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Re: gEDA-user: thermal vias in pcb
I use a number of parts with backside thermal pads. Draw the rectangle as you describe to comfortably surround the vias. Then with the mouse over the rectangle hit 's'. This will flood the thermal reliefs on the vias. If you want to ever de-solder the part from the back, make sure the pad on the opposite side has the solder resist cleared.
Joe T
On 3/6/07, Dave N6NZ <n6nz@xxxxxxxx> wrote:
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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