I read the article on page 17 of the January issue with great interest as I am familiar with the efforts Lucent has put forth to make its cleanrooms some of the best in the industry. I work with FM Global, their property insurance carrier. Your article correctly points out many positive features of the fan filter units used there, but one very important issue was not covered: The combustibility of the actual unit. Lucent specifically had these units designed such that the entire assembly is noncombustible. The housing and structural components are noncombustible (metal) and the filter assembly is a Factory Mutual Research (FMR) Approved (UL Class 1) filter.

The reason I point this out, and hope that perhaps you will do, is that Lucent saw the need to maintain its efforts in striving for a noncombustible cleanroom environment. Many others in the industry do not take the time to do this. There are fan filter units being sold and installed that have combustible insulation or are actually constructed of combustible materials. Many times the firm purchasing these type units is not told of the potential problems. Forums such as your magazine help “get the word out.”

If you or your staff desire more information on fan filter units, or the many other issues relating to reducing the combustible loading inside cleanrooms please feel free to contact our Mr. Heron Peterkin in FMR (781-762-4300, ext. 4722). Thank you for your time and attention.

Coleman E. Cashion, P.E.
Senior Engineering Specialist
Factory Mutual Insurance

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The cleanrooms industry is faced with the challenge of embracing the contamination control needs and assisting in the educational process of the HVAC industry. If we educate, get involved, these guys will not only be your first line of defense in battling contamination, but one of your strongest lines of defense, no matter what market you're in.

And, according to my gut instincts, they're ready to get on board.

As so often is the case in many manufacturing processes, certain functions can practically co-exist but not be aware of the issues they have in common. This thought, although grammatically cumbersome, ran through my mind as I conducted several exploratory discussions at the recently concluded International Air-Conditioning, Heating, Refrigerating Exposition (AHR Expo) in Atlanta—sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and the Air-Conditioning and Refrigeration Institute (ARI).

I spent a good portion of my time at the show speaking to heating, ventilation and air conditioning (HVAC) contractors and engineers, looking for fresh angles for “new project” stories. You may not know these guys too well. They're coming in on the front end of a project; for the most part working under the guidance of a design/engineering firm and, in many of the large jobs, they're following your specs. They're the infrastructure guys who, in some cases, pack up the trucks and head out while you can still see through the walls.

Yet, they're at an interesting stage in the evolution of their work. I asked one contractor if he was working on any interesting cleanroom projects at the time. “You know what,” he said, cocking his head as if instantly puzzled, “I think I just finished one, but I'm not sure.” I handed him an issue of CleanRooms and told him to keep in touch.

The HVAC industry is starving for cleanroom information, insight and relevant product knowledge. They're seeing “clean” job opportunities pop up as the demands for cleaner, safer products are filling their pipeline of work. They're getting more involved in projects and slowly realizing the contamination control role they can play, but they're just now becoming aware of what make makes a cleanroom clean.

Cleanroom projects are the growth market for these guys, the new blip on their radar. As an involved industry player, it's time to invite a local HVAC contractor over for a cup of coffee. You might be surprised what you both could take away from the conversation. And by the way, look to our news and technical pages over the next few months. We'll be exploring some to “surprisingly simple,” yet practical contamination control technologies that the HVAC industry has to offer—cost-effective applications that make long-term sense for almost all of our markets.

On the edge: We've been justly accused of setting the standards in the industry over the years. This year will be no exception. As you may know, Fed-Std-209E will be “put to rest” at some point during the next six months. On first word, CleanRooms will install the ISO nomenclature in our descriptions of room cleanliness. We've offered you both in our text over the last 12 months, so now would be a good time to get to know your Fed-Std-209E equivalents.

Michael Levans
Chief Editor

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Molding and packaging device and method
The invention is an apparatus as well as a method for manufacturing articles such as syringe barrels, substantially free from contaminants. The apparatus is an enclosure defining at least an ISO Class 5 (Class 100) environment, and includes molding isolation and packaging isolation modules. Any contaminants that may exist within the enclosure are removed by horizontal and vertical laminar airflows directed into air filter units. The molding temperature may be selected, rendering fabricated articles substantially free from contaminants. The molding isolation and packaging isolation modules keep the articles free from contaminants from the time the articles are molded to the time the articles are placed in sealed containers for shipment.
Patent number: 6,145,277
Date granted: November 14, 2000
Inventors: Mark Lawecki, Eugene A. Gelblum; Michelle Robinson;
Ralph E. Wolstenholm; and Eugene B. Wolstenholm, of Medrad Inc. (Indianola, PA).

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Method of cleaning gases
The method and apparatus clean a gas to prevent contaminating the surface of a substrate in a localized space. A photocatalyst, illuminated with light, comes in contact with the gas to be treated. Any noxious gases are removed from the treated gas. Alternatively, an apparatus comprising an ultraviolet radiation source, a photocatalyst, a photoelectron emitter and an electrode is installed in a selected area of the localized space and the gas to be treated is passed through the unit, whereby noxious gases and particles are removed from the treated gas.

The invention can be used in cleanrooms—such as those in semiconductor fabrication plants, liquid crystal fabrication plants and precision machine manufacturing plants—where the outgassing of hydrocarbons is a contamination source.
Patent number: 6,159,421
Date granted: December 12, 2000
Inventor: Toshiaki Fujii, Kanagawa-ken, Japan

Cleanroom floorboard
The floorboard has a support unit and a tile unit. In the support unit, a plate part has a number of engaging holes on its upper surface. The support part is vertically and integrally formed along the edge of the lower surface of the plate part. Reinforcing ribs are integrated with both the plate part and the support part. In the tile unit, a cover part engages with the upper surface of the plate part. A number of engaging projections are formed on the lower surface of the cover part at positions corresponding to the engaging holes of the support unit. Each of the engaging projections has a ventilation hole at its central position.

The tile unit is firmly welded to and integrated with the upper surface of the support unit through an injection-molding unit. This simplifies the process of manufacturing the floorboard, keeps it free from emitting any odors or toxic gases, and makes it useful for lengthy periods of time.
Patent number: 6,155,013
Date granted: December 5, 2000
Inventor: Chae-Won Kim, Seoul, Rep. of Korea

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Flow control apparatus
The apparatus controls the volume of air that is supplied to and fumes that are exhausted from an electronic semiconductor manufacturing wet bench. This type of wet bench typically utilizes corrosive chemicals such as acids to etch the wafers. During the filling and use of the acid, the noxious fumes produced must be exhausted to prevent user exposure. The volume of air that is moved through the wet bench can significantly impact the cost of operating the wet bench. This cleanroom-quality air must be processed and filtered to remove particles that could contaminate the semiconductor wafer. The flow control apparatus reduces the cost of operation by varying the amount of air flow through the wet bench between high and low flow conditions, which are dictated by the nature of the activity that is occurring within the wet bench.

