Fast PCB design has unique characteristics that enable it to handle high-speed frequency signals. Some of these features are as follows:

Low Dk and Df dielectric materials: Dielectric materials are extremely important for the signal integrity of high-speed printed circuit boards. For high-frequency applications, dielectric materials need to have low Dk (dielectric constant) and Df (dissipation factor). Materials with lower Dk will be able to handle higher frequency signals with less attenuation of the signal. Materials with low Df do not generate heat when processing high-frequency signals. The low Dk and Df of the material are crucial for signal integrity. Rogers 4000 series, Isola I-Tera, and Panasonic Megatron-6 dielectric materials are some popular high-speed materials.

Differential pair routing: Communication standards that require high-speed signals typically use differential pairs. Differential pair PCB routing is a design technique that creates balanced transmission systems to transmit differential signals on printed circuit boards.

The definition of difference means equal and opposite. Differential pairs are used for high-speed communication protocols such as Ethernet, RS-485, HDMI, DDR4, etc. Most differential pair signals have a predefined impedance that strictly follows the length of the differential pair signal. On a PCB, they are easily distinguished by two isolated parallel traces of wiring between two ICs or ports.

Impedance control routing: Impedance control is an important component of high-speed signals. High frequency signals have strict impedance tolerances. There are two types of impedance control traces on high-speed PCBs, namely differential pair impedance control traces and microstrip or single impedance control traces.

Length matching trace: The length matching on the PCB ensures that signal traces (especially high-speed signals) have the same length, mainly for time synchronization. Signals like GMII have 8 data lines and are time sensitive at high speeds. The length matched routing is easy to distinguish, and they usually have additional sine wave curves when routing along the channel.

Special stacked layers: High speed PCB boards typically have 4 or more layers. They have special stacking required to handle high-speed PCBs. High speed signals require a reference plane or return path, which is essential for the signal integrity of high-speed signals. This is why a dedicated layer is used as an empty ground reference plane. High speed printed circuit boards have at least one power plane, as high-speed lines are usually not routed on the same plane as the power network. High speed PCBs can have more than 2 core wires to improve insulation and crosstalk. High speed PCB boards require strict dimensional tolerances, as the impedance and track width of high-speed tracks depend on layer stacking.

Tracking geometry: High speed PCB boards have unique routing geometries. High speed lines are usually short and of uniform length. The high-speed signal wiring cannot have a 90 degree bending angle, and the bending is mostly formed by obtuse angles or curves. Some high-speed signals have matching lengths, so they can resemble sine waves.

EMI protection: High speed PCB boards are susceptible to EMI or electromagnetic interference, so special measures need to be taken to protect high-speed signals from EMI. Use through-hole stitching or through-hole pools with grounding networks on high-speed boards. Through hole stitching is typically used in conjunction with dedicated grounding planes to reduce EMI on PCBs. In high-speed communication, weak pull-down resistors are often used to pull down the receiver and transmitter pins, which can protect the PCB from EMI when the communication channel is idle.

Dedicated power supply transmission: High speed printed circuit boards have dedicated power layers used to power the components of the PCB. Usually, one of the inner layers of a PCB is used as a dedicated power layer, placed next to the ground layer. This approach also helps to reduce EMI. The power is transmitted to the IC through a through-hole. Please note that a single PCB can have multiple power layers. The power supply of the IC is provided by decoupling capacitors, which are used to filter high-frequency noise from the power grid.

Designing and manufacturing high-speed circuit boards is not an easy task, but as long as the correct technology and practices are adopted, high-speed PCB design can be achieved. Some recommended practices are-

Correct material selection: For high-speed printed circuit boards below 2 GHz, FR-4 material is sufficient. If the wiring is short, the PCB does not require special materials. However, when it exceeds 2 GHz, it is recommended to use specialized high-speed materials. In theory, you can use the optimal PCB dielectric material with the lowest dielectric constant and dissipation factor, but cost is the limiting factor here. High speed PCB materials are often more expensive, and the better the quality, the higher the cost. The dielectric material only needs to be sufficient to handle the highest frequency signal on the PCB.

Correct selection of layer stack: The layer stack on high-speed printed circuit boards greatly affects the routing impedance and signal integrity. It is usually recommended to place all high-speed signals on the top or bottom layer, and to place a grounding plane below them, and the power plane should be isolated from high-speed signals as much as possible. Therefore, the ideal layer stack for a 6-layer PCB would be:

In this stack, each signal layer has a ground reference plane, and both high-speed signal layers are isolated using dielectric cells. Of course, you can use layer stacking based on your understanding of high-speed PCB requirements.

Control impedance: High speed signal routing requires impedance control routing. The impedance of the wiring must be calculated and carefully checked, as the impedance of the wiring is a sensitive parameter that maintains the integrity of the wiring signal. Failure to maintain appropriate impedance control may result in signal reflection, incompatibility with transceivers, and high signal attenuation.

Design rule checking and signal integrity tools: It is recommended to use many signal integrity and design rule checking tools on the designed PCB. Debugging hardware problems after PCB manufacturing is expensive and difficult. Therefore, it is recommended to conduct simulation testing on design files in software tools such as AnSys and HyperLynx, which can issue early warnings of errors and compromises in key factors such as signal integrity, dimensional tolerances, thermal management, and insulation before starting design and manufacturing.

High speed printed circuit board design is a tedious task, and both designers and manufacturers must be flawless in order to deliver high-speed PCB boards. Therefore, choosing a PCB supplier is crucial for PCB manufacturing and wise assembly.

If pursuing cost-effective FPC manufacturing services, choosing a Chinese manufacturer is the best choice. As a manufacturing powerhouse, China has abundant resources, cheap labor, and a large number of technical personnel. We recommend Haibo, a Chinese FPC assembly service provider with over 10 years of experience, who has performed outstandingly in various aspects

Efficient and reasonable quotation:There is an efficient quotation process to assist you in making decisions, providing reasonable prices and highly competitive quotes in China.
High quality and reliable products:Produce high standard printed circuit boards, manufacture and test according to specifications, international standards, and internal controls, and conduct pre production inspections to ensure robust processes.
Quick and on-time delivery:The assembly equipment is in good condition, with high productivity, minimal downtime, short delivery time, and also provides urgent services.
Timely and effective response:Always respond to customer needs, provide accurate information, answer questions through multiple channels, and offer one-stop services.
Strong technical strength:China's FPC manufacturing technology is leading, and Haibo has a complete SMT solution that covers assembly, inspection, and other capabilities. It also provides prototype production and customization services.