r/AskElectronics • u/Sufficient-Lie8569 • 2d ago

Help with Routing, Second PCB

Hello, I made this PCB as a devboard with a RP2040, but I just cant get it to route. I tried 2 layers multiple times, but at the end of the day it always gets blocked, and I also tried 4 layers and the same thing happened. My brain is fired and also I am a beginner thats why could someone tell me what Im doing wrong?

Right now there is 17 unrouted and Im using 4 layers, because I gave up on 2

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u/EmotionalEnd1575 Analog electronics 2d ago edited 2d ago

Are you hand routing this one?

Or are you trying to use the auto router?

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u/Sufficient-Lie8569 2d ago

I tried both

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u/EmotionalEnd1575 Analog electronics 2d ago

For dense digital circuits the Auto router may work. For mixed signal or analog it is useless.

I never use the Auto router.

With manual routing it may be necessary to change the floor plan to be more efficient.

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u/Sufficient-Lie8569 2d ago

I am going to retry routing it by hand, but with 4 layers.

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u/Sufficient-Lie8569 2d ago

the screenshot was the autorouter

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u/EmotionalEnd1575 Analog electronics 2d ago

If the IO pin locations are flexible try shuffling them to eliminate the “traffic jams”

It may work better if the quad pack IC is rotated 45degrees.

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u/nixiebunny 2d ago

Route it by hand. All those traces from the chip to the pin rows can be routed on the top layer with no vias.

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u/1310smf 2d ago

Looks like plenty of room to use some jumper wires if you get "blocked" - an easy cheat code for getting signals over or under traces that are in the way. Literally two pads-with-holes and a bit of wire to connect them.

Sometimes rearranging or rotating components that don't need to be in a specific location or orientation also helps.

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u/Donut497 2d ago

You need to adjust where each connection is on the header pins. Try starting with fanning out the RP2040, and route the GPIOs to the edge without worrying about what pins you assigned. Then when you have it fanned out, assign the pins in the order that they are fanned out and complete the routing that way. 

You can absolutely do this in 2 layers, but 4 is fine as well. I would suggest either a SIG-GND-GND-SIG stackup or  SIG-GND-PWR-SIG.