Ultrasonic Cleaning: Fundamental Theory and Application

The various ultrasonic parameters, or degrees of freedom, available to the process engineer define what the ultimate limits are for the cleaning process. The traditional degrees of freedom available in an ultrasonic cleaning system have included modulation of a single center frequency (sweep), variable duty cycle, and amplitude control at a single frequency. All of these variables allow control of gross, or macroscopic, variables, such as raw power, into the fluid. The latest class of aqueous cleaning technology allows all of the aforementioned parameters, but at multiple center frequencies in a single process tank. Multiple center frequencies allow precise microscopic tuning of the energy in the individual cavitation event. Understanding and optimizing the parameters yields maximal cleaning efficiency with minimal substrate damage. Unlike many popular ultrasonic papers available, the descriptions here are fully referenced and arrived at through sound physical reasoning. This paper intends to undertake the ambitious task of illuminating the various physical effects of these parameters in such a way as to shed as much light and as little heat as possible on this often less than intuitive subject. It is the authors' desire that this paper is not a final description, but the beginning of a dialog.