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86 DESIGN007 MAGAZINE I OCTOBER 2020 of chip-scale packaging in the mid-'90s and the Occam Process idea are both easily identifiable "cases in point" in my career. Most roadmap activity is a rather mundane exercise of extrapolating current technology trends. However, technology trends are not always linear. Often, they are punctuated with newer developments that, while not always foreseen, have future impacts and directions that were not fully appreciated at the time. More on this subject a bit later. For printed circuit technology (like all elec- tronics, in general), the mantra has always been "smaller, lighter, cheaper, better, faster." If you think critically about that hierarchy of desires and have some appreciation of science and engineering, and if you achieve the first "smaller" objective, all the other objectives fall in line. Smaller is lighter, cheaper, and faster, so it's automatically better. Let's look at the most common metrics in PCB technology: minimum line-and-space size, minimum hole (or via) size, and circuit layer count. These circuit features have always trended down while operating frequencies have steadily risen. On the other hand, layer counts, the other major mechanical metric for PCBs, have typically risen, but they have also been going down. This stems from changes in component technology that have taken place over the years. In the 1970s, com- ponents were almost exclusively through-hole mounted and wave soldered into position. The problem was that if electronic products were to become smaller, components would need to be smaller, too, and/ or more function would have to be carried out by larger components, which would be fewer in number. Enter surface-mount technology (SMT) in the 1980s (Fairchild Instru- ments' early IC packages in the 1960s were actually surface-mount devices and the Apollo, as shown in Figure 1). Original SMT devices were those electronic devices where the compo- nent leads are provided on two or four sides of a smaller footprint device designed to be soldered directly to the surface rather than mounted through the holes drilled in a PCB. SMT ame- liorated a good deal of electrical parasitic effects and returned a great deal of board space to the product developer because plated through- hole technology took up a surprising amount of area—something that has not always been fully appreciated. Here is where we circle back to my earlier allusion to show how road- maps can lead technologists down less than optimal technology roads Figure 1: Apollo computer boards used surface-mounted IC packages. The dual in-line package (DIP) ultimately replaced it before it was upstaged by surface mount a decade later. (Source: NASA)

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