Unveiling Insights Into Partial Discharge and Design and Encapsulation Challenges in DCB-Based Power Converters for Aerospace Applications

Abstract

This study combines comprehensive analyses of design parameters with encapsulation solutions of Direct Copper Bond (DCB) substrates used in high voltage power converter modules, focusing on partial discharge (PD) activity under varying pressures for aerospace applications. A detailed PD investigation on triple junction points as the main culprit of the failure in power electronics was conducted, and the design and material aspects through experimental and simulation analysis were examined. PD initiation and extracted information are presented for three common pad geometries on two types of substrates (AlN and G-10/FR4). The results reveal better performance of the AlN that has higher permittivity, i.e., 20-30% and 10-20% higher PD inception voltage (PDIV) than G-10/FR4 at ambient and low pressures, respectively, and 40-65% lower PDIV at low pressures due to the higher rate of gas ionization compared to the ambient pressure. The study also explores the impact of pad geometric design such as corner smoothness and spacing on electric field intensity, with an introduced pressure- and temperature-dependent ionization model coupled with 3D finite element model to quantify the impact of the pressure on the gas ionization and PD initiation. Furthermore, an extensive experimental and numerical study of PD on liquid and gel encapsulated DBC substrates at ambient and low pressures was also conducted. Two silicone gels (Dowsil $^{\text {TM}}~3$ -4170 and Sylgard $^{\text {TM}}~527$ ) and one refrigerant dielectric liquid (fluorinert FC40) were investigated as encapsulating dielectrics for high voltage applications. The results reveal that different silicone gels, despite similar dielectric properties, can exhibit drastically different PD resistance due to intrinsic bulk properties and self-healing capabilities, outperforming liquid-based encapsulants. This highlights the significance of dielectric fluid and gel insulations characteristics to the performance of HV modules for aerospace applications.

Keywords

• Aerospace application
• direct copper bond (DCB) substrate
• electrical insulation
• encapsulation
• fluorinert
• high power converters