Ultrasonic Wire Research Articles

Nano features of Al/Au ultrasonic bond interface observed by high resolution transmission electron microscopy

Nano-scale interfacial details of ultrasonic AlSi1 wire wedge bonding to a Au/Ni/Cu pad were investigated using high resolution transmission electron microscopy (HRTEM). The intermetallic phase Au 8Al 3 formed locally due to diffusion and reaction activated by ultrasound at the Al/Au bond interface. Multilayer sub-interfaces roughly parallel to the wire/pad interface were observed among this phase, and interdiffusional features near the Au pad resembled interference patterns, alternately dark and bright bars. Solid-state diffusion theory cannot be used to explain why such a thick compound formed within milliseconds at room temperature. The major formation of metallurgical bonds was attributed to ultrasonic cyclic vibration.

Fabrication and Performance of a 40-MHz Linear Array Based on a 1-3 Composite with Geometric Elevation Focusing

The fabrication and performance of a 256-element high-frequency (40-MHz) linear array is described. The array was fabricated using a high-frequency 1-3 PZT-polymer composite material developed in our laboratory. The spacing of the pillars in the composite was chosen to match the 40-microm center-to-center element spacing of the array electrodes. The element electrodes were created using photolithography, and connections to the electrodes were made using ultrasonic wire bonding. The array was focused in the elevation direction by geometrically shaping the composite material using a cylindrical die with a 6-mm radius of curvature. The resulting transducer produced pulses with a -6 dB two-way bandwidth of 50% and a peak-to-peak pressure of 503 kPa when excited with a +/-30 V monocycle pulse. The measured one-way (-6 dB) directivity for a single array element was 24 degrees and the -3 dB one-way elevation beamwidth was measured to be 130 microm. The radiation pattern for a focused 64-element subaperture was measured by mechanically translating the aperture above a needle hydrophone. A -3 dB one-way beamwidth of 97 microm was found at a depth of 6 mm. The one-way radiation pattern decreased smoothly to less than -30 dB at a lateral distance of 640 microm.

A Coupled Fluid-Structure Model of a Therapeutic Ultrasound Angioplasty Wire Waveguide

Ultrasonic longitudinal displacements, delivered to the distal tips of small diameter wire waveguides, are known to be capable of disrupting complicated atherosclerotic plaques during vascular interventions. These ultrasonic displacements can disrupt plaques not only by direct contact ablation but also by pressure waves, associated cavitation, and acoustic streaming developed in the surrounding blood and tissue cavities. The pressure waves developed within the arterial lumen appear to play a major role but are complex to predict as they are determined by the distal tip output of the wire waveguide (both displacement and frequency), the geometric features of the waveguide tip, and the effects of biological fluid interactions. This work describes a numerical linear acoustic fluid-structure model of an ultrasonic wire waveguide and the blood surrounding the distal tip. The model predicts a standing wave structure in the wire waveguide, including stresses and displacements, and requires the incorporation of a damping constant. The effects on waveguide response of including an enlarged ball tip at the distal end of the waveguide, designed to enhance cavitation and surface contact area, are investigated, in addition to the effects of the surrounding blood on the resonant response of the waveguide. The model also predicts the pressures developed in the acoustic fluid field surrounding the ultrasonic vibrating waveguide tip and can predict the combinations of displacements, frequencies, and waveguide geometries associated with cavitation, an important event in the disruption of plaque. The model has been validated against experimental displacement measurements with a purpose built 23.5 kHz nickel-titanium wire waveguide apparatus and against experimental pressure measurements from the literature.

