That doesn't make any sense.
If you have to get rid of a lot of heat, you need a decent heat sink, for sure. Big heat sinks are *expensive*, though, so you don't want to go making them bigger just to save a tiny dab of thermal interface material (TIM).
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Except that you have grease between the particles. It's not solid silver, or whatever.
fat
Of course it isn't all silver, but so what? (I invite you to look up the th eta of bulk silver--it's a bit higher than 2.5 W/m/K.) ;)
Cheers
Phil Hobbs
The particles don't contact one another very well. Diamond particles in grease or epoxy aren't much better than ceramic ones.
If the particles become spacers it can be a net loss.
The standard Dow silicone gease flows under pressure, so thins out all it can. The phase-change glop usually doesn't flow, so enforces a gap.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The copper improves lateral heat conduction and reduces hot spots. An aluminum heat sink might be theoretically 0.1 K/W with air flow, but a transistor can see a much higher theta because it sits on a local hot spot.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
phase-change can be a win if it solders the part to the heatsink.
-- This email has not been checked by half-arsed antivirus software
Do you then trust it to insulate 1000 volts?
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The reliability and performance of a heatsink IS theory, because you don't want to experience failures. The 'yield of the materials' is probably rather important if your heatsinking includes a nut-and-bolt connection (overtorque is a big problem, seen nearly as often as loose nuts-and-bolts floating around the box).
Really good heatsinking is mechanically demanding, and too expensive (in my experience) to be ignored in any kind of production environment. It's also a field with a plethora of snake-oil salesmen. And, those snake-oil salesmen have sold a lot of bad heatsinks to engineers.
Case in point: my stereo (Dolby 5.1, actually) was well designed EXCEPT there were heavy heatsinks depending on the solder joints of TO220 packages for support. 100 percent failure in the field.
Well, just hope it doesn't continue to flow.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Oh you need some sort of spring washer/ clamp that will take up the changes... If you need more delta x, bellville's in series.
Well that's my idea anyway... I'll let you know if/when it fails. (again :^) George H.
With extruded aluminum heatsinks, lateral conduction has never been a problem. Our MEs don't have much trouble keeping the entire heatsink with 1C. Cast heatsinks aren't nearly as good, though have other properties that tend to make them the better choice.
Since the phase change temperature seems to coincide something a little worse than the worst case operating condition, it's unlikely to continue to flow.
What did you think that "phase change" meant?
-- Bill Sloman, Sydney
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