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This master thesis was carried out for Saab Avitronics, a business unit of Saab AB active in electronic systems for military aircrafts. Reliability and weight are of crucial importance in this environment. To improve reliability and lower the weight graphite may be used for electronics cooling. Graphite is an anisotropic material and has thereof high thermal conductivity in two directions (in-plane) and a relatively low conductivity in the third direction (through thickness).The purpose of this thesis was to investigate if graphite is an adequate thermal conductor to use in PCB carriers. The carriers support and cool the PCB by diverting the heat dissipation from the PCB components to the edge. The focus of the thesis work was on redesign of a high power card carrier that was near its maximum capacity for heat transport.The work was carried out by generating design ideas on how graphite sheets could be used in the carrier and by performing design analyses consisting of practical tests and computer simulations. The tests were composed to exam different graphite sheets with different conductivity in-plane and through thickness and of investigating how graphite is affected by damp environment. Simulation was carried out to evaluate the impact of the anisotropic structure at different thicknesses on the spreaders.The result showed that the low conductivity through thickness have greater impact at thicker sheets. Improving the conductivity through thickness at the expense of lower in-plane conductivity did not decrease the temperature difference in this test. Sheet with higher in-plane conductivity performs best. The result showed that the conductivity in-plane has greater impact on the heat distribution than that through thickness. The graphite is somewhat affected by humidity and therefore needs to be coated. The anisotropic impact affects more for carriers with hot spots.The work resulted in design recommendations on how graphite could be used in a redesign of the carrier and considerations about environmental demands. By using graphite in different carrier designs the temperature can be decreased and/or the weight reduced. vi vii

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