ASTM E2090-12(2020)
(Test Method)Standard Test Method for Size-Differentiated Counting of Particles and Fibers Released from Cleanroom Wipers Using Optical and Scanning Electron Microscopy
Standard Test Method for Size-Differentiated Counting of Particles and Fibers Released from Cleanroom Wipers Using Optical and Scanning Electron Microscopy
SIGNIFICANCE AND USE
5.1 This test method provides for accurate and reproducible enumeration of particles and fibers released from a wiper immersed in a cleaning solution with moderate mechanical stress applied. When performed correctly, this counting test method is sensitive enough to quantify very low levels of total particle and fiber burden. The results are accurate and not influenced by artifact or particle size limitations. A further advantage to this technique is that it allows for morphological as well as X-ray analysis of individual particles.
SCOPE
1.1 This test method covers testing all wipers used in cleanrooms and other controlled environments for characteristics related to particulate cleanliness.
1.2 This test method includes the use of computer-based image analysis and counting hardware and software for the counting of densely particle-laden filters (see 7.7 – 7.9). While the use of this equipment is not absolutely necessary, it is strongly recommended to enhance the accuracy, speed, and consistency of counting.
1.3 The values stated in SI units are to be regarded as the 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2090 − 12 (Reapproved 2020)
Standard Test Method for
Size-Differentiated Counting of Particles and Fibers
Released from Cleanroom Wipers Using Optical and
Scanning Electron Microscopy
This standard is issued under the fixed designation E2090; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Techniques for determining the number of particles and fibers that can potentially be released from
wiping materials consist of two steps. The first step is to separate the particles and fibers from the
wiper and capture them in a suitable medium for counting, and the second step is to quantify the
number and size of the released particles and fibers.
The procedure used in this test method to separate particles and fibers from the body of the wiper
is designed to simulate conditions that the wiper would experience during typical use. Therefore, the
wiper is immersed in a standard low-surface-tension cleaning liquid (such as a surfactant/water
solutionorisopropylalcohol/watersolution)andthensubjectedtomechanicalagitationinthatliquid.
Theapplicationofmoderatemechanicalenergytoawiperimmersedinacleaningsolutioniseffective
in removing most of the particles that would be released from a wiper during typical cleanroom
wiping.Thistestmethodassumesthewiperisnotdamagedbychemicalormechanicalactivityduring
the test.
Once the particles have been released from the wiper into the cleaning solution, they can be
collected and counted. The collection of the particles is accomplished through filtration of the
particle-laden test liquid onto a microporous membrane filter. The filter is then examined using both
optical and scanning electron microscopy where particles are analyzed and counted. Microscopy was
chosen over automated liquid particle counters for greater accuracy in counting as well as for
morphological identification of the particles.
The comprehensive nature of this technique involves the use of a scanning electron microscope
(SEM) to count particles distributed on a microporous membrane filter and a stereo-binocular optical
microscopetocountlargefibers.Computer-basedimageanalysisandcountingisusedforfieldswhere
the particle density is too great to be accurately determined by manual counting.
Instead of sampling aliquots, the entire amount of liquid containing the particles and fibers in
suspension is filtered through a microporous membrane filter. The filtering technique is crucial to the
procedure for counting particles. Because only a small portion of the filter will actually be counted,
the filtration must produce a random and uniform distribution of particles on the filter.After filtration,
the filter is mounted on an SEM stub and examined using the optical microscope for uniformity of
distribution. Large fibers are also counted during this step. Once uniformity is determined and large
fibersarecounted,thesamplestubistransferredtotheSEMandexaminedforparticles.Astatistically
valid procedure for counting is described in this test method. The accuracy and precision of the
resultant count can likewise be measured.
This test method offers the advantage of a single sample preparation for the counting of both
particles and fibers. It also adds the capability of computerized image analysis, which provides
accurate recognition and sizing of particles and fibers. Using different magnifications, particles from
0.5to1000µmorlargercanbecountedandclassifiedbysize.Thisprocedurecategorizesthreeclasses
of particles and fibers: small particles between 0.5 and 5 µm; large particles greater than 5 µm but
smaller than 100 µm; and large particles and fibers equal to or greater than 100 µm. The technique as
described in this test method uses optical microscopy to count large particles and fibers greater than
100 µm and SEM to count the other two classes of particles. However, optical microscopy can be
employed as a substitute for SEM to count the large particles between 5 and 100 µm .
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2090 − 12 (2020)
1. Scope 3. Terminology
1.1 This test method covers testing all wipers used in 3.1 Definitions of Terms Specific to This Standard:
cleanrooms and other controlled environments for characteris- 3.1.1 automaticcounting,n—countingandsizingperformed
tics related to particulate cleanliness. using computerized image analysis software.
