environment controls

Cleanroom is essentially a controlled environment with the following characteristics:

- Airborne particles generation is limited
- Airflow patterns are controlled
- Temperature and humidity are controlled
- Air pressure is regulated

contamination control

Contamination control is accomplished by continuously "flushing" the cleanroom with highly filtered air that is forced in through High Efficiency Particulate Air (HEPA) filters. HEPA filters can prevent over 99.97% of particles measuring greater than 0.3 microns in size from entering the cleanroom.

air flow control

Air Flow Control is accomplished by one of the two basic design: Horizontal Laminar Air Flow and Vertical Laminar Air Flow. In Horizontal Laminar Flow, HEPA filters in a wall force clean air from one side of the room to the other. In Vertical Laminar Flow, HEPA filters on the ceiling push clean air down to the floor. In both cases, air is forced through the filters at a rate of about 100 feet per minute, traveling in a uniform, piston-like fashion known as Laminar Air Flow.

Temperature/Humidity Control

Typical temperature and humidity specification is 21 degree Celcius and 30-70% RH respectively. If the process is not affected by temperature/humidity conditions which fall outside of human comfort ranges, it is not necessary to design to tight tolerances. Tight tolerances will result in unnecessarily escalated costs.

pressure control

Depending on the type of facilities, cleanrooms sometimes have a positive pressure, and sometimes a negative pressure. Positive pressure means that air pressure in the cleanroom is greater than the air pressure outside the room. This helps to prevent the inflow of particles from the outside when doors are opened. Air pressure can be adjusted through the cleanroom air handling system.

class designation

US Federal standard 209E or ISO 14644-1 define the cleanliness class designation. Under FS 209E, six classes have been established namely Class 100,000, 10,000, 1,000, 100, 10 and 1. ISO 14644-1 adds three additional classes - two cleaner than class 10 and one dirtier than class 100,000. Class 100 would mean that no more than 100 particles larger than 0.5 microns would exist in any given cubic foot of air.

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