High-speed PCB is a special printed circuit board
High-speed PCBs are mainly used in high-speed digital circuits, and it is necessary to ensure the integrity of signal transmission. High-frequency PCBs are mainly used in high-frequency (frequency above 1 GHz) and ultra-high frequency (frequency above 10 GHz) electronic equipment, such as RF chips, microwave receivers, RF switches, vacant tuners, frequency selective networks, etc. Unlike high-frequency PCBs, when designing high-speed PCBs, more factors such as signal integrity, impedance matching, signal coupling, and signal noise need to be considered.
In order to meet these requirements, high-speed PCB needs to use special materials and special processes. In high-speed PCB design, it is very important to choose a suitable high-speed CCL material. Data center switches and AI servers are important application areas for high-speed boards. AI servers usually have the characteristics of large memory, high-speed memory, and multi-core processors, which require PCB specifications and performance to match.
The demand for high-speed boards in automotive intelligence has increased. Driven by electrification, intelligence and networking, the demand for mid-to-high-end PCBs in areas such as ADAS (Advanced Driver Assistance System), smart cockpit, power system electrification, and automotive electronic functional architecture continues to increase. Electronic control units (ECUs) with features such as integration, multi-function, and high performance will drive an increase in the demand for related high-end automotive boards.
High-speed CCL is the core material of high-speed board
CCL is one of the main materials of PCB
CCL, Copper Clad Laminate, is a board material made by impregnating electronic fiberglass cloth or other reinforcing materials with resin, covering one or both sides with copper foil, and then hot pressing. Its upstream mainly includes raw material industries such as copper foil, resin, and glass fiber cloth, and its downstream mainly includes communication equipment, consumer electronics, automotive electronics and other fields.
The performance, quality, processability in manufacturing, manufacturing level, manufacturing cost and long-term reliability and stability of PCB largely depend on CCL. As the core substrate material in PCB manufacturing, CCL mainly plays the role of interconnection, insulation and support for PCB, and has a great influence on the transmission speed, energy loss and characteristic impedance of signals in the circuit. The technical development trend of CCL is consistent with the technical development trend of PCB, which is mainly reflected in miniaturization, high level, flexibility and intelligence.
For example, HDI PCBs and carrier-like boards have higher requirements for the miniaturization ability of CCL; high multi-layer through-hole boards and backplanes have higher requirements for the number of layers and structure of CCL; flexible PCBs and rigid-flex PCBs have higher requirements for the flexibility and reliability of CCL; packaging substrates and embedded component boards have higher requirements for the integration and intelligence of CCL.
According to different reinforcing materials, CCL can be divided into glass fiber cloth-based CCL, paper-based CCL, and composite-based CCL. Among them, the reinforcing material used in glass fiber cloth-based CCL is glass fiber cloth, which is suitable for the manufacture of consumer electronics products. When the PCB motherboard is bent, the glass fiber can absorb most of the stress, so the glass fiber cloth-based CCL has good mechanical properties.
Paper-based CCL uses wood pulp fiber paper, which is mainly used in the manufacture of electronic products such as computers and communication equipment. The composite matrix CCL uses wood pulp fiber paper or cotton pulp fiber paper as the core reinforcement material, and glass fiber cloth as the surface layer reinforcement material, which is widely used in the manufacture of high-end home appliances and electronic equipment. According to different insulating resins, CCL can also be divided into epoxy resin CCL, polyester resin CCL, and phenolic resin CCL. According to different mechanical properties, CCL can be divided into rigid CCL and flexible CCL.
According to the size of CCL’s own dielectric loss (Df) and dielectric constant (Dk), CCL can be divided into two types: high-speed CCL and high-frequency CCL. High-speed CCL emphasizes its own dielectric loss (Df), and the grades of high-speed CCL commonly used in the market are also divided according to the size of dielectric loss (Df). Compared with high-speed CCL, high-frequency CCL pays more attention to the size and change of the dielectric constant (Dk), as well as the stability of the dielectric constant (Dk). CCL accounts for about 30% of PCB production cost, and its dielectric constant (Dk) and dielectric loss factor (Df) values directly determine the performance of PCB. The lower the dielectric constant (Dk), the faster the signal transmission speed; the smaller the loss factor (Df), the smaller the signal transmission loss.
Upstream materials have a huge impact on CCL performance
CCL has three raw materials: copper foil, resin, and glass fiber cloth, accounting for nearly 90% of the total cost. The proportion of raw materials of different CCL products will be slightly different. According to the data of the Qianzhan Industry Research Institute, copper foil, resin, and glass fiber cloth account for about 42.1%, 26.1%, and 19.1% of the cost of copper-clad laminates, respectively. Copper foil is used to form signal lines and power layers. Factors such as the type, thickness and roughness of the copper foil will affect the transmission loss and impedance matching of the signal.
Generally speaking, in order to reduce conductor loss, copper foil with low roughness, low resistivity and appropriate thickness needs to be selected. At present, the commonly used types of copper foil are HTE (high elongation), RTF (reverse), HVLP (low profile), etc. Among them, HVLP copper foil has the lowest roughness and is suitable for high-frequency and high-speed signal transmission.