The PCB Routing that Benefits the Most from Interactive PCB Auto Routing

October 17, 2017 Altium Designer

Worker on roof





Years ago I helped to re-roof a house, and the first task was to remove the old shingles. Pulling up shingles one at a time, I was very proud of my efforts until a professional roofer came over to me shaking his head. Using a scoop shovel like a snow plow, he removed a couple a hundred shingles in less time than it took me to pull up five by hand. I learned up on the roof that day to always look for better ways to get the job done.


When routing a PCB design, we also want a more efficient way to get the job done. You as a designer are probably aware of how much time is takes to manually get the cleanest route possible.  You’re probably also aware of Auto routers, which will do the job faster, but often with undesirable routing results. Now, like how the shovel was a better way to remove shingles, we have a better way to route using an auto-interactive router.


For those of you who aren't familiar with the term auto-interactive router, this is a relatively new routing technology. It is designed to give you trace routing that has the look and precision of manual routing but at approximately one connection per second. Auto-interactive routing is not a batch auto router and is not designed to route your entire board. Instead, it is interactive PCB auto routing where you have the control and the router does the work.


While auto-interactive routing can generally speed up your process, there are areas of circuitry that benefit from it. Particularly, single or multiple nets that need to be connected in a specific order without changing layers. More specifically this can be, point-to-point routing, BGA breakout routing, and bus routing.


Point-to-point trace routing

As you know, PCBs have many point-to-point connections. These can be short nets that connect component pins in tight circuitry groups, via escape patterns from SMT pads or nets that run the length of the board. These are not difficult to manually route, but they take time. An auto router will route them very fast, but you may be left with undesirable routing on the rest of the board. You could restrict the auto routing to just the short connections, but that requires additional setup time before you can use the auto router.


An auto-interactive router is incredibly fast when routing these same nets. You will simply select the nets that you want to route and then engage the router. Using the design rules that you have already established in the database, the auto-interactive router will use the shortest possible path to route the traces. It will also do this without the cumbersome setups that an auto router requires.


Computer motherboard circuitry

An auto-interactive router works well to connect short point-to-point connections





BGA trace routing

Before manually routing traces out of a BGA, you’ll need to take the time to figure out the best connection order of the nets. This ordering is important so that the designer can route the traces in the most efficient patterns possible to connect the BGAs. Efficient routing patterns not only leave open space on the board for additional routing but will reduce or eliminate the need for vias. Vias take up space that you may need for other routing, and they can introduce undesirable signal characteristics. Using an auto router for BGA routing may actually increase your via count as it typically does not choose the best connection order of the nets.


This is where using an auto-interactive router can be handy. It can quickly order the BGA connections for you. It will evaluate your selected nets in order to evenly distribute the traces on the board layers that you have enabled for routing. The auto-interactive router will then route the traces to connect the BGAs together in clean and precise routing patterns without using vias. These clean routing patterns will give you the additional board space that you will need for trace tuning or other routing edits later on.


Computer motherboard trace routing

Bus routing is another strength of an auto-interactive router



Bus trace routing

Often times buses are manually routed to create a clean routing pattern. If the bus is not routed in a clean pattern, it could cause problems with the signal characteristics of the bus. The downside is that manually routing a clean bus pattern takes a lot of time. Buses can have a lot of nets in them, and some boards may have several different buses as well. For example, double data rate (DDR) circuitry is an example of multiple bus routing with high net counts.


An auto-interactive router will route the nets of a bus for you, but it will do it under your control. First, you will select the nets of the bus that you want to route. Next you will draw a path on the board that you want the bus routing to follow. This path is a template that specifies the direction and width of the bus to the router. The auto-interactive router will then follow the path to route the traces all while obeying the design rules at the same time. The router does this work very quickly, and the results are a very clean bus routing pattern.


Just as the shovel was a much better way to remove shingles, an auto-interactive router is a much better way to route your PCB design. Knowing the best ways to use this router will be the key to your success, and we’ve talked about three of those ways. Point-to-point, BGA, and buses are all areas of routing that an auto-interactive router can help you to do a better job.


Routing is part of the PCB design process that Altium can help you to do a better job with. Altium Designer 18 is PCB design software with powerful resources, including auto-interactive routing with ActiveRoute. Would you like to find out more about how ActiveRoute will be able to help you to route your next PCB design? Talk to an expert at Altium.


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About the Author

Altium Designer

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

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