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Old 2nd March 2003, 04:25 AM   #1
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Default Heatsinks: Cu vs. Al

I'm confused about the entire copper vs aluminum debate. I hear that copper is superior to aluminum when it comes to drawing heat away from the transistor, but not as good as aluminum at getting rid of it. How is this possible?

Thermal Conductivity
@ 0 - 100°C
Al 237 W m-1 K-1
Cu 401 W m-1 K-1

Specific Heat @ 25°C
Al 900 J K-1 kg-1
Cu 385 J K-1 kg-1

From what I see, copper conducts better but it can't hold as much heat as aluminum. Regardless of capacity, wouldn't you care more about conductivict of heat?
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Old 2nd March 2003, 04:48 AM   #2
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Default Heatsinks: Cu vs. Al

True, aluminum would slow temperature rise but would also hold the temperature longer after the source of heat is removed.
Aluminum is popular because it is cheap and easily extruded.
When I can afford it, and can chose between the two , copper is what I use. For CPU cooling systems, copper is available, for power audio aluminum is very available.
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Old 2nd March 2003, 04:51 AM   #3
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The ability to radiate heat away into an environment
is a function of the shape and size, the thermal conductivity
of the material, and the color of the surface. All other things
being equal, superior thermal conductivity = 'better ability to
get rid of it".
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Old 2nd March 2003, 05:26 AM   #4
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So would it be a good idea to get a very thin sheet of copper from www.onlinemetals.com, corrugate it and mount transistors to it?
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Old 2nd March 2003, 05:49 AM   #5
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For heatsink types and information try

http://www.wakefield.com/

or

http://www.aavid.com/

There are lots of technical papers listed at:

http://www.aavidthermalloy.com/technical/index.shtml

and probably a few at wakefield as well.
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Old 2nd March 2003, 05:53 AM   #6
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Not necessarily. Thin sheet has surface area, but not much conductivity, probably less SA than you'd want given the cond.

The best solution would be to take a slab of copper (or silver, for that extra-cool reduction in microphonics and flattening of frequency response ...sorry), braze Cu wires to its backside, and coat those with aluminum, which is then anodized black (black is most emissive to radiation). The aluminum can probably be skipped altogether if a fan is used.

Me, I'd just cut up some styrofoam, glue it together in the shape of a heatsink, bury it in sand, and pour aluminum all over it!

Tim (been doing a lot of lost-foam casting lately )
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Old 2nd March 2003, 05:59 AM   #7
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Quote:
Not necessarily. Thin sheet has surface area, but not much conductivity, probably less SA than you'd want given the cond.
So you mean that the last few fins are too far away from the transistor to pull much heat away from it? A corrugated design would be easiest, but wouldn't a thinner metal do a better job since it's surface area to mass ratio is a lot bigger?



Thermal resistance in C/W means that for every watt of power dissipated by the device, it and the heatsink get "C" degrees hotter right?
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Old 2nd March 2003, 06:01 AM   #8
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I believe so, yes...

Tim
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Old 2nd March 2003, 06:41 AM   #9
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Hi Solid,

Although Nelson answered your original question, I thought I’d provide a link to some threads that “debated” around this topic. You can see some more viewpoints on the subject.
http://www.diyaudio.com/forums/searc...der=descending

Rodd Yamashita
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Old 2nd March 2003, 07:15 AM   #10
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Thanks for the link. On another note, what was it I saw in that thread about heatsinks making noise?!? One guy said he clapped and the fins rang! Someone else said even while driving a dummy load, the heatsink made a ringing noise. How is this possible?
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