ASTM E2090-00

Standard Test Method for Size-Differentiated Counting of Particles and Fibers Released from Clean Room Wipers Using Optical and Scanning Electron Microscopy

SCOPE
1.1 This test method covers testing all wipers used in clean rooms 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 ). 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.
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: 09-May-2000
• 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

• Replaced By: ASTM E2090-06 - Standard Test Method for Size-Differentiated Counting of Particles and Fibers Released from Cleanroom Wipers Using Optical and Scanning Electron Microscopy
• Effective Date: 01-Nov-2006
• Referred By: ASTM E2312-11(2019) - Standard Practice for Tests of Cleanroom Materials
• Effective Date: 10-May-2000

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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:E2090–00
Standard Test Method for
Size-Differentiated Counting of Particles and Fibers
Released from Clean Room Wipers Using Optical and
Scanning Electron Microscopy
This standard is issued under the fixed designation E 2090; 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 (e) 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
solution or isopropyl alcohol/water solution) and then subjected to mechanical agitation in that liquid.
The application of moderate mechanical energy to a wiper immersed in a cleaning solution is effective
in removing most of the particles that would be released from a wiper during typical clean room
wiping.This test method assumes the wiper is not damaged by chemical or mechanical activity during
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 the 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
fibers are counted, the sample stub is transferred to the SEM and examined for particles.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.
E2090–00
1. Scope and are primarily used in clean rooms in the semiconductor,
data storage, pharmaceutical, biotechnology, aerospace, and
1.1 This test method covers testing all wipers used in clean
automotive industries.
rooms and other controlled environments for characteristics
3.1.3 effective filter area, n—the area of the membrane
related to particulate cleanliness.
which entraps the particles to be counted.
1.2 This test method includes the use of computer-based
3.1.4 fiber, n—aparticlehavingalengthtodiameterratioof
image analysis and counting hardware and software for the
10 or greater.
counting of densely particle-laden filters (see 7.7-7.9). While
3.1.5 illuminance, n—luminous flux incident per unit of
the use of this equipment is not absolutely necessary, it is
strongly recommended to enhance the accuracy, speed, and area.
consistency of counting. 3.1.6 particle, n—a unit of matter with observable length,
1.3 The values stated in SI units are to be regarded as the
width, and thickness.
standard.
3.1.7 particle size, n—the size of a particle as defined by its
1.4 This standard does not purport to address all of the
longest dimension on any axis.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Test Method
priate safety and health practices and determine the applica-
4.1 Summary of Counting Methods—See the following:
bility of regulatory limitations prior to use.
Counting Technique Particle Size Range
>100 µm 5–100 µm 0.5–5 µm
2. Referenced Documents
A B
Stereobinocular optical microscope 203 NA
manual
2.1 ASTM Standards:
Scanning electron microscope 30003 2003 auto NA
D 1193 Specification for Reagent Water
manual or
B
F 25 Test Method for Sizing and Counting Airborne Par- automatic
ticulate Contamination in Clean Rooms and Other Dust-
A
See Footnote 2.
B
Controlled Areas Designed for Electronic and Similar
NA = not applicable.
Applications
F 311 PracticeforProcessingAerospaceLiquidSamplesfor
5. Significance and Use
Particulate Contamination Analysis Using Membrane Fil-
5.1 This test method provides for accurate and reproducible
ters
enumeration of particles and fibers released from a wiper
F 312 Test Methods for Microscopical Sizing and Counting
immersed in a cleaning solution with moderate mechanical
Particles from Aerospace Fluids on Membrane Filters
stress applied. When performed correctly, this counting test
2.2 Other Documents:
method is sensitive enough to quantify very low levels of total
ISO 14644-1 Cleanrooms and Associated Controlled Envi-
particle and fiber burden. The results are accurate and not
ronments – Classification of Air Cleanliness
influenced by artifact or particle size limitations. A further
Fed. Std. 209E Airborne Particulate Cleanliness Classes in
advantage to this technique is that it allows for morphological
Cleanrooms and Clean Zones
as well as X-ray analysis of individual particles.
