Decontaminating the cleanroom requires good science
Proper cleanroom maintenance is good science. Whether you are operating just one small Class 10,000 cleanroom facility or a billion dollar-plus state-of-the-art submicron semiconductor manufacturing fab, cleanroom maintenance can no longer be considered just another janitorial service.
By IAN M. WALLIS
Maintaining a cleanroom environment within manufacturing process specifications is no easy task. The cleanroom environment is under constant attack by potentially fatal contaminants generated by three major factors: the manufacturing processes that take place within the cleanroom, cleanroom personnel and the endless stream of equipment and materials brought into the cleanroom environment daily.
A properly designed cleanroom staffed by personnel who understand and follow proper cleanroom protocols can keep these particles to near-zero levels. But near-zero levels many not be good enough.
Particles travel along air currents in the cleanroom and most are carried back to the air filtration system for entrapment and removal. However, many of the remaining particles tend to settle on or near critical production areas. Settling particles are affected by numerous physical forces such as static, ionic attraction, humidity, gravity and Van der Waal forces — to mention just a few — which cause them to bond to surfaces in such a manner that their removal becomes very difficult, at best. This is where the properly trained and equipped cleanroom housekeeping crew can help.
Personnel training is mandatory
Training is the essential element in developing a good cleanroom maintenance team. Workers must have a thorough understanding of exactly what a cleanroom is and what purpose it serves. Equally important is imparting a knowledge of exactly what it is we are trying to clean and why. Housekeeping staffers do not necessarily need a degree in particle science, but some knowledge of particle size, movement and adhesion qualities is essential if they are expected to perform their duties at the required levels. Without this knowledge, all subsequent training means nothing.
Instilling good personal hygiene habits and teaching the proper gowning procedures are perhaps the two most important aspects of this initial training phase. These should be followed closely by a comprehensive understanding of proper cleanroom protocols.
Only after trainees have mastered the above, should they be introduced to the methodology — or good science — of cleaning a cleanroom. This methodology includes defining a list of prohibited materials that must never be taken into a cleanroom and the introduction of accepted cleansing equipment and materials. Proper instruction in cleaning procedures and the ultimate monitoring and verification of cleanliness levels round out a proper cleanroom cleaning methodology.
Equipment selection key to success
The cleaning needs of any particular cleanroom are not necessarily related to the class of cleanroom being serviced. Each case requires individual analysis of not only the cleanroom`s cleanliness requirements (class of cleanroom), but also of the amount and type of contaminants generated within the cleanroom by manufacturing processes and personnel. The gowning requirements of cleanroom personnel must also be taken into consideration, along with the airflow characteristics of the cleanroom. It is important to note that not all areas within a specific cleanroom will require the same cleaning methodologies and frequency of cleaning.
Once the cleaning needs are established, thought should be given to the types of cleaning equipment that should be used in a cleanroom environment.
Vacuums. Most modern cleanroom facilities have built-in central vacuuming systems that allow ease of cleaning and remote disposal of the waste products. These systems can be either dry or wet/dry vacuums. In many cases, fabs are equipped with both types. The beauty of central vacuum systems is the absence of exhaust airflows in the cleanroom itself. There are generally three types of portable vacuums used in cleanroom maintenance: a cleanroom vacuum on which the exhaust air flow is equipped with a HEPA filter, a hospital vacuum on which the HEPA filter is connected to the vacuum`s motor, and a hazardous materials` vacuum in which both the motor and exhaust lines are equipped with HEPA filters.
Portable vacuum systems are used in cleanrooms that don`t have a central system and as a supplemental system for those that do. The selection of a portable vacuum system to fit the task is essential. Most portable vacuums, including some designated as “cleanroom compatible” or as “decontamination units,” are not recommended for critical cleanroom use because only the exhaust air flow is usually connected to the HEPA filtration system. In critical use cases, the use of a double-filtered hazardous materials vacuum system is recommended.
It`s imperative to maintain all filters and ancillary equipment for all vacuum systems in proper working order and cleanliness. Ancillary equipment includes hoses, nozzles and other precision cleaning attachments of various sizes and shapes. Equally important is the selection of materials used in these attachments. You wouldn`t want to use a material that could scrape the surface being cleaned, thereby creating additional particle generation.
Portable backpack-type vacuums with the proper filtration systems for both types of exhaust air flow have become a popular choice for cleanroom use. They allow more mobility for hard to reach areas, such as behind process equipment, and in areas such as walls and ceilings where a ladder can be utilized for proper extension.
Although used for many non-hazardous but still critical cleaning operations, the “hazardous materials vacuum” was originally designed for cleaning up wet chemical spills. The recommended procedure for dealing with chemical spills is to notify the facility`s Chemical Safety Officer before anyone attempts to clean up the spill. In most cases, this individual will deal with the problem.
There is always a possibility that housekeeping staff could become involved with a chemical cleanup. Therefore, it`s important that they are properly educated in this area because of the ever-present danger of fire, explosion, and harmful or poisonous fumes. It`s also imperative that your tools — in this case, the hazardous materials vacuum — are properly cleaned after each use to avoid any potential chemical incompatibility or harmful reactions during its next use.
