Outgassing characteristics of heated PTFE membrane filters with a thermoplastic support

Airborne molecular and particle contamination in clean rooms reduces product quality and yield. In this study we investigated the outgassing characteristics of heated, expanded polytetrafluoroethylene (ePTFE) membrane filters that were supported by a thermoplastic layer because these filters represent a potential source of contamination. Two filter types were evaluated: ePTFE membrane filters supported by PTFE and ePTFE membrane filters supported by a polyester laminate. Filters were heated in a cyclic fashion by varying the temperature of the particle free nitrogen challenge gas. During heating, the concentration and size distributions of particles downstream of the filter were measured. The results show that at a temperature of 200°C, high concentrations (>10 ⁷ particles/cm ³) of ∼20 nm particles formed downstream of the polyester filter due to the nucleation of organic vapours that outgassed during heating. Additional experiments showed that after the outgassing ceased and the filter was cooled, subsequent heating would generate more particles. Filters with PTFE support that were cyclically heated in a similar fashion generated no particles at 200°C and very few particles at 260°C suggesting they are more suitable for use in a manufacturing clean room when elevated temperatures are present.