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1. A Review of Insulation Challenges and Mitigation Strategies in (U)WBG Power Modules Packaging

   https://doi.org/10.1109/TPEC60005.2024.10472278  

   Adhikari, Pujan; Ghassemi, Mona (February 2024, 2024 IEEE Texas Power and Energy Conference (TPEC))

   In the ever-growing landscape of electrical power demand, the future of power electronics module packaging lies in the realm of wide-bandgap (WBG) materials, including silicon carbide (SiC), gallium nitride (GaN), and cutting-edge ultra WBG (UWBG) materials like diamond, aluminum nitride (AlN), and hexagonal-boron nitride (h-BN). These materials offer superior properties to traditional silicon-based devices, promising higher power density, reduced weight, and increased operating temperature, voltage, and frequency. However, pushing the boundaries for power electronics modules presents challenges in insulation systems as the encapsulation material and the ceramic substrate may not withstand the functional parameters, potentially leading to unfavorable conditions like high field stress and partial discharge (PD), ultimately resulting in insulation failure. This paper presents a thorough analysis of the characteristics of the electrical insulation materials used in power electronics devices based on the research in WBG packaging conducted in recent years. The significance of maximum electric field stress at triple points (TPs) is examined. Furthermore, the paper reviews the strategies and techniques employed to mitigate the challenges related to maximum field stress and PDs in both encapsulation and substrate materials. It is concluded that the mitigation strategies are promising in improving insulation systems for packaging, but the studies lack their implementation under actual operating conditions of WBG power modules. 

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2. A Comprehensive Review of Mitigation Strategies to Address Insulation Challenges within High Voltage, High Power Density (U)WBG Power Module Packages

   https://doi.org/10.1109/TDEI.2024.3382070  

   Adhikari, Pujan; Ghassemi, Mona (January 2024, IEEE Transactions on Dielectrics and Electrical Insulation)

   Within the expanding domain of electrical power demand, the future of power module packaging is entwined with the progress of (ultra) wide bandgap (UWBG) materials. These materials, like silicon carbide (SiC), aluminum nitride (AlN), and diamond, offer advantages with higher power density, decreased weight, and expanded operational abilities regarding temperature, voltage, and frequency. However, the pursuit of pushing these limits confronts challenges within insulation systems, which may struggle to endure the demands of these parameters, potentially resulting in unfavorable conditions like high electric field, space charge accumulation, electrical treeing, and partial discharge (PD), leading to insulation failure. The emphasis of this paper is to review the insulation challenges within (U)WBG power modules and recent research in mitigating the electric field stress at triple points (TPs) and resolving the PD issues. The manuscript first discusses the high electric field stress issue at triple points. Then, ceramic substrate materials, encapsulation materials, and the influence of harsh weather conditions on them are reviewed. The space charge, electrical treeing, and PD issues within encapsulation materials are analyzed under practical operation conditions of (U)WBG power modules like high frequency, temperature, and square wave pulses. Finally, the various strategies to alleviate the associated insulation challenges are meticulously discussed. While the identified mitigation strategies are able to strengthen insulation systems for packaging, their validation under actual operational conditions of (U)WBG power modules remains relatively unexplored, representing a potential avenue for further investigation. This review offers a valuable framework by providing the constraints of the current studies and recommendations for the future that can be utilized as a reference point for future research endeavors. 

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3. Navigating Strategies to Mitigate Insulation Issues Within High Power Density (U)WBG Power Module Packages: A Comprehensive Review Emphasizing Alternative Encapsulation Materials

   https://doi.org/10.1109/TIA.2024.3520096  

   Adhikari, Pujan; Ghassemi, Mona (March 2025, IEEE Transactions on Industry Applications)