3. Terminology
6. Apparatus
3.1 Definitions of Terms Specific to This Standard:
6.1 Scanning Electron Microscope, with high-quality imag-
3.1.1 automatic counting, n—counting and sizing per-
ing and computerized stage/specimen mapping capability.
formed using computerized image analysis software.
6.2 Stereo-Binocular Optical Microscope, with at least
3.1.2 clean room wiper, n—a piece of absorbent knit,
403-magnification capability equipped with a two-arm,
woven, nonwoven, or foam material used in a clean room for
adjustable-angle variable-intensity light source and a specimen
wiping, spill pickup, or applying a liquid to a surface.
holding plate.
3.1.2.1 Discussion—Characteristically, these wipers pos-
6.3 Orbital Shaker, that provides 20-mm (; ⁄4-in.) diameter
sess very small amounts of particulate and ionic contaminants
circular motion in a horizontal plane at 150 r/min.
6.4 Microanalytical Stainless Steel Screen-Supported Mem-
brane Filtration Apparatus, with stainless steel funnel, TFE-
This test method is under the jurisdiction of ASTM Committee E21 on Space
Simulation andApplications of Space Technology and is the direct responsibility of
fluorocarbon gasket and spring clamp.
Subcommittee E21.05 on Contamination.
6.5 Vacuum Pump, capable of providing a pressure of 6.5
Current edition approved May 10, 2000. Published July 2000.
kPa (65 mb) (49 torr) or lower.
The counting of particles 5 to 100 µm by optical microscopy is not described
in this test method. However, procedures for counting particles in this size range are
6.6 Cold Sputter/Etch Unit, with gold or gold/palladium
described in the Test Methods F 25 and F 312.
foils.
Annual Book of ASTM Standards, Vol 11.01.
6.7 Video Camera (3-CCD preferable), that can be attached
Annual Book of ASTM Standards, Vol 15.03.
Annual Book of ASTM Standards, Vol 14.02.
to the stereo-binocular microscope and a monitor to provide
Available from American National Standards Institute, 11 W. 42nd St., 13th
video microscopy capability.
Floor, New York, NY 10036.
6.8 Personal Computer (486-Type Processor or Better) and
AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700
Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS. Monitor.
E2090–00
6.9 Frame-Grabbing Hardware and Image Analysis Soft- 9.2 In the SEM study, to determine the values of the start
ware, compatible with the personal computer. and the end areas for the computer-assisted automatic particle
6.10 Hand-Operated Tally Counter. counting, it is necessary to perform the size calibration study
6.11 Stage Micrometer, with 0.1- and 0.01-mm subdivi- by experimenting with standard-sized particles such as poly-
sions. styrene microspheres or actual particles of known dimensions
6.12 Horizontal, Unidirectional Flow Workstation, with which can be ascertained by using the micrometre bar mea-
ISO Class 5 (Fed. Std. 209 Class 100) or cleaner air. surement tool available on most SEMs.
9.3 To prepare a stub with 0.5- and 5-µm spheres, add ;10
7. Materials
µLof each of the 0.5- and 5-µm sphere suspensions to a beaker
containing 500 mL of deionized water.
7.1 Deionized Water, in accordance with Specification
–6 –1
9.4 Filter the solution using a new membrane filter.
D 1193, Type III, 4.0 3 10 (V-cm) or better.
9.5 PreparetheSEMstub.Savethestubinacleancontainer
7.2 Clean Room Gloves (for example, unpowdered latex
as a standard size reference for the automatic particle counting
gloves).
at 200 and at 30003.
