ASTM_E_2090_-_12.pdf

Designation:E209012Standard Test Method forSize-Differentiated Counting of Particles and FibersReleased from Cleanroom Wipers Using Optical andScanning Electron Microscopy1This standard is issued under the fixed designation E2090;the number immediately following the designation 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()indicates an editorial change since the last revision or reapproval.INTRODUCTIONTechniques for determining the number of particles and fibers that can potentially be released fromwiping materials consist of two steps.The first step is to separate the particles and fibers from thewiper and capture them in a suitable medium for counting,and the second step is to quantify thenumber 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 wiperis designed to simulate conditions that the wiper would experience during typical use.Therefore,thewiper is immersed in a standard low-surface-tension cleaning liquid(such as a surfactant/watersolution 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 effectivein removing most of the particles that would be released from a wiper during typical cleanroomwiping.This test method assumes the wiper is not damaged by chemical or mechanical activity duringthe test.Once the particles have been released from the wiper into the cleaning solution,they can becollected and counted.The collection of the particles is accomplished through filtration of theparticle-laden test liquid onto a microporous membrane filter.The filter is then examined using bothoptical and scanning electron microscopy where particles are analyzed and counted.Microscopy waschosen over automated liquid particle counters for greater accuracy in counting as well as formorphological 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 opticalmicroscope to count large fibers.Computer-based image analysis and counting is used for fields wherethe 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 insuspension is filtered through a microporous membrane filter.The filtering technique is crucial to theprocedure 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 ofdistribution.Large fibers are also counted during this step.Once uniformity is determined and largefibers are counted,the sample stub is transferred to the SEM and examined for particles.Astatisticallyvalid procedure for counting is described in this test method.The accuracy and precision of theresultant count can likewise be measured.This test method offers the advantage of a single sample preparation for the counting of bothparticles and fibers.It also adds the capability of computerized image analysis,which providesaccurate recognition and sizing of particles and fibers.Using different magnifications,particles from0.5 to 1000 m or larger can be counted and classified by size.This procedure categorizes three classesof particles and fibers:small particles between 0.5 and 5 m;large particles greater than 5 m butsmaller than 100 m;and large particles and fibers equal to or greater than 100 m.The technique asdescribed in this test method uses optical microscopy to count large particles and fibers greater than100 m and SEM to count the other two classes of particles.However,optical microscopy can beemployed as a substitute for SEM to count the large particles between 5 and 100 m2.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 1.Scope1.1 This test method covers testing all wipers used incleanrooms and other controlled environments for characteris-tics related to particulate cleanliness.1.2 This test method includes the use of computer-basedimage analysis and counting hardware and software for thecounting of densely particle-laden filters(see 7.7 7.9).Whilethe use of this equipment is not absolutely necessary,it isstrongly recommended to enhance the accuracy,speed,andconsistency of counting.1.3 The values stated in SI units are to be regarded as thestandard.1.4 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 standard to establish appro-priat