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

[Bill Gatliff <bgat@xxxxxxxxxxxxxxx>]

DJ Delorie wrote:
>>   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.
>   

All great ideas, everyone.  Thanks!

But I think the big-picture lesson here is to "go get a toaster oven".  :)


b.g.

-- 
Bill Gatliff
bgat@xxxxxxxxxxxxxxx



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