Clean Up Time

For the past two years, those operating and designing cleanrooms have known a change was in the air—quite literally—as the International Organization for Standardization (ISO) is in the process of developing a new set of standards for cleanrooms. The development of these documents marks the first attempt to standardize cleanroom practices internationally.

07/01/2002


For the past two years, those operating and designing cleanrooms have known a change was in the air—quite literally—as the International Organization for Standardization (ISO) is in the process of developing a new set of standards for cleanrooms.

The development of these documents marks the first attempt to standardize cleanroom practices internationally. Specifically, these new standards (see Table 1, p. 44) are the product of Technical Committee 209, "Cleanrooms and Associated Controlled Environments," and according to the ISO itself, the documents provide for the: " standardization of equipment, facilities and operational methods for cleanrooms and associated controlled environments."

The ISO is a veteran organization in this area, having created the whole ISO 9000 series of quality-control standards for manufacturing facilities. ISO's hope is that the new cleanroom standards will give operators and designers a common series of references, as opposed to the numerous and frequently conflicting country-specific standards currently in use.

At the same time, the legal and regulatory ramifications of these standards are still being sorted out. In Asia, some regulatory agencies have adopted the standards, while others have not. But in Europe, each of these standards becomes mandatory six months after its final publication.

In the United States, reaction has been mixed. Many companies have adopted a wait-and-see approach to the new regulatory issues, while others have crafted plans to demonstrate compliance. Perhaps the most notable event occurred last November, when the U.S. General Services Administration (GSA) decided to retire Federal Standard 209E and adopt the first two standards. The former GSA standard—first published in 1963 and last revised in 1992—was a requirement for those conducting business with the federal government. And although use was never mandated outside of government transactions, the document gained acceptance as the de facto standard in the cleanroom industry.

But even though the federal government has made the switch to the ISO standards in its own facilities, this does not preclude companies from continuing to use FS 209E in transactions outside the government realm. The FDA, for example, has yet to weigh in with an official position on the ISO documents and continues to refer to the federal standard.

Getting to know the new standards

Regardless of the regulatory uncertainty, those involved in cleanroom design, construction or operation will sooner or later encounter the ISO standards, and therefore require a basic understanding of their content. For the time being, the first two standards released—at least the pair adopted by GSA—hold the most weight. As of now, only three of the eight expected documents have been released. This article concentrates on the first two standards ISO 14644-1 and -2.

ISO 14644-1, Classification of Air Cleanliness , was released in 1999. Although it primarily impacts owners and firms that certify cleanrooms, designers and consultants who serve the cleanroom industry can benefit from a basic understanding of its requirements.

Those familiar with FS 209E will feel right at home with ISO 14644-1 because the ISO document directly parallels 209E's methodology, but adds some improvements. Both standards define various classes of cleanroom airborne-particulate concentrations and provide the statistical methodology for certifying cleanrooms.

Contrary to common perceptions, neither document mentions average room velocity; filters; direction or uniformity of airflow; or classification of cleanroom furnishings for that matter. Simply put, both standards require that a room with an average airborne concentration of x particles per cubic meter and y microns in size may be classified as a "class- z " room.

There are also a number of differences between the two documents, from units of measure to the number of available classes.

Unlike FS 209E, ISO 14644-1 uses only metric units, referring to airborne particle concentration in terms of particles per cubic meter. Although many who are more versed in the traditional English measurement system dig in their heels when pushed to use metric units, the symmetry of the numbers, when converted, makes the transition easy. Also, ISO uses a standard particle size of 0.1 micrometers (mm), while FS 209E is based on a 0.5-micrometer particle size (see Table 2, p. 45).

Corresponding to the more detailed measurement, ISO 14644-1 adds three new cleanliness classes (see Table 3, p. 45). Two of these classes are "cleaner" than those in FS 209E (ISO Class 1 and 2) and one is less stringent (ISO Class 9).

The cleaner classes will most benefit state-of-the-art semiconductor facilities. The cleanest class in 209E allows a maximum of 10 particles per cubic ft.—a number that was too great for many semiconductor manufacturers that were already requesting 1 particle per cubic ft. So the semiconductor facilities that needed to be cleaner had to "work off-scale" on 209E by creating their own class definition. The federal standard provided a methodology to do this, but the result ended up being rooms assigned class numbers like "0.47." Thus, operators were using their own terms to describe the state of their cleanroom. Since there wasn't a common terminology for describing where they were off-scale, confusion resulted.

