Degradation of adhesive bonds with short current pulses

Degradation of adhesive bonds powered by rectangular very short current pulses of the width of 1 /spl mu/s and frequency of 1 kHz of high amplitude has been examined. The amplitudes of the pulses have been 5 and 10 A. Power supported by these pulses into the adhesive bonds has been chosen very low to cause very low increase of the temperature of the bond only. Therefore changes of examined electrical parameters have been dominantly caused with effects different from effects caused by thermal aging. The specimens have been prepared by mounting of resistors with "zero" value on a test board with Cu layout which has made 4-point measurement of the bonds possible. Seven resistors have been mounted on one board. Two types of isotropic electrically conductive adhesives with Bisphenol A resin binder and Ag filler have been used. Resistance of the bonds has been measured. The pulses have been applied at the normal temperature and at the temperature of 90/spl deg/C, the time of application of the pulses has been 90 minutes. It has been found that the current pulses influence resistances of the bonds; amplitude of the pulses has not influenced changes of the resistances substantially. Unlike the examination of current-induced degradation with DC current of higher density on properties of the joints published in S. Kotthaus et al. (1998), the increase of normalized resistance with the time of application of the current pulses has not been found so explicit. It has also been found that changes of resistances depend on the number of applied pulses.