Characteristics of bonds produced by full ceramic and composite ultrasonic transducers

Two types of ultrasonic transducers: full ceramics (lead zirconate titanate, PZT) and composite (PZT embedded in a polymer) transducers, were used for wire bonding. Al wire is 32 μm in diameter and bond pads contain Au/Ni/Cu trilayer coating on PCB boards. Bonding Al wire on the pads was processed on three different power levels and with various bond times at each bond power to compare the bonding performance of the two types of transducers. The actual bond areas were measured after the Al wire had been removed in a base solution. Bonding kinetics was analyzed based on actual bond areas. Pull strength test was used to examine bonding quality. The fractured bonds were examined using a scanning electron microscope.The results show that the bonding rate by the full ceramic transducer is faster than that by the composite transducer in the initial stage. A maximum bond strength is attained after a certain bond time which is different depending on the bond power. This maximum bond strength produced by the composite transducer occurs at longer bonding time. The widths of the bonds produced by the composite transducer are significantly narrower than those of the bonds produced by the full ceramic transducer. The reduced bond width gives rise to higher bond strength. [Copyright &y& Elsevier]