The circuit board is the heart of all electronic devices. Usually more common is a single-layer or double-layer circuit board, because their level design is simple, so it can be put into the use of a large number of relatively simple electronic devices. When it comes to high-end devices, because of the complexity of the circuit and the requirements for volume, it is usually necessary to use multi-layer circuit boards. The 4 layer circuit board is one of them, and it is mostly used in the use of computer boards.
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By reading this 4 layer PCB design guideline, we can fully understand the structure of the 4 layer PCB and 4 layer PCB design rules in the 4 layer PCB design.
4 layer PCB design is the process of manufacturing the 4 layer PCB. The 4 layer PCB is composed of four layers of conductive copper material, and several layers of insulating substrate are separated in the conductive copper layer. The multi-layer structure of a four-layer PCB allows for more complex circuit design and higher performance than a single-layer or double-layer PCB. There are some rules that we should understand and follow in 4 layer PCB design to obtain 4 layer PCB best practices.
4 layer PCB will be used to route the electrical signals and the structure of 4 layer PCB is shown below.
Top: The top layer mainly contains all the components' placement and also this layer will be used for the signal routing.
Inner 1: We can use this layer for the ground layer. So in this layer, it can be achieved with a flat copper layer. Using the GND plane return path will provide low impedance for signals is routed at the top level.
Inner 2: This layer is also the same as the second layer, we can use it as a power layer from this layer the power will be distributed to the different sections of the PCB.
Bottom: This layer is also used for placing the components and also for the route of the signals.
In the 4 layer configuration, we can use depending on our need for designing the PCB as shown below
Signal-Ground-Power-Signal
Signal-Power-Ground-Signal
Ground-Power-Ground-Signal
Number of Signals
EMI/EMC Consideration
Signal Integrity
Power Integrity
Board Size
Number of Components(Density)
PCB Cost
DFM (Design for Manufacturing) Check
Material Choosing
Here are the details of the certain things we need to consider.
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Number of Signals: Before we go for the 4 layer PCB design we should see what different types of signals are there and also the different types of power.
EMI/EMC Consideration: Using the ground plane we can reduce the EMI issue or other things we can use as shields to reduce the EMI issue.
Signal Integrity: For the high-speed signals we should provide the grounding properly so it will help to prevent the cross-talk problem because high-speed signals need a return path so here the ground is worked as a low impedance for signals.
Power Integrity: In the PCB, the power plane is used to distribute the power for the complete PCB so we can use the multiple layers for the power plan so it can easily distribute the power without having any disturbance.
Mainly board size will be considered as per the number of components so in this case, we should consider the number of power and singles on this base; hence, we will go for the multilayer PCB
Number of Components(Density): This will play a major role in 4 layer PCB design. We will determine the number of layers in the 4 layer PCB layout according to the number of components, but if there are too many components, we should use multi-layer PCB, which we can call the density of PCB.
PCB Cost: As per the number of layers the cost will increase this is the main disadvantage
When we go for the manufacturing of the PCB we should know the DFM/DFA/DFT. Once sending the fabrication file to the manufacturers, they will start to manufacture based on our Gerber file. So before sending the Gerber file, we should check the proper layout design like track width, track spacing, components placements and spacing between pad to pad, pad to via, pad to track etc.
Material Choosing: The manufacturer will use the materials in the 4 layer PCB design according to our requirements and will design the type of board depending on our application. The manufacturer will give you a reasonable recommendation on the design materials you request in the 4 layer PCB design. Each manufacturer has its own laminating and manufacturing equipment, and they can determine the thickness of the PCB and the thickness of the dielectric material according to the different applications of 4 layer PCB best practices.
We should route the signals adjacent to the ground plan (taking the reference as a GND).
To avoid the cross-talk issue, Try to route all the signals orthogonally.
Providing the proper ground reference.
Try to reduce the number of the via.
Use the shielding for better EMI.
Avoid the signal routing in the POWER or GND plan.
Try to provide the proper track thickness and spacing between the two tracks.
Try to route the track at 45 degrees without sharp bending.
Placement should be as per the circuit flow.
Connectors are placed on the edge of the PCB.
Additional Resources:
My rules-of-thumb:
-First and foremost: every design and factory is different, at least somewhat. Don't just do 2 or 4 layers just because that's how you've always done it, talk to your factory or PCB supplier.
-In prototyping, you can make shortcuts that are not good for real production. Your board, as it is, looks just fine for a prototype. Besides, in prototypes and really small quantities, the bare costs don't matter that much, the setup costs dominate.
-For real production, you want to be real confident about your design and spend some extra effort for that. For example (disclaimer: without knowing what the circuit does), I don't really like your power supply routing; the return paths are not necessarily clear, straight and shortest possible, and traces on the edges are more susceptible for noise. Also, I don't like the small area with tight routing. I'd try to split that up so that the ground flows between the traces, and take the long lines (assuming I'm not looking at a differential transmission line) to the top layer to make the plane more solid. In other words, rather than 3" tracks in the plane layer, I'd aim for 1" on bottom, 1" on top, 1" on bottom. Also, there are several places where moving a component or a via just a bit would allow the plane to flow around and between tracks, vias and parts. And btw, the 3v line about one third from bottom left corner has some sharp V angles, not something you want to do in quantities.
-When the design is noise sensitive (audio, measurement circuit) or high speed logic, it needs a solid ground plane. Sometimes, you can arrange "solid enough" plane (see above), but if you can't, multilayer it is.
-For me, 4 layer board is about 30% more expensive than a 2 layer board. In my designs, almost always using more layers allows much more tighter routing, resulting in more than 30% reduction in board area. Therefore, in most cases a 4 layer board turns out the be cheaper than 2 layers, and I'll get a unbroken ground plane as a bonus. Talk to your factory, they'll know the pricing with your quantities.
-Another issue you want to ask your factory about is single or two sided component placement. Single sided is cheaper, but needs a bigger board, and that cost more. The money involved in this and the above tradeoff is big enough that you want to ask. For me, that is several dollars per board. Ten dollars per board on a thousand boards is worth a few days of extra work, but for ten boards, not.
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