The controller monitors the status of the wet bench during operation. The display panel indicates in CFM the actual flow through the wet bench, and status lights show normal, marginal and alarm conditions. The operator can push a purge button to open the control damper to its full position if there is a spill or other unsafe condition. The operator can manually set the flow from low or high flow condition to the reverse.
Patent number: 6,152,818
Date granted: November 28, 2000
Inventors: Steven D. Jacob, Louis Hrkman, Jr.,
and Michael Laport, Siemens Building Technologies, Buffalo Grove, IL

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Wall system
The non-progressive wall system can be 11 to 12 feet high and does not require excessive demolition of adjacent panels and framing posts. It does not use a continuous horizontal header. Instead, the system consists of framing posts and connector blocks mounted to the ends of framing members. At the connection where four wall panels are joined at a common point, the connector blocks abut each other and serve to splice aligned framing posts and to provide structural integrity to the framing members. This arrangement permits selective removal of the framing posts and adjacent wall panels. The wall system also meets the lateral load and deflection requirements for non-progressive wall systems greater than eight feet high.
Patent number: 6,155,014
Date granted: December 5, 2000
Inventor: S. Ross Wagner, Tigard, OR

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Ceiling arrangement
The ceiling arrangement can be used for securing and supporting filter/ventilation units in cleanrooms. The design comprises profiled beams with end faces and connecting members. The connecting members have at least two end faces that provide a flush connection to the end faces of the profiled beams. For each one of the flush connections, the end face of the connecting member or the end face of the profiled beam has a groove. Before assembly, a dry sealing member is inserted into the matching grooves. After assembly, a reliable sealing action in the abutment area is ensured. When the filter/ventilation unit must be repaired or exchanged, one of the profile beams can be removed then resealed.
Patent number: 6,158,186
Date granted: December 12, 2000
Inventor: Eugen Feller, Grafenau, Germany

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Textile laundering system
The textile laundering system is installed in a controlled environment and may be used to launder cleanroom garments. It includes a washing machine, a dryer and a device for measuring the number and sizes of particles present within textiles. The washing machine has a loading and an unloading side and equipment access panel and is situated within a sealed opening in a vertical partition. It uses only water that is substantially free of ions, minerals and organic material. The equipment access of the washer and dryer are enclosed within a service chase.
Patent number: 6,128,931
Date granted: October 10, 2000
Inventor: Robert L. Woods,
Advanced Micro Devices Inc.
(Sunnyvale, CA)

Contamination control system
The system, which relates to contamination control of fluids with media contained in a replaceable assembly, includes a housing having a cartridge input-output port and an application input-output port. The cartridge can be coupled to the cartridge input-output port and can completely fit in the interior of the housing. A dual isolation surface is provided between cartridge and housing so that they can be separately isolated at the fluid interface. The isolation interface is resiliently engageable to make the fluid path open and close. The cartridge body has a multi-region interior chamber. The chamber, which is in fluid communication with an input and an output and defines a fluid flow path that is larger than any dimension of the body.

Double containment results from the housing containing the cartridge and the cartridge containing the purification or filtration media. A fluid isolation interface isolates the housing from the atmosphere when a cartridge is not coupled to the housing.
Patent number: 6,149,718
Date granted: November 21, 2000
Inventors: Cathy L. Cowan, Canton, CT;
and Luciano M. Melluzzo, New Britain, CT

Send your inventions
Information on the patents highlighted was obtained through the U.S. Patent and Trademark Office. Inventors who have been granted patents within the last six months for new cleanroom and contamination technology are encouraged to submit them to CleanRooms magazine for publication. Send a brief description of the invention along with a detailed drawing to Mark A. DeSorbo, associate editor, CleanRooms, 98 Spit Brook Road, Nashua, NH 03062, or e-mail at [email protected].

Mark A. DeSorbo

NICE, FRANCE—European Union (EU) leaders continue to cope with mad cow disease outbreaks amid negotiations on several issues regarding proposed food safety legislation and the establishment of an agency that attempts to mirror the U.S. Food and Drug Administration.

However, a spokesperson for the U.S. Department of Agriculture's Food Safety and Inspection Service says the EU has not formally asked the United States for advice, nor has guidance been offered.

Meanwhile, the EU estimates that dealing with the mad cow crisis could cost about $1 billion and put agricultural programs at risk. EU executives report that cost of carrying out mandated tests for mad cow on cattle over 30 months, along with a “purchase for destruction” program, are expected to diminish the agricultural budget.

Mad cow, also known as bovine spongiform ecephalopathy (BSE), causes prions, proteins in the brain, to change shape, affecting other brain cells and forming sponge-like holes in brain tissue, which leads to dementia and ultimately death. Health officials throughout the world believe grain and vegetable feed that is made with the remains of the same animals it is intended for is the cause of the brain-debilitating disease.

In early February, the United Nations said Eastern Europe, the Middle East, North Africa and India had the highest risk among countries outside Western Europe of harboring mad cow disease.

All told, about 125 cases have been discovered throughout Europe. The human variant of the illness, Creutzfeldt-Jakob Disease (CJD), has killed 90 people in England, France and Ireland.

US on the alert
The mad cow scare has heightened concerned in the United States, as well. In January, the U.S. Food and Drug Administration (FDA) advisory panel recommended that anyone who had lived in France, Portugal or Ireland for a total of 10 years since 1980 be prohibited from donating blood. Regulations adopted last year excluded anyone who lived in England for six months between 1980 and 1996.

The American Red Cross has also urged the FDA to apply the six month rule to all of Western Europe, which would cut the supply of donors by about five percent, even though there is no evidence that the disease can be transmitted through blood.

A week after the FDA recommendation, the agency investigated whether people would be at risk of mad cow disease as a result of 1,200 cattle that may have been fed the ground-up remains of other cattle by mistake. The agency contends that people are not at risk of contracting mad cow disease. In addition, some imported German candy that may have been made with gelatin from at-risk cattle probably also poses no threat, the FDA said.

Mad cow takes its toll
The outbreak is indeed spreading madness throughout Europe. According to Reuters, German Health Minister Andrea Fischer, democratic party Chancellor Gerhard Schroeder as well as several other officials resigned in early January, saying the public had lost faith in their ministry.

While Germany, France and Ireland prepared to slaughter more than 400,000 cattle, Italy continued to hash out its first case of mad cow disease, which was discovered in late January. Health Minister Umberto Veronesi's suggestion to ban the traditional Tuscan T-bone delicacy outraged restaurateurs and the meat industry, both of who openly talk of revolt.

