Tag Archives: TIMs

Thermal Interface Materials for Electronics

As the name suggests, TIMs are Thermal Interface Materials that the electronic industry typically uses between two mating surfaces. They help to conduct heat from one metal surface to another. TIMs are a great help in thermal management, especially when removing heat from a semiconductor device to a heat sink. By acting as a filler material between the two mating surfaces, TIMs improve the efficiency of the thermal management system.

There are various types of material that can act as TIMs, and there are important factors that designers must consider when selecting a specific material to act as a TIM for a unique application.

Every conductor has its own resistance which impedes the flow of electrical current through it. Impressing a voltage across a conductor starts the free electrons moving inside it. Moving electrons collide against other atomic particles within the conductor, giving rise to friction and thereby generating thermal energy or heat.

In electronic circuits, active devices or processing units like CPUs, TPUs, GPUs, and light-emitting diodes or LEDs generate copious amounts of heat when operating. Other passive devices like resistors and transformers also release high amounts of thermal energy. Increasing amounts of heat in components can lead to thermal runaway, ultimately leading to their failure or destruction.

Therefore, it is desirable to keep electronic components cool when operating, thereby ensuring better performance and reliability. This calls for thermal management to maintain the temperature of the device within its specified limits.

It is possible to use both passive and active cooling techniques for electronic components. It is typical for passive cooling methods to use natural conduction, convection, or radiation techniques for cooling down electronic devices. Active cooling methods, on the other hand, typically require the use of external energy for cooling down components or electronic devices.

Although active cooling can be more effective in comparison to passive cooling, it is more expensive to deploy. Using TIMs is an intermediate method to enhance the efficiency of passive cooling techniques, but without excessive expense.

Although the mating surfaces of the component and its heat sink may appear flat, in reality, they are not. They typically have tool marks and other imperfections such as pits and scratches. The presence of these imperfections prevents the two surfaces from forming close physical contact, leading to air filling the space between the two non-mating surfaces. Air, being a poor conductor of heat, introduces higher thermal resistance between the interfacing surfaces.

TIMs, being a soft material, fills a majority of the gaps between the mating surfaces, expelling the air from between them. In addition, TIMs have better thermal conductivity than air does, typically, 100 times better, and their use considerably improves the thermal management system. As such, many industrial and consumer electronic systems use TIMs widely for ensuring efficient heat dissipation and preventing electronic components from getting too hot.

The electronic industry uses different forms of TIMs. These can be thermal tapes, greases, gels, thermal adhesives, dielectric pads, or PCMs that change their phase. The industry also uses more advanced materials such as pyrolytic graphite, as these are thermally anisotropic.

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.