Thermal conductivity measurement of adhesives and other TIM (Thermal Interface Materials)

Thermally conductive adhesives, potting compounds and gap fillers, also commonly referred to as TIM, are used wherever components are to be thermally contacted. Until a few years ago, the main area of application for these materials was in microelectronics, e.g. to reliably dissipate the heat loss from highly integrated circuits or power semiconductors into cooling systems. With the progress of electric vehicles, the market for such products has grown considerably. They have become an indispensable key component that ensures the performance and longevity of the vehicle battery. Future applications include electrical energy storage for wind turbines and in the field of electrolysis for the production of hydrogen.


Increasing demands on TIM

In theory, thermal conduction is mathematically described in many publications, however, the practical implementation in real systems is often exposed to unknown quantities and provides the developers of such systems with many influencing parameters to achieve optimization. TIM are mostly composed of binders with a high content of inorganic fillers with high intrinsic thermal conductivity.

However, the effective thermal conductivity in a specific component is not only additively composed of the individual intrinsic thermal conductivities of the different components of the TIM, but is also determined by the thermal contact resistances of the materials present in the complete component. These can affect both the bonding of the substrate to the TIM and the conduction in the TIM through the fillers themselves.

In view of these changing requirements, users, adhesive manufacturers and corresponding research institutions are faced with the task to develop products with increased thermal performance. For this workprecisely determined characteristic values for thermal conductivity are required and shout form the basis for component design and for thermal simulation calculations.


Extensive measurement capabilities at Fraunhofer IFAM

Fraunhofer IFAM has many years of experience in the experimental determination of thermal conductivities. The available measuring instruments fully cover the range from plastics with low thermal conductivities to highly thermally conductive metal and ceramic substrates. In this way, in the case of adhesives and gap fillers, measurements are not only possible on substance samples, but also on samples where, for example, the adhesive is part of a material composite.

In detail, Fraunhofer IFAM has the following measurement capabilities:

  • Measurement with stationary plate systems and dynamic procedures according to standardized methods.
  • Thermal conductivity range: 0.1 W/mK - 400 W/mK
  • Accessible temperature range: room temperature up to 300 °C
  • Measurements on coatings and bonded joints, down to layer thicknesses of 25 µm
  • Investigations of materials with direction-dependent thermal conductivity
  • Monitoring of the aging of thermally conductive compounds under temperature or hydrothermal load

In addition to the determination of pure material properties, the institute offers further services: