Process Control for HDI Fabrication


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A subject that gets very little discussion but is essential to the HDI process is automation. That is, the control of chemical concentrations in our many PCB processes and, especially, those that have been mechanized and can change very rapidly. HDI is one of those series of processes where control is the key to high yields. This topic has been a favorite of mine ever since graduate school, where I majored in process control theory and especially after I took a graduate course in instrumental analytical chemistry taught by a chemical engineering professor. In that class, we built over 40 analyzers and titrators using a LEGO-like modular analytical system, including the electronics. This showed me how simple this problem and its solution really is.

We all know that the most significant chemical processes are controlled by key chemical concentrations. This paper introduces to production management and technical personnel low-cost approaches to simple low-cost methods of monitoring and controlling chemical processes used in PWB fabrication, chemical coatings, sensor manufacturing and electroplating/electroforming. These are techniques like specific gravity that cost as little as $30 through ion-specific electrodes and simple color-wheel comparators (like pool chemistry chlorine analysis) to battery-powered spectrophotometers that run only a few hundred dollars. All these techniques can be taught and  used by production personnel. A formal lab is not required, but these techniques can be used by labs to increase their productivity and number of chemistries controlled.

To read the full version of this article which appeared in the April 2018 issue of PCB007 Magazine, click here.

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