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What is the meaning of inner layer in PCB? What is its role?

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In PCB (Printed Circuit Board) design, Internal Planes usually refer to the conductive layers located between the top and bottom layers of the PCB, and they are only found in multilayer PCB boards. The number of internal planes can vary depending on the design requirements of the PCB, generally multilayer boards contain at least two internal planes, while some complex designs may contain up to dozens of internal planes.

The main functions of inner layers are as follows:

Electrical Connections: 

Inner layers are electrically connected to the signal layer and other inner layers through Via, Blind Via and Buried Via. These vias allow circuits between different layers to be interconnected, allowing for complex circuit designs.

Power and Ground Layers: 

The inner layers are typically used as Power Planes and Ground Planes to provide stable power and ground potentials for the circuit. These layers help reduce power supply noise and improve circuit stability and performance.

Signal Isolation: 

The inner layer can be used as a shielding layer to isolate electromagnetic interference between different signal layers and improve the circuit's anti-interference capability.

Thermal Management: 

The copper layers of the inner layers help to dissipate and balance the heat on the PCB, helping to maintain the thermal stability of the circuit.

Mechanical Strength: 

Although the main role of the inner layers is electrical, they also help to increase the overall mechanical strength of the PCB board, especially in multilayer boards where the inner layers can provide additional support.


Optimised Wiring: 

Inner layers provide additional space for the layout of signal lines, which helps to optimise the wiring scheme, especially in complex circuit designs, and can effectively reduce line crossings and congestion, improving the efficiency and reliability of the wiring.

Reduced Signal Loss: 

The use of an inner layer can reduce loss during signal transmission, especially in high-speed circuit designs, where the inner layer can provide a lower impedance path, helping to maintain signal integrity.

Enhanced Electromagnetic Compatibility (EMC): 

The design of the inner layer can improve the EMC of the PCB board and reduce the emission and susceptibility to Electromagnetic Interference (EMI) through a proper layout of the ground and power layers.

Improve Design Flexibility: 

The use of inner layers increases the flexibility of PCB design. Designers have the flexibility to adjust the number and layout of inner layers as needed to accommodate different design requirements and performance goals.

Reduced Cost: 

In some cases, the number of external connections and components can be reduced through the judicious use of inner layers for wiring and power/ground layers, thus helping to reduce overall costs.

In summary, inner layers play a key role in PCB design, and their proper planning and use is essential to ensure the performance, reliability and cost-effectiveness of the circuit. Designers need to consider the functionality and performance requirements of the circuit as well as the manufacturing process to decide how to make the most effective use of the inner layers.

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