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14 The PCB Design Magazine • January 2015 could be used to produce a board on photore- sist-coated blanks. TLA judge Charles Pfeil recalls entering the PCB career path when his father's company hired him part-time in high school to inspect the finished Rubylith designs for scratches. "Was the fabrication process so exact that a scratch that could only be seen through a mag- nifier could really affect the result?" Pfeil asked. "I dared not say anything for fear of losing my cushy $1.75 per hour job!" There was one other "technology" that was fairly rare, yet used with success. TLA judge Gary Ferrari was just out of school and design- ing gears by using ink on linen. Because he was so good at it, he was moved to PCB design where they laid out the boards by drawing on linen sheets with ink! CAD systems had been used with some de- gree of success in the late '70s and '80s (and some existed even in the '60s), but in the late '80s they become nearly universal. Good thing, because SMT had arrived shortly before and de- sign difficulty rose immediately. As soon as SMT was introduced, a small ex- plosion of package types began to appear. An- other judge, Andy Kowaleski, remembers the introduction of the BGA package, and he made an interesting observation. "The introduction of the BGA package led to a massive increase in multilayer boards," said Kowalewski. "Once that happened, the rest of the board could be packed with components like never before, so boards got smaller and more functional (usually both)." That is a thumbnail sketch of the situation up until today, when high-speed signal integ- rity issues can be more problematic than ever before. High speed generates heat, and that has to be dealt with too. And all the while, boards are more complex and need to be designed in less time than ever before! We'll take a look at those trends. But first, check out Figure 2, which illustrates the chang- es we've seen since 1994 in the designs sub- mitted to the TLA program. Probably the most striking thing to notice is the highlighted red line, which represents the number of leads per square inch. It is surprising that this trend can be so steep, but still continue for 20 years unin- terrupted. On average, that number went from 42 to 304 leads per square inch over that time. Over that same period, the number of average leads per part has diminished by nearly 50%, PAST AND FuTuRE TRENDS IN PCB DESIgN continues feature Figure 2: This is a 20-year analysis of several key factors in PCB designs. There are several clear trends.