Natural graphite sheet heat sinks for power electronics

In this thesis, a multi-disciplinary investigation of using natural graphite sheet (NGS) for heat sink applications is presented with focus on thermal performance, electromagnetic performance, reliability, cost, energy efficiency, and environmental impact. NGS heat sinks are a promising alternative for weight-sensitive applications in which the heat sink is protected by a case. Contrary to the conventional metals, NGS is also predicted to be feasible at high temperatures or in corrosive environments. To provide the basis for the heat sink design, the thermal conductivity, thermal diffusivity, electrical conductivity, thermal emissivity, coefficient of thermal expansion, and compression behavior are measured and reported in an easy-to-use form. It is shown experimentally that the the thermal contact resistance at metal-NGS interfaces is comparable to metal-metal ones with thermal interface materials, and that the poor through--plane thermal conductivity can be mitigated by embedding heat pipes in NGS heat sinks. The conducted common-mode electromagnetic emissions cannot be reduced by using NGS heat sinks, but potential to reduce the radiated emission by 12 to 97 % was identified. Complex implications on reliability arising from replacing conventional metal heat sinks with NGS ones are discussed. The cost of NGS heat sinks produced in high volumes is predicted to be a double that of mass-produced conventional aluminum ones. The environmental impact of production, manufacturing, and end-of-life management of NGS is reviewed and compared to the conventional heat sink materials. A case-specific approach to evaluating the feasibility of using NGS heat sinks is recommended and the major steps are outlined. The technology is considered to be ready for a transfer to the industrial research and development stage. An audiovisual summary of the work is available at https://www.youtube.com/playlist?list=PLaX55SIXaD20NQQ2JLP-7abmET7l-6LS4.