Title :
Dynamics of Ultrasonic Transducer System for Thermosonic Flip Chip Bonding
Author :
Long, Zhili ; Wu, Yunxin ; Han, Lei ; Zhong, Jue
Author_Institution :
Dept. of Mechatron., Central South Univ., Changsha, China
fDate :
6/1/2009 12:00:00 AM
Abstract :
Thermosonic flip chip bonding is used in certain fine pitch IC packaging for its unique features. By using this bonding process in this paper, 1 mm times 1 mm chip with 8 gold bumps has been bonded onto a silver-coated substrate. Dynamical properties of transducer system, which is the key component for providing the ultrasonic energy, have been investigated using finite element model (FEM) and measurement using impedance analyzer and laser Doppler vibrometer (LDV). The simulation results show that the ultrasonic transducer vibrates by coupling with all excited modes, therefore resulting in complicated motions during bonding. The third axial mode, which includes 1.5 wavelengths and 3 nodes, is the dominant working vibration. However, this axial mode is severely disturbed by undesirable non-axial modes such as flexural modes. There are some other unwanted parasitic modes close to dominant mode. Measured velocities of the transducer horn show that the system vibrates under several modes simultaneously. The impedance measurements reveal additional frequencies overlapping the working frequency. All non-axial modes of the ultrasonic transducer disturb the bonding process and degrade the bonding quality. A subtle control is needed to obtain unique axial mode and stable vibration for high bonding quality.
Keywords :
finite element analysis; flip-chip devices; lead bonding; tape automated bonding; ultrasonic bonding; ultrasonic transducers; vibrations; axial mode; excited modes; fine pitch IC packaging; finite element model; flexural modes; gold bumps; impedance analyzer; impedance measurements; laser doppler vibrometer; nonaxial modes; parasitic modes; silver-coated substrate; thermosonic flip chip bonding; ultrasonic energy; ultrasonic transducer system; working vibration; Bonding processes; Finite element methods; Flip chip; Frequency; Gold; Impedance measurement; Integrated circuit packaging; Ultrasonic transducers; Ultrasonic variables measurement; Wavelength measurement; Dynamical properties; finite element method (FEM) analysis; thermosonic flip chip bonding; ultrasonic transducer;
Journal_Title :
Components and Packaging Technologies, IEEE Transactions on
DOI :
10.1109/TCAPT.2009.2017380