Cooling effects of infrared radiative inorganic fillers in heat dissipation coatings at temperatures below 400 K

Heat dissipation for electronic devices has attracted extensive interest because the reliability, lifetime, and performance are seriously affected by temperature increases during the operation. The effects of inorganic fillers in heat dissipation coatings on the temperature reduction of heat sources between 310 and 400 K were investigated. Acrylic coating films with calcium fluoride, pyrolytic boron nitride, and silicon carbide particle fillers were formed on pristine aluminum plates that were then heated in a closed system. A significant temperature reduction of about 17 K was obtained at the surface of a heat source with an acrylic coating film including calcium fluoride particles on the aluminum plate; under equivalent conditions, the uncoated aluminum plate temperature reached 373 K. The materials used in the coatings were characterized by wavelength-dependent infrared absorption and emission properties. Although the overall emissivity in wide wavelength range is previously considered to be the most crucial variable in radiative cooling, materials have specific infrared absorption and emission properties depending on their physical structures. Therefore, elucidating the relationship between the characteristics of an individual heat emission material and its cooling effects is necessary in order to design more effective heat dissipation measures based on radiation. It was confirmed that the selection of an appropriate filler material with specific infrared emission properties corresponding to the emitting wavelength at the given temperature of the objects to be cooled was important. Distinctive radiative cooling effects were thus obtained, even in the relatively low-temperature range examined here, by the selection of appropriate materials with radiative properties in the temperature range of interest.