What is PCB? Analysis of High-speed PCB Industry Chain

1. High-speed PCB is a special printed circuit board usually used in high-speed digital circuits

1.1.PCB is the key electronic interconnection component of electronic products
Printed circuit board is referred to as PCB (Printed Circuit Board). The PCB substrate is composed of conductive copper foil and an insulating and heat-insulating material in the middle. It uses a mesh of small lines to form predetermined circuit connections between various electronic components. This connectivity makes the PCB a key electronic interconnect for electronic products, and as a result, the PCB is known as the "Mother of Electronics." PCB can be divided into organic material boards and inorganic material boards according to materials. According to different structures, they can be divided into rigid boards, flexible boards, rigid-flex boards and packaging substrates. According to the number of layers, it can be divided into single-panel, double-panel and multi-layer boards. The upstream of the PCB industry chain mainly involves the manufacturing of related raw materials, such as copper clad laminates, prepregs, copper foil, copper balls, gold salts, dry films and inks. The midstream segment is mainly PCB manufacturing. The downstream is the wide range of applications of PCB, including communications, consumer electronics, automotive electronics, industrial control, medical, aerospace, national defense and semiconductor packaging and other fields.

The development trend of PCB technology is mainly reflected in miniaturization, high-rise, flexibility and intelligence. Miniaturization means that with the development of miniaturization and functional diversification of consumer electronic products, PCBs need to be equipped with more components and reduced in size, requiring PCBs to have higher precision and miniaturization capabilities. High-rise refers to the high-speed and high-frequency development of the computer and server fields in the 5G and AI era. PCB needs to work at high frequency and high speed, have stable performance, and undertake more complex functions, requiring PCB to have more layers and a more complex structure. Flexibility means that with the rise of emerging applications such as wearable devices and flexible displays, PCBs need to have good flexibility and bendability to adapt to different shapes and spaces, requiring PCBs to have better flexibility and reliability. Intelligence refers to the development of the Internet of Things, smart cars and other fields. PCB needs to have stronger data processing capabilities and intelligent control capabilities to achieve interconnection and automatic management between devices, requiring PCB to have higher integration and intelligence.

1.2. High-speed PCB is a special printed circuit board
High-speed PCB is mainly used in high-speed digital circuits and needs to ensure the integrity of signal transmission. High-frequency PCB is mainly used in high-frequency (frequency above 1 GHz) and ultra-high frequency (frequency above 10 GHz) electronic equipment, such as radio frequency chips, microwave receivers, radio frequency switches, vacant tuners, frequency selection networks, etc. Different from 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 PCBs need to use special materials and adopt special processes. In high-speed PCB design, it is crucial to select appropriate high-speed CCL materials. Data center switches and AI servers are important application areas for high-speed boards. AI servers usually have features such as large memory, high-speed storage, and multi-core processors, which require PCB specifications and performance to match them. The port speed of domestic mainstream data center switches is evolving from 10G/40G to 400G/800G. According to a report released by Dell’Oro, it is expected that by 2027, 400Gbps and higher speeds will account for nearly 70% of data center switch sales, all of which are inseparable from the application of high-speed PCBs.

The demand for high-speed boards due to automobile intelligence is increasing. Driven by electrification, intelligence and connectivity, the demand for mid-to-high-end PCBs in ADAS (Advanced Driving Assistance Systems), smart cockpits, power system electrification, automotive electronic functional architecture and other fields continues to increase. Electronic control units (ECUs) with features such as integration, multi-function, and high efficiency will drive increased demand for related high-end automotive boards.

2. High-speed CCL is the core material of high-speed boards, and the high-end field is mainly dominated by Taiwanese and Japanese companies.

2.1.CCL is one of the main materials of PCB
CCL, the full name of Copper Clad Laminate, is a plate-shaped 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. It has the characteristics of good dielectric properties and mechanical properties. Its upstream mainly includes copper foil, resin, fiberglass cloth and other raw material industries, and its downstream mainly includes communication equipment, consumer electronics, automotive electronics and other fields.

PCB's performance, quality, processability in manufacturing, manufacturing level, manufacturing cost, and long-term reliability and stability depend largely 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 signal transmission speed, energy loss and characteristic impedance in the circuit. The technological development trend of CCL is consistent with that of PCB, which is mainly reflected in the aspects of miniaturization, high-rise building, flexibility and intelligence. For example, HDI boards and carrier-like boards have higher requirements on CCL’s micronization capabilities. High multilayer through-hole boards and backplanes require higher layer count and structure requirements for CCL. Flexible boards and rigid-flex boards require higher flexibility and reliability of CCL. Package substrates and embedded component boards have higher requirements for CCL integration and intelligence.

