Method and apparatus for filling liquid crystal display (LCD) panels

A system, apparatus, and method for filling a display panel having first and second plates, with liquid crystal material, includes a nozzle for depositing a layer of liquid crystal material over a surface of a first plate of the panel, a scanning arm, coupled to the nozzle, for uniformly forming the layer of liquid crystal material over the surface of the first plate of the panel, and an attachment mechanism for placing the second plate over the first plate having the liquid crystal material thereover, thereby to form the display panel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to a method and apparatus for 
filling a display panel, and more particularly to a method and apparatus 
for filling a liquid crystal display (LCD) panel with liquid crystal 
material. 
2. Description of the Related Art 
Currently, many methods exist for filling liquid crystal display panels. 
However, such methods are extremely time-consuming, and thus the 
throughput is low for displays incorporating such liquid crystal panels. 
Several attempts have been made to improve the speed, while maintaining 
cleanliness, with which the liquid crystal (LC) material filling process 
occurs. Recent improvements have been disclosed in the above-mentioned 
U.S. patent application Ser. No. 09/062,275, incorporated herein by 
reference. However, this method has drawbacks in that the application of 
edge pressure may give rise to cracking of the glass comprising the front 
and back faces of the panel. 
Additionally, other conventional methods have attempted to increase the 
efficiency of the LC material filling process and LCD panel fabrication. 
However, these methods relating to displays (e.g., especially flat panel 
displays) still are problematic, and fail to provide a rapid liquid 
crystal filling process for the otherwise substantially completed panel. 
Specifically, none of the conventional systems and methods provides for 
efficiently applying the liquid crystal between the plurality (e.g., two) 
of panel plates, enabling a uniform distribution of the liquid over the 
entire interior surface either prior to or after vacuum pump-down. Such a 
feature would allow for a rapid uniform distribution of the liquid crystal 
with minimum air entrapment and bubble formation (e.g., both of which are 
major concerns in the LCD fabrication art). 
Furthermore, uniform distribution of the liquid obviates the need for 
substantial additional time for liquid diffusion or re-arrangement to 
provide the necessary smooth, continuous and uniform distribution of the 
liquid crystal medium within the panel. 
Thus, with conventional methods, a large time period is required for the 
liquid crystal material to spread uniformly and continuously throughout 
the panel from individual droplets deposited onto the panel or by back 
pressure filling after pump-down with the two portions of the panel 
affixed to one another, and drawing in the liquid through a narrow channel 
from a liquid crystal reservoir. 
For example, in one conventional method, at least one precision applicator 
or "micro syringe" is used as a delivery system for the liquid crystal 
material, for depositing an array of precisely spaced droplets onto a 
plate making up one half of an LCD panel. The droplet deposits are made at 
atmospheric pressure. However, filling is not performed within the vacuum 
chamber, thereby increasing the difficulty in handling and making the 
filling process more prone to contamination. 
Additionally, the micro-syringe delivery system is very costly and 
cumbersome to operate, since the precision of the volume of each droplet 
required is such that if the total amount of liquid (e.g., by all of the 
micro-syringes) is off by even a small amount (e.g., 5%), the panel either 
will be partially collapsed or will be bulged outwardly after the two 
plates of the panel are joined. Moreover, this conventional method has no 
mechanism or method for bleeding off excess material. Thus, there is 
little, if any, margin of error for the total volume of the droplets 
deposited onto the panel plate. Further, the micro-syringe is expensive 
and requires extremely accurate calibration. 
Other systems are known which pump out the panel, then place one partially 
opened edge in a trough of LC material, and expose the system to backfill 
pressure to fill the panel. This is a very complex, as well as very 
time-consuming, procedure. 
Yet another disadvantage of the conventional systems is that some systems 
are unable to use both spacer beads and lithographically placed studs for 
providing a predetermined, uniform gap between the first and second panel 
plates of the display. Specifically, some conventional methods may only 
use either of the spacer beads or the lithographically placed studs. 
