Large Particle Reduction by Porous Membrane Filter

The objective of this study is to propose a laboratory test method for confirming LPC (large particle count) reduction by porous membrane filters, which are generally thought to have higher particle removal performance than melt-blown filters. CMP slurries were filtered by porous membrane filters and a nonwoven depth filter. Then LPC reduction of the filtrates was estimated by a particle counter in conjunction with control membrane test, in which pressure drop increase of a filter (a control membrane) was an indicator of LPC. Difference of LPC for filtrates from each type of filter was small by the particle counter and significant by the control membrane method, but with the porous membrane filter exhibiting lower LPC by the both methods. The results demonstrate that a combination of particle counter and control membrane method can reveal difference of filter performance in LPC reduction with confidence. Further, to show pressure drop increase could be an indicator of LPC, pressure drop increase of the control membrane enhanced by large particles was examined.