   The future of packaging for power modules hinges on the advancement of (U)WBG) materials like SiC, AlN, and diamond. However, pushing these boundaries faces significant challenges in insulation systems, which must withstand the demanding parameters involved. The repercussions include high electric fields, space charge accumulation, electrical treeing, and partial discharge (PD), all of which can lead to power module failure. This paper delves into reviewing these challenges within insulation materials of (U)WBG power modules and recent research aimed at mitigating electric field stress at triple points (TPs) and addressing PD issues. Beginning with the issue of high electric fields at TPs, the paper explores space charge, electrical treeing, and PD problems within encapsulation materials under practical operating conditions, such as high frequency, and high temperatures. Various strategies to tackle these insulation challenges are thoroughly discussed. While three prevalent mitigation strategies can address electric field issues at TPs, their validation under high-temperature conditions of (U)WBG power modules remains relatively unexplored, suggesting a potential shift towards alternative encapsulation materials. It is observed that the high-temperature dielectric liquids emerge as a promising solution to address thermal stresses for temperatures up to 350 °C with their stable dielectric properties and breakdown strength under repeated tests. Overall, this review provides a valuable framework by outlining the limitations of current mitigation strategies and offering recommendations for future research endeavors, with a particular emphasis on alternative encapsulants. 

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4. Effects of Frequency and Temperature on Electric Field Mitigation Method via Protruding Substrate Combined with Applying Nonlinear FDC Layer in Wide Bandgap Power Modules

   https://doi.org/10.3390/en13082022  

   Mesgarpour Tousi, Maryam; Ghassemi, Mona (April 2020, Energies)

   null (Ed.)

   Our previous studies showed that geometrical techniques including (1) metal layer offset, (2) stacked substrate design and (3) protruding substrate, either individually or combined, cannot solve high electric field issues in high voltage high-density wide bandgap (WBG) power modules. Then, for the first time, we showed that a combination of the aforementioned geometrical methods and the application of a nonlinear field-dependent conductivity (FDC) layer could address the issue. Simulations were done under a 50 Hz sinusoidal AC voltage per IEC 61287-1. However, in practice, the insulation materials of the envisaged WBG power modules will be under square wave voltage pulses with a frequency of up to a few tens of kHz and temperatures up to a few hundred degrees. The relative permittivity and electrical conductivity of aluminum nitride (AlN) ceramic, silicone gel, and nonlinear FDC materials that were assumed to be constant in our previous studies, may be frequency- and temperature-dependent, and their dependency should be considered in the model. This is the case for other papers dealing with electric field calculation within power electronics modules, where the permittivity and AC electrical conductivity of the encapsulant and ceramic substrate materials are assumed at room temperature and for a 50 or 60 Hz AC sinusoidal voltage. Thus, the big question that remains unanswered is whether or not electric field simulations are valid for high temperature and high-frequency conditions. In this paper, this technical gap is addressed where a frequency- and temperature-dependent finite element method (FEM) model of the insulation system envisaged for a 6.5 kV high-density WBG power module will be developed in COMSOL Multiphysics, where a protruding substrate combined with the application of a nonlinear FDC layer is considered to address the high field issue. By using this model, the influence of frequency and temperature on the effectiveness of the proposed electric field reduction method is studied. 

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5. Alternative Encapsulation Material Combined with Geometric Techniques for Electric Field Mitigation Within (U)WBG Packages Under High Frequencies

   https://doi.org/10.1109/IPMHVC55105.2024.11002847  

   Adhikari, Pujan; Ghassemi, Mona (May 2024, IEEE)

   As power modules based on (U)WBG materials gain attention for their potential to revolutionize high-voltage, high-power density applications, their optimal performance is hindered by current insulation materials. The high electric field stress at triple points (TPs) and encapsulant's diminishing breakdown field strength at high temperatures significantly limit the application of power modules to below 200°C. Therefore, alternative encapsulation materials are essential for hightemperature applications. This paper proposes a novel solution involving replacing standard silicone gel (SG) encapsulant with high-temperature encapsulation composites created by integrating micro- and nano-sized fillers into a silicone elastomer matrix. Additionally, the ceramic structure is redesigned into a mesa configuration, featuring a trench at the base of the metal electrodes. The results from modeling and simulation of COMSOL Multiphysics demonstrate that this combined approach significantly reduces field stress at TPs. Although effective at lower frequencies, further design modifications, such as altering the metalized substrate into a protruding structure, are necessary for optimal electric field mitigation at frequencies above 10 kHz. This research addresses the critical issues of high electric field values at TPs and the limited temperature tolerance of current encapsulation materials, which are challenges exacerbated under high-frequency square pulse operation. By resolving these issues, this work represents a valuable advancement in utilizing highvoltage, high-power density (U)WBG power modules at demanding frequency environments. 

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