What is a Heat Sink?

A heat sink is a metallic part used to transfer heat from a device (electronic components like amplifiers etc.) to the surroundings, in order to prevent the device from overheating. 

Heat is transferred by conduction from the device to the heat sink. And is transferred by convection from the heat sink to the surrounding fluid (air). Heatsinks increase the contact surface area between the device and the surrounding air, thereby increasing the opportunity to dissipate heat. This is why most heat sinks have fins separated by a distance. The fins increase/maximize the surface area of a heat sink so that more heat can be dissipated. 

Copper or aluminum are the most used metals for the construction of heatsinks. Both metals have very high thermal conductivity, copper has a slightly higher thermal conductivity than aluminium but aluminium is lower in cost and has lower density i.e., less weight. The thermal conductivity of the aluminum is 235 W/mK.

Performance of a heatsink is characterized by its thermal resistance i.e., the difference in temperature between the surrounding air around the heatsink and the device surface in contact with the heat sink per unit of input power. Thermal resistance is denoted by the symbol θ and has the unit °C/W.

Q:Heat dissipation rate in Watt

: Temperature difference in °C

Where,

Junction temperature (T_J): Temperature of the hottest part of the device.

Case temperature (T_C): Temperature of the surface of the device which is in contact with the heatsink assembly.

Surrounding Air Temperature (TA): Temperature of the air surrounding the heat sink.

θ_JC: Junction-to-case thermal resistance. It is the difference in temperature between the junction (T_J) and the case (T_C) for a unit of input power.

T_C is always lower than T_J due to the junction-to-case thermal resistance (θ_JC).

θ_CA: Case-to-ambient thermal resistance. It is the difference in temperature between the device surface (T_C) and the surrounding air (T_A) for a unit of input power.

The performance of the heatsink assembly is defined by the case-to-ambient thermal resistance (θ_CA).

Heat Sinks are used in a wide range of RF products that handle high power levels like Amplifiers, Attenuators and Terminations to help dissipate heat generated during operation to the atmosphere. If a heat sink is not used, the device could heat up and deviate from its normal/expected operation.

Here are some images of RF Products with Heatsinks: