The classification of PCB copper foil is mainly divided according to its use and function, mainly including the following categories:

1. Signal layer copper foil: used to transmit signals between functional modules on the circuit board.

2. Power layer copper foil: used to carry power supply and provide good current transmission capability.

3. Ground layer copper foil: Mainly used as the ground layer of the circuit board, providing good ground lead connection and shielding effect.

4. Planar copper foil: used to balance signal transmission, ground leads and power leads, providing overall balance and suppressing electromagnetic interference.

5. Reserve copper foil: An unconnected area reserved in the design for subsequent needs.

The manufacturing technologies of PCB copper foil mainly include electrolytic copper foil, rolled copper foil and etched copper foil.

Electrolytic copper foil is obtained by depositing a copper layer on a metal substrate through electrolysis. It has good conductivity and ductility.

Calendered copper foil is made by rolling copper material into a thin film through pressure, which has high strength and ductility.

Etching copper foil is to remove part of the copper layer on the metal substrate through an etching process to form the required copper foil pattern.

In terms of material selection, PCB copper foil usually uses high-purity copper as the main material, because copper has good conductivity and ductility and can meet the conductive performance requirements of PCB boards. In addition, in order to improve the corrosion resistance, oxidation resistance and wear resistance of copper foil, some alloying elements, such as nickel, zinc, etc., may also be added.

In short, PCB copper foil is an important component of electronic products. Its classification, grade, manufacturing technology and material selection directly affect the performance and quality of electronic products. With the continuous advancement and development of technology, PCB copper foil will also be continuously upgraded and optimized to provide better support for the innovation and development of electronic products.

The roughness grade of PCB copper foil varies according to specific classification standards.

Roughness is generally represented by three codes: Ra, Rz, and Ry plus numbers. Among them, Ra is more reflected in the drawing markings.

1. Contour arithmetic mean deviation Ra

Within the sampling length, the arithmetic mean of the absolute value of the distance between points on the contour line along the measurement direction (Y direction) and the reference line.

2. Micro roughness ten-point height Rz

It refers to the sum of the average value of the five maximum contour peak heights and the average value of the five maximum contour valley depths within the sampling length.

3. Maximum profile height Ry

The distance between the top line of the highest peak and the bottom line of the lowest valley of the profile within the sampling length.

Based on the surface roughness of copper foil, different roughness levels will affect the performance and use of copper foil. In actual applications, the appropriate copper foil type and roughness grade should be selected according to specific needs.

Depending on the specific copper foil type, for example:

 * STD copper foil (standard copper foil): its roughness size is about 7~8μm.

 * RTF copper foil (reversed copper foil): its roughness size is about 4~6μm.

 * HVLP/VLP copper foil (low/ultra-low roughness copper foil):

The roughness size of low-roughness copper foil is about 3~4μm, and the roughness size of ultra-low roughness copper foil is about 1.5~2μm.

The roughness grade of PCB copper foil has a great impact on its electrical and mechanical properties. Here are some specific instructions on the different copper foil roughness levels:

1. **Low Profile or VLP Copper Foil**:

    - **Roughness Range**: Typically less than 2μm (microns).

    - **Application**: Suitable for high-frequency, high-speed circuits, and occasions requiring good electrical performance and fine circuit design. Low-roughness copper foil provides more uniform current distribution and smaller signal delay.

    - **Features**: The surface is smooth, which can reduce electrical noise and signal distortion, but the cost is relatively high.

2. **Standard roughness copper foil (STD copper foil)**:

    - **Roughness Range**: Usually between 5-10μm.

    - **Application**: Is the most common type of copper foil and is suitable for most conventional PCB manufacturing. It provides a balance between good conductivity and cost-effectiveness.

- **Features**: Moderate roughness allows certain electrical performance and mechanical strength, widely used in various circuit board designs.

3. **Reversed Copper Foil (RTF Copper Foil)**:

    - **Roughness Range**: Usually between 2-6μm.

    - **Application**: Suitable for applications requiring higher mechanical strength and heat resistance, such as thick copper plates, high-power electronic equipment, etc.

    - **Features**: The surface is relatively rough, providing better adhesion and weldability, but may introduce some electrical noise in high frequency applications.

4. **High roughness copper foil (Heavy Copper or High Thickness copper foil)**:

    - **Roughness Range**: Not primarily characterized by roughness, but rather by thickness, usually greater than 1 ounce/square foot (oz/ft²).

    - **Application**: Mainly used in situations requiring high current carrying capacity, such as power distribution boards, battery boards, etc.

    - **Features**: Thick copper foil can provide better heat conduction and higher current carrying capacity, but may also increase manufacturing costs and processing difficulty.

In addition to the above classification, there are some other factors that may also affect the roughness of copper foil, such as the manufacturing process of copper foil, surface treatment (such as anti-oxidation treatment, sandblasting treatment, etc.) and hot pressing parameters in the PCB manufacturing process.

Choosing the appropriate copper foil roughness grade is critical to ensuring PCB board performance and quality. Designers and engineers need to consider electrical performance, mechanical strength, cost and other relevant factors to select the most appropriate copper foil type and roughness grade based on the specific needs of the circuit. Of course, I'm happy to continue the discussion about PCB copper foil roughness grades.

