What is A High-Speed PCB?
We call a PCB with a signal transmission frequency above 1GHz a high-speed printed circuit board.
What are the advantages of using high-speed PCBs?
To improve the signal frequency and solve the EMI problem of electronic products, high-speed PCBs were manufactured. After the design of the high-speed PCB gained great success, its contribution to EMI is increasingly important. Almost 60% of EMI problems can be solved by high-speed PCBs.
What materials are used in high-speed PCBs?
Materials with heat resistance, mechanical toughness, and good (reliability)
Materials with stable Dk /Df parameters (small coefficient of variation with frequency and environment)
Materials with good impedance control
Materials with low roughness of the copper foil surface
Choosing glass fiber cloth with small flat openings is recommended.
What tips should I consider when designing a high-speed PCB?
Several tips on designing a high-speed PCB are described below.
1) Use design software with advanced options
Engineers need to know the design software that can provide advanced options. Software tools require a lot of sophisticated features to be able to design high-speed PCBs in CAD software. You need to have a better understanding of powerful CAD tools.
2) High-speed routing
When it comes to high-speed routing, designers need to understand the rules of basic routing, including not cutting off ground layers and keeping the routing short. Therefore, please prevent crosstalk over a certain distance on digital lines and shield all factors which may generate interference for the signal integrity.
3) Routing with impedance control
For some signals of about 40-120 ohms, they need impedance matching. The characteristic impedance matching is revealed by antennas and many differential pairs.
Designers need to understand how to calculate the width of the routing and the necessary stack-up of the impedance value. If the impedance value is not correct, it may have a serious impact on the signal, which can lead to data corruption.
4) Traces with length matching
There are many lines in the high-speed memory bus and interface bus. These lines can operate at very high frequencies, so the signal should be transmitted simultaneously from the sender to the receiver. In addition, it requires a feature called length matching. Therefore, the most common standards define the tolerance values that need to be matched to the length.
5) Minimize the area of the current return circuit
High-speed PCB designers need to follow basic rules, such as designing a continuous ground layer and reducing the area of the current return circuit by optimizing the current return path of the routing, as well as placing many stitched vias.
What are some best practices for manufacturing high-speed PCBs?
High-speed PCB design skills are mastered, which ensures signal integrity.
The materials of high-speed PCBs are properly selected to ensure the performance of the signal transmission.
Production control is performed. The main control points during the production are the width of circuits, layer spacing, vias plated with copper, the copper thickness of circuits, the thickness of the solder mask, etc.
What is the cost of ownership when it comes to high-speed PCBs?
The following factors will affect the cost of high-speed PCBs.
Material (the substrate material, the thickness of the substrate, the copper thickness)
The manufacturing equipment used
Difficulty of production
Customer’s requirements
The chosen packaging method
The chosen delivery method
How to Design High-Speed PCB?
High-speed PCB design is a relatively complex process that requires full consideration of signals, impedance, transmission lines, and many other technical elements. The following technical points can provide some reference.
Use multi-layers for routing reasonably.
The shorter the lead between the pins of high-speed circuit devices, the better.
Implement ground surrounds for particularly important signal lines or local units.
High-frequency signal line placed on the surface layer is prone to produce larger electromagnetic radiation. The high-frequency signal line should be placed between the power layer and the ground layer. The radiation generated will be much less due to the absorption of electromagnetic waves by the power layer and the bottom layer.
What is the difference between a high-speed PCB and a standard PCB?
For a standard PCB, people are mainly concerned about the short circuit, insulation, and other issues of the metal wire. However, with the pursuit of high performance of electronic products, the signal transmission frequency needs to be increased and people are more concerned about the signal integrity design of high-speed PCB.
Are there any special considerations when handling high-speed PCBs?
Special considerations lie in the high-speed PCB design and production when handling high-speed PCBs.
The length of the differential routing should be matched.
The routing should not cross incomplete ground planes.
Do not place test points on any differential high-speed signal lines.
Do not route high-speed signal lines near or below crystals, oscillators, switching power supplies, mounting holes, magnetic devices, or periodic signal chips.
Try to route high-speed signal lines on the top and bottom layers with a full reference ground layer. It is not recommended to route the lines on the inner plane.
Keep the distance from the high-speed signal to the edge of the reference ground layer more than 90mil.
Pay attention to the handling of socket and connector wiring.
Coppe trace width, space, and layup structure must be precisely controlled to meet the tight impedance value.
TDR impedance tests are usually needed when high-speed PCBs are finished.
Proper material types should be chosen to meet the desired functions.
A flat surface finish is needed for high-speed PCBs, and we always advise ENIG for ENEPIG surface treatment.
What is the maximum data transfer rate achievable on a high-speed PCB?
The theoretical maximum data transfer rate achievable on a high-speed PCB is 10.0GPs (Gigabits per second) by far, but this is improving continisouly.
Are there any special tools or processes required when designing a high-speed PCB?
There are required PCB design software tools and EDA simulation tools used when designing a high-speed PCB such as Cadence, Mentor, PADS, Altium, HyperLynx, HFSS, ADS, etc.
It is worth noting that one software tool may be suitable for one PCB project, while another software tool can be better used for other types of projects. Therefore, it is very important to find the right PCB design software tool.
What are the basic specifications and suppliers of high speed PCB material?
High speed material can be FR4, ceramic, PTFE or PTFE reinforced material with 1 Ghz to 100 Ghz. There are several famous high speed PCB materials suppliers such as: Rogers, ISOLA, Ventec, ITEQ, TUC, SHENGYI,Panasonic, Taconic, etc.