“Florence is rebelling and will defend the symbol of Tuscan cuisine,” an editorial in the city's newspaper La Nazione said. “The health minister is very much mistaken if he thinks he can destroy centuries-old traditions and a piece of our identity with the sweep of a pen and a speech.”

Mad-cow-like disease in US
Although the FDA and the Red Cross have concerns that mad cow will rear its ugly head in the United States, other records from The Center for Food Safety (CFS), obtained on the agency's Web site indicate that the disease, or some form of it, is already here, and has been for some time.

On January 7, 1999, CFS filed two legal petitions demanding that the FDA and the Centers for Disease Control and Prevention (CDC) act immediately to monitor, regulate and prevent “mad cow” type diseases in the US, saying people, deer, elk and sheep are dying.

The legal petitions, which charge the United States efforts have been “grossly inadequate,” were filed on behalf of a 30-year old Utah man, R. Douglas McEwen, who is now terminally ill with CJD.

“McEwen hunted deer and elk. It is feared that he may have contracted CJD by eating or handling deer or elk infected with mad deer disease,” a newsletter on the Web site said. “There is additional concern because McEwen was a frequent blood donor, and may have contaminated blood products internationally. McEwen is a petitioner in the local action along with the CFS.”

The second legal petition demands that the FDA tighten animal feed regulations on animal feed and practices, which the CFS says can lead to mad cow-type diseases in animals and humans.

“Current regulations allow calves to be fed milk replacement containing cattle blood protein, and pigs to be fed back to pigs and cattle,” the CFS Web site indicates. “US sheep infected with scrapie, a mad cow-type disease, can be used for pet and pig feed.”

The petition would require meat suppliers to maintain paperwork on meat supply sources for 10 years instead of just one year. “They are only required to keep paperwork for one year, which makes the information useless because CJD infection can remain dormant for years before symptoms occur,” according to CFS.

At the time of this report, Mexico issued a temporary import ban on Brazilian beef products, officially joining Canada and the United States in the measure to avoid mad cow disease and its deadly human variation.

The announcement came just after an agriculture official told Reuters that Mexico was in talks with its North American Free Trade Agreement partners to impose a ban on all beef products from Brazil, including gravy, corned beef, gelatins and other beef products or products made with beef components.

There has been an export ban on British beef since 1996, when BSE hit British cattle. German officials and farmers had insisted that the country was free of the disease because it did not use animal products in feed, widely thought to be a source of transmission for the disease.

But since systematic testing was begun last fall, nine cases have so far been confirmed. Officials say it is the result of grain and vegetable feed being tainted with animal matter.

Beef sales throughout Europe, according to the EU, have plummeted by nearly 30 percent, and many countries throughout the world, such as Kuwait, have banned the importation of European beef and ruminants.

Mark A. DeSorbo

SHANGHAI, CHINA—Imagine that the over-the-counter cold medicine you gave to your sick child ends up being a deadly dose of a counterfeit drug that results in their death.

What would be an extreme case scenario in the United States is a reality in China, for that is just what happened when Chi Suzhen bought what she thought was a remedy for her 12-year-old daughter.

But less than three days later, the girl died from what doctors told her was a deadly dose of counterfeit medicine. Although the family made numerous attempts to find out how the poorly manufactured drugs had made it onto the store shelves, government officials were unable to provide answers.

The Chi family, who told UPI they plan on suing the pharmacy that sold them the medicine, is not alone in their grief. According to the Shanghai Drug Administration, drug poisonings killed an estimated 200,000 Chinese and hospitalized 2.5 million in 1999.

Crackdown continues
State Drug Administration (SDA) officials, however, have stepped up efforts to crack down on substandard drugs by revising existing regulations as well as mapping out new laws to meet demands from consumers and aid the country's entry into the World Trade Organization (WTO).

In fact, the SDA is setting up a national information network, which will aid in the supervision and management of pharmaceuticals and medical devices.

In interviews with Chinese media, namely Beijing-based newspaper China Daily, SDA officials say they blame counterfeit over-the-counter and prescription drugs—many of which they say contain raw, unprocessed ingredients—for the majority of the deaths.

With increasing pressure, both at home and from abroad, to combat abuses in the country's $40-billion pharmaceutical market, China has been getting tough on the manufacturers of counterfeit medicines. Over the last year, the government has closed down at least 113 pharmaceutical factories and nearly 15,000 illegal drug distributors.

Augmenting the SDA's efforts, China's State Administration for Industry and Commerce (SAIC) launched a crackdown on false advertising that aims to eliminate misleading medical ads, some of which promise everlasting life and increased sexual potency. Advertisers who promote medicines, nutritional supplements or other health products by disguising advertising as biographies or feature stories will be severely punished, according to the SAIC.

Zheng Xiaoyu, SDA director, says other reforms currently being carried out in the health care sector would require hospitals and clinics to purchase medicine through a competitive bidding process, which is aimed at reducing kickbacks in the prescription drug industry.

Business is booming
Meanwhile, Medrad Inc., a Pennsylvania-based subsidiary of Germany's Schering AG, is partnering with Vincent Medical Manufacturing Co. (Hong Kong) to produce disposable syringes in China.

In a prepared statement, John P. Friel, president and chief executive of Medrad, said the company anticipates lower production and shipping costs for syringes supplied from the new facility. “This will give us a better opportunity to serve our customers and eliminate our shipping cost,” he added.

At a recent press conference, Yu Mingde, director of the Pharmaceutical Department of the State Economic and Trade Commission (SETC), said competition will heat up after China's entry to the WTO, adding that the sector would be open to foreign companies in 2003.

China, he indicated, represents one of the fastest-growing over-the-counter (OTC) drug markets in the world, with approximately $1.4 billion in sales last year. Given a rapidly aging population, and a vast untapped rural market, he claims China's OTC market will surpass that of the U.S. market.

Yet local drug retailers in China have gotten off to a slow start, according to the Economist Intelligence Unit, a U.K.-based information provider. China has about 120,000 pharmaceutical retailers. Most are small and inefficiently run. As a sector, they suffered losses in 15 provinces in 1998. Only 200 pharmaceutical retailers have formed chains.

At the time of this report, however, the Xinhua News Agency reported that Zhongxin Pharmaceutical Group Corp. (Singapore) set up a chain subsidiary in Tianjin to become the largest pharmacy chain in China.

With 248 retail outlets in Tianjin, the new subsidiary will offer new services such as home delivery, evening delivery.

FDA says GMP violations are to blame

Mark A. DeSorbo

ROCKVILLE, MD—Although a voluntary recall was issued on 39 injectables in mid-December, the U.S. Food and Drug Administration (FDA) recently issued an urgent warning that called for distribution of the medicines to cease, saying Phyne Pharmaceuticals (Scottsdale, AZ) “delayed taking prompt and appropriate action” to remove the products it paid AMRAM Inc. (Rathdrum, ID) to manufacture.

