Cleanroom filters—Requirements and markets

摘要

Demands for removal of smaller and smaller particles continue in the cleanroom industry. Purification of cleanroom air increasingly involves elimination of molecular contamination, and gas-phase contaminants are major problems for semiconductor manufacturers. Therefore, suppliers of filter fibers, media, and assembled filters continue to improve their products to meet these demands. The most important parameters in filters are efficiency and pressure drop. Cleanroom air-handling systems consume large amounts of energy so that even a slight decrease in pressure drop pays dividends in energy-cost reduction, which is significant as the cost of electricity continues to rise. Fan electricity costs are a considerable expense for most cleanroom operators as well. Therefore, selecting a filter with the required efficiency and least pressure drop is a high-priority consideration. The HEPA filter (High Efficiency Particulate Air filter) removes small particles that are entrained in an essentially gas-phase system, the gas usually being air. It has a minimum efficiency of 99.97 percent in removing particles measuring 0.3 μm (i.e., only three out of 10,000 particles 0.3 μm in size penetrate the filter) and it reaches its rated efficiency when the velocity of the gas passing through it is 3 to 5 fpm. ULPA filters provide a minimum of 99.999 percent efficiency (0.001 percent maximum penetration) on 0.3-μm DOP smoke particles.