PROJECT TITLE :
Surface discharges in silicone gel on AlN substrate
AlN substrate is widely used together with silicone gel to encapsulate power electronic circuits. It is known that the weakness of the insulation system is surface discharges propagating at the gel-substrate interface. In this research, the character of surface discharges in gel, on numerous substrates was investigated. The results are as follows: the most stopping length of cavities on AlN substrate was additional than twice than that on other substrates, and lightweight emission due to discharges in cavities on AlN substrate was totally different from that on alternative substrates; for AlN substrate, tip of the cavity emitted light-weight whereas other half failed to emit lightweight, and for different substrates, all the trail along the cavity emitted light-weight. These results indicated that the surface of the AlN substrate is degraded by discharges and becomes conductive. We have a tendency to have confirmed this assumption by measuring the conductivity of the cavity path: 5 kΩ/100 μm for that on AlN and higher than one MΩ/a hundred μm for Al2O3 and glass substrates. The high electrical field at the tip of conductive path elongates the cavity stopping length on AlN substrate compared with others. In order to analyze the degradation process of AlN substrate surface, energy dispersive X-ray spectroscopy analysis was carried out. Reduction of nitrogen element on the cavity path was seen, indicating that generation of Al will increase the conductivity of cavity path. We have a tendency to have experimentally shown that oxidation treatment of the AlN substrate considerably reduces the cavity stopping length.
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