[Amps] heat sinks

[Manfred Mornhinweg]

Ron,

>    With the high cost aluminum I can't help but wonder if something like
> copper sheeting could be used instead.   (1/4" thick or so)

Copper is nearly twice as good a thermal conductor as pure aluminium, 
per volume, and the usual aluminium alloy used for extrusions is worse 
than pure aluminium. That makes copper roughly 3 times better than 
extruded aluminium. But copper is also 3.3 times heavier than aluminum, 
so that its thermal conductivity per weight is slightly worse than a 
typical aluminium alloy, and much worse than pure aluminium. So 
technically copper is the better material for high density heatsinks and 
for hot spots (like heat spreaders), while aluminium is better for the 
outer parts of normal heatsinks, and for complete low density heatsinks, 
which are more limited by metal-air thermal resistance than by the bulk 
material thermal resistance.

The cost of metals varies all the time. Right now copper is 3.23 times 
as expensive as aluminium, per weight. So a copper heatsink having the 
exact same shape and size as an aluminium heatsink would cost 10.66 
times as much! That's prohibitive, except in applications where the 
better conductivity of copper is a deciding advantage.

And if you were to make a copper heatsink with thinner structures, so as 
to emulate the thermal resistance of an aluminium heatsink, that copper 
heatsink would end up costing about 3 times as much as the aluminium 
heatsink, weighing almost the same, but being far more fragile due to 
the thin fins.

That's why copper heatsinks are rare.

Instead of 1/4" thick copper, 1/2" thick pure aluminium conducts heat 
slightly better, weighs only 61% as much, and costs only one fifth as much!

Copper is convenient only for small pieces where thermal flow crowds, 
like right under a high power transistor, or from a high power 
transistor to highly turbulent cooling water.

Manfred


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