Conversely, the less-clean ISO-9 classification will be appropriate for those industries whose technology is pushing them to begin using cleanrooms, such as electroplating line, mushroom farming and paint-spray applications. Using FS 209E, such facilities could not get consideration as a cleanroom, and thus there were no applicable standards.

Other differences

Other features in ISO 14644-1 go beyond measurements and classes. For example, the standard introduces the concept of an "outlier" to the cleanroom classification process. An outlier can be defined as a data point that is far from the average of other data points. For example, say that during the certification process for an ISO-2 room, the following particle counts are collected: 89, 105, 92, 83, 7, 218, 100, 97 . Intuitively, we would know what to do with the 7 and 218: look around, make sure no one was watching and throw them out. With the ISO standard there's no need to feel guilty as it allows for these data points to be thrown out as long as there is adherence to certain requirements.

Additionally, ISO 14644-1 requires fewer sample locations for the cleaner classes—ISO 1 through 5—than FS 209E, something that may present an issue with more rigorous clients. However, since the intent of ISO 14644-1 is to form the basis of an agreement between a buyer and a seller, the stipulated number of locations may be viewed as a minimum, and a larger number of locations can always be specified. Keep in mind that when using ISO 14644-1, the design team will need to specify the use of the standard, the occupancy state when tested ( as-built, at rest or operational ), the ISO class required and the size of the measured particles. Thus, for rooms ISO 5 and cleaner, obtaining client input regarding the number of sample locations would be prudent.

Testing and monitoring

The second document of the ISO series, published in 2000, is ISO 14644-2, Specifications for testing and monitoring to prove continued compliance with ISO 14644-1 . This second standard is intended to be used in conjunction with ISO 14644-1, because while ISO 14644-1 simply takes an older standard and improves upon it, ISO 14644-2 mandates entirely new requirements.

ISO 14644-2 describes a methodology whereby operators of cleanrooms are required to prove continued compliance with ISO 14644-1, and more. As the "Scope" section of the standard alerts us: "Additional tests are specified."

So while ISO 14644-1 is directed more to owners and cleanroom certifiers, ISO 14644-2 is of particular interest to both designers and cleanroom operators, who will have to design and maintain the monitoring systems required.

The document defines the intervals for testing as:

  • Continuous : updating that occurs constantly.

  • Frequent : updating at intervals not exceeding 60 minutes.

  • Intervals : updating at intervals such as 6, 12 or 24 months.

The maximum time interval of testing for compliance with particle concentration limits is six months for rooms of ISO Class 5 and cleaner, and 12 months for the remaining classes.

Additional tests outside the criteria of ISO 14644-1 are also listed in the "Normative" section: airflow volume or airflow velocity at 12-month maximum intervals; and air pressure difference at 12-month maximum intervals.

In addition, Annex A of the "Informative" section lists optional tests that are to be conducted at maximum intervals of 24 months:

  • Installed filter leakage.

  • Airflow visualization.

  • Recovery.

  • Containment leakage.

This section also provides for the extension of these specified intervals if a facility is equipped with instrumentation for continuous or frequent monitoring. Requalification of the facility is required following significant repairs, alterations or interruption of airflow.

In addition, the standard requires routine monitoring of airborne particle concentration and other parameters according to a written plan, which is based on a risk assessment. Any condition found to exceed the specified limits requires remedial action and retesting. A comprehensive report is specified to prove continued compliance with the standard.

The monitoring specified in ISO 14644-2 may require the installation of real-time data acquisition systems. As a result, facility designers will need to consider the integration of instrumentation, as well as building automation into such monitoring systems.

Even though the document sets out some important testing guidelines, there are flaws. So, while at first glance 14644-2 appears to be a concise and reasonable standard to use as a reference in project specifications, unfortunately this is not the case. During the 10 years it took to write the standard—with the participation of 19 nations employing a plethora of languages—some things came unglued. As a result, inconsistencies and ambiguities abound.

For example, those that have used the document over the last two years are in a peculiar situation: ISO 14644-2 mandates the use of the test procedures described in ISO 14644-3—a document that has not yet been published. So however well intentioned, the standard is of much greater value to the legal community than to those who design, build or operate cleanrooms.

