El control total de la contaminación en Salas Blancas y Estériles

Evaluating sample preparation techniques for cleanroom wiper testing

Using mechanical energy and a surfactant solution to remove wiper particles can approximate actual conditions of use.

CLEANROOM TECHNOLOGIES

Using mechanical energy and a surfactant solution to remove wiper particles can approximate actual conditions of use.

The testing of cleanroom wipers has evolved over the past 20 years from simply shaking a material and visually approximating the amount of lint released to much more complex methods of separating particles from the wiper followed by quantification using sensitive analytical instrumentation. Controversies such as wet versus dry testing—removing particles via immersion in liquid as opposed to agitation in air—which predominated in the late 1980s, have today mostly been resolved in favor of wet testing.1,2 Published by the Institute of Environmental Sciences in June 1992, IES Recommended Practice 004.2 details two methods for removing particles from a wiper for subsequent enumeration using a laser-based liquid particle counter (LPC) or optical microscopy.2 The first technique involves gently immersing the wiper in deionized (DI) water, the second a more vigorous shaking of the wiper in a vessel containing DI water.

An earlier research project at Texwipe examined the available techniques for counting wiper
particles in liquid suspensions.3 The work demonstrated the deficiencies of devices such as laserbased LPCs, leading us to develop and recommend a measurement based on scanning electron microscopy (SEM). The use of SEM metrology for particle counting provides a method that is sufficiently sensitive to discern with great accuracy the number of particles released during sample preparation.3–5 However, the issue of how to prepare test samples in a manner that closely approximates the actual conditions of use invited further research. Thus, we proceeded to compare existing techniques with new and modified methods for removing particles from a wiper for subsequent counting. This article describes those experiments and discusses their results.

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