According to different reinforcing materials, CCL can be divided into glass fiber cloth-based CCL, paper-based CCL, and composite-based CCL. The reinforcing material used in fiberglass cloth-based CCL is glass fiber cloth, which is suitable for the manufacturing of consumer electronics products. Glass fiber can absorb most of the stress when the PCB motherboard is bent, giving the glass fiber cloth-based CCL good mechanical properties. Paper-based CCL uses wood pulp fiber paper and is mainly used to manufacture electronic industrial products such as computers and communication equipment. Composite-based CCL uses wood pulp fiber paper or cotton pulp fiber paper as core reinforcement material and glass fiber cloth as surface reinforcement material. It is widely used in the manufacture of high-end home appliances and electronic equipment. Depending on the insulation resin, CCL can also be divided into epoxy resin CCL, polyester resin CCL, and phenolic resin CCL. Based on 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 high-speed CCL and high-frequency CCL. High-speed CCL emphasizes its own dielectric loss (Df). The high-speed CCL grades 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 dielectric constant (Dk), and the stability of dielectric constant (Dk). CCL accounts for approximately 30% of the PCB production cost, and its dielectric constant (Dk) and dielectric loss factor (Df) values directly determine PCB performance. The lower the dielectric constant (Dk), the faster the signal is transmitted; the smaller the mass loss factor (Df), the smaller the signal transmission loss.

High-speed CCL refers to a copper-clad laminate with high signal transmission speed, high characteristic impedance accuracy, low transmission signal dispersion, and low loss (Df). High-speed boards are divided into many grades. Generally, the M series of the benchmark company Panasonic is used for comparison, such as M4, M6, M7, etc. The larger the number, the more advanced it is and the higher the transmission rate it can adapt to. The M4 level is a low loss level material, which roughly corresponds to a transmission rate of 16Gbps, the M6 level is a very low loss level material, and the M7 level is super ultra low loss, which roughly corresponds to a transmission rate of 32Gbps.

The core requirement of high-speed boards is low dielectric loss factor (Df). The smaller the Df, the more stable it is and the better the high-speed performance. Dielectric loss factor (Df) is a characteristic of resin. Generally speaking, reducing Df is mainly achieved through the resin, substrate and substrate resin content. The epoxy resin used in ordinary CCL is mainly FR-4, and its Df value is above 0.01. High-speed CCL needs to be modified on this basis or add resin materials such as PPO/PPE. Among various resin materials, PTFE and hydrocarbon resin (two typical high-frequency materials) have the lowest Df value, below 0.002. The Df of the resin used in the final high-speed material is between that of the high-frequency material and FR-4.

High-frequency CCL refers to a copper-clad laminate with an operating frequency above 5GHz, suitable for ultra-high frequency fields, and an ultra-low dielectric constant (Dk). It also requires the dielectric loss factor (Df) to be as small as possible. PCB made of CCL as the core raw material can be regarded as a capacitive device. When there is signal transmission in the wire, part of the energy will be accumulated by the PCB, causing transmission delay. The higher the frequency, the more obvious the delay. Similar to high-speed CCL, the main method to reduce Dk is to modify the insulating resin, glass fiber, and overall structure used. Currently, the mainstream high-frequency CCL on the market is mainly realized by using polytetrafluoroethylene (PTFE) and hydrocarbon resin material processes. Among them, CCL using PTFE is the most widely used. It has the advantages of small dielectric loss, small dielectric constant, small change with temperature and frequency, and a thermal expansion coefficient close to that of metal copper foil.

2.2. Upstream materials have a huge impact on CCL performance

Copper-clad laminates have three major raw materials: copper foil, resin, and fiberglass cloth, accounting for nearly 90% of the total cost. The raw material proportions of different copper clad laminate products will be slightly different. According to data from the Qianzhan Industry Research Institute, copper foil, resin, and fiberglass 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 copper foil will affect signal transmission loss and impedance matching. Generally speaking, in order to reduce conductor loss, it is necessary to choose copper foil with low roughness, low resistivity and appropriate thickness. Currently, commonly used copper foil types include HTE (high extensibility), 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.

Copper foil is a thin sheet metal material made from pure copper or alloy by rolling or electrodeposition. It is the main raw material of CCL. Copper foil thickness is generally between 5-105 microns and width is between 5-1370 mm. Copper foil has good electrical conductivity, thermal conductivity, ductility, corrosion resistance and other characteristics, and is widely used in electronic and electrical appliances, automobiles, aerospace, building decoration and other fields. Copper foil can be divided into two categories according to the production method: rolled copper foil and electrolytic copper foil. Rolled copper foil is a copper foil made by rolling copper ingots in multiple passes. Its thickness is generally between 0.006-0.1mm, and it is mainly used in the field of flexible CCL. Rolled copper foil has the advantages of smooth surface, uniform thickness, and fine crystallization, but the cost is relatively high and it is suitable for the manufacturing of high-end products. Electrolytic copper foil is a copper foil that uses the principle of electrolysis to deposit a layer of pure copper on a metal substrate. Its thickness is generally between 0.006-0.04mm. Electrolytic copper foil has the advantages of low cost, high production efficiency, and adjustable thickness. However, it has shortcomings such as rough surface and uneven crystallization, so it is suitable for the manufacturing of mid-to-low-end products.

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