SUMMARY OF THE INVENTION 
In view of the foregoing and other problems of the conventional systems and 
methods, it is an object of the present invention to provide a simplified 
and more efficient method for filling an unassembled LCD panel at 
atmospheric pressure. 
Another object is to provide a less costly method and apparatus for filling 
the LCD panel. 
Yet another object is provide a method and apparatus in which both spacer 
beads and lithographically placed studs may be provided selectively for 
providing a uniform, predetermined spacing between first and second panel 
plates of the display. 
In a first aspect of the present invention, a system for filling a display 
panel having first and second panel plates, with liquid crystal material, 
includes a nozzle for depositing a layer of liquid crystal material over a 
surface of a first panel plate having peripheral edges to form a shallow 
cavity for containing the material, a scanning arm, coupled to the nozzle, 
for uniformly forming, preferably in a single scan, the layer of liquid 
crystal material over the surface of the first plate of the panel, and an 
attachment mechanism for placing the second plate over the first plate 
having the liquid crystal material thereover, thereby to form the display 
panel. The peripheral edges preferably include an unpolymerized sealant. 
In a second aspect of the invention, an apparatus for filling a liquid 
crystal display panel including first and second plates, at least one of 
the first and second plates having a drain opening, includes a nozzle for 
emitting liquid crystal material, a scanning unit for scanning the nozzle 
to apply uniformly a predetermined amount of liquid crystal material, 
preferably in a single scan, over an entirety of a surface of the first 
panel plate at atmospheric pressure, and a robotic arm for positioning a 
second panel plate over the first panel plate. 
In a third aspect, a method for filling a liquid crystal display, includes 
steps of scanning a nozzle to apply uniformly a predetermined amount of 
liquid crystal material, preferably in a single scan, over an entire 
surface of a first panel plate forming a portion of the liquid crystal 
display, at atmospheric pressure, robotically positioning the second plate 
over the first panel plate, and providing a cut-out section in one of the 
first and second panel plates to allow for excess liquid crystal material 
to drain without deforming the first and second panel plates assembled 
together to form the liquid crystal display. 
Thus, with the invention, a uniform layer of liquid crystal is deposited 
over a surface of a plate forming the panel, utilizing a unique 
cylindrical spray nozzle. The nozzle is moved across the plate, thereby 
covering the entire area of the panel plate with the requisite liquid 
crystal material preferably in a single scan. 
With the present invention, when first and second plates are affixed to 
form the LCD panel, the liquid crystal material is uniformly dispersed. 
Thus, the method takes substantially little, if any, additional time to 
diffuse or re-distribute into the space between the two plates. 
Hence, with the unique and unobvious features of the present invention, the 
filling time is reduced from several hours to minutes, thereby greatly 
enhancing the throughput of fabrication of the panels. 
Thus, the present invention overcomes the difficulties of the conventional 
methods and systems in several ways. 
First, a first panel plate, not yet affixed to the second plate, is sprayed 
with a continuous and predetermined amount of liquid crystal material per 
unit area. Secondly, the second panel plate is aligned and attached to the 
first panel automatically (e.g., robotically). Any excess liquid crystal 
material is given a means for escaping from the two affixed plates so that 
a slight overfill of the liquid is not problematic (e.g., no bulging or 
the like results as in the conventional methods), as the inventive panels 
include a small region which permits excess fluid to flow out from the 
panel. 
Generally, it is desirable to slightly overfill the plate leading to a much 
more reliable uniform distribution of the liquid crystal and assuring 
there is sufficient liquid crystal material within the panel channel. 
Additionally, the inventive panel may selectively employ either spacer 
beads and lithographically placed studs for providing a uniform, 
predetermined spacing between first and second panel plates of the 
display.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
Referring now to the drawings, and more particularly to FIG. 1, there is 
shown a preferred embodiment of the present invention. 
FIG. 1 illustrates a general environment for forming the inventive LCD 
panel. 
