In this paper two possible ways are investigated to create accurate thermal models without having validated information on the thermal properties of the applied thermal interface materials. One way is the calibration of a detailed numerical thermal model based on the physical information which can be derived from experimental structure functions. In the paper we show a complete calibration procedure using a TO-220 package as an example. Another approach is the generation of dynamic compact models based on real measurements. In order to apply this approach one has to identify the junction-to-case thermal resistance of the tested package using the JEDEC JESD 51-14 standard.