4 Layer Multi Layer PCB

Demand for high-speed, high-performance, and miniaturized devices continues to increase, as does the need for complex and small printed circuit boards (PCBs). As a result, PCBs have become smaller than ever before, available in various configurations, and customized according to application requirements. Therefore, PCB manufacturers are developing various multi layer PCBs. Among them, 4 layer multi layer PCB is commonly used in various applications. These multi layer PCBs are a key part of various electronic devices as well as communication equipment.

What is a 4-layer Multi layer PCB?

Of all the multilayer types, the most common is the 4 layer multi layer PCB. The stackup of 4 layer multi layer PCB is extremely strong, it consists of top layer, inner layer 1, inner layer 2, and bottom layer for routing electrical signals. Both inner layers (inner layers 1 and 2) are located between the top and bottom layers.

Therefore, a 4-layer multi layer PCB means 2 signal layers + a positive voltage layer (VCC layer) + a ground layer (GND layer) or 3 signal layers + GND layer. In a 4-layer multi layer PCB design, more surface area is available for traces. Therefore, this design structure provides excellent routing for both low-speed and high-speed signals.

A general 4 layer multi layer PCB is composed of the top and bottom layers as signal layers, and the middle two layers as power layer and ground layer. The power layer and the ground layer can play an isolation role in the middle and reduce interference.

For larger 4 layer multi layer PCBs, PCB boards with relatively loose components can also be completed with two layers. If the layout of the two layers is difficult and cannot be arranged, it is easy to cause interference, and 4 layers can be used to solve the problem of overcrowding.

Stacking Type of 4-layer Multi layer PCB

When contacting a 4-layer multi layer PCB manufacturer, they will provide two standard structures for a 4-layer multi layer PCB. The VCC and GND layers here are organized according to the application requirements.

Type 1: Signal-GND-VCC-Signal: In this 4-layer multi layer PCB design, the top layer is preferably the key signal. In terms of layer thickness, the impedance control core board should not be too thick. This helps reduce the distributed impedance of the ground plane and power supply.

Type 2: GND-Signal-Signal-GND: This stackup is ideal if you don't want to use via paths to connect all types of ground pins. To improve the EMC performance of multi layer PCBs, it is a good idea to always place signal layers close to the planes. Utilize large cores between the ground and power planes to maintain the overall thickness of the substrate.

Advantages of 4-layer Multi layer PCB

Due to its beneficial properties, 4-layer multi layer PCBs are widely used in many electronic applications. Some of the major advantages offered by these multi layer PCBs are as follows:

1. Smaller quality-driven design: This is one of the important reasons for using a 4-layer multi layer PCB. Due to their multilayer design construction, they are inherently smaller than single-sided PCBs. This is beneficial for modern electronic devices such as smartphones, tablets and laptops. Since it is a multi-layer design, it requires a thoroughly planned design and precision when installing the components. This helps reduce unnecessary errors and ensures high-quality results.

2. Excellent durability: As mentioned above, these multi layer PCBs can not only bear the weight, but also withstand the pressure and heat applied to bond them together. Additionally, multi layer PCBs have increased durability due to the multilayer insulation between circuit layers.

3. Higher packing density: These multi layer PCBs increase packing density by combining multiple layers onto one board. The interconnection between the proximal regions makes the connection between the boards closer.

4. Lightweight structure: In a 4-layer multi layer PCB, multiple connectors are required to interconnect or connect separate single-layer and double-layer circuit boards. It helps simplify circuit design and reduce its weight.

Application of 4-layer Multi layer PCB

The key advantages of these multi layer PCBs contribute to their popularity in various industries. The following are some important applications where these multi layer PCBs are widely used:

●Heart monitor

●Computer

●GPS technology

●File server

●Mobile phone

●Data storage.

●Signal transmission

●Mobile phone transmission and repeater

●Fiber optic receiver

4-layer Multi layer PCB Layout Principle

The PCB industry is developing rapidly. Nowadays, except for a few small household appliances that are two-layer boards, most PCB board designs are multi-layer, and the common ones are 8 layers, 12 layers, or even higher. What we traditionally call a 4-layer multi layer PCB is the top layer, bottom layer, and two middle layers. Below we take the design of a 4-layer multi layer PCB as an example to explain the matters that should be paid attention to when wiring a multi layer PCB, for the reference of electronic designers.

