Copper vs Aluminum

[tronester]

Over the past year or so, copper heatsinks have become all the rage, and now it seems just about every aftermarket heatsink uses them. My question is, if they are so great, why did they not use them years ago? Price? If I remember correctly, people used to claim that copper does have a better thermal conductivity, but it wasnt as good as aluminum because it could not disapate the heat as quickly. With the advent of 60mm fans that push 40cfm, the copper could be used. Is this correct? Yet today I see even low powered 20cfm fans being used with copper heatsinks. Does anyone else see a problem with this? Or was I just misinformed in the past, and the real reason copper was not used was because of its price?

 

[CTho9305]

copper melts at a higher temperature, and I think it is harder to mill.

 

[Shalmanese]

There was no real demand, th old celerons and P2's werent pushing much wattage out and i really wasn't until the easily unlockable Athlons that the demand for aftermarket HSF's really took off. the combined effect of high heat output and easy, casual overclocking lead to a huge boom in the market for HSF's. That combined with the fact that most athlons those days were sold OEM rather than retail.

 

[Leo V]

I heard people say that copper is inferior to aluminum for air dissipation. E.g. copper is good for internal heat transfer but aluminum is better for dissipating it into the air. (Which explains the copper/alum combo heatsinks.) Is this claim true?

 

[rgwalt]

Copper has a better heat transfer coefficient than aluminum by almost a factor of two. Aluminum has a lower contact resistance, but it is negligble. As far as the performance of the two metals in transferring heat to the air, IIRC, the material doesn't make that much difference. Surface roughness is a factor, but I don't think that there is much difference in the performance of the two materials.

Copper hasn't been used for heatsinks because of the higher melting point and poor machining characteristics when compared with aluminum.

Ryan

 

[Leo V]

Aha! Thanks for clearing this up.

 

[Mingon]

The majority of heat sinks are made of extruded Aluminium, copper is comparatively harder to extrude and more costly, these sort of things reduce profit on a £5 product.

 

[Noriaki]

Originally posted by: Leo V
I heard people say that copper is inferior to aluminum for air dissipation. E.g. copper is good for internal heat transfer but aluminum is better for dissipating it into the air. (Which explains the copper/alum combo heatsinks.) Is this claim true?

It is true, but as rgwalt said, the difference in dissipation is minimal especially compared to the heat transfer coefficient.

I think that the main reason for the copper/alum heatsinks is partly the same as why alum-only heat sinks were popular for so long. It's much easier to machine alum into the shape you want, and if you already have alum machines you can just produce an alum heatsink with a copper inlay and get most of the benefits of the heat transfer of copper, while saving by re-using your alum machining facilities. No cost to get new machines, and it's easier to machine alum than copper. So in a way it's the best of both worlds.

I think that the performance difference between an all Copper HS, and a Copper with Alum fins (assuming all else is equal) would probably be fairly small. But it allows to retain their Alum maching "expertise" and equipment, and get the greater heat transfer coeff.

This is an educated guess, I do not claim to be an expert on heatsinks, but I don't think that the performance difference alone is motivation enough to have a Copper/Alum.

Though perhaps, the ease of dissipation of Alum provides a marketting tool?

Also I believe that Alum is lighter than Copper (lower Atomic weight anyways), so perhaps they get better surface area/mass? That's a possible performance booster. But I think that the mass is important in heat absorption as well, so that may be counter-productive.

 

[HokieESM]

I personally think that it IS price. But overall price--including cost of manufacturing. Copper is more expensive in bulk than aluminum, but not so much so that it would be difficult to mass-market an all-copper heatsink. And copper isn't THAT difficult to machine, if you're starting from SCRATCH. However, the tooling/knowledge to machine aluminum is widely available and well-documented. So a startup company can easily obtain the expertise to manufacture what they design out of aluminum.

In terms of heat transfer, copper is superior as a bulk material. BUT, the amount of heat transfer from the heatsink is the convection coefficient (h) times the exposed area (A) times the difference between the heatsink temp (Ths) and the ambient (T0), or, if you like:

q=hA(Ths-T0)

The thermal conductivity of copper ONLY effects the Ths term.... the area and the heat transfer coefficent play JUST as big a role, and are only influenced by design (not material). So, in short, a well designed aluminum heatsink is quite possibly more effective AND cheaper to produce.

As far as going bi-metallic (Cu and Al, for example), that presents a whole different set of problems. Its rather difficult to weld copper correctly.... not to mention, you create resistance to heat transfer every time there is an interface between two parts.

This engineering/economic analysis kind of thing is really at the core of every manufacturing situation.... sometimes for our good, and sometimes for the company's profit.

 

[rgwalt]

HokieESM-

You sound like you *might* be a chemical engineer. Am I right?

Ryan

 

[Nerdwannabe]

There was no need for copper heatsink back in the Pentium 2, III or AMD K6 age.

Also, heatsinks technology was still pretty low back then.

Manufacutures were already struggling to put out 10:1 fin height vs fin gap heatsinks during the slot one PIIs.
Not to mention playing with copper.