Actually, what I was hoping to do was use 4 oz. copper on one side and
2 oz. copper on the other. The 4 oz. side would have the heavy power
stuff and the 2 oz side would have the surface mount I.C.'s and control
circuits. Talk about short signal paths from logic to power MOSFET's,
it would be the thickness of the board. We have used bus bars in the past
for TO-220 designs and plan to at least to connect some of the sources
of the MOSFET's.
I was thinking of making kind of square "U" shaped piece of copper 5 mm thick that had a cutout of 10 mm square to fit around the D2PAK. The PCB would have copper that conducted heat from the MOSFET to the heatsink. This leaves a strip of less than 1 mm around the D2PAK. When I do the math of 1 mm *30mm(for three sides)*.07mm(for 2 oz. copper) I get 1.2 degrees C per watt. If I go to 4 oz. copper I get .6 degrees C per watt. This copper is thick enough so that it is higher than the top of the D2PAK so a big Aluminum heatsink could be through bolted on to cover lots of these pieces of copper. If I use a Silpad (Berquiest) of the cheap type (gray color) the copper to Aluminum thermal resistance would be .58 degrees C per watt. If I use the Silpad K10 (tan color) it goes down to .26. So, if I add the two for D2PAK to Aluminum thermal resistance I get 1.46 degrees C per watt for 2 oz. copper and .86 for 4 oz. copper. For reference a TO-247 with a gray silpad is 1.5 degrees C per watt and with a Silpad K10 (tan) is .66.
At any rate, with my proposed system I could imagine 50 watts continuous especially for 4 oz. copper. BUT, I realize these are just a bunch of numbers and formulas. 50 watts on the 4 oz. copper would mean a temperature gradient of 30 degrees C and 2 oz. would give 60 degrees C over a distance of just 1 mm. Can an FR4 board handle that?
Does anyone know the thickness of the copper on a plated through hole? The cross sectional copper area will of course depend on the diameter of the hole. Also, its thermal properties would be greatly effected if it were full of solder.
What am I missing here? Any comments appreciated. This has to be done right for high volume production, 10,000 per quarter.
Gary Allbee wrote:
Heart: In addition to Rob Malos reply, I have also "heard" of 4oz copper available upon request Rob commented:"If you do plan to use 2oz or 3oz copper do discuss it with your SMD* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To join or leave this list visit: * http://www.techservinc.com/protelusers/subscrib.html * - or email - * mailto:[EMAIL PROTECTED]?body=leave%20proteledaforum * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *