BY Robert McIlvaine, President, McIlvaine Company
Flat-panel displays (FPDs) are a high-growth segment of the cleanroom industry, particularly in Asia. So while it is a very important market in this region, it is a small market in North America and Europe. Liquid crystal displays (LCDs) are the most common type of flat-panel displays and have been widely used since the early 1970s. LCDs account for about 80 percent of the entire flat-panel market, with thin-film transistor liquid crystal displays (TFT-LCDs) a large percentage of that. TFT-LCDs are used in notebook computers, desktop monitors and TVs.
Other technologies are organic light-emitting diode (OLED), plasma display panels (PDP), field emission displays (FEDs), and flexible panels. The OLED industry has experienced high annual growth rates due to the increased demand for small displays for cell phones, MP3 players and car stereos.
Some of the world’s largest cleanrooms are in flat-panel display manufacturing facilities. A flat-panel plant in Asia has cleanroom space five times larger than the largest U.S. 300 mm chip plant. Although a flat-panel display facility has many similarities to a semiconductor fab, it also has several important differences. For example, in flat-panel display manufacturing, there is little concern regarding molecular contaminants. Due to the nature of the techniques, these do not greatly affect device operation.
Despite the large feature size of many microns for active-matrix LCDs, the process is actually sensitive to much smaller particles. Particles that are smaller than a micron are a serious problem because they can cause shorts between metal layers.
While HEPA air filtration captures the airborne particles, there are special considerations for the flat-panel display industry. The first is that the substrate can be a source of particulate, especially as it is moved about. Bumping an edge of the substrate into something, for example, can lead to a shower of debris. Because the substrates are large and nonconductive, there is also more chance for electrostatic charging. Not only can that damage devices, but it can also make the plate act like a particle magnet.
One of the challenges is the size of the substrate, which today can be 400 millimeters on a side. Constant changing of the standard display size has presented problems to manufacturers of tools, automated transfer equipment and minienvironments. Most of the major production tools in TFT facilities are housed in minienvironments.
The potential for airflow irregularities is greatly magnified by the volumetric dynamics of production tools, which are much larger than their microelectronics counterparts. Even the cassettes used to transport flat-panel substrates are roughly the size of an office desk.
Further aggravating airflow management concerns are the extensive networks of material handling systems that are typical in the latest-generation flat-panel facilities, where material handling is virtually 100 percent automated. Automation includes equipment interface systems and floor-supported conveying systems, stockers and rail-guided vehicles (RGVs). Integration of these systems with the total cleanroom design is key to a successful project. Ground-based transport systems, automated guided vehicles (AGV) or manual guided vehicles (MGV) are used for glass handling in pilot facilities.
A ballroom-type design is common. The ballroom configuration provides the flexibility to accommodate the variety of tool configurations and sizes found in FPD manufacturing, and it simplifies the installation of very large tools. Individual tools for state-of-the-art TFT-LCD and PDP facilities are 20 to 40 meters long and 7 to 10 meters wide. Fully integrated lines for these facilities may be up to 100 meters in length.
Cleanliness classes range from ISO Class 4 in localized areas where the product is exposed to air to ISO Class 7 space, which is typical for cleaning and polishing the glass substrate before it enters the production fabs and for packaging the finished product. The general production environment typically is ISO Class 6.
Due to the low wall-to-floor area ratio in FPD cleanrooms, the pressurization component of makeup air can be relatively low. Adding process exhaust can drive the need for makeup air to levels approaching one million CFM.
Taiwan and South Korea are competing for leadership in key display segments. In 2004, South Korea had a 46 percent share of worldwide TFT-LCD shipments, compared to Taiwan’s 44 percent. Taiwan is expected to overtake South Korea in TFT-LCD manufacturing output by 2006.
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South Korea is expected to have 64 percent of the global plasma display panel (PDP) market share in 2005, while Japan is predicted to have 35 percent of the PDP market. PDPs are more appropriate for use in televisions that measure more than 40 inches diagonally.
The flat-panel display industry-with thousands of garmented personnel working in ballroom cleanrooms-is a big market for clothing, gloves, wipes, and other consumables. Table 1 shows the breakout by year of the world flat-panel display cleanroom purchases by country and region, with 2004 as the baseline. Percentages in future years are calculated based on 2004 figures. For example, Japan purchased 34 percent of the flat-panel cleanroom consumables in 2004. In 2008, it will purchase 65 percent of the world consumables relative to 2004.
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In 2008, Taiwan will be the leading purchaser of consumables for FPD plants (see Fig. 1), and sales in South Korea and Taiwan will more than double (see Fig. 2).
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Beyond 2008, growth should continue at a double-digit rate. As a result, the flat-panel display industry will be a major cleanroom market.
Robert McIlvaine is president and founder of the McIlvaine Company, Northfield, Ill.