February_EDFA_Digital

edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 1 4 In addition, insteadof placing and gluing the test struc- ture on the AE sensor (Fig. 2, left), the indenter is arranged vertically and directly coupled to the AE sensor (Fig. 2, right). This has the advantage that the acoustic wave is coupled at the location of the highest sensor sensitivity which is in the center of the cylinder surface. Moreover, the newly developed coupling concept eliminates the time- consuming and complicated gluing as well as removing of the chip from the sensor which can cause a destruction of sensitive structures. This new concept better meets the requirements of the AEmeasurement in terms of stability, strength, and accuracy. Fig. 3 shows the final prototype of the indenter glued on an AE sensor. This indenter design was successfully used in the following AE crack detection experiments. [1] Fig. 1 Vertical probe contacting a CMOS technology pad stack and thereby inducing oxide cracks, [1] left, vertical probes, right top, and imprint on Al-Cu top surface, right bottom. Fig. 2 Modification of the contact needle and sensor coupling concept. [1]