Which is a better heatsink copper or aluminum? It's a complex question, with many factors. Let's look at some physical properties:

· thermal conductivity (Wm⋅KWm⋅K)

· volumetric heat capacity (Jcm3⋅KJcm3⋅K)

· density (gcm3gcm3)

· anodic index (VV)

· copper: 400

· aluminium: 235

· copper: 3.45

· aluminium: 2.42

· copper: 8.96

· aluminium: 2.7

· copper: -0.35

· aluminium: -0.95

What do these properties mean? For all the comparisons that follow, consider two materials of identical geometry.

Copper's higher thermal conductivity means the temperature across the heatsink will be more uniform. This can be advantageous since the extremities of the heatsink will be warmer (and thus more effectively radiating), and the hot spot attached to the thermal load will be cooler.

Copper's higher volumetric heat capacity means it will take a larger quantity of energy to raise the heat sink's temperature. This means copper is able to "smooth out" the thermal load more effectively. That might mean brief periods of thermal load result in a lower peak temperature.

Copper's higher density makes it heavier, obviously.

The differing anodic index of the materials might make one material more favorable if galvanic corrosion is a concern. Which is more favorable will depend on what other metals are in contact with the heat sink.

Based on these physical properties, copper would seem to have superior thermal performance in every case. But how does this translate to real performance? We must take into account not only the heatsink material, but how this material interacts with the ambient environment. The interface between the heatsink and its surroundings (air, usually) is very significant. Furthermore, the particular geometry of the heatsink is significant as well. We must consider all these things.

A study by Michael Haskell, Comparing the Impact of Different Heat Sink Materials on Cooling Performance performed some empirical and computational tests on aluminium, copper, and graphite foam heatsinks of identical geometry. I can grossly simplify the findings: (and I'll ignore the graphite foam heatsink)

For the particular geometry tested, aluminium and copper had very similar performance, with copper being just a little bit better. To give you an idea, at a 1.5 m/s airflow, copper's thermal resistance from the heater to the air was 1.637 K/W, while aluminium was 1.677. These numbers are so close it would be difficult to justify the additional cost and weight of copper.

As the heatsink becomes large compared to the thing being cooled, copper gains an edge over aluminium due to its higher thermal conductivity. This is because the copper is able to maintain a more uniform heat distribution, drawing the heat out to the extremities more effectively, and more effectively utilizing the entire radiating area. The same study did a computational study for a large CPU cooler and calculated thermal resistances of 0.57 K/W for copper and 0.69 K/W for aluminium.