Thermal Interface Materials (TIMs) and their advantages

The operation of electronic components, especially in power electronics, generates heat that must be dissipated. Otherwise, power losses occur that lead to damage in the electronics. Therefore, these components are usually linked to heat sinks, cooling plates, heat pipe systems or heat exchangers. However, due to mechanical tolerances, unevenness and roughness on the surfaces of the components and heat sinks, air pockets always remain after assembly, which severely impede heat transfer. Thermal interface materials (TIMs) fill these gaps. Thanks to their high thermal conductivity and their ability to make contact with the surfaces, they help to transfer heat quickly from the heat sources to the heat sinks.

Thermal Interface Materials (TIMs) enable efficient dissipation of heat generated in electrical components during operation. In this way, they prevent potentially harmful overheating that cannot be avoided by simply using heat sinks. After all, when two different surfaces are thermally connected (such as a transistor and a heat sink), the effective contact area is clearly in the low percentage range – usually less than ten percent – due to inevitable unevenness of the surfaces. Conversely, this means: Well over 90 percent of the remainder consists of air cavities that dissipate almost no heat due to the low conductivity of air. Consequently, thermal resistance is very widespread at these points. TIMs even out such gaps and unevenness and, with their high thermal conductivity, ensure that heat is transferred quickly and efficiently to the heat sinks.

In addition, there are also thermal conduction materials that can provide reliable electrical insulation between the heat sink and the component under electrical potential, or phase-change materials that, when melted during the transition from a solid to a liquid phase, are able to optimize thermal contact by covering the entire surface. Thermally conductive elastomers – for example, gap fillers and gap filler pads – conform ideally to the surfaces and can thermally bypass large gaps even in the range of several millimeters.

The two most commonly used thermal interface materials (TIMs) are thermally conductive greases and gap fillers.

The liquid or paste-like greases fill unavoidable roughness and unevenness between the power component and the heat sink. They minimize thermal contact resistance and thus enable more efficient heat dissipation. The composition of thermally conductive greases depends on the application. Their disadvantage is that they are permanently fluid and can only be applied in a process-safe manner with great effort. There is a high risk of smearing and of pumping out during operation. From the viewpoint of robust design, their use in applications exposed to mechanical shocks and vibrations is therefore critical.

In contrast, gap fillers consist of soft, highly thermally conductive elastic polymers – usually two-component as well as form-in-place curing or in solid form as pads. Compared to pastes, they can be individually shaped and are therefore often used when large gaps need to be covered (up to more than ten millimeters) or when several components of different, non-planar heights need to be covered in order to dissipate heat into a common heat sink. Their reliability and elastic properties make them well suited for applications subject to high mechanical stress.

Other variants of TIMs are available, for example, as adhesives, films, foils or potting compounds.

Thermal Interface Materials (TIMs) are used wherever heat from power electronics needs to be dissipated through heat sinks to maintain the functionality of a product.

For example

• in the automotive sector (e.g. infotainment, assistance and convenience, control units, bus controllers, servo motors, power semiconductors, batteries and chargers for e-mobility, etc.),
• in avionics (e.g. fly-by-wire flight controls, electronic MCD, radar systems and military applications),
• in all areas of IT technology (e.g. notebooks, industrial computers, routers, servers, memory, graphics cards, driver chips, gaming),
• in energy generation (e.g. inverters, inductors),
• in medical technology,
• or in the field of consumer electronics

The composition of thermal interface materials (TIMs) depends on the thermal requirements of the application, their mission profile and is also determined by the operating temperature range. TIMs often contain silicone as a base matrix. However, in the case of sensitive electrical contacts or other critical requirements (for example, the risk of paint rejection), silicone-based TIMs must not be used. This is because their outgassing can cause damage. In these cases, TIMs consisting of silicone-free polymers are used.

In order to achieve the desired heat-conducting properties, TIMs are filled with, for example, ceramic powders of zinc oxide, aluminum oxide, aluminum hydroxide, boron nitride or metal powders of aluminum, copper, graphite and silver particles, among others, depending on the desired requirement.

For professional use, the optimum TIM must be selected for the specific application. This requires in-depth design-in consulting. This forms the basis for efficient thermal management and thus the safe function and long service life of electronic components. At HALA you will find a wide range of TIMs – whether insulating or electrically conductive.

The best thing to do is to contact us directly – we will advise you at any time, free of charge and conveniently online.