Electronic communication products have gone through many stages, including 1G, 2G and 3G. They are now moving to the fifth-generation communication product stage. 5G has better performance than 4G when it comes to peak rate, spectrum efficiency and time. There have been significant changes in PCBs and copper-clad materials. These have led to new requirements on PCBs and copper-clad materials.
This article will begin from the perspective of 5G communication terminals and suggest PCB technology, Copper-clad Laminate technology, upstream and downstream glass cloth, Resin, and other technical requirements to provide reference in the PCB Industry.
Key technical indicators of 5G
The 5G technology will allow everyone to enjoy a mobile internet experience. They will have to overcome many technical challenges. Solving these problems will lead to many technological improvements and breakthroughs.
There will be many MIMO antennas in the 5G age. This change in Massive MIMO antennas will increase the overall power of the amplifier, which will require a higher power efficiency. In order to increase power efficiency, it is important to find ways to reduce the losses of the board that contains the power amplifier.
The complexity of the PCB board also increases due to the increased number of radiation units. Multi-layer PCB board antennas are more complex to apply than traditional double-sided PCB antennas.
PCB requirements and technical difficulties of 5G communication devices
Technical requirements for 5G PCB
The front-end design space has been severely squeezed due to the trend towards miniaturization of communication products and their increasing capacity. Communication chip manufacturers are forced to create higher-speed ICs to meet the demands of small-volume, high-capacity products. As the rate increases, however, the pressure placed on engineers responsible for signal integrity does not lessen but rather intensifies. The implementation of high-rate products is possible with fewer traces.
However, the increased rate leads to more stringent requirements for signal quality and the margins are getting smaller. The UI for a signal with a 10Gbps rate can have a bit-width of 100ps. However, a signal at 25Gbps only has a 40ps bit-width. This means that every link in the channel must be optimized to achieve every ps of margin quantity.
This is a full-link diagram for a high-speed device, from the Driver IC to the Receiver IC. It includes IC packaging, subcard PCB design and backplane PCB. It is important to design and process the PCB motherboard correctly to guarantee the quality of all channels.
As the fifth-generation mobile communication product, 5G uses many new technologies. However, it can’t do without PCBs as carriers. The PCB requirements are increasing, particularly for substrate materials, PCB processing technology, and surface Processing. The demands are very high.
As the operating frequency for 5G communication devices continues to increase, new requirements are placed on the PCB production process. Microstrip lines, grounded coplanar waveguide circuits and multi-layer PCBs for millimeter wave are typically located on the outermost layer. The millimeter wave range is the highest frequency in the microwave field and PCB accuracy requirement increases with frequency.
Comparing the PCB processing capabilities of 5G and 4G
The appearance control requirements: Defects are not permitted on the microstrip line in key areas. This is because high-frequency lines do not transmit current but rather high-frequency electrical pulses. Pits and gaps are also not allowed on high-frequency conductors.
Controlling corner sharpness: To improve the gain, the direction, and the standing wave of an antenna, avoid the resonance frequency shifting to high frequencies, increase the margin in the antenna design, the corner sharpness must be controlled strictly, such as control (EA), e.g. ≤20um or 30um.
For 112G single-channel high-speed products, it is necessary to lower Dk and Df and to use new technologies in resin, glass cloth, and copper foil. The PCB back drilling should be more accurate, and thickness tolerance control and smaller pore size, etc.
HDI High-density Technology Application: This includes second-order HDI application, multiple-lamination technology, an asymmetrical design, holes as small as 0.15mm, high-density wall spacing of 0.20mm, and mixed-pressure pressures from different system materials.
5G PCB Technology Challenge
The hole spacing on PCBs must be reduced for 5G chips. The hole wall spacing should be no more than 0.20mm, and the aperture diameter should not exceed 0.15mm. This high-density design poses many challenges for CCL materials, PCB processing technologies, and other factors.
With an aperture as small as 0.15mm, and a maximum aspect of 20:1, it is important to solve the problems of needle breakage when drilling, improving the aspect ratio capabilities of PCB plating and the copper-free wall problem.
The solder pad can be lifted
To reduce signal losses, the annular rings of high-speed materials should be as small as they can, between 5.0mil and 3.0mil. However, the bonding force of the copper foil to the resin in the high-speed material is less than the conventional FR4 materials. The pad may warp, or the surface PP will crack when the PCB is reflow-soldered or wave-soldered due to thermal stress.
