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10 The PCB Design Magazine • January 2015 feature contained no surface mount components, and may have even included vacuum tubes! (Figure 1) Until the late '70s or early '80s, most boards were designed using tape to represent traces and pads, and a Mylar sheet as the PCB. Boards were often designed at a 4:1 scale. In the '70s, double-sided boards became common, but with no SMT capability, the sec- ond side was strictly for copper, not compo- nents. (Sometimes, though, prototypes were "fixed" by cutting traces on the back and in- stalling jumpers or, sometimes, resistors or ca- pacitors). Double-sided boards were designed on Mylar using blue tape for one side, and red tape for the other. Why? In the days of tape and Mylar, the fin- ished tape-out was photographed at a 1:4 scale to produce a 1:1 film negative. The negative was then projected onto the photoresist-coated board and developed to reveal the trace design. For double-sided boards, two types of film were As part of the team that administers the Men- tor Graphics Technology Leadership Awards (TLA) for the best PCB designs, I have been able to see and record a great deal about how the designs have evolved over the years. This year, because it's the 25 th year of the TLA program, I asked some of our senior judges to relate their early experiences and history. In this article, I'll explore those inputs as well as the data we have collected over the years, and add just a bit of trend forecasting. A Short History of the PCB World The judges' feedback painted a clear picture of how PCB design and design tools became what they are today. Most of the judges began their PCB career when boards were single sided, by David Wiens MenTor GrAPhICS CorP. Past and Future Trends in PCB Design

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