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    The Top Reasons Why PCB Design Software with Auto Routing Can Save You Time

    Altium Designer
    |  November 1, 2017
    Cartoon of man sleeping in bed

    I’ve been designing printed circuit boards long enough that my family has sadly grown accustomed to me spending more time at work than at home. When deadlines are looming, everyone knows I’ll be working late nights at the office.

    Modern PCB design software with auto-routing tools can help you cut down your routing time, but not everyone is a fan of these features. I know all the arguments against using an auto-router because I’ve been using them for years. As time has progressed and the core algorithms in an auto-router have become more advanced, some designers are singing a new tune about their key features.

    Auto-routers have evolved and are more useful now than they used to be. Instead of producing a board full of confusing and unusable routing, today’s auto-routers are more configurable. The best auto-routers are interactive, where the user can take control over the auto-routing process. Once you learn how to best use these more advanced auto-interactive routers, you’ll be amazed at how they can help you cut down your design time. The world of PCB design software with auto-routing has changed, and there are some great ways an advanced auto-interactive routing utility can cut down your layout time.

    Picture of black box input output process
    Auto routing a PCB used to be a black box mystery

    Auto Routers: Out of the Black Box and into Your PCB Design Software

    Unless you’re a hardcore optimization programmer, auto-routing can seem like a secretive black box technology that we can’t control. In the past, this was certainly true, and most designers I know are unwilling to yield control over their design to a tool they can’t control. You activate the tool, it reads through your layout data, and returns disappointing results.

    It’s true that fully automated routers do not always produce desirable routing in complex systems, and the results require some time to manually clean. The other possibility is the auto-router algorithm simply can’t accommodate all the design rules for a given layout, and it returns a result stating the design is unroutable. Problems like these have caused many designers (including yours truly) to lose confidence in auto-routers.

    PCB design software with auto routing can help your design

    Today it’s a different story, as auto-routers are vastly improved. Many of them are embedded in your PCB design software instead of being a third party black box application. This allows you to use the design rules that you already have set up, and it eliminates the need to interface with another application. PCB design software with auto-routing provides fully automated and interactive modes, which allow you to target specific areas of your design and help guide the router to create a useful layout.

    How Can Different Auto-Routing Modes Aid Layout?

    The entire point of auto-routing is to decrease your design time while laying out a manufacturable, fully-functional PCB. Auto-routers come in different flavors, and they are like sulfuric acid: dangerous if mis-used, but very useful in particular situations. Here are the three common modes you’ll find in PCB design software with auto-routing:

    1:Point-to-point Auto-routing

    Perhaps the simplest use for an auto-router is to connect simple point-to-point nets. You select the nets that you want to route, and the router will automatically route the traces while trying to comply with your design rules.

    In order for the tool to work successfully, you need to create an initial layout that doesn’t set up the auto-router to fail. Don’t put unnecessary components in the way of a critical net, then disallow use of vias, and then limit trace lengths to be too short. This an example of a situation where the auto-router will fail to comply with all design rules. Identify the portions where the auto-router can’t fail, and it probably won’t.

    2:Batch Auto-routing

    Unlike the older “black box” auto-routers, modern batch routers are much more configurable. They use the design rules that you’ve already created in your PCB design software, giving you some measure of control. A batch auto-router is a great tool to use to route miscellaneous nets that don’t carry stringent design rules.

    3:Auto-interactive Routing

    This is a variation on the two points above, but it allows a human to guide the autorouter. You can tell the tools to route individual traces or a group of nets to specific points on the board. The auto-router will determine the best path for traces between these points. This combines the best aspects of manual routing and auto-routing. It can also reduce the amount of cleanup as an odd route may only exist between two points, rather than throughout a large section of the board.

    Auto-interactive routing in action. The user selects different points in a layout, and a standard auto-routing feature fills in traces between these points.

    Why Use PCB Software With Auto-Routing?

    When my peers first encouraged me to look again at auto-routing, both in terms of function and when they should be used, I initially resisted. Eventually, my need to increase my productivity forced me to reconsider, and I gave auto-routing another look. Here are some areas where an auto-router has really helped me:

    1. Short or long point-to-point nets. These nets can take a long time to route manually, especially when your board is dense and complex. Now, whether they are short pin-to-pin nets or long nets that cross the entire board, the router puts them in much faster than I ever could.

    2. Non-critical miscellaneous routing. At the end of a design when I have a bunch of leftover nets to route (e.g., short traces between passives or DIP packages), an auto-router is a great tool to finish up the layout.

    3. Routing cleanup. Batch auto-routing will try to route your entire board if you can’t limit the tool to specific nets, which is not ideal in complex devices. However, you can determine which sections of a complex board can be easily accommodated with an autorouter, and which nets will have odd routing. Simply route any other nets by hand or with an auto-interactive router, and you can finish off the remaining connections with an autorouter.

    If you’re working on a more complex board, such as with fine-pitch high-count BGAs or other high pin-count components, you’re better off using an auto-interactive router. These boards can get very complex, very quickly (especially once you consider any supporting passives), and you’ll need to interject your creativity to create a functional layout. For the remaining portions of a board that are not critical, feel free to use an auto-router to finish off the layout.

    Could you use some help to shorten your design time? If so, then take another look at auto routing, it’s changed a lot over the years. Today’s PCB design software with auto routing, like Altium Designer®, can help you to get your designs to the finish line sooner. Who knows, you may even end up sleeping better as well.

    Would you like to find out more about how Altium’s auto-routing tools can help you? Talk to an expert at Altium.


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    Fast and High-Quality Routing

    About Author

    About Author

    PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

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