Posted on: July 1, 2014

What is a heat sink?

A heat sink is an electronic device made of good thermal conducting material and usually attached to an electronic device to dissipate the unwanted heat. It is used to cool the circuit components by dissipating the excess heat to prevent overheating, premature failure, and improve the reliability and performance of the components.

The heat sink operation is based on Fourier’s law of heat. Whenever a temperature gradient exists in a body, heat transfers from the high temperature sections to the lower temperature areas. The three different ways in which the heat can be transferred are through radiation, convention or by conduction.

Thermal conduction occurs whenever two objects at different temperatures are in contact. This involves the collisions between the fast molecules of the hotter object with the slow moving molecules of the colder object. This leads to the energy transfer from the hot object to the cooler object. A heat sink thus transfers the heat from the high temperature component such as a transistor to the low-temperature medium such as air, oil, water or any other suitable medium through conduction and then convection.

What is a Heat Sink
Image Credit – ECN Mag

There are two types of heat sinks, namely the passive heat sink and the active heat sink.

1. Active heat sinks use cooling fan or blower to cool the heat sink. These have excellent cooling performance but require periodic maintenance due to the moving parts.

2. Passive heat sinks do not use any fans and have no moving parts and are more reliable.

The heat sinks can further be classified by their physical designs and shapes, material used and more. Typical heat sinks are:

  • Stamped
  • Machining
  • Bonded-fin
  • Folded-fin
  • Forged Heat Sinks
  • Single Fin Assembly Heat Sinks
  • Swaged Heat Sinks
  • Skived Heat Sinks

The heat sink acts as a heat exchanger and usually designed to have maximum surface area in contact with the cooling medium such as air. The performance is dependent on the material used, surface treatment, physical features such as protrusion design, air velocity and attachment methods. Thermal pastes, compounds and conductive tapes are some of the materials used between the component’s heat spreader surface and the heat sink surface so as to improve the heat transfer and hence performance of the heat sink.

Metals with excellent thermal conductivity such as diamond, copper and aluminum make the most efficient heat sinks. However aluminum is more commonly used due to its lower costs.

Other factors that affect a heat sink’s performance include:

  1. Thermal Resistance
  2. Airflow
  3. Volumetric resistance
  4. Fin density
  5. Fin spacing
  6. Width
  7. Length

Heat sinks are used to cool various electronics components whose heat dissipation abilities are is insufficient to dissipate all the excess heat. These devices include:

  • Power transistors, thyristors and other switching devices
  • Diodes
  • Integrated circuits
  • CPU Processors
  • Graphic processors
  • LEDs