PCB007 Magazine

PCB-Apr2018

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74 PCB007 MAGAZINE I APRIL 2018 Article by Happy Holden I-CONNECT007 Introduction A subject that gets very little discussion but is essential to the HDI process is automa- tion. That is the control of chemical concentra- tions in our many PCB processes and, especial- ly, 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 analyt- ical chemistry taught by a chemical engineer- ing professor. In that class, we built over 40 an- alyzers and titrators using a LEGO-like modu- lar analytical system, including the electronics. This showed me how simple this problem and its solution really is. We all know that the most significant chem- ical processes are controlled by key chemical concentrations. This paper introduces to pro- duction management and technical personnel low-cost approaches to simple low-cost meth- ods of monitoring and controlling chemical processes used in PWB fabrication, chemical coatings, sensor manufacturing and electro- plating/electroforming. These are techniques like specific gravity that cost as little as $30 through ion-specific electrodes and simple col- or-wheel comparators (like pool chemistry chlorine analysis) to battery-powered spectro- photometers that run only a few hundred dol- lars. 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 num- ber of chemistries controlled. This is especially true for the crucial copper electroplating process. As shown in Figure 1, five very important characteristics of copper plating—throwing power, leveling, crack resis - tance, maximum current density, and appear- ance—are controlled by six parameters, five of which ar e chemical concentrations: brighten- er, leveler, copper concentration, sulfuric acid,

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