Particles equal to or larger than 1 μm in size can significantly reduce the yield in the microelectronics industry. This is particularly evident in the packaging stage of manufacturing when chips are inter-connected, because of the relatively large areas that must be kept contamination-free during this process. Monitoring is usually done with optical particle counters. The low particle concentrations in clean-rooms, however, result in low counts and high variability. This article presents a monitoring system that uses a virtual impactor to concentrate particles between 0.65 to 2.5 μm dia and counts them with a 0.3 L/min (lpm) particle counter. Theoretical concentration enhancement ratios versus particle size are given. The use of the virtual impactor in a clean environment is demonstrated. Tests show that the transition between the concentrated sizes is sharp. The dependence of the ratios versus particle size is in qualitative agreement with theory. An aerosol concentrator could be used to give more accurate micron-size particle concentrations through a data inversion process, if experimental calibration curves are provided.

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