ASTM E2090-06
(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
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 ). 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.
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Designation:E2090–06
Standard Test Method for
Size-Differentiated Counting of Particles and Fibers
Released from Cleanroom Wipers Using Optical and
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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. A number 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
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 cleanroom
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 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
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employed as a substitute for SEM to count the large particles between 5 and 100 µm .
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E2090–06
1. Scope 3.1.2.1 Discussion—Characteristically, these wipers pos-
sess very small amounts of particulate and ionic contaminants
1.1 This test method covers testing all wipers used in
and are primarily used in cleanrooms in the semiconductor,
cleanrooms and other controlled environments for characteris-
data storage, pharmaceutical, biotechnology, aerospace, and
tics related to particulate cleanliness.
automotive industries.
1.2 This test met
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