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16 The PCB Design Magazine • May 2016 out the autorouter all together. Designers have begun realizing that spending all their time try- ing to get a good outcome in a complex auto- routing environment is an equivalent or even longer phase of the design cycle than if they simply hand routed sections of their board. The reason for this is because autorouters require certain setup for a good outcome. Main- stream designs are becoming full of BGA break- outs, diff-pairs and nets tuned in all axes (not just X and Y, but through the Z as well!), and areas where all these complexities neck down and tune under completely different rules. But teaching the autorouter all of this can some- times take so long that the user might as well have used manual routing to accomplish what in many cases is a better outcome than any- thing a routing algorithm could produce. To better fill in for the gaps in the full au- torouters, EDA vendors are now offering some very nice semi-automatic routing options such as routing all wires of a bus line together, rout- ing and tuning diff-pairs one at a time, or re- gion at a time, and handling breakouts from dense pin arrangements in various systematic ways. The very basics of the process are also im- proving with better visualization such as real- time, guided routing and quick via placement without the need for so many mouse clicks. All of these options are continually honed and im- proved, providing greater flexibility in response to designers' increasing level of difficulty. While EDA software has run the gauntlet between fully manual, to fully automatic, to everything in between, it's fair to say that au- to-routing will remain an ever-evolving area of the design cycle. The vendors all provide tools to help users get their jobs done, with different strengths and weaknesses, but it seems that the sweet spot for this area of design is in the semi- automatic: neither manual, nor fully automatic. Auto-Tuning High-speed design and auto-tuning are an area of complexity that are continually running into roadblocks. There is no advisable fully au- tomated solution to this area of design. Try au- to-tuning 24 wires all at once, and you have no- win collisions. Try just a few wires at a time, and your remaining wires can't find enough space to trombone their way together. Back and forth you go, until you delete all the wires and start manually tying up wire after wire, using every mil of space you can to save space for the next tune. But here is the ingenuity of it: as you are stuck routing your wire and tuning as you want it tuned, automation is right at your fingertips. Figure 4: As higher densities, tuning and diff pairs become more prevalent in mainstream PCB de- signs, autorouters are struggling to keep up with more complex anomalies. It becomes a question of whether such anomalies are worth trying to algorithmically improve, or whether hand routing is returning to the picture. Figure 5: Programming a full autorouter to break out a diff pair bus line and tune the pairs ac- curately could take hours. Using newer bus line routing options and auto-tuning per diff pair to allow for close checking of the outcome has be- come much preferred among designers. THE STATE OF THE ELECTRONIC DESIGN AUTOMATION NATION