IEST G-CC035 1-2009 Design Considerations for Airborne Molecular Contamination Filtration Systems in Cleanrooms and Other Controlled Environments.pdf

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1、 Institute of Environmental Sciences and Technology Contamination Control Division IEST-G-CC035.1 Guideline CC035.1 Design Considerations for Airborne Molecular Contamination Filtration Systems in Cleanrooms and Other Controlled Environments Arlington Place One 2340 S. Arlington Heights Road, Suite

2、100 Arlington Heights, IL 60005-4516 Phone: (847) 981-0100 Fax: (847) 981-4130 E-mail: iestiest.org Web: www.iest.org 2 Copyrighted material Institute of Environmental Sciences and Technology IEST-G-CC035.1 IEST-G-CC035.1 Institute of Environmental Sciences and Technology Copyrighted material 3 This

3、 Guideline is published by the Institute of Environmental Sciences and Technology to advance the technical and engineering sciences. Use of this document is entirely voluntary, and determination of its applicability and suitability for any particular use is solely the responsibility of the user. Thi

4、s Guideline was prepared by and is under the jurisdiction of Working Group 035 of the IEST Contamination Con-trol Division. Copyright 2009 by the Institute of Environmental Sciences and Technology First printing, July 2009 ISBN 978-0-9787868-8-5 PROPOSAL FOR IMPROVEMENT: The Working Groups of the In

5、stitute of Environmental Sciences and Tech-nology are continually working on improvements to their Recommended Practices and Reference Documents. Suggestions from users of these documents are welcome. If you have a suggestion regarding this document, please use the online Proposal for Improvement fo

6、rm found on the IEST website at www.iest.org. Institute of Environmental Sciences and Technology Arlington Place One 2340 S. Arlington Heights Road, Suite 100 Arlington Heights, IL 60005-4516 Phone: (847) 981-0100 Fax: (847) 981-4130 E-mail: iestiest.org Web: www.iest.org 4 Copyrighted material Inst

7、itute of Environmental Sciences and Technology IEST-G-CC035.1 IEST-G-CC035.1 Institute of Environmental Sciences and Technology Copyrighted material 5 Design Considerations for Airborne Molecular Contamination Filtration Systems in Cleanrooms and Other Controlled Environments IEST-G-CC035.1 CONTENTS

8、 SECTION 1 SCOPE AND LIMITATIONS . 7 2 REFERENCES 7 3 TERMS AND DEFINITIONS . 7 4 BACKGROUND . 9 5 FILTER DESIGNS 13 6 SYSTEM DESIGN 16 7 SYSTEM PERFORMANCE EVALUATION 19 FIGURE 1 EXAMPLES OF LOCATIONS FOR AMC FILTRATION SYSTEMS 11 A1 RELATIONSHIP BETWEEN CHALLENGE, BREAKTHROUGH, AND PENETRATION 21

9、A2 RELATIONSHIP BETWEEN PENETRATION, EFFICIENCY, END POINT, AND CAPACITY . 22 TABLE 1 ACTIVATED CARBON CHARACTERISTICS . 13 2 LOADED NONWOVEN CHARACTERISTICS . 15 3 FILTER CONSTRUCTION COMPARISON . 15 APPENDIX A BASICS OF AMC REMOVAL 20 B BIBLIOGRAPHY . 23 6 Copyrighted material Institute of Environ

10、mental Sciences and Technology IEST-G-CC035.1 IEST-G-CC035.1 Institute of Environmental Sciences and Technology Copyrighted material 7 Institute of Environmental Sciences and Technology Contamination Control Division Guideline 035.1 Design Considerations for Airborne Molecular Contamination Filtrati

11、on Systems in Cleanrooms and Other Controlled Environments IEST-G-CC035.1 1 SCOPE AND LIMITATIONS 1.1 Scope This Guideline describes areas of concern when consi-dering filtration systems that will be effective in elimi-nating trace amounts of airborne molecular contamination (AMC), here defined as l

12、ess than 1 part per million by volume (ppmv), from the air supplied to cleanrooms and other controlled environments. This document discusses various applications, potential points of use, filtration methods, materials of construc-tion, performance comparison, and follow-up assess-ment, secondary imp

13、acts of the filters on the rest of the heating, ventilating and air-conditioning (HVAC) sys-tem, and exterior impacts on the filtration system (in-cluding environmental conditions, upsets, and spills). The Guideline establishes the types of information required to design and implement an effective A

14、MC filtration system. While this document is targeted at cleanroom facilities, it could also provide a framework for other applications such as, but not limited to, lami-nar flow stations, minienvironments, isolators, and glove boxes. 1.2 Limitations Because of the large number of combinations of va