Vibration characteristics of the capillary in ultrasonic wire bonders

Currently ultrasonic wire bonders with precision capillary tips are widely used in the packaging industry for bonding wires to ICs and circuits. However, the quality and strength of a bond are affected significantly by the vibration of the bonding capillary. It is, therefore, necessary to study the vibration characteristics of the capillary for better understanding and for developing a non-perturbative and low-cost monitoring device for improving bonding quality control. In this paper, the vibration characteristics of the capillary are presented in terms of natural frequency and vibration modes using finite-element models. The predicted displacement profile along the capillary is compared with the measurement using a non-contact laser interferometer. In general, a good agreement between the prediction and measurement is obtained, and it shows that the interferometer may be a good monitoring tool for characterization of capillary tip vibration, as well as providing a reference for other monitoring devices.

Numerical analysis of ultrasonic wire bonding: Part 2. Effects of bonding parameters on temperature rise

The thermo-structural analysis of ultrasonic wire bonding is performed by means of 3D finite element method. A special focus has been placed on monitoring the temperature rise during ultrasonic vibration. An equivalent method is used to simulate the wire and bond pad, where the large volumes of wire and bond pad are effectively reduced to small computational magnitudes. The history of temperature changes in the wire-bond pad-substrate interfaces influenced by varying bond forces and bond pad sizes is specifically studied. It is shown that the maximum bulk temperature obtained upon completion of ultrasonic vibration is far lower than the melting temperatures of the wire and bond pad materials, indicating that the bulk temperature rise due to ultrasonic vibration is not directly responsible for ultrasonic wire bonding. A large bond pad size usually leads to a lower temperature rise, and when the pad size reaches a certain value, the effect of bond pad size on temperature rise becomes insignificant. A higher bond force results in a marginally higher temperature rise than a lower bond force, which does not necessarily affect the wire bondability.

Real-Time Quality Evaluation of Wire Bonding Using Input Impedance

Input characterizes the dynamic property of a linear system. A few existing technologies thus exploit input electrical of wire bonders as the signature to monitor ultrasonic wire bonding processes. However, the waveforms of impedance in these technologies are evaluated only approximately. To overcome the shortcoming, we propose a method to detect the true waveforms of both the real and imaginary part of the input impedance. In the method, the voltage and current at the input port of a wire bonder are probed and processed to obtain via Hilbert Transform. Because dynamics of a bonding process represented by these waveforms is fully responsible for the resulted bonding quality, a quality evaluation system based on pattern recognition of these waveforms is further proposed. An artificial neural network using back propagation as training scheme learns from a set of training data to correlate a few features of the waveforms with the bonding strength of the corresponding bond identified by shearing tests. Through a set of verification data, the built system is validated to be capable of evaluating bonding quality right after a bonding process. The proposed method is not only in situ and real-time, but also sensorless, which means that the system is easy to be implemented without interfering operation

A microslip model of the bonding process in ultrasonic wire bonders Part I: Transient response

Ultrasonic wire bonders with precision capillary tips are widely used for bonding electrical wires to IC chips and circuits. The industry is driving wire-bonding technology towards increased yields, decreased pitch, and ever decreasing cost. However, many technical and material issues will be involved in achieving these goals, such as bond quality monitoring, new failure modes, reliability problems in new plastic mold compounds, and increasing wire sweep problems, in particular lack of the quantitative understanding and validated mathematical model of the bonding process. In this paper, a microslip model is proposed for the bonding process based on the bonding pattern observed, i.e. the wire is bonded at the periphery while the centre is left unbonded. A bilinear hysteresis restoring force is assumed in the microslip model because of its simplicity. The transient displacement response is calculated, and its pattern shows very good agreement with the experiment.

