The PCB Design Magazine

PCBD-Dec2014

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52 The PCB Design Magazine • December 2014 This is the third and last article in a series discussing the core elements of effective PCB routing (control, quality, and performance). I recommend reading the August article on con- trol and the October piece on quality, because they provide background information that will help when reading this article. The primary attraction with autorouting compared to manual routing is the speed. In the previous articles, I emphasized the fact that user control, quality and performance are all required for a successful routing environment. Most autorouters are incredibly fast; but if the quality is lacking, the results require too much editing. When the quality is poor, the time to clean up the routing results is sometimes more than it would be to manually route it from the beginning. The sketch router provides the de- signer with performance that is normally only associated with autorouting while at the same enabling user control and route quality. What is it about the sketch router that en- ables high performance compared to manual routing? There are two factors: escape optimi- zation and multiple netline routing. Escape Optimization With BGAs and large connectors, hundreds and sometimes thousands of netlines run be- tween them. If the BGA is an ASIC or an FPGA SkETCH ROUTING column by Charles Pfeil MenTor graPHICs Sketch Routing, Part 3: Performance Figure 1: Tangled netlines mean a difficult routing challenge.

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