ISO Enters Last Lap in Formalizing New Cleanroom Classifications

BY Susan English

Geneva, Switzerland — Headquarters for the International Organization for Standardization (ISO) has just released its new Draft International Standard (DIS) for cleanrooms and associated controlled environments. ISO/DIS 14644-1, “Cleanrooms and associated controlled environments, Part 1: Classification of airborne particulate cleanliness for cleanrooms and clean zones” establishes three new classes of cleanliness. It also prescribes the standard method of testing, and includes a procedure for determining the concentration of airborne particles by mathematical formulas. Both industry and regulatory interests provided the impetus for DIS, and its creation was marked by a spirit of global cooperation. It incorporates many of the “Recommended Practices” of the Institute of Environmental Sciences and much of Federal Standard 209E, while assigning new ISO classification levels of air cleanliness in cleanrooms and associated controlled environments. This “keystone” document is the first of 10 to be produced by ISO`s Working Group 209 (ISO/TC209) (See “ISO/TC209 Sets Global Cleanroom Standards” CleanRooms, Aug. 1996, p. 27).

Other documents will cover subjects such as cleanrom testing for compliance, biocontamination, metrology and test methods, cleanroom design and construction, cleanroom operations, minienvironments and isolators and terms, definitions and units. DIS 14644-1 is available for sale from the Institute of Environmental Sciences. It is presently out for review by all ISO member nations, and the deadline for receiving all comments is May. After a two-month period for incorporating those comments, it will be republished as a formal ISO Standard, which is expected to be this August.

Although non-mandatory, the ISO standard is significant in that it sets a universal standard for classifying cleanrooms, says TC209 committee chairman Dick Matthews.

The standard adds three new classes: ISO-1 (10 particles/m3 at 0.1&#181m), ISO-2 (100 particles/m3 at 0.1&#181m) to accommodate the trend toward more jam-packed chips and smaller wafer geometries; and ISO-9 (35,200,000 particles/m3 at 0.5 &#181m, which is intended to provide a guideline for the pharmaceutical industry in monitoring more gross particles, where the criteria is not as strict. ISO-1 and -2 would be comparable to a Federal Standard 209E Class 0.1 and a Class .01– if such classifications existed — says Matthews, while ISO-9 would be similar to a hypothetical Class 1,000,000.

ISO-1 and -2 sprang from the necessity of broadening the categories to accommodate changing technologies on the one hand and real world applications on the other. In the microelectronics industry, smaller and smaller line widths will mean monitoring for ultrafine particles in the nanometer range. ISO Class 9 is designed to facilitate better particle monitoring with powders and filling operations in the pharmaceutical industry. In addition, the standard offers something that does not exist in many other standards, and only to some extent in Federal Standard 209E: a procedure for calculating alternative levels of air cleanliness for particle populations not within the classification size range. Says Matthews: “Let`s say you have to control a 0.15 micron particle to so many units: the formula takes the particle size, the class you`re trying to get, and tells you how many particles you can have at that size in order to be at, say, ISO Class 3.” n