Cleanroom Ceilings, Floors and Walls
Buyer beware: There is no easy way to choose which floor, wall or ceiling is best for your cleanroom. Depending on your application, sifting through products can be similar to buying a car – so many choices, not enough information.
By Lisa A. Coleman
Since there is no Consumer Reports listing for the contamination control industry and if you`re building a cleanroom for the first time, chances are, you will need to do a lot of research on your own before choosing the right system. It`s up to you to do all the work. While some publications offer guidelines on material selection, there are no official suggested lists of materials to be used in cleanrooms. However, the ISO Working Group 4 “Cleanroom Design and Construction,” is currently addressing the issue.
Most consultants recommend consultation from a “cleanroom astute” architect and engineering (A&E) firm to do the research for you and pick the right materials for your space. The first thing you need to define, however, is what class of cleanroom you need. If you`re investigating materials for the first time, here are some tips.
The Top Five Qualities
If you`re undecided about whether to use aluminum honeycomb wall panels, epoxy-painted walls or 2-in. T-bar ceilings vs. the new “flush-grid” systems, consultants caution that your choice of material should not be made on any single criterion. There are some important qualities the materials you choose should have. Look for cleanability, cost, durability, flexibility, and maintainability. One good rule to follow during the selection process is: “Smooth surfaces with no rough edges,” recommends Ralph Kraft, owner of RKI Cleanroom Services (Rochester, NY), a consulting service for building and operational management of cleanrooms and cleanroom construction. With this in mind and knowing the class of room you need, you can begin to evaluate materials using the following yardsticks:
Cleanability. In the biopharmaceutical and biotechnology industry, cleanrooms usually need walls that can be easily cleaned and wiped down to prevent viral or bacterial contamination. “In the biotech market, cleanability is really a paramount concern,” says Architect Dana Watts of Symmes Maini and McKee Associates (SMMA; Cambridge, MA). Cleanroom materials need to be easily cleanable but rugged enough to dissuade bacterial buildup and stand up to strong cleaning solutions. The chemicals used for cleaning are a contributing factor in material selection. Says Technician Scott Kouri of Porta-Fab Corp., (Chesterfield, MO), “Depending on the concentration, chemicals may eat through certain materials, while other materials can withstand cleaning solutions. For example, a vinyl or fiberglass panel might not withstand a diluted HCL cleaning solution while a painted steel surface may.”
Cost. Microelectronics fab construction can cost up to $1 billion. The faster the fab is built, the sooner products can reach the market. Keeping a lid on construction costs is sometimes the greatest concern. “Cheaper and better” is the slogan for many semiconductor companies. However, knowing just how cheap you can go with material selection takes research and experience. “Money is going to be a very important factor,” says Fred Musano, Jr., vice president for Neslo Manufacturing (Wolcott, CT). “If your budget is thin, you`re not going to go with a Cadillac. The most important thing the customer is going to look at is dollars. Customers need to know what they`re going to spend.”
Cost and the “look” of the cleanroom can go hand-in-hand. A cleanroom can cost between $200 to $1,000 per ft2. Compared to $50/ft2 for space in an office environment, a cleanroom is almost 20 times the cost of a regular office. Says Gary Devloo, president of Lepco (Houston, TX): “The reason cleanrooms are so expensive is that all the air that`s moving through the room, the filtration, the ultrapurity piping, waste and exhaust systems–all those things drive up the cost of the facility. But you don`t necessarily see that when you walk into a room. When you walk into a cleanroom that costs $500 per ft2, you want it to look like it cost $500 per ft2. After spending all that money on mechanical systems, people will sometimes then put extra money into the walls and ceilings not for performance but just to make it look good.” Devloo adds that the cleanroom user who hires a turnkey designer/builder like Lepco will have a lot of say about how the cleanroom will look. “They`re trying to make the rooms look as hi-tech as possible,” says Devloo.
Durability. Obviously, cleanrooms must have durable materials to meet the requirements of the environment, the cleaning solutions, vibrations, the equipment, and the air filtration system. Lepco`s Devloo cites the chemicals used in the room as a very important criterion in material selection. “If the room is chemically intensive,” he says, “you`d put in a troweled-in epoxy resin flooring, like Stonhard for chemical resistance.”
Durability also depends on the class of cleanroom being built. For example, a sub-Class 1 room could not have a wood core wall system because the wood could cause particulate and contaminate the space. Semiconductor fabs tend to choose aluminum because of its durability. However, it`s not simply the material, but the construction of the entire wall, floor or ceiling system that must be durable for your application`s needs.
