As the “mother of electronic products,” the printed circuit board (PCB) plays a crucial and foundational role throughout the entire electronics industry chain. With the rapid development of downstream application areas such as IoT technology, automotive electronics, and 5G communications, the PCB market—including the high-frequency PCB segment—holds tremendous growth potential in China. Today, you’ll learn about what high-frequency PCBs are, the key parameters of high-frequency PCBs, why it’s important to test PCB signal integrity, the testing requirements for high-speed signal integrity, and common testing methods, including time-domain analysis, frequency-domain analysis, and eye diagram analysis.

When processing and testing high-frequency PCB boards or high-frequency antennas, beginners often encounter issues because they’ve chosen the wrong type of high-frequency PCB, resulting in unsatisfactory product performance. Today, let’s briefly discuss: What are the common high-frequency PCB materials, and how should you choose the right one?

A high-frequency circuit board is a specialized type of printed circuit board with relatively high electromagnetic frequencies, and it’s considered one of the more challenging types of PCBs to design. So, what aspects should we pay attention to when designing high-frequency circuit boards?

1. How can we avoid high-frequency interference? Avoiding high-frequency interference means minimizing the electromagnetic field interference caused by high-frequency signals—also known as crosstalk. One effective approach is to increase the distance between high-speed signals and analog signals. Additionally, it’s important to pay attention to noise interference from the digital ground to the analog ground.

2. How should we choose a PCB substrate? Selecting a PCB substrate requires striking a balance between meeting design requirements, manufacturability, and cost. Design requirements encompass both electrical and mechanical aspects.

3. How can we address signal integrity issues? Signal integrity essentially comes down to impedance matching. The solution lies in terminating the signals and adjusting the routing topology.

4. How can differential routing be implemented for a clock signal line with only one output pin? Differential routing makes sense only when both the signal source and the receiving end are operating with differential signals. Therefore, differential routing cannot be used for a clock signal that has only one output pin.

Fifth, how is differential signaling implemented? First, the lengths of the two traces should be as equal as possible. Second, the spacing between the two traces—this spacing is determined by the differential impedance—must remain constant at all times, meaning the traces must stay parallel. There are two ways to achieve parallelism: one is for the two traces to run on the same routing layer, and the other is for them to run on adjacent layers, one above the other.

6. Consider whether a matching resistor can be added between the differential pairs at the receiver end. A matching resistor is typically added between the differential pairs at the receiver end; its value should equal the differential impedance, which will help improve signal quality.

7. Why should differential pairs be routed closely and parallel to each other? The term "appropriate proximity" refers to the fact that the spacing between the traces affects the value of the differential impedance—a critical parameter in differential pair design. The requirement for parallel routing is also aimed at maintaining consistent differential impedance.

8. How to handle certain theoretical conflicts encountered in practical wiring.

Basically, it’s correct to isolate and separate the analog and digital grounds. Be mindful that signal traces should, as much as possible, avoid crossing over areas where the grounds are separated. Also, don’t allow the return current paths for power and signals to become excessively large.