How to Manage Signal Integrity and EMI in PCB Design—and Avoid Costly Delays
Printed circuit board (PCB) design has long been at the core of electronic systems we use every day, from cell phones and iPads to aviation controls and medical devices. But as these systems grow more advanced—think AI, autonomous vehicles, robotics, even brain chip implants—managing PCB signal integrity and electromagnetic interference (EMI) has become increasingly critical.
Not doing so can lead to costly delays and malfunctions. For instance, when a company designs a PCB, it typically must be certified for EMI performance. If it does not meet the EMI requirements, it could take a significant amount of time to redesign the board, prototype it, test it and submit it for another certification.
Problem is, effective signal integrity and EMI management can be a real challenge for today’s high-speed, high-frequency electronics, which require complex PCB stackups (i.e., the layers of a PCB), new technology tools and sector-specific expertise.
A set of informed best practices and industry experience is therefore critical for those designing high-tech PCBs. At Actalent, these attributes have helped us cut down the development time for PCBs by more than half and solve urgent issues for companies in sectors like transportation, healthcare, robotics and industrial products, to name just a few.
Best Practices for Managing Signal Integrity and EMI
At Actalent, our teams follow a set of internal best practices, based on extensive experience and exposure to various standards, that ensure the successful development of PCBs—no matter their application. We also leverage them to help create PCB guidelines and standards for companies that are tailored to their unique needs and specifications.
Here is a high-level overview of our best practices:
1. Design Layout and Stackup
- Select dielectric material with low dielectric constant and low loss tangent, which creates better thermal stability for high-frequency applications.
- Properly partition analog and digital sections and trace separations to avoid noise coupling.
- Ensure proper stackup design with dedicated power and ground planes that can mitigate EMI by providing a clean return path for signals.
2. Signal Routing
- Employ controlled impedance routing for high-speed signals. This can minimize reflections and signal degradation by maintaining consistent trace widths and lengths for critical signals.
- Implement differential signalling and delay matching for noise immunity and reduced susceptibility to EMI.
- Attempt routing with reduced stub length and maintain proper trace spacing to avoid crosstalk between signals.
- For high-frequency applications, it is especially critical to minimize the loop area of signal traces and return paths. To do so, the traces should be routed short and straight, avoiding sharp bends and corners; the return path should also be placed as close as possible to the signal trace. Additionally, use a proper ground or power plane as a return path and ensure that there are no splits or breaks in the plane.
3. Grounding and Decoupling
- Implement a solid grounding strategy with low impedance paths to manage return currents effectively.
- Use strategically placed decoupling capacitors to stabilize power supply voltages and reduce noise.
4. EMI Shielding and Filtering
- Employ EMI shielding techniques like copper pours, ground planes, and shielding cans to contain EMI.
- To achieve effective filtering and decoupling, use capacitors, inductors, ferrite beads and resistors with appropriate values and types—placing them as close as possible to the source and load of the signal or the power.
- Manage signal reflections by adding termination resistors on both the transmitter and receiver side. This ensures that signals are transmitted properly.
5. Simulation and Testing
- Use simulation tools to analyse signal integrity and EMI performance during the design phase. These simulations can be done with signal integrity tools such as Cadence Sigrity, Siemens HyperLynx, Ansys SI wave or Zuken CR8000.
- Conduct thorough testing and validation, including signal integrity tests and EMI compliance checks, to ensure design robustness.
Best Practices in Action
Recently, an aerospace and defence company approached us with an urgent request: to optimize their PCB in terms of signal integrity/EMI requirements, which were failing. If they didn’t act fast, it could spell expensive delays and high-stakes malfunctions.
In this instance, the company didn't have best practices and standards in place to achieve the requirements, which in turn affected the quality of the PCB and resulting product. That’s where we came in. Drawing on our internal best practices and industry experience, we were able to successfully navigate signal integrity and EMI issues when redesigning the company’s PCB.
This is just one example of an increasingly prevalent pain point for companies developing the high-frequency electronics of tomorrow. By carefully managing signal integrity and EMI, PCB designers can create the robust electronic systems capable of meeting the demands of today's technology-driven world.
