CCL industry is in the middle of the whole PCB industry chain and provides raw materials for PCB industry. Copper clad laminate (CCL) is a kind of plate-like material made by impregnating, drying, cutting and stacking electronic glass fiber cloth or other reinforcing materials with resin adhesive, covering one or both sides with copper foil and hot pressing, It is mainly used to make printed circuit board (PCB), which plays the role of interconnection, insulation and support for PCB. It is the upstream industry of fiberglass, PCB, and the downstream industry of electrical appliances, such as glass fiber, aluminum foil, and so on
5g was initially put into commercial use in 19 years, with core materials, high-frequency copper clad laminates and other products. The upstream raw materials are basically similar to the traditional copper clad laminates. After being produced as a high-frequency circuit board suitable for high-frequency environment by downstream PCB manufacturers, it is applied to base station antenna module and power amplifier. Modules and other equipment components are finally widely used in communication base stations (antennas, power amplifiers, low-noise amplifiers, filters, etc.), automotive auxiliary systems, aerospace technology, satellite communication, satellite television, military radar and other high-frequency communication fields.
5g high frequency technology puts forward higher requirements for the circuit. RF circuits with operating frequency above 1GHz are generally called high frequency circuits. In the process of mobile communication from 2G to 3G and 4G, the communication frequency band has developed from 800MHz to 2.5GHz. In the 5g era, the communication frequency band will be further improved. The PCB board will be equipped with antenna elements, filters and other components in 5g RF. According to the requirements of the Ministry of industry and information technology, it is expected that the early deployment of 5g will use the 3.5GHz band, and the 4G band is mainly about 2GHz. Generally, electromagnetic waves with a wavelength of 1-10mm in the 30-300ghz band are called millimeter waves.
When 5g is commercially available on a large scale, millimeter wave technology ensures better performance: extremely wide bandwidth, the available spectrum bandwidth of 28ghz band can reach 1GHz, and the available signal bandwidth of each channel of 60GHz band can reach 2GHz; The corresponding antenna has high resolution, good anti-interference performance and miniaturization; The propagation attenuation in the atmosphere is faster, and the short-range safe communication can be realized.
In order to meet the requirements of high frequency and high speed and deal with the problems of poor penetration and fast attenuation of millimeter wave, 5g communication equipment has the following three requirements for PCB performance:
1. Low transmission loss; 2. Low transmission delay; 3. High characteristic impedance precision control. There are two ways to increase the frequency of PCB. First, the processing technology requirements of PCB are higher. Second, high-frequency copper clad laminate is adopted – the substrate material that meets the high-frequency application environment is called high-frequency copper clad laminate.
Dielectric constant (DK) and dielectric loss factor (DF) are two main indexes to measure the properties of high frequency copper clad laminates. The smaller and more stable DK and DF are, the better the performance of high-frequency and high-speed substrate is. In addition, in terms of RF board, PCB board has larger area and more layers, which requires higher heat resistance (TG, high temperature modulus retention) and stricter substrate thickness tolerance.
There are several common high-frequency and high-speed materials for circuit boards: hydrocarbon resin, polytetrafluoroethylene, LCP liquid crystal polymer, PPE / PPO, etc.
(1) Hydrocarbon resin
Hydrocarbon resin refers to polyolefin homopolymer or copolymer, including butadiene styrene copolymer, butadiene homopolymer, styrene homopolymer, styrene / DIVINYLBENZENE copolymer, styrene butadiene divinylbenzene copolymer, etc.
① Excellent dielectric properties: DK ≈ 2.4 / DF ≈ 0.0002 ② high heat resistance ③ good chemical resistance and poor adhesion
（2） PTFE flexible membrane
The melting temperature and melt viscosity of polytetrafluoroethylene resin are relatively high. The common commercial forms are resin dispersion, resin suspension and resin powder. Common processing methods include molding / turning, impregnation / molding, extrusion / molding, etc. due to the disadvantages of large linear expansion coefficient and low thermal conductivity of PTFE, it needs to be strengthened and modified. Modified membrane products usually y include: polytetrafluoroethylene + ceramics, polytetrafluoroethylene + glass fiber cloth, polytetrafluoroethylene + ceramics + glass fiber cloth
(3) LCP liquid crystal polymer
Liquid crystal polymer, LCP for short. It is a new high-performance special engineering plastic developed in the early 1980s.
According to different formation conditions, liquid crystals can be divided into thermotropic liquid crystals melted by heating and lyotropic liquid crystals dissolved by solvent.
After being heated, melted or dissolved by the solvent, this material will lose the macro size, shape, hardness, rigidity and other properties of the solid, obtain the fluidity of the liquid material in appearance, and maintain the orientation and order of the crystalline material So as to form anisotropy in physical form and form a transition state with both liquid fluidity and orderly arrangement of crystalline molecules. This intermediate form becomes a liquid crystal state.
From the perspective of molecular design, there are three main types of commercial LCPs:
One is the copolymerization of rigid molecular monomers of polyphenylene ring;
The second is to introduce naphthalene ring into the molecular structure;
Third, aliphatic segments are used in molecular chains.
Different types of LCPs have different melting points according to different molecular structures. Generally speaking, their heat resistance is type I > type II > type III.
Polyphenylene oxide is a high-strength engineering plastic developed in 1960s. Its chemical name is poly 2,6-dimethyl-1,4-phenyl ether, abbreviated as PPO (polyphenylene oxide) or PPE (polyphenylene ether), also known as polyphenylene ether or polyphenylene ether.
The two methyl groups block the active sites of the two ortho positions of the phenolic group and make it rigid ↗， stability ↗， Heat and chemical resistance ↗。
Ether bonds increase flexibility but deteriorate heat resistance.
The two methyl groups are hydrophobic nonpolar groups, which reduce the water absorption and polarity of PPO macromolecules, block the two active points of phenolic groups, and make PPO molecular structure have no hydrolyzable groups, with good water resistance and moisture absorption. Good performance, dimensional stability and electrical insulation. A large number of rigid phenol aryl rings, the rigidity of the molecular chain and the force between the molecular chains make the molecular chain difficult to rotate internally, resulting in its melting point ↗、 Melt viscosity ↗、 mobility ↘、 Processing difficulties.
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