Mitigating High Electric Field Stresses in Power Modules Utilizing Field Grading Materials

In this study, a comparative analysis of the electric stress reduction capabilities between nonlinear field grading materials (NLRFG) and materials with functional capacitive field grading composites (FCFGC) is conducted. The FCFGC materials are created by blending Barium Titanate (BTO) powder, a ferroelectric substance, into a Polydimethylsiloxane (PDMS) matrix. On the other hand, the NLRFG materials are produced by blending semiconductive Zinc Oxide (ZnO) powder into a PDMS matrix. To assess the material properties of the composites, experiments are performed to characterize both the nonlinear conductivity and permittivity of these fabricated materials. Surface flashover experiments are carried out using DC (0 Hz) and unipolar square waveforms with 60 Hz and 5000 Hz on direct bonded copper (DBC) power substrate. This process entails applying a coating of pure PDMS along with NLRFG and FCFGC, containing filler loadings of 45%. According to the results, incorporating NLRFG leads to a rise in the flashover voltage (SFV) by roughly 69.4%, 22.0%, and 8.1% at frequencies of 0 Hz, 60 Hz, and 5000 Hz, respectively. Conversely, incorporating FCFGC leads to a rise in the SFV by approximately 32.5%, 64.1%, and 58.5% at frequencies of 0 Hz, 60 Hz, and 5000 Hz, respectively. Moreover, numerical models are utilized to perform electric field analyses of the power substrates. These models integrate the field-dependent characterized properties of the composites, offering a more thorough comprehension of the experimental results.