Issue



ISO 14644-3 represents fresh approach setting the standard


01/01/2003







By Mike Fitzpatrick and Ken Goldstein, Ph.D.

While the tone of some of the previous ISO documents has bordered on the autocratic, ISO/draft International Standard (DIS) 14644-3 represents a refreshing change in its approach. Instead of mandating methodologies, it merely offers a series of recommended tests and allows the user to determine which to use.

Some may consider ISO 14644-3 to be a rehash of material already adequately covered in Institute of Environmental Sciences and Technology (IEST; Rolling Meadows, Ill.) Recommended Practice (RP)-6.2 or the National Environmental Balancing Bureau's (NEBB; Gaithersburg, Md.) procedural standards for certified testing of cleanrooms. However, ISO 14644-3 provides material on topics not addressed in the previous standards and will prove a valuable tool when used in conjunction with ISO 14644-1 and ISO 14644-2.

ISO 14644-3 includes the typical ISO sections covering scope, normative references, terms and definitions followed by sections on testing procedures, documentation and the informative annexes.

Terms and definitions

The standard's "Section 3: Terms and Definitions" includes terminology associated with the testing methods and the hardware items used in these tests: optical particle counters; condensation nucleus counters; differential mobility analyzers; cascade impactors and witness plates. The list of definitions is both informative and timely. This section should not be overlooked.

If nothing else, terms and definitions help bridge the communication gap as the contamination control discipline develops and moves outward in a number of directions. At the same time, new technology is applied differentially—some new users see an immediate need and adopt new cleanroom technology, while other application areas decide not to utilize the newer technologies.

The result is that communication suffers as some of us begin to use different terms or, in some cases, use the same old term to describe something different. We should be able to arrive at a common terminology; the new ISO standard will certainly help us speak a common language.

Testing procedures

The standard's "Section 4: Testing Procedures" provides a table listing, including recommended tests, the corresponding test procedure (described in Annex B), the recommended instrumentation (described in Annex C) and the corresponding ISO standard that requires use of the test.

Readers of the document will immediately note the inclusion of tests for several environmental parameters beside airborne particle concentration. The term "cleanroom" implies control of airborne particle levels only, and any facility that meets this criterion is, by definition, a cleanroom.

However, most of us deal with rooms that require control of many other environmental parameters: temperature; humidity; air velocity; pressure; airflow uniformity and directionality. These additional parameters are not discussed in ISO 14644-1 or Federal Standard 209E. ISO 14644-3 describes these additional parameters and provides a uniform terminology and testing methodology that should be considered where these parameters are to be controlled.

Interestingly, the new standard is silent with respect to a few areas of concern in microelectronics facilities: radio frequency interference/electromagnetic interference (RFI/EMI), lighting wavelengths and levels, sound levels and vibration levels.

Principles and purposes

A particular strength of this standard is Section 4.2, which describes the principles and purposes behind each of the individual recommended tests. While ISO 14644-3 provides testing methodologies for 14 different parameters, all of the tests may not be appropriate for each particular cleanroom.

Section 4.2 describes the purpose for conducting each test, giving the reader guidance as to which tests are most appropriate for their specific facility. The recommended tests offered in ISO 14644-3 include:

  1. Airborne particle count for classification and test measurement of cleanrooms and clean air devices;
  2. Airborne particle count for ultrafine particles;
  3. Airborne particle count for macroparticles;
  4. Airflow;
  5. Air pressure difference;
  6. Installed filter system leakage;
  7. Airflow visualization;
  8. Airflow direction;
  9. Temperature;
  10. Humidity;
  11. Electrostatic and ion generator;
  12. Particle deposition;
  13. Recovery;
  14. Containment leak

Although most of these tests are familiar to those who use IEST RP-6.2 and NEBB, one new test not contained in those documents will be welcomed by many: Airborne Particle Count for Macroparticles. While many of us have been focused on making cleanrooms cleaner, some industries have been concerned with making cleanrooms dirtier.

By dirtier cleanrooms we mean those that control the airborne particle concentrations of particles larger than 5 microns. Hardly a week goes by that we don't hear, "I don't care about submicron particles. My process requires that I control 20-micron particles."

Spray-paint applicators, electro-platers, laminators and mushroom farmers of the world rejoice, for your voice has been heard. The Airborne Particle Count for Macroparticles test contained in ISO 14644-3 now allows you to classify your cleanroom based on particle sizes greater than 5 microns.

Documentation

No ISO standard would be complete without a section describing a lengthy documentation process. ISO 14644-3 will prove a disappointment to those ISO aficionados who feel that the main purpose of any standard is to generate a bunch of reports and kill a lot of trees. The documentation section is short and to the point, and its authors are to be commended.

As with other ISO 14644 standards, some of the most useful information is contained in the informative annexes. In 14644-3, these sections include: Annex A: Choice of recommended tests of an installation and the sequence in which to carry them out; Annex B: Recommendations for test methods; Annex C: Test Instrumentation (for the tests listed in Annex B); and Annex D: References.

ISO/DIS 14644-3 is a document that will be of interest to anyone who owns, operates or tests cleanrooms and is available from the IEST's Web site (www.iest.org). III

Michael A. Fitzpatrick is program director of microelectronics for Lockwood Greene. A senior member of the IEST, he is chairman for WG012 (Considerations in Cleanroom Design) and WG028 (Minienvironments).

Ken Goldstein is principal of Cleanroom Consultants Inc. in Phoenix, Ariz., and is a member of the CleanRooms Editorial Advisory Board.