WHAT IS LCD?
Liquid crystal displays (LCDs) consist of liquid crystals that are activated by electric current. They are used most frequently to display one or more lines of alpha-numeric information in a variety of devices: fax machines, laptop computer screens, and so on.
MANUFACTURING PROCESS:
Preparing the glass substrates
First, the two glass substrates must be cut to the proper size, polished, and washed. Cutting can be done with a diamond saw or scribe, while polishing involves a process called lapping, in which the glass is held against a rotating wheel that has abrasive particles embedded in it. After being washed and dried, the substrates are coated with a layer of silicon dioxide.
Making the electrode pattern
Next, the transparent electrode pattern must be made on the substrates. This is done by completely coating both front and rear glass surfaces with a very thin layer of indium tin oxide. Manufacturers then make a mask of the desired pattern, using either a silk-screening or photolithography process. A mask with the desired pattern is placed over the glass, and the glass is bombarded with ultraviolet light. This light causes the resistive layer it shines on to lose its resistance to etching, allowing the chemicals to eat away both the exposed photoresist and the indium tin oxide below it, thus forming the pattern.
Applying the polymer
After the electrode pattern is in place, the substrates must be coated with a polymer. The polymer allows the liquid crystals to align properly with the glass surface. Polyvinyl alcohol, polyamides, and some silanes can be used.
After coating the glass, manufacturers then stroke the polymer coat in a single direction with soft material. This can result in small parallel grooves being etched into the polymer, or it may simply stretch the polymer coat. In any case, this process forces the liquid crystals to lie parallel to the direction of the stroke. If LCD makers want to align liquid crystals perpendicular to the glass surface, another technique is used: coating the glass with an amphophilic material. This is material whose molecules display affinity for water at one end of the molecule and repulsion from water at the other end.
Applying the sealant and injecting the liquid crystal
A sealing resin is next applied to the substrates, followed by plastic spacers that will give the liquid crystal cell the proper thickness. Next, the liquid crystal material is injected into the appropriate area between the two glass substrates. The thickness of the LCD cell is usually restricted to 5-25 micrometers. To make LCDs more visible, polarizers are added. These are usually made from stretched polyvinyl alcohol films that have iodine in them and that are sandwiched between cellulose acetate layers. Colored polarizers, made using dye instead of iodine, are also available. Manufacturers glue the polarizer to the glass using an acrylic adhesive and cover it with a plastic protective film. They can make reflective polarizers, which also are used in LCDs, by incorporating a simple metal foil reflector.
Final assembly
After the polarizer film is attached, the unit is allowed to age. Finally, the finished glass display assembly is mounted to the circuit boards containing the control and drive electronics.
Quality Control
LCDs are made under highly controlled conditions in a clean room environment to maximize yield. "Clean rooms" have special air filtering devices designed to keep all dust particles out of the room, and workers inside the room must wear special clothing. Nonetheless, many LCDs have to be discarded because of imperfections. To minimize the rejection rate, each active device is inspected and as many are repaired as possible.
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DISCLAIMER
The information is provided by Tecquisition for general informational and educational purposes only and is not a substitute for professional legal advice. If you have any feedback, comments, requests for technical support or other inquiries, please mail us by tecqusition@gmail.com.
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