Historically, the determination of the concentration of cleaning agent in high precision electronic cleaning baths has depended on any one of several possible measurable parameters. Refractive Index (RI) is by far the most common. RI methods are excellent tools for use in simple systems where a single solute dominates the signal. In these situations, it is possible to characterize and calibrate how that solute affects the signal. However, the introduction of flux residues during the wash bath lifetime complicates the bath chemistry/physics to such an extent that RI signals no longer provide the same insight.
The introduction of flux residue has an enormous influence on the Refractive Index. Alternative means of measuring cleaning agent are necessary if cleaning agent concentration is to be known throughout the life of the bath. With a means to accurately measure bath cleaning agent, closed loop automated process control on the cleaning bath is possible; automating this labor intensive step in the production of electronic boards. We have found that acoustic measurements of cleaning bath solution are relatively independent of pH, conductivity, and dissolved solids in some of the most flux loaded baths. Utilizing acoustic sensing technology, field data was gathered from two beta site locations assessing the accuracy of the technology in fresh as well as contaminated wash baths.