In Particles on Surfaces – Part 2, we learned that thin liquid layers between particles and surfaces serve as the binding forces between the two. By lowering the surface tension of this liquid layer – typically water – we can decrease the binding force and assist in the removal of particles.
Isopropyl alcohol (IPA) - as discussed in detail in “Pre-Wetted Wipers Optimized for Application-Specific Cleaning” and in “Why is Isopropyl Alcohol the Choice for Cleanroom Cleaning?” – will serve this purpose admirably. But merely irrigating a surface with IPA and leaving it untouched will not solve the problem; true, the surface tension of the thin liquid layers will be reduced until the IPA evaporates, but nothing will cause the particles to leave the surface. Energy must be applied to the surface along with the IPA to remove the particles. Furthermore, the removed particles must be trapped to avoid particle re-deposition. A cleanroom wiper, dampened with an IPA solution is the perfect tool to accomplish this. The wiping action removes the particles which are then held in the fabric’s interstices.
What concentration of IPA is optimum? How damp should the wiper be? These questions were addressed in “Pre-Wetted Wipers Optimized for Application-Specific Cleaning” and the case for pre-wetted wipers will be seen to be quite persuasive.
Next up: What’s the most effective method of wiping?
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