Design And Control Of High Frequency Ultrasonic Transducer System For Thermosonic Bonding

The piezoelectric transducer and its driving system are one of the key componentsof high frequency thermosonic bonding equipments, and the research on its structureand driving control methodology has important academic and application values. Toimprove the efficiency and quality of thermosonic IC bonding, this dissertationstudies on the dynamic design theory of flexible connection structure for highfrequency ultrasonic transducer, exciting signal source of the power ultrasound,dynamic tuning of control strategies and bonding temperature. The followingcontributions have been achieved:The flexible connection structure of high-frequency ultrasonic transducer forthermosonic wire bonding is proposed based on the electromechanical equivalenttheory, finite element analysis(FEA) and modular design concept. Thus the influenceof the inflexible joint on the energy distribution of longitudinal vibration can bereduced and the modal concentration problem of high-frequency transducer is solved.A125kHz ultrasonic transducer has been designed, whose energy transmission lawand resonance characteristic have been investigated.The admittance model of equivalent circuit adjacent to the resonant frequency ofthe ultrasonic transducer is established, and it is concluded that the static category andthe dynamic resistance are the major influence factors for electrics matching andresonant feature of the ultrasonic transducer and it is not necessary for thehigh-frequency ultrasonic transducer to design matching circuit when the transducerpossesses minor static capacitance. Both theory and regulation of the dynamic tuningfor high-frequency ultrasonic transducer based on current and impedance phasefeedback technology are presented.The technologies, including the direct digital synthesis technology, detectingmethod of the current real effective value and signal phase in RF field, precisemeasurement technique of the temperature and virtual instrument technology, areimported into the driving system design of the high-frequency thermosonic transducer.An embedded system based on high speed AVR microprocessor is developed.Experimental test results of the driving system show the high quality power ultrasonicsignal generation, quick measurement for real effective value of the current andimpedance phase between signals, self adapting tuning control, precise temperature control and highly active data communication can be realized using the system, and itprovides a perfect hardware basis for the prototype development of the thermosonicbonding.The method of the divide-and-conquer strategy, such as binary search andbranch-bound algorithm, are utilized to design the control algorithm for dynamictuning of the thermosonic transducer system. Based on the current and impedancephase feedback technology, the quick tuning control strategies are presented. Throughself-adaption of the threshold value and frequency search field, the robust andefficiency of the search algorithm are improved. The simulation and test resultsindicate that the tuning control of binary search algorithm based on impedance phasedetecting possesses a better research ability for resonant frequency.Mathematical model of the temperature rising system for thermosonic bondingprocess is obtained through system identification method and a temperature controlleris developed with fuzzy PID adaptive control algorithm, the simulation and testresults indicate that the fuzzy PID self adaptive controller has strong capacities ofresisting disturbance and better robust performances and control precision, thetechnology is fit to temperature accuracy control of the thermosonic wire bondingprocess with multi field coupling, time varying and hysteresis.The above research achievements enrich the design theory of high-frequencyultrasonic transducer and control strategy of driving system for thermosonic bonding,and it has great significances on promoting the development of microelectronicspackaging equipments.