cooling options and challenges of high power semiconductor modules

Introduction Trends in power electronics systems and devices over the last decade have placed increasing demands on the efficiencies of the thermal management systems used for power MOSFET and IGBT modules. The pressure to decrease the size of power electronics systems and, subsequently, the module, has resulted in a 50% footprint area reduction of some IGBT modules. This has resulted in higher power dissipation densities for the IGBT die as well as the module due to denser packing of the die. Increases in switching frequencies and voltage ratings of IGBTs also result in higher power dissipation at the die level. Even though a portion of the die power losses has been offset by advances in both MOSFET and IGBT chip design, the cooling capabilities of present modules limit the device performance. Power modules used in Hybrid Electric Vehicles (HEV) provide an additional challenge in that the inlet temperature of the coolant can be over 100C, requiring low temperature differentials (20 – 30C) between the die and the coolant to keep the IGBT comfortably below the maximum operating temperature of 150C, while simultaneously dissipating high heat fluxes. In other HEV designs, less efficient liquids, namely oil or transmission fluid, may be the only coolants available for cooling the power module. Faced with the challenges of efficiently and economically cooling increasing power dissipation densities with low temperature differentials, power semiconductor module designers are turning to new heat sink technologies. In this article, several methods for reducing the thermal resistance of power modules are presented and compared in the context of a baseline 1200V isolated base IGBT power module design.