Detailed particle microcontamination measurements were made in Class 100 and Class 10 [unidirectional flow, or vertical laminar flow (VLF)] environments used as final assembly and electro-optical assembly areas, respectively, at Particle Measuring systems, Inc. (PMS). Two groups of measuring instruments monitoring the two areas included four laser particle counters (LPCs) and three condensation nucleus counters (CNCs). The utility of both types of measurements in these environments is discussed relative to sensitivity, flow rate, and background noise. These data indicate that the statistical advantage of CNC's over 1 cu ft/min LPCs can only be achieved at flow rates > .050 cu ft/min. The most prevalent range of particle sizes is limited to those near the most penetrating particle size. The higher count rate of lower flow rate CNC and LPC instruments was also found to be a factor in quantifying episodic events and transient populations. Outside ambient air was shown to be the major contributor to in-room particle counts under the conditions studied here.
Effect of Instrument Flow Rate, Sensitivity, and Background Noise on Cleanroom Particle Count Statistics
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Robert Knollenberg, Brett Haley, David Steidtmann; Effect of Instrument Flow Rate, Sensitivity, and Background Noise on Cleanroom Particle Count Statistics. Journal of the IEST 1 November 1995; 38 (6): 18–29. doi: https://doi.org/10.17764/jiet.2.38.6.u76281n1184547p1
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