In the field of thermal management, "thermal conductivity" is arguably the most frequently mentioned and most easily exaggerated parameter. Once a material is labeled "high thermal conductivity," it is often assumed to possess excellent heat dissipation capability by default. However, in real-world engineering applications, the situation is far more complex.
First and foremost, a fundamental concept must be clarified: thermal conductivity is a bulk property of the material, whereas heat dissipation is a system-level boundary issue. Thermal conductivity describes how quickly heat transfers within the material itself, while heat dissipation depends on whether heat can be effectively removed from the material's surface and released into the surrounding environment. Even if a material boasts exceptional thermal conductivity, if the heat reaching its surface cannot be promptly expelled across the boundary, the end result will be simultaneous temperature rise in both the material and the entire system.
Precisely for this reason, in many application scenarios, "fast heat conduction" often merely means that temperature uniformity is achieved more quickly-but it does not necessarily translate to lower system temperatures. To truly understand the engineering value of a thermal interface material, one must pay attention to several additional critical indicators.
01 Specific Heat Capacity and Thermal Diffusivity
Whether a material is suitable for heat dissipation is not determined by thermal conductivity alone; specific heat capacity and thermal diffusivity are equally important factors that cannot be overlooked.
Specific heat capacity refers to the amount of heat required to raise the temperature of a unit mass of the material by 1°C. Materials with low specific heat capacity experience rapid temperature rise upon absorbing a small amount of heat and lack the ability to "store heat and buffer temperature increases." Conversely, for intermittent heat sources involving start-stop cycles, pulses, or load fluctuations, materials with high specific heat capacity can often serve as a more effective "thermal buffer reservoir."
Thermal diffusivity is a comprehensive indicator that describes a material's ability to achieve temperature uniformity during heating or cooling processes. It essentially reflects the speed at which heat propagates through the material. Thermal diffusivity is determined by thermal conductivity, density, and specific heat capacity, expressed as:
Thermal Diffusivity = Thermal Conductivity / (Density × Specific Heat Capacity) , with units of m²/s.
Compared to thermal conductivity alone, thermal diffusivity holds greater engineering significance when describing transient heat dissipation behavior. A higher thermal diffusivity implies that the material can both conduct heat more rapidly and avoid sharp local temperature spikes due to energy accumulation.
For example, copper and CVD diamond film present a classic contrast. Copper has a thermal conductivity of approximately 400 W/m·K, moderate specific heat capacity, and relatively high density. CVD diamond film can exceed 1000 W/m·K in thermal conductivity but has lower specific heat capacity and smaller density. In certain transient, high-heat-flux applications, diamond film-with its extremely high thermal diffusivity-can suppress hot spot formation more quickly. However, in scenarios requiring a certain thermal storage capacity, its overall heat capacity may still fall short compared to a bulkier copper block.
02 Anisotropic Thermal Conductivity
Next, consider graphite, graphene, and pyrolytic graphite-materials that have gained significant attention in recent years. These materials typically exhibit strong anisotropic thermal conduction characteristics: their in-plane thermal conductivity can reach as high as 1500–2000 W/m·K, while through-thickness thermal conductivity often measures only 5–20 W/m·K.
If the heat flow direction does not align with the material's dominant thermal axis, the so-called "ultra-high thermal conductivity" can be almost directly nullified. In practical material design and fabrication, controlling filler orientation often relies on external field induction or specific processing techniques. For instance, leveraging differences in magnetic or electrical properties of fillers, an applied magnetic or electric field can induce directional alignment of lamellar structures to construct high-speed vertical thermal pathways. Alternatively, during processes such as blade coating, extrusion molding, or fiber transfer, shear forces can promote horizontal alignment of flakes along the flow direction. Only through precise orientation control can phonon transport be efficiently directed along the primary thermal axis, thereby truly converting a material's anisotropic advantages into perceptible heat dissipation performance in end products.
03 Other Critical Factors at the System Level
When heat finally reaches the "last step of dissipation," the intrinsic properties of the material are no longer the sole protagonists. Surface emissivity, surface morphology, and the presence of effective convective conditions all significantly influence the ultimate heat dissipation outcome.
Take aluminum as an example: the same substrate material can exhibit drastically different heat dissipation performance depending on its surface condition. In natural convection or vacuum environments, a mirror-polished aluminum surface has extremely low emissivity, which hinders radiative heat dissipation. In contrast, after anodizing, coating application, or surface roughening, the aluminum surface's emissivity can be substantially increased, thereby markedly improving radiative cooling capability.
Furthermore, there is an issue that is often overlooked in engineering practice: many thermal interface materials (TIMs) actually serve as interfacial components within a system. Common products such as thermal greases, gap pads, and phase-change materials derive their value not solely from their bulk thermal conductivity. More critically, their worth lies in their ability to consistently and reliably eliminate air gaps and reduce contact thermal resistance over the long term.
In real-world systems, interfacial thermal resistance can account for 30% to 70% of the total thermal resistance-its impact can even outweigh differences in the bulk thermal conductivity of the materials involved. Within this context, the viscoelastic properties of the material are particularly important. Factors such as compressive deformation capability, stress relaxation characteristics, and long-term creep behavior all directly influence the material's service stability and reliability under sustained mechanical pressure.