In FIG. 1, a base plate 1 of a vacuum chamber (not shown) includes a 
recessed section 2. Recessed section 2 may be one of a plurality of 
substantially similar (or identical) sections for allowing batch 
processing of the display panel liquid crystal application. Liquid crystal 
filling takes place before a plurality of plates (e.g., first and second 
panel plates) comprising the liquid crystal display, have been affixed 
together. 
It should be noted for extra cleanliness, the vacuum chamber is used for 
processing, although the vacuum chamber need not be used for all of the 
process steps. The only crucial step requiring vacuum is the step when the 
two plates are superposed. Here, all air bubbles entrapped are removed by 
way of the reduced pressure. Thus, pump-out is performed before the plates 
are permanently sealed. 
Thus, with the present invention, all of the processing steps may be 
performed either in the vacuum chamber, or only some steps may be 
performed in the vacuum chamber. For example, first the recessed first 
panel plate is positioned in ambient atmosphere, and is sprayed with the 
liquid crystal material. Then, the first plate is placed in the vacuum 
chamber, and the chamber is pumped-out to evacuate any air bubbles. Then, 
the second plate is placed over the first plate, and affixed together by 
virtue of the sealant. Curing may take place in the vacuum chamber or the 
ambient atmosphere. Alternatively, as mentioned above, all steps may take 
place in the vacuum chamber. 
The panel plates may have any suitable dimensions, with the recessed 
portion 2 being formed in advance to receive panel plates of a 
predetermined size depending on the application for the LCD panel. Thus, 
LCD panels may be formed for any of a plurality of devices having 
different configurations and sizes (e.g., computer monitor displays, 
laptop displays, watches, calculators, toys, etc.). 
Generally and as described in further detail below, one of the first and 
second panel plates comprising the otherwise substantially completed panel 
is inserted within one of the recessed portions 2. A second panel plate, 
which may be a portion of the overall assembly in a second, nearby 
section, is for attachment to the first panel plate. The attachment is 
performed, for example, manually or automatically (e.g., through 
robotics). 
The recessed portion 2 is configured so that there is a precise dimensional 
fit (e.g., substantially within a range of about 10-25 microns) between 
the dimensions of the recessed portion 2 and those of the panel plate. 
Once again, such dimensions will depend on the size of the LCD panel and 
thus its application, as discussed above. 
Additionally, as shown in FIG. 1, there is a slotted recessed drain channel 
3 at one end of the base plate 1. This channel 3 aligns with a cut-out 
opening (e.g., opening 30 shown in FIG. 3 and described in further detail 
below) of the bottom panel plate. Alternatively, both top and bottom panel 
plates may have an opening opposite one another. The recessed drain 3 of 
the base plate 1 allows for excess liquid crystal material to flow 
thereout when the first and second panel plates are affixed, as described 
below. 
Turning to FIGS. 2(A) and 2(B), the structural details are shown of an 
apparatus 20, according to the present invention, for filling the first 
and second panel plates with liquid crystal material. 
The apparatus 20 includes a nozzle fixture 21 which may have a 
substantially cylindrical shape. Obviously, other shapes are also 
envisioned by the present invention and are believed to be well within the 
grasp of the originally skilled artisan. The cylindrical nozzle fixture 21 
feeds a liquid crystal material (and spacer beads if desired for 
maintaining a predetermined gap between the first and second panel plates 
1A, 1B) as droplets or as a spray onto the panel plate. 
It is noted that spray may be preferable to the droplets, especially if 
performed in a vacuum. If sprayed, it is preferable to undertake this step 
with the chamber evacuated, for ease of operation. Further, it is noted 
that the spacers may be in the form of beads or lithographically placed 
studs for maintaining a uniform spacing between the two panel plates of 
the assembly. 
The nozzle fixture 21 can be formed from metal (e.g., stainless steel), 
plastic such as polyvinyl chloride or the like, ceramics, and/or any of a 
number of other materials that are not chemically reactive with the liquid 
crystal material. 
