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.
