Minkyu Choi

A new type of piezostack-driven jetting dispenser for semiconductor electronic packaging: modeling and control

This paper presents a new type of piezostack-driven jetting dispenser which can be applicable for semiconductor packaging processes. After describing the structural components of the dispensing mechanism and the operating principle, the dynamic modeling is undertaken by considering the behavior of the piezostack, hydraulic magnification, dispensing needle and adhesive fluid. In the modeling, fluid models for the adhesive fluid and hydraulic magnification are derived using a mechanical model which is analogous to the corresponding lumped parameter model. The governing equation of motion is then established by integrating the fluid models with the structural model. Subsequently, the dynamic behavior of the dispenser and its dispensing amount are investigated through both computer simulation and experiment by applying a sinusoidal driving voltage input. In addition, a control system is designed and experimentally realized to control the dispensing flow rate (dispensed amount) of the dispenser.

Design of a Novel Jetting Dispenser Featuring Piezostack and Linear Pump

This article presents a novel jetting dispenser featuring piezoelectric actuator incorporated with a linear positive displacement pump, to achieve high dispensing flow rate with small dot size. A multi-stack type of piezoelectric actuator is adopted and its output displacement is amplified via a hydraulic magnification mechanism. After describing the configuration and operating principle of the proposed dispensing system, static modeling is undertaken by analytical method to determine design parameters. The analytical result is then proven by finite element analysis. Subsequently, structural dynamic modeling and fluid dynamic modeling are analytically undertaken. In the dynamic modeling, fluid—solid interaction is considered to predict the dispensing dot size and average flow rate of the dispenser. Dispensing performances are investigated by changing the driving voltage of the piezostack actuator and velocity of the linear piston of the pump.

Design and performance evaluation of a new jetting dispenser system using two piezostack actuators

This paper presents a new jetting dispenser system which is adaptable to various packaging processes such as light emitting diode packaging and flip chip packaging. The proposed dispenser system is driven by piezostack actuators and a lever-hinge mechanism. In order to improve jetting performances such as accurate dispensed amount and adaptability to high viscosity fluid, two piezostack actuators are used. By activating the two actuators dually, the angular displacement of the lever can be controlled to produce a required motion of the needle. Firstly, the configuration and working principles of the proposed jetting system are explained, the design of the dispenser is then conducted and significant geometric dimensions of the dispenser are presented. In the design process, several operational requirements such as the maximum needle stroke, operational frequency, and amplification ratio of the lever-hinge are considered. The principal design parameters of the jetting dispenser system are determined from static and modal analysis using the finite element analysis. After obtaining the dimensional characteristics, the control logic for the dispensing operation is explained using a feed-forward controller. The piezostack-driven jetting dispenser system and control devices are then fabricated to evaluate the dispenser performance. It is shown experimentally that by changing the input voltage conditions, the amount of fluid dispensed by the proposed jetting system can be effectively controlled to achieve the desired jetting performance.

Speed Control of DC Motor using Electrorheological Brake System

This study presents robust control performance of a direct current (DC) motor with brake system adopting the giant electrorheological (GER) fluid, whose distinguished feature is an extremely high value of yield stress. As a first step, Bingham characteristics of the GER fluid is experimentally investigated using the Couette type electroviscometer. A cylindrical type of electrorheological (ER) brake is then devised based on the Bingham model, and its braking torque is experimentally evaluated. The ER break is then incorporated with a DC motor. After formulating the governing equation of motion for the DC motor with ER brake system, a sliding mode control algorithm, which is very robust to external disturbances and parameter uncertainties, is synthesized and experimentally realized in order to achieve desired rotational speed trajectories. The tracking responses of the control strategy are then evaluated for various sinusoidal trajectories. In addition, their tracking errors are evaluated and compared with those obtained from traditional PID controller.

Design and Control of Jetting Dispenser Driven by Piezoelectric Actuator

This paper presents a new type of jetting dispenser for the integrated circuit (IC) fabrication and surface mount technology The proposed system is featured by the piezoelectric actuator and hydraulic magnification device. After describing structural component of the dispensing mechanism and its operation principle, both the fluid modeling and the hydraulic magnification modeling are undertaken with a lumped-parameter method based on the analogy of the fluid system and mechanical system. A mathematical governing equation is then derived by integrating the fluid model with the mechanical model of the driving piston and piezoelectric actuator. Subsequently, in order to achieve a desired dispensing amount, control algorithm adjusting duty cycle of the driving voltage is synthesized and control responses are presented in time domain.

