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Multilayer PCB design: an introduction to the basics

Multilayer PCB design

Multilayer PCB design has become increasingly important in recent years, as the demand for more advanced and compact electronics continues to grow. Multilayer PCBs are essentially multiple printed circuit boards stacked on top of each other, connected by plated through-holes, and encapsulated in a single unit. This allows for more components to be incorporated into a smaller form factor, making them ideal for high-density electronic applications.

Multilayer PCB design is a complex process that requires a deep understanding of electronics engineering and PCB design principles. This type of PCB design involves the creation of circuit boards with multiple layers of conductive material that are used to route electrical signals. These boards are used in a wide range of electronic applications, from consumer electronics and computers to aerospace and medical devices.


The circuit board can be divided into single-side, double-layer and multi-layer PCB according to the number of layers, and the multi-layer board refers to the circuit board with more than 4 layers. For many miniaturized products and high-speed products, multilayer boards are used, such as mobile phones, routing, switches, etc. So, what are the advantages of multilayer PCB? What is multilayer PCB design? How to design multi-class PCB? What do I need to pay attention to? This article will explain them all below.

What is multilayer PCB design?

The basics of multilayer PCB design involve creating a circuit board that has multiple layers of conductive material. These layers are separated by insulating materials and are used to route electrical signals between different components on the board. In most multilayer PCBs, there are at least two layers of conductive material, but there can be as many as eight or more. The number of layers and the thickness of the conductive material can vary depending on the specific requirements of the application.

What’s the advantage of multilayer PCB?

advantage of multilayer PCB

The main advantage of multilayer PCB is that they allow for a higher density of components and circuits, compared to single layer PCBs. This is because the multiple layers of conductive material can be used to route signals and power between different components, reducing the need for external connections and allowing for smaller, more compact circuit boards.

Another advantage of multilayer PCBs is that they can be designed to improve signal integrity and reduce electromagnetic interference (EMI). This is because the multiple layers of conductive material can be used to separate different types of signals, reducing the risk of interference between different circuits. Additionally, the use of insulating materials between the layers can help reduce the amount of EMI that is generated by the board.

What’s the process of multilayer PCB design?

The first step in multilayer PCB design is to determine the number of layers required. The number of layers depends on the complexity of the design, the number of components, and the desired electrical performance. Common layer counts include four, six, and eight layers, but designs can have anywhere from two to ten layers or more.

Once the number of layers has been determined, the next step is to arrange the components on the PCB. This is done using a PCB layout software tool. The software allows the designer to place components and define the electrical connections between them. It is important to consider the arrangement of components to ensure optimal signal routing, minimize signal interference, and allow for proper heat dissipation.process of multilayer PCB design
The next step is to define the electrical routing between the components. This involves specifying the width, spacing, and layer assignment of the electrical connections. The electrical routing should be designed to ensure signal integrity, reduce cross-talk, and prevent signal reflection. It is also important to consider the impedance and crosstalk of the signal, as well as the overall electrical performance of the design.

Once the electrical routing has been defined, the next step is to generate the Gerber files, which are used to create the photomasks for the PCB fabrication process. The Gerber files contain information about the layer stack-up, electrical connections, component placement, and other design information.

Finally, the multilayer PCB is manufactured by a PCB manufacturer. The manufacturer uses the Gerber files to create photomasks, which are then used to create the individual layers of the PCB. The layers are then laminated together to form the final multilayer PCB.

Considerations during multilayer PCB design

● Selection of the number of layers. The stacked design is preferably an even number of layers;
● All signal layers are adjacent to the ground plane as much as possible, and the two signal layers are avoided as far as possible.
● On the same signal layer, the direction of most wiring should be consistent;
● Signal type. The choice of the number of layers also depends on the type of signal they need to transmit. Signals are classified as high frequency, low frequency, ground or power.
● It is best to place the components on one side, and arrange the position and orientation of the interface components reasonably.
● Components with close electrical connections are best placed together.

Multilayer PCB lamination

Multilayer PCB lamination

With the continuous emergence of high-speed circuits, the complexity of PCBs is getting higher and higher, in order to avoid the interference of electrical factors, the signal layer and the power layer must be separated, so multilayer PCB design is involved. Before designing a multilayer PCB, the designer needs to determine the board structure to be used according to the size of the circuit, the size of the board, and the requirements of electromagnetic compatibility (EMC), that is, to decide whether to use 4 layers, 6 layers, or more layers and multilayer PCB lamination structure .

