There are several modern methods to solve EMI problems in PCB design. These methods include the use of EMI suppression coatings, the selection of appropriate EMI suppression parts, and EMI simulation design. In this article, we will focus on the role and design techniques of PCB layered stacking in effectively controlling EMI radiation.
Power Busbar and Capacitor Placement:
Placing capacitors with suitable capacity close to the power pins of the IC can ensure a fast output voltage jump. However, the finite frequency response of capacitors can limit their ability to generate the harmonic power necessary to drive the IC output cleanly across the full frequency band. Transient voltages developed on the power busbars create a voltage drop across the inductance of the decoupling path, which is the main source of common-mode EMI interference.
Solving Power Busbar Issues:
To address these issues, it is important to consider the power plane around the IC as a high-frequency capacitor that harvests the energy leaked by discrete capacitors, providing high-frequency energy for a clean output. Additionally, a well-designed power supply layer with low inductance can significantly reduce common mode EMI.
PCB Stacking and Layer Spacing:
A well-designed pair of power planes with low inductance is essential to facilitate decoupling and effectively control common-mode EMI. The layer spacing, materials between the layers, and operating frequency are crucial factors in determining the effectiveness of the power plane design.
Electromagnetic Shielding and Layering Strategy:
To shield and suppress EMI, a good layering strategy involves placing all signal routing on one or several layers adjacent to the power or ground planes. The power layer should be adjacent to the ground layer with minimal distance between them, known as the “layering” strategy.
Conclusion:
The PCB layered stackup design examples in this article assume a layer spacing of 3 to 6 mils. Additionally, stacking strategies that facilitate electromagnetic shielding and EMI suppression are essential for effective PCB design.