Hello,
I’m a beginner, how do you route in 4 layers ? Can I reserve layers 2 and 3 for power supplies and ground? What is the general use of layers 2 (In1.Cu) and 3 (In2.Cu) ?
With 2 layers I use one layer 100% for GND.
When I can’t connect everything at one layer (with GND at second) I use 4 layers. But I have both inside layers as GND.
If you have In1 as GND and In2 as VCC then when fast signal track jumps trom top to bottom the return current jumps from GND to VCC. Because of this near each via on your signal track you should have capacitor blocking VCC to GND layers, while having both them GND you need only a GND via.
If you don’t have fast signals then it is not a problem.
I like the Sig/PWR - GND - GND - Sig/PWR stackup as well with 4-layer boards. One additional benefit is the PWR/GND spacing is generally much closer than if PWR - GND are on layers 2 & 3, so it makes a better high frequency capacitor.
If you:
- route traces mostly in one direction on the top and the other direction on the bottom layer
- pour PWR on top and bottom
- pound some vias to connect top/bottom PWR pour
You can reach most areas that need power pretty easily with a copper PWR pour on top and bottom because the cuts caused by the traces are in opposite directions. KiCad will tell you if you if anything is not connected.
In case it is not obvious, to create a GND plane on a layer, simply draw a copper pour that fills the layer, and attach it to GND.
I’ve collected some notes here:
Sorry, I don’t quite understand what you mean ? Is the return current annoying ?
Not sure exactly what your KiCad related question is ? can you explain please ?
It can be. The best thing I learn was to concentrate on the return path/current than on the real net.
DC and Audio type AC will flow “as the crow flies” with regards to the return current. However, faster edges (ie digital edges) will want to have the return current under the trace (ie Vcc or GND). This makes sense as this will be where the inductance is the lowest. The return current will look like a gausian curve under the trace and this is also where the rule of thumb of 3W comes from to minimise cross-talk.
When it comes to stackups like this, H.Ott is the GOAT
https://hott.shielddigitaldesign.com/techtips/pcb-stack-up-2.html
if you are concerned about EMI you cannot go wrong with this as a 1st pass consideration
Not annoying, but it is a key parameter in PCB design. You could say that PCB design is about optimizing return current paths.
Every current flows in a circuit. The emission from the circuit and its sensitivity are determined by its surface. When the return current flows exactly under the track, the surface is determined by the distance between the track and the GND layer (which is why In1 is better as return path than bottom). In times when everyone carries a mobile phone, even circuits with audio signals must be designed as RF circuits.
Thank you for this for this explanation, I understand better but I don’t master everything but I think that it will come with time…
Thank you, I’ll watch this video later
Thanks for the link!
In 2020 I have linked here articles that I believe are worth printing and reading with marker in your hand:
I guess you don’t have one. Closing this thread and moving to Projects.
? Sorry I don’t understand what don’t you understand about my question ? There are many answers to my question. I think I have enough information to think about it. Yes I’ll close this topic. Doesn’t it close by itself ?
You are right that you don’t understand.
But you are wrong that RaptorUK don’t understand anything about your question.
RaptorUK perfectly understands your question and just kindly tells all of us that this forum is not a place for this discussion. This forum is intended to help with using KiCad itself (and tries to limit discussions only to it).
Your question is not about your problems with KiCad software itself (which function to use to reach what you want). Your question is general about PCB design and not about using KiCad. So should not be asked here and we should not discuss it here but rather send you to ask it at another forum that is intended for such questions.
Hope you understood.
At first I just answered your question and supposed the discussion will not be followed.
Ok Sorry, now I understand whatRaptorUK means. To be honest, I didn’t know where to ask this question in the right thread.
This is a Kicad forum about help/discussion about Kicad.
@RaptorUK is doing the right thing, like several of us do, ensure the discussion is kicad
Can I have a ground plane, oh I use Kicad
Can Kicad reserve planes for ground
Can I reserve layers 2 and 3 for power supplies and ground? What is the general use of layers 2 (In1.Cu) and 3 (In2.Cu) ?
Kicad doesn’t reserve planes for power and ground, this is what you do.
I do this all the time where I will reserve a layer for GND and use one contiguous gnd and then I do not do any other tracking. the constraints rules in theory should flag a DRC IF other traces non-gnd are routed on a named layer.
In short, if the question can be phrased such that is a kicad question NOT a generic PCB design I am sure several of us can help
I have seen many times people with not KiCad questions being send to eevblog so being here since 2017 I am there since end of 2024.