Amusement parks often feature small raceways with gasoline-powered, two-passenger mini-cars going around a multi-lane track. Drivers can experience the thrill of steering and accelerating while trying to beat friends or family to the finish line. There’s a catch though. A rail-like barrier positioned in the middle of each lane prevents cars from moving from one lane to another.
Consider the amusement park like a circuit: designing the amusement park requires understanding the flow of power from gates (power supply) through pathways (traces) touching all the major attractions and necessary features of the park (components). While there might be significantly more hands and minds involved with planning the layout of an amusement park than a circuit board, a PCB designer still has a lot of work to optimize their traces for routing.
Using a PCB editor, the PCB designer will have to consider the connections and interactions between all components required to make the board functional. Furthermore, you’ll have to be wary of the various design rules and design standards required to avoid shorts, meet manufacturing demands, and maintain board integrity. Let’s show you the ropes on tools to get your board routed.
PCB Routing Options: Getting Your Board Routed
Once you have your board outline created to meet form factor requirements and you have part placement based on footprints, your design is ready to be routed. But traces aren’t just like using a paint brush and drawing lines willy-nilly. You’ll need to be wary of everything from component-component interactions, power distribution, and heat generation to layers, vias, and pads.
Often you will have manufacturing specifications that coincide your board creation and these will help guide you in terms of how to route your traces and avoid circuit board failure. While routing your traces, though, you’ll need to pay attention to trace widths to avoid overcrowding and creating soldering issues like solder bridges. Furthermore, keeping track of trace angles as well as enabling enough space around mounting holes will need to be added to your list of concerns.
On top of it all, you’ll need to ensure that your traces and net connections don’t overheat the board by working in necessary vias or with proper planning of your traces during layout. In your PCB editor, net connections will display what pins need to be connected and where to place the copper from a manufacturing standpoint. With these being just some of the bare requirements for routing, you’ll understand why routing tools have come such a long way.
Not the Autobahn: Traditional Autorouters
Now, the mini-car raceway attraction is the amusement park version of a routing tool, or auto-routing. Like it or not, fledgling race car drivers have no choice but to follow a predetermined path established by narrow design rules. When a driver steps into the car, it doesn’t automatically choose a speed and begin steering along the path. Instead, the driver takes control so that the mini-car doesn’t continually bump into the barrier.
In the same way, a traditional autorouter follows instructions given by a designer, adheres to behavior parameters, and then provides a response that maximizes reliability and signal strength. With all this, an autorouter:
Establishes the direction and route of each net on a PCB,
Determines a routing sequence for the nets, and
Routes each net in the predetermined sequence.
When you input nicely-spaced components, placement grids, and efficiently designed paths, an autorouter produces a finished PCB layout with little to no problems with trace lengths, the number of routing holes, vias, and signal crosstalk.
Autorouters can make your design process smoother and easier if they are adept enough
(Alt text: Auto-interactive router on traces in Altium Designer)
Tried and True But Still Blue
While mini-car raceways are fun, physical limitations prevent any creative behaviors from emerging. Drivers don’t have the option of reversing their course and cannot go past preset speeds. But despite limiting freedom, design rules—specifically in this raceway example—eliminate chaos. Any driver attempting to veer into the next lane gives his or her passenger a rude awakening as the undercarriage of the car slams into the barrier. If they could change lanes and go faster, seven-year-old drivers would become young gun versions of “The Intimidator.”
Well-known approaches such as grid, geometric, and shape-based autorouting solutions restrict flexibility. Grid routers split the design into grid segments that ignore space and objects. Using grid segments, on the other hand, translates into vertical layers with tracks running from the top of the PCB to the bottom and horizontal tracks running from one side of the PCB to the other. Because no variation from vertical or horizontal layers occurs, increasing the density of the board design requires more and more layers.
Instead of relying on a grid, shape-based routing uses a gridless approach that requires full awareness of every obstacle in a design. Shape-based routing identifies the real shape of obstacles, defines the space between obstacles as a series of rectangles, and avoids the obstacles when generating a path. The routing path follows the edges of the rectangles.
However, geometric constraints limit the effectiveness of shape-based routing because routing only occurs at right angles and by coordinates. In addition, the routing paths associated with contiguous rectangles can only extend in vertical and horizontal directions.
Adaptability is the Future of Design
As consumer and industrial products become smaller and more complex, devices may require variations in PCB shapes and different component orientations. As consumer awareness drives changes in product design, PCB design and autorouting require adaptability.
For example, PCB designs often rely on Ball Grid Arrays that use staggered grids of pins to take advantage of pin density or rotate components to efficiently utilize space. To achieve an efficient design, you may need to consider the flow of connection lines, assign a layer in a particular direction, and route connections on that layer in that direction. Shape-based routers can handle different component shapes and mixed technologies by using special routines that convert right-angle corners to diagonal paths.
While you are figuring what routing needs your board has, though, the time is slipping by and the traces are haltingly getting laid out. How does your board then transition, with all appropriate nets and traces, pins and pads, vias and mounting-holes, into manufacturing in the easiest and most efficient manners?
Topological Routing Approaches
In some ways, using special routines gives a short-term approach to adaptability. However, using a topological router establishes a long-term approach that solves current and future design problems. Topological routing offers the adaptability not seen with traditional autorouting tools. The topological approach solves problems caused by geometric constraints and reliance on coordinates as a frame of reference.
How does this occur? Topological routing builds a triangulated map of the space between adjacent obstacles. Routing algorithms built around spatial analysis weave between pairs of obstacles from the route starting point to the route ending point. As a result, topological routing does not rely on shapes and allows a path to occur at any angle. This natural approach to autorouting provides efficient routing and decreases the number of vias.
Finding the right adaptive routing software will ensure your traces get placed optimally
(Alt text: Auto-interactive router on traces and object avoidance in Altium Designer)
In contrast to the fairly rigid approach taken by grid routing, geometric routing, and shape-based routing, topological routing does not geometrically tie to the routing space. A topological map of a PCB emerges through the linking of each obstacle on the board to neighboring obstacles. Looking at the map from above gives the impression of seeing connected webs. Routing paths step from one web strand to another until reaching the target. In this way, the routing path weaves between each pair of obstacles.
Natural paths occur because of the separation of the mapping space from the routing space. With that separation in place, the strict adherence to right angles does not exist with topological routing. As a result, the mapping process mimics the work of designers and yields high completion rates and speeds. Paths cross the PCB in the most direct fashion while loosely maintaining assigned layer directions.
This gives you the flexibility needed to decide whether a track will or will not fit through a routing channel and the adaptability needed to logically assign channels to non-standard geometric shapes, dense arrays of staggered-pin components, and varying shapes or configurations of components.
Modern topological routers adapt to different challenges by using mature routing algorithms and multiple types of routing engines. Using Altium’s Situs™ as an example, the routing engines include a memory router, pattern routers, a power and ground router, a wavefront router, shape-based push and shove routers and a significant number of heuristic routers.
In addition, the Situs autorouter relies on a strategy file built from thought processes to define patterns of thought and control the routing engines with instructions contained within the strategy file. The instructions show how to route the board, set weights for different routing engines for an empty routing space, and change the engine weights for dense routing spaces.
Altium Designer provides a powerful, easy-to-use tool that can simplify the process of implementing a variety of routing options, including autorouting, manual routing, or a combination. To give Altium Designer a test drive, sign up for a the best PCB design software.
And to learn more about PCB routing options to maximize the adaptability of your PCB design, talk to an expert at Altium.
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