Young-Jae Kim

Electrohydrodynamic Jet Printing Capable of Removing Substrate Effects and Modulating Printing Characteristics

Electrohydrodynamic jet printing (EHDP) technique is widely used for the direct writing. However, in the existing EHDP method, the printing characteristics are affected by the printing substrate used, and the printed line width is determined by the geometry of the nozzle. We propose an EHDP method which is capable of (1) removing the effect from the substrate, and (2) controlling the line width through the ON/OFF control of the each nozzle in the nozzle array. Printing characteristics of our EHDP system were examined and successful ON/OFF control of the nozzle array were demonstrated. By using the proposed EHDP, it is expected that stable meniscus regardless of the effect from substrate and different line widths even using the same nozzle can be achieved.

The Effects of Driving Waveform of Piezoelectric Industrial Inkjet Head for Fine Patterns

This paper presents the effect of driving waveform for piezoelectric bend mode inkjet printhead with optimized mechanical design. Experimental and theoretical studies on the applied driving waveform versus jetting characteristics were performed. The inkjet head has been designed to maximize the droplet velocity, minimize voltage response of the actuator and optimize the firing frequency to eject ink droplet. The head design was carried out by using mechanical simulation. The printhead has been fabricated with Si(100) and SOI wafers by MEMS process and silicon direct bonding method. To investigate how performance of the piezoelectric ceramic actuator influences on droplet diameter and droplet velocity, the method of stroboscopy was used. Also we observed the movement characteristics of PZT actuator with LDV(laser doppler vibrometer) system, oscilloscope and dynamic signal analyzer. Missing nozzles caused by bubbles in chamber were monitored by their resonance frequency. Using the water based ink of viscosity of 4.8 cps and surface tension of 0.025N/m, it is possible to eject stable droplets up to 20kHz, 4.4m/s and above 8pL at the different applied driving waveforms.

High productivity and damage-free ultrasonic anisotropic conductive film (ACF) bonding for touch screen panel (TSP) assemblies

In this study, bonding time for touch screen panel (TSP) assemblies were reduced by two third using an ultrasonic (U/S) horn which fits the shape of the entire TSP bonding area. Most TSPs have at least two bonding areas on the substrates with different heights due to structural design of touch sensing. Using conventional thermo-compression anisotropic conductive film (ACF) bonding, each bonding area should be separately bonded to perform suitable interconnections with uniform pressure and a temperature due to the step height among the bonding areas. However, in U/S bonding, the bonding area could be bonded all at the same time using the U/S horn which fits the bonding area. The test vehicles were capacitive TSPs which consist of three layers of polyethylene terephthalate (PET) substrates. The TSP had three separated bonding areas. Two of them were on the double layer PET substrate. The other one located in the middle of the whole bonding area was on the single layer PET substrate. Therefore, the middle bonding area was 210 μm lower than the other two bonding areas. This complicated TSP structure requires three separate ACF bonding using conventional ACF bonding method. When using a fitted U/S horn, the in-situ ACF temperatures for all bonding areas showed negligible deviation less than 5°C. After U/S bonding for 15 seconds at 2 MPa bonding pressure and 150°C ACF temperature, the adhesion strength of the ACF joint was higher than 650 gf/cm. No damage was observed on the electrode and the substrate. Also, the ACF joints had stable electrical continuities. In conclusion, U/S ACF bonding with fitted horn was successfully demonstrated for high productivity TSP assemblies.

Modeling and Characterization of an Industrial Inkjet Head for Micro Patterning on Printed Circuit Boards

A conceptual design using computational fluid dynamics (CFD) and micro-electro-mechanical systems (MEMS) fabrication has been performed to develop an industrial inkjet head for micro-patterning on printed circuit boards. The printhead has been fabricated with silicon and silicon on insulator (SOI) wafers by MEMS process and silicon to silicon bonding method. The measured displacement waveform from piezoelectric actuator by Laser Doppler Vibrometer (LDV) was used as input data for the three-dimensional flow solver to simulate the droplet formation. The mechanism of droplet ejection from piezoelectric-type inkjet heads was investigated by simulating two-phase flows of the air and metal inks. Parametric studies are followed by the design optimization process to deduce key factors to inkjet head performance. The effects of nozzle geometry, pulse amplitude, ink viscosity, and micro bubble formation were also investigated based on numerical simulations. The present design tool based on two-phase flow solver and experimental measurements has shown its promising applicability to various concept designs of industrial inkjet system for micro-patterning on electronic chips and boards.Copyright

The Fabrication of Monolithic Micro Droplet Ejector using MEMS

This paper presents the fabrication of a micro droplet ejector for the application of digital printing system. The ejector makes the ink droplets of approximately 80 squaremum diameter on demand. The ejecting system is the type of face-shooter. The method of actuating membrane is bending mode using d31 of PZT. The size of ejector is 27.6 mm x 27.75 mm x 1.1 mm, and the pitch between nozzles is 2.54 mm, 10 npi. The nozzle and restrictor are very important part for the performance of the ejector such as droplet size and velocity. Therefore, the roundness and straightness of nozzle and depth profile of the restrictor have an influence on the characteristic of droplet. Those are made by deep silicon etching technique for the accuracy and uniformity. The ejector is successfully operated and the measured ejection speed, size of droplet and the ejection frequency are 1 m/s, 80 mum and 1 kHz, respectively.

Conceptual Design of Industrial Inkjet Head for Micro Patterning on Printed Circuit Boards

A conceptual design using computational fluid dynamics and experimental fabrication has been performed to develop an industrial inkjet head for micro-patterning on printed circuit boards. The measured displacement waveform from piezoelectric actuator by Laser Doppler Vibrometer was used as input data for the three-dimensional flow solver to simulate the droplet formation. The mechanism of droplet ejection from piezoelectric-type inkjet heads was investigated by simulating two-phase flows of the air and metal inks. As a preliminary approach, liquid metal jetting phenomena are identified by simulating droplet ejection, droplet formation, and wetting on the substrate in a consequent manner. Parametric studies are followed by the design optimization process to deduce key factors to inkjet head performance: nozzle geometry, droplet size, ejecting speed, ejecting frequency, and ink viscosity. The present design tool based on two-phase flow solver and experimental measurements has shown its promising applicability to various concept designs of industrial inkjet system for micro-patterning on electronic chips and boards.© 2007 ASME

Hybrid on Demand Jetting System for Ultra Fine Droplet based on Electrohydrodynamic and Piezoelectric Actuation

This paper demonstrates a hybrid jetting system (HJS) using both electrohydrodynamic (EHD) force and mechanical actuation to generate ultra fine droplets with drop on demand (DOD). In the proposed HJS, liquid meniscus was formed by a piezoelectric actuator and jets were generated by EHD force. Jetting characteristics were also examined for hydrophobicity and hydrophilicity of a surface of a capillary. With the HJS, on demand jetting of femto-liter was achieved with a frequency of 5 kHz.