How to Reduce EMI in PCB Design?

Electromagnetic interference (EMI) is a type of electromagnetic interference, in which energy is transmitted from one electronic device to another through radiation/conduction, and destroys the signal quality, causing failures. It exists in almost every corner of our lives. For example, when our mobile phone is close to a running radio, we will hear a buzzing sound, which is electromagnetic interference. This problem has always troubled PCB designers, who must ensure that the electronic products they design can comply with EMC(Electromagnetic Compatibility). In fact, it is difficult to completely avoid electromagnetic interference, but we can reduce EMI as much as possible during the design process. In this article, we list several important design rules to reduce electromagnetic interference in PCBs. Let’s dive right in.

What Causes Electromagnetic Interference in PCB?

There are various factors, which contribute to the generation of electromagnetic interference in PCB:

• Due to their high rate of state transitions, high frequency digital circuits including micro processors and memory devices may be the common cause.
• Switching power supplies and fast switching transistors are major of EMI radiation due to their rapid current variations.
• If the signal traces are designed or routed in a poor way especially those that are carrying high-frequency signal, they become a source of EMI since they act as antennas.
• Loops on the ground level and poor grounding are also sources of EMI due to interference currents. When power planes are not joined seamlessly, they create impedance discontinuities, further leading to signal reflections and EMI.
• These problems can be aggravated by improper positioning of the component and inadequate shielding, which is why EMI is one of the major challenges of PCB design.

Why Is Important to Reduce EMI?

Firstly, it complies with the regulatory measures like the use of FCC regulations and the CE marking that is compulsory in the markets where electronic devices are sold. Failure to adhere to guidelines could result to increased expenses such as redesign, late entry of product to the market, and possibly legal problems.
Secondly, the reduction of EMI enhances the performance and the quality of electronic items in use. High levels of EMI can affect the signal quality to an undesirable level, resulting in data corruption, systemic failures or total failure of the device. In sensitive applications such as medical equipment or automotive electronics, such problems could be fatal.
Also, decreasing EMI results in a better user experience as the respective devices’ operation is not affected by other devices in close proximity like for example a mobile phone interfering with a radio.
Finally, a good EMI design also results in the enhancement of power efficiency and heat dissipation, translated as longer battery life in portable products, and increased product life.

Key Design Principles of Electromagnetic Interference Reduction

Common EMC issues with PCBs are basically related to design failures that stem from interference from traces, circuits, vias, and other related features on the board. This section will introduce basic PCB design principles and best practices from several different aspects to reduce electromagnetic interference problems:

1. Ground Plane

• Maximize ground area:On a large ground area, signals can be dispersed more easily to reduce crosstalk and noise. Therefore, we need to increase the ground area within the PCB as much as possible. If the ground layer is too small, we can create a multi-layer PCB.
• Use split ground planes carefully: Splitting should be done selectively because if the cut planes are poorly positioned, it is possible to obtain slot antennas, which will enhance EMI radiation.
• Minimize connections between separate ground planes: Ideally, link split ground planes at just one location. Several points of ground connections can be problematic in that they introduce loops, which in turn mean added emissions from your PCB.
• Optimizing Bypass Capacitor Placement: Solder bypass or decoupling capacitors to the ground plane in an appropriate manner with minimized return current paths and loop sizes, so as to reduce EMI.

2. Trace Layout

• Bend Design: Replace sharp 90-degree bends with rounded or 45-degree angles. This helps maintain consistent impedance and reduces signal reflections.
• Signal Separation: It may be desirable to filter high speed signals (as for example clock lines) from low speed ones. It is advisable that the analog and digital signals are separated to reduce on the level of interference.
• Return Path Optimization: Design short, direct return paths to minimize the loop areas and hence minimizing the EMI.
• Differential Pair Routing: Route differential tracks close to get better coupling and move noise into common-mode which is less problematic for differential inputs.
• Via Usage: When designing the PCB vias, it should be done wisely because the vias cause an increase in signal amplitude and bring added inductance and capacitance. For the case of differential pairs, one must try to minimize the usage of vias as much as possible. Only in case of necessity use a common oval anti-pad to reduce the parasitic capacitance.

3. Component Arrangement

• Separate Analog and Digital:If you have both analog and digital circuits in the same design, shield analog circuits from digital circuits and use as many layers as you can with separate grounds.
• Protect Analog from High-Speed:Apply some protection by shielding the analog circuits with the ground signals. In multi-layer PCBs, put ground planes in between the analog traces and high speed signals.
• Manage High-Speed Components: Reduce and segregate rapidly, small parts that generate more EMI. Minimize the coupling of high speed signals and ensure they are short and located near the ground planes.

4. EMI Shielding
   

If the complete elimination of EMI is not possible, one has to opt for PCB shielding. Whole circuit boards are kept away from EMI sources with the help of external shields such as Faraday cages, and internal shields isolate particular sensitive components within the boards. Cable shielding, using conductive coatings or braided covers, helps contain high-frequency signals and reduce EMI transmission.

Final Thoughts

In conclusion, reducing electromagnetic interference is a critical aspect of PCB design that cannot be overlooked. With an understanding taken in the causes of EMI and applied design techniques, an engineer can produce higher-functioning circuits on the PCB that can operate safely from the EMI risks. Since modern electronic devices are becoming more and more sophisticated and are practically in every corner of our lives, this also means that the problem of EMI will continue to be more and more critical in the future. Although the problems of EMI reduction can be complex, working with reliable PCB design specialists can change the situation for the better. That is the place of MOKO enters in the picture. Using our know-how in high-performance PCB design, we are ready to assist you in tackling the problems associated with EMI reduction and assisting you in achieving electromagnetic compatibility. Get in touch with MOKO Technology right now!