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16 The PCB Design Magazine • January 2015 meaning even more density than the leads/in 2 number alone indicates. Interestingly, one trend that appeared in the first decade has leveled out. The minimum trace width decreased by nearly 50% over the first five years of the awards and then has been mostly stable since then. The total number of metal layers had two "growth spurts" and now also seems to have leveled out around 14. Future Trends So what does this trip down memory lane tell us about the trends for the future? • The clearest message, and the one that has continued unabated, is that the boards submitted to the TLA awards have been on a long and fairly steep linear increase in complexity. Not only are there more com- ponent leads from fewer components, but the average board area is shrinking at the same time. • The reduction of the number leads per part, combined with the increasing ratio of passives to active components, points to integration of more and more functional- ity onto silicon with performance criteria that demand high volumes of resistors and capacitors for signal and power integrity. • Over the last five years, layer counts have stayed about the same, while area has dropped 29%, and densities have gone up by 25%. You can see the density increase more dramatically over the last 20 years, highlighted in the chart on the right. • Signal integrity on the submitted designs was extremely important with 92% of the entries employing SI tools during the design. One thing is certain: PCB designs will not be getting simpler in the future! PCBDESIgN PAST AND FuTuRE TRENDS IN PCB DESIgN continues feature David Wiens is a product marketing manager at Mentor Graphics. In the cover feature article of the journal Science, researchers at the university of Illinois at urbana- Champaign describe a unique process for geometri- cally transforming 2D micro/nanostructures into ex- tended 3D layouts by exploiting mechanics principles similar to those found in children's "pop-up" books. Complex, 3D micro/nanostructures are ubiqui- tous in biology, where they provide essential func- tions in even the most basic forms of life. researchers noted that existing methods for form- ing 3D structures are either highly con- strained in the classes of materials that can be used, or in the types of geom- etries that can be achieved. "Conventional 3D printing tech- nologies are fantastic, but none offers the ability to build microstructures that embed high performance semiconduc- tors, such as silicon," explained John rogers, a Swan- lund Chair and professor of materials science and engineering at Illinois. "We have presented a remark- ably simple route to 3D that starts with planar precur- sor structures formed in nearly any type of material, including the most advanced ones used in photon- ics and electronics. A stretched, soft substrate im- parts forces at precisely defined locations across such a structure to initiate controlled buckling processes that induce rapid, large-area extension into the third dimension. The result transforms these planar materi- als into well-defined, 3D frameworks with broad geo- metric diversity." Compatibility with the most advanced materials (e.g. monocrystalline inorganics), fab- rication methods (e.g., photolithogra- phy) and processing techniques (e.g. etching, deposition) from the semi- conductor and photonics industries suggest many possibilities for achiev- ing sophisticated classes of 3D elec- tronic, optoelectronic, and electro- magnetic devices. New Process Transforms 2D into 3D Microarchitectures

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