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Here is a common misconception held by those who don’t fully understand the PCB layout process or how to wield today’s high-level EDA tools: "All I need to do is push the autorouter button, let the computer route all the signal traces, and get the layout 100% routed. It’s a no-brainer. Anyone can do it. It should take less than a few hours.”
Well, sure, if you’re in a hurry to check the box indicating you’re finished with the layout. But your results will look like a plate of spaghetti and most likely not function correctly, if at all, while not passing SI/EMC testing. Good luck with that mindset and methodology.
As you can see, there’s a lot of confusion about autorouting. I will discuss routing and autorouting in general terms, my initial distrust of routers, and the “a-ha” moment that changed my mind. Then, for specific autorouting techniques, I will focus primarily on the Siemens router.
Routing vs. Autorouting
Let’s start by setting the baseline for “routing” regarding signal traces. Traditional routing is done by manually connecting (routing) all signal traces from point to point, mouse click by mouse click. Then, we manually make any trace constraint modifications/adjustments as necessary to meet the design requirements. Once 100% routing is achieved, a design rule check (DRC) is performed, and all flagged errors must be addressed—after the fact. This legacy methodology is very labor-intensive and time-consuming, to say the least.
The form of routing most utilized today is “manual interactive routing,” with only a few higher-end tools possessing automation-assisted interactive routing capabilities. This manual interactive routing is a combination of human effort, along with software tool utilization, and some limited automation. The key here is that the user is manually performing and controlling each and every mouse click of the routing process, but with the addition of tool automation assisting/restricting and guiding the user along the way, and according to the constraints that were implemented.
To read the entire article, which originally appeard in the June 2025 Design007 Magazine, click here.
