The CeNSe Cleanroom is located in room 369 of the ASTeCC building. It is designed as an ISO 5 or class 100 cleanroom though actually tests much better. The filtered fluorescent lighting in photolithography cleanrooms contains no ultraviolet or blue light in order to avoid exposing photoresists. The spectrum of light emitted by such fixtures gives virtually all such spaces a bright yellow color.
A "cleanroom"is an environment, typically used in manufacturing or scientific research, that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapors. More accurately, a cleanroom has a controlled level of contamination that is specified by the number of particles per cubic meter at a specified particle size. To give a perspective, the ambient air outside in a typical urban environment might contain as many as 35,000,000 particles per cubic meter, 0.5 μm and larger in diameter, corresponding to an ISO class 9 cleanroom.
Cleanrooms can be very large. Entire manufacturing facilities can be contained within a cleanroom with factory floors covering thousands of square meters. They are used extensively in semiconductor manufacturing, biotechnology, the life sciences and other fields that are very sensitive to environmental contamination.
The air entering a cleanroom from outside is filtered to exclude dust, and the air inside is constantly recirculated through high efficiency particulate air (HEPA) and ultra low penetration air (ULPA) filters to remove internally generated contaminants.
Equipment inside the cleanroom is designed to generate minimal air contamination. There are even specialised mops and buckets. Cleanroom furniture is also designed to produce a low amount of particles and to be easy to clean.
Common materials such as paper, pencils, and fabrics made from natural fibers are often excluded; however, alternatives are available. Cleanrooms are not sterile (i.e., free of uncontrolled microbes) and more attention is given to airborne particles. Particle levels are usually tested using a particle counter.
Some cleanrooms are kept at a positive pressure so that if there are any leaks, air leaks out of the chamber instead of unfiltered air coming in.
Low-level cleanrooms may only require special shoes, ones with completely smooth soles that do not track in dust or dirt. Entering a cleanroom usually requires wearing a cleanroom suit.
In cheaper cleanrooms, in which the standards of air contamination are less rigorous, the entrance to the cleanroom may not have an air shower. There is an anteroom, in which the special suits must be put on, but then a person can walk in directly to the room (as seen in the photograph on the right).
Some manufacturing facilities do not use fully classified cleanrooms, but use some cleanroom practices together to maintain their cleanliness requirements.
Cleanrooms are classified according to the number and size of particles permitted per volume of air. Large numbers like "class 100" or "class 1000" refer to US FED STD 209E, and denote the number of particles of size 0.5 µm or larger permitted per cubic foot of air. The standard also allows interpolation, so it is possible to describe e.g. "class 2000".
Small numbers refer to ISO 14644-1 standards, which specify the decimal logarithm of the number of particles 0.1 µm or larger permitted per cubic metre of air. So, for example, an ISO class 5 clean room has at most 105 = 100,000 particles per m³.
US FED STD 209E cleanroom standards
|Class||≥0.1 µm||≥0.2 µm||≥0.3 µm||≥0.5 µm||≥5 µm|
ISO 14644-1 cleanroom standards
|Class||≥0.1 µm||≥0.2 µm||≥0.3 µm||≥0.5 µm||≥1 µm||≥5 µm|
Cleanroom class comparison
Because 1 m³ is approximately 35 ft³, the following classes are mostly equivalent, although the testing standards differ.
|ISO 14644-1||FED STD 209E|
BS 5295 cleanroom standards
|Class||≥0.5 µm||≥1 µm||≥5 µm||≥10 µm||≥25 µm|
Note that Class 1 also requires that the greatest particle present in any sample does not exceed 5 μm