CAMBRIDGE, UK – With the ever-increasing need for heat dissipation, high-performance thermal interface materials (TIMs) with higher thermal conductivity and other properties are becoming essential. Driven by this trend, a number of high-performance TIMs are emerging. This article primarily introduces the advantages and drawbacks of advanced carbon-based TIMs. However, it is worth noting that many other TIMs offer superior performance. The recent TIM market report from IDTechEx, “Thermal Interface Materials 2024-2034: Technologies, Markets, and Opportunities”, offers a holistic view of the TIM industry.

Carbon-based TIMs overview

Carbon materials provide high thermal conductivity as raw materials. The raw carbon fillers often have a thermal conductivity over 1000 W/m·K (in-plane rather than through-plane). Within the scope of carbon-based high-performance TIMs, the main competitors include carbon fiber, graphite, carbon nanotubes, and graphene. There is also emerging interest in diamond-based TIMs.

Graphite-based TIMs: graphite sheets and graphite TIMs

Graphite is a highly thermally conductive material, extensively used as a heat spreader (XZ in-plane to prevent hot spots). Typical examples include phone batteries or displays where a thin layer of graphite is used.

There are also instances of graphite acting as a TIM, either by using it for conductive fillers or modifying the sheets to provide some through-plane advantages (which blurs the line between a TIM and a heat spreader).

Graphite has excellent in-plane conductivity (x-y) but relatively poor through-plane (z) conductivity. This property is beneficial for avoiding hot spots and achieving good homogeneity, which is why it is frequently used in smartphones. However, it is not effective for the key challenge of dissipating heat from the source.

One example of a graphite sheet product is NeoGraf's HITHERM, which has an in-plane conductivity of around 800 W/m·K (note that other players claim values over 1000 W/m·K) but is limited to 7 W/m·K through-plane. To enhance the through-plane thermal conductivity of graphite sheets, vertically aligned graphite could potentially be used. However, the cost would increase significantly; IDTechEx has noticed that the cost per m² can increase by 10 times for vertical graphite compared to regular graphite sheets.

Another commonly used graphite-based TIM is graphite paste, where graphite is used as a thermal filler. Graphite pastes typically have a thermal conductivity between 5 and 15 W/m·K, with a retail price between US$0.03/ml and US$3/ml, depending on the quality and purity of the graphite, quantity purchased, supplier, and other factors. It is worth noting that this cost is estimated by IDTechEx, and there might be some outliers. For a more detailed cost analysis, please refer to IDTechEx’s research report, “Thermal Interface Materials 2024-2034: Technologies, Markets, and Opportunities”.

Boron nitride-based TIMs

Boron Nitride (BN) has always been a fascinating filler material for enhancing thermal conductivity. It exhibits a remarkable thermal conductivity of up to 600 W/m·K (although many are around 300 W/m·K), which is significantly higher than many other materials, and is electrically insulating. Furthermore, BN is non-toxic and possesses excellent chemical and thermal stability, capable of withstanding temperatures above 1000°C without degradation. This stability simplifies its handling and storage when compared to other filler materials, reducing the risk of chemical reactions or safety hazards.

The form of BN used, such as hexagonal BN (h-BN) or cubic BN (c-BN), can impact its performance. Hexagonal BN, for example, is known for its layered structure that promotes high thermal conductivity while minimizing agglomeration. This is particularly true if the synthesis process maintains minimal impurities, enhancing the material's dispersion within a composite.

However, the primary barrier to the widespread adoption of BN fillers is their high cost. BN fillers typically range from US$50/kg to US$65/kg, influenced by factors such as volume, supplier, purity, and form. These costs are considerably higher compared to other fillers, leading to their use as secondary rather than primary fillers in many applications. This economic constraint means that BN is often incorporated in smaller quantities to achieve the desired thermal conductivity improvements without significantly increasing the overall cost of the material. A more detailed comparison of BN’s thermal conductivity, density, dielectric strength, and use cases is included in “Thermal Interface Materials 2024-2034: Technologies, Markets, and Opportunities”.

Conclusion

As the demand for efficient heat dissipation continues to rise, the need for high-performance TIMs with superior thermal conductivity and other critical properties becomes increasingly evident. This article has highlighted the advantages and limitations of advanced carbon-based TIMs, such as graphite, carbon fiber, carbon nanotubes, and graphene. Graphite sheets, known for their high thermal conductivity, play a significant role in heat management solutions, though they face challenges with through-plane conductivity.

In addition to carbon-based TIMs, boron nitride (BN) stands out for its impressive thermal conductivity, electrical insulation, and exceptional chemical and thermal stability. Despite these advantages, the high cost of BN fillers, ranging from US$50/kg to US$65/kg, limits their widespread adoption, often relegating them to secondary filler roles in various applications.

To gain a comprehensive understanding of the TIM industry and explore the latest advancements, technologies, market trends, and opportunities, refer to IDTechEx’s latest research, “Thermal Interface Materials 2024-2034: Technologies, Markets, and Opportunities”. This resource provides an in-depth analysis of various TIMs, including detailed comparisons of thermal conductivity, density, dielectric strength, and use cases, offering valuable insights for professionals and researchers in the field.