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 months removes particles. Recalibrating and cleaning ionizing grids every six months ensures the proper ion release rate. Cleanrooms should be reclassified every 6 months 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.