Why is copper laid on PCBs? There are several key reasons for copper implementation:

1. **EMC (Electromagnetic Compatibility)**: For large-area ground or power supply copper, it serves as a shielding mechanism, while specific ground planes, such as PGND, offer protection.

2. **PCB Process Requirements**: Copper is typically added to PCB layers with minimal routing to ensure proper electroplating or prevent deformation during lamination.

3. **Signal Integrity**: Copper is used to provide a complete return path for high-frequency digital signals, helping to minimize interference and reduce the complexity of DC network routing.

Additionally, copper is also used for heat dissipation and for specific device mounting requirements.


1. One of the main advantages of copper paving is the reduction of ground wire impedance (a significant portion of what is commonly referred to as anti-interference comes from the decreased impedance of the ground wire). Digital circuits experience numerous spike currents, making it even more crucial to lower ground wire impedance. It is widely accepted that a large ground plane should be used for circuits containing digital components, while for analog circuits, the ground loop formed by copper paving can introduce electromagnetic coupling interference, outweighing the benefits (except in high-frequency circuits). Therefore, not all circuits require a full copper layer (BTW: mesh copper paving generally performs better than a solid block of copper).

2. The purpose of circuit copper laying includes:

1. Laying copper and connecting it to the ground wire helps reduce the loop area.

2. A large copper area effectively lowers the resistance of the ground wire, reducing voltage drop. When operating at high frequencies, it is important to separate the digital and analog grounds and lay copper for each, linking them at a single point. This single point can be connected with a wire wrapped around a magnetic ring several times. However, if the frequency is not too high or the operating conditions of the device are not critical, this can be more relaxed. The crystal oscillator, acting as a high-frequency emission source, can have copper spread around it, and the shell of the crystal oscillator can be grounded for better performance.

The classification of FPC (Flexible Printed Circuit) boards is based on their substrate material and structure, organized as follows:

1. **Single-layer Soft Board Structure (FPC)**

This type of flexible board represents the simplest form of FPC. It typically consists of base material + transparent adhesive + copper foil, which are all purchased as raw materials. Additionally, the protective film and transparent adhesive are separately purchased materials. The copper foil is processed by etching and other methods to form the required circuit. After reaching the protective film, drilling is done to expose the relevant pads. Once cleaned, the copper foil and adhesive are bonded using a rolling process. The exposed pads are electroplated with gold or tin for protection. The final product consists of a flexible slab, and smaller circuit boards of the required shape are typically stamped out. Sometimes, solder masks are directly printed on the copper foil without a protective film, which reduces costs, but compromises the mechanical strength of the board. Unless high strength is not required and the price needs to be as low as possible, it is preferable to apply a protective film method.

2. **Double-layer Soft Board Structure (FPC)**

The FPC double-layer soft board structure is used when the circuit becomes too complex for a single-layer board or when additional copper foil is required for grounding and shielding. This structure typically involves adding a via to connect each layer of copper foil. The process begins similarly to single-layer boards, with the substrate + transparent adhesive + copper foil. Vias are created by drilling holes through the substrate and copper foil, followed by plating a certain thickness of copper after cleaning. Once the vias are completed, the subsequent production process is almost identical to that of a single-layer board.

3. **Double-sided Soft Board Structure (FPC)**

The structure of the FPC double-sided soft board features pads on both sides and is primarily used for interconnecting with other circuit boards. Although it shares similarities with the single-layer board structure, the manufacturing process is quite different. Its raw materials include copper foil, protective film, and transparent adhesive. First, holes are drilled in the protective film at the required pad positions. Then, copper foil is applied, and the pads and leads are etched. Afterward, another drilled protective film layer is applied.