FDA spokesman Jason Brodski says one of the injectables, Colchicine, which is used to treat gout, was labeled as containing 0.5mg/ml, but was actually formulated at a concentration of 5mg/ml.

Three people, he says, became seriously ill because of the miscalculation. Although the condition of one person was not available, two people were admitted last December to Paoli Memorial Hospital (Paoli, PA), where they were listed in critical condition, a spokesman said. They were later transferred to the Hospital of the University of Pennsylvania in Philadelphia and then released.

Brodski says the injectables were manufactured under substandard conditions, and nationwide recalls follow FDA inspections of Phyne and AMRAM. During the inspections, FDA found violations of requirement for good manufacturing practices.

“These products lacked assurance of sterility and potency,” Brodski adds.

Along with Colchicine, the following injectables have also been recalled: Adenosine Monophosphate; Ascorbic Acid Injection; Beet Ascorbic Acid Injection; Biotin; Vitamin B-12(Cyanocobolamin); Dexpanthenol; Disol, USP Brand of EDTA; Echinacea Homeopathic Injection; Edetate Disodium Endocrine; Adrenal Cortex Extract (ACE); Folic Acid; Germanium Sesg.(Sesguloxide); L-Glutathione or Glutathione; Human Chorionic Gonadotropin; Hydrochloric Acid; Iron 59 Injection; Liver Injection, Crude; Lypo-Vite Injection; Magnesium Chloride Injection; M.I.C.; Procaine Hydrochloride Injection; Pyridoxine HCL (B-6); Sodium Thiosalicylate; Superoxide Dismutase (S.O.D.); L-Taurine Injection; Thiamine HCL; Thymus Extract; Choline Chloride; Diphenhydramine; Glycyrrhizen; Chlorpheniramine Injection; Hydrogen Peroxide; Hydroxocobalamin; MIC with Folic Acid; Niacin; Pangamic Acid; and Riboflavin

Any adverse reactions experienced with the use of these products should also be reported to the FDA's MEDWATCH Program at 1-800-FDA-1088, 1-800-FDA-0178 (fax). Write to MEDWATCH, HF-2, FDA 5600 Fishers Lane, Rockville, MD 20852-9787, or log on to the MEDWATCH Web site at www.fda.gov/medwatch.

RECOMMENDED PRACTICES

by Robert L. Mielke

A comprehensive look inside the work of one of the most active contamination control programs in the country.

When establishing a comprehensive contamination control program, one looks for tools (standards and practices) to assist in setting up the program. One such tool is the recommended practices that have been written by the Institute of Environmental Sciences and Technology (IEST). This series of practices, which has been ongoing since 1982, addresses contamination control topics such as clean air filters (HEPA, ULPA), cleanrooms and clean air device testing, cleanroom supplies (garments, wipers, gloves, etc.), and cleanroom design, cleanroom operation, etc.

The IEST Contamination Control Division has 34 Standards and Practices Working Groups. Through the efforts of these groups, more than 25 documents have been released for publication. Members of the various working groups devote their time and expertise to produce contamination control Recommended Practices (RP) and standards relating to cleanrooms and what it takes to make them operate.

The IEST Contamination Control Working Groups operate under a detailed policy in order to ensure fairness and balance. Thus, they provide the cleanroom industry with standardized procedures based on peer-reviewed applications of cleanroom technology. During the writing process, meetings are generally held twice a year. Currently, recommended practices must be reviewed within three years of their last published date. At this time, the IEST is reviewing their documents and could be pulling some of its practices if they do not meet all the requirements.

New working groups are formed when enough interest is generated on a specific contamination control topic, and the IEST Contamination Control Division deems there are enough resources to proceed with the topic. There have been times when a working group was formed but then had to be disbanded when the interest waned.

The working groups have so far generated the following documents:

· IEST-RP-CC001.3: HEPA and ULPA Filters covers basic provisions for HEPA and ULPA filter units as a basis of agreement between customer and supplier. Filters that meet the requirements of this RP are suitable for use in clean-air devices and cleanrooms that come within the scope of FED-STD-209, ISO 14644-1, 2, & 4, and for use in supply air and contaminated exhaust systems that require extremely high filter efficiency (99.97% or higher) for submicrometer particles.

· IEST-RP-CC002.2: Unidirectional Flow Clean-Air Devices includes definitions, procedures for evaluating performance, and major requirements of unidirectional flow clean-air devices.

· IEST-RP-CC003.2: Garments Required in Cleanrooms and Controlled Environments provides non-mandatory guidance to the specification, testing, selection and maintenance of apparel and accessories appropriate for use in cleanrooms and controlled environments.

· IEST-RP-CC004.2: Evaluating Wiping Materials Used in Cleanrooms and Other Controlled Environments describes methods for testing wipers used in cleanrooms and other controlled environments for characteristics related to both cleanliness and function.

· IEST-RP-CC005.2: Cleanroom Gloves and Finger Cots discusses parameters and tests that apply to gloves and finger cots using, whenever possible, standard tests approved by the American Society for Testing and Materials (ASTM) or government agencies. Where these bodies have developed no such tests, appropriate new tests have been devised. The specific intended use of the glove or finger cot being evaluated will determine which tests are appropriate for determining its acceptance or non-acceptance.

· IEST-RP-CC06.2: Testing Cleanrooms provides tests that evaluate and characterize the overall performance of the cleanroom and clean zone system. Included are recommended test equipment requirements and testing procedures for determining performance parameters. Where the type of cleanroom affects the test method, alternative procedures are defined.

· IEST-RP-CC007.1: Testing ULPA Filters covers production testing of filters for particle penetration and pressure drop of ultralow penetration air filters (ULPA). The penetration range of the procedure is 0.001% to 0.0001% using particle counters

· IEST-RP-CC008-84: Gas-Phase Adsorber Cells covers the design and testing of modular gas-phase adsorber cells for use where high-efficiency removal of gaseous contaminants is required. Two types of cells are discussed with respect to leak performance, materials, design, construction, packaging, installation, calculation of residence time and quality assurance requirements.

· IEST-RD-CC009.2: Compendium of Standards, Practices, Methods, and Similar Documents Relating to Contamination Control lists standards, practices, methods, technical orders, specifications and similar documents developed by government, industry and technical societies in the United States and other countries, which are related to the field of contamination control.

· IEST-RD-CC011.2: A Glossary of Terms and Definitions Relating to Contamination Control defines terms relating to contamination control and contains lists of frequently used abbreviations and acronyms. It also contains a list of IEST Recommended Practices and lists the RPs by subject area.

