Qian Xie

Epoxy/h-BN composites based on oriented boron nitride platelets with high thermally conductivity for electronic encapsulation

Owing to the miniaturization of power electronics and the development of portable and flexible devices, demands for highly thermally conductive, mechanically flexible, and electrically insulating composites have substantially increased. The high thermal conductivity of boron nitride (BN) platelets is expected to endow polymer composites with high thermal conductivity. Whilst BN is a typical two dimensional materials, which has anisotropic thermal conductivity. We have reported an remarkably increase in the in-plane thermal conductivity of the BN/epoxy composites through the fabrication of the horizontally aligned and densely packed BN in the epoxy matrix via a vacuum-assisted self-assembly technique. In addition, we compared the influence of the different BN particle sizes on the thermal conductivity of the composites. In this study, the range of BN particles sizes used are 5–8 μm, 15–20 μm and 25–30μm, respectively. The results indicated that the BN with lager size in matrix renders the composites high thermal conductivity at same content. The larger BN platelets can more easily form conductive chains of filler compared to the smaller filler particles. Meanwhile, the smaller filler particle can more easily scatter phonons suppressing heat transfer. It is clear that epoxy with aligned BN platelets has great promising for high thermal conductive insulating materials for the power microelectronics integrated in packaging.

Thermal conductivity and electric breakdown strength properties of epoxy/ alumina /boron nitride nanosheets composites

Dielectric polymer composites with high thermal conductivity and high electric breakdown strength are needed for high voltage devices. Epoxy resins is an excellent electrically insulating material, but low thermal conductivity limits its applications. This work aims to effectively enhance the thermal conductivity and keep the breakdown strength of composites as high as possible. In this study, α-alumina (α-Al2O3) particles with an average size of 0.2μm, and boron nitride nanosheets (BNNSs) with an average diameter of 1μm and thickness of around 40nm were homogeneously mixed with epoxy resin, and a three-phase composite was thus obtained. The superiority of this method is that three-phase composites not only show significantly increased thermal conductivity but also have higher breakdown strength in comparison with that of the two-phase α-Al203/epoxy composites. It is clear that epoxy with hybrid fillers has great promising for high thermal conductive insulating materials for the high voltage insulation.

Thermal and electrical properties of BNNPs/TiO 2 -Epoxy three-phase nanocomposites

Thermally conductive polymer composites without the deterioration of electrical insulating property are highly desirable for electronic packaging and high voltage devices on account of their ease of processing, flexibility and low cost. In this paper, high thermoconductive boron nitride nanoplatelets (BNNPs) with an average diameter of 5 to 8μm and thickness of around 50nm and semiconductive titania nanoparticles (TiO2 NPs) with an average size of 30nm were homogeneously mixed with epoxy resin to obtain a novel kind of three-phase composite. Moreover, the thermal and electrical properties of the specimens with different loadings of nanofillers were investigated. It is found that the thermal conductivity, the glass transition temperature and the dc volume resistivity all show significantly increase in the three-phase nanocomposite with 20wt% BNNPs and 1wt% TiO2 NPs when compared to neat epoxy resin.

In-situ observation of electrophoresis of conductive and semi-conductive micro particles in epoxy resin

Electrophoresis phenomena of conductive and semi conductive micro particles in liquid epoxy/anhydride mixture were in-situ observed by optical microscopy. The polymer mold with plate electrodes which provide horizontal electric field was made for the observation. Graphite, copper and titanium dioxide micro particles were studied in this paper. Because of the existence of space charge, micro particles moved together with liquid epoxy towards electrode under DC electric field. The aggregation and alignment of particles were studied and the theoretical analysis was given. The study shows that the viscosity of epoxy decides the flow type and laminar flow is ideal for the formation of alignment structure, indicating that the suitable moment of applying electric field is the key to produce the high temperature curing epoxy with anisotropic properties. This work shows that the radius, density and shape of particles also affect the alignment under electric field.