Flexibility. Some material vendors say flexibility will save money in the long-run. Flexibility means the system can be moved or changed without incurring a huge expense. However, it can also mean the ability to use cleanroom materials as the owner`s needs dictate. Porta-Fab`s Kouri says the ability of the cleanroom owner and designer to change a room is key, “so they`re never locked into the original design.” However, says Pace Co. (Portland, OR) Director of Research, Craig Ludwig, “Companies want it [the cleanroom] to go up quickly. They want the flexibility to change processes very quickly. And they want fewer, simpler, and better-designed components.”
Maintainability. A question that should be asked of any vendor is “are floors, walls and ceiling easy to maintain?” advises SMMA`s Watts. Cleanability and maintainability both should be priorities for material selection, he suggests.
The Materials
Ceilings. Depending on the application, the ceiling can be the most important part of the floor-wall-ceiling trio. The cleanroom ceiling contains the HEPA or ULPA filter units which make the room “clean,” as well as lighting and sprinkler heads. Also, ceiling systems may be required to support separate minienvironments or material handling equipment. SMMA`s Watts says, “If somebody had a really limited budget but a little extra money in the kitty, you might find them going to a more expensive ceiling system rather than a more expensive wall system, especially if it`s a laminar flow room.”
The most popular systems in use today range between the newer “flush grids” or conventional T-bar grid systems. Both types of ceilings are based on a support grid suspended from the building`s structural system. The grid is composed of extruded aluminum shapes or an inverted “T” cross section to support the ceiling components, which can be installed from the top. Ceiling components include the HEPA/ULPA filter units, lighting units, or may also include blank panels made out of the same materials as the walls. The advantage of this type of system is that ceiling components can be placed anywhere without serious structural alterations. The disadvantage is the potential for particle leakage emanating from the space above the suspended components.
Pace Co. has addressed the problem by designing its Clean-Trak 2.6(TM) ceiling system with a narrower grid and installing a diffuser that distributes air radially through beveled edges to virtually eliminate the dead air zones created by suspended T-bar ceiling designs. “I think one of the most important things is that, whatever systems you choose,” advises Pace`s Ludwig, “they work together. Typically, I`d say ceilings are one of the more complex systems, because they kind of `do it all.` “
Other considerations in choosing a ceiling component in combination with the filtration systems are light fixtures, the class of cleanroom, and whether or not your cleanroom will need a seismic bracing system. According to Pat Beatrice, cleanroom products sales manager for Farr Co. (El Segundo, CA), if your cleanroom is located in an earthquake prone area, seismic considerations are a “must.” “A 1.5-inch T-bar is fine, but it`s not considered a seismic system. A 2-inch T-bar or gel system is.” The 2-inch system is hung from turnbuckles and threaded rods. “And depending on the location, you may have to go to a higher seismic level. That means hanging every filter and light fixture and having a sound structural system.”
Floors. Choosing materials for a cleanroom floor is very dependent on the application. This is the one area that probably takes the most abuse in the form of heavy traffic from pedestrians and wheeled carts, as well as cleaning solvents and chemical spills.1 (Also, see “Evaluating Flooring for Cleanrooms,” CleanRooms, October 1995, p. 29). If the cleanroom is in a microelectronics facility, conductive or static dissipation is required via the flooring or by ionizers and by other methods.
One of the lowest cost floor coverings is vinyl tiles or sheets laid over a concrete structural floor. Brittle floor covering can cause particulates, therefore, the floor covering should be pliable but not too soft that it will tear. Also, outgassing must be considered. In his book, author Michael Kozicki says, “When you begin to see floor wear, it means that the floor is actually in an advanced stage of breaking up. The wear you see is actually due to degradation of the surface finish.”2 Once this happens, particulate generation increases. Not all cleanrooms require vinyl floor coverings. Many require perforated, solid or grated panels and/or raised access flooring. Perforated flooring may be required to maintain laminar air flow.
Walls. One of the most economical ways to construct a wall system is to use standard construction materials and then cover or coat them with a low-contamination layer. Gypsum wall board can be bonded with a thin vinyl layer, and in some cases, vinyl can be used instead of paint, which outgasses. Also, epoxy painted wall board is frequently used in Class 100,000 and above cleanrooms. Vinyl, too, has a tendency to outgas, but high quality vinyl mixed with another substance can mitigate the problem. For rooms at Class 100,000 and above, a more expensive wall system would be a wood core with a hard plastic laminate. However, wood cores can often create particulates. Stronger and safer than a wood-core wall, is an aluminum honeycombed panel system.
