Get familiar with cleanroom basics, from standard classifications and types to mechanical systems.
A cleanroom is an environment that is designed, built and operated to provide cleanliness, control and/or isolation for certain processes.
The purpose of a cleanroom is to protect the product or the process from contamination, to restrict access to the product or process and to contain any hazards located in the cleanroom.
Cleanroom technology is commonly used in manufacturing and research and development, in several industries, including nanotechnology, defense, microelectronics, pharmaceuticals, biotechnology, and medical devices.
Once you’ve made the decision to build a cleanroom, what happens next? Your individual process needs and variables must be examined thoroughly.
Cleanroom technology standards ensure that cleanrooms have little to no contamination, which is anything that could corrupt the process or make the product impure. Contamination is defined by a specified number of certain size particles per cubic foot of air.
The particle size measured in cleanrooms are typically 0.5 microns (µm) or larger in diameter. For perspective, a human hair is 60–80 microns wide and outside air has about 35,000,000 0.5µm and larger-sized particles sized per cubic foot of air.
Cleanrooms are defined by their level of cleanliness; more specifically, the amount of particles found in the air.
Cleanroom classifications include a class 1 cleanroom or ISO class 3, which by today’s standard, typically has one .5 micron sized particle per cubic foot of air, for which a typical HEPA is rated. Cleanrooms range up to class 100,000 or ISO class 8, which includes up to 100,000 particles at .5 microns.
Cleanrooms are built with smooth, hard and easily cleanable surfaces to minimize contamination. Walls, ceilings and floor systems are all designed to minimize internal particulate. Temperature control, humidity control, static control, and sound and light levels are all critical factor.
Another key factor is the way air enters, is filtered, circulates and leaves a cleanroom. Outside air is filtered to exclude particulates, and the air inside is constantly circulated through High Efficiency Particulate Arrestors (HEPAs) and/or Ultra Low Particulate Arrestors (ULPAs) to remove internally generated contaminants.
People are the largest particle producer in a cleanroom and many precautions are made to protect the product. Personnel enter and leave cleanrooms first through gowning rooms, then often through airlocks by following strict cleanroom standards. They wear protective clothing such as coveralls, hairnets, facemasks, booties and gloves. Materials and equipment are next in line as generators of contamination, which limits what they can be made out of when used in a cleanroom.
The cleanliness level of a cleanroom is typically set at the beginning through the cleanroom design analysis and depends on the product to be made. In some cases, particulates can have a crucial impact on the performance of the product. In other cases it can contaminate the product. The various cleanroom types, cleanroom air delivery systems, and analysis of the process and the design help determine the level of cleanliness to be accomplished.
With today’s cleanroom technology, they are tending to certify at least one classification cleaner at rest than specified. However, the amount of air used to certify a cleanroom as specified in the ISO standards can vary. A facility’s energy savings, which helps the competitive nature of businesses, depends on the type of process used and the protocol maintained. These savings can be accomplished by specifying different levels of cleanliness or operating systems in such a manner that the level of cleanliness maintained meets the qualifications, but uses control systems such as particulate counters, to maintain but not exceed the cleanliness level.
Cleanrooms are typically energy inefficient compared to standard building systems. This is because pressure, temperature, humidity, particulate levels, light levels, static levels, sound levels, vibration levels and other criteria can critically impact the performance of the product being made in the cleanroom. Controls are employed through the mechanical, electrical and process systems to ensure that systems do not impact the product and, in fact, in many cases enhance the product. As a result, the tighter control means more energy expended to control these variables.
There are three primary mechanical systems for cleanrooms:
This system, as named, supplies the air directly to the HEPA filters through a ducted system and back from the returns to the air handler through duct work.
This system directly ducts the air to the HEPA filters but uses a plenum, either constructed for this purpose or via the building envelope, to allow air to return from the room returns to the air handler with limited or no duct work.
This system involves pressurizing a prefabricated plenum or stick-built plenum with a ceiling that creates a pressurized zone containing the HEPAs and supplying the air to the room. The return plenum is used with limited to no duct work.