Re: gEDA-user: Thermal via in pad

[Dan McMahill <dan@xxxxxxxxxxxx>]

Steve Meier wrote:
> I think that this is a non-issue. I have built bords with these types of
> vias in pads many times. Thermal shielding is more of an issue when you
> are attempting to attach a device to a pad. In that case, you don't want
> a via connecting directly to a large ground or power plane without
> thermal relief as the plane would transfer and disipate the soldering
> heat.


"If its not hard to solder too, it's not grounded well enough!"

- Me

All jokes aside, there is some truth to this.

With regards to packages like the QFN in the picture that was in this 
thread, IC designers often times are counting on you having lots of vias 
on that bottom side ground pad both for providing a very low electrical 
impedance connection to a ground plane and also for providing a low 
thermal resistance to a ground plane.  I put 15 vias on the ground pad 
of the last board I did with a 68 pin QFN on it.  For soldering, placing 
the board on a hot plate helps.

I've also used a very large plated through hole on the backside before 
when I was planning on hand soldering without having a hotplate or other 
things to help heat through the board.

Do be aware that in either case, a fine tip iron is likely to not be enough.

-Dan



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