The more expensive wall systems are made of aluminum wall panels, which are usually produced in sheets. While aluminum forms an oxide to protect itself from the air, it is susceptible to harmful acidic vapors that can cause corrosion. To counter corrosion, the aluminum is sometimes treated with chemically stable hard coatings. Anodization–a process that deliberately thickens the oxide coating on the surface is then used to make the aluminum inert. One advantage of this process is that it chemically bonds the oxide and metal. Enamel can also be used to coat aluminum. A less expensive alternative to aluminum is sheet steel, however, steel also must be coated because it corrodes easily and cannot be anodized. If the coating becomes chipped, it could flake off. Another alternative is high-quality stainless steel that does not require a coating. But stainless steel too, generates particles.
The use of glass in cleanrooms can be of value to allow cleanroom workers visibility outside the room and add aesthetic appeal. Glass must be tempered or laminated and coated to block ultraviolet light. Says SMMA`s Watts, “Frequently, clean spaces have walls between process areas…We`ve put glass in these areas to open up one room to another and make the space feel larger–or just to achieve visual communication in order to make spaces feel less claustrophobic.”
Stick-build vs. Modular
One of the most important considerations in material selection is whether to stick-build or use prefabricated, modular construction? Do you build from the ground up or do you have major cleanroom systems constructed off-site and brought in when ready to be clipped together?
“There are areas where it is beneficial to have stick-build grid systems,” says Pace`s Ludwig. “I would characterize one of those areas as an existing build- ing, or even a new building, where there are a lot of nooks and crannies cut up by sections that are convoluted–areas where you have to skirt around stair towers and columns.” According to Ludwig–stick-build accommodates those small areas particularly if vertical flexibility is a requirement, where equipment of varying heights will be brought into the cleanroom after it has been built. However, the ever-changing nature of the semiconductor industry requires ever faster fab construction to get product to market, and prefabrication facilitates this trend. Says Ludwig, “With Pace`s system, we`ve taken all the work `out of the field` and brought it to our shop. While the client is building the concrete shell, we`re building a ceiling module that`s as complete as possible by the time it gets to the job site. So, in essence, all they have to do is put it up and plug it in.”
Says Porta-Fab`s Kouri: “The biggest reason someone buys our wall system is that it`s modular. If the company leases space and then decides to buy a building, it can essentially take the entire building with it.” Modularity provides flexibility, especially if a cleanroom needs to be reconfigured.
But, Lepco`s Devloo believes people are too caught up with modular systems. He says he has rarely had a cleanroom owner want to move their space. “It`s not the structure that becomes a real, fixed-in-place setup,” says Devloo, “It`s the process tools. Once you`ve put all your process tools in the room, done the process fit-up, added the piping and electrical, you`ve already spent much more than the cost of a wall system. So it really becomes a moot point whether or not you have modular walls.” However, Devloo adds that modularity is good for certain applications, such as small rooms with minienvironments, but, he believes the “movability” quality so touted by modular wall manufacturers is based on a misconception. “Nobody ever really moves a cleanroom. If you spend one million dollars on a cleanroom, the odds of your moving it two or three years later are pretty remote, because by that time, you`ve got $5 million of equipment attached to it.”
Finding a Contractor
Many cleanroom consultants agree that first-time cleanroom owners should use a “cleanroom-astute” architectural/engineering design firm or a cleanroom design/build contractor. (For more information, see “Asking the Right Questions: Selecting a Cleanroom Design Firm,” CleanRooms, July 1995, p. 12.) Says RKI`s Kraft: “Anybody that`s looking to build or upgrade a cleanroom should go with a contractor that knows how to build a cleanroom. If they don`t, they risk wasting their time and money in the long-run.” Kraft`s consulting firm audits cleanrooms for efficiency. “Over the years, I`ve seen people go with a regular commercial contractor that knows nothing about building cleanrooms. Then when the company`s efficiency drops to zero–they wonder why!”
Kraft endorses specialty cleanroom design/build firms because he has seen too many cleanroom building mistakes that were “dictated by price by the end-user. “An astute cleanroom design/build or A&E firm will guide the user in the proper direction,” says Kraft. Not only does consulting a “cleanroom-astute” A&E or design/build firm bring rewards in the finished cleanroom, it is also valuable in the process of choosing construction materials. “There are a lot of good cleanroom wall, ceiling panel, and flooring manufacturers. If you stay with them, you`re not going to be caught short,” says Kraft. n
References
1.Kozicki, Michael N., Stuart A. Hoenig, and Patrick J. Robinson, Cleanrooms: Facilities and Practices, Van Nostrand Reinhold (New York, NY), 1991, p. 49-100.
