Why do so many PCB designers choose copper plating? Is it necessary?

After all PCB design content is completed, the last critical step is usually carried out-copper laying.

Copper laying is to cover the unused space on the PCB with copper surface. Various PCB design software provide intelligent copper laying function. Usually the area where copper is laid will turn red, indicating that this area is covered with copper.

So, why is copper laid at the end? Isn’t it possible not to pave it?

For PCB, laying copper has many functions, such as reducing the impedance of the ground wire and improving the anti-interference ability; connecting to the ground wire to reduce the loop area; and helping to dissipate heat, etc.

1. Copper laying can reduce the ground impedance and provide shielding protection and noise suppression.

There are a lot of spike currents in digital circuits, so it is more necessary to reduce the ground impedance. Copper laying is a common method to reduce the ground impedance.

Copper laying can reduce the resistance of the ground wire by increasing the conductive cross-sectional area of the ground wire; or shorten the length of the ground wire and reduce the inductance of the ground wire, thereby reducing the impedance of the ground wire; it can also control the capacitance of the ground wire so that the ground wire can be The capacitance value of the line is appropriately increased, thereby improving the conductive performance of the ground wire and reducing the impedance of the ground wire.

A large area of ground or power supply copper can also play a shielding role, helping to reduce electromagnetic interference, improve the anti-interference ability of the circuit, and meet EMC requirements.

In addition, for high-frequency circuits, copper laying provides a complete return path for high-frequency digital signals, reducing DC network wiring, thereby improving the stability and reliability of signal transmission.

2. Copper laying can improve the heat dissipation capacity of PCB. In addition to reducing the ground wire impedance in PCB design, copper laying can also be used for heat dissipation.

As we all know, metal is a material that is easy to conduct electricity and heat. Therefore, if the PCB is covered with copper, the gaps in the board and other blank areas will have more metal components, and the heat dissipation surface area will increase, so it is easier for the overall heat dissipation of the PCB board. Copper paving can also help distribute heat evenly and prevent the creation of localized hot areas.

By evenly distributing heat to the entire PCB board, local heat concentration can be reduced, the temperature gradient of the heat source can be reduced, and heat dissipation efficiency can be improved.

Therefore, in PCB design, copper laying can be used to dissipate heat in the following ways:

• Design the heat dissipation area: According to the heat source distribution on the PCB board, reasonably design the heat dissipation area, and lay enough copper foil in these areas to increase the heat dissipation surface area and heat conduction path.
• Increase the thickness of copper foil: Increasing the thickness of copper foil in the heat dissipation area can increase the heat conduction path and improve heat dissipation efficiency.
• Design heat dissipation through holes: Design heat dissipation through holes in the heat dissipation area to conduct heat to the other side of the PCB board through the through holes, increasing the heat dissipation path and improving heat dissipation efficiency.
• Add heat sinks: Add heat sinks to the heat dissipation area to conduct heat to the heat sink, and then dissipate heat through natural convection or fan radiators to improve heat dissipation efficiency.

3. Copper laying can reduce deformation and improve PCB manufacturing quality.

Copper laying can help ensure the uniformity of electroplating, reduce the deformation of the board during the lamination process, especially for double-sided or multi-layer PCBs, and improve the manufacturing quality of PCBs.

If there is too much copper foil in some areas and too little in some areas, it will lead to uneven distribution of the entire board. Copper laying can effectively reduce this gap.

4. Meet the installation needs of special devices.

For some special devices, such as those that require grounding or special installation requirements, copper laying can provide additional connection points and fixed support to enhance the stability and reliability of the device. Therefore, based on the above advantages, in most cases, electronic designers will lay copper on the PCB board. However, copper laying is not a necessary part of PCB design.

In some cases, copper routing may not be appropriate or feasible. The following are some situations where copper laying is not appropriate:
① High-frequency signal lines: For high-frequency signal lines, copper laying may introduce additional capacitance and inductance, affecting signal transmission performance. In high-frequency circuits, it is usually necessary to control the routing of the ground wire to reduce the return path of the ground wire instead of over-laying copper. For example, copper plating will affect the signal of the antenna part. Laying copper in the area around the antenna part can easily cause the signal collected by weak signals to receive relatively large interference. The antenna signal is very strict for the amplification circuit parameter settings, and the impedance of the copper layer will affect the performance of the amplification circuit. Therefore, the area around the antenna part is generally not covered with copper.

② High-density circuit boards: For circuit boards with higher density, excessive copper laying may cause short circuits or grounding problems between lines, affecting the normal operation of the circuit. When designing high-density circuit boards, you need to carefully design the copper layout to ensure sufficient spacing and insulation between lines to avoid problems.

③. Too fast heat dissipation and difficult welding: If the component pins are fully covered with copper, it may cause heat dissipation too fast, making desoldering and repair difficult. We know that copper has a high thermal conductivity. Therefore, whether it is manual soldering or reflow soldering, the copper surface will quickly conduct heat during soldering, causing the temperature of the soldering iron to lose, which will affect the welding. Therefore, the design should try to use "cross flower pads" to reduce heat dissipation and facilitate welding.

④. Special environmental requirements: In some special environments, such as high temperature, high humidity, corrosive environments, etc., the copper foil may be damaged or corroded, thus affecting the performance and reliability of the PCB board. In this case, it is necessary to select appropriate materials and processing methods according to specific environmental requirements, rather than over-plating copper.

⑤. Special-level boards: For special-level boards such as flexible circuit boards and rigid-flexible composite boards, copper laying design needs to be carried out according to specific requirements and design specifications to avoid problems with the flexible layer or rigid-flexible composite layer caused by excessive copper laying. 

To sum up, in PCB design, it is necessary to make the appropriate choice of copper laying or no copper laying according to the specific circuit requirements, environmental requirements and special application scenarios.

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