Multiple modal vibration and FEM analysis of ultrasonic transducer for thermsonic flip chip bonding

The dynamics of ultrasonic transducer for thermosonic flip chip bonding is investigated. Velocities of mark points on transducer and bonding tool, which represent different modal vibrations, are sampled by a laser Doppler vibrometer. The results show the axial vibration is dominant while it is disturbed by other non-axial components. It means that the ultrasonic transducer system vibrates complicatedly, which couples the axial and non-axial components simultaneously. The effect of non-axial vibration influences significantly the bonding quality such as chip tilting and poor bonding strength. The multiple vibrations of ultrasonic transducer is analyzed by finite element model. It is found that ultrasonic transducer vibrates in coupling resultant of all allowable modes being excited. The origin and corresponding control method for multiple vibrations is brought forward.