Some basic PCB layout vocabulary can be found here.

Preparation

• Make sure the schematic is as complete as possible before starting layout. If major sections are added or changed on the schematic while layout is ongoing it can really mess up the process.
• Consider the desired stack-up of the board:
  • How many layers will you need? Generally 2, 4, or 6 layers are a good starting point, depending on the complexity of the board.
  • Make sure to include at least one ground plane (probably two for a 6-layer board). Ground planes shield from interference between different signal layers, and also make it really easy to route components to ground: just put a ground via!
  • If the board will carry a lot of high-speed signals, it’s probably a good idea to use controlled impedance traces [need to probably make another page on this]

Component Placement

• In general, try to place components in a way that makes sense:
  • Group together components that are part of the same subcircuit.
  • Place components in a way that minimizes trace lengths and required vias.
• Place decoupling capacitors as close as possible to the parts/pins they are intended to decouple. Include a via to the ground plane at the ground terminal of the decoupling cap.
• Try to have connectors on the edges of the board.

Rooms

Rooms are great for organizing your components into subcircuits, and especially good when you have multiple copies of a subcircuit that you want to duplicate the layout for.

Project → Project Options → Class Generation, check the box that says “Generate Rooms” for the schematic page you care about

Routing

• Place all your components before starting routing. It’s fine to move them around later, but it’s a good idea to have a general idea of where everything will go before starting routing.
• Avoid 90-degree angles in traces, except in a 3-way intersection. In general, it’s best to have 45-degree angles in traces as seen here:

• If there are lots of traces running between two subcircuits, try to get them to run all in the same sort of direction like in the image above. It’s cleaner and won’t require as many vias.
• It’s often better to use polygons for power nets if the board has a designated power layer (Place → Polygon Pour).
• Trace width and spacing is important, especially for high-current or high-speed signals:
  • For high-speed signals a good rule of thumb is the 3W rule - traces should be at least 3 of the trace width apart (measuring center-to-center).
  • For high-speed signals trace width can also matter if you’re working with controlled impedance [need to probably make another page on this]
  • For any trace carrying a meaningful current (like power traces, for example) we need to make sure the trace doesn’t get too hot. A good resource for this is the Saturn PCB Toolkit (free to download) - under Conductor Properties you can input the parameters of the trace in question to see the estimated heat increase. Typically a rise of 10-20°C above ambient temperature is acceptable.

Designing for Manufacture/Assembly/Testing

• Use thermal relief for pads, especially those connected to a large pour like ground. This helps during soldering by making sure the heat is concentrated around the pad instead of spreading out throughout the rest of the net.