Characterisation of HEPA and ULPA filters by proposed new European test methods

Abstract

The rapid development of microelectronic technology, with the increased storage density of today's VLSI circuitry, requires clean-rooms of class M1 (US Federal Standard 209E). In such clean-rooms the air needs to be approximately 350 times cleaner than in a ‘traditional’ class M3.5 (class 100 according to US Federal Standard 209D), and the filters should have penetrations and leaks up to 1000 times lower than usual. This situation raises several questions. Are existing standardised test methods capable of measuring the efficiency of and leaks from such filters? If not, what are the most important changes which have to be made to allow such filters to be fully characterised? How are such filters to be manufactured, and when manufactured, how can they be tested in large-scale production? The paper highlights some aspects of a new approach to filter testing, and takes into consideration the latest developments in European standardisation with regard to HEPA and ULPA filters.