Low Power Ultrasound Delivered Through a PTCA‐Like Guidewire: Preclinical Feasibility and Safety of a Novel Technology for Intracoronary Thrombolysis

Low power ultrasound delivered through an angioplasty-like guidewire may be effective for intracoronary thrombolysis. We evaluated the preclinical feasibility and safety of such wire. In 15 anesthetized Yucatan minipigs, the ultrasonic wire was advanced percutaneously into all three coronaries. Each coronary was randomized to long activation (6 minutes), short activation (3 minutes), or control (3 minutes indwelling, no activation). The energy delivered was 0.14 +/- 0.01 W/cm of active length (20 kHz). No changes in heart rate, rhythm, or arterial pressure occurred during wire positioning or activation. Mean lumen diameter (MLD) by quantitative angiography was not significantly different pre- and postintervention (2.36 +/- 0.12 mm vs 2.36 +/- 0.11 mm for long activation, P = 0.96; 2.33 +/- 0.15 mm vs 2.34 +/- 0.14 mm for short activation, P = 0.54; 2.30 +/- 0.12 mm vs 2.33 +/- 0.12 mm for control, P = 0.21). There were no angiographic stenoses at 60 or 90 days follow-up. Compared with baseline, MLD at follow-up increased in all the three groups (2.40 +/- 0.13 mm vs 2.53 +/- 0.11 mm, P = 0.004 for long activation; 2.37 +/- 0.17 mm vs 2.52 +/- 0.14 mm, P = 0.023 for short activation; 2.20 +/- 0.12 mm vs 2.33 +/- 0.11 mm, P = 0.001 for the control group). By histology, there were no clinically significant pathologic changes in coronary morphology. Use of a transverse cavitation therapeutic wire is feasible and well tolerated acutely in the normal porcine coronary. At 60 and 90 days, no angiographically apparent damage, no clinically significant pathologic changes, and no adverse events were seen. This technology may be safely used during percutaneous coronary intervention. Further studies are justified to evaluate its efficacy for intracoronary thrombus ablation.

Effects of bonding force on contact pressure and frictional energy in wire bonding

A numerical study is made of the elasto-plastic deformation taking place in ultrasonic wire bonding based on the finite element method. A special focus has been placed on how the important wire bonding parameters, such as bond force and power, affect the contact pressure along the wire–bond pad interface. It is shown that the contact interface had a long elliptical shape, and the maximum contact pressure occurred always at the periphery of the contact interface, which is consistent in the current 2D and 3D finite element analyses. The normalised real contact area as well as the maximum frictional energy intensity varied in a similar manner to the contact pressure, with the maximum values occurring at the periphery of contact interface, where weld is preferentially formed in practical wire bonding. A higher bond force does not result in a higher contact pressure, or higher frictional energy intensity, suggesting that a high bond force is not directly correlated to better wire bondability.

A microslip model of the bonding process in ultrasonic wire bonders part II: steady teady state response

Ultrasonic wire bonders with precision capillary tips are widely used for bonding electrical wires to IC chips and circuits. The industry is driving wire-bonding technology towards increased yields, decreased pitch, and ever decreasing cost. However, many technical and material issues will be involved in achieving these goals, such as bond quality monitoring, new failure modes, reliability problems in new plastic mold compounds, and increasing wire sweep problems, in particular lack of the quantitative understanding and validated mathematical model of the bonding process. In a previous paper [Hu CM, Guo N, Du H, Li WH (in press) A microslip model of the bonding process in ultrasonic wire bonders - Part I: transient response. Int J Adv Manuf Technol], a microslip model has been proposed for bonding process based on the bonding pattern observed, i.e. the wire is bonded at the periphery while the centre is left unbonded. A bilinear hysteresis restoring force is assumed in a microslip model because of its simplicity. The predicted transient responses show good agreement with the experiment. In this paper, the analysis is extended to steady- state response, and discussion and comparison are made with respect to the transient response.

Numerical analysis of ultrasonic wire bonding: Effects of bonding parameters on contact pressure and frictional energy

The elasto-plastic large deformation taking place in ultrasonic wire bonding is analysed by means of 2-D and 3-D finite element method. A special focus has been placed on how the important wire bonding parameters, such as bond force and power, affect the contact pressure along the wire-bond pad interface. It is shown that the contact interface had a long elliptical shape, and the maximum contact pressure occurred always at the periphery of the contact interface, which is consistent in the current 2-D and 3-D finite element analyses. The normalised real contact area as well as the maximum frictional energy intensity varied in a similar manner to the contact pressure, with the maximum values occurring at the periphery of contact interface, where weld is preferentially formed in practical wire bonding. A higher bond force does not result in a higher contact pressure, or higher frictional energy intensity, suggesting that a high bond force is not directly correlated to better wire bondability.

