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60 PCB007 MAGAZINE I SEPTEMBER 2025 H A P PY 'S T EC H TA L K # 4 3 In over 50 years as a PCB process engineer, the one skill I acquired in college that has been most beneficial is engineering statistics. Basic statistics was part of my engineering fundamentals classes, but I petitioned the dean to let me take the engineer- ing statistics graduate course because I was creating a senior thesis for my honors focus and needed more training on Design of Experiments (DOE). I was recruited by Hewlett-Packard for its new semiconductor fabrication facility in Palo Alto (CA) specifically because of my undergraduate degree in chemical engineering and my master's degree in electrical engineering with an emphasis on control engineering. After working in the new facility and as the only chemical engineer in the company, the semiconductor VP asked if I would be open to "going down the hill" to help out the struggling PCB multi- layer plant with its process problems. I took him up on his offer even though I had no knowledge or experience in printed circuit manu- facturing. However, I had the tools and knowledge to solve the process problems. My first impression: Making a PC multilayer was convoluted. It involved materials engineering, pho- tolithography, complicated etching, lamination technology, CNC drilling and routing, screen printing, chemical deposition, electroplating, and electrical testing. To learn, I read the only book on PCBs I could find, Printed Circuits Handbook (1967), by Clyde F. Coombs, and then I contacted all the suppliers involved with some of these problems. Thanks to my DOE training, I whittled down the long list of variables and discovered the root cause of the production problems: The MEs, EEs, and chemists in the PCB engineering group had made the usual mistake of trying to solve the problems by holding everything constant and varying one variable at a time. They also focused on the quantitative variables, disregarding the qualitative variables. I didn't do that. The Need for Statistical Tools The discussion of quality and customer satisfaction shows how important variables are to PCBs. Any loss goes to the bottom line. So, what are some of the tools to help improve process yields? Process control comes to mind. We use four criteria to select the correct statisti- cal tool for problem analysis (Figure 1). Chemical processes have always been difficult to control in printed circuit manufacturing. These uncontrolled factors can creep into our processes. by Happy Holden, I-C onne ct0 07