Heat sinks are thermally conductive components or devices that absorb and dissipate heat generated by electronic components. Heat sinks cool high-powered devices to prevent overheating. The reliability of electronic components is generally reduced by the square of an increase in temperature. For example, doubling the ambient temperature around a component renders the component 25% less reliable than at the lower temperature. Heat sinks are therefore essential in dissipating generated heat and improving component longevity.

A list of devices which commonly use heat sinks is found below.

• Computers: central processing units (CPU) and graphics cards. Heat sinks became essential to computers in the 1990s when processor speeds, and therefore the heat generated by the processor, increased exponentially.
• Optoelectronics: light-emitting diodes (LED) and lasers. Cooling is essential in LED and laser use, as device performance and lifespans are functions of their temperature.
• Soldering. Heat sinks were commonly used to protect nearby electronic components during soldering processes, although modern semiconductors can typically dissipate heat without protection. Some components, such as reed switches, still require heat sink protection when in close proximity to soldering.
• High-power semiconductors, such as transistors.

Types of Heat Sinks

Heat sinks are typically classified by production method and form factor. Information about the most prominent types is contained in the table below.

Table image credits: IXBT Labs | Kunze | Carlton-Bates | IXBT | Electronics Cooling | Advanced Thermal Solutions | IXBT

Theory and Design

Heat sinks transfer thermal energy from a high-temperature device to a lower temperature medium. This medium is typically air, but may also be water, a refrigerant, or oil.

An excellent, comprehensive video on heat sink design and its relation to electrical design.

Video credit: EEVblog / CC BY-SA 4.0

Heat sink design depends heavily on Fourier's law of conduction; the formula with regards to a single axis (x) is shown below. (It is important to note, as shown in the video above, that Fourier's law is the thermal analog of Ohm's law.)

where:

q_k = heat flow per area and time

k = conductivity constant

A = surface area of heat transfer

dT = temperature difference

dx = material thickness

The image below illustrates the importance of this formula in heat sink design. As shown in the heat flow diagram at the bottom right of the image, heat sinks must have sufficient surface area and thickness to properly dissipate temperature.

Image credit: Patrick M. Len

The simplest heat sink could consist of a single piece of thermally conductive metal. The protective case of the device containing the heat-generating component could theoretically function as a heat sink as well. However, most heat sinks use fins to increase surface area and create optimal air flow patterns, as shown in the table above.

Material Considerations

Heat sinks are typically constructed using aluminum alloys, most of which have high thermal conductivity values. Copper is considerably denser and more expensive than aluminum, but has superior thermal conductivity, corrosion resistance, and more efficient heat absorption. Various applications and industries, such as power plants, HVAC systems, geothermal heaters and coolers, and electronic systems employ copper heat sinks.

Composite materials such as synthetic diamond, AISIC, Dymalloy, and copper-tungsten pseudoalloy are occasionally used as chip substrates or submounts, which double as heat sinks.

Standards

Heat sinks may be produced, tested, and used according to specific published standards. A list of example standards is found below.

NAS4122 - Extruded heat sinks

SAE AIR1957 - Heat sinks for airborne vehicles

NAS4121 - Formed heat sinks

References and Resources

ATS—Heat sink types: The pros and cons (2 parts)

Sukhvinder S. Kang, "Advanced Cooling for Power Electronics," paper presented by invitation at International Conference on Integrated Power Electronics Systems, 6-8 March 2012, Nuremberg, Germany (pdf).

Image credits:

Ohmite Manufacturing Co. | Rego Electronics