Variation of Fatigue / Electric Properties with Reducing Thickness of Laminated Copper Films and Its Controlling Geometric Structural Factor

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(1)An ultrasonic acoustic reflectivity measurement and fatigue damage in a surface thin filmFor the fatigue test, two-model specimens of the epoxy-bonded film and diffusion-bonded film were prepared for the S45C base and the pure copper film. The epoxy-bonded specimen has the resin layer between the S45C base and the pure copper film, in contrast to the diffusion-bonded film. As a result, there is a difference between both model specimens in surface fatigue damage observation and ultrasonic acoustic reflectivity during fatigue.(2)Fatigue crack propagation evaluated by electric resistance and ultrasonics in copper film bonded to base metal with resinAs model specimens of surface film-bonded materials, pure copper films with a thickness of 100μm were bonded to the surface of steel base plate with epoxy resin. The distribution of the initial electric resistance was measured on both copper film and base plate by a direct current potential drop technique. As a result, there was a good agree … More ment between the measured and theoretical values. From the fatigue testing results, it was shown that the measured electric resistance increased with the fatigue crack length on the copper film, which was almost equal to the theoretical value calculated for a central slit in a plate with finite width. In addition, the internal crack length during fatigue was examined by ultrasonic testing for the film-bonded specimen. As a result, there was a difference in the fatigue crack length between the surface copper film and the inner base plate. In this connection, this method was available for measurement of electric resistance during fatigue crack propagation on the copper film bonded with resin, irrespective of the crack length in the inner base plate.(3)Fatigue damage evaluation using electric resistance measurement in copper filmThe fatigue testing of the copper films was conducted to the specimen, for which the electric resistance was possible to be measured for the appropriate number of cycles during fatigue. The electric resistance was measured by four-point probe method and the periphery of the notch root was observed at the appropriate number of cycles. Then, relationship between fatigue damage and change of electric resistance was discussed. As a result, the electric resistance of the copper film reduced when slips were observed at first near the notch root by fatigue testing. For the subsequent fatigue testing, the value of the electric resistance increased and then converged upon the smaller value obtained before fatigue testing. Less