· IEST-RP-CC012.1: Considerations in Cleanroom Design makes recommendations regarding factors to consider in the design of cleanroom facilities. This discussion is limited to those environmental conditions that typically confront cleanroom designers and users. This RP is intended to provide users with a means to establish performance criteria for cleanrooms.

· IEST-RP-CC013-86-T: Equipment Calibration or Validation Procedures covers definitions and procedures for calibrating instruments used for testing cleanrooms and clean air devices, and for determining intervals of calibration.

· IEST-RP-CC015-87-T: Cleanroom Production and Support Equipment suggests many approaches for the design, installation and operation of production and support equipment used within a cleanroom or at a clean workstation so as to minimize the contribution of that equipment to the contamination of the product. It is intended to improve communication among the equipment designer, production layout personnel, production management, quality assurance and project management. It may also serve as an educational device to assist buyers in the preparation of bid specifications.

· IEST-RP-CC016.1: The Rate of Deposition of Nonvolatile Residue in Cleanrooms provides a uniform method and basis for determining the rate of deposition of nonvolatile residue (NVR) on surfaces in cleanrooms. In the design of the heating, ventilating and air conditioning system, the selection of suitable filters, and the selection of materials used in the construction of the cleanroom, the user should specify the requirements for the rate of deposition of NVR. Designers of cleanrooms should consider the maximum deposition rates suggested by this Recommended Practice when the deposition of NVR can affect the performance of products.

· IEST-RP-CC018.2: Cleanroom Housekeeping-Operating and Monitoring Procedures provides guidance for maintaining a cleanroom at the level for which it was designed. It is intended for use as a guide to establish appropriate housekeeping procedures. In addition, test procedures are provided for use in establishing the frequency and in monitoring the effectiveness of the housekeeping. The test methods also help to determine appropriate levels of surface cleanliness for specific cleanrooms.

· IEST-RP-CC020.2: Substrates and Forms Used for Documentation in Cleanrooms applies to substrates and forms used in cleanrooms for the purpose of documentation. Specifically included are copy paper, writing paper, labels, tags, self-adhesive notes, perforated and punched forms, envelopes, bound materials and all printed versions thereof.

· IEST-RP-CC021.1: Testing HEPA and ULPA Filter Media discusses test methods for physical and filtration properties of high-efficiency particulate air and ultralow penetration air filtration media.

· IEST-RP-CC022.1: Electrostatic Charge in Cleanrooms and Other Controlled Environments discusses methods for specifying and evaluating the effectiveness of techniques for controlling electrostatic charge. Controlling electrostatic charge reduces surface contamination and electrostatic discharge. This document describes methods of testing, provides guidelines for verifying charge neutralization and resistivity of surfaces and materials, and describes typical control systems and their applications.

· IEST-RP-CC023.1: Microorganisms in Cleanrooms provides guidelines for the control and quantitative measurement of viable air and surface contamination. Included is an introduction to the methods and devices currently available for the quantification of airborne and surface viable contamination.

· IEST-RP-CC024.1: Measuring and Reporting Vibration in Microelectronics Facilities establishes levels of vibration sensitivity to ensure that vibrations occurring in the facility or at the site are below those levels. This RP is intended to provide guidance in the microelectronics industry but may also apply to pharmaceutical and biological research, metrology laboratories and other contexts in which vibration control is important.

· IEST-RP-CC026.1: Cleanroom Operations offers guidance for maintaining the integrity of the cleanroom during ancillary operations. These operations include preparation of supplies and materials; modification of the facility; and installation and repair of equipment. Procedures are given for verifying the cleanliness of the equipment, the workstation and the area after these ancillary operations are completed.

· IEST-RP-CC027.1: Personnel Practices and Procedures in Cleanroom and Controlled Environments provides a basis for establishing personnel procedures and the development of training programs for cleanrooms and associated environments, not including specialized information needed for operations requiring control of living microbial contaminants.

· IEST-RP-CC029.1: Automotive Paint Spray Applications includes guidelines and recommended procedures for controlling dirt contamination (particles, fibrous material, etc.) in controlled environments used for paint spraying.

· IEST-RD-CC033.1: Building Code Reference Handbook: A Guide to Alternative Code Compliance Issues in the Semiconductor Industry is a reference guide for code issues that require alternative compliance approaches in order to design, construct or operate semiconductor facilities.

· IEST-RP-CC034.1: HEPA and ULPA Filter Leak Tests covers definitions, equipment and procedures for leak testing HEPA and ULPA filters in the factory as they are produced, at the job site before they are installed and after they are installed in cleanrooms and unidirectional-flow, clean-air devices.

Several Recommended Practices are scheduled for release in the next six months. These will include:

• IEST-RP-CC031.1: Method for Qualitative Analysis of Outgassed Compounds from Cleanroom Materials and Components.
• IEST-RP-CC016.2: The Rate of Deposition of Nonvolatile Residue in Cleanrooms
• IEST-STD-CC1246.1: Product Cleanliness Levels and Contamination Control Program
• IEST-RP-CC028.1: Minienvironments
• IEST-RP-CC001.4: HEPA and ULPA Filters
• IEST-RP-CC006.3: Testing Cleanrooms

IEST is also the Secretariat for Technical Committee 209 of the International Standards Organization (ISO/TC 209), charged with writing a series of international standards for cleanrooms and associated controlled environments. These documents are in various stages of development. Those currently available include: ISO 14644-1:1999, Cleanrooms and associated controlled environments—Part 1: Classification of air cleanliness; and ISO 14644-2:2000, Cleanrooms and associated controlled environments—Part 2: Testing and monitoring to prove continued compliance to ISO 14644-1. Soon to be released as a standard is ISO 14644-4, Cleanrooms and associated controlled environments—Part 4: Design, construction and start up of facilities.

The IEST Contamination Control Division has recently released four Technical Guides that serve as complementary documents to ISO 14644-1 and ISO 14644-2. Included in the series are IEST-G-CC001: Counting Airborne Particles for Classification and Monitoring of Cleanroooms and Clean Zones; IEST-G-CC1002: Determination of the Concentration of Airborne Ultrafine Particles; IEST-G-CC1003: Measurement of Airborne Macroparticles; and IEST-G-CC1004: Sequential-Sampling Plan for Use in Classification of the Particulate Cleanliness of Air in Cleanrooms and Clean Zones. Three of these Guides (1002, 1003, and 1004) are referenced in ISO 14644-1 and thus will serve as sources of additional information on specific topics covered by the Standard.

In May of 2000, IEST received ANSI accreditation to write and publish American National Standards using the Canvass Method. This means that IEST will upgrade some of its RPs to American National Standards. IEST, through the Canvass Method, will submit the cleanroom standards that have been and will be published by ISO to become ANSI/ISO standards. These ANSI/ISO standards will be equivalent to the ISO standards but will have the American National Standard “stamp” on them.

