High Voltage Stress-Lifetime Study of Insulated Printed Circuit Boards

High voltage technology is a niche in spacecraft business and is very important since it enables highly-efficient radio frequency amplification with travelling wave tube amplifiers, a significant payload element for a telecom spacecraft, as well as for thrust by electrical propulsion. Furthermore, numerous scientific instruments rely on high voltage. Pending on the equipment usage, in a space environment (and on the way there), voltages above 200V must be considered as high voltage. Standards for high voltage (HV) on printed circuit board (PCB) designs either do not exist yet or differ in the distance and material thickness rules. Furthermore, the parameters and sources, demonstrating how the rules (if existing) were determined, is not available. Heritage and current designs either avoid high voltage on PCBs, or are based on qualified heritage designs, where the true margin for lifetime until electrical breakdown is not known. Overall, there is a need for research into this field, to refine design rules for HV PCBs for different space environment compatible coating, potting, and PCB substrate materials, based on lifetime measurements under known parameters, to enable better prediction of design durability. In summary, typical single- and double-layer PCB design variants and typical isolation systems have been tested. The results find the electrical breakdown level is strongly depending on the insulation material and method. In comparison to bare PCBs, Parylene almost doubles the isolated voltage, filled epoxy is ∼8 times better. Furthermore, the variance of time until breakdown for a given high voltage is very high. Therefore, large design margins for high voltage isolation are recommended.