5. **Ultra-Fine Copper**:

    - **Roughness range**: less than 1μm.

    - **Application**: Mainly used for PCB manufacturing of high-precision, ultra-fine lines, especially in the fields of microelectronics, high-frequency and microwave electronic equipment.

    - **Features**: The surface of ultra-fine copper foil is extremely smooth, which can significantly reduce electrical noise and signal loss and improve the reliability of the circuit. However, due to its high manufacturing cost, it is usually only used in special applications.

6. **High Conductivity Copper**:

    - **Roughness Range**: May be similar to traditional copper foil, but the focus is on its conductive properties.

    - **Application**: Suitable for applications requiring extremely high conductive properties, such as high frequency, high-speed signal processing, high-power electronic equipment, etc.

    - **Features**: Highly conductive copper foil achieves higher conductivity than traditional copper foil by optimizing the purity, crystal structure and surface treatment of copper. This helps reduce signal attenuation and delay, improving the overall performance of the circuit.

7. **Special surface treatment copper foil**:

    - In addition to basic roughness classification, copper foil can also undergo various surface treatments, such as chemical etching, electroplating, sandblasting, etc., to improve its electrical, mechanical or welding properties.

    - **Application**: Depending on the specific processing method and purpose, these specially treated copper foils can be used in various special occasions, such as enhancing welding strength, improving corrosion resistance, improving heat dissipation performance, etc.

- **Features**: Special surface-treated copper foil has unique physical and chemical properties, and the performance of the copper foil can be customized according to specific needs.

When selecting the roughness level of PCB copper foil, other factors need to be considered, such as PCB manufacturing process, welding requirements, working environment, etc. In addition, as technology continues to advance, new copper foil materials and manufacturing processes are also emerging, which may further expand the roughness range and performance of copper foil.

Therefore, when selecting copper foil, it is recommended to work closely with PCB manufacturers, material suppliers and circuit design engineers to ensure that the copper foil selected can meet the various requirements and performance standards of the circuit board. At the same time, we should also pay attention to the latest technological developments and market trends in order to adjust and optimize circuit design in a timely manner.

Application of copper foil roughness in high-speed PCB

Problems caused by skin effect

With the development of communications, cloud computing, cloud storage technology, and the development of higher Ethernet and cloud servers, PCB will further develop in the direction of high speed/high frequency, and PCB signal transmission performance will also restrict high-speed transmission technology to a certain extent. development of. In the 4G era, the PCB single-channel signal transmission rate has increased from 10Gbps to 25Gbps, and it is expected to further increase to more than 50Gbps in the 5G era.

The high speed/high frequency of signals means that signal transmission is increasingly concentrated on the "surface" of wires (called the skin effect). When the frequency reaches 1GHz, the signal transmission thickness on the wire surface is only 2.1μm. If the conductor surface roughness is 3-5μm, the signal transmission is only carried out within the thickness range of the roughness; when the signal transmission frequency is increased to 10GHz, The signal transmission thickness on the conductor surface is 0.7μm, and the signal transmission is carried out within the roughness range. When signals are transmitted in the roughness range, the standing waves and reflections of the transmitted signals will become more and more serious, causing the signal transmission path to become longer and the loss to increase.

Due to the existence of skin effect, if high-speed PCB continues to use conventional (STD) copper foil, the result will be: As the signal transmission frequency increases, the signal "distortion" caused by the skin effect becomes more and more serious. Therefore, the application of low-roughness copper foil on current high-speed materials is becoming more and more widespread. Mid Loss materials and Low Loss materials both use reversed (RTF) copper foil as standard copper foil; Very Low Loss materials are also standard. RTF copper foil, but most customer designs use ultra-low profile (HVLP) copper foil; for Ultra low loss materials, HVLP copper foil has become standard. The surface morphology of STD, RTF and HVLP copper foil (thickness 0.5oz) can be seen through scanning electron microscope and metallographic microscope. The matte surface roughness (Rz) of STD copper foil is about 5 μm, and the smooth surface roughness is 3 μm; the matte and smooth surface roughness of RTF copper foil is about 3 μm; the smooth and matte surface roughness of HVLP copper foil are both within 2 μm. It is understood that copper foil suppliers are currently developing NP copper foil with a surface roughness of less than 1 μm. Due to unresolved reliability issues, actual products have not yet been applied.

Although the surface of HVLP copper foil is relatively smooth, the existing PCB process will cause the surface roughness of the copper foil to increase, affecting the effect of HVLP copper foil. According to the inner layer circuit production process, the inner layer needs to go through dry film pre-treatment and browning process. After these two processes, the surface roughness Rz of HVLP copper foil will increase from the original 1.5 μm to about 3 μm. In order to solve this problem, there are also low-roughness processes on the market. Compared with traditional browning chemicals, this process does not micro-etch the surface of HVLP copper foil. Instead, it sinks a layer of HVLP copper foil after cleaning it. Tin, and use siloxane to modify the surface. When siloxane is pressed with PP, it can play a bridging role and increase the bonding force between copper foil and PP to a certain extent.