Maintaining cleanrooms and clean manufacturing areas
Key concepts Cleanrooms and clean manufacturing areas require special maintenance considerations. Sources of contamination are environment, process, tools, and people.
- Cleanrooms and clean manufacturing areas require special maintenance considerations.
- Sources of contamination are environment, process, tools, and people.
As products become smaller and more sensitive to dust, vapors, and other airborne particles, the use of cleanrooms and clean manufacturing operations becomes more important. In these environments, the maintenance challenge is to increase cleanliness, minimize contamination, and keep equipment running. That challenge requires using materials, tools, and processes that will not affect the cleanliness of the finished product.
There are four sources of contamination in cleanrooms or clean manufacturing: environment, process, tools, and people. Cleanliness levels vary, based on customer needs, but operating costs are directly proportional to the level of cleanliness required. The greater the demand for cleanliness, the greater the expense.
Cleanrooms are highly controlled manufacturing areas designed to limit the amount of contamination. Federal standard 209E classifies cleanrooms by the concentration of air particles 0.5 micron in diameter or larger. (An average human hair is about 50 microns in diameter.)
A Class 1000 cleanroom, for example, has fewer than 1000 of these particles in a cubic foot of air, while a Class 10 cleanroom has fewer than 10 particles less than or equal to 0.5 micron in diameter per cubic foot.
Cleanroom environments are strictly controlled, using high-efficiency particulate attenuation (HEPA) filters to remove airborne particles, ionizing grids to neutralize static that attracts particles, and heating, ventilating, and air conditioning (HVAC) equipment to exhaust air and particles outside the cleanroom and maintain positive cleanroom air pressure.
Work is a dirty process and can contaminate any cleanroom. Any movement-walking, lifting, vacuuming, or even wiping down workstations-creates particles. Tools and equipment produce organic contaminates from sources such as lubricants. Robotics and zero-maintenance equipment are preferred inside cleanrooms, but they are not always feasible.
There are special furnishings, vacuums (which exhaust outside the cleanroom), notepads, and cleaning solutions designed specifically for cleanroom use. They are made of nonshedding materials. All oils and greases used in a cleanroom must be tested using a Fourier transform infrared analysis (FTIR) to identify organic residues and contaminates. If contaminate levels are too great or cannot be removed easily with cleanroom-approved cleaning solutions, the lubricants cannot be used.
Maintenance workers must understand the cleaning process for any item brought into the cleanroom. Even “clean” products bound for use in a cleanroom must be washed with deionized (DI) water and special surfactants before entering a cleanroom. Seemingly clean (no visible dirt or grease) tools brought into the cleanroom must be treated with nonshedding cleanroom wipes and isopropyl alcohol.
Particle contamination is typically detected visually. One common detection method uses ultraviolet light. An operator checks an item’s cleanliness by placing it under an ultraviolet light source, which makes all materials that fluoresce (such as cotton fibers and greases) glow for easy detection.
People are the most difficult contamination sources to control, so training is essential-and drama helps. Monitoring the general plant’s airborne particle content for 1 min will easily yield more than a million particles, while the particle content of HEPA-filtered air inside a small, vinyl-curtained work surface may contain only 15-20 particles. This demonstration, usually done early in training, proves the importance of following cleanroom protocol.
One major portion of training is suiting up (gowning) in cleanroom-approved garments. Everyone entering the cleanroom must wear cleanroom garments. At a minimum, this wardrobe includes cleanroom suits, gloves, safety glasses, hairnets, hoods, and facial hair and shoe coverings. Gowning components are donned in a specific order to ensure street clothing does not contaminate cleanroom garments.
Regular maintenance procedures-daily, weekly, monthly, and quarterly-help ensure cleanroom compliance, no matter what the cleanroom class. For example, positive-pressure air should be running at full-flow in a Class 10 cleanroom for at least 30 min before cleaning to ensure clean, fresh air within the room. Cleaning starts at the highest point and works toward the floor. Every surface, corner, and ledge are first vacuumed, then damp-wiped with a cleanroom wipe. Operators wipe surfaces one way-either downward or away from themselves-since a “back-and-forth” scrubbing motion can create more particles than it removes. They also use a clean surface of the wipe or sponge with every new stroke to guard against redeposition of contaminates. On walls and windows, the wiping movement must be parallel to the airflow.
Floors are neither waxed nor buffed (materials and processes that contaminate the room), but are cleaned with a DI water and isopropyl alcohol mixture.
Cleanroom equipment maintenance also requires special procedures. For example, to prevent the spread of grease and to contain its airborne molecular contamination (AMC), equipment needing lubrication is isolated with polycarbonate shields. A fully gowned maintenance worker wears three pairs of latex gloves to perform this maintenance. After greasing equipment, the maintenance worker removes the outer glove, turning it inside out under the shield to contain the grease. If this procedure is not followed, the maintenance representative could leave grease on the door or other surfaces while leaving the cleanroom, and all operators who subsequently touched that doorknob would spread the grease and organic contaminates.
