ASTM E2088-2006(2011) Standard Practice for Selecting Preparing Exposing and Analyzing Witness Surfaces for Measuring Particle Deposition in Cleanrooms and Associated Controlled En.pdf

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1、Designation: E2088 06 (Reapproved 2011)Standard Practice forSelecting, Preparing, Exposing, and Analyzing WitnessSurfaces for Measuring Particle Deposition in Cleanroomsand Associated Controlled Environments1This standard is issued under the fixed designation E2088; the number immediately following

2、the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is inten

3、ded to assist in the selection,preparation, exposure, and analysis of witness surfaces for thepurpose of characterizing particle deposition rates in clean-rooms and associated controlled environments, particularly foraerospace applications.1.2 Requirements may be defined in terms of particle sizedis

4、tribution and count, percent area coverage, or productperformance criteria such as optical transmission or scatter.Several choices for witness surfaces are provided.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of th

5、e user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 The values stated in SI units are to be regarded as thestandard.2. Referenced Documents (Note 1)2.1 ASTM Standards:2E1216 Practice for Sampling fo

6、r Particulate Contaminationby Tape LiftF24 Test Method for Measuring and Counting ParticulateContamination on SurfacesF312 Test Methods for Microscopical Sizing and CountingParticles from Aerospace Fluids on Membrane Filters2.2 ISO Standard:ISO 14644-1 Cleanrooms and Associated ControlledEnvironment

7、sPart 1: Classification of Air Cleanliness32.3 Government Standards:Fed-Std-209 Airborne Particulate Cleanliness Classes inCleanrooms and Clean Zones4IEST-STD-CC1246 Product Cleanliness Levels and Con-tamination Control Program5NOTE 1The Institute of Environmental Sciences and Technology hasseveral

8、Recommended Practices which may also be useful.3. Terminology3.1 Definitions:3.1.1 bidirectional reflectance distribution function(BRDF)the scattering properties of light reflected off sur-faces, expressed as the ratio of differential outputs of radiancedivided by differential inputs of radiance. Su

9、rface contami-nants scatter the incident radiation in all directions and withvariable intensities. The BRDF is a method to quantify thespatial distribution of the scattered energy.3.1.2 cleanliness levelan established maximum allowableamount of contamination in a given area or volume, or on acompone

10、nt.3.1.3 cleanrooman environmentally conditioned area inwhich temperature, humidity, and airborne contaminants arecontrolled by design and operation. High-efficiency particulateair (HEPA) filters or better are usually required to achieve theair cleanliness level. Air particulate cleanliness is class

11、ified inaccordance with or .3.1.4 contaminantunwanted molecular and particulatematter that could affect or degrade the performance of thecomponents upon which they reside.3.1.5 contaminationa process of contaminating.3.1.6 contamination controlorganized action to controlthe level of contamination.3.

12、1.7 controlled areaan environmentally controlled area,operated as a cleanroom, but without the final stage of HEPA(or better) filters used in cleanrooms.1This practice is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and is the direct responsibi

13、lity ofSubcommittee E21.05 on Contamination.Current edition approved Sept. 1, 2011. Published February 2012. Originallyapproved in 2000. Last previous edition approved in 2006 as E2088 06. DOI:10.1520/E2088-06(2011).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM

14、 Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Although Fed-Std-

15、209 has been cancelled, it still may be used and designationsin Fed-Std-209 may be used in addition to the ISO designations.5Available from Institute of Environmental Sciences and Technology (IEST),Arlington Place One, 2340 South Arlington Heights Road, Suite 100, ArlingtonHeights, IL 60005-4516, ht

16、tp:/www.iest.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.8 critical surfaceany surface of an item or productwhich is required to meet established cleanliness level require-ments.3.1.9 demonstrated equivalencethe condition

17、 in which amethod of measurement has passed a series of tests to showthat it gives equivalent results to those of a standard measure-ment.3.1.10 environmentally controlled areacleanrooms, con-trolled areas, good housekeeping areas, and other enclosuresthat are designed to protect hardware from conta

18、mination.Cleanliness is achieved by controlling air purity, temperature,humidity, materials, garments, and personnel activities.3.1.11 fibera particle 100 m in length with a length todiameter ratio of ten or more.3.1.12 image analysisthe measurement of size, shape,number, position, orientation, brig

