Thermal interface materials (TIMs) are increasingly adopted, with the market size expected to exceed US$8 billion by 2034. Thermal fillers are crucial in TIMs as they directly affect properties such as thermal conductivity, viscosity, cost, abrasiveness, and several other factors.
TIM fillers typically are the most expensive ingredients in TIM formulations; therefore, the selection of TIM fillers needs to balance good thermal conductivity, decent mechanical properties, and an acceptable price.
There is a variety of TIM fillers, including alumina, aluminium hydroxide (ATH), aluminium 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 comparing different fillers. IDTechEx’s new market research report, “Thermal Interface Materials 2024-2034: Technologies, Markets, and Forecasts,” covers a more in-depth analysis.
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. Alumina fillers have low thermal and electrical conductivity, making them ideal for electronics applications.
However, despite their benefits, alumina fillers have 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 often has a much lower loading percentage due to its edgy geometries.
An interesting trend in TIMs for electric vehicle (EV) batteries is the transition from alumina fillers to ATH fillers. ATH fillers have significantly lower costs than 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.
ATH fillers also have flame retardancy as they can decompose endothermically, releasing approximately 35% of their weight as water vapour, 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”.
Some applications also need high-performance TIMs, which are commonly used as low-cost thermal fillers. Examples include boron nitride 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, impeding heat transfer. Hence, smaller fillers are employed as additives to reduce defect density.
Besides the fillers mentioned above, there are 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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