Konstruktion av värmespridare med grafit för flygelektronik
This master thesis was carried out for Saab Avitronics, a business unit of Saab ABactive in electronic systems for military aircrafts. Reliability and weight are of crucialimportance in this environment. To improve reliability and lower the weight graphitemay be used for electronics cooling. Graphite is an anisotropic material and hasthereof high thermal conductivity in two directions (in-plane) and a relatively lowconductivity in the third direction (through thickness).The purpose of this thesis was to investigate if graphite is an adequate thermalconductor to use in PCB carriers. The carriers support and cool the PCB by divertingthe heat dissipation from the PCB components to the edge. The focus of the thesiswork was on redesign of a high power card carrier that was near its maximumcapacity for heat transport.The work was carried out by generating design ideas on how graphite sheets could beused in the carrier and by performing design analyses consisting of practical tests andcomputer simulations. The tests were composed to exam different graphite sheets withdifferent conductivity in-plane and through thickness and of investigating howgraphite is affected by damp environment. Simulation was carried out to evaluate theimpact of the anisotropic structure at different thicknesses on the spreaders.The result showed that the low conductivity through thickness have greater impact atthicker sheets. Improving the conductivity through thickness at the expense of lowerin-plane conductivity did not decrease the temperature difference in this test. Sheetwith higher in-plane conductivity performs best. The result showed that theconductivity in-plane has greater impact on the heat distribution than that throughthickness. The graphite is somewhat affected by humidity and therefore needs to becoated. The anisotropic impact affects more for carriers with hot spots.The work resulted in design recommendations on how graphite could be used in aredesign of the carrier and considerations about environmental demands. By usinggraphite in different carrier designs the temperature can be decreased and/or theweight reduced.