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Re: gEDA-user: Thermal via in pad

Darrell Harmon wrote: 
David Kuehling wrote:

Hi,

I just noticed that punching a via into a large ground pad does not
produce a non-copper (clearance) ring around the via, as it would do for
vias inside polygons, see screenshot:

http://user.cs.tu-berlin.de/~dvdkhlng/via-in-pad.png

I guess such kind of via wouldn't be manufacturable since it isn't
thermally shielded from the surrounding pad?

Or is it just a bad idea to connect die-attach-pads directly with vias?

David

I assume this is an exposed pad type part. Most of these use the exposed pad either for a good RF ground or heatsink or both. Some I have used call for a matrix of vias in the pad (one called for 64 15 mil vias). For hand soldering, I usually do a large hole in the middle so I can solder the exposed pad and a ring of small vias around the edge. For reflow, just the matrix of vias with no thermal (not on the ground plane it connects to either).

Darrell Harmon

What Darrell said with emphasis on matrix of vias. I wouldn't use just a single via on that part.

One school of thought is if it isn't hard to solder too, its not grounded well enough!

I would not use thermal relief in the middle of the pad.

-Dan


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