Nondestructive Ultrasonic Inspection of Braze Bonds in High Current Electrical Contact Assemblies

Ultrasonic techniques are being increasingly used for nondestructive testing and quality control of bonds between the electrical contacts and the support members of the contact assemblies. The state-of-the-art of this valuable tool is analysed and discussed from a control standpoint. Two ultrasonic techniques, namely, the delayed pulse echo and the through-transmission, are described and discussed with respect to their limitations and merits for the brazed bond quality between the silver-cadmium oxide or silver contact and the copper support. The Instrument calibration technique, the range of test frequencies and the resolution of the voids are determined, for various thicknesses of the contact and the support material. The instrumentation and data including C-scan chart recording of the voids for discrete components as well as for continuous bonding of strip materials are presented and discussed.