How Do Printed Circuit Boards Affect Signal Integrity?

Printed Circuit Boards

Printed circuit boards (PCBs) are the foundation of electronic devices ranging from calculators to high-performance supercomputers. They are made up of copper wires, dielectric layers, metal traces and other components that are assembled through through-hole soldering, surface mount technology (SMT) or ball grid array assembly (BGA). As such, PCBs must be durable to endure multiple manufacturing processes and deliver reliable performance. However, many factors can degrade signal integrity. These include the characteristics of the signal, system impedance, propagation delays, attenuation, crosstalk and voltage fluctuations that result in signal distortion. The PCB layout is also a significant contributor to these issues.

The design of a printed circuit board pcba starts with component placement and drilling. This step is important for ensuring that each component has an unobstructed route to its destination. Next comes trace routing, which involves converting rubber-band net connections into drawn traces and planes using CAD tools. Proper trace routing is essential for ensuring that the signals can be accurately transmitted and received.

Once the traces are drawn, they must be matched in length, which can take time and effort. As such, designers must be careful to avoid common mistakes that can cause signal integrity problems. For example, placing a differential pair of traces side-by-side is likely to cause crosstalk, where the victim signal mimics the characteristics of the aggressor signal. This can overpower the desired data transmission and lead to data errors.

How Do Printed Circuit Boards Affect Signal Integrity?

Another source of signal degradation is the PCB’s resistance and dielectric dissipation. These properties can increase the rise time of a digital signal, which reduces maximum possible speed. This is a common issue with high-speed traces. To prevent this, designers must make sure that the signal’s rise time is at least four to six nanoseconds.

A clean power delivery network is also critical for good signal integrity. This involves minimizing the number of vias on the board and ensuring that they are properly spaced. In addition, the PCB must not contain areas of blockage on the reference planes. These areas can interfere with the signal’s return path, which can lead to excessive noise and electromagnetic interference.

Finally, the PCB must be free of voids and other defects that could affect the signal’s strength. These include holes that do not fully penetrate the circuit board and areas of uneven solder mask thickness. The latter can cause a parasitic effect where the signal is reflected off of the circuit board and back into its source.

Getting the best signal integrity requires careful attention to detail during each phase of the PCB design and fabrication process. This includes performing in-process testing to identify problems before they can cause a loss of signal quality. In-process testing can be performed on a physical prototype or virtual simulation of the printed circuit board.

In addition to preventing EMI, in-process testing can help to improve the yield of a final product. It can also identify and resolve any manufacturing issues before they become costly. By addressing these concerns, manufacturers can produce more functional and reliable products.

Leave a Reply

Your email address will not be published. Required fields are marked *