Sorry, 

I have been to busy to comment for some time... 

I want to clarify another 'assumption'... :)
The calcs that my Mechanical Engineer colleague did were to evaluate a
soldered transistor with a large thermal contact area kind of like a
DPAK package with thermal vias in the pad that it was soldered to... and
the thermal transfer was to be thru those vias to the back side of the
board and a heat sink that was flush with the opposite side of the
board, and probably a thermal gap pad to take care of any air gaps after
the board was screwed don't tight to the heatsink... 

The 'calculator' is just a spread sheet with some standard thermal
equations in it and it allows me to change the thickness of the board,
the diameter of the via and the thickness of the copper plated in the
barrel. It also allows me to simulate putting a solder plug in the hole
and check the thermal resistance effect of that solder plug being
there... BTW...it was an ideal solder plug filling the via top to bottom
with no voids and flush with the top and bottom surfaces. 

We wanted to see how it would perform under the conditions we were
designing it into a product and the thermal resistance of the via with,
or without solder in it was the question... We determined that thicker
copper plating in the barrel was more effective than the solder plug by
a reasonable margin. Seeing that the solder plug was less effective and
was also fraught with variable inconsistent hard to control features...
like voids, lumps, flow issues, etc...  So we chose the cleaner approach
without the solder plugs. It worked for us in our tests.  


This had nothing to do with thermal relief pad features on planes in
boards with leaded components. Completely different subject. 


Bill Brooks | Datron World Communications, Inc.
PCB Designer/Engineer | Office: 760-602-7004| Fax: 760-597-3777 |
[log in to unmask]
1808 Aston Avenue, Suite 230, Carlsbad, CA 92008 | www.dtwc.com
Performance You Require. Value You ExpectTM

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