Breakdown of Water Saturated Printed Circuit Boards in Dielectric Encapsulation for Deep-Sea Applications

Developments in deep-sea technologies has led to pressure tolerant electrical and electronic systems. These systems do not use pressure resistant enclosures, but instead rely on the encapsulating material to transfer the forces to the embedded components and to provide electrical insulation and protection against water and corrosion. When designing high voltage, high power electronic systems on printed circuit boards (PCBs), the choice of encapsulating material and the integrity of the interfacial boundaries are critical to ensure adequate insulation. In this study, the effect of water ingress on the high voltage breakdown behaviour between two tracks on an encapsulated PCB is investigated. A group of PCBs, with different gaps between their conductive tracks, are encapsulated in an RTV-silicone gel and then immersed in de-ionized-and sea-water respectively to study its breakdown voltage and discharge characteristics over time. Prolonged immersion in deionised water shows a reduction in the breakdown strength between the tracks as well as anomalous breakdown on the rear surface of the PCBs whereas the breakdown behaviour did not change significantly over the evaluation period for the sample immersed in seawater. These results may have been caused by weak bonding between surfaces and the deposition of salts in the outer layer of the test specimens.