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In recent years, with the coordinated evolution of “network-computing-endpoint” systems, the development of integrated air-ground-space information systems, and the continuous expansion of specialized application scenarios, electronic devices have imposed increasingly stringent demands on thermal management materials. Thermal interface materials must not only exhibit outstanding thermal conductivity but also maintain long-term stability under complex operating conditions, adapt to diverse packaging forms, and withstand extreme environmental conditions. Consequently, TIM materials featuring high thermal conductivity, high reliability, and ease of application have become a core element for enhancing product competitiveness in the electronics manufacturing industry.
Fundamental Concepts and Technical Mechanisms of Thermal Interface Materials
Thermal interface materials are composites formed by incorporating various thermally conductive fillers (such as oxides, nitrides, and carbon materials) into polymer matrices like silicone, epoxy resin, polyurethane, or acrylic. Their core function lies in filling microscopic gaps between heat-generating components and heat sinks, eliminating air trapped due to surface irregularities. This establishes efficient thermal conduction pathways, significantly reducing interfacial thermal resistance.
Research indicates that any apparently smooth solid surface exhibits microscopic undulations. When two materials contact, the actual contact area constitutes only about 10% of the apparent surface area, with the remainder occupied by air. Given air's extremely low thermal conductivity (approximately 0.026 W/m·K), these microscopic air gaps severely impede heat transfer. Thermal interface materials effectively fill these voids through their excellent wettability and deformability, reducing interfacial thermal resistance by several orders of magnitude. This ensures efficient heat transfer from the chip to the heat sink.
Based on their position within the thermal structure, TIMs can be categorized into several types:
TIM1: Located between the chip and the metal heat spreader, serving as the chip's “first line of defense” for heat dissipation. It must possess extremely high thermal conductivity and long-term reliability.
TIM2: Positioned between the metal heat spreader and the heat sink. This layer typically demands superior mechanical properties and ease of application.
TIM1.5: A novel structure emerging in recent years eliminates the metal cover plate, enabling direct contact between the heat sink and the bare die surface. While this configuration significantly shortens the heat transfer path and enhances cooling efficiency, it imposes stricter demands on the TIM material's mechanical stress resistance and interface stability.
Types and Technical Characteristics of Mainstream Thermal Interface Materials：
1. Thermal Pads
Thermal pads are typically manufactured using silicone as the base material, filled with thermally conductive particles such as aluminum oxide, boron nitride, or aluminum nitride. They are produced through mixing and calendering processes. Their thermal conductivity generally ranges between 1–10 W/m·K, with some high-performance products exceeding 15 W/m·K. Thermal pads offer excellent compression recovery and electrical insulation, making them suitable for diverse TIM applications. However, prolonged exposure to high temperatures may cause deformation or oil migration, compromising interface stability.
2. Thermal Grease
Thermal grease is a paste-like composite material based on silicone oil and supplemented with high-thermal-conductivity fillers. It exhibits excellent temperature resistance (-50°C to +230°C) and low oil separation characteristics, with thermal conductivities typically ranging from 1–10 W/m·K. While higher filler ratios enhance thermal conductivity, they increase paste viscosity, impairing interface filling and inadvertently raising thermal resistance. Additionally, prolonged high-temperature operation may trigger “pump-out” effects, making it more suitable for TIM2 scenarios than TIM1.5 structures.
3. Thermal Conductive Gels
Thermal conductive gels are polymeric gel materials composed of silicone oil, thermal fillers, and crosslinking agents. They feature semi-solid consistency, low stress, and anti-sag properties, making them suitable for automated dispensing processes while effectively mitigating thermal-mechanical stress damage to chips. Their thermal conductivity typically ranges between 1–8 W/m·K, primarily serving consumer electronics, servers, and automotive electronics.
4. Thermal Encapsulants
Beyond thermal conductivity, thermal encapsulants provide insulation, sealing, and protective properties. They are widely used for module-level thermal management in photovoltaic inverters, automotive electronic control units, and industrial power supplies. With thermal conductivities typically ranging from 1.0–5.0 W/m·K, these materials emphasize balanced performance, including flowability, cure speed, and aging resistance.
5. Thermal Insulation Sheets
Thermal insulation sheets are laminated materials composed of glass fiber or polyimide substrates coated with silicone composite systems. With thermal conductivities generally ranging from 0.8–1.5 W/m·K, they prioritize insulation strength and voltage resistance, commonly used in power modules and new energy vehicle electric drive systems. Recent developments in new materials like boron nitride-based insulating sheets have further enhanced their combined thermal conductivity and insulation performance.
6. Liquid Metals
Liquid metals, primarily gallium-based alloys, feature ultra-high thermal conductivity (20–80 W/m·K) and extremely low thermal resistance, making them ideal for high-power chip cooling. However, their strong corrosivity, high electrical conductivity, and challenging encapsulation properties limit widespread adoption. They are currently mainly used in extreme cooling scenarios like lasers and aerospace applications.
7. Thermal Double-Sided Tape
Thermal double-sided tape is a functional material featuring adhesive layers on both sides of a polymeric base film. Beyond its thermal conductivity of 0.5–3.0 W/m·K, it offers excellent bonding strength and gap-filling properties. It is suitable for integrated thermal bonding designs between heat sinks and housings in LED lighting fixtures and mobile devices.
8. Indium Metal Foil
Leveraging its high thermal conductivity, excellent ductility, and low melting point, indium metal foil is primarily used in high-end thermal management applications such as optoelectronic devices and power semiconductors. Typically exceeding 99.99% purity, it achieves near-perfect interface bonding under high-temperature and high-pressure conditions.
9. Graphene Thermal Pads
Graphene thermal pads are lightweight, flexible materials using graphene as a thermal filler. They offer thermal conductivities ranging from 20–200 W/m·K with extremely low thermal resistance and thicknesses as thin as 0.01 mm. Widely adopted in 5G equipment and premium consumer electronics, they are poised to surpass traditional materials in TIM 1.5 applications. Notably, Chinese enterprises have established a relatively complete industrial chain layout in the graphene thermal interface material sector.
10. Carbon Fiber Thermal Interface Material
Carbon fiber thermal interface material utilizes carbon fiber as its reinforcing skeleton, with thermal conductivity ranging from 5–50 W/m·K. It offers advantages such as lightweight properties, high strength, and corrosion resistance, making it suitable for high-end equipment sectors like aerospace and new energy vehicles.
Market Landscape and Development Trends：
Statistics indicate that the global thermal interface material (TIM) market has reached nearly $10 billion. Though a niche segment within fine chemicals and electronic materials, TIM plays a critical role in ensuring the reliable operation of high-power electronic devices. Currently, international companies still dominate the high-end TIM1 and TIM2 markets. However, with domestic enterprises' sustained investments in material R&D, process optimization, and application solutions, the localization substitution process is accelerating.
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