Heat sinks are like any other product in the always-advancing field of computers. Companies are constantly striving to find lighter, more conductive materials to make efficient heat sinks. They don't need to be made from just one material. For example, some heat sink producers are bonding copper and aluminum together. The design consists mainly of aluminum (for its lightweight properties) surrounded by a copper plate (for its high rate of thermal conductivity). These are great -- in theory -- but if the copper doesn't bonded tightly with the aluminum, which is often the case in inexpensive heat sinks, the copper plate can do more harm than good.
In October 2008, the firm Applied Nanotech announced that the future of heat sinks is an isotropic material called CarbAl. CarbAl is made up of 20 percent aluminum and 80 percent of two different carbon-derived materials with excellent thermal conductivity. Applied Nanotech was excited about the material because it has a thermal conductivity of 425 W/mK (higher than both aluminum and copper) and has a density similar to aluminum. Basically, CarbAl is more conductive than copper and weighs the same as aluminum, making it the best of both worlds.
Another material that's gaining popularity with heat sink producers is a natural graphite composite material. It's not as conductive as copper, but it's close with a thermal conductivity of 370 W/mK. But the real advantage of graphite is its weight -- it weighs just 70 percent of the weight of aluminum.
Whatever the material, there is one rule of thumb for heat sinks: inexpensive ones cost more in the long run. Many of the cheaper heat sinks on the market contain fans that use sleeve bearings. Sleeve bearings often break down after a very short period of time due to problems with their lubrication. While heat sinks with fans using ball bearings are more expensive, they last far longer than sleeve bearings and are cheaper in the long run. We'll talk more about how to choose a heat seat on the next page.