Re: gEDA-user: OT: soldering QFN packages with exposed bottom pad?

[DJ Delorie <dj@xxxxxxxxxxx>]

>   I would think that mounting the chip upside down would allow
> better heat distribution?? I could be wrong. You may need a heat
> sink?

The whole point of the bottom pad is to get heat out of the chip;
there are expectations like having copper and vias under the pad to
get the heat to the opposite side of the pcb where it can be
dissipated.

If you flip the chip over, the heat can only be dissipated by the air
contact with the pad itself.  It would probably work for a while, but
may not be reliable that way.  The data sheets often tell you how many
square inches of copper on the other side are needed for various
situations.  I suppose you could hand-solder some copper foil or
desolder braid to the pad, as long as you're careful to not short the
pins.


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