I have found that there's no greater satisfaction than wrestling over a tough question with a multitude of viewpoints and finally coming up with one, agreeable answer, even if it wasn't the one you suggested. If you have not availed yourself of the opportunity to participate in the IEST Standards and Practices Program, I encourage you to do so.

Those who have many years of experience have a chance to share their knowledge. Those with less experience have a chance to challenge the experts.

For further information on these Guides, Recommended Practices, and Standards, contact IEST at 940 East Northwest Highway, Mount Prospect, Illinois 60056, website www.IEST.org, e-mail [email protected], or phone 847-255-1561.

Acknowledgments. The author wishes to thank Irma Komro and Corrie Roesslein of IEST for their help in the preparation of this paper.

Robert L. Mielke is a senior metrology engineer for Abbott Laboratories, North Chicago, IL. Prior to joining Abbott in 1992, he was employed for 24 years as an expert in metrology and contamination control by the U.S. Department of Energy's Mound Facility. He holds a B.S. from Miami University of Ohio. He has presented over 30 papers on contamination control related topics.

_______________________________

The IEST Contamination Control Standards and Practices Committee is divided into five sub-committees covering the general categories of filtration, operational products, procedural, facilities, and environmental control. The five sub-committees with their respective working groups (WG) are as follows:

Sub-Committee 1: Filtration
· WG-CC001: HEPA and ULPA Filters
· WG-CC002: Unidirectional Flow Clean-Air Devices
· WG-CC006: Testing Cleanrooms
· WG-CC007: Testing ULPA Filters
· WG-CC008: High-Efficiency Gas-Phase Adsorber Cells
· WG-CC021: Testing HEPA and ULPA Filter Media
· WG-CC034: HEPA and ULPA Filter Leak Tests

Sub-Committee 2: Operational Products
· WG-CC003: Garment System Considerations for Cleanrooms and Other Controlled Environments
· WG-CC004: Evaluating Wiping Materials Used in Cleanrooms and Other Controlled Environments
· WG-CC005: Gloves and Finger Cots Used in Cleanrooms and Other Controlled Environments
· WG-CC020: Substrates and Forms for Documentation in Cleanrooms
· WG-CC025: Evaluation of Swabs used in Cleanrooms
· WG-CC032: Packaging Materials for Cleanrooms

Sub-Committee 3: Procedural
· WG-CC013: Procedures for the Calibration or Validation of Cleanroom Test Equipment
· WG-CC014: Calibrating Particle Counters
· WG-CC018: Cleanroom Housekeeping-Operating and Monitoring Procedures
· WG-CC019: Qualifications for Agencies and Personnel Engaged in the Testing and Certification of Cleanrooms and Clean-Air Devices
· WG-CC026: Cleanroom Operations
· WG-CC027: Personnel in Cleanrooms
· WG-CC029: Contamination Control Considerations for Paint-Spray Applications
· WG-CC100: FED-STD-209: Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones

Sub-Committee 4: Facilities
· WG-CC012: Sub-Group 1; Cleanroom Design Considerations
· Sub-Group 2; Installation of Cleanroom Production Equipment
· WG-CC024: Measuring and Reporting Vibration in Microelectronics Facilities
· WG-CC028: Minienvironments
· WG-CC030: Cleanroom Electrical Systems (joint WG with IEEE)
· WG-CC033: Environmental Code and Definitions

Sub-Committee 5: Environmental Control
· WG-CC016: The Rate of Deposition of Nonvolatile Residue in Cleanrooms
· WG-CC022: Electrostatic Charge in Cleanrooms and Other Controlled Environments
· WG-CC023: Microorganisms in Cleanrooms
· WG-CC031: Outgassing Performance Criteria for Cleanroom Materials
· WG-CC901: MIL-STD-1246: Product Cleanliness levels and contamination control program
· WG-CC902: MIL-HDBK-406: Contamination control technology: Cleaning materials for precision pre-cleaning and use in cleanrooms and clean work stations
· MIL-HDBK-407: Contamination control technology: Precision cleaning methods and procedures

There are two additional Working Groups that write reference documents reporting directly to the IEST Contamination Control Vice-President. They are:
· WG-CC009: Compendium of standards, practices, methods, and similar documents relating to contamination control
· WG-CC011: A glossary of terms and definitions relating to contamination control.

Be sure to attend Bob Mielke's presentation on IEST Recommended Practices at CleanRooms East 2001 in Boston. For more information, call 603-891-9267 or register on-site.

AIR MANAGEMENT

by Richard V. Grout

Fan type and configuration are important considerations in air recirculation

Figure 1. Distributed RAHs, 100 percent filter coverageClick here to enlarge image

Advances in fan technology make it possible for fab owners to realize significant savings in operational costs compared to approaches employed in the past. Numerous air-management concepts have been devised over the years using different types of fans to recirculate air in semiconductor fabrication facility cleanrooms. In these facilities, three types of air-moving apparatus predominate: (1) fan-filter units, (2) distributed recirculating air-handling units (RAHs) and (3) fan tower units.

Figure 2. Fan tower RAHs, 100 percent filter coverageClick here to enlarge image

We have attempted to establish a uniform, equitable basis by which to compare these options. To do so, we defined a standard cleanroom module to which each option could be applied. Within the standard module we further defined two cases of filter coverage: 100 percent filter coverage, such as one might encounter in a photolithography area; and 25 percent filter coverage as is typical for a fab equipped with minienvironments.

The standard cleanroom module is 20 feet wide by 80 feet long. This module is intended to represent one segment of a larger ballroom space consisting of similar modules set side by side and mirrored about a central aisle. All filters are mounted in the ceiling and individually supply air at 70 feet per minute (0.35 m/s), regardless of the filter coverage. Air flows vertically in the cleanroom and passes downward through a perforated raised access floor.

In the 100 percent filter-coverage case, the air continues downward through the structural support floor into a clean-classified subfab space. In the 25 percent filter-coverage case, the access floor is made high enough to permit all of the air to return beneath the access floor, allowing the subfab to be non-classified. For both cases, return air then rises vertically at the outer perimeter of the cleanroom. The air-moving apparatus is installed in the outer vertical air passage, or above the cleanroom ceiling. All air-moving systems are acoustically treated as necessary to achieve Noise Criterion 55, which equates to 62.5 dBA. The end result of this uniformity is that from inside the cleanroom there is practically no way to discern the type of air-moving system that is installed.

