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December 2014 • The PCB Design Magazine 55 two ends of the netlines out of the BGAs or con- nectors (or any other components for that mat- ter) and order them in a manner that enables completion of the routing without additional vias. It is an approach that makes an incredible difference in performance. Note the example in Figure 2. The routing looks clean, but the order- ing of the traces required to route without vias is not simple. Multiple Netline Routing The second aspect of the sketch router that enables high performance is the fact that it can consider routing from one to hundreds of net- lines at the same time. One example I recent- ly did was to route 765 netlines between two BGAs. I used six layers, and using a number of different sketch paths, it routed 650 of them in 18 minutes. Each time the sketch router is used, it attempts to route all the selected netlines and if it fails, they remain selected and the sketch router can be used to route them on the next layer, even reusing the previous sketch path if desired. Keep in mind, this routing was accom- plished without any extra vias other than the existing fanout vias. Figure 3 is an example of this routing on one layer. How long would it take you to route 650 netlines on six layers using only fanout vias? Video Examples As with the previous two parts of this series, we've published a video on YouTube that will give you a much better idea of the performance than still illustrations can. Click here to watch. PCBDESIGN Charles Pfeil is an engineering di- rector in the systems Design Divi- sion at Mentor graphics. He was the original product architect for Xpedition PCB and an inventor of XtremePCB. Pfeil has been in the PCB industry over 40 years as a designer, own- er of a service bureau, and has also worked in marketing and engineering management at racal-redac, asI, Cadence, PaDs, and veriBest. To contact him, click here. PART 3: PERFORMANCE continues Figure 3: sketch router on one layer, routing 151 netlines in 6.5 minutes. sketch routing