Ultrasonic evaluation of high voltage circuit boards

Preliminary observations indicate that an ultrasonic scanning technique may be useful as a quick, low cost, nondestructive method for judging the quality of circuit board materials for high voltage applications. Corona inception voltage tests were conducted on fiberglassepoxy and fiberglass-polyimide high pressure laminates from 20° to 140° C. The same materials were scanned ultrasonically by utilizing the s ingle transducer, throughtransmission technique with reflector plate, and recording variations in ultrasonic energy transmitted through the board thickness. A direct relationship was observed between ultrasonic transmission level and corona inception voltage. The ultrasonic technique was subsequently used to aid selection of high quality circuit boards for the Communications Technology Satellite.