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Advances in Thermal Management for High Power Density Automotive Power Semiconductor Module
Keywords: Automotive power module, Thermal management, Liquid cooling
Automotive power semiconductor modules has been becoming one of the critical growth sectors for power semiconductor industry, in which high power density and high reliability standard are required for high performance and high safety Hybrid and Electric Vehicles (HEV/EV). The power chips and modules with high power density and low loss are preferred by automotive industry, but an increased thermal resistance (Rth) could be resulted from the high power density design. Increase of Rth is a key factor affecting power module performance and reliability. One of the technology trends of HEV/EV development is to cool the power electronic system by sharing the coolant with engine, leading to elimination of additional cooling circuit and reduction of cost and volume/weight. The temperature of engine coolant is about 30C higher than current power electronic system coolant, so the junction temperature (Tj) will be elevated by 30C in a standard module. This will restrict the output power and current and accelerate assembly degradation. Therefore, it is essential to optimize the thermal management for automotive to reduce Rth and enhance heat spreading efficiency. Thermal management for low Rth and high efficient cooling designs are proposed to automotive and high quality power modules. The typical advanced solutions include direct liquid cooling (DLC), double side cooling (DSC), direct isolating substrate cooling (DIC), phase change cooling (PCC) etc. These technologies have advantages in thermal performance, reliability, volume and weight, but also have limitations in heat-transfer coefficients, as well as in manufacturability. In this work, the advances in thermal management for high power density automotive power semiconductor module are addressed in details. Thermal and overall performances are compared with the above mentioned solutions. The 650V/600A module is selected as a benchmark and designed with different cooling technologies, but the materials and packaging technologies are same. The schematic cross sections of module with different thermal management will be presented in the paper. Rth J-H (junction to heat sink) and Rth J-F (junction to fluid) are compared to propose an optimized cooling method. The different mounting ways such as pressure contact with thermal interface layer and solder attach are taken into account. It is supposed that PCC is the most promising solution to automotive power module. Tj is calculated at the worst case of power dissipation in HEV/EV mission and at different coolant temperature. The reliability and lifetime of modules with different cooling method are predicted at a typical HEV/EV mission. On the other hand, the electrical performance such as the max output current and power are simulated versus cooling temperature for modules with different thermal management methods. They are limited by the max operational Tj (Tjop), the temperature margin (Tj) between junction and coolant, and Rth J-F. In addition, the aspects of volume, weight, cost and manufacturability of module with different thermal management methods are discussed, which can help trade-off of power module design and selection for manufacturers and customers. The detailed background, description of the advanced thermal management solutions and evaluation results will be presented in the full manuscript.
Yangang Wang, Senior Principal Engineer
Dynex Semicomductor Ltd
Lincoln, Lincoln

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