Integration of Power Electronics Building Block Using Polyimide Substrates

Abstract

The advancement of silicon carbide (SiC) devices has enabled a new generation of high-density, fast-switching power converters for automotive, marine, and aerospace applications. One of these converters is the SiC-based Power Electronics Building Block (PEBB), which integrates semiconductor devices, gate drivers, magnetics, and other components into modular, flexible converters. To fully leverage the benefits of SiC and the PEBB concept, this work explores advanced packaging and integration strategies that enhance power density and manufacturability. This research focuses on an advanced converter-level packaging approach, referred to as the common substrate concept, as a replacement for traditional ceramic-based power module converter designs. The common substrate acts as a multifunctional platform that directly mounts and interconnects all essential components, including semiconductor dies, gate drivers, sensors, magnetics, capacitors, and ancillary circuitry. This integrated approach simplifies system architecture, reduces the number of discrete elements, and improves scalability for manufacturing. The key enabling technology behind this concept is a new generation of polyimide substrate and its unique electro-thermal-mechanical behavior. Polyimide substrates offer significantly greater design flexibility than traditional ceramic-based designs. They support thicker copper layers and thinner dielectric layers, which can enhance electrical and thermal performance while enabling higher levels of integration. However, these advantages introduce new challenges. The extreme material parameters of polyimides, such as high capacitive coupling and relatively low thermal conductivity, make it difficult to apply conventional design rules developed for ceramic and epoxy-based substrates. To address this gap, this work completes a comprehensive electro-thermal-mechanical study on polyimide substrates. Finite element analysis (FEA) is used to evaluate the electrical and thermal behavior of polyimide substrates and parametrization of geometric variables is conducted to assess their influence on key performance metrics like thermal resistance and electromagnetic interference (EMI). This design space serves as a guide for navigating tradeoffs and selecting optimal configurations for specific application requirements. In addition to simulation, the research investigates the thermo-mechanical implications of polyimide substrates, particularly the effects of thick copper layers and large-area warpage. Experimental thermal cycling and warpage measurements are conducted to validate the mechanical reliability. These findings help inform limitations of polyimide substrates and highlight tradeoffs for use in high-power applications. To validate the proposed design space, two design points are selected and fabricated into full-bridge 1.7 kV SiC power modules. These prototypes are experimentally evaluated for key performance metrics including hard switching losses, zero-voltage switching (ZVS) range, common-mode EMI, and thermal resistance. The results confirm that switching node capacitance layout is a primary driver of polyimide substrate behavior. These insights are then applied to the design of the PEBB, where the common substrate is refined using the validated design space. This work presents a methodology for designing and implementing polyimide-based substrates in power electronics. By bringing together simulation and experimentation, it provides an understanding of the benefits, limitations, and tradeoffs of polyimide substrate technology and its application in common substrates for future PEBB system.