Development of smart transducer with embedded sensor for automatic process control of ultrasonic wire bonding

A ring-shaped lead zirconate titanate (PZT) piezoceramic sensor has been integrated with the Langevin-type piezoceramic driver of an ultrasonic wire-bonding transducer to form a smart transducer for in-situ measurement of three essential bonding parameters: namely, impact force, ultrasonic amplitude and bond time. This sensor has an inner diameter, an outer diameter and a thickness of 12.7 mm, 5.1 mm and 0.6 mm, respectively. It has a specifically designed electrode pattern on the two major surfaces perpendicular to its thickness along which polarization is induced. The process-test results have indicated that the sensor not only is sensitive to excessive impact forces exerted on the devices to be bonded but also can track changes in the ultrasonic amplitude proficiently during bonding. Good correlation between the sensor outputs and the bond quality has been established. This smart transducer has good potential to be used in automatic process-control systems for ultrasonic wire bonding.

Design Of A New Wind Tunnel Facility AtIndustrial Engineering School In Badajoz(Spain)

The Industrial Engineering School, part of the University of Extremadura, located in Badajoz (Spain), has been founded by the European Community under the regional development program of research facilities, and it is actually under the process of construction. The aerodynamic channel is that of the Eiffel type, also called open flow. Thus, it is inside a 25 meter long and 6 by 6 meter wide room, taking the air from the room and evacuating it to the same room without temperature conditioning. The instrumentation included consists of that used to measure the air velocities, such as a pitot-static probe, ultrasonic and hot wire anemometers, differential pressure sensors to record the pressure distribution over solid bodies and an aerodynamic balance to measure forces and moments over solids inside the air flow. There are also other instruments such as high-speed cameras, a thermal camera and, if the budget allows it, a Particle Image Velocimetry system (PIV). As part of the development, an agreement has been signed between the University of Extremadura (Industrial Engineering School) and the Polytechnic University of Madrid (Aeronautical Engineering School) in order to gain experience by sharing knowledge and information.

Thin film thermal sensor for real time measurement of contact temperature during ultrasonic wire bonding process

Abstract The slender, thin film, K-type thermocouple, fabricated through sputtering deposition, is employed to probe the contact temperature of the frictional interfaces during the ultrasonic wire bonding process. This thin film sensor is of thickness of 1 μm and with three different line widths that are 100, 80 and 20 μm, respectively. Contents of the sensor were demonstrated to be similar to the original K-type targets. Comparison of the thermoelectric relation of the sensor before and after the bonding processes ensured that the sensor operated appropriately during the bonding process. To help the analysis, modeling the temperature variation of the sensor based on a lumped system was also presented and discussed. Results show the currently fabricated sensor worked very well for the contact temperature measurement during the bonding process. For the same bonding condition, the recorded temperature increased with the reduction of the line width of the thermal sensor. The lumped system analysis indicated this increasing was mainly contributed by the reduction of the thermal inertia in the junction region that resulted from the decrease of the line width. With the advantage of the thin film thermal sensor, more sensitive and less invasive, the current measurement acquires temperature rise up 300 °C at the duration of bonding that, at least, is 150 °C higher than the available data in the literatures. Measurement result obtained by the present slender, thin film, thermal sensor is believed more close to true contact temperature.

