Don't coolers normally do copper blocks with aluminum fins to save on cost without much performance loss?
It'd be completely dependent on use case.
My theory/2c ( disclaimer: not an engineer )
I assume cooler designs are heavily dependent on:
- the max design temperature for the die/junction (e.g. 95C)
- the max (and typical) heat generated per second (e.g. 65W = 65 joules/sec)
- the chip's surface area (e.g. 81sq. mm)
- how long the different heat loads would be sustained (e.g. 5 min? 90 min? 24/7?)
- how fast heat can be dissipated into another medium (air/liquid) - though obviously the design itself will determine this, and
- how much heat can be dissipated before reaching saturation (e.g. max operating temp of liquid systems or max ambient temperature)
The more heat being generated, or likewise the smaller the die surface area, the faster the heat will need to be moved
away from the die surface, bearing in mind the (max) temperature at the die junction is what really matters. To this purpose, copper shims (AKA heatspreaders) or cold plates are often used to spread the heat away from the quickly, thereby effectively increasing the contact area between the die and the heatsink / dissipating element(s).
This is also probably why a lot of designs employ heatpipes/vapour chambers, as obviously the aim is to pull heat from the die into the heatsink and subsequently the air.
I imagine if the heat being generated is sufficiently low - or the surface area is already large enough - there may no be any benefit to adding any copper, if aluminium can already adequately spread/absorb the energy fast enough it won't blow past max operating temps at the die surface.
