Noise and vibration characteristics of cleanroom fan filter units

Abstract

Fan filter units (FFU’s) are used increasingly by the microelectronics industry to provide recirculation air in cleanrooms. Such units usually consist of one or more direct-drive blowers located in a small discharge plenum and a HEPA or ULPA filter. There may be several hundred FFU’s in a large cleanroom. The noise and vibration generated by FFU’s differ greatly between manufacturers. Since it is difficult to apply external noise and vibration mitigation, it is important to select an FFU model with appropriate noise and vibration levels, so that a cleanroom served by these units will meet the prespecified noise and vibration criteria. Unfortunately, FFU manufacturers usually do not provide enough information for predicting the FFU generated sound-pressure spectrum or vibration in a cleanroom. In this paper, simple noise and vibration measurement methods will be described, which can be used as a basis for specifying FFU performance without special testing facilities. Measured data will be presented for a number of units. Procedures will be demonstrated to predict the performance of a cleanroom which uses FFU’s as the primary source of recirculation air.