Go get it

So there we have it—two new standards that engineers should run right out and buy: the first, ISO 14644-1, because of its technical excellence and value to the cleanroom industry; and the second, ISO 14644-2, for purposes of perusing it, studying it and—most importantly—running it by your legal department.

Overall, however, the market and technology will continue to drive the processes of cleanroom design, not regulation. While the uncertain state of acceptance and enforcement for these ISO standards will present a dilemma for some designers, the documents do not address design as much as the processes of design, construction and operations. If the standards are accepted by industry, it will be a boon to design firms, who will most likely have to double their staff—at client expense—just to keep up with all the paperwork.

Table 1 - ISO Standards

Standard

Title

Status

These are the eight proposed ISO cleanroom standards, along with their current progress toward publication. Prior to final approval, each standard is issued first as a DIS (Draft International Standard) and then as a FDIS (Final Draft International Standard). Each standard contains a "Normative" (mandatory) section and an "Informative" (non-mandatory) section. The informative sections contain a series of annexes, each of which addresses a particular application or topic.

14644-1:1999

Classification of Air Cleanliness

Pub. 1/1/99

14644-2:2000

Specifications for Testing and Monitoring to Prove Continued Compliance with ISO 14644-1

Pub. 9/1/2000

14644-3

Methodology and Test Methods

Pending Action

14644-4:2001

Design, Construction and Startup

Pub. 5/1/2001

14644-5

Cleanroom Operations

DIS 3/1/2001

14644-6

Terms, Definitions and Units

Pending Action

14644-7

Separative Enclosures

DIS 3/1/2001

14644-8

Molecular Contamination

Pending Action


Table 2 - Comparing Standards

ISO 14644-1

Fed. Std. 209E

Class

0.1 mm particles/m3

Class

0.5 mm particles/ft3

1

10

1

1

2

100

10

10

3

1,000

100

100

5

10,000

1,000

1,000


Table 3 - Comparative Classes

ISO Class

Fed. Std. 209E

1

N/A

2

N/A

3

1

4

10

5

100

6

1,000

7

10,000

8

100,000

9

N/A


Author Information

Michael A. Fitzpatrick is Program Director of Microelectronics for Lockwood Greene Engineers. He has been involved with semiconductor facilities for more than 23 years and instrumental in the development of methods to decrease time-to-market in the construction of manufacturing facilities. A senior member of the Institute of Environmental Sciences and Technology (IEST), he is chairman for WG012 (Considerations in Cleanroom Design) and WG028 (Mini-environments) and a vice president of the IEST. Mike is a member of the Arizona State University ACE Cleanroom Task Force and lectures as part of the ASU Cleanroom Construction Program.


The Rest of the Standards

In addition to ISO 14644-1 and 14644-2, one other ISO cleanroom standard has been published, and a few others are on the way.

ISO 14644-4, Design, Construction and Startup , is a document that, according to ISO, "will be a primer on the design and construction of cleanrooms. It will cover all aspects of the process from design development to startup and commissioning."

It describes a design methodology called "programming," which is already commonly used. The standard also provides a section on construction that borrows heavily from IEST RP-012—even to the point of repeating errors from it. Further, it gives an extensive methodology for startup and commissioning, an activity that is frequently not given the attention it deserves. It also specifies the substantial documentation and reporting procedures that a design team will be required to follow.

ISO 14644-5, Operations , which is in the draft stage, is a document directed primarily toward owners and operators of cleanrooms. It covers protocol, gowning, routine maintenance and cleanroom cleaning issues. It will be of interest to those designers concerned with the layout and furnishing of gown rooms and supporting spaces.

The remaining documents in this series have yet to be released, so their impact on the design community cannot yet be determined. It is almost certain, however, that ISO 14644-8, Molecular Contamination , will address the topics of outgassing of cleanroom materials and the installation of airborne molecular contamination (AMC) filtration, making it applicable to those who design cleanrooms.

While, in many cases, all of these documents will merely formalize practices that most designers already follow, the standards require a level of reporting and documentation far beyond that presently used on most projects. Thus, designers of cleanroom facilities will need to be familiar with the additional requirements they impose.



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