Your Market Analysis: Cleanroom filters — Requirements and markets
06/01/2005
By Robert McIlvaine
Demands for removal of smaller and smaller particles continue in the cleanroom industry. Purification of cleanroom air increasingly involves elimination of molecular contamination, and gas-phase contaminants are major problems for semiconductor manufacturers. Therefore, suppliers of filter fibers, media, and assembled filters continue to improve their products to meet these demands.
The most important parameters in filters are efficiency and pressure drop. Cleanroom air-handling systems consume large amounts of energy so that even a slight decrease in pressure drop pays dividends in energy-cost reduction, which is significant as the cost of electricity continues to rise. Fan electricity costs are a considerable expense for most cleanroom operators as well. Therefore, selecting a filter with the required efficiency and least pressure drop is a high-priority consideration.
The HEPA filter (High Efficiency Particulate Air filter) removes small particles that are entrained in an essentially gas-phase system, the gas usually being air. It has a minimum efficiency of 99.97 percent in removing particles measuring 0.3 μm (i.e., only three out of 10,000 particles 0.3 μm in size penetrate the filter) and it reaches its rated efficiency when the velocity of the gas passing through it is 3 to 5 fpm. ULPA filters provide a minimum of 99.999 percent efficiency (0.001 percent maximum penetration) on 0.3-μm DOP smoke particles.
The main components of a HEPA or ULPA filter are a frame, filter medium (usually filter paper), separator, adhesive and gasket. HEPA filters are made in many sizes; they can be smaller than one square inch or as large as twenty square feet. There are many variations in shapes-square, rectangle and cylindrical are the most common. Each size and shape has its own special use.
The HEPA filter is most economical when used to remove particles of about 2 μm in size and smaller. Much less expensive filters are effective in removing particles larger than this. Therefore one or two stages of prefilters are usually employed to protect the final filter.
Most HEPA filters are constructed so that the filter paper is arranged in a large number of parallel pleats. The pleats are very narrow and very deep. A typical 2-foot by 4-foot by 6-inch HEPA filter contains 140 to 190 such pleats. These pleats act to straighten the direction of gas as it flows through the filter. In addition, the resistance of HEPA filter paper to gas flow is reasonably uniform, which means that approximately equal volumes of gas move simultaneously through each pleat of the filter. These two factors-the uniform resistance of the filter paper and the large number of parallel pleats-cause the air to flow uniformly 12 inches downstream of the HEPA filter face.
The cost of filters correlates with their efficiency; the higher the efficiency, the higher the cost. Increased efficiency causes higher pressure drop which raises the energy costs.
Since gases used in silicon etching and other processes will also attack the glass fibers of the filtration media releasing ionic contaminants, particularly boron, semiconductor manufacturers now specify filter media with reduced boron content.
Sealants are adhesives or other gasket materials used to prevent leaks between the filter pack and the filter frame. Semiconductor manufacturers request test data when their processes are sensitive to certain outgassing and trace-element contamination.
Air filters used in the life sciences must be able to withstand the rigors of the necessary decontamination processes, yet still retain their filtration design integrity. The two most important filter criteria for life-sciences applications are filtration performance and compatibility with decontamination materials and procedures. Cleanability and chemical compatibility limit the choice of HEPA frame material to smooth stainless steel or aluminum: stainless steel is normally used for filters in production equipment, while aluminum is often used as frame material in HVAC system filters.
Most life-science users have opted for gel-seal frames on their HVAC system HEPA filters because gel seals, when properly installed, provide the most positive seal of the frame to the end-use location.
Suppliers
Glass fiber filter media is produced by a number of companies, although Johns Manville (JM) has a large market share. JM offers a wide range of fiber diameters (0.2 μm to 5.50 μm). Lauscha (LFI) offers glass microfibers in a similar diameter range and produces borosilicate glass and alkali silicate (low-boron) glass microfiber for the full range of filtration applications.
There are a number of companies providing microglass filter media. Lydall and Hollingsworth & Vose (H&V), for example, are large international participants in this market.
H &V HiPerm Plus is a filtration media with low air resistance. This product is offered in an efficiency range of 99.92 percent to 99.9995 percent when tested with DOP aerosol. These products are designed to process in both deep-pleat and minipleat applications.
