JamesSneed :
Physics on TH.
Copper has a lower specific heat capacity which means it will get hotter than aluminum faster but its because it is conducting more heat not because it isn't able to dissipate more heat. Copper will also dissipate heat faster as well due to the lower specific heat capacity which of course makes it more ideal for a heat sink. With that said copper is almost 3 times more dense than aluminum which is where the "aluminum dissipates heat faster" comes from if you compare the same sized copper "thing" vs same sized aluminum "thing". If you compare the same mass instead of physical size copper wins hands down. If they make the fins on the heat sink thinner so the mass of the copper is close to the aluminum the copper will win in conducting and dissipating heat but the fins are the most efficient part on the heat sink already so it wont impact CPU cooing that much(1-2c).
Specific Heat Capacity: How much heat a material can hold before it's temperature rises. This is directly proportional to thermal resistance. "Specific" because it refers to a certain amount of the material, hence making the numbers comparable. It's measured in Joules per degrees C. Lower is better.
Al(s) 0.89
Cu(s) 0.38
This doesn't seem right to me, and I can't find anything about specific heat being proportional to thermal resistance. Let's look at the heat equation (in one dimension):
(p)(c)dT/dt - (k)d^2T/dx^2 = q
p is density, c is specific heat capacity (so p time c is volumetric heat capacity), k is thermal conductivity, q is heat flux, T is temp, t is time, x is distance.
According that equation, (specific) heat capacity only affects the time dependant portion (first term) of the equation. In other words, it only affects how long it takes to reach steady state. And I would argue that (pseudo) steady state performance is the most important case for a heatsink, representing it's ability to handle prolonged heavy load.
And intuitively to me, it seems like you'd want a high heat capacity for a good heatsink. That would allow the heatsink to handle higher power for short durations/low duty cycle without heating up too much.
Edit: I'll readily admit that I only have a fairly basic knowledge of thermodynamics, maybe I'm just out of my depth here and missing something, or making some wrong assumptions.