Table of Contents
Thermal conductivity as a key parameter
Lightweight construction is a strategic driver of innovation in numerous high-tech sectors – from aerospace and electromobility to power electronics. However, it is precisely these materials that pose an often underestimated challenge: thermal management. Polymers have low thermal conductivity, which hinders heat dissipation. Materials such as carbon fiber reinforced plastics (CFRP) or thermally conductive polymer compounds, i.e. polymers with fillers, enable improved heat transport properties, maintain weight savings and open up new design freedoms.
Electronic components, sensors and power electronics modules generate considerable amounts of heat during operation. If this heat is not dissipated efficiently, there is a risk of temperature peaks, which can lead to functional limitations, ageing or even abrupt failure.
In order to predict thermally critical conditions and select suitable materials, precise knowledge of their thermal conductivity is essential. This is precisely where thermophysical material characterization comes in.
The article sheds light on how modern lightweight materials behave thermally, what risks arise for electronic systems – and how suitable measurement technology can be used to gain differentiated insights into heat transport properties. It incorporates current scientific work that shows new ways of optimizing polymer and CFRP composites both mechanically and thermally – without compromising the electrical integrity of the components.
Thermal conductivity in theory and practice
Thermal conductivity is a key parameter for the thermal behavior of materials. It describes the ability of a material to transport thermal energy by conduction, typically expressed in watts per meter and Kelvin (W/m-K). In practice, a high thermal conductivity means that thermal energy can be efficiently dissipated from the point of origin to cooler areas. Insufficient heat dissipation, on the other hand, leads to local overheating and accelerated failure of electronic components.
The analysis of thermal conductivity in anisotropic materials such as carbon fiber reinforced plastics (CFRP) is particularly complex. Here, the thermal conductivities differ greatly between the fiber direction (in-plane) and the direction perpendicular to it (through-plane). This strong anisotropy can become a critical bottleneck in applications with localized heat generation – for example under power transistors.
Polymers usually have a very low thermal conductivity in their basic form (<0.3 W/m-K), but offer enormous potential for optimization through the targeted integration of thermally conductive fillers. The overview by Ali et al. (2021) shows various approaches to reinforcing polymers with carbon fibers (CF) and the effect this has on heat transfer properties. The type, quantity and orientation of the fibers have a significant influence on the resulting thermal conductivity.
Another concept is the combination of diamond particles and carbon fibers in an epoxy matrix. This creates a densely packed, two-dimensional conductive network that allows a significant increase in thermal conductivity without compromising electrical insulation (Zheng, J., et al., 2024). This is particularly relevant for use in electronic housings, where high heat dissipation with simultaneous electrical isolation is required.
The quantifying evaluation of these properties requires high-resolution, time-dependent measurement methods. Classic steady-state methods often reach their limits here, especially with thin or anisotropic materials. In such cases, the laser flash method offers an elegant solution by measuring the thermal diffusivity α via the transient response to a defined heat pulse. In conjunction with the specific heat capacity and the density, the actual thermal conductivity can be calculated from this.
This combination of materials science development and precise measurement technology makes it possible to test materials specifically for their thermal suitability and adapt them structurally – a decisive step for the reliable functioning of thermally stressed electronic systems in lightweight structures.
Laser Flash Analyzer: Precision in thermophysical characterization
The reliable determination of thermal conductivity is essential in order to predict the behavior of lightweight materials under thermal stress. Precise, direction-dependent analysis is particularly important for anisotropic or heterogeneous materials such as CFRP or filled polymer compounds. Here, the laser flash method has established itself as one of the leading methods. A key advantage of LFA is that it does not require direct thermal contact with the sample, which avoids measurement errors due to contact resistance.
The measuring principle of the Laser Flash Analyzer (LFA) is based on a transient, non-contact method for determining the thermal diffusivity (α) of a test specimen. The underside of the sample is briefly heated by an energy pulse. A detector on the opposite sample surface measures the temperature rise over time. The thermal diffusivity can be determined from the time it takes for the temperature to reach a certain level.
The thermal conductivity (λ) results from the multiplication of thermal diffusivity (α), specific heat capacity (cp) and density (ρ):
\lambda = \alpha \cdot c_p \cdot \rho
\quad \text{where} \quad
\begin{cases}
\lambda : \text{thermal conductivity (W/m·K)} \\
\alpha : \text{thermal diffusivity (mm²/s)} \\
c_p : \text{specific heat capacity (J/kg·K)} \\
\rho : \text{density (kg/m³)}
\end{cases}
\)
The application of the LFA goes beyond pure measurement: by coupling it with modeling approaches such as finite element analysis (FEA), the values determined can be transferred directly into thermal simulations for component layouts or housing designs. This gives engineers the opportunity to identify critical hot spots as early as the design phase and avoid them constructively.
This makes the Laser Flash Analyzer an indispensable tool in materials development and quality assurance – especially for applications in which thermal performance is crucial for the service life of electronic components.
Case study polymer compounds: thermal conduction through filler engineering
Polymer compounds are among the most versatile materials in modern materials science. Their mechanical, electrical and thermal properties can be specifically adapted through matrix selection and filler design. For thermal management in electronic systems, the challenge is to increase the intrinsically low thermal conductivity of polymers using suitable additives – without significantly impairing electrical insulation or processability.
