Advanced Materials and High-Performance Thermal Pastes
May 08, 2023 Yulin Wang
Thermal Interface Materials (TIMs) come in different forms, including thermal pads, thermal grease, gap fillers, thermal paste, and thermal gels. Thermal gel and thermal paste, two of the most commonly used forms, have gained significant momentum over the past several years, especially in the EV, data center, and 5G industries. Typical commercialized TIMs have thermal conductivities (TC) lower than 5 W/m∙K, regardless of their forms. However, with the constantly growing power density, high-performance TIMs with high TC, good mechanical properties, and low costs have gained significant momentum.
Thermal pastes consist of two parts, including matrix and fillers. The matrix is typically made of polymers with good mechanical properties (e.g., high flexibility and low Young's modulus) and low TC. By contrast, fillers are highly conductive materials with higher stiffness, lower flexibility, and higher costs compared with matrix materials. In reality, the choice of TIMs needs to find a balance between multiple factors, including mechanical properties, costs, and TC. This article aims to provide an overview of filler materials by type.
Depending on filler materials, fillers can be primarily split into the following two categories:
Metals or metal oxides have been widely known as materials with superior thermal conductivities. However, the issue with traditional metals is that air gaps may form between heat sinks and electronics due to the intrinsic hardness of high-melting-point metallic materials, resulting in poor contact and significant interfacial thermal resistance.
To mitigate this issue, liquid metals with low melting points, such as gallium (Ga), eutectic gallium-indium alloy (EGaIn), eutectic gallium-indium-tin alloy (GaInSn), and other Ga-based metals, have gradually evolved into a new generation of promising advanced TIMs. The intrinsic liquidity and conformability of liquid metals allow them to fill air cavities between the surfaces of two materials, thus reducing the interfacial thermal resistance.
On the other hand, the fluidity of liquid metals may result in leakage during the application, contaminating high-power devices and even causing short circuits for certain applications. Arieca and Nissan Chemical recently codeveloped a liquid metal embedded elastomer (LMEE) technology where gallium-based liquid metal alloy droplets were embedded into a soft elastomer resin to create a soft and highly deformable circuit. More analysis and examples of novel metal-based TIMs are included in the IDTechEx report, "Thermal Interface Materials: Technologies, Markets, and Forecasts 2023-2033".
Comparison of Thermal Conductivity of Metal Fillers with Costs Comparison and Commercial Use Cases in IDTechEx's latest research "Thermal Interface Materials: Technologies, Markets, and Forecasts 2023-2033". Source: IDTechEx
Carbon fillers: Graphite
Carbon fillers typically present very high TC as raw materials. In the context of TIMs, the main candidates are carbon fiber (pitch-based), graphite, carbon nanotubes (CNTs), and graphene. Although they all present good conductivities, they are all at differing stages of maturity. This section only focuses on the benefits and challenges of graphite-based carbon fillers. Graphite is a highly thermally conductive material, extensively used as a heat spreader (e.g., graphite sheets in phone batteries and/or displays). However, through-plane TC is significantly lower than in-plane TC, which fundamentally restricts its practical adoption as a TIM.
Over the past few years, many companies have worked on increasing z-plane TC. For instance, Panasonic developed a pyrolytic graphite sheet (PSG) based pad with a maximum z-plane TC of up to 10W/m∙K. Graphite can also be used in thermal pastes. A typical example is the thermal paste from Fischer Elektronik, where the maximum TC of the thermal paste can go up to 10.5W/m∙K. The main limitation is that when it comes to this level of thermal conductivity, the manufacturing process gets complicated and costly, thereby limiting its bulk manufacturability.
These are only two of the many examples included in IDTechEx's latest research, "Thermal Interface Materials: Technologies, Markets, and Forecasts 2023-2033". The report also analyzed other common carbon fillers, including graphene, carbon fiber, and carbon nanotubes, with a detailed analysis of the costs, physical properties, cost comparisons, current market status, opportunities, and limitations.
Comparison of Thermal Conductivity of Common Fillers with more details about the costs comparison in IDTechEx's latest research, "Thermal Interface Materials: Technologies, Markets, and Forecasts 2023-2033". Source: IDTechEx
To find out more about this IDTechEx report, including downloadable sample pages, please visit www.IDTechEx.com/TIM. For the full portfolio of research available from IDTechEx please visit www.IDTechEx.com/research.