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46 DESIGN007 MAGAZINE I NOVEMBER 2020 As the typical PCB design becomes more complex, so do the techniques and strategies required—not only to complete the design but also to create a functioning product that performs to specification. Autorouters have improved dramatically over the past 20 years, allowing the PCB designer to produce seem- ingly hand-crafted results in an incredibly short time. However, the autorouter is guided by design constraints, and there are only so many rules that can be practically defined. Every situation is different, requiring unique tradeoffs. The limiting factor with any auto- router is describing just what it is that human decision-makers actually do. PCB designers need to understand the under- lying high-speed issues of the design based on simulation (Figure 1) and then translate these into corresponding design constraints. Constraints can always be altered on the fly if a particular constraint is too tight, provid- ing the designer can justify the easing of the specification and that the product is still manufacturable. Firstly, a pre-layout simulation defines the extent of placement. Controlling the place- ment of devices limits maximum trace length, reduces flight-time-delay and skew, and assists in compliance with timing specifications. To obtain a high route-completion rate, component Routing Strategies for High-Speed PCB Design Beyond Design by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA Figure 1: Develop high-speed design constraints based on pre-layout simulation.

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