How to Choose the Board Thickness of PCB

The setting of the thickness of the PCB and the thickness for every layer is an important process that requires comprehensive considerations. In this article, we will give some advice based on our nearly 20 years of experience with our team;

Here, we will take a 1.6mm 4-layer PCB as a sample.

I. PP and Core

Prepreg: PP for short, PP in PCB board factory is often translated as semi-cured film or film. PP is used as an insulating material between adjacent layers of PCB board. In a PCB board factory, the insulating layer formed by PP is called the dielectric layer.

Core, a hard, copper-clad board with a specific thickness on both sides, is the basic material for printed circuit boards. The lamination materials of multilayer boards are mainly Prepreg and Core.

Differences between PP and Core

1. Function: Prepreg is like adhesive and insulator while core is the basic material of PCB

2. Electrical conductivity: PP is not conducive while Core has two layers of copper on two sides, it is the conductive medium of PCB

3. Flexibility: PP can be curled while Core is solid

II. Board Thickness for Different Layer Counts

Single Sided and Double-Sided PCB

For single-sided or double-sided PCBs, due to the layout being relatively easy, normally there is no need to use thick board, generally choose 0.8mm to 1.6mm thickness. Such board thickness can not only meet the requirement for mechanical strength, but also can keep good electric performance, and lower manufacturing costs as well.

Multilayer PCB

For multilayer PCB, the choice of board thickness should be considered according to circuit layout, component quantity, heat dissipation requirement, and mechanical strength or other factors.

• 4-layer PCB: for a 4-layer PCB, the board thickness can be 1.6mm~2.0mm, with the board thickness, the PCB can take more circuit layers and layout and maintain enough mechanical strength.
• 6 and more layer PCB: for 6 and more layer PCB, the board thickness normally needs to be over 2.0mm. As the layer count increases, circuit layout and density will increase accordingly, which requires a thicker board to offer better mechanical support and electric performance.

III. PCB Board Thickness Setting

1. Normal thickness: based on the IPC standard, normal PCB thickness includes 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm, etc. Among them, the thickness of 1.6mm is regarded as the balance point on most occasions, it can meet the requirements of various applications with good stability and reliability.
2. Application Scenarios

For the products with small sizes or equipment with low power consumption, 0.4mm or 0.6mm thin boards can be chosen.

For the equipment with large power consumption, 1.6mm or thicker PCB should be chosen, to offer better mechanical support and heat dissipation performance.

• Heat dissipation requirement: for electronic devices with high power or high integration, heat dissipation is a vital factor that needs to be considered. In this case, the board thickness should be thicker to provide better heat dissipation performance.
• Mechanical strength: for some applications, the PCB needs to withstand high mechanical stress, for example, vibration, shock, etc. Under such occasions, the board thickness should be thicker to improve its mechanical strength.

IV. Every Layer Thickness Setting

1. Stack-up structure design: The stacking structure of PCB should follow the principle of symmetry, including the dielectric layer, copper coil thickness, and symmetry of the graphic distribution. This will be helpful to ensure the total performance and stability of the PCB.

2. Thickness of Dielectric Layer

• Recommend the thickness of dielectric layer should be over 0.1mm, to prevent voltage breakdown.
• Inner layer(for example, 1st~4th layer)thickness can choose 0.1mm

3. Thickness of Copper Coil

• The thickness of the copper coil will influence the trace width and space, inner copper weight normally should be over 0.5oz. Generally, the final copper thickness of PCB is the base copper thickness plus the copper thickness of plating.
• As the number of layers increases, the complexity of signal transportation increases as well. Proper copper thickness is helpful to ensure the signal quality.
• In some high-power density electronic products, for example, inverters, it is necessary to take into account the heat dissipation requirements by reasonably selecting the thickness of the inner and outer copper foils. It is necessary to take into account the heat dissipation requirements by reasonably selecting the thickness of the inner and outer copper foils.

4. Adjust and Set

• In the design software(for example, Altium Designer), the thickness information of each layer of the PCB can be checked and adjusted in “Layer Stack Manager”
• While adjusting, please note that the thickness of every layer will influence the final thickness of the PCB.
• After making sure of the stack-up structure, the designer should check the process capabilities, for example, copper thickness, prepreg specification, etc, these parameters will influence the final board thickness and PCB performance.

V. Precautions for Board Thickness Choosing

1. Board type: different t board have different mechanical and electrical performance. When choosing board thickness, needs to fully consider the board types influence on total performance.

2. Manufacturing cost: increasing the board thickness will lead to higher manufacturing costs. Therefore, under the condition of meeting the requirement, the board thickness should be thinner to lower cost.

3. Circuit density: The thicker board can include more circuit layers, and improve the circuit density. However, too high circuit density will cause heat dissipation problems and degradation of electrical performance.

VI. Conclusion

In conclusion, when choosing the board thickness during the design of PCB, needs to consider comprehensively circuit layout, component quantity, heat dissipation requirement, mechanical strength, manufacturing cost, and other factors. With a reasonable choice, it can ensure the PCB has nice electrical and mechanical strength, the meantime, lower manufacturing costs, and improve the competitiveness of the final product.