19、htness, and other parametersof small objects using the combination of a microscope, animaging sensor, and a dedicated computer system. Imageanalysis can be used to perform particle counts or measureparticle dimensions automatically, with far greater accuracythan manual techniques.3.1.13 micrometre (

20、m)a unit of measurement equal toone millionth of a metre, or approximately 39 millionths of aninch, for example, 25 m is approximately 0.001 in. The term“micron” has been used but is not a recommended SI unit.3.1.14 nonvolatile residue (NVR)soluble material re-maining after evaporation of a filtered

21、 volatile fluid or precipi-tate from a gas phase, usually reported in milligrams per unitarea (or volume).3.1.15 particle depositionthe settling of airborne particlesonto surfaces resulting from electrostatic or dynamic condi-tions, or both, in cleanrooms or other controlled environments.3.1.16 part

22、icle fallout (PFO)a standard particle deposi-tion method used by the European aerospace community thatuses black glass witness surfaces and measures particle scatterin parts per million.63.1.17 particle size(1) the apparent maximum linear di-mension of a particle in the plane of observation, as obse

23、rvedwith an optical microscope; (2) the equivalent diameter of aparticle detected by automatic instrumentation. The equivalentdiameter is the diameter of a reference sphere having knownproperties and producing the same response in the sensinginstrument as the particle being measured; (3) the diamete

24、r ofa circle having the same area as the projected area of a particle,in the plane of observation, observed by image analysis; (4) thesize defined by the measurement technique and calibrationprocedure.3.1.18 particulate contaminationdiscrete mass of solidmatter, size often measured in micrometres (m

25、), whichadversely affects critical surfaces of component and hencesystem performance.3.1.19 percent area coverage (PAC)fraction of the sur-face that is covered by particles, reported in percent as totalparticle projected area divided by total area of the surface.3.1.20 precision cleaningcleaning of

26、hardware surfacesapproved by established facility methods or methods specifiedor provided by the customer with verification to a specifiedcleanliness level.3.1.21 visibly cleanabsence of particulate or molecularcontaminants when viewed from a specified distance withnormal (or corrected to normal) vi

27、sion with a specifiedillumination level.3.1.22 witness surface (WS)a contamination-sensitivematerial used instead of direct evaluation of a specific surfacewhen that surface is either inaccessible or is too sensitive to behandled.3.1.22.1 optical witness surface (OWS)witness surfacefrom which contam

28、inants may be analyzed by optical methods.3.1.22.2 particle witness surface (PWS)witness surfacefrom which particulate contaminants may be analyzed bystandard optical or electron microscopic methods.4. Summary of Practice4.1 Particle deposition in controlled environments is deter-mined by collecting

29、 particles on a clean witness surface for aspecified period of time or operational activity, then retrievingthe witness surface and quantifying the particle populationcollected.4.2 Witness surfaces (WS) are typically surfaces that lendthemselves to traditional microscopic or image analysis tech-niqu

30、es for sizing and counting particles on the surface, but maybe an optical surface that is evaluated on the basis of thechange in its optical properties or may be a witness surface thatbest represents the surface material of interest which issubsequently evaluated by extracting a sample from the surf

31、aceand sizing and counting particles removed from the witnesssurface.4.3 This practice does not address real time particle depo-sition measurements involving particle counters on site withcontinuous recording over a specified period of time.5. Significance and Use5.1 This practice provides a standar

32、d approach to measuringparticle deposition, or fallout, in cleanrooms and other con-trolled environments. It is based on the use of a witness surfaceto collect particles that deposit from the surrounding environ-ment and subsequently sizing and counting the particles byconventional methods. Several

33、options are introduced, withlimitations and guidelines for selecting the best choice for theintended application.5.2 This practice is applicable across numerous industriesincluding aerospace, microelectronics, and pharmaceuticals.6. Selecting Witness Surfaces6.1 Considerations for selecting WS inclu

34、de available meth-ods of analysis, precision and accuracy required, size ofparticles of concern, actual material of critical surfaces ofconcern, and cost. Preferably, the WS should be a surfacematerial which best represents the actual critical surface and6The Euramark Model 255 PFO photometer has be

