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PCBD-May2016

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12 The PCB Design Magazine • May 2016 is a gross simplification. A typical FR-4 board is layer upon layer of core and prepreg materials that have specific heights and requirements. Even the typical copper route has a height that should be taken into account. As designs are be- coming denser and more complex, greater at- tention is given to how to design a stackup with the best materials and configuration that satisfy both cost and the design requirements. To aid designers and engineers in this area of greater attention, there is a movement to- ward pre-layout, software driven, stackup build- ers which help predict the board characteristics more accurately, and with greater signal integ- rity, which reduces the need for as many design changes throughout the layout process. Engi- neers and designers can more closely examine a board stackup, with visual cues for dielectric (prepreg) layers in between metal layers, blind and buried vias, as well as trace widths and heights within the stack. They can also attempt to prevent unexpected manufacturing flaws be- cause many of these stackup builders include the manufacturer's specs or allow companies to build their own proven specs into the system for reliable re-use. Since there are a vast number of manufac- turers, and so many of them tend to have their own specs, Intercept chose many years ago to upgrade its stackup options to take height, di- electrics, and materials into account for easier output and drawing creation. But a more widely recognized expert in this area is Polar Instru- ments Inc., which has created its Speedstack tool set to allow quick and accurate stackups to be built and analyzed prior to the actual layout phase of the design cycle. They have even be- gun offering materials libraries that are either a generic set of information for easy building, or an actual list of materials as specified directly from some manufacturers. (Note: Materials li- braries are offered as a service to customers, but are not guaranteed to be fully up to date at any given time.) The Constraint Browser Nearly every mid-to-high-end software ven- dor now offers full design constraint capabili- ties, from building simple design rules all the way to complex, formula-driven high-speed constraints. This is an area of automation that has allowed a boom in the high-density board THE STATE OF THE ELECTRONIC DESIGN AUTOMATION NATION Figure 1: A view of a stackup built in Polar Instruments' Speedstack HDI software.

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