2. Ibid, p. 55.
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A Class 10,000 cleanroom that incorporates Lepco`s Membrane Diffusion ceiling system to make Class 100 zones over work areas in Honeywell Optotronics (Dallas, TX).
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A Class 10 non-progressive bay and chase design utilizing ceilings from Gordon Inc. (Bossier City, LA), walls from Plascore (Zeeland, WI), and conductive flooring from Forbo. Photo is courtesy of Lepco.
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Perforated panels for access floors are quite common. Shown are Pace`s Access Floor Perforated Panels–these types of floor panels allow laminar air flow.
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A Pace ceiling system being installed. Ceilings are often considered one of the most important parts of a cleanroom because they contain other valuable cleanroom systems–such as filtration, lighting, and sprinkler heads.
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The CR 300D variable width cavity wall from Neslo (Wolcott, CT). The cavity can function as a return air plenum without the need for duct work. The cavity system is achieved with double 3-5/8 inch studded walls that can create a variable width cavity depending on the cleanroom`s need for return air flow.
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A Class 100 expatial lab that uses welded sheet vinyl flooring at NASA (Houston, TX). Photo is courtesy of Lepco.
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Access flooring means just that–being able to remove a panel to access the cleanroom subfloor for piping, electrical conduit and process equipment needs. Shown is Pace`s Access Floor system.
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The Sylab Walkable Maintenance Ceiling from Clestra Cleanroom, Inc. (North Syracuse, NY) is designed specifically for aseptic and clean containment applications. Sylab is a cleanroom ceiling that can be maintained from above to eliminate the need for catwalks. It is made of heavy gauge steel finished with a baked-on acrylic enamel or powder epoxy finish.
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Optical Imaging Systems–the largest flat panel display facility (Northville, MI) in North America–uses Plascore`s return air wall into the process service chase. Photo courtesy of Lepco.
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One of the newer types of cleanroom ceilings is the flush-surface ceiling system, such as Pace Co.`s Clean-Trak 2.6 flush grid system that is 2.6-inches wide. (Inset) Inside a Pace ceiling: top fluid seals maintain a leak-free ceiling system.
Is “White” Always Right?
Today`s architects are trying to educate end-users and manufacturers away from the traditional white cleanroom materials to a more colorful palette. The variation in color and pattern can be a great benefit to worker morale and productivity.
Greys, light blues, peachy-mauves, and greens have been incorporated into some recent cleanrooms, says Dana Watts, an architect with Symmes Maini and McKee Associates (Cambridge, MA). “One of the things we`re interested in is making cleanrooms that are different from the typical white-floor, white-ceiling rooms.” Cleanrooms, by their very nature are high velocity air environments where people dress alike in cleanroom garments; architects, such as Watts try to mitigate these issues by attempting to break up the repetitive “feel” of the room and create a more ergonomic environment. In some cleanrooms, such as biotechnology laboratories, people often work with toxic chemicals, making for an unaesthetic room. “They`re hostile environments, and we`ve tried in some of our projects to acknowledge that and make them better spaces for the workers, by using color and floor patterns or alternating colors,” says Watts.
He says it`s been a little frustrating to achieve the use of color in designing cleanrooms because of the narrow choice of colors presently offered by manufacturers in floor, wall and ceiling materials. “Unfortunately, I think that when cleanrooms were first developed, the notion was `white` means `clean.` That`s been reinforced in the materials. Out of all the material vendors I know, they all have a standard white.
One of the biggest problems with incorporating color into the design of a cleanroom, is the pressure to build the cleanroom as fast as possible to guarantee quick time-to-market. Microelectronics firms particularly have to move chips out to the street quickly to beat the competition. Using color in building materials can often add to the fab`s cost or construction time because materials must be special ordered. Watts says his firm has been working with a lot of material vendors to deal with these issues. If the interior design of the rooms is viewed at the outset of the project and color decisions made early on, then products can be ordered in a timely fashion and the schedule impacts can be avoided.
As color choices increase and more colors become “standard,” pricing issues will also be eliminated. Watts is hopeful that eventually, color will evolve into a very acceptable form for cleanrooms. “As [cleanroom] owners see the benefit of doing it, and as they continue to get positive feedback from the people working in these rooms, I think it will evolve into something that moves away from the present choice of one color–white.”–LC
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Patterns and colors can freshen a cleanroom, making it ergonomically appealing, creating a better work environment. Shown is a ball-room type of cleanroom designed by Symmes Maini and McKee Associates (Cambridge, MA).
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