In the design and manufacture of electronic products, the printed circuit board (PCB) plays a crucial role. PCB proofing, that is, the process of small batch trial production of PCB, is a key link for electronic engineers to submit production requests to the circuit board factory after designing the circuit and completing the drawing of the PCB. PCB proofing not only involves the standard process flow, but also includes a variety of special processes to meet different design needs and application scenarios. This paper will deeply discuss several special processes in PCB proofing, including goldfinger processing, impedance control, blind hole and buried hole technology, thick copper PCB, multi-layer special laminated structure, shaped hole, deep groove control, etc.
1. Gold Finger
The gold finger is a gold-plated column on the edge of the PCB connection, mainly used to assist the connection of the PCB with the computer motherboard or other equipment. Gold finger through gold-plated treatment, significantly enhance the electrical conductivity and wear resistance, to ensure the stability and reliability of signal transmission. Common gold-plating processes include electroless nickel plating (ENIG) and electroplating of hard gold. Electroplated hard gold because of its high adhesion and hardness, especially suitable for frequent insertion and removal of occasions, such as the gold finger of memory. This process not only improves the durability of the connector, but also reduces the risk of poor contact and signal loss.
2. Impedance control
In high-speed circuit design, impedance control is a key process to ensure signal integrity. The characteristic impedance value of the PCB must match the electronic impedance of the head and tail components to avoid signal reflection, scattering, attenuation or delay. In order to achieve this goal, engineers need to accurately design PCB impedance bars and impedance lines, controlling wire resistance, inductance and capacitance. This process is especially important for high-speed circuits, because it directly affects the transmission quality of the signal and the stability of the system.
3. Blind hole and buried hole technology
Blind and buried holes are common special hole structures in high density interconnect (HDI) PCBS. Blind holes are holes that are drilled out of the top or bottom layer of the PCB but do not penetrate the entire board layer, while buried holes are located entirely in the inner layer of the PCB. The application of these holes reduces the number of layers and size of the PCB, improves electromagnetic compatibility, reduces costs, and simplifies design work. Blind hole and buried hole technology make it possible to interconnect any layer inside the circuit board, which greatly improves the flexibility and integration of circuit design.
4. Thick copper PCB
Thick copper PCB refers to a circuit board that uses thicker copper foil than a standard PCB in the manufacturing process. The standard copper foil thickness is generally about 35 microns, and the copper thickness of the thick copper plate can reach 105 microns or even higher. Thick copper plates with high current carrying capacity, good thermal management performance and enhanced mechanical strength are suitable for high power, high current and harsh environment applications, such as automotive electronics and industrial control systems. Thick copper PCB not only extends the service life of electronic products, but also greatly helps to streamline the volume of products.
5. Multi-layer special laminated structure
By arranging signal layer, power layer and ground layer reasonably, the multi-layer special laminated structure realizes effective signal isolation and electromagnetic interference suppression. For the design of a large number of signals, large device density, and high signal frequency, the use of multi-layer special laminated structure can significantly improve the EMC performance of the PCB, ensuring the integrity of the signal and the stability of the system. This structure not only improves the integration of the circuit board, but also reduces the noise and interference during signal transmission.
6. Shaped holes
Special-shaped holes refer to non-circular holes encountered in PCB production, such as 8-figure holes, diamond holes, square holes and sawtooth holes. According to the design requirements, these holes are divided into copper in the hole (PTH) and copper in the hole (NPTH). With the development of diversified electronic products, shaped holes are widely used in the fixing and interconnection of special components, improving the flexibility and adaptability of PCB. The application of shaped holes not only meets the needs of complex design, but also improves the overall performance and reliability of the circuit board.
7. Control the deep tank
Depth control groove is to process a specific depth groove on the PCB to meet the installation and fixing needs of special components. This process is often used to fix heat sinks, connectors, or other components that require precise depth control, improving PCB assembly accuracy and reliability. The application of the control groove not only simplifies the installation process of the components, but also ensures good contact and heat dissipation between the components and the PCB.
8. Half hole/wrapping process
The half-hole process is to form a partially penetrated hole at the edge of the PCB, while the wrapping is to add an additional layer of copper foil at the edge of the hole to enhance the connection strength. These processes are often used in the design of edge connectors and special interfaces, improving the reliability and durability of the connection. The half-hole and wrapping process ensures the stable operation of the PCB in harsh environments by adding additional connection points and enhancing structural strength.
9. Electroplating nickel gold and nickel palladium
Electroplating nickel gold refers to the method of electroplating, so that the gold particles are attached to the PCB board, forming a layer of uniform and fine, strong adhesion coating. The process can greatly increase the hardness and wear resistance of the PCB, effectively prevent the diffusion of copper and other metals, and adapt to the requirements of hot pressure welding and brazing. Nickel palladium is a layer of nickel, palladium and gold on the surface of the printed line copper layer in the PCB proofing by chemical method, so that the PCB board can achieve good electrical conductivity, corrosion resistance and friction resistance. These two surface treatment processes have been widely used in PCB proofing, improving the overall performance and reliability of the circuit board.
10. PCB proofing process and precautions
PCB proofing is a complex and fine process, involving circuit design, plate selection, processing technology, circuit configuration, solder resistance layer and screen printing layer configuration, shape processing and other links. Before PCB proofing, it is necessary to provide detailed information and requirements to the processing plant, including special process requirements, assembly mode, assembly quantity, positioning holes and reference point Settings, special material requirements, and production cycle and delivery requirements. At the same time, in the PCB proofing process, it is also necessary to pay attention to size problems, color problems, line problems and solder resistance types to ensure the smooth progress of processing proofing and meet customer needs.
To sum up, there are a variety of special processes in PCB proofing, and each process has its own unique application scenarios and advantages. Through the rational use of these special processes, not only can improve the overall performance and reliability of the PCB, but also meet the needs of complex designs and high-performance applications. In the future design and manufacturing of electronic products, these special processes will continue to play an important role in promoting the continuous development and innovation of electronic technology.
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