Heatsink Guide - The Basics of Cooling & Heatsink Technologyby Tillmann Steinbrecher on January 5, 2000 12:02 AM EST
- Posted in
In order be efficient, a heatsink must be designed in a way that it will take advantage of this effect. There are two ways to achieve this goal:
- Make the surface area of the heatsink as big as possible
- Provide the best possible amount of air flow across the heatsink
In addition to these two factors, the heatsink must be designed in a such way that good thermal transfer is possible inside the heatsink (meaning that the heat can easily travel from the lower part of the heatsink, that is in contact with the CPU, to the fins, where the actual heat dissipation takes place). The part of the heatsink that is in contact with the CPU must be very flat in order to allow good thermal transfer. But even if the surface appears to be perfectly flat, there will still be small air gaps in the contact area between CPU and heatsink. Therefore, a thermal interface material, like thermal compound or a thermoconductive pad must be used.
So, in order to design an efficient heatsink, a solution would be to make it as big as possible, and add a very powerful fan. Another solution would be to let it have very fine fins, and use a clever design that allows the airflow from the fan to travel easily through the heatsink - by using a heatsink design that avoids turbulence and high air pressures inside the cooler. Of course, the ideal solution would be the combination of both solutions
Almost all heatsinks are made of aluminum. Why? The low cost and great mechanical characteristics make it very suitable for producing heatsinks. Generally, a pure metal has better thermal conductivity than an alloy. However, most heatsink manufacturers use aluminum alloys because of their better mechanical characteristics.
Many people wonder why copper isn't widely used for heatsinks - copper has a thermal conductivity that's almost twice as high as the thermal conductivity of aluminum (393 W/mK, as opposed to 221 W/mK). However, the performance of a heatsink doesn't only depend on the thermal conductivity of the material, so a copper heatsink certainly won't be twice as efficient as a heatsink made of aluminum. Therefore, the better thermal characteristics of copper do not justify the significantly higher cost and other considerations (rigidity, weight). Also, copper is not very suitable for extrusion (which is the preferred production method for heatsinks - see page 3). However, there are some heatsink models that are made of copper and aluminum. Here, usually the base plate is made of copper (or has a copper inlay), and the fins are made of aluminum.
"A black object radiates the best - so all heatsinks should be black". True? Not really. Remember, most of the heat is dissipated using forced convection - and for this effect, the color is irrelevant. When doing a comparison test of two otherwise identical heatsinks with a different color, the measured performance difference is usually negligible. The main reason why heatsink manufacturers anodize their heatsinks is to make them look more attractive. Heatsinks exist in a variety of colors - black, silver, but also blue, green, gold, and red. For the performance, it doesn't make any major difference.