The thermal resistance of copper is lower than aluminum as is its electrical resistance. This is the case with all precious metals. From lowest to best conductivity of heat and electricity; aluminum, copper, silver, gold, platinum. That is the scale of the precious industrial metals excluding high noble metal processes and alloys. The bottom line on the video heatsink are as previously stated light weight against brittle silicon pcb and aluminum is way cheaper and easier to work with. It's all economics mostly but some heatsink manufacture use a copper heat spreader with a massive aluminum fin structure to get the most surface area per unit of weight.
Sir, your knowledge of the relevant chemistry is inadequate. I shall attempt to remedy the situation.
I refer you now to WebElements.com, and the image below which has been reproduced from there in terms of the WebElements copyright.
Nature's best performers in terms of thermal conductivity for pure metals are the group 11 metals. Copper, Silver, and Gold. The relative value of precious and semi precious metals have nothing to do with their thermodynamic properties. The value of a metal is completely arbitrary in humans terms, and is a result of its rarity, and/or usefulness for a particular purpose. For example, if copper was more scarce than gold, it would traditionally (in pre-industrial times) have been hardly be more valuable than gold, simply because it tarnishes, discolours skin, and as such its desirabity as a cosmetic metal would have been low when compared to gold.
But I digress.
As you can see from the graph, Platinum's (group 10, next to gold) TC is woefully inadequate for heatsink use. Even a heatsink made from pure silicon, would offer better thermal conductivity. And yet, ultra-pure silicon is in fact used as a thermal
insulator on the Space Shuttle's exterior tiles....
Copper's thermal properties seem too good to be true - it closely follows that of Silver, the metal with the highest thermal conductivity, yet it is cheap and abundant. However, aluminium's popularity is due to a number of factors, notably, Aluminium's high TC:density ratio, BUT PRIMARILY, its low melting point. The low melting point allows extrusions to be made very cheaply. Molten Aluminium is "squeezed" through a shaped orifice, which are cooled to form long extrusions (complete with fins, etc). These are then cut up into individual items and machined for detail)
What is interesting, is that while pure carbon (a non-metal) has a low thermal conductivity, nothing beats carbon in one of its allotropic forms, which of course is pure diamond.
Another thing, the core of a cpu is not called a "PCB". PCB is notionally "Printed circuit board", but actually it stands for what the early circuit boards were traditionally made of - Polychorinated Biphenyls. Today, the substrates used for circuit boards are much less hazardous.
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