Not sure about specifics on each part, but I can tell you there is a lot of
issues relating to correct assembly of those middle pads on QFN parts,
generally related to incorrect amounts of paste in the wrong spots
producing either voiding or issues where the rest of the qfn doesn't end up
soldered up correctly.

Personally, if it's truly optional, and not needed for heat dissipation,
I'm not sure I would even consider atttaching it.

-forrest

On Tue, Aug 21, 2012 at 10:35 AM, Bob Blick <bobblick@ftml.net> wrote:

> In Microchip's packaging document and also the PIC datasheet (in this
> case for the 16F884), in the "land patterns" section, the center pad is
> called "Optional Center Pad" for the QFN packages.
>
> Is that really optional? I can't think of any upside for leaving it out.
> I welcome any thoughts on it.
>
> Thanks,
>
> Bob
>
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