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PCBD-Oct2014

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44 The PCB Design Magazine • October 2014 ThIS IS SkETCh ROUTING, PART 2: QUALITY continues design and the constraints are set up properly, fulfilling the objective quality metrics will be accomplished—the only problem is that it may take a long time. Tuning the nets in matched sets or tuning for phase matching is clearly a pains- taking process if it all has to be done manually. The most effective routing environment for ob- jective quality is to have high levels of automa- tion under the control of the designer. Subjective Quality Subjective quality is not so easily defined or accomplished. We have all heard that design- ers spend time trying to make the routing look pretty or look like art. I suggest that it is actu- ally something else. It is a matter of efficiency. Designers want to route efficiently, meaning the traces are direct without excessive meandering, vias used only when absolutely necessary, no ex- tra jogs without purpose, and the traces spaced evenly. Efficient routing is a primary method for attaining the objective quality. It is not a coinci- dence that efficient routing often appears artistic because we tend to associate symmetry, balance, and repeated patterns with what know as graphi- cal art. Mentor Graphics conducts the Technology Leadership Awards program each year, with cus- tomers submitting designs to be judged. Awards are given out in each technology segment and an overall winner is celebrated. I was a judge in the last event, and along with the other judges, we found it is sometimes hard to determine if a design is truly simple, or if it is really complex, yet routed so well that it only looks simple. If routing a design in the most efficient manner re - sults in the design looking simple, we can call it art but I prefer to look at it as routing excellence. This is my definition of subjective quality. I be- lieve that providing this kind of quality is funda- mental and is required for any automated rout- ing methods to be widely adopted by designers. Any designer who has been manually rout- ing PCBs for years also understands that most of us display a bit of obsessiveness in our routing methods, especially when it comes to even spac- Figure 2: Subjective quality = efficient routing. sketch routing

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