Some specialized cleanroom equipment also must be maintained, including HEPA filters and ionizing grids. Vacuuming HEPA filters every 3 mo removes particles. Recalibrating and cleaning ionizing grids every six months ensures the proper ion release rate. Cleanrooms should be reclassified every 6 mo by confirming that the air particle count meets the cleanroom class designation.
Useful tools in contamination detection are air and surface particle counters. Air particle counters can check contaminant levels at set intervals or around-the-clock at varied locations. Particulate levels should be measured at activity centers where products would be-at tabletop height, near conveyors, and at workstations, for example.
Surface particle counters should be used to monitor operator workstations. If a product breaks, the operator can use this device after a cleaning procedure to determine if additional cleaning is needed. Air pockets and crevices where particles can collect should be given special attention.
Although they are not nearly as stringent, maintenance activities for clean manufacturing are related to those for cleanroom manufacturing. In the most basic sense, clean manufacturing follows current good manufacturing practices. Essentially, it’s good housekeeping.
As with cleanroom operations, cleanliness is a four-part equation: environment, process, tools, and people. How stringent clean manufacturing guidelines need to be is based on the products and customer requirements.
Controlling air temperature and humidity levels in all work areas is a good first step in clean manufacturing. It may eliminate the need to open windows, which would admit outdoor airborne dirt.
Training staff on preventive maintenance procedures and determining wardrobe guidelines are the next steps in cleanliness control. All operators should understand their individual role in maintaining a clean facility, know what they can and cannot wear on the production floor, and know how their individual work areas should be maintained.
For greater cleanliness control, manufacturing facilities can be segmented into “dirty” and “clean” work areas. The “dirty” work areas, such as toolroom operations, should be placed far away from cleaner, product-assembly sites. Stringent manufacturing areas should be in the middle of the building-the easiest space to keep clean.
In very stringent clean manufacturing sites, production materials are stored in central material handling facilities and conveyed to assembly rooms as needed, via a closed-loop system. This approach eliminates dirty boxes and containers from the production floor. Equipment that produces heavy exhaust should be fitted with pressure-controlled exhaust systems to remove exhaust from the production area.
Equally important as maintaining equipment is determining how any new process, lubricant, or procedure will affect the cleanliness of the finished product.
Use of spray lubricants, for example, which produce airborne particulates, may need to be eliminated. Consider using a lubricant only if its residue can be easily removed from the product with isopropyl alcohol. Silicon-based lubricants may require cleanup with hexane or benzene. In cases where extreme cleanliness is needed, use of such a lubricant should be considered only if it does not come into contact with the product. Avoid over-lubrication, since using extra oil on equipment will only increase the likelihood of contaminating supposedly clean products.
Both cleanrooms and clean manufacturing require a solid commitment from all staff. The benefits include cleaner products and manufacturing facilities, potential new markets for products, and the opportunity to present the production facility as a selling point to customers.
-Edited by Richard L. Dunn, Editor, 630-320-7141, email@example.com
Cleanroom maintenance tips
Here are some cleanroom maintenance tips to control contamination.
Dedicate cleanroom tools and equipment. Keep one set of tools and test equipment inside the cleanroom. This approach saves the time and aggravation of having to clean tools before bringing them into the cleanroom and the danger of cleanroom contamination caused by someone in a hurry.
Train your staff. Anyone who might enter the cleanroom must understand the importance of proper cleanroom protocol. They must be shown how a “quick trip” to the cleanroom without proper attire to retrieve a forgotten tool, for example, releases millions of particles, requires immediate full-scale cleaning, and could downgrade cleanroom classification.
Select equipment with minimal or zero maintenance requirements. The less chance for contamination, the better.
Monitor outside service personnel. If cleanroom equipment is serviced by vendors, ensure they also follow proper cleanroom procedures. Do not allow equipment manuals into the cleanroom unless they are printed on cleanroom paper and are never removed from the cleanroom. If a vendor or maintenance worker must refer to a manual, photocopy the necessary pages and tape them to a window outside the cleanroom or use manuals printed on special cleanroom paper.
Keep a supply of cleanroom vinyl gloves. Some workers may develop latex glove allergies. This problem can be serious if the latex contact is not stopped. If a worker’s hands become red or develop a rash after removing the gloves, have the worker wear vinyl gloves in the future.
Expect the unexpected. Overzealous staffers with long mop handles can poke holes in ceiling-mounted HEPA filters. Shortened mops could eliminate a costly investment in new filters, which cost about $700 each.
Adjust for seasonal changes. Following OEM recommendations on filter and DI water changes is normal procedure. But in the spring and fall filters must be changed more frequently to offset increased outdoor particle counts caused by such natural occurrences as airborne pollen and water contaminated with leaves and algae.
Encourage routine preventive maintenance. Every few hours, all cleanroom operators should monitor their own workstations with a surface particle counter for contamination. If particle counts are high, they should immediately wipe down all surface areas and determine the particulate source.