What are the contents and requirements of the multi-layer PCB process?

1.What is multilayer pcb

The biggest difference between PCB multilayer boards and single-sided and double-sided boards is the addition of internal power layers and ground layers. Power and ground networks are primarily routed on the power layer. Each substrate layer on a PCB multilayer board has conductive metal on both sides, and a special adhesive is used to connect the boards together, with insulating material present between each board. However, PCB multi-layer wiring is mainly based on the top and bottom layers, supplemented by intermediate wiring layers.

Therefore, the design method of multi-layer PCB board is basically the same as that of double-sided PCB board. The key is how to optimize the wiring of the internal electrical layer so that the circuit board layout is more reasonable. The inevitable result of multifunctional development, large capacity and small size.

With the continuous development of electronic technology, especially the extensive and in-depth application of large-scale and ultra-large-scale integrated circuits, multi-layer PCBs are rapidly developing in the direction of high density, high precision and high level of digitization. Thin lines, small aperture penetration and blind via technologies (such as buried vias and high plate thickness to aperture ratio) can meet market needs. PCB multilayer printed boards are widely used in the manufacturing of electronic products due to their flexible design, stable and reliable electrical performance and excellent economic performance.

Especially with the extensive and in-depth application of large-scale and ultra-large-scale integrated circuits, multi-layer PCBs are developing in the direction of high density, high precision and high level of digitization. Thin lines, small aperture penetration and blind via technologies (such as buried vias and high plate thickness to aperture ratio) can meet market needs. PCB multilayer printed boards are widely used in the manufacturing of electronic products due to their flexible design, stable and reliable electrical performance, and excellent economic performance. Especially with the extensive and in-depth application of large-scale and ultra-large-scale integrated circuits, multi-layer PCBs are developing in the direction of high density, high precision and high level of digitization.

Thin lines, small aperture penetration and blind via technologies (such as buried vias and high plate thickness to aperture ratio) can meet market needs. PCB multilayer printed boards are widely used in the manufacturing of electronic products due to their flexible design, stable and reliable electrical performance and excellent economic performance. Blind technologies such as blind hole technology and high plate thickness to aperture ratio can meet market demand.

PCB multilayer printed boards are widely used in the manufacturing of electronic products due to their flexible design, stable and reliable electrical performance, and excellent economic performance. Blind hole technology, high plate thickness to aperture ratio and other blind technologies can meet market demand. PCB multilayer printed boards are widely used in the manufacturing of electronic products due to their flexible design, stable and reliable electrical performance, and excellent economic performance.

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2. Multi-layer PCB production process

(1) Cutting: According to the specifications of your own processing equipment, cut the PCB board into the size required for the production line.
(2) Inner layer pattern production: The inner layer of a multilayer board usually uses a thin double-sided copper-clad substrate. After the inner layer circuit is formed on the surface, it is pressed, developed after exposure, and unnecessary copper foil is etched to remove. Then automated optical inspection (AOI) is used for inspection.
(3) Lamination: The inner plates will be stacked according to the designed lamination structure. The prepared inner plates, prepregs and outer copper foils will be laminated in order, and then hot-pressed to form a whole.
(4) Drilling: After the PCB circuit board is pressed together, interconnections need to be formed between the various layers. At this time, holes need to be drilled, and then a conductive copper layer is made on the hole wall to achieve interconnection.
(5) Electroless copper deposition and full-board electroplating: Chemical methods are used to deposit a thin layer of copper on the insulating hole walls. Full-board electroplating uses electroplating to add holes on the hole walls that have completed electroless copper deposition and have conductive properties. The wall copper is thick.
(6) Outer layer circuit pattern: the whole process of transferring the outer layer circuit to the copper clad board.
(7) Graphic plating: Plate a layer of copper and tin with the required thickness on the exposed copper of the circuit pattern or on the hole wall.
(8) Film removal: Use NaOH solution to remove the anti-electroplating covering film layer to expose the non-circuit copper layer.
(9) Etching: Use chemical reaction method to etch away the copper layer in non-line parts.
(10). Solder resist: carries and connects electronic parts.
(11) Character: A mark provided for easy identification.
(12) Surface treatment: Protect the areas that need to be welded or contacted, and prevent the exposed copper foil from oxidizing in contact with air, causing poor welding or poor contact.
(13) Forming: The shape required by the customer is produced through mold stamping or CNC machine.

3. Introduction to PCB multilayer board process

(1).Multilayer board structure

A multilayer board is usually composed of multiple copper layers and dielectric layers stacked alternately. The copper layer is used for wiring, and the dielectric layer is used for insulation and support. In a multilayer board, the number of copper layers and dielectric layers can be adjusted as needed.
The structure of a multi-layer board may include inner layers, outer layers and ground layers. The inner layer is the central part of the board, which is coated with copper foil on both sides. The outer layer is on both sides of the inner layer, one side is coated with copper foil, and the other side is usually used for mounting components or surface mounting. The ground layer is copper foil and is used for power and ground connections, which are located between the inner layer and the outer layer respectively.

