The thinning trend of information and communication electronic devices is adding constraints to the development of applicable heat-dissipation solutions. Phase-change heat-dissipation solutions that have been applied to portable electronic devices tend to rapidly decrease thermal performance when the thickness is reduced to 0.7 mm or less. As an alternative to traditional thermal-management approaches for practical applications, this study attempted to develop a method of improving the through-plane thermal conductivity based on a graphite sheet that can focus on the heat-transport function. We aimed to achieve the heat-transport function within a certain effective length by using the high in-plane thermal conductivity of the graphite sheet, as well as to improve heat transfer in the through-plane direction in the heat in and out area. Composite materials used as TIM(Thermal Interface Material) focus on improving isotropic thermal conductivity by combining polymer, metal, graphite, etc. as a filler. Conversely, the composite material heat-dissipation solution developed in this study differed in that the direction of thermal conductivity was designed depending on the location and function of heat input and output. First, a heat-dissipation composite material with a width of 15 mm and a length of 80 mm suitable for mobile devices was designed, and a TPU film coating considering shock resistance and a structure to install Cu vias in the heat input and output area were also designed. Through simulation analysis, the effect of Cu via and graphite thickness on thermal conductivity and the insulation effect of TPU were evaluated. Through experiments, we confirmed that about 11 % thermal-conductivity improvement effect was obtained by installing Cu vias in the heat load input area of the 0.6 mm-thick graphite sheet. Thermal conductivity can also be improved by about 4.4 % under experimental conditions in a vacuum environment owing to the effect of thermal insulation of some sections by coating with TPU(Thermo-Plastic Polyurethane) film. As regards commercialization, the through-plane thermal conductivity can be improved by about 80 % by the piercing process applied to the heat-dissipation composite material. However, although the structural transformation in which the graphite film in the graphite sheet redirected by the through-hole process can help improve the through-plane thermal conductivity, whether such process can also help improve the heat-transfer rate in the in-plane direction requires further research. Accordingly, we plan to proceed with the via-formation process by boring into graphite sheets in the future.