7.3 Fine-Point, Duckbill Tweezers.
9.6 For the manual procedure at 30003, avoid counting
7.4 Forceps, two pairs, with flat gripping surface tips.
particles having approximate linear lengths of 25 mm and up,
7.5 GlassBeakers,1.5L,cleanedinaccordancewith10.2.1.
as those will have sizes larger than 5 µm as determined from
7.6 Polyethylene Photographic Tray, approximately 250 by
measurements done against the micrometre bars at various
340 by 45 mm cleaned in accordance with 10.2.1.
magnifications in the SEM.
7.7 Polycarbonate Membrane Filters (typically 0.1- to
0.8-µm pore size), white, and 25-mm diameter.
10. Procedure
7.8 Petri Slide,47mm.
10.1 The procedure consists of two parts: preparing the
7.9 SEMAluminum Specimen Stubs, typically 32-mm diam-
sample and counting the fibers and particles. Fibers and
eter by 10-mm height.
particles greater than 100 µm are counted using an optical
7.10 Polystyrene Latex Microspheres (sizes 0.5 and 5 µm)
microscope at 203 magnification; large (between 5 and 100
for use in calibration (see Section 9).
µm) and small (between 0.5 and 5 µm) particles are counted
7.11 Carbon Paint, for SEM stub preparation.
using an SEM at 200 and 30003 magnifications respectively.
7.12 Low-Surface-Tension Cleaning Liquid—Any 8- to 10-
9 Both manual and computer-aided automatic counting methods
mole ethoxylated-octyl- or nonyl-phenol-type surfactant pre-
are used in this procedure.
pared as a 0.1 % stock solution in deionized water. This
10.1.1 SamplePreparation—Samplepreparationconsistsof
solution will facilitate the release of both nonpolar and polar
two steps:
contaminants and can serve as a general test standard across
10.1.1.1 Preparation of a background filter stub and
industries.However,thistestmethodisnotlimitedtoaspecific
10.1.1.2 Preparation of the sample filter stub containing
cleaning solution and only requires that the cleaning liquid
particles released from a clean room wiper.
used be relatively free of particles and fibers. It is recom-
10.2 Preparation of a Background Filter Stub—To measure
mended that the cleaning liquid most relevant to the product
the background level of particles from the glassware, polyeth-
end use be considered for this test method.
ylene tray, and filtration system, it is necessary to prepare an
experimental blank.
8. Preparation of Apparatus
10.2.1 Thecleaningofthephotographictray,glassware,and
8.1 Setting Up Stereo-Binocular Optical Microscope—See
the filtration apparatus should be accomplished in the follow-
Section 10.
ing manner:
8.2 Fiber Counting by Optical Microscopy—See Section
10.2.1.1 Clean the photographic tray thoroughly by rinsing
10.
the inner surface at least five times with deionized water.
8.3 Setting Up Scanning Electron Microscope (SEM)—See
10.2.1.2 Ultrasonicallycleantheglassware,storagecontain-
Section 10.
ers, and filtration assembly then thoroughly rinse using deion-
8.4 Particle Counting by SEM—See Section 10.
ized water.
10.2.1.3 Allow all containers and assemblies to drain dry in
9. Calibration and Standardization
the unidirectional flow workstation.
9.1 For the fiber counting by optical microscopy, the size
10.2.1.4 Store all containers and assemblies, including the
calibrationat203magnificationcanbedonebycomparingthe
photographic tray, in the clean workstation to prevent environ-
fiber sizes, as visualized in the video monitor, with the rulings
mental contamination.
on the stage micrometer (with 0.1- and 0.01-mm subdivisions).
10.2.2 The choice of the cleaning solution should reflect the
For this test method, a linear dimension of 8 mm in the video
liquid that the wiper will come in contact with during actual
screen equaled 100 µm.
use. A typical example of a cleaning solution would be a
low-concentration surfactant/deionized water mixture (see
7.12). This mixture serves well as a standard for general
“Image-Pro Plus,” Version 3.0, available from Media Cybernetics, has been
comparative purposes since it facilita
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