Introduction to Routing in a PCB
After placing components, it’s time to start thinking about routing the design. In the previous section, we introduced just a few of the design rules that are needed to ensure your design is manufacturable. Before you start routing the board, it’s a good idea to quickly review a few of the important design rules so that you can route things efficiently. Once the design rules are created, you can get started with routing, and you won’t have to worry about manually checking everything in your layout as you route your traces.
Routing Rules and Strategy in a PCB
In the last section, we looked at the initial placement of components in a demonstration project. Before you start routing, it will be important to decide which components absolutely cannot move in the PCB layout. Some components, like connectors or large ICs that have a heat sink, will need to have a fixed location and should not be moved in the design. Other components can often be shifted as you figure out routing throughout the PCB layout.
Sometimes, you do not know which components will need to move and which components you can leave fixed in your initial placement. Therefore, to prevent the need for a lot of re-routing, it’s important to come up with a strategy for how to approach the board. There is no best strategy for every PCB, but there are some important points to think about:
- Using polygons vs. traces: Some nets are best routed with polygons, while others must be routed as traces.
- Layer transitions: Which layers will you be routing on, and how many layer transitions through vias will you need to make? Ideally, you should try to minimize the number of layer transitions.
- Routing topology: Some signals can be routed as buses, while others must be routed point-to-point. Sometimes, groups of signals need to be routed in parallel (side by side) because data is being carried on multiple traces at once. This is a more advanced rule that we’ll examine in a later lesson.
The most important routing rules to consider in a new design center around three areas: clearances, trace geometry, via size, and impedance. Some of these points are handled inside Altium Designer and other ECAD applications automatically, either through design rules or a setting in your program. The video below will show you how to quickly access and start using the routing features in Altium Designer.