High-speed PCB design refers to any design where the integrity of the signal begins to be affected by the physical characteristics of the PCB, such as layout, packaging, interconnect, and layer stacking. Furthermore, when you start designing boards and encounter problems such as delay, crosstalk, reflection, or emission, you will enter the field of high-speed PCB design.

The focus on these issues makes high-speed design so unique. You might be used to designing a simple PCB that focuses on component placement and wiring. However, when using high-speed designs, it is more important to consider factors such as their distance from the signal, the width of the signal, where they are placed and what kind of track they are. The connection. Furthermore, with these factors in mind, it will reach a higher level in your PCB design process.

High speed PCB design skills

1. Know design software that offers advanced options

It needs many complex functions to be designed in CAD software at high speed. Also, there may not be many programs for amateurs, and there are often no advanced options based on the Web suite. Therefore, you need a better understanding of powerful CAD tools.

2. Highways

When it comes to high-speed wiring, designers need to understand the rules for basic wiring, including not cutting ground connections and keeping wiring short. Therefore, prevent crosstalk at a certain distance on the digital line and shield all interference generators so as not to damage signal integrity.

3. Cabling with impedance control

For some signals of about 40-120 ohms, it requires impedance matching. The cue for characteristic impedance matching is the antenna and many difference pairs.

It is important that the designer understand how to calculate the line width and the necessary impedance values for the lamination. If the impedance value is not correct, the signal may be severely affected, resulting in data corruption.

4. Length matching trace

There are many lines in the high-speed memory bus and interface bus. These lines can operate at very high frequencies, so it is crucial that signals travel simultaneously from the sending end to the receiving end. In addition, it requires a feature called length matching. Therefore, the most common standard defines the tolerance values that need to match the length.

5. Minimize loop area

High – speed PCB designers need to know some tips, high – frequency signals can cause EMI, EMC and other problems. Therefore, they need to follow basic rules, such as having continuous grounding and reducing loop area by optimizing the current return path of the wire, and putting in many suture holes.

Matters needing attention in high-speed PCB design

PCB layout is very important

Without a doubt, efficient PCB manufacturing in high-speed circuits is important to the end result. However, the PCB layout was not considered in the first place. Therefore, it will have a significant impact on the design to achieve the necessary functions and successful PCB manufacturing, such as high-level planning and compliance with important factors. In addition, you need to address some issues prior to PCB layout, such as manufacturing design (DFM) practices and additional considerations for high-speed PCB requirements.

Poor layout can cause performance problems when starting testing or when used in PCB manufacturing. To make matters worse, the need to evaluate PCB failures or performance issues and reassemble the prototype layout requires more cost and time to redesign or rework.

Notes for PCB design

In practice, high-speed PCB designs have many limitations for designers, as you need to meet various signal speed and other design requirements. Therefore, to achieve the high-speed circuit board design shown below, some factors need to be considered:

Schematic note: It is well known that a good schematic can lay a good foundation for PCB design. Therefore, depending on whether you are a PCB designer or an electrical engineer, the schematic diagram can be treated differently. In general, it treats a schematic as a means of communication that can be connected to a circuit board. But schematics can make a big difference in organizing and presenting your high-speed designs. Therefore, as much information as possible is available on the design schematic, such as wire length, necessary component placement, PCB manufacturer information, and so on.

Trace length adjustment: When using a high-speed interface, you need to adjust the trace length to synchronize the signal transmission with the data line. However, the interface may fail at maximum frequency, or it may not work at all because it is not synchronized. Moreover, the higher the interface frequency, the higher the length matching requirements. Therefore, in the case of parallel interfaces, you just need to adjust the length of all the lines. It is important to be sure to adjust the length of these lines to get the desired length in a set of signals.

PCB materials and requirements for high speed stacking: This will affect your high speed design, such as layer stacking structure and PCB material.

High speed placement strategy: Because changing pad size and component clearance maximizes high speed connection length, it can be designed for high speed using a variety of methods to optimize component placement and improve component occupying area for high speed.

Differential pairs and line-length routing: It is important to route differential pairs in high-speed designs so that pairs of signals can exist simultaneously.

Crosstalk, impedance control, and parallelism considerations: In high-speed design, there are many factors that can adversely affect your design. In addition, there are techniques to consider, such as how to minimize the impact on the design.

Understand ribbon and microstrip lines: In general, for high-speed designs, it requires multiple methods of routing. If highway routing is to be implemented, it is desirable to have a better understanding of strip and microstrip routing techniques.

Cabling topology and best cabling practices: Typically, a specific shape or topology is required if the circuit paths required for high-speed cabling are to be implemented. Also, it’s good to explore various ways to track line lengths, escapes, return paths, etc.

Simulators: For high-speed design, simulation is of great benefit before, during, and after the layout begins. Therefore, you should have a better understanding of PCB design software to learn tips and tricks for simulation design.

How do YOU know if you need a high-speed PCB design?

1. Is there a high-speed interface on the board?

A quick way to find out if you need to follow high-speed design guidelines is to check if you have high-speed interfaces, such as DDR, PCI-E, or even video interfaces, such as DVI, HDMI, etc.

All of these interfaces need to follow some high-speed design rules. In addition, please provide the exact specifications for each data in the documentation.

2. Ratio of trace length to signal wavelength

In general, if the wavelength of your message is the same as the line length, your PCB will definitely require high-speed design. Because some standards (such as DDR) require that the length of the line match the minimum tolerance.

A good rough number is if your cable length and wavelength can be kept within an order of magnitude of each other. Then, it’s a good idea to check the high-speed design.

3. PCB with wireless interface

As you know, each PCB has an antenna, and whether it’s through a connector or something on the board, high-speed signals need to be designed. In addition, the on-board antenna requires a tight impedance to match the tuning length.

For boards with SMA connectors or similar connectors, you need to connect them to a connector with a specific impedance value.

conclusion

In short, learning about high-speed PCB design depends on another project. Although there are many factors to consider when designing for high speed. Fortunately, the CAD software you use for PCB design will provide you with assistance, such as impedance calculators, routing length reporting options, differential pair routers, and other tools.