4 layers PCB

1.TOP-GND-POWER-BOTTOM
2.GND-S1-S2-POWER
3.TOP-POWER-GND-BOTTOM
4.GND-SI+POWER-S2+POWER-GND
5.S1G1-GND-POWER-S1G2
6.GND-S1-S2-POWER

6 layers PCB

1.TOP-GND02-S03-PWR04-GND05-BOTTOM
2.TOP-GND02-S03-S04-PWR05-BOTTOM
3.TOP-S02-GND03-PWR04-S05-BOTTOM
4.SIG-GND-SIG-PWR-GND-SIG
5.GND-SIG-GND-PWR-SIG -GND

8 layers PCB

1.S1-S2-GND-S3-S4-POWER-S5-S6
2.S1-GND1-S2-POWER-GND2-S3-POWER-S4
3.S1-GND1-S2-POWER-GND2-S3-GND3-S4
4.S1-GND1-S2-S3-POWER-S4-GND2-S5
5.S1-GND1-POWER1-S2-S3-GNS2-POWER2-S4

10 layers PCB

1.TOP/S1-GND1-S2-S3-GND2-POWER-S4-S5-GND3-BOTTOM/S6
2.TOP/S1-GND1-S2-GND2-S3-GND3-POWER-S4-GND4-BOTTOM/S5
3.TOP/S1-GND1-S2-POWER1-S3-GND2-POWER2-S4-GND3-BOTTOM/S5

Multilayer PCB manufacturing process-23 steps

Multilayer PCB manufacturing process-23 steps

1.Cutting
The original copper clad laminate is cut into a board that can be made on the production line.

2. Grinding
Removes oxidation and increases the roughness of the copper surface, which facilitates the adhesion of the film to the copper surface.

3. Inner layer imaging
The process of transferring the inner wiring pattern to the PCB board:
Dry film – exposure – development – etching – film removal – testing.

4. Browning
Chemical treatment results in a homogeneous organometallic layer structure with good adhesion properties to enhance the bond strength after platen between the inner copper layer and the prepreg.

5. PCB Lamination
With the help of the adhesion of the PP sheet, the various layers of the line are bonded into a whole. In actual operation, copper foil, PP prepreg, inner plate, outer steel plate and other material processes are required to be superimposed, and then sent to the vacuum heat press machine for lamination.

6. PCB Drilling
Make the vias between the layers of the circuit board to achieve the purpose of connecting the layers.

7. X-Ray detection
The only analysis inside the board, defect detection.

8. Hole detector /verifier inspection
Check the problems of large holes, small holes, pores, missing holes, and plate appearance.

9. Pre-treatment of copper immersion
The walls of the drilled holes are cleaned and descaled by chemical methods.

10. Copper immersion (PTH)
Also called chemical copper. After drilling, the PCB board undergoes redox reaction in the copper immersion cylinder to form a copper layer, thereby metallizing the hole, so that copper is deposited on the surface of the original insulated substrate to achieve electrical communication between layers.

11. Panel Plating
Thicken the PCB board that has just come out of the copper surface and hole.

12. Slice test
It is used to evaluate the quality of electroplating holes, such as coating dispersion uniformity, copper thickness, etc.

13. Outer layer wiring
The process is the same as the inner line.

14. Solder mask
A layer of solder mask is applied to the surface of the board by screen printing ink, and after pre-baking, the pad and hole to be welded are exposed by exposure development, and the other places are covered with a solder mask layer to prevent short circuit during welding.

15. Characters/legend
The required text, trademark or part symbol is made by the text inkjet machine.

16. Post-baking
Bake the ink to a cured state.

17. Surface Treatment
The copper surface is treated to prevent the board from being oxidized by moisture. Common surface treatment methods are tin spraying, gold immersion, OSP and so on.

18. Molding
The PCB is cut into the desired shape and size with a CNC molding machine.

19.V-CUT
In the position where the circuit board is to be divided, a V-shaped straight shallow groove is cut on both sides.

20. Ultrasonic cleaning
Cleaning flux, ionic contaminants, etc.

21. Electrical Testing
Through flying probe or automatic testing machine, electrical performance is checked for open and short circuits.

22. FQC
The appearance, size and aperture, plate thickness, marking, etc. of the plate are checked to ensure that all customer requirements are met.

13. Packaging and shipment
The qualified products are shipped through vacuum plastic packaging.

Conclusion

In conclusion, multilayer PCB design is a critical aspect of modern electronics development. Themultilayer PCB design is the position relationship and distance relationship between the power layer, the ground layer and the signal layer.The process of designing multilayer PCBs involves determining the number of layers, arranging components, defining electrical routing, generating Gerber files, and finally, manufacturing the final product. By understanding the basics of multilayer PCB design, engineers and designers can create more advanced and compact electronics that meet the demanding needs of the modern world.

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