• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.108-108
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• 2007

Inkjet printing is a non-contact and direct writing associated with a computer. In the industrial field, there have been many efforts to utilize the inkjet printing as a new way of manufacturing, especially for electronic devices. The etching resist used in this process is an organic polymer which becomes solidified when exposed to ultraviolet lights and has high viscosity of 300 cPs at ambient temperature. A piezoelectric-driven ink jet printhead is used to dispense $20-40\;{\mu}m$ diameter droplets onto the copper substrate to prevent subsequent etching. In this study, factors affecting the pattern formation such as printing resolution, jetting property, adhesion strength, etching and strip mechanism, UV pinning energy have been investigated. As a result, microscale Etch resist patterning of printed circuit board with tens of ${\mu}m$ high have been fabricated.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1542-1543
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• 2007

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. Using the water based ink of viscosity of 11.8 cps and surface tension of 0.025N/m, it is possible to eject stable droplets through 64 nozzles average velocity of 4.05 m/s with standard deviation of 0.06 m/s and average diameter of $29.2\;{\mu}m$ with standard variation of $0.5\;{\mu}m$.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.8
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• pp.45-50
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• 2008

An ink jetting measurement system has been developed such that the velocity as well as the volume of ink droplets can be measured. In order to measure the ink droplet, a strobe LED light was synchronized to the droplet firing signal in order to obtain frozen droplet images. Then, a LabVIEW based software was developed for the analysis of the droplet image. For the efficient droplet analysis, a user generated rectangular shaped ROI (Region of Interest) was used. By using ROI, the ink droplet image can be easily isolated from the other structures such as printhead and the processing area can be minimized.

• Journal of computational fluids engineering
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• v.17 no.2
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• pp.65-70
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• 2012

The droplet ejection behavior from drop-on-demand printhead are investigated numerically in terms of the non-dimensional parameters. The numerical simulation is performed using a volume-of-fluid model. It is important to eject droplet within the printability range, where the droplet is ejected in stable manner without satellite droplets. Generally, the printability range has been determined by Z number, which is the inverse of Oh number. However, it is found that the ejection of droplets with same Z number can exhibit different behavior depending on the value of Ca and We number. Therefore, it is insufficient to determine the printability range only with Z number. Instead, other non-dimensional parameters, such as Ca and We number, should be considered comprehensively.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.455-460
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• 2007

A self-sensing circuit for piezo inkjet has been designed in order to monitor the operating condition during printing. In order to verify the circuit, both ink droplet images from strobe LED and vibration signals from the laser vibrometer were measured and compared with self-sensing signal. Experimental results show that self-sensing signal was effective in detecting the pressure wave change due to the bubble trapped in inkjet printhead.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.366-372
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• 2007

Self-sensing measurement of piezo inkjet and its application are discussed. The pressure wave inside the inkjet dispenser was measured by current measurement due to self-sensing capability of PZT. The pressure wave measured from current was verified by commercially available laser vibrometer. Here, two applications using self-sensing signal were discussed: waveform design for high speed jetting and condition monitoring. For waveform design, two pulse waveform was designed based on self-sensing signal such that the pressure wave after droplet formation can be minimized. For condition monitoring, self-sensing signal was shown to be effective in detecting air bubble trapped in inkjet printhead.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.4 s.235
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• pp.526-533
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• 2005

Reliability problem in inkjet printhead, one of MEMS devices, is also very important. To eject an ink drop, the temperature of heater must be high so that ink contacting with surface reaches above $280^{o}C$ on the instant. Its heater is embedded in the thin multi-layer in which several materials are deposited. MEMS processes are the main sources of residual stresses development. Residual stress is one of the factors reducing the reliability of MEMS devices. We measured residual stresses of single layers that consist of multilayer. FE analysis is performed using design of experiment(DOE). Transient analysis for heat transfer is performed to get a temperature distribution. And then static analysis is performed with the temperature distribution obtained by heat transfer analysis and the measured residual stresses to get a stress distribution in the structure. Although the residual stress is bigger than thermal stress, thermal stress is more influential on fatigue life.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.562-565
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• 2008

Measuring system for piezo inkjet droplet and ink jetting status was developed. In order to measure the jetting performance, two different approaches have been used. One is to use the self-sensing capability of the piezo actuator in the printhead. The other is to use the droplet image from a CCD camera. The software as well as hardware using two approaches was developed. The self-sensing signal as well as meniscus motion was shown to be useful in monitoring jetting conditions. Furthermore, ink properties such as viscosity and speed of sound, which is related to jetting performance, can be understood.

• Journal of ILASS-Korea
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• v.17 no.1
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• pp.20-26
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• 2012

Inkjet printing is one of the direct writing technologies and is able to form a pattern onto substrate by dispensing droplets in desired position. Also, by inkjet technology manufacturing time and production costs can be reduced, and procedures can be more efficient. To form a metal pattern, it must be harmonized with conductive nano ink, printing process, sintering, and surface treatment. In this study, micro patterning of conductive line has been investigated using the piezoelectric printhead driven by a bipolar voltage signal is used to dispense $20-40{\mu}m$ diameter droplets and silver nano ink which consists of 50 nm silver particles. In addition, hydrophobic treatment of surface, overlap printing techniques, and sintering conditions with changing temperature and times to achieve higher conductivity.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.188-190
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• 2004

As an effort to reduce cost and lead-time and to increase flexibility and responsiveness, manufacturers are using digital printing in numerous process steps. Typically, these processes require the precise dispensing of various fluids. Piezo ink jet printheads are proving to be reliable tools for depositing active materials such as light emitting polymers (LEP) for mobile phone displays and color filter inks for liquid crystal displays. Ink jets are also being used to provide uniform coatings of polyimide alignment layers and spacers for LCDs. Success with legend printing on PCBs using ink jets has encouraged the design of equipment for directly printing both etch resist and solder mask for PCBs. Development of printers for passive components such as capacitors and resistors is underway. This paper will present the attributes of an ink jet printhead designed to a precision deposition tool and discuss how it is being used to digitally print electronic and flat panel display components. Status of commercialization of digital printing will be discussed along with issues to be resolved before wide adoption takes place.