In common use, it is a metal object brought into contact with an electronic component's hot surface — though in most cases, a thin thermal interface material mediates between the two surfaces. Microprocessors and power handling semiconductors are examples of electronics that need a heat sink to reduce their temperature through increased thermal mass and heat dissipation (primarily by conduction and convection and to a lesser extent by radiation). Heat sinks are widely used in electronics, and have become almost essential to modern integrated circuits like microprocessors, DSPs, GPUs, and more.
A heat sink usually consists of a base with one or more flat surfaces and an array of comb or fin-like protrusions increase the heat sink's surface area contacting the air, and thus increasing the heat dissipation rate. While a heat sink is a static object, a fan often aids a heat sink by providing increased airflow over the heat sink — thus maintaining a larger temperature gradient by replacing the warmed air more quickly than passive convection achieves alone — this is known as a forced air system.
CPU heat sink with fan attachedHeat sinks are made from a good thermal conductor such as copper or aluminum alloy. Copper (401 W/(m·K) at 300 K) is significantly more expensive than aluminum (237 W/(m·K) at 300 K) but is also roughly twice as efficient as a thermal conductor. Aluminum has the significant advantage that it can be easily formed by extrusion, thus making complex cross-sections possible. The heat sink's contact surface (the base) must be flat and smooth to ensure the best thermal contact with the object needing cooling. Frequently a thermally conductive grease is used to ensure optimal thermal contact, such compounds often contain colloidal silver. Further, a clamping mechanism, screws, or thermal adhesive hold the heat sink tightly onto the component, but specifically without pressure that would crush the component.
A motherboard heat sinkDue to recent technological developments and public interest, the retail heat sink market has reached an all time high; many companies now compete to offer the best heat sink for PC overclocking enthusiasts. Prominent aftermarket heat sink manufacturers include: Aero Cool, Cooler Master, Foxconn, Thermalright, Thermaltake, Swiftech, and Zalman. Efficient heat sinks are vital to overclocked computer systems because the better the various microprocessors' cooling rate, the faster the computer can operate without instability; generally, faster operation leads to higher performance.
Temporary heat sinks are sometimes used while soldering circuit boards, preventing excessive heat from damaging sensitive nearby electronics. In the simplest case, this means partially gripping a component using a metal crocodile clip or similar clamp.
More recently, synthetic diamond cooling sinks are being researched to provide better cooling. Also, some heat sinks are constructed of multiple materials with desirable characteristics, such as phase change materials, which can store a great deal of energy due to their heat of fusion.