7 PCB Design Tips to Solve EMI/EMC Issues
The electromagnetic compatibility (EMC) will monitor the generation of the radiated and conducted electromagnetic interference (EMI) from electronic circuitry. Poor EMI/EMC, noise generation and poor signal transmission are found to be the key reasons for electronic circuitry failure. It is estimated that the failure rate due to electromagnetic interference (EMI) from electronic circuitry for prototype PCB is as high as 50%. A poor PCB design is the ultimate cause of unwanted EM emission or susceptibility towards it.
More critical applications involving mil-grade, aerospace, and healthcare will witness a higher failure rate. These industries are placing stringent regulations in terms of PCB design and manufacturing processes. The telecommunication sector is one of the key sectors that is driving demand for EMI free PCBs. For example, telecommunication businesses and mobile phone manufacturers are pushing for new reforms to suppress unwanted radiations and improve connectivity. The advent of 5G will further boost the demand for EMI free PCB over the coming years.
How to Design EMI free PCBs?
How to design board with low or absolutely zero electromagnetic interference? Well, it isn’t impossible. All you need are world-class industry experts who will tell you the best design practices to follow for neglecting EMI/EMC problems in your design. Another option is to read the entire blog and perhaps, you will gather a set of engineering knowledge that you might not have.
The below design practices will make sure you do not create antennas, which will emit electromagnetic energy. Or these best design practices will nullify the potential signal return paths that may increase unwanted EM emissions.
In a multi-layer PCB design, it is important to route return paths for I/O pins on the layout design. The multi-layers stack-up will also play a critical role, particularly in high-power and digital applications. Signal tracing from component to the processor should be properly routed to avoid any return path, which can lead to common-mode signal generation.
The use of surface-mount devices (SMD) instead of leaded devices will further reduce EMI/EMC issues. Surface-mount devices (SMD) offer lower inductances in comparison with RF energy. Additionally, SMDs offer higher density due to closer component placements. This is particularly critical in a two-layer or four-layer circuit board. However, the rising complexity in the PCB design will create more problems associated with line spacing or trace spacing. Yet, the dense physical dimensions of SMDs will offer more effectiveness and noise-control.
Leaded components with higher inductances will generate a resonate frequency of more than 100 MHz. Due to which the adoption of a large number of through-hole components is not recommended as they generate excessive noise.
Here is a list of techniques to reduce EMI/EMC problems:
1. Line/Trace Spacing
We have discussed the importance of line spacing in a previous article. However, talking about line spacing strictly in terms of EMI/EMC from the PCB designer’s perspective is an entirely different ball game. We are well aware of the fact that the EMI (electromagnetic interference) is propagated through the edge of the board. To avoid EMI propagation, it is preferred that PCB traces should be bent at a 45-degree angle on their edges. It is also recommended to avoid microstrips and adopt striplines. Other important design practices include avoid layer changes and avoid routing for high-speed signals over the slots. Also, PCB designers should keep differential traces at close proximity.
2. Importance of Shielding:
EMI/EMC shielding protects the signal transmission from external noise and prevents information loss. The key purpose of EMI/EMC shielding is to minimize the effect of EMI and RFI on the electronic circuitry. EMI/EMC shielding is carried out by adding a metallic screen for absorbing the electromagnetic interference.
3. Controlled Impedance for Transmission Line Design
It is important to design a PCB with the right line impedance that matches the source impedances to suppress EMI/EMC. Controlled impedance also decides the signal rise and fall times. The impedance of traces also depends on the PCB materials used on the board. Read why controlled impedance matters.
4. Importance of Grounding
Reducing EMI/EMC totally depends on how effectively PCB designers apply the ground plane in their design. You must be careful while splitting ground paths. Adoption of a large, unbroken ground reference plane, and connecting it to the ground plane with the ground vias will reduce interference. Designers must provide return paths for the ground plane. Trying a zero-impedance ground is an ideal scenario in most cases.
Adding a low-pass filter for attenuation with ferrite core inductors during the high-speed signal transmission can go a long way. The decoupling capacitors are used for faster switching between IC power and ground connections, thus limiting the radio frequency emissions. This will also reduce resonance in the electronic circuit.
6. Avoid Antennas
Try to avoid antennas at any cost. Special attention must be given towards unconnected stubs and traces without return paths.
7. Separate sensitive components
You need to assign different PCB areas for diverse circuits in order to keep oscillator circuits away from other components. Additionally, high-speed components must be separated away from disturbing signals and from I/O connections.
These practices will attenuate and eliminate EM emissions at the source as well as designing for clean and smooth signal transmission. Did we miss anything? Please let us by commenting down below. Until then, add all these awesome PCB design ideas into your next design for EMI free PCBs.
Tags: EMI, pcb design, signal integrity