The study on failure mechanisms of bond pad metal peeling: Part B––Numerical analysis

According to the results of Part A of this paper [Microelectron. Reliab., this issue], the vertical tension loading transferred from the capillary is clarified as the direct driving force for bond pad metal peeling. Furthermore, the crack on the bonding pad is identified as the direct cause of the pad peeling. However, the major driving force for the crack that is correlated to the four main loadings described in the part A of this paper is not clarified. In order to find the driving force for the crack, whole ball bonding process of ultrasonic wire bonding is simulated by finite element method. The results of this study indicate that the horizontal vibration of the capillary controlled by ultrasonic power of the bonding machine has the most serious effect on the crack on the bonding pad as well as its propagation into the oxide layers in SDRAM chip. Thus it can be the major driving force for the crack.

Dynamic characteristics of stacked piezoelectric transducers of ultrasonic wire bonders used in integrated circuit packaging

Currently ultrasonic wire bonders with precision capillary tips are widely used for bonding wires to integrated circuit (IC) chips and circuits. However, the quality and strength of a bond may be affected significantly by the change of vibration during the bonding process. It is therefore important to understand the dynamics of the bonding process as well as the vibration characteristics of the bonding system, so bonding quality may be monitored. This paper reports the study on the dynamic characteristics of the stacked piezoelectric transducers used in the ultrasonic wire bonding system. The vibration characteristics are first analysed using the finite element method with resonant frequency and vibration modes. The predicted impedance response is compared with the measurement using a high-pressure (HP) impedance analyser. The displacement profile along the transducer assembly, which includes a piezoelectric stack, clamping and horn sections, are also analysed. The effects of multilayer and polarization on the response of the transducer are discussed. It was found there is good agreement between the prediction and measurement, and bending and extension modes may be excited differently according to the polarization configuration used in the multilayer stack.

Ultrasonic angioplasty transmission member

The ultrasonic angioplasty transmission wire has regions of reduced cross-sectional diameter to improve flexibility of the ultrasonic angioplasty transmission wire and to compensate for degradation of longitudinal displacement due to acoustic losses along the length of the ultrasonic angioplasty transmission wire. One or more constraining members are disposed on the ultrasonic angioplasty transmission wire at one or more of the regions of reduced cross-sectional diameter where transverse vibration of ultrasonic energy transmitted by the ultrasound transmission wire is amplified, to constrain transverse vibration at these areas to reduce stress and reduce fracturing, while allowing longitudinal movement. The transmission wire has an elongated shaft including, in atomic percent, from about 28 to about 52 percent nickel, from about 48 to about 52 percent titanium, and up to about 20 percent of at least one alloying element selected from the group consisting of palladium, chromium, and hafnium.

2128 気液二相流における超音波計測とワイヤーメッシュトモグラフィ計測の比較

2128 気液二相流における超音波計測とワイヤーメッシュトモグラフィ計測の比較

Ultrasonic ablation catheter transmission wire connector assembly

An ultrasonic angioplasty device includes a catheter and a connector assembly for interconnecting an ultrasound transmission member to an ultrasound transducer. A rotation control device is provided that prevents the ultrasound transmission member from rotating relative to the catheter. Rotation is prevented by a fastener aligning the connector assembly with the elongated catheter body, or a key member that fits in a correspondingly shaped slot in a proximal shaft portion of the catheter, for preventing rotation of the connector assembly relative to the catheter.

Placement of piezoelectric ceramic sensors in ultrasonic wire-bonding transducers

Three identical lead zirconate titanate (PZT) sensor rings have been inserted in different locations of an ultrasonic wire bonding transducer driver in order to measure the bonding parameters. Voltage outputs from these three sensors were compared in order to find an optimal position for the sensor placement. One side of the PZT sensor ring is partially coated with a specially designed electrode pattern and the rings are only poled in this small region. With this specific electrode pattern, sensor resonance can be eliminated and the sensor has a flat frequency response. From the sensor signals, different bonding qualities can be distinguished. Hence, the transducer can provide a feedback for real-time bond quality control and thus can be called a ‘smart transducer’. The optimum position is found to be near the back of the transducer if second harmonic detection is used. By placing the sensor at this optimized position, an in situ automatic wire bonding process control system can be implemented.