When electronics engineers design PCBs, they must follow best practices for trace routing. This helps maintain PCB signal integrity and reduce electromagnetic interference (EMI).
Minimized crosstalk
Crosstalk can occur between adjacent traces on a single PCB layer, or those that are parallel and vertical to each other between two layers. When it happens, the signal from one trace overpowers another because it has more amplitude than the other.
A best practice is to keep the separation between traces to 3× the trace width. Doing this can safeguard 70% of the electrical field from this interference. Unaddressed crosstalk can negatively affect the signal-to-noise ratio, so it’s best to mitigate it as early as possible within the design phase.
One option is to use crosstalk calculators. Once users input values like trace spacing, substrate height and source voltage, the tool can calculate the PCB’s coupled voltage and crosstalk coefficient. These options eliminate the longer time frames associated with manual calculations and the errors that can happen as a result.
Expected performance
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Engineers may need to improve signal integrity in PCBs if tests show the products repeatedly fail to perform as anticipated. Sometimes, such failures become apparent before the PCBs get produced at scale. However, signal integrity issues may only be noticed during mass production or when customers begin using the products in the field.
Signal integrity relates to the quality of the transmitted signal and whether the signal can propagate without distortion. Problems with signal integrity can span beyond the PCB and introduce or create EMI that affects nearby devices. Efforts to improve signal integrity begin at the schematic and layer-design stages. Making the most appropriate decisions at that time can affect how well the PCB performs.
For example, when traces are the correct thickness, they aid in thermal management by keeping the components from overheating. That is increasingly important, particularly as many of the products containing PCBs get progressively smaller.
Better quality
PCB manufacturers invest heavily in quality control to ensure reliable products. For example, X-ray scans can identify hidden defects in a non-destructive way. X-ray inspection technology is often a critical part of quality assurance.
However, paying attention to trace routing provides a visual option for spotting issues that could improve PCB signal integrity. Assembly workers can find potential problems earlier and fix them before it becomes too time- and labor-intensive.
For example, they should check that traces do not have sharp bends, which are particularly problematic for high-power or high-frequency traces. Designers should ideally keep the traces running in straight lines. In cases where the board’s design and intended application require trace-length equalization, people can look for delay lines. They usually look like squiggles on the PCB’s surface.
Correct placement
Technologies like 3D printing have dramatically changed how people can design and manufacture electronics. However, even as 3D printers allow users to print circuits, reduce waste and enhance efficiency, they shouldn’t ignore the best practices associated with trace routing and other specifics.
For example, being strategic about component placement can reduce EMI in PCBs. Even if you’ve used an appropriate trace width and checked for unnecessary bends, problems can still occur due to the location of certain parts.
As an example, because inductors create magnetic fields, they should not be placed end to end or too close to each other. In cases where there’s no choice but to do that, choose a perpendicular alignment to minimize mutual coupling. Alternatively, select toroidal inductors, which are less likely to cause magnetic field issues. Ensure the traces used to connect inductors are not wider than necessary. Otherwise, they could begin acting like antennas and cause unwanted emissions.
Consider using an advanced design tool to make it easier to follow the principles associated with trace routing and other best practices. Some trace-routing design products allow users to switch between 2D and 3D designs. A survey of users using advanced tools found they spend about 45% of their time routing in 3D, enabling benefits from real-time visualizations. Users can also perform specific actions in the 3D realm—such as trimming a layer’s pads—before trying them on a real-life design.
Take trace routing seriously
These are some actionable ways to minimize EMI and prioritize PCB signal integrity in future designs by focusing on trace routing. Following well-established principles during your design stage can prevent many problems that lead to poor PCB performance during internal testing or real-world use.
It’s also helpful to use digital project-management tools that track changes, including trace-routing decisions, which help find the possible root causes of newly identified issues. These products are also convenient because they typically work in the cloud, eliminating geographic limitations.
About the author
Emily Newton is a technical writer and the editor-in-chief of Revolutionized. She enjoys researching and writing about how technology is changing the industrial sector.
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