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

1、Designation: E 2088 06Standard Practice forSelecting, Preparing, Exposing, and Analyzing WitnessSurfaces for Measuring Particle Deposition in Cleanroomsand Associated Controlled Environments1This standard is issued under the fixed designation E 2088; the number immediately following the designation

2、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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is intended to assist i

3、n 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 sizedistribution and c

4、ount, 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 the user of this

5、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:2E 1216 Practice for Sampling for Particulate

6、Contaminationby Tape LiftF24 Test Method for Measuring and Counting ParticulateContamination on SurfacesF 312 Test Methods for Microscopical Sizing and CountingParticles from Aerospace Fluids on Membrane Filters2.2 ISO Standard:ISO 14644-1 Cleanrooms and Associated ControlledEnvironmentsPart 1: Clas

7、sification 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 Recommended P

8、ractices 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. Surface contami

9、-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 acomponent.3.1.3 clea

10、nrooman 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 classified inaccor

11、dance with FED-STD-209 or ISO 14644-1.3.1.4 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 contam

12、ination.3.1.7 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 direct resp

13、onsibility ofSubcommittee E21.05 on Contamination.Current edition approved April 1, 2006. Published April 2006. Originallyapproved in 2000. Last previous edition approved in 2000 as E 2088 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at ser

14、viceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute, 25 W. 43rd St., 4thFloor, New York, NY 10036.4Although Fed-Std-209 has been cancelled, it still may be used and de

15、signationsin Fed-Std-209 may be used in addition to the ISO designations.5Available from the Institute of Environmental Sciences and Technology, 5005Newport Dr., Suite 506, Rolling Meadows, IL 60008.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,

16、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 in which amethod of measurement has passed a series of tests to showthat it gives equivalent results to those of a st

17、andard measure-ment.3.1.10 environmentally controlled areacleanrooms, con-trolled areas, good housekeeping areas, and other enclosuresthat are designed to protect hardware from contamination.Cleanliness is achieved by controlling air purity, temperature,humidity, materials, garments, and personnel a

18、ctivities.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, brightness, and other parametersof small objects using the combination of a microscope, animaging sensor, and a dedicated

19、computer system. Imageanalysis can be used to perform particle counts or measureparticle dimensions automatically, with far greater accuracythan manual techniques.3.1.13 micrometre (m)a unit of measurement equal toone millionth of a metre, or approximately 39 millionths of aninch, for example, 25 m

20、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 volatile fluid or precipi-tate from a gas phase, usually reported in milligrams per unitarea (or volume).3.1.15 parti

21、cle depositionthe settling of airborne particlesonto surfaces resulting from electrostatic or dynamic condi-tions, or both, in cleanrooms or other controlled environments.3.1.16 particle fallout (PFO)a standard particle deposi-tion method used by the European aerospace community thatuses black glass

22、 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 observedwith an optical microscope; (2) the equivalent diameter of aparticle detected by automatic instrumentation. The eq

23、uivalentdiameter is the diameter of a reference sphere having knownproperties and producing the same response in the sensinginstrument as the particle being measured; (3) the diameter ofa circle having the same area as the projected area of a particle,in the plane of observation, observed by image a

24、nalysis; (4) thesize defined by the measurement technique and calibrationprocedure.3.1.18 particulate contaminationdiscrete mass of solidmatter, size often measured in micrometres (m), whichadversely affects critical surfaces of component and hencesystem performance.3.1.19 percent area coverage (PAC

25、)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 hardware surfacesapproved by established facility methods or methods specifiedor provided by the customer with verific

26、ation to a specifiedcleanliness level.3.1.21 visibly cleanabsence of particulate or molecularcontaminants when viewed from a specified distance withnormal (or corrected to normal) vision with a specifiedillumination level.3.1.22 witness surface (WS)a contamination-sensitivematerial used instead of d

27、irect 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 contaminants may be analyzed by optical methods.3.1.22.2 particle witness surface (PWS)witness surfacefrom which particulate