3.1.2 cleanroomwiper,n—apieceofabsorbentknit,woven,
1.2 This test method includes the use of computer-based
nonwoven, or foam material used in a cleanroom for wiping,
image analysis and counting hardware and software for the
spill pickup, or applying a liquid to a surface.
counting of densely particle-laden filters (see 7.7 – 7.9).While
3.1.2.1 Discussion—Characteristically,thesewiperspossess
the use of this equipment is not absolutely necessary, it is
very small amounts of particulate and ionic contaminants and
strongly recommended to enhance the accuracy, speed, and
are primarily used in cleanrooms in the semiconductor, data
consistency of counting.
storage, pharmaceutical, biotechnology, aerospace, and auto-
1.3 The values stated in SI units are to be regarded as the
motive industries.
standard.
3.1.3 effective filter area, n—the area of the membrane
1.4 This standard does not purport to address all of the
which entraps the particles to be counted.
safety concerns, if any, associated with its use. It is the
3.1.4 fiber, n—aparticlehavingalengthtodiameterratioof
responsibility of the user of this standard to establish appro-
10 or greater.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3.1.5 illuminance, n—luminous flux incident per unit of
1.5 This international standard was developed in accor-
area.
dance with internationally recognized principles on standard-
3.1.6 particle, n—a unit of matter with observable length,
ization established in the Decision on Principles for the
width, and thickness.
Development of International Standards, Guides and Recom-
3.1.7 particle size, n—the size of a particle as defined by its
mendations issued by the World Trade Organization Technical
longest dimension on any axis.
Barriers to Trade (TBT) Committee.
4. Summary of Test Method
2. Referenced Documents
4.1 Summary of Counting Methods—See the following:
2.1 ASTM Standards:
Counting Technique Particle Size Range
D1193Specification for Reagent Water
>100 µm 5–100 µm 0.5–5 µm
F25Test Method for Sizing and CountingAirborne Particu-
A B
Stereobinocular optical microscope 20× NA
late Contamination in Cleanrooms and Other Dust- manual
Scanning electron microscope NA 200× auto 3000× manual or
Controlled Areas
B
automatic
F312Test Methods for Microscopical Sizing and Counting
A
See Footnote 2.
Particles from Aerospace Fluids on Membrane Filters
B
NA = not applicable.
2.2 Other Documents:
5. Significance and Use
ISO 14644-1Cleanrooms and Associated Controlled Envi-
ronments – Classification of Air Cleanliness
5.1 This test method provides for accurate and reproducible
ISO 14644-2Cleanrooms and Associated Controlled Envi-
enumeration of particles and fibers released from a wiper
ronments – Part 2: Specifications for testing and monitor-
immersed in a cleaning solution with moderate mechanical
ing to prove continued compliance with ISO 14644-1
stress applied. When performed correctly, this counting test
Fed. Std. 209EAirborne Particulate Cleanliness Classes in
method is sensitive enough to quantify very low levels of total
Cleanrooms and Clean Zones
particle and fiber burden. The results are accurate and not
influenced by artifact or particle size limitations. A further
1 advantage to this technique is that it allows for morphological
This test method is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of SpaceTechnology and is the direct responsibility of as well as X-ray analysis of individual particles.
Subcommittee E21.05 on Contamination.
Current edition approved April 1, 2020. Published May 2020. Originally
6. Apparatus
approved in 2000. Last previous edition approved in 2012 as E2090–12. DOI:
6.1 Scanning Electron Microscope, with high-quality imag-
10.1520/E2090-12R20.
The counting of particles 5 to 100 µm by optical microscopy is not described
ing and computerized stage/specimen mapping capability.
inthistestmethod.However,proceduresforcountingparticlesinthissizerangeare
6.2 Stereo-BinocularOpticalMicroscope,withatleast40×-
described in the Test Methods F25 and F312.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
magnification capability equipped with a two-arm, adjustable-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
angle variable-intensity light source and a specimen holding
Standards volume information, refer to the standard’s Document Summary page on
plate.
the ASTM website.
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
6.3 Orbital Shaker, that provides 20-mm ( ⁄4-in.) diameter
4th Floor, New York, NY 10036, http://www.ansi.org.
circular motion in a horizontal plane at 150 r/min.
Cancelled Nov. 29, 2001 and replaced with ISO 14644-1 and ISO 14644-2,
FED-STD-209E may be used by mutual agreement between buyer and seller.
6.4 Microanalytical Stainless Steel Screen-Supported Mem-
AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,732
brane Filtration Apparatus, with stainless steel funnel, TFE-
N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
www.access.gpo.gov. fluorocarbon gasket and spring clamp.