1. When connecting more than 3 points, try to let the line pass through each point in turn, which is convenient for testing, and the length of the line should be as short as possible.

2. Try not to put wires between the pins, especially between and around the pins of integrated circuits.

3. The lines between different layers of multi layer PCB should not be parallel as much as possible, so as not to form actual capacitance.

4. The multi layer PCB wiring should be as straight as possible, or a 45-degree broken line to avoid electromagnetic radiation.

5. The ground wire and power wire should be at least 10-15mil above (for logic circuits).

6. Try to connect the floor polylines together to increase the grounding area. Be as neat as possible between the lines.

7. Pay attention to the uniform discharge of components to facilitate installation, plug-in and welding operations. The characters are arranged in the current character layer, and the position is reasonable. Pay attention to the orientation, avoid being blocked, and facilitate production.

8. The structure of multi layer PCB components should be considered more. The negative electrode of SMD components should be marked on the package and at the end to avoid space conflicts.

9. At present, multi layer PCBs can be used for 4-5mil wiring, but usually 6mil line width, 8mil line spacing, and 12/20mil pads. Wiring should consider the influence of sink current, etc.

10. The functional block components should be put together as far as possible, and the components near the LCD such as zebra strips should not be too close.

11. Multi layer PCB via holes should be painted with green oil (set to negative-multiple value).

12. It is best not to place soldering pads or space under the battery holder, and the size of PAD and VIL is reasonable.

13. After the multi layer PCB wiring is completed, carefully check whether each connection (including NETLABLE) is really connected (bright method is available).

14. The oscillating circuit components should be as close as possible to the IC, and the oscillating circuit should be as far away as possible from areas susceptible to interference such as antennas. The ground pad should be placed under the crystal oscillator.

15. For multi layer PCBs, multiple methods such as reinforcement and hollowing out components should be considered to avoid excessive radiation sources.

4-layer Multi layer PCB Stack-up Design

When designing a 4-layer multi layer PCB, there are generally three methods for stacking in theory:

1.1 power layer, 1 ground layer and 2 signal layers are arranged in this way: TOP (signal layer), L2 (ground layer), L3 (power layer), BOT (signal layer).

2.1 power layer, 1 ground layer and 2 signal layers are arranged in this way: TOP (power layer), L2 (signal layer), L3 (signal layer), BOT (ground layer).

3.1 power layer, 1 ground layer and 2 signal layers are arranged in this way: TOP (signal layer), L2 (power layer), L3 (ground layer), BOT (signal layer).

The advantages and disadvantages of these three methods:

Method 1, this scheme is the main stack design scheme of 4-layer multi layer PCB. There is a ground plane under the component surface, and the key signal is preferably placed on the TOP layer; as for the layer thickness setting, there are the following suggestions: to meet the impedance control core board (GND to POWER) should not be too thick to reduce the distributed impedance of the power and ground planes; to ensure the decoupling effect of the power plane.

Method 2, mainly in order to achieve a certain shielding effect, put the power supply and ground plane on the TOP and BOTTOM layers of the multi layer PCB, but this solution has at least the following defects in order to achieve the ideal shielding effect:

1. The distance between the power supply and the ground is too far, and the impedance of the power plane is relatively large.

2. The power and ground planes are extremely incomplete due to the influence of component pads and so on.

Due to the incomplete reference plane, the signal impedance is not continuous. In fact, due to the use of a large number of surface mount devices, the power supply and ground of this solution can hardly be used as a complete reference plane when the devices are getting denser. The expected shielding effect is very low. Difficult to implement; option 2 has a limited scope of application. But in individual boards, Option 2 is the best layer setting solution.

Method 3: This solution is similar to solution 1, and is applicable to the situation where the main components are laid out in BOTTOM or the bottom layer of key signals is wired.

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