A structure that is mechanically attached to a device that generates heat, in order to lower the overall thermal impedance between the point source of the heat within the device and its cooler surroundings.
The fundamental aspects to consider in heatsink design are:
- Surface area - you want to maximise the surface area as this is where the thermal transfer to the coolant medium takes place.
- Aerodynamics - the coolant medium needs to be able to easily flow around the heatsink
- Thermal transfer - heat flow within the heatsink needs to be good to get the heat out to the fins and so maximise the use of the large area.
- Contact - you need to maximise the contact with the part needing to be cooled and maximise the efficiency of the contact. This also needs to be maintained over the lifetime.
Number of Fins
Making the fins thicker will increase the heat transfer through the heatsink and to the fins, but will reduce the number of fins that can be fitted within a given package space and hence thereby reducing the surface area available for heat transfer. In addition, the thickness of each fin has to be sufficient to withstand any vibration that the part may experience in service.
The orientation of the heatsink will have an effect on it's efficiency, especially when relying on natural air convection.
Efficiency versus orientation: note that maximum is with the fins oriented vertically.
A rough surface finish will increase the surface area. If a positive air flow is being used over the heat sink then a rough surface will lead to a thicker boundary layer and this will act as a barrier and reduce heat exchange.
Thermal cycling must be taken into account when designing any heat sink.