Flat panel display manufacturing.

LCD Equipment
Crystec Technology Trading GmbH

In the realm of modern technology, understanding flat panel display manufacturing is essential. Here we delve into the intricacies of passive and active liquid crystal displays (LCDs) along with the critical steps involved in their production. The relevant equipment descriptions can be discovered through the links embedded in the text. Together with our esteemed partners in Japan and Korea, we are equipped to provide an extensive array of machinery for almost every production phase, even if some of these machines are not detailed on our website.

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Working principle

Liquid crystals

Liquid crystals are unique organic molecules that exhibit crystal-like properties while remaining liquid at standard temperatures. Due to their weak intermolecular forces, these molecules can be aligned using weak electromagnetic fields. The optical anisotropy of the liquid crystal molecules, characterized by different refraction indices for various molecular axes, is utilized to create visible images. Depending on their orientation, the panel appears either transparent or dark.

Passive LCDs

The construction of a passive matrix LCD involves multiple layers. The primary components include two glass plates sealed together. A polarizer is affixed to the front glass plate to polarize incoming light in one direction. The light then traverses the front glass layer, passing through an Indium Tin Oxide (ITO) electrode, which is covered with a passivation layer, often referred to as a hard coat. A polyimide layer is used to align the liquid crystal fluid. This fluid responds to electric fields by changing its orientation, rotating the polarization of incoming light. The thickness of the liquid crystal layer is maintained by spacers, which uphold a fixed distance between the two glass plates. Without an electric potential between the two plates, the polarized light rotates 90 degrees as it passes through the liquid crystal. Conversely, when potential is applied, the light remains unchanged. The light further passes through another polyimide layer, another hard coat layer, the rear ITO electrode, and the rear glass, where it either transmits through or gets absorbed by the rear polarizer, depending on whether it has been rotated 90 degrees. This technology has also found utility in the creation of smart windows.

Active matrix LCDs

The prevalent active matrix technology utilizes thin-film transistors (TFT) made of amorphous or polycrystalline silicon located on the rear glass of the LCD. Amorphous silicon TFTs are simpler to manufacture, making them suitable for most large displays today, whereas poly-silicon TFTs offer better performance but require higher deposition temperatures, limiting their application to smaller screens.

Coloured LCDs

Color in LCDs is achieved by applying color filters to the interior of the front glass sheet, typically using red, blue, green, and black matrix filters.

Manufacturing Process

The front and rear glass plates are produced in distinct production lines. Typically, several displays (4-6) are manufactured from one glass plate. The rear glass functions as the substrate for TFT production in active matrix LCDs. The production of transistors is achieved through various PECVD and sputter steps atop the ITO layer. Subsequent applications involve hard coating, polyimide, and spacers.

The front glass plate incorporates color filter layers alongside ITO, hard coat, polyimide, and sealing elements. In assembly, the two glass plates are positioned, combined, and secured with UV-cured polymer spots. This process is chiefly conducted under vacuum conditions known as the ODF-Process. The raw panels are pressed and heated to cure the seals, resulting in a stable panel structure. Following this, large panels are scribbled and broken down into final display sizes, and edges are smoothed. The individual displays are filled with liquid crystal fluid, closing the opening in the seal, followed by the application of polarizers on both sides. Finally, the display is ready, and the mounting of electronic components along with packing commences.

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TFT production on the rear glass

The creation of TFTs includes several vacuum processing steps utilizing PECVD for the deposition of a-Si and gate dielectric insulation layer, complemented by sputtering for creating data and scan metal lines and ITO layers. The typical sequence of process steps includes: deposition of gate metal, patterning, anode oxidation, depositing silicon nitride, and additional patterning steps.

Colour filter application on the front glass

The color filter application process is critical; it is often costly due to the high materials expenses and low yield. Various methods are employed for the application of color filters to the front glass, including spinning dye or pigment filter material, doctor blade technology, and foil application.

ITO deposition

Indium tin oxide (ITO) is typically applied through sputtering technology.

Hard coat

The SiOx and SOG passivation layer is printed on using flexo printing technology before curing and annealing in a furnace.

Polyimide (PI) layers

Polyimide layers are printed onto substrates using flexo printing technology and require a proper cure process via inert gas, achievable through clean convection ovens or on hot plates.

Spacer

To ensure a uniform distance between glass plates, small spacers are created. Currently, litho spacers are most commonly used. Traditional methods involved spray application.

Seal deposition and cure

For large-scale factories, screen printing serves as the best method for seal deposition, combining high throughput with performance. For smaller volumes with diverse designs, seal dispensing is more effective.

Contact creation

External contacts are created by printing on the glass substrate with Ag paste, employing the screen printing technique.

Cell Assembly

In the assembly machine, glass plates are aligned and secured with UV-cured polymer spots. This operation can also be performed under vacuum conditions.

Hot press oven

The curing of the seal post-assembly process must occur under pressure to ensure appropriate seal thickness.

Liquid crystal fluid filling.

Modern ODF technology facilitates liquid crystal filling during assembly, where the LCD panels are placed in a vacuum chamber.

Polarizer attachment.

After thorough surface cleansing, polarizer foils are applied parallel to the rubbing direction of the pertinent polyimide layer, finalizing the LCD fabrication process.

Cleaning

Comprehensive cleaning iterations are integral throughout the LCD manufacturing process to ensure optimal results.

Inspection

Critical inspection phases are mandatory, particularly the final assessment, which can be conducted either manually or through automatic inspection machines.

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