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36 The PCB Magazine • April 2014 by Dan Smith raytHeon From Single-Sided to HDI: The "Three Phone Call Method" Works! One experiences both extreme joy and anxi- ety when watching a prototype PCB being pow- ered up for the first time. The test bench sur- rounding the new board resembles an operating room, with probes attached everywhere to an array of oscilloscopes, multimeters, and other indicators. All eyes of the project team surround- ing the test bench watch the darting eyes of the main electrical engineer, frantically reading each monitor/display for its analysis. More times than not, the silence is broken by this electrical en- gineer when he erupts with the exclamation, "Wow! The circuit works!" To all PCB fabrication process engineers who are not present at that moment, but whose skills and knowledge base over the years have made those words possible, I want to begin by thank- ing you for all that you have done to advance the quality and integrity of the electronics industry. Your dedication to continue to fabricate high- quality boards and panels ever since Paul Eisler (the father of PCB fabrication) made his first ra- dio with a PCB needs to be recognized by all in our industry. In my first score of years in electronics, I had the good fortune of learning PCB fabrica- tion in creating single and double-sided proto- type boards as an R&D technician in a crude, but effective PCB fab lab. I learned first-hand about raw materials, photo-imaging, etching, plating and drilling by fabricating prototypes for new design concepts to address our cus- tomer's product needs. Although I was never able to add the soldermask or silkscreen layers to these boards because we only did the proof- of-concept, I did come to better understand the materials' characteristics and design challenges when I changed careers from being a technician to a PCB designer. Early in my design career, every time I had the chance to tour a local fabrication shop, I would somehow find out who the main process engineer was, and then spend time with that per- son at the end of the tour. I would question him relentlessly about everything I saw that I did not understand. To my amazement, every fabrica- tion process engineer understood my quest for knowledge, and succinctly answered every ques- tion about fabrication I posed to them. To this day, I cherish those meetings, and now share all of that information I have assimilated when I teach the PCB design process. My favorite process engineer was someone I only interacted with via telephone, because the fabrication house that I sent my prototype de - signs to was more than 1,000 miles away. We'll call this engineer Tom; his name is changed in this story only to protect him from future phone call bombardment. Tom came highly recommended by a program manager for which I designed prototype boards for more than six years. In our initial conversation about the first prototype design I was about to send him (a six- layer multilayer design with just through-holes), F e a t u r e