# Four Layer PCB Design

I'm new designing printed circuit. I designed some 2 layers PCBs (not too complex). I would like to know maybe a list of concepts that I need to check in my PCBs, or to know.

I would like to jump to 4 layers pcbs, but everytime that I've looking in Google information, it's much complex than 2 layers. Impedance tracks, resistance of the tracks, decoupling capacitors for some impedance, EMIS, and the stack of course. I know this concepts separately, but when I'm designing I don't really know much more than the datasheet can tell me.

I want to put a capacitor for decoupling some signal in a four layer PCB, but I want to know how it's affecting to my circuit and why I'm placing it in this place.

Any book or course or reference will be very helpfull for me. Thanks in advance.

Edit: I read in other post this two books that can help me

• Eric Bogatin's Signal and Power integrity Simplified
• High Speed Digital Design: A Handbook of Black Magic
• For the same circuit and density of PCB 4-layer is considerably easier because you usually can have a full ground plane and power plane regions or a full power plane so decoupling and layout are eased considerably. What kind of circuits are you planning on designing that require controlled impedance? RF? Commented Sep 4, 2020 at 11:31
• The circuits that i design generally have differential pairs, and RF signals for Bluetooth and wifi. But for example too i read that it's difficult to design sometimes if you have an ADC in your circuit because you have to minimize the noise. And right now i have everything, differential pairs, RF, Buck Conversor( so i need to mach it with the RF for the EMI of the buck) and an ADC. I want to know the design guidelines for this kind of things and the ecuations,etc... I mean, i want to order my pcb and know that it is going to work well with efficency. Commented Sep 4, 2020 at 11:45
• Regarding stack-up specifically, someone asked the same question here: electrical.codidact.com/questions/277418 Commented Sep 4, 2020 at 12:56

I would like to jump to 4 layers pcbs, but everytime that I've looking in Google information, it's much complex than 2 layers. Impedance tracks, resistance of the tracks, decoupling capacitors for some impedance, EMIS, and the stack of course. I know this concepts separately, but when I'm designing I don't really know much more than the datasheet can tell me.

I'm hesitant to answer this because I'm also inexperienced, but in my limited design experience 4 layer design is less complex than 2 layer because you have a dedicated ground and power plane. Conversely, when trying to make a 2 layer board work, you need to put a lot of care into minimizing the loop area of your power and ground traces as you route them through the signal layers. Dave Jones did a whole series of EEVBlog episodes about this:

I think probably what you mean is that when you look at things designed with 4 layer boards they're generally more complex projects, which makes sense of course. But going to 4 layers doesn't mean you have to start worrying about controlled impedance or decoupling whereas you could ignore them otherwise. That depends on your project, and you'd need the same things on a 2 layer design, possibly more so in the case of decoupling.

I want to put a capacitor for decoupling some signal in a four layer PCB, but I want to know how it's affecting to my circuit and why I'm placing it in this place.

But in general you place them in the same place on a two or a four layer board: as close as possible to the thing you are decoupling and in a way that minimizes the current loop area. Usually this is much easier on a 4 layer board since you aren't cutting up your power and ground with lots of signal traces.

I want to know the design guidelines for this kind of things and the ecuations,etc... I mean, i want to order my pcb and know that it is going to work well with efficency.

Since the cost of 4 layer board prototyping has fallen down to almost the same as 2 layer, I would certainly use a 4 layer board here. It will make everything easier and make your errors less likely to be fatal to your circuit's functioning. I don't think there is any substitute for experience though, so you're probably going to end up with a bad design for your first project. But you have to learn somehow.

Beyond the obvious advantage of having a dedicated ground plane and power plane (The two additional layers are used mainly for that purpose), it makes routing traces much easier. Practically you don't need routing for ground and power. Only signals have to be traced. If the device is not high frequency or ultra sensitive, you can use the power plane and to a less extent the ground plane to trace signal lines when it's difficult or impossible to do otherwise.

It's not only easier to design, it also makes the size of the board smaller. Traces and vias take the most of the area. Having them on several levels reduce to physical area of the PCB.

You don't have to worry about about track capacitance, EMI, decoupling in any other way that you would with 2 layers. In any case 4 layers offers only advantages. Take care carefully about that only with high frequencies or projects with specific subtleties.

4 layers PCB's are almost twice the cost of double layer ones for the same size. If someone can find prototypes 4 layers PCBs at the cost of 2 layers ones, good, but I guess it's because handling cost is more significant. But since the size will be smaller, it compensates. 2 layers PCBs will be always the cheapest solution for simpler circuits where 4 layers offer no advantage.

From my experience, for rf circuits, use layer 2 as ground plane and layer 3 as supply plane assume rf components are placed on layer 1.

• This is worst 4 layer stackup, suggestion. not my words though. Never put power and ground plane on layer 2 and 3 of 4 layer board. WHY? EMI Commented Sep 20, 2020 at 23:04
• The power plane will not be continuous but small planes where ever required. Does that reduce emi? Coz one of the board I was working on was designed in this way and still works fine! Btw the didn't do the layout for that. Commented Sep 21, 2020 at 1:43
• I can try to explain but I think best explanation can be given by the legend Rick Hartley himself. youtu.be/ySuUZEjARPY Commented Sep 21, 2020 at 3:21
• Okay. How you suggest the stack up should be? Commented Sep 21, 2020 at 3:22
• gnd--sig/power--sig/power--gnd or sig/power--gnd--gnd--sig/power. If you don't want to watch full video(but everybody should), you can focus around 1H40 where he describes 4 layer board. But all 2 hours is pure gold. Commented Sep 21, 2020 at 3:27