Effects of thermally conducting particles on resistance to tracking failure of polyimide/BN composites

Polyimide (PI) film, as a special type of engineering plastic film, is a kind of basic insulating material and is widely used in electrical and electronic industry. However, polyimide film has a relatively low thermal conductivity so it may be damaged by thermal breakdown. One approach to obtain a higher thermal conductivity composite is to introduce inorganic fillers with high thermal conductivity. The purpose of this paper is to study the effect of boron nitride (BN) particles on thermal accumulation and tracking failure process. In this paper, polyimide samples were prepared with different weight ratios. The thermal conductivity of 2.58 W/m-K was obtained for the composites that was loaded h-BN(hexagonal boron nitride) with the mass fraction of 80 wt%. Tracking failure process under different pulse frequency was measured with a digital camera and an infrared thermal imager. The CCD camera was used to observe the failure process and the infrared imager was used to measure the thermal accumulation and decay process. Obtained results showed that the addition of BN fillers had a significant inhibitory effect on tracking failure process. With increasing the mass fraction of BN, the time to tracking failure increased obviously. The ability to inhibit tracking was improved by reducing the temperature at the concentrated discharge region and increasing the heat dissipation region. High frequency discharges were more easily to cause the thermal accumulation, which was unfavorable to the reliability of materials. It is concluded that the tracking resistance can be improved by adding BN particles.