Altium Designer 20 Changed My PCB Routing Techniques
I just finalized my first PCB design using Altium Designer 20®. At the same time, I tested some new AD20 features, and in this article, I’ll share my thoughts about new PCB routing tools which had the biggest impression on me: sliding, and any-angle routing. Having read about and watched videos on these PCB routing tools beforehand, I was eager to try them out. These new features have given me more options for my PCB routing techniques.
New PCB Routing Techniques in Altium Designer 20
I have experience with trying to route curved traces with have 45-degree PCB routing techniques, and I got frustrated when trying to fit all traces in the required area. AD19 already had a kind of “any-angle routing” as you were, in fact, free to select any angle while routing. But when adding and enabling clearance design rules, I was not able to get close enough to edges or rounded objects, and had to keep clearances much larger than needed. Meanwhile, minimizing clearance manually increased routing time—and still the result didn’t satisfy me. Based on this frustration, I had high hopes for sliding and any-angle routing.
An improved Sliding feature changed my PCB routing techniques for small groups of traces. Instead of routing all traces at first go, I did a quick and dirty routing for a group of traces without taking care of angles, optimal clearances, or other details. However, I did the final grouping and layout optimization by utilizing the sliding feature afterwards, and in that way arranged them in the most convenient positions in the layout area. It seemed to work well that at first, I defined stack-up, and then determined width and clearance rules according to target impedance and cross-talk minimization.
After this rough layout routing, I grouped traces and moved them to their final positions by sliding. The sliding feature also worked well for traces routed using any-angle routing. When sliding routed traces towards a “locked” trace (select Walkaround Obstacles), the slide trace takes the same shape while still respecting the minimum clearance rule. For a small group of traces, these PCB routing techniques allow you to route traces quickly while still satisfying design rules. In Figure 1, you can see examples showing that there are a lot of options for how to arrange traces just by sliding.
When sliding traces close to the board outline or cutout area, the trace takes the shape of the edge of the PCB while satisfying the predefined board edge clearance rule, as presented in Figure 2. I see clear benefits for this when designing printed or structural electronics. In these situations, the board area is never rectangular, but more or less follows the part shape. With sliding, I can draw a straight trace and just push it to the edge of the board area. This allows the traces to follow the closest allowed location to the edge of the PCB. This lets me use the maximum amount of layout area, not just areas where we managed to put 45 angle traces. AD20 made sliding of individual or grouped traces in a smart way, which is a very useful feature for packing traces in an optimal area or maybe even in a minimum area. The benefit of this is especially notable when working with boards that have curved edges.
Any angle routing finds out the shortest needed trace between two points. Figure 3 shows an example where a highlighted trace was routed with 45-degree angles and the lighter trace is a proposed path created with any-angle routing. As you can see the trace changes angles in a smart way when avoiding vias. The same happened also with any obstacles, like other traces and components, while keeping routing smooth and fluent. I routed lots of traces by any angle routing and in all cases I was able to find out the shortest path for a trace, even in challenging situations where there were obstacles with many sizes and shapes. This gave me a new PCB routing rule: minimum trace distance principle.
The minimum trace distance design principle can have a couple of benefits. One example is when designing capacitive sensors. These sensors measure extremely small capacitances, even less than 1 pF. Because of this, designing routing with minimum parasitic capacitance is important. Every routed trace has parasitic capacitance (and parasitic inductance), which depends on the layer thickness and PCB trace width in the design. Capacitance per unit length can be obtained quickly from the impedance profiler in the layer stack manager, and total capacitance is then just multiplying length of trace with capacitance per length.
Another example case is situations where a fast rise time causes signal integrity problems. With the 45-degree routing topology, the length of a trace can be long enough to cause problems, but straightening the line with any-angle routing might bring the trace length below the critical length. I won’t say any-angle routing alone solves this problem, as you still need to place termination if the rise time is too fast on a short trace. However, any-angle routing gives you a tool to find the minimum trace length. After shortening the trace, you still need to determine whether termination is needed or not.
In printed circuits, using the minimum trace length minimizes trace resistance. In these kinds of applications, shortening the trace length is always beneficial, as the resistance of printed traces always plays an important role. Every bit of resistive loss you can remove from the trace is worth the effort.
Any-angle routing is also an excellent PCB routing technique in crowded layout areas. So far, 45-degree routing was jamming in “rush” conditions, but this is an easy job for any angle routing. Crowded areas where there are many vias, components, restriction areas or other obstacles in a small area, are easiest to layout with any-angle routing. Instead of jamming a trace does with 45-degree angles, any-angle routing finds the most suitable angle for trace such that can bypass obstacles while still complying with the clearance rule. Any angle routing allows “hugging” obstacles with minimum clearance with any trace shape. You can see an example of this in Figure 4 below.
When designing layout, we also need to think about crosstalk. One reason for crosstalk is too small clearance between traces compared to thickness of dielectric between trace and reference plane. While I did routing by any angle routing I noticed that it is rare that traces are travelling in parallel with minimum allowed clearance. Instead, traces go slightly different directions, because rarely do the shortest distances between two sets of points lead in exactly in the same direction, as we can see in Picture 5. Due to this, in many cases clearances between traces were bigger than the minimum allowed, which means less cross talk. And through any angle routing, this happened accidentally. Someone could say the layout isn't exactly beautiful, but at the end of the day, does it need to be if it just works better?
After finishing my PCB layout, I concluded that sliding and any-angle routing provide the following useful benefits:
- Sliding allows quick grouping of traces. No matter what the angle is, grouping can be done smoothly while considering clearance rules.
- With the sliding feature, you can utilize a full PCB or printed electronics layout area, which is especially valuable in cases when the layout area is curved shaped.
- Any-angle routing finds the shortest path for the trace. With this you can use the minimum trace length principle, which minimizes parasitic capacitance, inductance, and resistance in PCB traces.
- Any angle routing gives huge benefits in crowded layout areas. It definitely makes routing faster by offering a lot more freedom for routing directions.
- Using the minimum trace length principle with any angle routing, you “accidentally” decrease cross-talk, because you most probably do not route traces in parallel with minimum clearance.
Sliding and any-angle routing together changed my PCB routing techniques. These features make routing quicker and easier, as well as allowing you to be more flexible with your routing choices. In addition, these can also bring new opportunities to implement different routing principles, like minimum trace length. I had big expectations when starting my PCB layout, and after using these features, I see that these will prove incredibly useful in my PCB layout tasks.