Hal Amick

Vibration has long been recognized as a contaminant in a fab. The vibrations can come from many sources both within and exterior to the facility. For quite some time, designers and consultants have discussed means by which future vibrations from “unplanned” sources might be mitigated via design or construction. This article presents one possible approach for using the building itself to mitigate vibrations.

Concrete is the structural material of choice for the vibration-sensitive areas in a fab, via waffle slabs or concrete two-way grillages. Some benefits arise from altering the vibration damping characteristics of the concrete itself. A recent research project examined various options for concrete damping modification, finding that the use of a particular family of admixtures was the most straightforward approach. We will look at damping itself and the role it can play in vibration control.

Several methods of altering the damping of concrete have been studied, but the most efficacious is the use of a particular group of polymer admixtures. These impart some significant improvements under certain circumstances, but concrete damping modification will not resolve all problems. The paper examines where this approach is useful, and where it is not justified or cost-effective.

 

Reprinted from Semiconductor Fabtech, No. 26, Cleanroom Section, June 2005