The nozzle fixture 21 preferably is hollow, and preferably contains an 
array of small holes 22 (e.g., micron-sized diameters) along the axis of 
the fixture 20 to allow a uniform amount of liquid crystal material per 
unit area to be ejected as the nozzle fixture 21 is scanned across the 
panel plate 1A. Holes 21 may have any configuration (e.g., circular, 
triangular, polygonal, etc.) so long as a uniform amount of liquid crystal 
material per unit area is ejected. 
The fixture 21 is coupled to a pressurized LC source 23 for feeding LC 
material to the small holes 22 and out to the panel plate 1A. 
It is noted that, alternatively to the small holes 22, a single continuous 
axial slot 220, as shown in FIG. 2(C), may be provided along the 
circumferential surface of the fixture to spray or deposit the LC material 
onto the panel plate. 
The nozzle fixture 21 is attached to a scanning arm 24 and the LC source 23 
(e.g., a reservoir) of liquid crystal material. The nozzle fixture 21 is 
movable by the scanning arm 24 (e.g., preferably implemented through a 
robotic arm or the like) in the direction of scan, as shown in FIG. 2(B). 
The nozzle fixture 21, the scanning arm 24, and the reservoir 23 are 
computer-controlled by a central processing unit 25 or the like, to 
maintain the proper pressure and travel speed to obtain the correct amount 
of liquid crystal deposit on the panel plate being assembled, as 
illustrated in FIG. 3. A fixed amount of LC controlled by the computer 25 
is ejected onto the panel plate under preparation. The LC is stored in a 
reservoir and the required amount for each scan is set by the computer 25. 
Preferably, a single pass (e.g., scan) is sufficient to provide the 
requisite amount of liquid crystal for each panel assembly. It is noted 
that the "requisite" amount depends on the application. For example, the 
requisite amount may be on the order of 1-cc. (e.g., for a 15-inch display 
panel with approximate 5 micron separation between the first and second 
plates). 
The liquid crystal material may be heated to a predetermined temperature, 
such as from substantially within a range of about 50.degree. C. to 
70.degree. C., to obtain a desired viscosity giving rise to a deposition 
speed consistent with the velocity of the nozzle over the panel plate. 
An array of nozzles of the type just described can be positioned within the 
chamber for increased batch processing with an array of panel plates 
positioned within the chamber for liquid crystal filling. 
It is noted that, while the exemplary embodiment of the present invention, 
illustrates the nozzle fixture 21 being movable by the scanning arm and 
robotics, it would be well within the grasp of the ordinarily skilled 
artisan taking the present invention as a whole to modify the inventive 
system to move the panel plates in relation to a fixed (stationary) 
fixture nozzle 21. 
As shown in FIG. 3, the sweep of the nozzle 21 delivering droplets (or 
spray) of liquid crystal material onto one of the panel plates during a 
scanning sequence is shown. For clarity and ease of understanding, a 
vacuum chamber shroud typically covering the details shown in FIGS. 1-3 is 
not shown. As described above, the above-described steps may be performed 
at atmospheric pressure unless the nozzle emits a fine spray in which case 
a vacuum atmosphere is preferred. 
As shown in FIG. 3, the scanning arm 24 automatically scans the fixture 
nozzle 21 across the panel plate 1A. In FIG. 3, "L" represents the corners 
of the bottom plate 1A, and specifically the reflecting corners of the 
bottom plate 1A for use with detectors described in further detail below. 
As shown, the lower plate 1A includes a drain opening 30 which is aligned 
with the channel 3 of the base plate 1. The chamber is now evacuated. 
Further, a cleaning mechanism 300 is provided for cleaning the opening 30 
for the overfill. Preferably, the cleaning mechanism 300 is formed by a 
cleaning brush, a wiper blade, a doctor blade, or the like. The cleaning 
mechanism 300 preferably is computer-controlled by CPU 25, thereby to be 
activated at a time before (or after) the placement of an upper panel 
plate 1B (described further below) onto the lower panel plate 1A. 