35、en found to be satisfactory.The sole source of supply of the apparatus known to the committee at this time isEuramark, 834 East Rand Rd., Unit 6, Box 823, Mt. Prospect, IL 60056. If you areaware of alternative suppliers, please provide this information to ASTM Interna-tional Headquarters. Your comme

36、nts will receive careful consideration at a meetingof the responsible technical committee,1which you may attend.E2088 06 (2011)2should be analyzed using the method which best represents theactual performance characteristics of interest. Additionally,certain surfaces may become charged, especially in

37、 dry envi-ronments, and this charging can effect the particle deposition.If WS are to monitor a vacuum environment they must be madeof low-outgassing, vacuum-compatible materials and heldsecurely in vacuum-compatible, low-particle shedding holders.6.2 Microscopic EvaluationWhen microscopic sizing an

38、dcounting of particles is the planned method of analysis, selectone of the following PWS, each of which is easily evaluateddirectly after exposure. Microscopic sizing and counting shallbe performed in accordance with Method F24 or Test MethodsF312.6.2.1 Membrane Filters, should be gridded for ease i

39、nmicroscopic particle counting and precleaned before exposure.Amembrane filter can be prepared as either a tacky or tack-freesurface. The membrane filter is cleaned and then either (1)immediately placed in a cleaned petri dish, (2) dipped intotrichloroethylene or methyl chloroform first so it will f

40、use tothe plastic petri dish, or (3) dipped into a prefiltered tackyadhesive and dried in a cleaned petri dish. The petri dish is thencovered and transported to the area being tested.6.2.2 Gridded Counting Slides, such as those used in Prac-tice E1216 may be used as WS. After exposure, a pressure-se

41、nsitive tape is applied to the slide to encapsulate thedeposited particles before moving them to a microscope foranalysis.6.2.3 Stainless or Other Surfaces, other materials may beselected as WS based on specific needs for durability or to bestrepresent the actual surface materials of interest. For t

42、hesePWS, particles are subsequently extracted from the surfacewith a fluid, filtered to collect the particles on a griddedmembrane, and subsequently analyzed microscopically. Note,the efficiency of the extraction method must be known orestimated.6.3 Other Particle Sizing and Counting MethodsParticle

43、characterization can also be performed using optical measure-ments other than manual microscopic methods. Highly pol-ished surfaces serve as WS and are selected based on theanalysis method chosen.6.3.1 The PFO instrument uses a smooth black glass plate40 by 45 mm protected from unintentional sedimen

44、tation by aplate holder. The effective sampling surface is circular with adiameter of 25 mm.6.3.2 Silicon wafers or disks shall be selected for imageanalysis or other surface scanning methods.6.4 Optical Witness Surfaces, (that is, mirrors or lenses)shall be selected to best represent the critical s

45、urface of interestin the environment being evaluated. Reflectance or transmis-sion measurements shall be made in the wavelengths ofinterest, and the OWS must be the correct size and shape forthe instrumentation planned for use.6.5 Gravimetric MethodsA gravimetric method can alsobe used, whereby a la

46、rge witness surface is rinsed with solventto extract the particles, filtered onto a dry, preweighed mem-brane filter, and then dried and reweighed on a laboratorybalance with a resolution of 0.01 mg. The difference in weightcan be a relative quantitative analysis of deposition based onweight. Note,

47、the efficiency of the extraction method must beknown or estimated. A preweighed membrane filter could alsobe used as the witness surface thus eliminating the extractionstep. Additionally, a quartz crystal microbalance with adhesivesurfaces can measure accumulated mass in situ.7. Preparation of Witne

48、ss Surfaces7.1 Witness Surface HoldersHolders should be designedto retain the witness surface securely and maximize the surfaceexposure. They should be made from smooth, cleanablematerials such as plastic, anodized aluminum, or stainless steel.A noncontact, easily removable, protective cover is requ

49、iredwhich prevents the collection of particulate contaminationduring transport of the surfaces between the test laboratory andthe controlled environment being evaluated. Holders shouldhave captive fasteners and tethers to prevent the holder orassociated hardware from impacting critical surfaces ifdropped. Holders should also be designed to be secured in thefacility being evaluated in either a vertical or horizontalorientation.7.2 Cleaning of HoldersHolders should be precisioncleaned in accordance with IEST-STD-CC1246 Level 100 orclean before inst