Advanced transducer technologies for electrical connections in microelectronic packaging

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Advanced transducer technologies for electrical connections in microelectronic packaging

 

Author: Li, Hing-leung
Title: Advanced transducer technologies for electrical connections in microelectronic packaging
Degree: Ph.D.
Year: 2004
Subject: Hong Kong Polytechnic University -- Dissertations.
Microelectronic packaging.
Electronic packaging.
Transducers.
Department: Dept. of Applied Physics
Pages: xvii, 191, 7 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2059329
URI: http://theses.lib.polyu.edu.hk/handle/200/1018
Abstract: Advanced transducer technologies have been developed for making electrical connections in microelectronic packaging industry. This work has focussed on chip level interconnection techniques including wire bonding and thermosonic flip chip bondings. The new transducer designs and technologies developed include: I) 1-3 Piezocomposite Transducers Lead zirconate titanate (PZT)/epoxy 1-3 composite rings were used to replace the conventional full PZT rings as the driving elements in wire bonding transducers. The vibration characteristics of 1-3 composite rings were studied and compared to a full PZT ring. The unique feature of suppressing planar resonance modes makes the 1-3 composite rings an attractive alternative to conventional PZT rings. The volume fraction of the 1-3 composite rings was optimized by a finite element method (FEM). Wire bonding transducers were fabricated and characterized. The dynamic behaviours of the transducers were also analyzed by FEM. The 1-3 transducer offers advantages such as purer axial resonance, lower mechanical quality factor and suppression of spurious modes. The composite transducer was installed on a commercial wire bonder for process study. The composite transducer was found to have wider operation windows (>50%) and finer pitch bondings (<10%). In addition, the composite transducer offered a much more consistent bonding results than a conventional PZT transducer. II) Thermosonic Flip Chip Transducers Transducers were designed using both the longitudinal and transverse approaches in thermosonic flip chip bonding. The dynamic behaviours of the transducers were modelled by FEM. Process study was conducted on the two approaches and the bonding defects of both longitudinal and transverse bondings were linked up with the transducer characteristics. It was found that the transverse approach was less susceptible to silicon cratering due to the lower stress induced during bonding. However, due to the insufficient transducer rigidity, it gave rise to more serious chip tilting defect. Both FEM and experimental findings agreed well with this argument. A novel push-pull transducer concept, with multi-support and driving, was proposed to overcome the shortcomings of both longitudinal and transverse transducers. It was found that the new transducer offers superior ultrasonic properties. The novel transducer design has high rigidity to maintain ideal bonding co-planarity for high pin count devices. The transverse vibration can also minimize the silicon cratering. The new transducer concept has been adopted in a commercial flip chip bonder. III) Multi-frequency Transducers Methodologies for designing the multi-frequency transducer were demonstrated. The nodal position matching method helps to identify the multi-frequency feature of a conventional transducer. A case study based on a commercial transducer was demonstrated. A new transducer design concept based on balanced wavelength has been developed. The novel design offers advantages of fine pitch bonding using higher frequency (>120 kHz) and robust bonding using a lower frequency (60 kHz). The special structure could allow the transducer to work in its fundamental mode as well as its second harmonics. Both FEM and experimental results showed that the transducer provided good ultrasonic properties at more than one frequencies.

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