Heat Spreading for Thermal Management

Proper thermal management is necessary for ensuring the performance and reliability of electronic devices. Conceptually, this is simple, starting with the transferring of unwanted heat from the source to a larger area for effective cooling by dissipation. However, an implementation may be a difficult task.

Devices that generate heat generally have surfaces that are not large enough or smooth enough. Therefore, they cannot efficiently transfer heat as their thermal impedance is not adequately low. Some devices may not have a planar surface, thereby increasing the challenge of thermal management. Moreover, the challenge can increase with the position of the component to be cooled. If the location of the hot component is deep within the system, extracting the potentially damaging heat may become further complicated.

Many applications depend on thermal greases and pastes for improving thermal conductivity. However, this can be tricky, especially as the coverage may be insufficient, and over-application may result in spillage onto circuit board traces causing short circuits. Another limitation is thermal greases and pastes can only move the heat perpendicular to the surface, and not laterally from the source.

Therefore, designers are now replacing thermal greases and pastes with a variety of TIMs or Thermal Interface Materials. These include fillers and heat spreaders for providing low thermal impedance. This is necessary for the effective transfer of heat while removing any concerns about PCB surface contamination.

TIMs can also meet specific system needs, as their structural design can allow the transfer of heat perpendicularly or laterally. Moreover, TIMs are available in a variety of thicknesses. This enables designers to match them to the requirement of specific applications. They can provide good reliability as they are mechanically stable at elevated temperatures, and they provide high electrical isolation. Furthermore, they are easy to apply.

Placing TIMs between the source of heat and a cooling assembly helps to improve the heat flow through better thermal coupling. Here, two factors improve the efficiency of the thermal coupling. First, TIMs have the ability to conform to surface irregularities. This eliminates pockets of insulating air that actually reduce the thermal conductivity of the interface. Second, TIMs have a high thermal conductivity that is necessary to effectively move heat from the source to the cooling assembly.

Würth Electronik offers TIM (blue) for filling in microscopic irregularities. These irregularities exist on the surfaces of components and cooling assemblies, reducing thermal coupling.

Apart from thermal conductivity, there are other concerns for selecting a specific TIM. One of them is the operating temperature—TIMs are available for different temperature ranges. Another is the distance between the mating surfaces.

Other concerns are whether the TIM needs compression for delivering the optimal amount of thermal transfer and whether the TIM has the withstanding capability for the compression pressure it will face. Würth Electronik offers TIMs with adhesive on one surface that enables mechanical fixing. TIMs may also have to provide electrical isolation.

TIMs made of synthetic graphite offer very high thermal conductivity. The WE-TGS family from Würth Electronik is a synthetic graphite heat spreader. It measures 297 x 210 mm and has a thermal conductivity of 1800 W/mK.