by Richard A. Matthews
The two documents with a common denominator in the family of new ISO global cleanroom standards are ISO 14644-3 and ISO 14644-6. One lists all the test methods pertinent to evaluating cleanroom performance. The other is the repository for all the terms, definitions and units applicable to cleanrooms.
Each document was produced by a separate Working Group. Japan is the convenor of ISO 14644-3, Metrology and Test Methods, and Switzerland is the convenor of ISO 14644-6, Terms, Definitions & Units.
One commonly asked question is “Which tests need to be performed to prove that a cleanroom is really a cleanroom?” The 88-page ISO Standard 14644-3 answers this question.
TITLE: Cleanrooms and associated controlled environments – Part 3: Metrology and Test Methods
SCOPE: Specifies the metrology and testing methods for characterizing the performance of cleanrooms and clean zones
STATUS: Currently awaiting translation into French and German so it can go out for Draft International Standard (DIS) vote by all the nations of ISO by December 2000
ISO 14644-3 places emphasis on the 14 recommended tests used to characterize cleanrooms and clean zones:
- airborne particle count for classification
- airborne particle count for ultrafine particles
- airborne particle count for macroparticles
- air pressure difference
- installed filter system leakage
- flow visualization
- air flow direction
- electrostatic and ion generator
- particle deposition
- containment leak
As identified in ISO 14644-1 and ISO 14644-2, some of these tests are mandatory and most are voluntary. The key controlling factor is the quality level the cleanroom owner desires and what measurements are necessary to help achieve that level.
The overall emphasis of these tests and their metrology is performance. We build and operate clean space to specific performance criteria to achieve a quality standard determined by end-user needs.
ISO 14644-3 does not specifically address measurements on products or processes in cleanrooms. Rather it covers the cleanroom performance characteristics that lead to the ability to measure product and process quality levels desired by the cleanroom owner.
Of the 14 recommended cleanroom qualification tests, choice of which tests will apply to a particular cleanroom is per agreement between buyer and seller.
There are three major annexes in ISO 14644-3. Annex A is by far the most user-friendly, for it lists all the recommended tests and provides a means of defining the sequence in which these tests are to be utilized in classifying and qualifying a cleanroom or clean zone.
Annex B details the individual test methods so there can be no misunderstanding between customer and supplier. This is important. Over 60 percent of the pages of ISO 14644-3 are contained in Annex B. Each test method is carefully described. How the test is conducted, any test limitations, and how the test data is reported are given here.
Annex C of ISO 14644-3 lists all the test instrumentation used by the 14 recommended tests. The performance parameters for each instrument are given, including the sensitivity limits, measuring range, acceptable error, response time, calibration interval, counting efficiency and data display.
For example, particle counting can be accomplished by utilizing a discrete particle counter, a condensation nucleus counter, a cascade impactor, a time-of-flight particle instrument or a piezo-balance impactor. You can find details of which instrument and test method is applicable to your need in Annex B and Annex C.
It is important to have clearly defined test methods and metrology when the value of a significant investment such as a cleanroom project must rest on very specific referee performance criteria. ISO 14644-3 provides these referee test methods, thereby providing stability and global uniformity to the base performance criteria for world class cleanrooms and clean zones.
The ISO 14644-6 document answers questions such as: “What is a cleanroom?” “What is a clean zone?” “How do you define an airborne particle?”
TITLE: Cleanrooms and associated controlled environmentsPart 6: Terms, definitions, & units
SCOPE: Defines those terms that require more specific description than is found in normal dictionary sources
STATUS: Will be sent out for DIS vote by all the nations of ISO in early 2001 ISO 14644-6 is the repository of all the common terms, definitions and units used in all the other ISO 14644 and ISO 14698 documents pertaining to cleanrooms and associated controlled environments.
It is a database of terms that is applicable to the new family of ISO cleanroom standards. Currently there are 162 entries in this database with more to be added before its publication. It has been important to harmonize these definitions so they have uniformity of meaning across these new cleanroom standards.
This 26-page standard is divided into two main sections. Annex A alphabetically lists all terms and definitions. Annex B lists these same terms and definitions by major category affinity group. For example, there are 23 specific terms listed under Biological Measurement. There are another 29 terms listed under Particle Measurement.
Both ISO 14644-3 and ISO 14644-6 are cross-referenced to the entire family of ISO cleanroom standards. This enables ease of use and clarity of terminology. It also provides a comfort level based upon specific performance criteria keyed to scientific baselines. Both of these documents are important assets for understanding the new family of ISO cleanroom standards.
Copies of these documents may be obtained for a nominal fee from the Institute of Environmental Sciences & Technology, 940 East Northwest Highway, Mt. Prospect, IL 60059 Phone: (847) 255-1561, Fax: (847) 255-1699. E-mail: [email protected].
Richard A. Matthews is founder of Filtration Technology Inc. (Greensboro, NC) and president of Micron Video International. He is chairman of the International Organization for Standardization Technical Committee ISO/TC209.