28、 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 particles on a clean witness surface for aspecified period of time or operational activity, then retrievingthe witnes

29、s surface and quantifying the particle populationcollected.4.2 Witness surfaces (WS) are typically surfaces that lendthemselves to traditional microscopic or image analysis tech-niques for sizing and counting particles on the surface, but maybe an optical surface that is evaluated on the basis of th

30、echange 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 surfaceand sizing and counting particles removed from the witnesssurface.4.3 This practice does not address real time part

31、icle 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 standard approach to measuringparticle deposition, or fallout, in cleanrooms and other con-trolled environments. It is based

32、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 options are introduced, withlimitations and guidelines for selecting the best choice for theintended application.5.2 T

33、his practice is applicable across numerous industriesincluding aerospace, microelectronics, and pharmaceuticals.6. Selecting Witness Surfaces6.1 Considerations for selecting WS include available meth-ods of analysis, precision and accuracy required, size ofparticles of concern, actual material of cr

34、itical 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 been found to be satisfactory.The sole source of supply of the apparatus known to the committee at this time isEuramark,

35、 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 comments will receive careful consideration at a meetingof the responsible technical committee,1which you may attend.E208806

36、2should be analyzed using the method which best represents theactual performance characteristics of interest. Additionally,certain surfaces may become charged, especially in dry envi-ronments, and this charging can effect the particle deposition.If WS are to monitor a vacuum environment they must be

37、 madeof low-outgassing, vacuum-compatible materials and heldsecurely in vacuum-compatible, low-particle shedding holders.6.2 Microscopic EvaluationWhen microscopic sizing andcounting of particles is the planned method of analysis, selectone of the following PWS, each of which is easily evaluateddire

38、ctly after exposure. Microscopic sizing and counting shallbe performed in accordance with Method F 24 or Test MethodsF 312.6.2.1 Membrane Filters, should be gridded for ease inmicroscopic particle counting and precleaned before exposure.Amembrane filter can be prepared as either a tacky or tack-free

39、surface. 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 fuse tothe plastic petri dish, or (3) dipped into a prefiltered tackyadhesive and dried in a cleaned petri dish. The petri dis

40、h is thencovered and transported to the area being tested.6.2.2 Gridded Counting Slides, such as those used in Prac-tice E 1216 may be used as WS. After exposure, a pressure-sensitive tape is applied to the slide to encapsulate thedeposited particles before moving them to a microscope foranalysis.6.

41、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 thesePWS, particles are subsequently extracted from the surfacewith a fluid, filtered to collect the particles on a griddedme

42、mbrane, and subsequently analyzed microscopically. Note,the efficiency of the extraction method must be known orestimated.6.3 Other Particle Sizing and Counting MethodsParticlecharacterization can also be performed using optical measure-ments other than manual microscopic methods. Highly pol-ished s

43、urfaces 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 sedimentation by aplate holder. The effective sampling surface is circular with adiameter of 25 mm.6.3.2 Silicon wafers or disks sh

44、all 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 surface of interestin the environment being evaluated. Reflectance or transmis-sion measurements shall be made in the wavelen

45、gths 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 large witness surface is rinsed with solventto extract the particles, filtered onto a dry, preweighed mem-brane filter, and th

46、en 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, the efficiency of the extraction method must beknown or estimated. A preweighed membrane filter could alsobe used as the wit

47、ness surface thus eliminating the extractionstep. Additionally, a quartz crystal microbalance with adhesivesurfaces can measure accumulated mass in situ.7. Preparation of Witness Surfaces7.1 Witness Surface HoldersHolders should be designedto retain the witness surface securely and maximize the surf

48、aceexposure. They should be made from smooth, cleanablematerials such as plastic, anodized aluminum, or stainless steel.A noncontact, easily removable, protective cover is requiredwhich prevents the collection of particulate contaminationduring transport of the surfaces between the test laboratory a

49、ndthe 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 installing the witness surface. It is recommendedthat cleaning and packaging be performed in an ISO 14644Class M3.5 (FED-STD-209 Cla