ASTM E2088-06(2011)

Standard Practice for Selecting, Preparing, Exposing, and Analyzing Witness Surfaces for Measuring Particle Deposition in Cleanrooms and Associated Controlled Environments

SIGNIFICANCE AND USE
This practice provides a standard approach to measuring particle deposition, or fallout, in cleanrooms and other controlled environments. It is based on the use of a witness surface to collect particles that deposit from the surrounding environment and subsequently sizing and counting the particles by conventional methods. Several options are introduced, with limitations and guidelines for selecting the best choice for the intended application.
This practice is applicable across numerous industries including aerospace, microelectronics, and pharmaceuticals.
SCOPE
1.1 This practice is intended to assist in the selection, preparation, exposure, and analysis of witness surfaces for the purpose of characterizing particle deposition rates in cleanrooms and associated controlled environments, particularly for aerospace applications.
1.2 Requirements may be defined in terms of particle size distribution and count, percent area coverage, or product performance criteria such as optical transmission or scatter. Several choices for witness surfaces are provided.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Aug-2011
• ICS: 13.040.35 - Cleanrooms and associated controlled environments
• Technical Committee: E21 - Space Simulation and Applications of Space Technology
• Drafting Committee: E21.05 - Contamination

Relations

• Replaces: ASTM E2088-06 - Standard Practice for Selecting, Preparing, Exposing, and Analyzing Witness Surfaces for Measuring Particle Deposition in Cleanrooms and Associated Controlled Environments
• Effective Date: 01-Sep-2011
• Referred By: ASTM E2312-11(2019) - Standard Practice for Tests of Cleanroom Materials
• Effective Date: 01-Sep-2011
• Referred By: ASTM E2352-19 - Standard Practice for Aerospace Cleanrooms and Associated Controlled Environments—Cleanroom Operations
• Effective Date: 01-Sep-2011
• Referred By: ASTM E2217-12(2019) - Standard Practice for Design and Construction of Aerospace Cleanrooms and Contamination Controlled Areas
• Effective Date: 01-Sep-2011

