Development of a LCD droplet generator and precision in situ droplet volume measurement system
Date Issued
2009
Date
2009
Author(s)
Chen, Jhih-Yuan
Abstract
Traditional liquid crystal injection method of TFT/LCD will face fierce challenge when the display size becomes larger and larger, because of its long process time. The advanced one drop filling (ODF) technique will become a key process trend to overcome. The amount of liquid crystal depends on the gap between two liquid crystal panels. Therefore, the height of spacer is the key point of determining the gap. Initial works will focus on the literature survey and optical measurement technique to realize the actual height of each spacer. A micro dropping dispenser using DOD technique will also be studied at the second stage. Variation in LC volume control will yield surface defect of the display.This paper presents the design, fabrication and tests of a piezoelectric type droplet generator, which can be used for liquid dispensing system. At the end of each liquid filling process, the remaining liquid has to be drained out and the parts have to be cleaned. A Teflon gasket is particularly designed to connect the main body and the nozzle holder. This design helps the dismantling process to be done easily and ensures the assembled structure to be fully sealed. The principle is to actuate a disk type PZT by a function generator to push the liquid out of the droplet generator and form a near-spherical droplet due to surface tension. In our research, we investigated the phenomenon of dispensing, in order to improve the accuracy and reliability of the droplet generator. There are three process parameters to be kept under control, namely, the quality of the nozzle, the voltage signals and the liquid properties. We expected to find out the best control parameters of the actuator in order to precisely control the total amount of the liquid crystal material. This research develops a multi-dispenser system to provide a method for dispensing liquid that enables increased efficiency by applying liquid from a plurality of liquid dispensing devices. Then, we could utilize the developed calibration procedure to achieve a goal by controlling the weight of drops. It is very useful that each time when the target weight of droplet was changed, the calibration procedure was not necessary to repeat again. In addition, the single drop weight can reach 1.14 mg by increasing the nozzle size.In addition to exciting the PZT, the signal generator also drives a light emitting diode LED that is used to observe the droplet formation phenomenon by means of stroboscopic technique. An online droplet volume measurement system is applied to the One Drop Fill (ODF) process of the liquid crystal display (LCD) manufacture. The developed system utilizes the stroboscopic technique to synchronize the triggering of the strobe light and the CCD camera. A steady image of the droplet can be captured online by the CCD camera. The method of precise volume estimation is based on the rotationally symmetric model of the droplet''s shape. Polynomial fitting is used to reconstruct the droplet profile. The image resolution can thus be enhanced by the sub-pixel technique. Compared to a precision electronic balance, the total weight measured by this system has an error being within ?0.3% and the computation time for each droplet is about 0.4 s. This all together fits the actual ODF requirements.
Subjects
One Drop Fill,
droplet generator
volume measurement
image processing
Type
thesis
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