Masters Theses

Date of Award

5-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

R. Bruce Robinson, Chris D. Cox

Committee Members

Bruce Tschantz

Abstract

The main source of wastewater contamination in the printed wiring board industry is from drag-out of process chemicals during the manufacturing process. Previous drag-out prediction equations are primarily a function of fluid viscosity and board withdrawal rate, and do not account for the many additional variables common in industry. A series of laboratory drag-out experiments were conducted on simulated alkaline cleaner/conditioner and microetch process baths to quantify drag out volumes for a range of fluid properties and process variables. Results of the experiments compared favorably with published drag-out volumes. The mean dragout volume for all experiments was around 91 mL/m², with literature values ranging from 16 to 203 mL/m². The results also indicate that previous predictive equations do not consistently predict drag-out for the range of variables in PWB manufacturing. Predictive equations for the alkaline cleaner/conditioner bath predicted values ranging from about 65 percent below to 40 percent above measured values. Two equations performed very well for the microetch bath, predicting values within 8 percent ,but others predicted poorly at 40 to 75 percent below measured values.

A predictive drag-out model was developed by statistical analyses of the experimental data. Dynamic viscosity, surface tension, board withdrawal rate, drip time, board hole density, tilting the board during the drainage period, and the type of board surface were identified as significant variables at a 10 percent level of significance. Parameters with the greatest impact on drag-out appear to be dynamic viscosity, surface tension, and board hole density. The empirical prediction equation provides a reliable method to predict drag-out as a function of variables relevant to PWB processes. Once the drag-out mass is determined, the wastewater quality can be predicted by applying a mass balance to the overall wet process.

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