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2088 − 06(Reapproved 2011)
Standard Practice for
Selecting, Preparing, Exposing, and Analyzing Witness
Surfaces for Measuring Particle Deposition in Cleanrooms
and Associated Controlled Environments
This standard is issued under the fixed designation E2088; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ISO Standard:
ISO 14644-1 Cleanrooms and Associated Controlled
1.1 This practice is intended to assist in the selection,
Environments—Part 1: Classification of Air Cleanliness
preparation, exposure, and analysis of witness surfaces for the
2.3 Government Standards:
purpose of characterizing particle deposition rates in clean-
Fed-Std-209 Airborne Particulate Cleanliness Classes in
rooms and associated controlled environments, particularly for
Cleanrooms and Clean Zones
aerospace applications.
IEST-STD-CC1246 Product Cleanliness Levels and Con-
1.2 Requirements may be defined in terms of particle size
tamination Control Program
distribution and count, percent area coverage, or product
NOTE 1—The Institute of Environmental Sciences and Technology has
performance criteria such as optical transmission or scatter.
several Recommended Practices which may also be useful.
Several choices for witness surfaces are provided.
3. Terminology
1.3 The values stated in SI units are to be regarded as
3.1 Definitions:
standard. No other units of measurement are included in this
3.1.1 bidirectional reflectance distribution function
standard.
(BRDF)—the scattering properties of light reflected off
1.4 This standard does not purport to address all of the
surfaces, expressed as the ratio of differential outputs of
safety concerns, if any, associated with its use. It is the
radiance divided by differential inputs of radiance. Surface
responsibility of the user of this standard to establish appro-
contaminants scatter the incident radiation in all directions and
priate safety and health practices and determine the applica-
withvariableintensities.TheBRDFisamethodtoquantifythe
bility of regulatory limitations prior to use.
spatial distribution of the scattered energy.
3.1.2 cleanliness level—an established maximum allowable
2. Referenced Documents (Note 1)
amount of contamination in a given area or volume, or on a
2.1 ASTM Standards:
component.
E1216 Practice for Sampling for Particulate Contamination
3.1.3 cleanroom—an environmentally conditioned area in
by Tape Lift
which temperature, humidity, and airborne contaminants are
F24 Test Method for Measuring and Counting Particulate
controlled by design and operation. High-efficiency particulate
Contamination on Surfaces
air (HEPA) filters or better are usually required to achieve the
F312 Test Methods for Microscopical Sizing and Counting
air cleanliness level. Air particulate cleanliness is classified in
Particles from Aerospace Fluids on Membrane Filters
accordance with Fed-Std-209 or ISO 14644-1.
3.1.4 contaminant—unwanted molecular and particulate
matter that could affect or degrade the performance of the
This practice is under the jurisdiction of ASTM Committee E21 on Space
components upon which they reside.
Simulation andApplications of Space Technology and is the direct responsibility of
Subcommittee E21.05 on Contamination.
Current edition approved Sept. 1, 2011. Published February 2012. Originally Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
approved in 2000. Last previous edition approved in 2006 as E2088 – 06. DOI: 4th Floor, New York, NY 10036, http://www.ansi.org.
10.1520/E2088-06(2011). Although Fed-Std-209 has been cancelled, it still may be used and designations
For referenced ASTM standards, visit the ASTM website, www.astm.org, or in Fed-Std-209 may be used in addition to the ISO designations.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Available from Institute of Environmental Sciences and Technology (IEST),
Standards volume information, refer to the standard’s Document Summary page on Arlington Place One, 2340 South Arlington Heights Road, Suite 100, Arlington
the ASTM website. Heights, IL 60005-4516, http://www.iest.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2088 − 06 (2011)
3.1.5 contamination—a process of contaminating. instrument as the particle being measured; (3) the diameter of
a circle having the same area as the projected area of a particle,
3.1.6 contamination control—organized action to control
intheplaneofobservation,observedbyimageanalysis;(4)the
the level of contamination.
size defined by the measurement technique and calibration
3.1.7 controlled area—an environmentally controlled area,
procedure.
operated as a cleanroom, but without the final stage of HEPA
3.1.18 particulate contamination—discrete mass of solid
(or better) filters used in cleanrooms.
matter, size often measured in micrometres (µm), which
3.1.8 critical surface—any surface of an item or product
adversely affects critical surfaces of component and hence
which is required to meet established cleanliness level require-
system performance.
ments.
3.1.19 percent area coverage(PAC)—fractionofthesurface
3.1.9 demonstrated equivalence—the condition in which a
that is covered by particles, reported in percent as total particle
method of measurement has passed a series of tests to show
projected area divided by total area of the surface.
that it gives equivalent results to those of a standard measure-
3.1.20 precision cleaning—cleaning of hardware surfaces
ment.
approved by established facility methods or methods specified
3.1.10 environmentally controlled area—cleanrooms, con-
or provided by the customer with verification to a specified
trolled areas, good housekeeping areas, and other enclosures
cleanliness level.
that are designed to protect hardware from contamination.
3.1.21 visibly clean—absence of particulate or molecular
Cleanliness is achieved by controlling air purity, temperature,
contaminants when viewed from a specified distance with
humidity, materials, garments, and personnel activities.
normal (or corrected to normal) vision with a specified
3.1.11 fiber—a particle >100 µm in length with a length to
illumination level.
diameter ratio of ten or more.
3.1.22 witness surface (WS)—a contamination-sensitive
3.1.12 image analysis—the measurement of size, shape,
material used instead of direct evaluation of a specific surface
number, position, orientation, brightness, and other parameters
when that surface is either inaccessible or is too sensitive to be
of small objects using the combination of a microscope, an
handled.
imaging sensor, and a dedicated computer system. Image
analysis can be used to perform particle counts or measure 3.1.22.1 optical witness surface (OWS)—witness surface
particle dimensions automatically, with far greater accuracy fromwhichcontaminantsmaybeanalyzedbyopticalmethods.
than manual techniques.
3.1.22.2 particle witness surface (PWS)—witness surface
3.1.13 micrometre (µm)—a unit of measurement equal to
from which particulate contaminants may be analyzed by
one millionth of a metre, or approximately 39 millionths of an standard optical or electron microscopic methods.
