Here's a chunky TO247 transistor clamped to a heat sink. The insulator is a 20 mil thick slab of aluminum nitride, a sample from Sienna Technologies. Silicone grease on both sides of the AlN.
The fet is rated for 446 watts and spec'd 0.28 K/W theta J-C, and, at
40 watts dissipation, I'm measuring 0.2 K/W from the top of the package to the surface of the heat sink.They can supply it in 13 mils thickness, too.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tue, 03 Nov 2015 14:28:43 -0800, John Larkin Gave us:
I used to get big 2" x 2" slabs of the stuff at 50 mils.
It is nice. The grease makes a nice interface too. Gotta have it in there for best results. Way better than that old thermal pad gasket matl.
They also gave me a sample, 2x2 by 13 mils thick. Nice folks. The other AlN sources have been, well, difficult.
The AlN conducts heat almost as well as aluminum, and about 40x better than the best sil-pad insulator.
Assuming the fet is 0.28 K/W, I'm measuring a negative thermal resistance for the insulator!
I meant to try this without the grease first. Maybe I'll clean it up and do that. It's a pain to assemble, with everything squirming around. We might machine a shallow pit in the heat sink to hold the AlN in place.
I'd like to use the IXYS isolated fets, but they seem to be either EOL or un-buyable.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I tried it again, with grease between the sink and the insulator but no grease on the transistor side. 0.68 K/W. Maybe that grease does help.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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