15、-riables, this document does not attempt to recommend specific filtration systems or filtration media for each application. This Guideline does not establish a test standard, although several applicable standards are referenced. This Guideline is not intended to address microbiological issues, radio

16、active issues, pollution control issues, or emergency response and safety sys-tems. Nor does this Guideline deal with respirators, as accepted test methods and standards exist for these devices. 2 REFERENCES 2.1 Reference documents The following documents are incorporated into this Guideline to the

17、extent specified herein. Users should apply the most recent editions of the references. IEST-RP-CC007: Testing ULPA Filters IEST-RP-CC031: Method for Characterizing Out-gassed Organic Compounds from Cleanroom Mate-rials and Components 2.2 Sources and addresses IEST Institute of Environmental Science

18、s and Technology Arlington Place One 2340 S. Arlington Heights Road, Suite 100 Arlington Heights, IL 60005-4516 Phone: (847) 981-0100 Fax (847) 981-4130 www.iest.org 3 TERMS AND DEFINITIONS Some terms are defined here for the purposes of this Guideline. If definitions are not provided, common usage

19、shall apply. absorption The attraction of a contaminant to a sorbent surface and the incorporation of the contaminant into the structure of the sorbent (e.g., water absorbing into a superabsorbent powder). acid A corrosive material that reacts chemically as an electron pair acceptor. 8 Copyrighted m

20、aterial Institute of Environmental Sciences and Technology IEST-G-CC035.1 activated Describing an adsorbent whose surface area has been extended through the creation of pores or other inter-nal openings. adsorption The attraction of a contaminant to a surface, includ-ing inner pore surfaces, of a me

21、dium by physical forces (e.g., van der Waals forces), where the conta-minant remains on the surface of the sorbent. airborne molecular contamination (AMC) Contamination present in the air in a gaseous state, as opposed to a liquid-droplet or solid-particle aerosol. NOTE: This definition is specific

22、to this Guideline, which deals with systems designed to remove ga-seous contaminants and control odor for the comfort of occupants. ambient air Air that is common to the particular environment of interest. For this Guideline, ambient air may be air at atmospheric pressure, uncontrolled, or condition

23、ed and controlled for temperature and humidity. base A corrosive material that reacts chemically as an electron pair donor. breakthrough (see also penetration) The measurable concentration of a specific contami-nant downstream of a filter system, usually expressed in absolute concentration units. Th

24、e ability to detect breakthrough depends on the detection limit of the measurement technique. A breakthrough curve is a continuous plot of contaminant breakthrough vs. time. bypass The deliberate or unintentional diversion of air around the filter medium in a filtration system. capacity The cumulati

25、ve amount of contaminant that is re-moved by a filter system within a specified time pe-riod or at a specified efficiency level. catalyst Any substance of which a small proportion notably affects the rate of a chemical reaction without itself being consumed or undergoing a chemical change. NOTE: Mos

26、t catalysts accelerate reactions, but a few retard them (inhibitors). challenge The AMC or mixture of AMCs upstream or at the inlet of a filtration system, either introduced inten-tionally for a test, or present in the actual application. channeling The disproportionately greater flow of gas through

27、 passages of lower resistance that can occur in fixed beds or columns of granular media due to nonuni-form packing, granule segregation, irregular sizes and shapes of the media, gas pockets, wall effects, and other causes. chemisorption (chemical adsorption) Chemical bonding of a molecular contamina

28、nt to a solid surface or to a chemical on that surface. cleanroom A room in which the concentration of airborne par-ticles, molecular contaminants, or both, are controlled to specified limits. concentration The quantity of one substance dispersed in a defined amount of another. For AMCs, two common

29、conven-tions are defined as weight per volume (e.g., g/m3) or volume per volume (e.g., ppbv). condensable A substance (other than water), typically having a boiling point above room temperature at atmospheric pressure, capable of condensation on a clean surface. contaminant Any unwanted substance pr

30、esent in or on a material or any surface within a clean zone. desorption The process by which adsorbed materials leave the substrates on which they are adsorbed and reenter the airflow. diffusion, molecular A process of spontaneous intermixing of different substances attributable to molecular motion

31、 (Brow-nian motion) and tending to produce uniformity of concentration. efficiency The fraction of a specific contaminant that is re-moved by the filter system, usually expressed as a percentage. efficiency curve A continuous plot of contaminant removal efficiency against time. end point The occurre

32、nce of the maximum permissible concen-tration of a specific contaminant in the air down-stream of a filter system. Also, the time when a pre-determined contaminant penetration or efficiency is reached. IEST-G-CC035.1 Institute of Environmental Sciences and Technology Copyrighted material 9 face velo

