This research investigates the optimal region to achieve balanced thermal and electrical insulation properties of epoxy (EP) under high frequency (HF) and high temperature (HT) via integration of surface-modified hexagonal boron nitride (h-BN) nanoparticles. The effects of nanoparticle content and high temperature on various electrical (DC, AC, and high frequency) and thermal properties of EP are investigated. It is found that the nano h-BN addition enhances thermal performance and weakens electrical insulation properties. On the other side, under HF and HT stress, the presence of h-BN nanoparticles significantly improves the electrical performance of BN/EP nanocomposites. The EP has superior insulation properties at low temperature and low frequency, whereas the BN/EP nanocomposites exhibit better insulation performance than EP under HF and HT. The factors such as homogeneous nanoparticle dispersion in EP, enhanced thermal conductivity, nanoparticle surface modification, weight percent of nanoparticles, the mismatch between the relative permittivity of EP and nano h-BN, and the presence of voids in nanocomposites play the crucial role. The optimal nanoparticle content and homogenous dispersion can produce suitable EP composites for the high frequency and high temperature environment, particularly solid-state transformer applications.

This paper investigates the electrical and thermal properties of pure epoxy resin (EP) and its micro–nano hybrid composites (20 wt% micro-AlN fillers with 1 wt% and 3 wt% nano-Al2O3 fillers; 50% micro-AlN with 3% nano-Al2O3 fillers) for power electronic packaging applications. Electrical properties such as space charge distribution, electrical conductivity and surface potential decay are measured. The thermal performance of the fabricated samples is estimated using thermal analysis devices. The hybrid composite consisting of 20 wt% micro-AlN and 1 wt% nano-Al2O3 fillers exhibits the least space charge accumulation, higher thermal conductivity and better thermal stability. However, the excessive addition adversely affects space charge and electrical conductivity properties. The micro–nano hybrid composites significantly exhibit higher electrical conductivity than pure EP. The microfiller addition from 20 wt% to 50 wt% significantly improves the thermal conductivity of the EP. The reduced space charge injection and accumulation in the hybrid micro–nano composites are attributed to the enhancement of the injection barrier and reduction of the charge carrier traps in these materials. A theoretical mechanism of the charge dynamics inside the samples under different test conditions is proposed to support the experimental results.

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This paper reports an enhancement of the nonlinear conductivity, thermal and mechanical properties of micro-silicon carbide/silicone elastomer (m-SiC/SE) composites by adding nano-aluminum nitride (n-AlN) for power module encapsulation applications. The electrical properties (such as nonlinear conductivity characteristics and transient permittivity obtained from polarization current, and trap distributions obtained from thermally stimulated depolarization current) and material properties (including thermo-gravimetric analysis, coefficient of thermal expansion, and thermal conductivity, tensile strength, strain at break and Young’s modulus) of the pure SE, m-SiC/SE microcomposites, m-SiC/n-AlN/SE hybrid composites are investigated. The effect of the m-SiC fillers and n-AlN fillers on physicochemical properties of the SE matrix is analyzed by FT-IR spectroscopy and crosslinking degree. The measured nonlinear conductivity and transient permittivity are used for electric field simulation under DC stationary and square voltages. It is found that the addition of n-AlN fillers in the SE hybrid composite improves the nonlinear conductivity characteristics and mitigates the electric field under DC stationary and square voltages, compared to the SE microcomposite. Furthermore, the m-SiC/n-AlN/SE hybrid composite has a higher thermal degradation temperature, thermal conductivity, tensile strength, Young’s modulus, and crosslinking degree than the SE microcomposite, whereas their CTE and strain at break are lower. It is elucidated that the m-SiC/n-AlN/SE hybrid composite with enhanced nonlinear conductivity and material properties is a promising packaging material for high-voltage power modules.

This paper reports the performance of an epoxy resin/silicon carbide whisker (EP/SiCw) composite (1–5 wt %) as the field-dependent conductivity (FDC) layer for electric field reduction in the high-voltage power module. The experiments consist of a field emission scanning electron microscope (FESEM), thermal conductivity, Fourier transform infrared (FT-IR) spectroscopy, thermally stimulated discharge current (TSDC), space charge, DC conductivity, and dielectric spectroscopy. The DC conductivity and dielectric spectroscopy are used for DC and AC stationary electric field simulations, respectively. The electric field reduction of EP/SiCw composites in the power module is analyzed, and the void defect in the FDC layer is also identified. The observed percolation threshold of the EP/SiCw composites is 3 wt %, and the DC electric field near the triple point decreases significantly by 74.8% under 10 kV when a 5 wt % EP/SiCw composite is applied for the FDC layer. It was found that the efficient threshold operating frequency of the FDC layer is around 10 kHz. The FDC layer can significantly reduce the electric field under AC voltage below 10 kHz. Although the power loss with the FDC layer increases obviously without the FDC layer, it is still lower than 1 W at 1 MHz, which is negligible for industrial applications. Notably, the void in the FDC layer is identified by the slowly increased dielectric loss with the increase of frequency through dielectric spectroscopy simulation.