Thermally conductive silicone sheets are core materials for thermal management in electronic devices, and their thermal conductivity directly determines heat dissipation efficiency. This parameter is influenced by multiple factors, among which material composition, filler characteristics, microstructure, density, thickness, temperature, and molding process are key variables.
Material composition is fundamental to the performance of thermally conductive silicone sheets. Silicon-based materials have become the mainstream matrix due to their chemical stability and temperature resistance, but their inherent thermal conductivity is limited, requiring fillers to improve overall performance. The choice of filler is crucial; metal oxides (such as alumina) and nitrides (such as boron nitride) are widely used due to their high thermal conductivity. Different fillers have significantly different thermal conductivity; for example, boron nitride has a much higher thermal conductivity than ordinary alumina, directly determining the upper limit of the composite material's thermal conductivity. Furthermore, the compatibility between the filler and the matrix also affects the formation of thermal conduction pathways; if the bonding force is weak, the interfacial thermal resistance will significantly weaken the thermal conductivity.
The characteristics of the filler allow for more precise control of the thermal conductivity. The filler content is the primary factor; when the filler forms a continuous network structure in the matrix, the thermal conductivity is significantly improved. However, excessive content can increase material brittleness and processing difficulty, thus requiring a balance between thermal conductivity and mechanical properties. The shape of the filler is also crucial; plate-like and fibrous fillers are easier to construct thermal conduction pathways than spherical fillers due to their larger contact area and shorter heat conduction paths. For example, fibrous boron nitride interwoven into a network within the matrix can significantly improve longitudinal thermal conductivity, while spherical fillers require a higher content to achieve a similar effect.
Microstructure is a hidden factor in thermal conductivity. The internal crystal structure, porosity, and particle arrangement of the material directly affect heat transfer efficiency. Ideally, the filler should be uniformly dispersed and tightly packed to reduce voids and defects in the heat conduction path. If the filler agglomerates or is unevenly distributed, it will create localized thermal resistance, leading to a decrease in thermal conductivity. For example, compression molding can compress the internal voids of the material, making the filler particles more closely contacted, thereby improving thermal conductivity; while injection molding may result in uneven distribution due to differences in filler flow, requiring subsequent optimization.
The relationship between density and thermal conductivity needs to be viewed dialectically. High density typically means the addition of more thermally conductive filler, resulting in tighter contact between filler particles, shorter heat conduction paths, and enhanced thermal conductivity. However, if the increased density stems from non-thermally conductive fillers or internal material defects (such as pores), it can actually hinder heat transfer. For example, in boron nitride-filled thermally conductive silicone sheets, density is positively correlated with thermal conductivity; however, adding excessive amounts of low-thermal-conductivity fillers may decrease thermal conductivity despite increased density. Therefore, optimizing density requires balancing filler type and uniform distribution.
Thickness affects thermal conductivity at the thermal resistance level. Theoretically, the thinner the thermally conductive silicone sheet, the lower the thermal resistance and the faster the heat transfer. However, excessive thinness may lead to insufficient mechanical strength, making it prone to breakage during installation, and it may not adequately fill the tiny gaps at the contact surface, thus increasing contact thermal resistance. In practical applications, the appropriate thickness must be selected based on equipment space and installation process. For example, laptop GPU cooling requires flexible, compressible, thin silicone sheets, while industrial power modules may use thicker, high-strength products.
Temperature's effect on thermal conductivity is negligible under normal operating conditions, but it requires careful consideration in extreme environments. As temperature rises, the thermal motion of material molecules intensifies, enhancing air conduction and radiation, potentially leading to a slight increase in thermal conductivity. However, within the common operating range of 0-50℃, this change has limited impact on heat dissipation. For equipment requiring long-term operation in high or low temperature environments, a dedicated temperature-resistant thermally conductive silicone sheet should be selected, as its thermal conductivity exhibits superior stability with temperature changes.
The molding process is the ultimate guarantee of thermal conductivity. Pressing processes use high pressure to arrange fillers in an orderly manner, forming a dense thermally conductive network; injection molding is suitable for complex-shaped products, but requires control of filler flow to avoid uneven distribution; high-temperature sintering can eliminate internal voids in the material, improving the continuity of the heat conduction path. Process selection must be combined with the product's shape, size, and performance requirements. For example, high-power LED heat dissipation requires compression-molded high-thermal-conductive silicone sheets, while irregularly shaped electronic components may use injection-molded products.
The thermal conductivity of a thermally conductive silicone sheet is the result of the combined effects of material composition, filler characteristics, microstructure, density, thickness, temperature, and molding process. In practical applications, it is necessary to comprehensively weigh various factors based on heat dissipation requirements, equipment operating conditions, and cost budget to select or customize the optimal solution in order to achieve efficient and stable thermal management.
