gEDA-user: thermal vias in pcb

[Dave N6NZ <n6nz@xxxxxxxx>]

What is the easiest way to create "thermal vias"? Not a via with a 
thermal relief -- I can do that :) .. but a via with no thermal relief 
punched into polygons on both sides of the board that ends up getting 
filled with solder to help create a large thermal mass to be used as a 
heat sink.

The application I am targeting is surface mount motor control and 
voltage regulator IC's.  So, a typical part will have a large bottom 
contact that is to be connected to large pad in the footprint.  Then, on 
the front and the back, as convenient, there are polygons that are also 
part of the ground plane, the top one overlaps and contacts the 
footprint pad.  Now, the trick: there is a field of small holes drilled 
into the polygons, with *no* thermal reliefs.  Drill size is chosen such 
that the vias wick up lots of solder and you end up with a nice metal 
mass.  See Freescale Ap-Note AN4005.

So, anyway, should I specify some kind of pin with clearance smaller 
than the pad?  How can I keep pcb's DRC from whining?  I'm sure the 
answer is simple but I'm not sure how to approach it.

TIA,
 dave


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