Cleanrooms have been around for quite some time now. Defined as manufacturing spaces in which the air content is strictly controlled conditions such as temperature, humidity and pressure are closely monitored and maintained to avoid contamination of the environment.
 

Cleanroom manufacturers pay strict attention to air particles and most clean-critical area, which is the area of clean room designs target prevention of air particles 0.5 microns in size or larger with air filters, but some industries are going after even smaller air particles. The size of of cleanrooms range from micro-environments to huge areas referred to as ballrooms.
 

Cleanroom fabrication includes conventional cleanrooms, hardwall modular cleanrooms, mini-environment cleanrooms and micro-environment cleanrooms. Cleanrooms can be divided into two areas: the critical area which is the area of cleanrooms where contamination can gain direct access to the production area which consists of the rest of cleanrooms.
 

Cleanroom contamination can come from just about anywhere. Skin flakes from people are the largest source of cleanroom contamination, but other sources are the facility itself (paint and coatings, air conditioning debris, construction materials, etc.), particles generated by tools (lubricants and emissions), fluids (floor finishes or coatings and cleaning chemicals) and particles generated by products such as silicon chips, quartz and aluminum. Cosmetics, perfume, hair care products and clothing debris are other sources of contaminants.

Cleanrooms came about during the space race of the 1960s. However, clean-rooms are now used in a wide variety of industries, such as chemical, printed circuit boards, computer, silk screening, biomedical, electronics, disc memory, photographic, aerospace, nuclear, optical, hybrid and circuitry.
ISO14644
Cleanrooms are classified by the cleanliness of their air. This is done according to ISO 14644-1, an international standard, having been adopted by the European Union in 1999, and the USA in 2001. However, according to the Scottish Society for Contamination Control (S2C2), a provider of information and training for cleanroom standardization, the most easily understood classification of clean-rooms is the U.S. Federal Standard 209. Though it called it “obsolete,” S2C2 says it is still widely used, and its nomenclature is expected to be in use for years to come.
Still, a range of cleanroom standards is being produced by the International Organization for Standardization (ISO) with committees of experts nominated by countries throughout the world writing them.
One is ISO 14644, which consists of the following parts, under the general title ‘Cleanrooms and Associated Controlled Environments:’
Part 1: Classification of air cleanliness:
This gives the airborne particle  limits for different classifications of cleanrooms. This standard also
gives the methods that should be used to measure the airborne particles when testing a cleanroom to
determine its class.
Part 2: Specifications for testing and monitoring to prove continued compliance with ISO 14644-1: This gives information, including time intervals, for testing a cleanroom to demonstrate continual compliance with the ISO 14644-1 standard.
Part 3: Test methods: This gives a description of the test methods that should be used to test the clean-room to show that it is working correctly.
Part 4: Design, construction, and startup: This gives general guidance as to how a cleanroom should be designed, constructed and made ready for handing over to the user.
Part 5: Operation: This gives general advice on how to run a cleanroom.
Part 6: Terms and definitions: This is a collection of all the definitions of terms used in the ISO cleanroom standards.
Part 7: Separative enclosures (clean air hoods, gloveboxes, isolator, mini environments): This gives information on clean air devices.
Part 8: Molecular contamination: This gives information on gaseous contamination in cleanrooms.

Possible Changes
ISO 14644-1 and ISO 14644-2, the two standards that deal with classification, testing and monitoring of cleanrooms to prove continued compliance were first published in 1999 and 2000, respectively. These two standards have been well accepted by the cleanroom industry, but it is thought that improvements could be made to them without causing any radical change.
Work started on revising the standards in November 2005 with a view to finishing around the end of 2008.
In its latest member newsletter, S2C2, says that possible changes to ISO 14644¬1 include the standard classification method being changed to classification by table, with the formula that is given in the standard to be used for intermediate classes (like the old 209E). In the classification table, it is being considered whether to remove, or annotate, some of the low counts as they suggest unreliable limits that demand too large sample volumes.
The graphical representation of the classes will be retained but the clarity improved.
Sample locations: In the present standard, the number

of sample locations is not class sensitive but only area sensitive. This has been dis­cussed, and it is likely that the present method will be retained.

Collection and evaluation of particle count data: In Annex B5.2 of the pre­sent standard, it is considered that there are some problems with the statistical approach that is currently used in the 95 percent upper confidence level (95 percent UCL).

An even distribution of contamination in a cleanroom is assumed. This is not always the case, says S2C2, particularly for non-unidirectional cleanrooms “in operation,” which can cause classifica­tion problems. There is a view that a 95 percent level of statistical confidence can be achieved with 5 or more sample locations (not 10 as today). This is still to be resolved. Today, many testers pre­fer to take more sample locations to avoid the complexity of applying the Student t-test. They would prefer to find a simple way of increasing sample numbers at the smaller numbers of lo­cations, and avoid the need to use the Student t-test.

The work group has to decide if they wish to have confidence in sampling for a complete zone or individual locations; the current standard generates confidence for a complete zone. The statistical issues are still to be resolved.

The situation of uneven particle dis­tribution has to be dealt with. This prob­lem may lead to a different approach for “as built” and “at rest” compared to “operational” occupancy state.

Annex F: Sequential sampling: This procedure is considered still effective. The specification given in Annex F is difficult to follow and will be rewritten to improve the clarity of the presentation.

Possible changes to 14644-2 include Testing vs. monitoring: It is considered that the normative section is unclear and there is a need to improve its clarity. The link between increased monitoring and less testing has to be made clearer. It is also thought that terms that have differ­ent meanings in different countries such as ‘qualification’ and ‘validation’, should be removed from the standard.  Tables of test frequencies: The pre­sent normative section is unclear and some parties do not agree with the re­quired testing frequencies. It may be that this section will be expanded and placed in an informative annex.

Real-time monitoring systems: A pos­sible new section (perhaps to an Annex) is required to specify the essential re­quirements of such systems S2C2 says.

Annex B: Risk assessment: This sec­tion is considered very poor and limited, and does not reflect current practice. It is likely that aspects of risk assessment, when they arise, should be dealt with in the main text and that Annex B removed.

ISO 14244 and the related ISO 14698, ‘Cleanrooms and Associated Controlled Environments–Biocontamination Con­trol,’ are not due for revision until Sep­tember 2008. However, S2C2 says it appears that they may benefit from an ear­lier review. The issues involved are being investigated, and a decision will be made as to whether an early start in revising these standards is required. FSM