Figure 3. Relative Energy Effectiveness, Standard Fans, 100 percent filter coverage (Operating point for each option is indicated in watts per cfm)Click here to enlarge image

We compare the three air-management concepts using two criteria: energy effectiveness and capital cost. To evaluate the energy effectiveness, we sought a measurement standard that would apply equally and fairly to a chosen air-management concept and that would be applicable to all locations at any time. The measurement we chose is expressed in terms of power per unit airflow, in this case watts per cfm. The power required to operate a given fan, measured in watts, is constant regardless of geographic location or of the passing years, even though the cost of that power will vary. The airflow rate, measured in cfm, is independent of the fan system in that it is dictated by filter coverage. The fewer watts that are required to move the required air volume the better the energy effectiveness.

We have attempted to include all possible cost impacts of each air-management concept, including mechanical, electrical, instrumentation and control, and building and structural costs. Capital costs are expressed in relative terms, with the expectation that the cost rankings will hold true in other geographical locations and over time.

Conventional approaches
First let us review what, until recently, has been the state of the art for air-moving apparatus used in the three air-management concepts of this study.

Fan-filter units. Fan-filter units typically consist of a centrifugal plug fan driven by a fractional horsepower motor, mounted in a sheet metal box in whose lower surface is mounted a HEPA or ULPA filter. Sound attenuating material is generally installed inside the box, as the fans tend to be noisy unless acoustic treatment is applied. The motor often has a multi-step or continuously variable speed controller.

Fan-filter units do not develop much static pressure. After air passes through the internal acoustic passages and the final filter, there is comparatively little motive force left to offset external static pressure losses. Care has to be taken to properly design each component in the external airstream to minimize these losses, which are caused by air friction. Often this means enlarging the air passages and over-sizing the sensible cooling coils to keep the air velocity, and thus the resultant air friction, to an acceptable level.

Figure 4. Fan-Filter Units, 100 percent filter coverageClick here to enlarge image

Distributed return air handlers (RAHs). Distributed air handling systems have typically been built around packaged air handling units consisting basically of a sensible cooling coil and a fan. Plug-type centrifugal fans have been employed more often than not due to their relative compactness compared to scroll fans. Sound attenuation is almost always required at the fan discharge. Centrifugal fans can develop as much static pressure as is needed to move the air through the various components of the recirculation loop. However, as the total airflow increases, so does the fan size, the fan cost, and the amount of noise that the fan generates. Therefore, multiple, smaller air-handling units, installed in parallel, typically are used. Figure 1 contains plan and section views of the standard cleanroom module with a conventional distributed RAH air-management system.

Fan Towers. Fan towers are nearly always built with vaneaxial fans. Vaneaxial fans offer the advantage that they can efficiently move large volumes of air against comparatively low static pressure. This is typically the set of conditions under which any cleanroom recirculating fan must operate. Vaneaxial fans also are relatively compact and efficient and, hence, are fairly inexpensive.

A disadvantage of these fans is that a large part of the total pressure generated is velocity pressure. This becomes a significant factor in the selection of the fan. Vaneaxial fans are typically the most noisy of the three fan types in this study. Extensive sound attenuation measures must be taken, which add cost and additional static pressure loss. Figure 2 again depicts the standard cleanroom module, but this time with a conventional vaneaxial fan tower system.

Historically, cleanroom air-moving systems have accounted for a large percentage of the energy budget. Referring to Figure 3, note that the energy effectiveness of traditional fan systems is approximately 0.4 watts per cfm. For a typical large fab with a recirculation rate of 2,000,000 cfm, operating 24 hours per day, and an electricity cost of $0.08 per kWh, this amounts to an annual cost of over $500,000.

Recent advances
In the last few years, fan systems have been introduced that make much more effective use of fan energy and thereby significantly reduce the annual operating cost.

Fan-filter units are now available with the fan, the motor and the motor controller engineered together as a package for optimum efficiency. One such package features a brushless, electronically commutated dc motor with an external rotor. The fan impeller is fitted directly onto the rotor. This mounting configuration allows heat transfer from the motor to be optimized. A Hall-effect sensor is used to detect the position of the rotor magnet each time it rotates. Control circuitry then precisely adjusts the motor voltage to match the torque requirement of the fan, thereby minimizing inefficiencies due to slip. Overall, the resultant motor efficiency is 75 percent to 80 percent, compared to less than 40 percent for phased split capacitor or shaded pole motor designs. With this improved efficiency comes the byproduct of quieter operation.

Figure 5. Fan-Filter Units, 25 percent filter coverageClick here to enlarge image

Because the fan uses a dc motor, its speed is infinitely variable. The controller can be set up so the rotational speed of the fan is remotely monitored and controlled. The on-off status of each fan-filter unit also can be remotely controlled and monitored.

Figure 4 depicts plan and section views of a fan-filter unit installation for the 100 percent filter coverage case. Note that the air passageways are quite large, which has a corresponding impact on the overall building size.

The 25 percent filter coverage case is depicted in Figure 5. The lower airflow allows the size of the air passageways to be reduced, so the effect on the building geometry is also greatly reduced.

Vaneaxial fan packages are now available that combine advanced fan engineering with aerodynamically and acoustically engineered sound attenuators. This type of package may be applied in either a fan tower or a distributed RAH to yield a quiet, efficient system.

Figure 6. Distributed RAH with vaneaxial fanClick here to enlarge image

To achieve the desired level of performance, the vaneaxial fan must be manufactured to close tolerances; the fan barrel must be nearly perfectly cylindrical so that the fan-blade clearance is minimized. Unlike centrifugal fans, two fan-selection variables can be manipulated to achieve optimum performance: rotational speed and blade-pitch angle. Finally, the inlet and outlet sound attenuators are custom engineered to maximize sound-attenuation performance without imposing the high static pressure penalty of off-the-shelf attenuators.

Figure 7. Distributed RAHs, 100 percent filter coverageClick here to enlarge image

In addition to these performance enhancements, the vaneaxial fan tower package can also be arranged so as to simplify maintenance. Each fan is spring-mounted on a movable dolly that is normally locked into place and attached to the inlet and outlet sound attenuators with a simple drawband. Ordinarily the fans are maintenance-free—there is only one moving part. However, when it is necessary to maintain or replace the fan, it is disconnected from the sound attenuators and wheeled as an assembly out of the air passageway and into an adjacent maintenance bay.

Figure 8. Distributed RAHs, 25 percent filter coverageClick here to enlarge image

Figure 7 is a plan and section view of a distributed RAH installation for the 100 percent filter coverage case.

If needed, vaneaxial fans can be selected with additional static pressure capacity to accommodate such items as prefilters or chemical filters. Fan-filter units generally do not have this capability. For uniformity, these items are not considered for any of the fan options analyzed in this paper.

Figure 9. Fan tower RAHs, 100 percent filter coverageClick here to enlarge image

Figure 6 depicts the physical configuration of a distributed RAH using a vaneaxial fan. Air enters the outer annulus, passes through a cylindrical cooling coil and enters the fan. The air is then discharged into the supply plenum via a sound attenuator. Access to the fan is gained through a hinged door or removable panel on the outer case of the RAH.