As shown in FIG. 4, a sealant 41 exists (e.g., set in advance) on the lower 
plate 1A or on both the lower and upper (second) plate 1B, and the second 
plate 1B is moved by a robotic arm 42, and is placed onto the lower 
matching plate 1A that has just been sprayed with the nozzle and evacuated 
of air bubbles. The robotic arm is a lifting arm to place the second (top) 
panel plate onto the first (lower) panel plate. 
As shown in FIG. 5, a system 50 for aligning plate 1B to plate 1A is 
provided. In the system 50, at least one focused laser 51 is positioned to 
obtain reflections from spots at reflecting corners 51a of the lower plate 
1A. These reflecting spots 51a serve as guide points in alignment 
calibration. An optical absorber 52 is provided at the corners of, for 
example, the upper plate 1B to provide the necessary optical contrast to 
provide for the alignment of the plates. A beam splitter, half-mirror, or 
the like 53 is provided intermediate the laser 51 and a detector 55. It is 
noted that after alignment, curing of the panel occurs, for example, by 
ultraviolet radiation. The curing light is not shown in FIG. 5. 
FIG. 5 shows a state in which the plates are not in alignment. 
Specifically, the top plate 1B must be moved in a leftward direction 
(e.g., to the reader viewing FIG. 5), to provide proper alignment. 
The lasers 51 (e.g., a single laser or a set of lasers) are movable from a 
position outside of each panel to the respective reflecting corners so 
that a reflection threshold is sensed by detectors 55. Detectors 55 
provide an input to CPU 25 for processing and analysis. A (movable or 
fixed) lens 56, such as a convex lens, is provided between the optical 
absorber 52 and the beam splitter/mirror 53 for appropriate spot focusing 
of the laser onto the panel corners. A similar arrangement is provided for 
the top plate 1B and is designated with like reference numerals with a 
prime ('). 
When proper alignment of the two plates 1A, 1B of the panel has been 
achieved, no reflections will be observed since the upper plate 1B 
contains the optically absorbing material 52, 52' to prevent reflections. 
The robotic arm 42 makes adjustments of the upper plate 1B with respect to 
the fixed lower plate 1A until the absence of or greatly diminished 
reflected laser detection agrees with the predetermined data dimensioning 
stored in a lookup table (LUT) or the like of CPU 25, for the particular 
panel size. It is noted that this is only one of many different well-known 
alignment methods in the art, for achieving plate-to-plate alignment. 
Manual/physical alignment pins or the like also could be used. 
The vacuum chamber 60, shown in FIG. 6, is now slowly refilled with an 
inert gas such as nitrogen to atmospheric pressure. FIG. 6 represents the 
state of the two plates of the panel being attached and aligned, at the 
conclusion of the process. 
At least one of the two plates (and preferably at least the lower plate) 
contains an adhesive (e.g., a sealant 41 shown in FIG. 4 and comprising 
for, example, light polymerizing sealant (or epoxy)) well-known in the 
art. The adhesive/sealant is necessary for affixing the two plates 1A, 1B, 
but this adhesive remains flexible until a final cure. The final cure may 
be performed, for example, by applying ultraviolet light to the panel, a 
step which is taken after the panel is removed from the vacuum chamber 60. 
Again, this curing step is well-known in the art and, for brevity, is not 
further described herein. FIG. 6 shows the completed panel having the 
first and second plates affixed together with the sealant and cured in the 
chamber. 
Turning to FIG. 7, an operation of the present invention will be described. 
Specifically, in operation of the present invention, first in step S71, 
first and second panel plates, each forming a half of the LCD display 
panel, are placed within a vacuum chamber 60 (shown in FIG. 6), but are 
left under atmospheric pressure. The two panel plates are separated, and 
at least one of the halves (e.g., plates) contains the sealing material. 
