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Altera_Forum's avatar
Altera_Forum
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15 years ago

Cyclone III package question about EQFP144

I noticed that the EQFP144 package has an exposed pad on the bottom. I did not account for this in my board layout. How big of a problem is this?

4 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Huge. The part will not work without that ground pad connected. You'll need to find some way to get sufficient grounding to that pad (drill a hole in the board or something).

    Sorry,

    Jake
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    What I meant to ask is what purpose this ground pad serves. Can I expect

    return currents from the core power or I/O power? Sunk currents from I/O?

    Just trying to figure out how well grounded it needs to be. The core power is pretty high current.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    You should mostly care for a low inductance connection, sufficient current capability will be achieved then as a side effect. To make it act as a device heatsink, you may want to connect it by multiple vias to a ground plane.

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Yes, I know, low inductance and high current capability are the same thing when dealing with high frequencies, and my next preproduction run will have a ground pad connected to the ground plane on one of the inside layers by 8 vias.

    For now I just want to power up the FPGA so I can discover whether there are any other problems with the design that need immediate fixing before the next revision. Problem is I have the 1.2V rail on a polygon right under the chip so fetching ground will either have to go by a wire to the back or out one of the corners.