PCB Design

4-Layer PCB Design Guidelines: Key Tips for Success

4 Layer PCB Design

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.

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.

What is 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.

Structure of the 4 Layer PCB

Structure of the 4 Layer PCB

4 layer PCB will be used to route the electrical signals and the structure of 4 layer PCB is shown below.

  1. Top: The top layer mainly contains all the components’ placement and also this layer will be used for the signal routing.
  2. 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.
  3. 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.
  4. Bottom: This layer is also used for placing the components and also for the route of the signals.

Stack up of the 4 Layer PCB

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
Stack up of the 4 Layer PCB

Stack up of the 4 Layer PCB

Key Factors to Consider in 4 layer PCB Design

  • 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.

  1. 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.
  2.  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.
  3. 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.
  4. 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.
  5.  Board Size: 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.
  6. 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.
  7. PCB Cost: As per the number of layers the cost will increase this is the main disadvantage
  8. DFM (Design for Manufacturing) Check: 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.
  9. 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.

Useful Routing Practices for 4 Layer Board

  1. We should route the signals adjacent to the ground plan (taking the reference as a GND).
  2. To avoid the cross-talk issue, Try to route all the signals orthogonally.
  3. Providing the proper ground reference.
  4. Try to reduce the number of the via.
  5. Use the shielding for better EMI.
  6. Avoid the signal routing in the POWER or GND plan.
  7. Try to provide the proper track thickness and spacing between the two tracks.
  8. Try to route the track at 45 degrees without sharp bending.
  9. Placement should be as per the circuit flow.
  10. Connectors are placed on the edge of the PCB.

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