These are the track and via sizes I usually use. is my default signal trace width and my default via size. Any larger traces and vias than that are used for routing power.
Before routing any traces, I always place all the components. My main strategy here is to separate the board into sections. First I place all the connectors on the board edge. Usually I like to place solder pads right in front of the connector but because of limited space on this board I’ll place them on the back.
The first section I’m then going to figure out is power protection and voltage regulation. Our main focus during component placement should be to find a layout with the shortest traces possible. Especially for power lines, longer traces create more inductance. Therefore I try placing the input power protection and buck converters right next to the ESC connector, where the power comes from.
Another advantage of placing the buck converters near the board edge is that this way we isolate the switching noise from the rest of the components. For example we should try keeping sensitive components like the IMU as far away as possible from our switching regulators.
When placing the components for the buck converter you should make sure to keep the input capacitors as close as possible to the input pin of the main IC, while still leaving enough space for wide traces or copper pours that lead into the VIN pad. The inductors should also be placed as close as possible to the buck IC, again ideally near the board edge and away from sensitive components.
Usually the output capacitors go near the output of the inductor, especially when there is no specific point the output is routed to, as on the 5V inductor. But in the case of our 10V output we know exactly where the load is located which is our VTX connector. As I have two capacitors on the output of the 10V buck converter I place one right next to the inductor and the other right next to the ESC connector to decouple more closely where the actual load is located. That way we work against the inductance created with the long 10V trace going to the VTX connector.
To continue the power flow with as little trace length as possible I place the Schottky diode for the 5V buck right after the inductor and next to that the two LDOs. Again here placing input and output capacitors as close as possible to the respective pins. As we also need to route VBUS to the LDOs I placed its diode next to the one from 5V.
Like this we have our complete power handling isolated to one side of the board.
After positioning all power handling components I start placing the main logic components starting with the largest ones. On this board these are the MCU, Flash and OSD chip. When doing this we also have to account for important components that need to be close to these chips. Both MCU and OSD have a crystal that should be placed as close as possible to the respective pads.
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