Re: gEDA-user: Thermal via in pad

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

Actually Dan,

Your joke is probably pretty good. The point of the pad (on voltage
regulators for example) is to dump heat. So a thermal relief to the
ground plane or power plane is counter productive. And using many vias
each with thermals would make soldering the device to the pad as
difficult as having fewer vias without thermals.

Steve M.

On Fri, 2007-01-12 at 16:45 -0500, Dan McMahill wrote:
> 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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