Substrate coupling method

Details Substrate coupling method Substrate coupling method

1999-09-30

2002-03-26

Ramsey, Kenneth J. (Department: 2879)

Electric lamp or space discharge component or device manufacturi

Process

With assembly or disassembly

C349S187000

Reexamination Certificate

active

06361389

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of substrates, and more particularly, to the field of coupling two substrates together by a means for coupling, optical laminate or like means for cohesively laminating by a viscous fluid.
BACKGROUND OF THE INVENTION
Liquid crystal display (LCD) devices are well known in the art and are useful for many applications in numerous industries (such as, for example, the avionics industry, consumer goods and the computer industry). Several types of LCD substrates are in production. The manufacture of LCD substrates typically require capturing a thin layer of liquid crystal between two pieces of transparent substrates, such as glass or plastic, forming a liquid crystal cell. When an electric field is applied, the field alters the molecular alignment of the liquid crystal, thus affecting the light that is passed through the crystal. This phenomena turns small windows of light known as pixels (picture elements) “on” and “off.” LCD displays are usually light-weight, require low power and provide precise viewing resolution. Further, LCD displays are now manufactured as rigid substrates or flexible substrates.
The liquid crystal must be in a particular orientation, or oriented in the correct direction, to operate properly. The orientation of the liquid crystal is achieved in the manufacturing process by rubbing the two plates with a polymer, creating parallel furrows. The most common type of LCD on the market today is a passive form in which all the pixels in each row are tied together, thus reducing the need to control each pixel independently. But, that means the pixels remain in a state between on and off, resulting in a loss of contrast. It also produces annoying ghost images, especially of moving objects, in either the rigid substrate or the flexible substrate form.
Researchers have been struggling for years to develop cost-efficient active displays in which each pixel is controlled by its own transistor. Active matrix displays are now available on laptops, but they are expensive to manufacture, partly because the transistors can be so easily damaged during the fabrication of the display screen. Some technologies not currently on the market could potentially reduce the cost, including ferroelectric liquid crystal cells (in which a thin film of transistors would be used to control the pixels individually). In a ferroelectric screen, each pixel would be either on or off, thus producing an image that is light and dark, like the numbers on a digital watch. At one time, it was thought that ferroelectric screens could not produce gray scales such as those needed to produce a photograph, thus severely limiting its use.
Fabrication of LCD displays has proven extremely difficult. When the polymer is rubbed across the film of transistors to provide alignment for the liquid crystal, it causes mechanical damage and electrostatic charges that can potentially damage the transistors. The yield of the transistors then decreases drastically, which affects the price of the finished LCD display substrate. And, because of the sensitivity of such screens, the screens must be protected, usually by adhering another substrate (such as a glass cover of equivalent dimensions) to the LCD substrate. An optical coating (such as an anti-reflective coating) may also optionally be coated on to the substrate which is coupled or otherwise adhered to the LCD display.
A current method of adhering a glass cover substrate to the LCD substrate is known as the “gravity pour” method. In this method, a clean LCD substrate is placed immediately adjacent to a clean protective substrate at a 90 degree vertical angle so that the LCD substrate and the protective substrate are parallel to each other and in close proximity to each other. Bond tape (such as VHB high bond tape manufactured by Minnesota Mining and Manufacturing), similar to double-sided tape, is then applied to the periphery edges of the LCD substrate (typically within 0.060 inches from the outer periphery). Then, the two substrates are precisely brought together so that the bond tape provides a seal between the periphery edges of the two substrates. In this construct, an air gap or air cell is created between the two substrates of known width (usually 0.025 inches to 0.045 inches apart, which are the typical commercial widths available for bond tape). Then, silicone or another like optical coupling material is poured between the two substrates along an opening in the top edge of the tape-bonded substrates and allowed to slowly permeate between the substrates by gravitational forces. Another opening (usually also located at the top edge) is also required to allow the air volume to escape from the air gap as the pour process continues. This gravitational pour process usually takes more than an hour and may or may not be successful in completely filling the entire air gap between the bonded substrates. The viscous fluid typically employed has a characteristic viscosity of about 150 cps, but can go as high as 4500 cps.
The problems associated with using the pour prior art adhesion process, however, are numerous. First, adhesive optical materials bond the substrates together to form an almost permanent, rigid planar beam. And, for example, filling all the air cell space between the two substrates is difficult due to the viscosity of the adhesion fluid which often leads to visible air volume space or air bubble formation between the substrates. Further, this process is slow, which means that unless the timing is precise for the complete permeation of the air gap with fluid, those optical fluids which undergo a chemical cure will do so before the substrate adhesion process is complete (since most viscous fluid pot life is approximately an hour). Thus, if the fluid cures too quickly before the gravity pour process is complete, it may require repeated pour processes, unusable substrates, partially bonded substrates or damaged substrates. The position of the substrates at 90 degrees also introduces substantial friction between the two substrates, which reduces the even flow of viscous fluid between the substrates during the injection process. And, because the gravity pour method results in inconsistent permeation, the final substrate does not always possess uniformity of color throughout the substrate. Moreoever, other manufacturers in the art have used fluids to optically couple substrates, however the gap between the substrates is very small as to transmit the axial deflection directly to the LCD substrate, which causes optical distortions which can persist. Finally, if the gravity pour process is not executed precisely under careful conditions, the two substrates, after bonding, sometimes exhibit a bowl shape in the middle of the substrates due to increased hydrostatic pressure, leading to an unusable LCD substrate. What is required is a novel process that allows the complete permeation of viscous fluid between two substrates which overcome the problems associated with the previous techniques.
BRIEF SUMMARY OF THE INVENTION
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The present invention is a novel method for optically coupling two or more substrates together. The method requires providing two clean substrates and positioning each at approximately a 20 degree angle (or an incline of various ranges) parallel to each other and in close proximity to each other. The two substrates are then sealed adjacent to each other by a means for sealing. A means for optically cohering (such as an optically clear fluid) is then de-gassed to remove any dissolved or remaining gas within the means. Then, a pressurized means for injecting (such as a pressurized syringe) is filled with the de-gassed optical laminate means, while a

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