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50 The PCB Design Magazine • May 2014 I first became aware of high-density inter- connection (HDI) design methodology in 1997 when a co-worker of mine came back from a training class that was taught by Happy Hold- en. "Little Dave" (since our department had two employees named David W.) came back excited to try this new design knowledge on a multilayer board stackup that only used blind and buried vias, with no through-hole vias. His excitement and dedication paid off, as he com- pleted the design with an autorouter exactly as he planned. Through Dave's success, our de- partment then started to create other designs using HDI stackups that were taught in Happy's class and our autorouter tool. I did a few complex designs that fit into the IPC Type III category. One of the more complex designs I attempted could only autoroute up to 98% completion after trying many setup files (with great assistance from "Big Dave") and our most powerful computer available within our group. I finished the design manually, and the board was fabricated and worked as designed. About six months later, when we upgraded our department's autorouter computer, I re- stored the design from archive, and re-ran the last autorouter configuration file on that 98% completed design. This time, the design was now 100% completely autorouted, and took about a third less time than on the previous "most powerful" computer. This one little re- investigation became the catalyst for my full immersion into HDI design research, reviewing the existing designs and now trying newer auto- routing approaches with a variety of more chal- lenging stackups, via spans, and via sizes. Each new redesign attempt created more curiosity to push autorouters and stackup methodologies to their absolute limits. Over the next few years, any article written on HDI that crossed my path became assimi- lated into my mental database. I met Mike Fitts by Dan Smith rAyTheon THE TOWN CRIER HDI Design Education: Is Anyone Interested? column

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