(2) Multilayer board stacking in PCB design

The way multilayer boards are stacked has an impact on their performance and manufacturing process. In PCB design, the stacking method is usually selected by the board manufacturer or customer and optimized as needed. Here are some common stacking methods:

a. Symmetrical stacking

Symmetrical stacking is one of the most common stacking methods. In this way, the number of internal layers of the PCB is equal and the structure of the board exhibits symmetry.

b.Asymmetric stacking

In contrast to symmetrical stacking, the number of internal layers in asymmetrical stacking is unequal. Asymmetric stacking can be used to increase the power plane of the board to improve its stability.

c. Reinforcement board

Reinforcement boards are usually used by PCBs with certain special requirements. The structure of this type of board is more complex, using thicker internal layers and multiple ground layers to increase the stiffness and strength of the board.

(3). Coated with copper

Copper coating is a process of attaching copper foil to multilayer boards. This process usually takes place between the inner and outer layers of the board.
To ensure adequate conductivity between different parts of the board, the copper foil must be melted and coated at specified pressures and temperatures. This allows for precise control in PCB design to optimize copper foil thickness and electrical performance.

(4). Internal layer alignment

In the manufacturing process of multilayer boards, the alignment of internal layers is crucial. If the internal layers are misaligned, electrical performance may be affected, causing the entire PCB to not function properly.
Internal layer alignment is performed at the board factory. The board factory uses optical or mechanical methods to determine the precise position and orientation of the board. This process must be carried out before copper coating and piercing.

(5). Perforation

Perforation is an important step in multilayer boards. This process is used to make the electrical connections through the board. Before perforating, the board must be aligned with the inner layer. This is to ensure that the perforations are accurately positioned so that there is a perfect electrical connection between the different layers of the board.
There are many methods of perforation, including mechanical perforation, laser perforation and stamping perforation. The perforation method should be selected based on the quality requirements and process limitations of the board.

(6). Coating and dipping

In multi-layer boards, there are coating and dip-coating processes on each dielectric layer. These processes help protect each layer of the board and reduce unnecessary impurities on the board. These processes should also be fully considered in PCB design.
Coating is the addition of a protective layer between each dielectric layer. This process can be performed using materials such as substrates, inks, and resins. Dip coating is done by impregnating the material into the interior of the dielectric layer to increase its strength.

(7). Heavy gold

Immersion gold is a common method to protect PCB. This process coats the surface of the board with gold, protecting the PCB from corrosion, oxidation, and damage.
Immersion gold can be performed using chemical treatments or electrochemical processes. Chemical treatments can give the PCB surface a uniform metallic appearance, and electrochemical processes are more time and cost-effective, but can result in uneven metal appearances.


(8). Methods for designing vias in multi-layer PCB

The importance of via technology in PCB design cannot be underestimated. Different layers of conductive materials are connected through vias to achieve signal transmission and power supply. The smoothness and quality of vias are crucial to the stability and reliability of the entire circuit.
In multilayer PCB design, vias are divided into two main types: blind vias and through holes. Blind vias connect only a few individual layers, while through vias connect all layers of the entire circuit board. When selecting the appropriate via type, factors such as board complexity, signal type, and bandwidth requirements need to be considered.
During the design process, it is crucial to select the appropriate size and number of vias. An aperture that is too small may cause problems such as current instability, signal loss, and voltage drops, while an aperture that is too large may cause current overload and uneven distribution. When determining the number of vias, you need to balance the performance requirements of the circuit board with the complexity of manufacturing.
Via hole design also needs to consider the via filling material. Common via filling materials include copper plating, thermosetting resin, polyimide, etc. The selection of filler material should be based on the application environment and requirements of the circuit board.
In the actual manufacturing process, vias should meet certain manufacturing specifications and requirements. These specifications include: the location and spacing of vias must meet the design requirements, the copper plating layer of the vias should reach a certain thickness and quality, and the hole wall quality of the vias must be good, etc. Strict adherence to these specifications ensures via quality and stability.
In multi-layer PCB design, the layout of vias is also very important. Reasonable via layout can optimize the performance and wiring effect of the circuit board. Generally speaking, the layout of vias should be distributed as evenly as possible to avoid excessive vias gathering in certain areas, thereby reducing the effectiveness of wiring and increasing the risk of signal interference.
In order to optimize vias in multi-layer PCB designs, design engineers should pay close attention to technology developments and practices. Proficient via technology and manufacturing processes can maximize the performance and reliability of PCBs. In addition, using advanced PCB design software and tools can also help designers better implement complex via designs.
Through an in-depth understanding and rational application of via technology in multi-layer PCB design, design optimization can be achieved. Reasonable via design can improve the performance, reliability and manufacturing efficiency of circuit boards.

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4. Summary

The application of multilayer boards in PCB design is becoming more and more common. During the design and manufacturing process, processes such as stacking, copper coating, internal layer alignment, perforation, coating, dip coating and immersion gold all require special attention.
As PCB designers, we need to understand the structure and performance of multilayer boards in order to make appropriate optimizations in the design. Only after understanding these multi-layer board processes can we provide our customers with perfect circuit board design and manufacturing solutions

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