Computer Cooling - Heat-sinks

Heat-sinks

A component may be fitted in good thermal contact with a heatsink, a passive device with large thermal capacity and with a large surface area relative to its volume. Heatsinks are usually made of a metal with high thermal conductivity such as aluminium or copper, and incorporate fins to increase surface area. Heat from a relatively small component is transferred to the larger heatsink; the equilibrium temperature of the component plus heatsink is much lower than the component's alone would be. Heat is carried away from the heatsink by airflow, either due to natural convection or by forced-air fan airflow. Fan cooling is often used to cool processors and graphics cards of high electrical power. In a computer a typical heat-generating component may be manufactured with a flat surface; a block of metal with a corresponding flat surface and finned construction, sometimes with a fan attached, is clamped to the component. To fill poorly conducting air gaps due to imperfectly flat and smooth surfaces, a thin skim of thermal grease, a thermal pad, or thermal adhesive may be interposed between the component and heatsink.

Heat is removed from the heat-sink by convection, to some extent by radiation, and possibly by conduction if the heat-sink is in thermal contact with, say, the metal case. Inexpensive fan-cooled aluminium heat sinks are often used on standard desktop computers. Heat-sinks with copper base-plates, or made of copper, have better thermal characteristics than aluminium; a copper heat-sink is more effective than an aluminium one of the same size, which is relevant with high-power-consumption components used in high-performance computers.

Passive heat sinks are commonly found on older CPUs, parts that do not dissipate much power, such as the chipset, computers with low-power processors, and equipment where silent operation is critical and fan noise unacceptable.

Usually a heat-sink is clamped to the integrated heat spreader (IHS), a flat metal plate the size of the CPU package which is part of the CPU assembly and spreads the heat locally, with a thin skim of thermal paste between them to compensate for surfaces not perfectly flat. The spreader's primary purpose is to redistribute heat; the finned heat-sink removes it more efficiently.

Several DDR2 and DDR3 sticks of RAM of capacity 2GB or greater, and system memory, are fitted with a finned heatsink clipped onto the top edge of the memory stick. The same technique is used for video cards that use a finned passive heatsink over the GPU.

Dust tends to build up in the crevices of finned heatsinks, particularly with the high airflow produced by fans. This keeps the air away from the hot component, reducing cooling effectiveness; removing the dust restores effectiveness.