Piezocomposite Ultrasonic Transducers for High-Frequency Wire Bonding of Semiconductor Packages

Piezocomposite ultrasonic transducers for high-frequency wire bonding of semiconductor packages are developed to alleviate the strong mode coupling and high mechanical quality factor intrinsic in piezoceramic transducers by using ring-shaped lead zirconate titanate (PZT)/epoxy 1–3 piezocomposites as the driving elements. In this chapter, the background and challenges involved in the state-of-the-art high- frequency wire-bonding process are described. The fabrication, resonance characteristics, and material properties of the piezocomposite rings having high PZT volume fractions in excess of 0.8 and with a small epoxy width of 77μm are reported. The structure, electrical characteristics, vibrational characteristics, and wire-bonding performance of a 136-kHz piezocomposite transducer are presented, together with those of a PZT piezoceramic transducer of similar structure. With the guide of a finite-element modal analysis, the nature of most experimental resonance modes in the two transducers is identified. The low lateral coupling of the piezocomposite rings effectively suppresses the nonaxial and many other spurious resonances in the piezocomposite transducer, retaining only the axial-mode resonances. Because of the effect of epoxy damping, the piezocomposite transducer exhibits a 2.4-times reduction in mechanical quality factor to a desired low value of 296. The process study confirms the value of the piezocomposite transducer in commercial wire bonders for enabling high-frequency wire-bonding technology.