Brice Mcpherson

Power-CAD: A novel methodology for design, analysis and optimization of Power Electronic Module layouts

Power Electronic Module (PEM) design requires simultaneous analysis of thermal, electrical, and mechanical parameters to design an optimal layout. The current design process being used by package designers involves a sequential procedure instead of a simultaneous process. Each design step involves the analysis of the thermal, electrical or mechanical aspects of the design. As a result, the designer has to iterate between the various design process steps in order to achieve an optimal design. This causes a substantial increase in the design cycle time. A new methodology has been developed and implemented in this work that helps to automate and optimize the PEM design process. Power-CAD uses an electrothermal simulation methodology, a parasitic extraction tool, and an optimization algorithm that helps to achieve an optimal layout for a discrete PEM. This approach promises to save time and money for the PEM design industry by significantly reducing the number of design cycles.

High Temperature SiC Power Module Packaging

Wide band gap semiconductors such as silicon carbide (SiC) provide the potential for significant advantages over traditional silicon alternatives including operation at high temperatures for extreme environments and applications, higher voltages reducing the number of devices required for high power applications, and higher switching frequencies to reduce the size of passive elements in the circuit and system. All of these attributes contribute to increased power density at the device and system levels, but the ability to exploit these properties requires complementary high temperature packaging techniques and materials to connect these semiconductors to the system around them. With increasing temperature, the balance of thermal, mechanical, and electrical properties for these packaging materials becomes critical to ensure low thermal impedance, high reliability, and minimal electrical losses. A primary requirement for module operation at high temperatures is a suitable high temperature attachment technology at both the device and module levels. This paper presents a transient liquid phase (TLP) attachment method implemented to provide lead-free bonding for a SiC half-bridge power module. This module was designed for continuous operation above 250 °C for use as a building block for multiple system level applications including hybrid electric vehicles, distributed energy resources, and multilevel converters. A silver-based TLP system was used to accommodate the device and substrate bond with a single TLP system compatible with the device metallurgy. A SiC power module was built using this system and electrically tested at a 250 °C continuous junction temperature. The TLP bonding process was demonstrated for multiple devices in parallel and large substrate bonding surfaces with traditional device and substrate metallization and no requirements for surface planarization or treatment. The results are presented in the paper.Copyright

Direct liquid cooling of high performance Silicon Carbide (SiC) power modules

Silicon Carbide (SiC) wide band gap power devices are capable of operating at extremely high current densities and switching frequencies. Systems embracing these benefits can achieve a substantial increase in power density. However, cooling becomes exponentially more difficult as the size of the modules lessens. Direct cooling of the power electronic modules, in which the liquid coolant flows over the surfaces of the base plate, is a highly effective approach to improve the thermal performance of a conversion system. Notably, it allows for a reduction of layers in the thermal stack-up and completely eliminates the need for a thermal interface material (TIM). In this work, Wolfspeed has taken the commercial CAS325M12HM2 SiC power module, which was specifically designed to take advantage of wide band gap power semiconductors, and developed a prototype variant to enable direct liquid cooling of the base plate. High surface area pin fins are formed in a concentrated density directly on the base plate, providing a quality means of heat removal as close to the semiconductor devices as possible. High thermal conductivity materials and attaches, including silver sintering paste and film, were utilized to achieve an optimized heat transfer path. The discussion presents the design, analysis, and testing of this direct cooled module. It focuses on various physical factors influencing the thermal performance and a comparison between different direct structural configurations and power levels.