Solution: The rings will get smaller and smaller. it is important to optimize resin fluidity, and lamination parameters to reduce defects such as pad warping and PP layer cracking.
High-speed and low-frequency copper-clad laminates are required for 5G communication.
5G communications products need to be faster and higher-frequency. High-frequency and high-speed signals are based on the transmission line loss, impedance, and delay consistency.
Dk/Df should be lower for PCB substrate materials. The greater the Df value, the more noticeable the hysteresis. Research hotspots for PCB copper-clad laminas in the industry focus mainly on Low Dk/Df and Low CTE and the development high thermal conductivity material.
Lower loss copper clad laminate material requirements
In the next 3 to 5 years, Internet of Everything 5G communication will be mass-produced, and Internet of Things 6G pre-research will begin. This will require high-speed copper-clad laminate technology in order to move towards lower loss Df and dielectric constant Dk as well as higher reliability and lower CTE. In parallel, copper-clad laminates, which are mainly made of resin, glass cloth and fillers, as well as copper foil, should also be developed in this direction.
Lower-loss resin materials
The traditional FR4 epoxy system cannot meet the 5G communication requirements. Copper-clad laminate Dk/Df resin Dk/Df must be smaller. The resin system will gradually move towards hybrid resins or PTFE materials.
The PCB thickness of 5G high-speed and high-frequency communication products is getting higher and higher, the aperture is getting smaller and smaller, and the PCB aspect ratio will be larger. This requires the copper-clad laminate resin to have lower losses. While the loss is reduced, hole wall separation or hole separation cannot occur.
Low-loss and low-expansion glass cloth technology
The Dk/Df of copper-clad glasses cloth must be reduced to meet the requirements of the 5G communication products, and 100x100mm chips. As shown below image, if the CTE is too high, defects like solder joint cracking can occur during PCBA assembly or welding. For low CTE high-speed copper-clad laminae, the CTE must be below 3.0ppm/℃.
In order to meet this requirement, glass cloth must be prepared with a lower CTE by modifying the formula of the raw glass fiber and the drawing process.
Media Thickness Stability
The characteristic impedance is affected by the uniformity, fluctuation and composition of the dielectric layers. The characteristic impedance values of dielectric layers made of resins 106, 1080, 2116 and 1035 are all different, even if they have the same thickness. It is easy to understand that characteristic impedances are different in every dielectric layer on the PCB. In order to reduce fluctuations in characteristic impedance values, it is important to use thin flat fiber cloth or fiberglass cloth for high-speed and high-frequency digital signal transmission PCBs. The Dk of the material must be kept within a range and the uniformity of thickness of the dielectric must be maintained. Be sure to keep the Dk value within 0.5.
Copper-clad laminates with higher thermal conductivity
Heat dissipation involves evaluating the temperature increase from the standpoint of circuit efficiency. Simulations have shown that using a method of higher thermal conductivity to reduce temperature rise is more effective than reducing Df. It is important to choose a material with high thermal conductivity and a smooth copper foil surface. This will help to reduce the heat generated by circuits operating in the millimeter-wave frequency band.
In general, copper-clad laminating boards manufacturers improve the thermal conductivity by adding thermally conductive fillers. Addition of too many thermally conductive fillers can make PCB drilling, electroplating and production yield difficult. It must be able to dissipate heat as required by 5G and 6G communication devices. Copper-clad laminating manufacturers are required to research new formulas in order to meet the requirement of thermal conductivity >=0.8W/mK.
Copper-clad laminates with higher reliability
The 5G communication devices are becoming increasingly integrated. PCB density was reduced from 0.55mm down to 0.35mm. The single-board HDI PCB thickness increased from 3.0mm up to 5.0mm. The MOT requirement has been increased from 130degC up to 150degC, and the copper-clad lamination is now required to be more heat resistant as well as CAF resistant.
The 5G network has seen major changes, including in peak rate, spectrum efficiency and delay. PCB and ICs are highly integrated, have high power, connect more components in a given area and use high-density design. PCBs have a challenge for copper-clad materials. This guide explores the requirements of high-speed copper-clad laminations and PCBs for 5G communication. We hope it will help you in 5G PCB manufacturing.