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I want to talk to you about a subject that gets little discussion but is essential to running a successful PWB facility: process control. This involves the control of chemical concentrations in our many PCB processes, especially those that have been mechanized and can change very rapidly.
I confess. I am a control nerd and highly analytical. My second degree is in EE control theory, and I see the world in terms of feedback loops and black boxes. Early in my career, I was volunteered for the technical programs for the California Circuits Association (CCA), which was created by my mentor Clyde Coombs. In discussions with fellow process engineers, it was clear that the chemical process controls that HP could afford and allow me to put in place were not able to be duplicated by much smaller PWB shops.
This topic has also been a favorite of mine ever since I started working as a process engineer in printed circuit fabrication. Fortunately, I took a graduate course in instrumental analytical chemistry taught by a chemical engineering professor. In that class, we built over 40 analyzers, spectrometers, and titrators using a Lego-like modular analytical system, including the electronics. This showed me how simple this problem and its solution really is.
Sure, you can buy sophisticated measurement tools and lab equipment. For cutting-edge processes, the chemistry lab is an important part of the process control. But there continues to be room for simple, “back pocket” tools and methods throughout the industry.
Thus, I set out to create a program of low-cost, easy process analytics that anyone could implement. These were simple enough for platers to control all the way up to instrumentation that required a chemist but allowed for many more analytical tests each day. Presented at the CCA monthly meeting, with the devices spread out over several tables, everyone could examine these techniques and look at the costs and how to use them.
Some of the techniques are not easy to find, such as the use of Clinistix that you can buy at any pharmacy that they use to check babies for phenylketonuria (PKU). These little plastic indicators cost $10 for 20 and are used to measure the hydrogen peroxide concentration in mild etches in less than a minute. Another example is using a simple $18 hydrometer to control etches, cleaners, acid, and plating in less than half a minute. Using these simple measurement techniques, the chemical concentrations can be used at a lower level and save costs (Figure 1).
The program was so successful that I have kept the ideas and built on them over the last 40 years. My crowning achievement in 2009 was the perfection of a small cyclic stripping voltammetry (CVS) unit that I could build for $200, replacing the laboratory $20,000 unit, allowing me to have a continuous CVS measuring unit on each copper plating tank. At that time in China, I had 68 2,000-liter copper plating cells/tanks in use, so the newly added controls greatly improved performance and yields.
The most significant chemical processes are controlled by key chemical concentrations. This program 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. Some techniques cost as little as $20 through ion-specific electrodes and simple color-wheel comparators, as well as pool chemistry chlorine analysis or battery-powered spectrophotometers that run only a few hundred dollars.
To read this entire article, which appeared in the November 2020 issue of PCB007 Magazine, click here.
