Thermal design of converters using discrete power components incorporating an IGBT and a freewheeling diode

This paper presents an extension to the common engineering practice of adding a constant thermal resistance to the manufacturer supplied transient thermal impedance from the semiconductor to the package bottom (Z_thetasJC) when mounting power components to a heat sink using electrically insulating pads. It is shown that, when those components contain more than one semiconductor, the proposed extension is necessary to avoid underestimation of the semiconductor junction temperatures, allowing an optimal use of the thermal capabilities of the semiconductors. A new, semi-intrusive measurement technique is used to validate this new design procedure with experimental data