The 25 percent filter coverage case is shown in Figure 8. Distributed RAHs require the installation of a structural fan deck to support the equipment. The interstitial space is part of the return air stream and must therefore be designed and operated to clean protocols.

Figure 10. Fan tower RAHs, 25 percent filter coverageClick here to enlarge image

Figure 9 contains plan and section views of a fan tower installation for the 100 percent filter coverage case. A tall, wide vertical chase is needed to accommodate the equipment. Air is drawn into the apparatus from the clean subfab and is discharged directly into the supply plenum. The fan itself resides in non-classified space.

The 25 percent filter coverage case is shown in Figure 10. Here the fan is mounted horizontally on a structural fan deck in the non-classified interstitial space. An air duct directs the supply air to the pressurized plenum directly below the deck.

Energy effectiveness—Figure 11 is a graph of the relative energy effectiveness for the 100 percent filter coverage case, applying the newer fan technologies to the three air-management concepts.

For each air-management option the static pressure loss, measured in inches water column, was calculated across the recirculation loop. The static pressure losses vary depending on the nature of the air passageways, and each option has unique characteristics. In all options the static pressure was intentionally kept to a practical minimum. Fans were then selected which would meet the airflow and static pressure requirements with the lowest power input. The static pressure requirement for each option is plotted against the corresponding energy effectiveness expressed in watts per cfm. The operating point for each option is indicated. Vaneaxial fans are in reality selected based on total pressure, which is the sum of static pressure and velocity pressure; however only the static pressure value is indicated to serve as a standard basis for comparison with the fan-filter unit option (fan-filter units use centrifugal fans which are selected based on static pressure only). The watts per cfm reported for the vaneaxial fan options includes the power necessary for static and velocity pressure.

Figure 11. Energy Effectiveness, Technologically Advanced Fans, 100 percent filter coverage (Operating point for each option is indicated in watts per cfm)Click here to enlarge image

As might be expected, the vaneaxial options tend to out-perform the fan-filter unit option because the vaneaxial fans and motors are inherently more efficient. Figure 12 is a graph of the energy effectiveness for the 25 percent filter coverage case. Again, the performance of the vaneaxial fan options is superior to that of the fan-filter units. In both the 100 percent case and the 25 percent case, the energy effectiveness is about double that of the older technologies, which means that the annual operating cost is halved.

Capital costs—Turning to capital costs, we must look not only at the cost of the air-moving equipment, but at the total cost that each air-management concept imposes on the facility in which it is installed. Tables 1 and 2 summarize these facility impacts.

Comments—The equipment cost of quality fan-filter units is about half-again higher than either distributed RAHs or fan towers. The basic reason is quantities. Even though the unit cost of a fan-filter unit is low compared to the other air-moving options, in our cleanroom module there are 200 such units and the total cost quickly exceeds that of the others.

Figure 12. Energy Effectiveness, Technologically Advanced Fans, 25 percent filter coverage (Operating point for each option is indicated in watts per cfm)Click here to enlarge image

The fan-filter units require larger air passageways in order to reduce static pressure losses. This increases both the overall building width and height. Distributed RAHs require a greater building height, similar to what is required for fan-filter units, but less building width. Fan tower units require a greater building width, but do not add to the height. A structural fan deck is required to support the distributed RAHs, but is not needed for the other two options.

Greater cooling coil surface is needed for the fan-filter units than for the other two options in order to keep the static pressure loss down. Each distributed RAH is supplied with a sensible cooling coil, so cooling water must be piped to each unit.

Click here to enlarge image

Fan-filter units can be set in a gasketed ceiling. We have assumed pressurized supply plenums for the other two options, which require a gel-track ceiling.

The electrical distribution cost is highest for fan-filter units. Even though the motors are much smaller, there are many more of them.

Click here to enlarge image

Finally, automation costs are higher for fan-filter units, again due to the large quantity of fans. Fan-filter automation cost can be and often are lowered by eliminating the monitoring functions, but this is done to the disadvantage of those who need to maintain the system. Even so, the comparative cost ranking of the three options remains intact.

Comments—The cost spread for the three fan options is all but eliminated in the 25 percent filter coverage case.

Figure 13. Relative facility costs for the three predominant air management conceptsClick here to enlarge image

The lower total airflow allows for air passageways whose dimensions are similar for each equipment option. However, since the subfab is no longer used as an air passageway, the fan tower unit is now too long to mount vertically. Instead, it is placed horizontally overhead on a structural fan deck. This eliminates the need for a wide vertical return air passageway. The building interstitial height in the case of fan-filter units is driven only by the need for the plenum to be accessible for maintenance purposes. The other two options require greater interstitial heights to house equipment and for the pressurized supply plenums. A structural fan deck is required to support the distributed RAHs and the horizontally mounted fan tower.

Greater cooling coil surface is still needed for the fan-filter units than for the other two options. Cooling water must still be piped to each distributed RAH.

The electrical distribution cost is now highest for distributed RAHs due to the reduced quantity of individual fan-filter units that need power wiring. The same relationship also now applies with respect to automation costs.

Figure 13 is a graph of the total relative costs of each option. For the 100 percent filter coverage case there is a clear distinction between the three air-management options. Facility costs are highest for the fan-filter unit option and lowest for the fan tower option. By reducing the amount of automation, the cost of fan-filter unit option draws closer to that of distributed RAHs.

For the 25 percent filter coverage case, the capital costs are approximately the same, with or without reduced fan-filter unit automation, although distributed RAHs are slightly higher.

Conclusion
Fan-filter units with electronically commutated dc motors operate much more efficiently than do models with conventional motors. Vaneaxial fans can now be obtained that are both efficient and quiet. Properly engineered vaneaxial fan systems also offer overall facility capital cost savings compared to other systems. Vaneaxial fan systems are simple in concept and are relatively easy to maintain. Vaneaxial fan systems also can be selected to meet additional static pressure requirements imposed by such items as prefilters or chemical filters.

Acknowledgments
Thanks to Michael O'Halloran for coming up with the basic idea for this paper, and to Rod McLeod and Willy Kohne for reviewing the draft manuscript. Thanks also to Steve Dikeman of AcoustiFLO Ltd and Zareer Cursetjee of Cleanpak International for help with the vaneaxial fan selections.

Editor's note: Variations of this article were presented at SEMICON Singapore 1999 and at CleanRooms Asia 2000.

Richard V. Grout is a senior mechanical engineer with IDC in Portland, OR. He has 28 years of experience in the design of building mechanical systems, including more than 15 years of project work on semiconductor manufacturing facilities. Those projects include facilities in Taiwan, Singapore, China, South Korea, Israel, Canada and the United States.