Design Of High Frequency Ultrasonic Transducer For Wire Bonding Application And Optimization Of Modal Frequencies

With the chip pin pitch getting smaller and smaller and theenterprise’s pursuit of higher productivity, the traditional ultrasonictransducer operating at60KHz can no longer meet the requirements oftoday’s market. The high frequency ultrasonic transducer of light weight andfast velocity can form the solder joints of high strength in smallerdeformation and shorter time. Having so many advantages, the highfrequency ultrasonic transducer will be widely used in the future. Because ofthe shortage of design and assembley, it is easy for the high frequencyultrasonic transducer to excite mode mixing phenomenon which becomes animportant factor that affects the quality of wire bonding. For these reasons,the high frequency ultrasonic transducer operating at135KHz is designed,and its modes mixing phennomenon is researched and modal frequencies areoptimization to suppress modes aliasing. In this paper, the following workshave been done.(1) Trough the equivalent circuit method, the two and a half wavelengthtransducer operating at135KHz is designed. According to the wavelengthcharacteristic, the transducer is composed of a half wavelength piezoelectricmotor and a two wavelength horn. The transducer’s design is accomplishedby calculating the size of the piezoelectric motor and horn respectively.(2) The dynamic characteristics of the transducer are analyzed throughthe finite element method. The modal and displacement characteristics of themotor, horn and transducer are studied to verify that the transducer designedcan be able to meet the design requirements. The modal frequeciescharecteristics are investigated to find that the modes aliasing is easilyexcited and there is a lot of room for optimization.(3) The modes mixing of the transducer is suppressed by optimizing its structure sizes. The sizes of the transducer are optimized based on sensitivityanalysis and the minimum interval of the frequencies between the workingmode and the non-work modes is increased from0.7KHz to4.6KHz, whicheffectively inhibites the mode aliasing.(4) The effects of the horn shape on the transducer’s mode aliasing areinvestigated. When the shape of the horn is conical, exponential, hangingchain type and step-type, the modal frequencies of the transducer are studiedrespectively. The research indicates that the frequency space between theworking mode and the nearby bending mode can be improved by changing thehorn shape. Also, we can use the step-type horn to change the the frequencyspace of the adjacent non-work modes in order to improve the optimizationspace.(5) The impedance characteristics of the transducer are tested using animpedance analyzer, and the simulation results agree well with the measuredones.