E2090 − 12 (2020)
6.5 Vacuum Pump, capable of providing a pressure of industries.However,thistestmethodisnotlimitedtoaspecific
6.5kPa (65mb) (49torr) or lower. cleaning solution and only requires that the cleaning liquid
used be relatively free of particles and fibers. It is recom-
6.6 Cold Sputter/Etch Unit, with gold or gold/palladium
mended that the cleaning liquid most relevant to the product
foils.
end use be considered for this test method.
6.7 Video Camera (3-CCD preferable), that can be attached
to the stereo-binocular microscope and a monitor to provide
8. Preparation of Apparatus
video microscopy capability.
8.1 Setting Up Stereo-Binocular Optical Microscope—See
6.8 Personal Computer (486-Type Processor or Better) and
Section 10.
Monitor.
8.2 FiberCountingbyOpticalMicroscopy—SeeSection10.
6.9 Frame-Grabbing Hardware and Image Analysis
6 8.3 Setting Up Scanning Electron Microscope (SEM)—See
Software, compatible with the personal computer.
Section 10.
6.10 Hand-Operated Tally Counter.
8.4 Particle Counting by SEM—See Section 10.
6.11 Stage Micrometer, with 0.1- and 0.01-mm subdivi-
sions.
9. Calibration and Standardization
6.12 Horizontal, Unidirectional Flow Workstation, with
9.1 For the fiber counting by optical microscopy, the size
ISO Class 5 (Fed. Std. 209 Class 100) or cleaner air.
calibration at 20× magnification can be done by comparing the
fiber sizes, as visualized in the video monitor, with the rulings
7. Materials
onthestagemicrometer(with0.1-and0.01-mmsubdivisions).
7.1 Deionized Water, in accordance with Specification
For the equipment described above, a linear dimension of
–6 –1
D1193, Type III, 4.0 × 10 (Ω-cm) or better.
8mm in the video screen equaled 100 µm. The conversion
factors are equipment-dependent and users of this test method
7.2 Cleanroom Gloves (for example, unpowdered latex
shall establish the relation between screen size and object size.
gloves).
9.2 In the SEM study, to determine the values of the start
7.3 Fine-Point, Duckbill Tweezers.
and the end areas for the computer-assisted automatic particle
7.4 Forceps, two pairs, with flat gripping surface tips.
counting, it is necessary to perform the size calibration study
7.5 GlassBeakers,1.5L,cleanedinaccordancewith10.2.1.
by experimenting with standard-sized particles such as poly-
styrene microspheres or actual particles of known dimensions
7.6 Polyethylene Photographic Tray, approximately 250 by
which can be ascertained by using the micrometre bar mea-
340 by 45 mm cleaned in accordance with 10.2.1.
surement tool available on most SEMs.
7.7 Polycarbonate Membrane Filters (typically 0.1- to
9.3 Toprepareastubwith0.5-and5-µmspheres,add10µL
0.4-µm pore size), white, and 25-mm diameter.
of each of the 0.5- and 5-µm sphere suspensions to a beaker
7.8 Petri Slide, 47 mm.
containing 500 mL of deionized water.
7.9 SEMAluminumSpecimenStubs,typically32-mmdiam-
9.4 Filter the solution using a new membrane filter.
eter by 10-mm height.
9.5 PreparetheSEMstub.Savethestubinacleancontainer
7.10 Polystyrene Latex Microspheres (sizes 0.5 and 5 µm)
as a standard size reference for the automatic particle counting
for use in calibration (see Section 9).
at 200 and at 3000×.
7.11 Carbon Paint, for SEM stub preparation.
9.6 For the manual procedure at 3000×, avoid counting
7.12 Low-Surface-Tension Cleaning Liquid—Any 8- to 10-
particles having approximate linear lengths of 25 mm and up,
mole ethoxylated-octyl- or nonyl-phenol-type surfactant pre-
as those will have sizes larger than 5 µm as determined from
pared as a 0.1% stock solution in deionized water. This
measurements done against the micrometre bars at various
solution will facilitate the release of both nonpolar and polar
magnifications in the SEM.
contaminants and can serve as a general test standard across
10. Procedure
“Image-Pro Plus,” Version 7, available from Media Cybernetics, has been
10.1 The procedure consists of two parts: preparing the
found to be satisfactory for this test method.
sample and counting the fibers and particles. Fibers and
The sole source of supply of the apparatus known to the committee at this time
particles greater than 100 µm are counted using an optical
is Media Cybernetics. If you are aware of alternative suppliers, please provide this
information to ASTM International Headquarters. Your comments will receive
microscope at 20× magnification; large (between 5
careful consideration at a meeting of the responsible technical committee, which
and100µm) and small (between 0.5 and 5 µm) particles are
you may attend.
7 counted using an SEM at 200 and 3000× magnifications
Triton® X-100 manufactured by Rohm and Haas Co. has been found to be
respectively. Both manual and computer-aided auto
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.