Kulicke & Soffa Industries is the world’s leading manufacturer of semiconductor wire bonding equipment. This “back-end” type of equipment provides ultrasonically welded interconnect wires between the wafer-level semiconductor circuitry (die) and the mounting package (frame) as shown in Fig. 3(a-c). The ultrasonic transducer delivers energy into a capillary tool using a “scrubbing motion” for welding tiny gold or copper wires, typically lessthan .001 inches in diameter. The single-piece construction “Unibody” transducer uses four diced, rectangular PZT8 piezoceramics, and is ideal for research studies (DeAngelis et al., 2009-2015). Portability across 100’s of wire bonding machines is required for the same customer device in production operations.
Assembly and Test Fig. 4 shows the piezo stack voltage versus preload calibration results for the lower “L” and higher “H” preload targets prior to assembly (DeAngelis et al., 2014). As shown in Fig. 4, the slope (N/V) is not constant so the effective d33 increases with preload. The maximum preload stress for PZT8 was empirically determined to be greater than 100MPa (DeAngelis et al., 2009), and the actual preload stress for each transducer assembly was computed from the calibrated slope via the press voltage during assembly. Fig. 5 shows the Bode plot results for the lower “L” preload case, and Fig. 6 shows the Bode plot results for the higher “H” preload case (both 1hr after build). It should be noted that the PZT8 “L” preload case was only tested prior to heat-treatment, since the same assembly parts were reused for the “H” preload case; two PZT4 transducers were built for the “L” and “H” preload cases.