The copper-clad laminate industry provides raw materials to the PCB industry. The copper-clad material is made of a flat plate by impregnating the electronic fiberglass cloth with resin adhesive, then drying, cutting and laminating them into plate material.

Copper foil is applied to one or both sides and then hot-pressed. They are mainly used in the manufacture of printed circuit boards and serve as an interconnection, insulation, and support for these PCBs. Electrolytic copper foils, wood pulp papers, fiberglass cloths, resins and other raw materials are used upstream in the industrial chain. The downstream products include PCBs.

The first commercial 5G networks are available in 2019. The downstream PCB manufacturers produce them into high-frequency circuit board suitable for high frequency application, including antennas, low-noise amplifiers, filters and power amplifiers. Automotive auxiliary systems, aerospace technologies, satellite communication, satellite TV, and other high-frequency communications fields.

PCB Circuits board must meet higher standards for 5G high frequency technology.

What is High-frequency circuits?

High-frequency circuits are radio frequency circuits that operate at frequencies higher than 1GHz. As mobile communication evolved from 2G, 3G to 4G, the frequency band of the communications has increased from 800MHz up to 2.5GHz. The communication frequency band is set to be improved in the 5G age.

In terms of radio frequency, PCB boards will include antenna elements and filters. According to requirements of the Ministry of Industry and Information Technology it is expected that the early 5G deployments will use the frequency band of 3.5GHz, and the frequency band of 4G is mainly 2GHz. Millimeter waves are electromagnetic waves that have wavelengths between 1 and 10 millimeters within the 30-300GHz band.

The millimeter-wave technology will be used when 5G commercialization is done on a large-scale. It offers better performance, with a wide spectrum, a bandwidth of 1GHz in the 28GHz range, and 2GHz in each 60GHz channel.

The PCB must meet the following requirements in order to achieve the high frequency, high speed and to overcome the issues of low penetrating powers and rapid attenuation speeds of millimeter wave.

1. Low transmission loss
2. Low transmission delay
3. Precision control of high impedance.

Two ways can increase PCB frequencies. The first is by increasing PCB processing requirements. The second is to use high frequency CCL, a substrate material that is designed for high-frequency applications.

There are two main indicators to measure the performance:
Dielectric constants (Dk)
Dielectric loss factors (Df).
The lower the Dk and Df, the more stable and better performing the high-frequency substrates are. PCB boards are larger and have more layers in RF boards. This means that the base material must have a higher heat resistance.

What materials are used for High-Frequency and High-Speed 5g PCB Boards

PCB boards are made of a variety of materials that can be used for high-frequency and high-speed applications: hydrocarbon resins, PTFE, LCP (liquid crystal polymer), PPE/PPO etc.

1) Hydrocarbon Resin

Hydrocarbon resin refers to polyolefin homopolymers or copolymers, including butadiene styrene copolymer, butadiene homopolymer, styrene, homopolymer, styrene/divinylbenzene copolymer, styrene- Butadiene-divinylbenzene copolymer, etc.

A.Excellent dielectric properties: Dk2.4/Df0.0002

B.Higher heat resistance

C.Good chemical resistance

D.Poor adhesion

2) PTFE flexible membrane

PTFE resin is characterized by a high melting temperature, and a viscosity of the melt. Resin dispersion is a common product form, as are resin suspensions and resin powders. Processing methods include extrusion/molding and extrusion/molding. PTFE must be modified and enhanced to overcome its limitations, such as a large linear expansion coefficient or low thermal conductivity. Modified membrane products include:

PTFE+ceramic

PTFE + Fiberglass cloth

PTFE + Ceramic + Fiberglass Cloth

3) LCP liquid crystal polymer

LCP is also known as Liquid Crystal polymer. It is a high-performance, special engineering plastic that was developed in the 1980s.

Liquid crystals are classified according to their formation conditions. Thermotropic LCP is heated until it melts, while Lyotropic LCP is dissolved into a solvent.

This material, when melted or dissolved in a solvent will lose its macroscopic properties such as size, shape and rigidity, but retain the crystalline orientation. A transition state forms that is anisotropic and has liquid fluidity with an ordered arrangement of crystal molecules. This intermediate state is the liquid crystal phase.

There are three types of LCPs that are commercially available.

A.copolymerization with rigid polyphenyl molecular monomers.

B.introduce a naphthalene-ring into the molecule;

C.use aliphatic segments as part of the molecular chains.

The melting points of the different types of LCP differ according to their molecular structure. In general, heat resistance of LCPs is arranged as type I>type 2>type 3.

4) PPE/PPO

Polyphenylene Ether is a high strength engineering plastic that was developed in 1960. Its chemical name is poly2,6-dimethyl-1,4-phenylene ether, referred to as PPO (Polyphenylene Oxide) or PPE (Polypheylene ether).

The two methyl group blocks the active points of two ortho-positions in the phenolic groups, making the material rigid, stable and heat resistant become higher.

Heat resistance is reduced by ether bonds, but flexibility is increased.

The two methyl group are non-polar hydrophobic groups that reduce water absorption, polarity, and the PPO macromolecules. They also block the two active points in the phenolic groups so there are no hydrolyzable phenolic groups.

It is highly hygroscopic and resistant to water. It has good properties, dimensional stabilty and electrical insulation. The rigidity of the molecular structure, as well as the force between molecular chains, makes it difficult for molecular segments to rotate. This results in a high melting point, high viscosity, and lower fluidity.

The above are commonly used materials for high-speed and high-frequency PCB manufacturing. With the advancement of technology, we believe that there will be more and better materials that can provide PCB manufacturing performance.