Single-phase driven ultrasonic motor using two orthogonal bending modes of sandwiching piezo-ceramic plates

A compact ultrasonic motor using sandwiching piezo-ceramic plates was developed, having advantages of low manufacturing costs, simple driving circuit, and high scalability. The stator is composed of two piezoelectric plates attached to a T-shaped steel body. Two orthogonal bending modes can be excited by driving one piezoelectric plate and the reversed motion of the rotor can be obtained by driving the piezoelectric plate on the opposite side. The prototype stator with a size of 15 mm × 2.44 mm × 2 mm, operated at 44.8 kHz, was experimentally characterized, and a maximum torque of 2 mN m was obtained. Maximum power of 2.3 mW and efficiency of 9% were produced with a load of 0.8 mN m at a rotation speed of 27 rpm.

Polarization orientation dependence of piezoelectric losses in soft lead Zirconate-Titanate ceramics

Dielectric, elastic and piezoelectric losses are investigated in soft Pb(Zr,Ti)O3-based piezoelectric ceramics in terms of polarization direction dependence of the properties. The difference of the mechanical quality factor at the resonance and anti-resonance frequencies were obtained by the impedance method. The polarization angle of the samples varied from 0 (E//PS) to 90 degree (E⊥PS) for “effective” k31 and k33 vibrating modes. The change in the piezoelectric losses is dominant in comparison to the dielectric or elastic losses in both vibration modes.

Design of a New Dispensing System Featuring Piezoelectric Actuator

This paper presents a novel type of hybrid dispensing head for IC fabrication and surface mount technology. The proposed mechanism consists of solenoid valve and piezoelectric stack as actuators, and provides positive-displacement and jet dispensing. The positive-displacement dispensing can produce desired adhesive amount without viscosity effect, while the jet dispensing can produce high precision adhesive amount. In order to determine the relationship between required voltage of the piezoelectric actuator and needle displacement, both static and dynamic analysis are undertaken, In addition, finite element analysis is performed in order to find optimal design parameters. Dispensing flow rate and pressure in the chamber are evaluated through fluid dynamic model.

Critical operating factors of a jetting dispenser driven by piezostack actuators: statistical analysis of experimental results

Abstract In this work, critical operating factors of a jetting dispenser driven by a dual type of the piezostack actuators are experimentally identified. As a first step, geometrical information and working principle of the jetting dispenser are briefly addressed. Subsequently, in order to investigate jetting performance eight important operating (or working) factors of the dispenser such as exciting stroke and frequency are chosen based on two levels for each factor. Then, in order to reduce the number of experiments, one-sixteenth fractional factorial design method is adopted and an experimental apparatus to measure the weight of a single dot is established. After measuring the weight of a single dispensed dot under each test condition, the effect of each operating factor on the jetting performance is analyzed using a statistical program. The main effects and interaction effects on the average and standard deviation of the weight of a single dispensed dot are then analyzed and discussed in details. In addition, the analysis of variance results for average single dot weight is undertaken to determine the specific values of the critical factors which can provide optimal jetting performances. Consequently, critical operating factors for a small amount and small weight variation of a single dot are identified, which directly represent the performances of a non-contact jetting dispenser driven by piezostack actuators such as dotting accuracy and dotting speed.

Design of Ultrasonic Vibrator for Conformal Coating Spray in LED Packaging

This paper presents the design of ultrasonic vibrator utilizing a piezoelectric actuator. After describing a geometric configuration of the proposed atomizer, an analytical model of the ultrasonic atomizer is formulated by considering liquid film surface theory and wave theory. The dynamic analysis is then undertaken using a finite element analysis to determine principal longitudinal vibration modes. An optimization is performed by taking the amplitude of the tip displacement as an objective function. The fluid flow characteristics of the proposed atomizer is also analyzed under operating conditions through commercial software FLUENT.