33、city The speed of the airflow across the cross-sectional area (perpendicular to the airflow) of a filter at the upstream side of the filter. filter A device or system used to remove contaminants from a gas flowing through it. impregnation Adding one or more chemicals (impregnants) to a surface in or

34、der to enhance the removal of selected molecular species from a gas. medium (plural: media) The filtering material in a filter; an adsorbent or che-misorbent used to remove airborne molecular conta-minants. Alternatively, a material containing an adsorbent or chemisorbent. minienvironment An environ

35、ment that provides localized control of airborne contaminants by means of an enclosure de-signed to isolate product-handling areas from person-nel and the surrounding room environment. outgassing The release of any gas-phase compound (e.g., conta-minant) from a solid surface; typically accelerated b

36、y heating, reducing pressure, or increasing flow. penetration The ratio of downstream concentration to challenge concentration of a specific contaminant for a filter system, expressed as a percentage. Related to effi-ciency by the expression: % Penetration = 100% - % Efficiency. pressure drop The di

37、fference in pressure between two points in an airflow system upstream and downstream of a filter system. residence time The theoretical time that an increment of gas is with-in the boundaries of the filters media. Calculated by the following expression: Residence time = Volume-tric flow / volume of

38、filter media in the filter system. shedding The generation and release of particles from the filter system into an airflow. volatile organic compound (VOC) An organic material, such as a solvent, that has a sig-nificant vapor pressure at ambient temperature and pressure; i.e., a significant portion

39、of the material is present as a vapor at equilibrium. Abbreviations AMC airborne molecular contamination FFU fan-filter unit HEPA high efficiency particulate air HVAC heating, ventilating, and air-conditioning MAH make-up air handler RAH recirculation air handler ppbv parts per billion (109) by volu

40、me (for an ideal gas equivalent to parts per billion molar) ppmv parts per million (106) by volume (for an ideal gas equivalent to parts per million molar) ULPA ultra-low-penetration air VOC volatile organic compound 4 BACKGROUND 4.1 Applications for AMC filtration The need for AMC control may apply

41、 to odor control, safety requirements, process yield improvements, and other situations. The level of required performance will determine the type of filter system acceptable for the application. This Guideline primarily addresses the removal of contaminants that are present in trace amounts (typica

42、lly 2 mm) are used in this format to minimize pressure drop. Care should be taken when filling the container to achieve a tightly packed bed. Otherwise, channeling or bypass of the contaminated air can occur. A variant of this for-mat, the “honeycomb” panel, uses separators within the container to k

43、eep sorbent particles from shifting during installation or use. Downstream dust filtration is required to control shedding from attrition of sorbent particles. There is no coverage of the surface area by adhesives or binders, but tight packing of irregularly shaped granules can effectively close off

44、 sections from direct contact with the contaminated air stream. 5.2.2 Bonded granular This format is essentially a loose granular bed where the sorbent granules or pellets have been cemented together to form a solid block or panel. This format makes handling of the sorbent easier than with a loose b

45、ed for installation and change-out. No container is necessary and there is essentially no shedding down-stream of the filter system. Bonded panels can be brit-tle and must be handled appropriately during shipping and installation to avoid breakage. Here again, larger granules or extruded pellets are

46、 used to minimize pressure drop, though pressure drop is generally higher for the same type and depth of sorbent than with a loose granular media. Different binding technologies are available, but all will cover some por-tion of the active surface area of the sorbent. Channe-ling is not a concern be

47、cause the granules or pellets are IEST-G-CC035.1 Institute of Environmental Sciences and Technology Copyrighted material 15 held in place. Bypass is eliminated by proper sealing at the edges of the panel. 5.2.3 Loaded nonwoven This is perhaps the most diverse group of filter media. All varieties inv

48、olve attaching sorbent particles to a nonwoven structure by some means to provide an easy-to-handle media for building a filter. This helps with installation and change-out while avoiding the weight and brittleness of the bonded panels. The two primary differences between the various products are th

49、e type of nonwoven technology used and the method of attaching the sorbent particles. Some of the common variants of each are shown in Table 2; there are many possible combinations. Table 2. Loaded Nonwoven Characteristics Nonwovens Sorbent Attachment Spunbond Adhesive Powder Meltblown Binder Slurry Carded Spray Adhesive Airlaid Adhesive Webs/Fabrics Wetlaid Bicomponent Fiber Foam A variety of sorbent particle sizes and loadings are used. Different attachment methods provide coverage of the active surface area ranging from 1% to 70%. Products