CAMBRIDGE, UK – Thermal interface materials (TIMs) are increasingly adopted, with the market size expected to exceed US$8 billion by 2034. Thermal fillers play a crucial role in TIMs as they directly affect properties such as thermal conductivity, viscosity, cost, abrasiveness, and several other factors. TIM fillers typically stand as the most expensive ingredient in TIM formulations; therefore, the selection of TIM fillers needs to find a balance between good thermal conductivity, decent mechanical properties, and an acceptable price.

There is a variety of TIM fillers, including alumina, aluminum hydroxide (ATH), aluminum nitride (AlN), zinc oxide (ZnO), magnesium oxide (MgO), and boron nitride (BN). Depending on the target applications and requirements, the filler materials, particle size, and filler mixing are proprietary to TIM formulators. Below are a few interesting findings based on the comparison of different fillers, with more in-depth analysis covered in IDTechEx’s new market research report, “Thermal Interface Materials 2024-2034: Technologies, Markets, and Forecasts”.

Alumina fillers are the most commonly used in the current market. They are effective for increasing thermal conductivity in epoxies at a low cost (USD 5.5-6.5/kg with the potential to go as low as USD 2-3/kg). It is worth noting that prices are largely dependent on filler size, grade, geometry, and order volume. In addition to thermal conductivity, alumina fillers also present low electrical conductivity, making them ideal for electronics applications. However, despite their benefits, alumina fillers come with several limitations, such as relatively low thermal conductivity compared with other high-performance fillers, abrasiveness, and low viscosity at high loading percentages. Alumina fillers can be broadly split into spherical alumina and ground alumina fillers, spherical alumina typically has higher costs than ground alumina. According to IDTechEx’s research, ground alumina can reduce costs by around 50% compared to spherical alumina. However, ground alumina, due to their edgy geometries, often have a much lower loading percentage.

An interesting trend in TIMs for electric vehicle (EV) batteries is the transition from using alumina fillers to ATH fillers. ATH fillers have significantly lower costs compared to alumina (20% to 40% lower, depending on volume, suppliers, and many other factors), but they also lead to lower thermal conductivity. Nevertheless, driven by the battery pack configuration transition from modular design to cell-to-pack design and even cell-to-pack 3.0 design by CATL, IDTechEx believes that the thermal conductivity required for TIMs in EV batteries is expected to decrease from around 3.5 W/mK previously to around 2.5 W/mK in the future. This lowering of thermal conductivity opens the possibility of using ATH fillers for EV manufacturers to further reduce costs. Additionally, ATH fillers also have flame retardancy as they can decompose endothermically, releasing approximately 35% of their weight as water vapor, thereby absorbing heat and reducing thermal runaway. More details on how EV battery pack configuration will affect thermal conductivity and TIMs employed in EV batteries are covered in the IDTechEx report, “Thermal Interface Materials 2024-2034: Technologies, Markets, and Forecasts”.

In addition to low-cost thermal fillers, some applications also need high-performance TIMs. Commonly used higher-performance TIMs include boron nitride fillers and AlN fillers. However, high performance comes with high costs. For instance, BN fillers can cost 10 times more than alumina fillers. Therefore, to balance thermal conductivity performance and cost, TIM formulators typically mix fillers where primary fillers are low-cost alumina, and secondary fillers are high-cost BN fillers or others. Additionally, TIM fillers with various particle sizes are also commonly used. Larger fillers can reduce specific surface area and interfacial thermal resistance, improving thermal conductivity. However, large fillers lead to high defect density, which can impede heat transfer. Hence, smaller fillers are employed as additives to reduce defect density.

Besides the fillers mentioned above, there are also opportunities for other fillers such as MgO, ZnO, and several others, although each presents its own challenges, such as toxicity and high costs. For more details on the benchmark comparison of TIM fillers, please refer to IDTechEx’s new report, “Thermal Interface Materials 2024-2034: Technologies, Markets, and Forecasts”.

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