The overview by Ali et al. (2021) systematically shows how the thermal conductivity of epoxy resins can be significantly increased by combining different fillers. For example, ceramic particles such as aluminum oxide (Al₂O₃) and carbon fibers (CF) were used as conductive additives. In combination, these were able to achieve a thermal conductivity of up to 3.84 W/m-K with a content of 74% Al₂O₃ and 6.4% CF – a more than 12-fold increase compared to the pure polymer(Ali, Z., et al.)
The thermal characterization can be carried out using laser flash analysis (LFA) in order to precisely determine the thermal diffusivity as a function of the filler type, geometry and concentration. It is shown that, in addition to the volume fraction, the spatial distribution and orientation of the fillers in particular are decisive for the effectiveness of heat transport. The addition of CF as a structuring phase supports the formation of percolating paths, which efficiently promote point-to-point heat conduction.
A central point of the work is the correlation between material structure and measurement result. The LFA measurements allow not only the evaluation of the absolute thermal conductivity value, but also conclusions to be drawn about the internal homogeneity and filler distribution. For example, poor dispersion can be recognized by increased scattering in the results.
This results in a clear recommendation for industrial practice: the thermal conductivity of polymer-based materials can be raised to a level that is suitable for demanding thermal applications through the targeted selection and combination of fillers and structure-adapted process technology – while at the same time maintaining electrical insulation and mechanical integrity.
Case study 2D thermal network: diamond and carbon fibers as functional heat conductors
A key problem with many polymer compounds with high thermal conductivity is the conflicting goals of thermal efficiency and electrical insulation. While carbon-based fillers – such as carbon fibers or graphene – are excellent heat conductors, they also have high electrical conductivity. This poses a fundamental challenge for electronic housings, printed circuit board materials or insulating substrates.
Zheng, et al. (2024) present a promising approach: a two-dimensional network of diamond particles structurally bonded in an epoxy resin matrix using short-fiber carbon fibers (CF). Diamond, an electrically insulating but highly thermally conductive material, forms the backbone of the thermal transport structure. The carbon fibers serve as links and connect the diamond particles laterally to form an efficient heat path.
This innovative configuration was systematically investigated in the study and the thermal characterization was carried out using laser flash analysis. The thermal conductivity calculated from this reached 2.653 W/m-K – a value that corresponds to an increase of over 1600 % compared to the unfilled matrix. At the same time, the specific electrical resistance remained at around 1.4 ∙ 1013 Ω∙cm, which confirms its suitability as an electrically insulating housing material.
In the material concept, diamond particles form the primary structure, CF the bridge structure – embedded in the matrix. This network enables a homogeneous distribution of heat conduction without overheating at certain points. Analysis of the microstructure using scanning electron microscopy confirmed the even distribution and effective bonding of the fillers to the matrix.
The key to success lies in the targeted geometric and chemical adaptation of the particles: tight packing and controlled orientation of the network make it possible to create percolating paths for heat conduction without risking an electrical short circuit.
For applications in the field of power electronic components, sensor technology or active cooling structures, this approach offers a promising compromise between high thermal performance and electrical safety. The study by Zheng et al. impressively demonstrates that functional material solutions for the thermal management of polymer-based systems are possible thanks to microstructured filler architecture and precise measurement technology.
Summary and recommendations for action
The ability to efficiently dissipate heat from electronic components is increasingly determining their reliability and service life – especially in lightweight structures based on CFRP or polymer compounds. The case studies examined show impressively how strongly the material structure, the choice of filler and the geometric design influence thermal conductivity – and how crucial precise measurement technology is in order to record these properties.
The transient method of Laser Flash Analysis (LFA) has proven to be an indispensable tool in all cases. Its strengths lie in its ability to provide reproducible and directionally resolved data, even with anisotropic and thin-walled samples. This allows not only a quantitative evaluation, but also conclusions on the effectiveness of structured thermal networks – as in the case of the 2D diamond CF network (Zheng et al., 2024) or the hybrid filler systems in polymers (Wang et al., 2020).
Several recommendations can be derived from these findings for industrial practice:
- Use measurement data as a basis for design: LFA measurements should be integrated into the development process at an early stage in order to define realistic thermal boundary conditions for the component design.
- Align heat conduction in a targeted manner: Anisotropic materials such as CFRP must be considered in terms of their orientation dependency. Structural modifications – e.g. interlayers – can be used to adapt the heat path.
- Use hybrid fillers: In polymer compounds, the combination of ceramic (electrically insulating) and carbon-based (thermally conductive) additives offers the best ratio of thermal performance and electrical safety.
- Planning thermal networks: Microstructured thermal networks demonstrate the potential of targeted filler engineering, even with limited volume fractions.
- Prepare simulation integration: The data measured with LFA should be transferred directly into thermal FEM simulations in order to identify hotspots at an early stage and avoid them on the layout side.
Overall, it is clear that the targeted optimization of thermal conductivity in CFRP and polymer compounds is not a product of chance, but the result of a precisely controlled interplay of material design, structural-mechanical understanding and metrological control. The Laser Flash Analyzer is not just a measuring device, but an integral part of modern material development in the thermal management of electrical systems.
References
- Ali, Z., et al.
Preparation, Properties and Mechanisms of Carbon Fiber/Polymer Composites with High Thermal Conductivity
MDPI Polymers, 2021, 13(1), 169
DOI: https://doi.org/10.3390/polym13010169 - Zheng, J., et al.
Enhanced thermal conductivity and electrical resistivity of epoxy composite by constructing a closepacked 2D network of diamond particles connected with chopped carbon fibers
Polymer Composites (2024)
DOI: https://doi.org/10.1002/pc.29728
