TFT-LCD glass substrate manufacturing method part one

TFT-LCD glass substrate manufacturing method: float method, flow hole down-drawing method, overflow melting method

The glass substrates currently used in commercial applications have main thicknesses of 0.7 mm and 0.6 mm, and are about to enter a thinner (such as 0.4 mm) thickness process. Basically, a TFT-LCD panel requires two glass substrates, which are used as the bottom glass substrate and the bottom plate of the color filter (COLOR FILT E R) (the cross-sectional view of the color filter is shown in Figure 1). Generally, the ratio of glass substrate manufacturing suppliers to the glass substrate supply of LCD panel assembly plants and their color filter processing and manufacturing plants is about 1:1.1 to 1:1.3.

The glass substrates used in LCD can be divided into two categories: alkali glass and alkali-free glass; alkali glass includes soda glass and neutral borosilicate glass, which are mostly used in TN and STN LCD. The main manufacturers include Japanese plate glass ( NHT), Asahi and Central Glass, etc., are mainly produced by the float process; the alkali-free glass is made of alkali-free aluminum silicate glass (Alumino Silicate Glass, the main components are SiO2, Al2O3, B2O3 and BaO, etc.), the total content of alkali metal is below 1%, mainly used in TFT-LCD, the leading manufacturer is Corning (Corning) of the United States, which mainly produces by overflow fusion process.

The characteristics of the ultra-thin flat glass substrate mainly depend on the composition of the glass, and the composition of the glass affects the thermal expansion, viscosity (strain, annealing, transformation, softening, and working point) of the glass, chemical resistance, optical penetration absorption, and various The electrical characteristics at various frequencies and temperatures, product quality is not only deeply affected by the material composition, but also depends on the production process.

In TN/STN and TFT-LCD applications, glass substrates require surface properties, heat resistance, chemical resistance, and alkali metal content. The following only describes the main physical properties that affect TFT-LCD glass substrates. :

1. Strain Point: It is an indicator of glass density, which must be resistant to the high temperature of the LCD production process of optoelectronic products.

2. Specific Gravity: For TFT-LCD, notebook computers are currently the largest market, so the density of the glass substrate is as small as possible to facilitate transportation and carrying.

3. Coefficient of Thermal Expansion: This coefficient will determine the expansion or contraction ratio of the glass material due to temperature changes. The lower the coefficient, the better, so as to minimize the thermal expansion and contraction of the large screen.

Other indicators related to physical properties include melting point, softening point, chemical resistance, mechanical strength, optical properties and electrical properties, etc., which can be regulated according to the specific needs of users.

In the entire glass substrate manufacturing process, the main technology includes three parts: feeding, sheet forming and post-processing. The feeding technology is mainly controlled by the quality of the formula. The first is to melt the glass raw material into a low viscosity and uniformity in a high-temperature furnace. For the glass melt, not only the physical and chemical properties of the glass must be considered, but also the best formula of raw materials must be selected without changing the chemical composition in order to effectively reduce the melting temperature of the glass, clarify the glass, and achieve the specific properties of the glass. Meet the needs of actual applications. The thin sheet forming technology is related to dimensional accuracy, surface properties and whether further processing and grinding are required to achieve special physical and chemical characteristics. The subsequent processing includes glass division, grinding, cleaning and heat treatment.

So far, there are three main process technologies for the production of glass substrates for flat-panel displays, namely Float Technology, Slot Down Draw and Overflow Fusion Technology. Due to the horizontal extension, the "float method" will have scars and unevenness on the surface, which requires surface grinding and processing. Therefore, the investment amount is relatively high, but it can produce wider glass products (width up to 2.5 km). It has the advantages of larger production capacity (about 100,000 square meters/month); the "overflow melting method" has the advantages of more controllable surface characteristics, no grinding, and simpler manufacturing process. It is especially suitable for products with thicknesses less than 2 mm ultra-thin flat glass, but the glass width produced is limited to less than 1.5 meters, so the production capacity is small. The float method can produce glass substrates suitable for various flat-panel displays, while the overflow melting method is currently only used in the production of TFT-LCD glass substrates.