Lydall LydAir® Commercial/Industrial Grades are comprised of glass microfiber media, ranging from 45 percent ASHRAE to ULPA (over 99.995 percent). These products are specifically designed to provide properties such as durability, dust-holding capability, and performance in harsh environments.
Filter media are also manufactured in Europe. Fabriano Filter Media’s (Sassoferrato, Italy) production is exclusively dedicated to microfiber glass filter media for air filtration. High Efficiency grades range from 99.95 percent up to 99.999995 percent, which corresponds to classes H13-U17 (EN1822).
There is now an alternative to microfiber glass. Membrane media are sponge-like films of polymers with pore sizes ranging from 0.03 to 0.5 μm. Membrane filtration has been touted as a superior alternative because of its nonshedding characteristics. This eliminates the possibility that there are small pieces of glass being emitted from the filter itself. Most important has been the promise of lower pressure drop for a given particle removal with membrane filter media.
Both W. L. Gore and 3M were early developers of membrane filter media. However, some of the optimism for a more cost-effective media for the large 2-foot by 4-foot filter applications seems to have waned. Nevertheless this alternative holds promise.
LydAir® MC is an e-PTFE membrane media for pleated HEPA and ULPA filters introduced by Lydall that is available prepleated or in rolls. These products are said to offer superior performance and physical properties versus traditional HEPA and ULPA media. End-use applications range from microelectronic cleanroom and laminar flow hoods to equipment protection and vacuum cleaner dirt-cup and exhaust filters. Lydall’s manufacturing capabilities include treatment of air filtration media with several antimicrobial agents.
Membrane media has made good penetration in the filters used in Winchester disk drives. Donaldson’s Adsorbent Breather Filter (ABF) is designed to provide protection from particles, hydrocarbons and acid gases. The high efficiency filtration membrane removes particles from incoming air and encapsulates the adsorbent elements. The adsorbent is specially formulated to control humidity and to adsorb acid gases and hydrocarbons from internal and external sources.
The disk-drive filter business is very big in Asia. Donaldson has opened a 30,000-square-foot facility in Wuxi, China. The facility features a 10,000-square-foot, ISO Class 5 (Class 100), raised-floor cleanroom for filter assembly and a state-of-the-art analytical laboratory for chemical analysis of contamination. Much of the output from this plant is for disk-drive manufacturers.
W. L. Gore is also a supplier of disk-drive filter media. The company produces membranes with pore sizes down to .03 μm in diameter. Gore membranes are also used in high-efficiency vacuum cleaners.
There are many more filter manufacturers than those making media; however, Camfil, American Air Filter (AAF), Flanders and Donaldson have a large presence.
Markets
Much of the growth in filter purchases is in Asia. Cleanroom filter purchases can be segmented into those for new facilities and those for replacement of filters at existing facilities. In addition to the final HEPA filter, there are typically one or more prefilters. The prefilters are much less expensive but are replaced more frequently than final filters. Therefore, the annual cost to the owner for the prefilters is comparable to that for the final filters. McIlvaine has forecasted the purchases of both new and replacement filters through 2008 (see Table 1).
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The U.S. will have a slight edge over Japan and nearly double the sales of any other country in the purchase of filters for new facilities.
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The replacement-filter market in the U.S. is substantially larger than in other countries. The difference between the new and replacement markets is that the replacement market is a function of the installed base whereas the new-filter market is a function of the growth rate. Countries such as Taiwan, South Korea, and China have much smaller installed bases but high growth rates (see Table 2).
The filter business is rapidly globalizing. Hollingsworth & Vose is building a new media facility in China. A number of filter companies have set up fabrication facilities in Asia. AAF, which has been the largest American-based filtration company throughout most of the 20th century, is now Malaysian-owned.
In the future, it will be increasingly difficult to label companies by geography. The acquisition of the IBM personal computer business by Lenovo provides a template for the future. The business will be operated out of New York, not China. So to think of AAF as a Malaysian business or Lenovo as a Chinese business will be misleading. Likewise, to think of Donaldson as a U.S. company or Camfil as a Scandinavian company will be equally misleading. As the filter business grows in the developing countries, the suppliers will increasingly become truly global.
Robert McIlvaine is president and founder of the McIlvaine Company, Northfield, Ill. The company first published “Cleanrooms: World Markets” in 1984 and has since continued to publish market and technical information for the cleanroom industry.