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NOVEMBER 2020 I PCB007 MAGAZINE 75 via fill and the automatic chemical control unit. Six basic sensors can be utilized: 1. Specific gravity (SG) 2. Specific ion 3. pH and ORP 4. CVS 5. Colorimetry 6. Conductivity Conclusion The chemical control of critical process solu- tions can be as simple as an indicator light at- tached to an SG sensor or a continuous analyz- er for a plating bath with the addition of bright- eners and levelers. The technology is simple and easy to implement. Most maintenance or- ganizations can accomplish the construction and installation with process engineering su- pervision. The payback is enormous, as this can reduce defects, improve productivity, in- crease reliability, and lower costs. Give it a try, and write up your successes. PCB007 Editor's Note: This article is a summary of the procedures in Chapter 4 from the e-book Au- tomation and Advanced Procedures in PCB Fab- rication, which is available for free download from I-Connect007. References 1. "Chemical Feedback Process Control," Pittsburgh An- alytical Conference, Paper No. 24, March 1983. 2. "Printed Circuit Plating Bath Process Control, Part II," Metal Finishing Magazine, March 1985. 3. Public Lab, "Assembling the Public Lab Lego Spec- trometer," December 13, 2017. Further Reading • "Sensor Fundamentals," National Instruments, March 14, 2019. • "Electrode Babysitter," Orion Research Newsletter, Vol. V, No. 1, Cambridge, Massachusetts, 1973. • Snyder, H. B., "Oxidation Reduction Potential: A Tool for Continuous Etching Control," California Circuits Asso- ciation, October 1972, pp. 71–88. • Anderson, N. A., Instrumentation for Process Mea- surement and Control: Third Edition, CRC Press. • Frazer, J. W., Kray, A.M., Selig, W., "Interactive-Exper- imentation Employing Ion-Selective Electrodes," Analyti- cal Chemistry, Vol. 47, No. 6, May 1975, pp. 869–875. • Frank, M.S., "Application of Specific Ion Electrodes to Electroplating Analysis," Plating and Surface Finishing, July 1971, pp. 686–693. • Basson, W.D., "Multichannel Colorimeter for Use With Continuous Flow System," Laboratory Practice, March 1974, p. 61. • Forsberg, O.J., "Incandescent Lamps Mate Well With Silicon Photosensors," EDN/EE, January 1972, pp. 44–47. • Matton, T.R., McSwiggen, P., George, S.A., "Printed Cir- cuit Plating Bath Process Control," Hewlett-Packard UV/ VIS Technical Note, January 1985. • Rothstein, M.L., "Control of Plating Chemistry by Voltammetric Techniques," Plating and Surface Finishing, November 1984, pp. 36–39. Happy Holden has worked in printed circuit technology since 1970 with Hewlett-Packard, NanYa/Westwood, Merix, Foxconn and Gentex. He is currently a contributing technical editor with I-Connect007.