It is also important to have a variety of materials available for cleaning up wet chemical spills. Chemical compatibility is equally important and each cleanroom housekeeper should know what products to use with what chemicals.
Mops. Mops and related floor cleaning equipment are perhaps the next most important item in a cleanroom maintenance program. Mop handles are available in a variety of noncontaminating materials, such as fiberglass or stainless steel. Selection is usually based on need; lighter products are best for cleaning ceilings and walls, while the heavier and more durable handles are better suited for floor cleaning applications.
The proper selection of a mop head for specific applications is even more important, however. Mop heads also are available in a wide variety of materials and configurations. Typical examples include sponge mops, which can be self-wringing, and string mops, which typically are made of PVA or polyester fibers.
Routine autoclaving of all mop heads prior to use in Class 100 critical/sterile environments is the only way to stop the introduction of any bacterial contamination into the sterile cleanroom environment.
One other thing about mop heads: In sterile environments, throw them away after just one use. That may sound expensive, but the damage that can result from transferring live bacteria or viruses can be devastating to a company`s bottom line. Also, never take a mop head that was used to clean one area of a cleanroom, such as the gowning area, into another area of the cleanroom, especially from a noncritical area to a critical area. Mop heads are expensive, to be sure, but not as costly as the damage cross contamination can cause.
Wipes. Cleaners probably use more wipes than any other single cleaning product or tool. The most important thing to remember is that selection should never be based on cost. Selection criteria should be based on intended usage, cleanliness, particle-shedding properties, chemical residue of the wiper content, static properties, absorbency and size. It`s important to remember that each specific cleanroom cleaning application may require a specific type of wiper. A wiper manufacturer should be consulted for the best wiper for various applications.
Cleaning materials. The two most commonly used cleaning materials are DI water and isopropyl alcohol (IPA). They are followed by a variety of commercially available floor, wall, ceiling, glass and multipurpose cleaning products.
Some of the major concerns when selecting cleaning materials include:
Product compatibility. Let`s not kill the product.
Process compatibility. Let`s not damage the equipment.
Cleanroom compatibility. Make sure the product can do its intended job, while at the same time ensuring that it doesn`t cause unwanted results. For example, IPA tends to remove moisture from whatever surface it comes in contact with. On unsealed vinyl floors, IPA reacts with the plastercizers and produces a fine, white powdery film that can shed or flake. When walked on, it creates small particle storms that can quickly throw a cleanroom out of spec. IPA also tends to remove paint and can etch plastic and Plexiglas. Despite these examples, IPA is a very popular cleaning material. However, care should be given to its use and applications.
Environmental compatibility. Check all ingredients. Some cleaning detergents have unacceptable levels of sodium, which can damage product and equipment.
One final note on cleaning products: The method of dispensing is very important. Squeeze bottles are preferred over spray bottles or aerosol cans.
Establish cleaning protocols
The Institute of Environmental Sciences preferred cleanroom cleaning protocol can be summed up in three words: vacuum, wipe, vacuum.
Vacuuming pulls loose particles from surfaces. Wiping provides the mechanical energy to remove more tightly bound particles, and cleaning solutions break the surface tensions and reduce adhesion forces. The second vacuuming removes loosened particles and cleaner residues. It is a time-tested method proven to be the most reliable and applicable to most general cleanroom cleaning applications.
The following are recommended protocols for specific cleaning applications:
Ceiling panels. Vacuum with a soft brush attachment. Wipe gently in a single direction using slightly overlapping strokes. Tack roll in a single direction, again using slightly overlapping strokes. Remove spots with a commercial cleaner, DI water and a woven polyester wiper. Vacuum with a soft brush attachment.
Lighting units. Vacuum horizontal surfaces with a soft brush attachment. Wipe surfaces of egg crate light diffusers with a wipe dampened with DI water. Open unit. Wipe bulbs. Vacuum horizontal surfaces with soft brush attachment. Close unit. Wipe trim pieces.
HEPA filtration units. Use extreme caution not to make contact with the HEPA filter. Vacuum with a soft brush attachment. Wipe horizontal surfaces of egg crate diffusers with a wipe dampened with DI water. Vacuum with a soft brush attachment. Wipe trim pieces.
Sprinkler heads. Gently wipe exposed surfaces only with a wipe dampened with DI water. Use extreme caution not to activate.
Walls. Vacuum with a soft brush attachment. Wipe with a wipe dampened in a solution of DI water and a commercial cleaning detergent (mixing solutions and using the appropriate ratio of DI water to detergent will depend not only on the task but also on what is being diluted — use caution). Wipe in one direction only using slight overlapping strokes. Mop entire surface with a commercial wall cleaning system. Mop from top to bottom using slightly overlapping strokes. Use a minimum of liquid to avoid splashing or dripping. Tack roll from top to bottom. Remove spots with a commercial cleaner and woven polyester wipe. Vacuum with a soft brush attachment.
