CONCENTRATION MONITORING CLOSED LOOP CONTROL - A TECHNOLOGICAL ADVANCEMENT

摘要

As with every process on the production floor, in order to ensure a reliable, repeatable and cost effective cleaning process, it is vital that all parameters are monitored and ultimately controlled. Equipment suppliers have done their part to ensure that parameters such as temperature, pressure, flow rate, and process exposure time are accurately controlled, but wash bath cleaning agent concentration has until today been a challenge given the available monitoring technology. Historically, refractive index, either in the form of hand held devices or automated systems, has been the tool of choice to measure the concentration of a solute in an aqueous solution. With fresh wash bath, refractive index is very accurate. However, as the wash bath becomes contaminated, that is accumulates impurities including flux residue resulting from the cleaning process, the refractive index reading will be skewed yielding an erroneous measurement that results in a false correction and ultimately an unstable process. This study focuses on exciting technological advancements made in concentration measurement and closed loop control utilizing new technology that can accurately measure aqueous cleaning agent concentration in the presence of flux loading. Comparative data will be presented confirming the reliability of this advanced process control methodology as compared to current methods.