Copper is the better conductor. It absorbs heat faster, but holds it longer. They make thin-fin HSFs with lots of surface area and big fans to help dissipate the heat. Copper is the trend for the high end cpus.
The way I understand it is that it does hold more heat as it is denser than aluminum, but it also spreads the heat out faster, so the heat is moved away as it tries to heat the copper block faster. It is also much heavier. I do not think a soilid copper heatsink is really nessisary, but a copper base or insert improves the performance a bit.
I had a cheap'o aluminum heatsink with a thin copper base (about 70x70mm). I bent it out to fit an 80mm fan (no overhange). Well I just got an SK-7 solid copper monster of a heatsink and with the same fan only improved my performance by 1-2'C (considdering it cost about twice as much I was dissapointed). The SK-7 is only about 65mm wide so some of the air from the fan is not forced through the heatsink. I think fanning the fins out to fit a larger fan is a wonderfull thing. It captures all the airflow and actually increases the space between the fins to increase the airflow. I have done this to a FOP32-1 with VERY good results too. I can cool my AthlonXP 1600+ (stock) and 1800+ (1.837Ghz) with a quiet 30 and 28db fan (respectively).
By the way, which manufacture make a good heatsink fan.
In other words, which one is good to buy for overclock CPU
that need to help in reducing heat to keep the system
stable. I prefer one that make for Pentium 4 2.53 GHZ.
Zalman has a nice one for P4. It is very big and heavy (over 700g for the solid copper one). Their CNPS-7000 series just rocks. Make sure it can fit your motherboard as it is 109mm across. It is very quiet and beats almost everrything out there. I have seen them for as little as $38 for the Cu/Al one ($45 for the solid copper one) at NewEgg. The copper/aluminum mixed one performs almost as good and is just under the required weight limit of 450g from Intel fot their P4s (incase you take the system to LAN parties or something like that).
Well if you wnat to get technical then there are three different answers, all of which are correct.
1. Copper absorbs much more heat (per degree C) than Aluminium.
2. Aluminium absorbs much more heat (per C) than Copper.
3. They are both absorb the same amount of heat (per C).
What, you dont believe all three? It's true, here's why.
- Copper has a higher heat capacity per unit volume.
- Aluminium has a much higher heat capacity per unit mass
- Molecule for molecule (that is, per mole) they both absorb almost exactly the same amount of heat per degree C.
Oh BTW, while I answered your specific question I should point out that thermal capacity (that is the ability to of a substance to absorb heat with limited temperature rise) is actually pretty irrelevent to heatsink performance. Heat capacity will delay the onset of over temperature should your heatsinks fan fail but it does nothing to reduce the steady state maximum temperatues and has no influence on the temperatures of a working heatsink/fan combo. The main factor that is important here is thermal conductivity and copper is definitly superior to Aluminium in that respect.
I heard pure glass is the best you will find, anywhere