Glass surfaces. Squirt commercial glass cleaner on woven polyester wipe. Apply to surface with dampened wipe. Squeegee (from top to bottom if on a vertical surface) to remove excess liquid. Wipe with a dry woven polyester wipe.
Piping systems. Use a wipe damped with a solution of DI water and a commercial cleanser. Again, use caution in the ratio of water to commercial cleanser. Wipe in one direction only using slightly overlapping strokes. Wipe top to bottom whenever possible. Use a minimum of liquid on wipes. Vacuum with a curved pipe attachment. Rewipe with a wipe dampened with the diluted cleansing solution to remove spots and stubborn grime. Revacuum with a curved pipe attachment.
Process equipment. Consult with an engineer, a group leader or an equipment operator prior to cleaning any process equipment. Clean only exterior surfaces. Do not clean in or near processing areas. Use wipes damped with a solution of IPA and commercial cleansers — again use caution when determining the ratio of IPA to commercial cleanser. First vacuum with soft brush attachment, then wipe surfaces in one direction only, using slightly overlapping strokes. Wipe from top to bottom and avoid any splashing or dripping of cleaning solution. Vacuum with a soft brush attachment.
Floors. Vacuum surface. Wash floor with a solution of DI water and a commercial floor cleanser using a clean, non-con taminating mop head. Rinse with DI water and a new, clean non-particulating mop head. The rinse water should be left on the floor long enough to completely saturate any film build-up. Then the rinse water should be mopped up, making sure to change the water after mopping every 10 to 15 square feet of floor surface. The water change is critical to the operation. Failure to change the water on a regular basis can lead to cross contamination, dragging potentially damaging contamination from one area to the next. After the floor is dry, it should be vacuumed with a special HEPA-filtered cleanroom vacuum.
There are a few general rules to remember when cleaning a cleanroom floor, regardless of its composition. Remember the three rules of thumb about what makes real estate more valuable — location, location and location. The same principle applies to proper cleaning of a cleanroom floor. The three secrets are clean water, clean water and clean water.
For most cleanroom applications, a good rule of thumb is to change the water after washing or rinsing approximately 15 square feet of floor space. In a Class 10 or Class 1 facility, that area should be reduced to at least every 10 square feet, perhaps even more often, depending on the critical nature of the cleanroom use. In some cleanrooms, the water is changed as many as 30, 40 or 50 times for just one floor.
Regardless of what type of flooring a cleanroom has, it is without question the dirtiest and most highly contaminated part of a cleanroom. After all, more than 80 percent of all cleanroom contamination winds up on the floor at one time or another and is then stirred up by foot traffic and put back into the ambient atmosphere. A clean cleanroom starts with a clean cleanroom floor.
Verification procedures
The verification process used to determine if the cleaning crew has done a good job in decontaminating the cleanroom can be as simple as a visual inspection or as sophisticated as present day science allows.
The visual inspection is, by far, the most widely used method. However, it is not nearly as reliable as more scientific methods. The visual method includes naked-eye inspections and the wiping of surfaces with white or black wipes. During naked-eye inspections, the areas being scrutinized should appear as bright as practical. Close attention to hard-to-clean areas must be maintained, and the viewer should utilize oblique angles and oblique lighting whenever possible.
Wiping surfaces with clean wipes (wet or dry) can be augmented with the use of ultra violet lighting, particularly on darker colored wipes and surfaces.
Conclusion
Proper cleanroom maintenance is the cheapest and best insurance to protect the $1 billion-plus investment required for today`s state-of-the-art cleanroom. It requires a commitment from the CEO all the way down to the most recently hired cleanroom maintenance technician. It is everybody`s job, not just the responsibility of the maintenance crew.
Proper cleanroom maintenance is good science and good sense.
Ian M. Wallis, president of Microcomplete Cleaning Services, Inc. of Newburyport, Mass., has more than 25 years experience in industrial and hospital maintenance. He is a member of the Institute of Environmental Sciences, the Parenteral Drug Association and the Massachusetts Biotech Council. He can be reached at 508-465-6222.
Editor`s Note: This article appeared originally in the Proceedings from the March 1997 CleanRooms East `97 Conference. To get a copy of the proceedings, please contact Ms. Nuala Kimball, CleanRooms Show Division, 10 Tara Blvd., 5th Floor, Nashua, NH 03062, phone (603) 891-9267.
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Proper cleanroom maintenance requires the proper selection of equipment.
This Nilfisk GB 726 vacuum cleaner can be used in up to a Class 100 cleanroom, when used with a HEPA filter, or up to Class 10 with a ULPA filter, making it appropriate for pharmaceutical packaging and food processing applications in critical cleanrooms.
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A cleaner vacuums the ceiling in a cleanroom to pull loose particles from the surface.
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Mops are one of the most important items used in cleanroom maintenance.
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Routine autoclaving of all mop heads used in Class 100 environments is the only way to stop the introduction of bacterial contamination into the sterile cleanroom environment.
what is the recommended dilution of IPA for conductive tiles?