Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – For liquid etchant
Reexamination Certificate
2001-03-30
2004-01-06
Mills, Gregory (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
For liquid etchant
C134S116000
Reexamination Certificate
active
06673195
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for etching a glass panel and more particularly, relates to an apparatus and a method for etching a plurality of glass panels on both sides of the panel simultaneously with improved thickness uniformity for fabricating thin glass panels used in liquid crystal displays.
BACKGROUND OF THE INVENTION
Liquid crystal display devices have been used for many years. In the beginning, their uses have been concentrated in small appliance applications such as electronic watches and calculators. LCD's are now used in applications for instrument panel numerical displays and graphical displays. Advantages presented by LCD's are their inherent properties of small thickness, lightweight, low driving voltage requirement and low power consumption. As a consequence, more recent applications of color LCD's can be found in small screen television sets, notebook computer display panels and video camera viewfinders as replacements for conventional CRT's.
A liquid crystal display device can be made either a color unit or a black and white unit. The device may also be constructed as a reflective-type or as a transmittive type, depending on the light source used. Since liquid crystal molecules respond to an externally applied electrical voltage, liquid crystals can be used as an optical switch or as a light valve.
A liquid crystal display cell is a single pixel that is constructed by two parallel glass plates, i.e. an upper glass plate and a lower glass plate. Both the upper plate and the lower plate have a polarizing film coated on its outer surface. A cavity formed between the two plates is filled with a liquid crystal material. One of the most commonly used liquid crystal material is of the twisted hematic (TN) type wherein the term twist refers to the tendency of the liquid crystal to form chains that rotate from one side of the gap between the plates to the other side of the gap. The degree of rotation can be controlled during the fabrication process.
When a light beam passes through the polarizer and the liquid crystal display cell, its polarization direction is rotated by following the physical rotation of the liquid crystal molecules. The polarizer on the exit side of the liquid crystal cell may be positioned such that it allows a rotated light beam to pass through the polarizer. When viewed from the side of the polarizer, the pixel or the liquid crystal cell thus appears clear, i.e. in a transmitting mode.
A transmitting electrical conductor such as indium-tin-oxide (ITO) is normally deposited on the inner surfaces of the glass plates. The transparent electrical conductor layer may be patterned into a series of mutually perpendicular lines. When a voltage is applied across the cell cavity by addressing the appropriate line on each side of the cell, liquid crystal molecules reorient themselves to follow the applied electrical field. The liquid crystal materials thus become untwisted. The passage of the untwisted light beam is blocked by the exit polarizer as long as the voltage is present. When the voltage is turned off the liquid crystal molecules return to their original state and the cell or the pixel becomes clear again. As previously described, typical voltages and currents required to activate the liquid crystal molecules are relatively low making it an ideal candidate for incorporation in a battery-operated equipment where low power consumption is essential. A typical twisted hematic (TN) liquid crystal cell used for small displays have a twist angle of 90°. More recently developed supertwisted nematic (STN) material forms a twist angle up to 270° and thus allow higher contrast so that many pixel elements can be multiplexed in a single display.
While the liquid crystal display device described above is the transmittive type, liquid crystal display devices of the reflective-type are also used. In a reflective-type liquid crystal device, one of the upper plate and the lower plate is replaced by a reflector plate which is light reflective and not transmittive. The reflector plate may be fabricated of a glass substrate with transistors or other active components built on top and coated with a metal reflective layer. In the reflective-type liquid crystal display device, the light source for illuminating the liquid crystal display is from the ambient such that a display is viewed in a reflective manner.
One of the characteristics for the reflective-type liquid crystal display device is the noise signals reflected from the top or the cover glass plate of the display device. In a conventional reflective-type liquid crystal display device, the reflector plate and the top cover plate are parallel to each other. When an outside light source is used to produce an image in the liquid crystal device under the reflective principal, the light reflected from the reflector plate and from the top plate have the same reflective angle. Since the light reflected from the top cover plate does not produce the image formed in the liquid crystal display, only noise signals are produced which decrease the contrast of the display device. Furthermore, the noise/signal ratio of the device is also increased which affects the quality of images produced by the display device.
For an LCD to be effectively utilized in applications of portable electronics, i.e. such as portable televisions and notebook computers, an important factor to be considered is the reduction of size and weight of the LCD unit. Since the driving circuit and the thin film transistors utilized on a LCD unit are the necessary elements and are already formed in a miniature scale that any further reductions in size and weight in these elements is not likely. The only possible element in the LCD unit to target a weight reduction is the glass substrate. Since proportionally the glass substrate is a heavy element in the LCD unit, methods for reducing the weight of the glass substrate have been the subject of investigation in the LCD industry.
To reduce the weight of a glass substrate, an obvious approach is to reduce its thickness. However, the thinning process of the glass substrate is difficult to carry out since thin glass can be easily damaged due to the reduction in mechanical strength and furthermore, the thinning process may cause surface roughness which directly effects the image quality of a LCD unit.
FIG. 1
is a graph illustrating U.S. Pat. No. 5,989,450 issued to Kim disclosing an etchant for etching glass substrates. In the method, an etchant solution that contains HF in water at a concentration of at least 5 vol. % and an alcohol such as ethanol, methanol, propanol, butanol and isopropyl alcohol to a concentration of about 5 vol. % is held in container
12
. A porous plate
14
generates bubbles
8
for separating the etch residue and particles from the surface of the glass substrate
21
. While the etch residue is more easily removed by the etchant that contains 5 vol. % alcohol, the method cannot achieve uniform etching on a large glass substrate, and furthermore, cannot be used to etch glass substrates that already have conductive elements formed in an edge portion of the substrate.
Another method, as shown in FIG.
2
and disclosed by U.S. Pat. No. 6,071,374 to Kim, illustrates an apparatus for etching a glass substrate which includes a first bath
13
containing an etchant, at least one porous panel
15
that has a plurality of jet holes
16
in the first bath, the porous panel contains the etchant to jet the etchant against the glass substrate
30
. A container
20
stores the etchant, and a pump
24
is used to supply the etchant from the container to the porous panel
15
by a connection between the pump, the container and the porous panel.
As shown in
FIG. 2
, the glass substrates
30
are fixed by at least a pair of projections
19
formed on a stand
18
and arranged between the porous panels
15
. When the pump
24
is operating, the etchant is sprayed onto the glass substrate
30
through the jet holes
16
by the press
Chen Tai-Hon
Huang Yuan-Chung
MacArthur Sylvia R.
Mills Gregory
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