As processors continue to up the ante on clock speed, a greater amount of heat is generated. Factors such as die shrinks and reduced power consumption help to keep the temperatures tame. On a far more obvious level, one can also see that heatsinks have progressed substantially from their humble days. A scant three years ago, most CPUs had tiny hunks of metal, with an equally tiny fan attached to it. If you wanted to increase your chances of a substantial overclock, it was time to change the fashion statement of your computer from drab beige box to au natural, it also wouldn't hurt to bust out a table fan. In a relatively short span of time, computer cooling has stepped from the stone-age into the err… the iron-age (well we're still using hunks of metal with fans on them and most computers still tend to be naked). Entire websites and companies have come to fulfill an overclockers' wet dream. Everything from thermal grease, to 7,000 RPM fans are offered. Heatsinks varying in size, shape, and composition, provide computer users with an even greater level of choice when it comes to cooling their little pets.
We aren't going to discuss any particular heatsinks in this article. This article will cover many of the principles behind heatsink choices. There are quite a few physics concepts behind all these hunks of metal, things "with alloys and compositions and things with ... molecular structures".
A little thermo
The purpose of a heatsink is to gather heat from the CPU. Just like cooking on the stove, the pan gathers heat from the burner beneath. In the case of a pan, even heating is the key concern; with heatsinks, this applies to a certain extent, but it's not like we're trying to cook the perfect crepe or anything. As long as heat is being taken away very quickly from the CPU, we are happy.
So how exactly does metal make this mysterious heat thing move? Heat transfer in metals is done on the microscopic level. Metals, by nature, have electrons that are not bound to one molecule; they are instead considered as a sea of electrons. Think of them as a bunch of commies if you want. It's not your bike, or my bike - but our bike! While this method doesn't exactly do wonders for personal property, it works miracles for heat transfer. This is one of the main reasons that metals are good conductors of electricity. All these electrons are put into a state of higher energy; from there, electron-electron collisions transfer heat away from the emitting source.
It's not enough just to have any metal though. There are many other considerations to be observed in the design of a heatsink. Before we get to those, it'll help if we lay down some ground rules, so we can figure out what we need to really think about.
Essentially, there are three processes that we have to worry about in designing a heatsink: thermal conductivity, thermal radiation, and thermal convection. The first is a measure of how well a particular metal can absorb and transmit heat within itself. The second concerns how well a metal performs in emitting forms of radiation - heat being one of them. If you are the unlucky owner of a fried Athlon, you might have been witness to radiation that was in the visible spectrum (a.k.a. the spark of death). Convection is the real biggie though, this is how well the heatsink transfers heat to another object, be it air or water.