 15 mil drill size).  Be sure to name all the vias

    GND as well.  The more copper you have in the vias, the more heat will

    be drawn to the opposite side of the board.  To make sure you have

    minimal thermal resistance, you can also add a polygon on the MASK

    layers (both sides).  If the ground pad needs to be soldered, also add a

    polygon or square on the component side PASTE layer.

     

    This amounts to a lot of different features all associated with one

    part, so you may consider the next method.

     

    Theoretically possible:

    The other method is to copy and modify the part itself.  I added an SMD

    pad to the top and bottom layers of the package as well as an array of

    through-hole pads.  I also added prolific GND pins to the symbol, one

    for each of the PTH pads and one for each of the SMD pads.

     

    Enjoy,

        - Chuck

     

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