inch, for example, 25 µm is approximately 0.001 in. The term
“micron” has been used but is not a recommended SI unit.
4. Summary of Practice
3.1.14 nonvolatile residue(NVR)—solublematerialremain-
4.1 Particle deposition in controlled environments is deter-
ing after evaporation of a filtered volatile fluid or precipitate
mined by collecting particles on a clean witness surface for a
from a gas phase, usually reported in milligrams per unit area
specified period of time or operational activity, then retrieving
(or volume).
the witness surface and quantifying the particle population
3.1.15 particle deposition—the settling of airborne particles collected.
onto surfaces resulting from electrostatic or dynamic
4.2 Witness surfaces (WS) are typically surfaces that lend
conditions, or both, in cleanrooms or other controlled environ-
themselves to traditional microscopic or image analysis tech-
ments.
niquesforsizingandcountingparticlesonthesurface,butmay
3.1.16 particle fallout(PFO)—astandardparticledeposition
be an optical surface that is evaluated on the basis of the
method used by the European aerospace community that uses
changeinitsopticalpropertiesormaybeawitnesssurfacethat
black glass witness surfaces and measures particle scatter in
best represents the surface material of interest which is
parts per million.
subsequentlyevaluatedbyextractingasamplefromthesurface
and sizing and counting particles removed from the witness
3.1.17 particle size—(1) the apparent maximum linear di-
surface.
mension of a particle in the plane of observation, as observed
with an optical microscope; (2 ) the equivalent diameter of a
4.3 This practice does not address real time particle depo-
particle detected by automatic instrumentation. The equivalent
sition measurements involving particle counters on site with
diameter is the diameter of a reference sphere having known
continuous recording over a specified period of time.
properties and producing the same response in the sensing
5. Significance and Use
5.1 Thispracticeprovidesastandardapproachtomeasuring
The 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 is
particle deposition, or fallout, in cleanrooms and other con-
Euramark, 834 East Rand Rd., Unit 6, Box 823, Mt. Prospect, IL 60056. If you are
trolledenvironments.Itisbasedontheuseofawitnesssurface
aware of alternative suppliers, please provide this information to ASTM Interna-
to collect particles that deposit from the surrounding environ-
tional Headquarters.Your comments will receive careful consideration at a meeting
of the responsible technical committee, which you may attend. ment and subsequently sizing and counting the particles by
E2088 − 06 (2011)
conventional methods. Several options are introduced, with 6.3.2 Silicon wafers or disks shall be selected for image
limitations and guidelines for selecting the best choice for the analysis or other surface scanning methods.
intended application.
6.4 Optical Witness Surfaces, (that is, mirrors or lenses)
5.2 This practice is applicable across numerous industries shall be selected to best represent the critical surface of interest
including aerospace, microelectronics, and pharmaceuticals. in the environment being evaluated. Reflectance or transmis-
sion measurements shall be made in the wavelengths of
6. Selecting Witness Surfaces interest, and the OWS must be the correct size and shape for
the instrumentation planned for use.
6.1 ConsiderationsforselectingWSincludeavailablemeth-
6.5 Gravimetric Methods—A gravimetric method can also
ods of analysis, precision and accuracy required, size of
particles of concern, actual material of critical surfaces of be used, whereby a large witness surface is rinsed with solvent
to extract the particles, filtered onto a dry, preweighed mem-
concern, and cost. Preferably, the WS should be a surface
material which best represents the actual critical surface and brane filter, and then dried and reweighed on a laboratory
balance with a resolution of 0.01 mg. The difference in weight
should be analyzed using the method which best represents the
actual performance characteristics of interest. Additionally, can be a relative quantitative analysis of deposition based on
weight. Note, the efficiency of the extraction method must be
certain surfaces may become charged, especially in dry
environments, and this charging can effect the particle deposi- known or estimated.Apreweighed membrane filter could also
be used as the witness surface thus eliminating the extraction
tion. IfWS are to monitor a vacuum environment they must be
made of low-outgassing, vacuum-compatible materials and step.Additionally, a quartz crystal microbalance with adhesive
surfaces can measure accumulated mass in situ.
held securely in vacuum-compatible, low-particle shedding
holders.
7. Preparation of Witness Surfaces
6.2 Microscopic Evaluation—When microscopic sizing and
counting of particles is the planned method of analysis, select 7.1 Witness Surface Holders—Holders should be designed
one of the following PWS, each of which is easily evaluated to retain the witness surface securely and maximize the surface
directly after exposure. Microscopic sizing and counting shall exposure. They should be made from smooth, cleanable
be performed in accordance with Method F24 or Test Methods materialssuchasplastic,anodizedaluminum,orstainlesssteel.
F312. A noncontact, easily removable, protective cover is required
which prevents the collection of particulate contamination
6.2.1 Membrane Filters, should be gridded for ease in
during transport of the surfaces between the test laboratory and
microscopic particle counting and precleaned before exposure.
Amembranefiltercanbepreparedaseitheratackyortack-free the controlled environment being evaluated. Holders should
have captive fasteners and tethers to prevent the holder or
surface. The membrane filter is cleaned and then either (1)
immediately placed in a cleaned petri dish, (2) dipped into associated hardware from impacting critical surfaces if
dropped. Holders should also be designed to be secured in the
trichloroethylene or methyl chloroform first so it will fuse to
the plastic petri dish, or (3) dipped into a prefiltered tacky facility being evaluated in either a vertical or horizontal
orientation.
adhesiveanddriedinacleanedpetridish.Thepetridishisthen
covered and transported to the area being tested.
7.2 Cleaning of Holders—Holders should be precision
6.2.2 Gridded Counting Slides, such as those used in Prac-
cleaned in accordance with IEST-STD-CC1246 Level 100 or
tice E1216 may be used as WS. After exposure, a pressure-
clean before installing the witness surface. It is recommended
sensitive tape is applied to the slide to encapsulate the
that cleaning and packaging be performed in an ISO 14644
deposited particles before moving them to a microscope for
Class M3.5 (FED-STD-209 Class 100) or better clean bench.
analysis.
7.3 Cleaning of WS—Membranefiltersshouldbeblankedor
6.2.3 Stainless or Other Surfaces, other materials may be
recleaned with filtered fluid before exposure. Tapes should be
selected asWS based on specific needs for durability or
...