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Heat sinks are thermally conductive components or devices that absorb and dissipate heat generated by electronic components.

 

Applications and Use

 heat sinks selection guide

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

 

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

 

Type

Description

Applications

Performance

Pros

Cons

Image

Extruded

Useful in most situations; easy to automate production after design is completed.

Many

Varies

Low cost

Limited to dimensions of extruded aluminum

 heat sinks selection guide

Stamped

Stamped from a single piece of metal; easy to automate production.

Low-power

Low

Low cost

Poor performance

 heat sinks selection guide

Bonded Fin

Produced by bonding individual fins to a base; relatively difficult to manufacture.

Large devices

Medium

Available in large sizes

Expensive

 heat sinks selection guide

Folded Fin

Fin pitch is optimized for air flow; may be plastic.

Ducted air

Exceptional

High heat-flux density

Expensive; ducting necessary

 heat sinks selection guide

Active

Includes a powered fan or blower for air movement; not a viable long-term solution; moving parts wear and break down.

Emergency or quick-fix situations

High

Simple, “Band-aid” solution

Poor reliability; high cost; recirculation of warm air

 heat sinks selection guide

Forged

Manufactured by compressing aluminum or copper.

Many

Medium

Low cost

Limited design

 heat sinks selection guide

Swaged

Similar to forged heat sinks; manufactured by forming metal to a die.

High-power

Medium

Ideal for power devices

Heavy and unwieldy; poor flow management

 heat sinks selection guide

Single Fin

Versatile devices; designed to be employed in tight spaces.

Most

Varies

Lightweight, low profile

Expensive

 heat sinks selection guide

Skived

Fins are cut (skived) from a single block of metal (usually copper).

Many

Medium-High

High fin density

Thick base and high weight; directionally sensitive

 heat sinks selection guide

Table image credits: IXBT Labs | KunzeCarlton-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.

Image credit: EEVblog

 

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.)

 

heat sinks selection guide

 

where:

 

qk = 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.

 

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.

 

 


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