The vacuum chamber 60 has preferably a recessed portion 2 into which one 
of the panel plates fits snugly (e.g., preferably with about 10-25 micron 
clearance). 
In step S72, the nozzle fixture (e.g., rod) 21, preferably having a 
substantially cylindrical shape or the like, with the array of small 
nozzle openings 22 (or the continuous slot 220) is swept along one panel 
plate (e.g., preferably the lower panel plate) positioned in the recessed 
portion of the chamber, by a scanning arm 24, to uniformly deposit the 
liquid crystal material using a predetermined volume of liquid crystal 
material per panel. Such a predetermined volume is determined by 
input/design parameter input to and processing performed by CPU 25. 
Further, it is noted that spacer material may be provided in the spray, or 
the spacers may be in the form of beads or lithographically placed studs 
for maintaining a uniform spacing between the two panel plates of the 
assembly. 
Thereafter, in step S73, the vacuum chamber 60 is evacuated (e.g., purged 
or pumped-out) to remove any air bubbles within the liquid crystal 
material on the panel plate 1A, thereby further smoothing out the 
distribution of the liquid crystal material between the panel plates 1A, 
1B, while simultaneously permitting any excess liquid crystal material to 
exude from the panel (through drain opening 3 shown in FIG. 1 and opening 
30 shown in FIG. 3). This is an important feature of the inventive 
structure and method, and reliably prevents either bulging of the panel or 
collapsing of the panel plates. In the present invention, no wedges are 
required for alignment since the robotic arm performs the alignment 
together with the alignment pins or laser reflection positioning tool. 
In step S74, a robotic arm 42 lifts and firmly places the second panel 
plate 1B over the first panel plate 1A containing the liquid crystal 
material. Positioning can be accomplished in a number of well-known 
methods. 
For example, laser reflections can be used by having small reflecting 
corners at particular corners of one or more of the panel plates, as 
described above. Alternatively, locating pins and corresponding holes on 
the two halves of the panel respectively can be used for alignment 
purposes. This method is well-known in the art. 
Then, in step S75, the opening 30 used for draining any excess material 
from the panel is cleaned (e.g., wiped) using a robotic cleaning mechanism 
40 (arm) or the like. 
In step S76, an additional sealant, such as for example, additional 
light-setting epoxy, may be applied on the edges of the panel plates, and 
is cured (e.g., hardened). The final seal makes use of cross linking the 
sealing compound using ultraviolet light, a process well-known in the art. 
The procedure described above can be performed with a plurality of panels 
simultaneously to allow for batch processing using only one set of robotic 
arms. 
With the unique and unobvious structure and method of the present 
invention, first and second plates are affixed efficiently together to 
form the LCD panel, and the liquid crystal material is uniformly 
dispersed. Thus, the method takes substantially little, if any, additional 
time to diffuse or re-distribute into the space between the two plates. 
Further, the precision equipment required by the conventional system and 
method for depositing droplets of LC material is not required by the 
invention. Instead, a hollow rod, preferably having a cylindrical shape, 
is used containing a plurality of small openings (or the continuous slot) 
along the outer periphery of the of the rod length to serve as a nozzle. 
The openings extend to the width of the panel plate, and the rod is swept 
along the length of the panel spraying and depositing the LC material 
under a controlled pressure. 
Hence, with the unique and unobvious features of the present invention, the 
filling time is reduced from several hours to minutes, thereby greatly 
enhancing the throughput of fabrication of the panels. 
Thus, the present invention overcomes the difficulties of the conventional 
methods and systems with an efficient, less-costly method and apparatus. 
While the invention has been described in terms of a single preferred 
embodiment, those skilled in the art will recognize that the invention can 
be practiced with modification within the spirit and scope of the appended 
claims. 
For example, while it has been discussed above that the lower plate is 
stationary and receives liquid crystal material from a scanning arm 
scanning thereover, the scanning arm could be stationary and the lower 
plate could be movable opposed to the scanning arm, thereby to receive the 
liquid crystal material.