Thermal design of high power semiconductor packages for aircraft electronic systems

The More Electric Aircraft is likely to require more extensive use of power electronics, for which thermal management will be a key issue. This paper presents an approach to designing integrated air cooled heatsinks which is being developed by Loughborough University as part of the CARAD funded Variable Frequency to Constant Frequency (VFCF) Converter project in collaboration with project partners TRW Aeronautical Systems, Mitel Semiconductor, AEA Technology and BAe Airbus. The paper shows how simple models of the heat transfer from heatsink fins, which are based on well established empirical correlations, may be utilised in combination with either simple analytical models or two dimensional finite element models of the heat conduction from the semiconductor die through the multilayer package structure to the base of the fins. These models allow the generation of design curves which may be used to rapidly explore a wide range of design options before selecting potential designs for more detailed evaluation using 3D FE analysis. In systems such as a VFCF convertor the semiconductor devices are switched at high frequency to ensure good input and output current waveforms. The power dissipated in the semiconductors, and therefore the heatsink weight, will however increase with the switching frequency, whereas the associated filtering components will be smaller and lighter at higher frequencies. The optimisation of the overall system weight therefore involves a tradeoff between the heatsinking and filtering requirements rather than just determining the optimum heatsink design for a specific power dissipatio

IGBT package design for high power aircraft electronic systems

This paper will discuss the design of semiconductor packages having integrated air cooled heatsinks for use in high power electronic systems. It will demonstrate how simple models of the heat transfer from the heatsink fins, which are based on empirical correlations, may be utilised in combination with either simple analytical models or two dimensional finite difference (FD) models of the heat conduction from the semiconductor die through the multilayer package structure to the base of the fins. These models allow the rapid evaluation of performance under both steady state and transient overload conditions, and can be used to rapidly explore a wide range of design options before selecting candidate layouts for more detailed evaluation using, for example, 3D FD analysis. Wind tunnel experiments, which will also be reported, have been carried out to verify the modelling results for different semiconductor device layouts. These trials demonstrate excellent agreement between the models and experimental results

Thermo-mechanical modelling of polymer encapsulated electronics

This paper reports on some initial results from a research project investigating a novel technology for the manufacture of recyclable polymeric modules with embedded electronic systems. The aim of this project is to develop a technology that fully encapsulates electronics for use in the demanding automotive environment. A two shot moulding technology protect delicate electronic circuitry mounted outside of the passenger compartment from extremes of temperature, vibration and humidity. The resultant components also be readily recyclable, making it possible to cost-effectively separate electronic components from the polymer at the end of vehicle life, allowing the recovery of high purity recyclate. The encapsulating polymers have low thermal conductivity, so the process of encapsulation introduce a thermally insulating barrier around the electronics, which impact on the dissipation of heat from the components. In addition, the thermal performance of the assembly is further affected by the high temperature environments within which some of these electronic modules have to operate, such as under the bonnet of a vehicle. This paper presents the results of preliminary models developed for investigating the thermal and mechanical issues arising during the operation of such encapsulated electronics. Analytical models and finite element techniques have been employed to simulate the thermo-mechanical behaviour of overmoulded printed circuit boards