Power semiconductors - Thermal problems (part 1)

Articles D 3 100 to D 3 109 provide an introduction to the physics of power components, and describe the electrical and physical principles used to produce discrete or integrated power components. The primary role of these power components is to act as switches in electrical energy conversion circuits, blocking high voltages and carrying high currents. Under these conditions, whether they are discrete power components, or integrated power components in hybrid or monolithic form, these devices dissipate a certain amount of electrical power in the form of heat. This electrical power dissipated in the form of heat, which in most cases is negligible compared with the electrical power converted, can nevertheless be significant even when the components are operating under perfectly normal conditions. In order to keep their operating temperature low enough to allow the component to continue working in an operational manner, it is necessary to carry out an appropriate analysis of the heat dissipation mechanism in the crystal, the housing and the associated cooling device. While the problem of the thermal design of the chip-housing-cooler assembly was already important for discrete power components, it becomes even more important when considering integrated power circuits in hybrid or monolithic form. Indeed, for the latter, the concentration of dissipated electrical power over a very small surface area means that the limit of 100 W/cm ² is quite easily reached, beyond which only high-performance cooling systems can be considered. The aim of this article is first and foremost to review the analytical and other methods available for assessing the temperature of the active zone of an electronic component in operation. In a second article , we will address the problem of interactivity between power dissipation and temperature with a view to discussing the validity of the junction temperature concept, and we will conclude our presentation with some considerations on the induced problems of thermal fatigue and reliability.