Table of Contents
Ever on a motorcycle and heard radio static? That’s EMI. Motorcycle spark plugs emit electromagnetic radiation when sparking, disturbing radio signal reception. Remember on a plane when asked to turn off electronics? That’s because device signals can interfere with plane navigation.
This EMI-induced interference underlines the importance of EMC in electronic design. PCB EMC ensures devices work reliably, not causing or being easily affected by EMI.
This article covers the basic concepts of EMC, provides some tips for PCB design, the most comprehensive summary of PCB EMC standards and the whole process during EMC testing. Let’s get started with ELEPCB!
Definitions of PCB EMC & EMI & ESD
What is EMC?
EMC(electromagnetic compatibility) is the capability of electrical systems and equipment to function properly without interfering with other systems or equipment or being interfered with by them. It is achieved by controlling the generation, propagation, and reception of electromagnetic energy to prevent unintended electromagnetic interference that could cause performance degradation or physical damage to the system or equipment.
What is EMI?
Electromagnetic Interference (EMI) is the degradation in the performance of a system or equipment because of electromagnetic disturbance. In other words, electromagnetic disturbance is the cause and EMI is the effect.
EMI can be divided into two main categories.
1. Continuous Interference:
This noise is produced by sustained electromagnetic radiation; it may be in the form of radio frequency or sustained oscillation. It usually emanates from nonshielded oscillators or other elements prone to the emission of electromagnetic radiation.
2. Impulse Interference:
It is characterized by short, high-energy bursts of electromagnetic energy. The impulses arise from sources such as Electro Static Discharge(ESD), lightning, and high-current circuit switching.
EMI may be transferred through various coupling mechanisms:
Conductive Coupling:
Interference in this category takes place through electrical conductors, such as power lines and cables.
Radiative Coupling:
It takes place when electromagnetic waves are transmitted from one circuit to another, for instance, in devices like motors, power lines, etc.
Inductive Coupling:
This takes place due to a magnetic field created between two parallel conductors.
Due to magnetic induction, a time-varying current in one conductor can easily induce a voltage in the other.
Capacitive Coupling:
Capacitive coupling may occur when two conductors are brought close to each other, allowing a capacitor-like effect.
One fluctuating voltage on a conductor may change the voltage on the other due to capacitive coupling.
What is ESD?
Electro-Static Discharge(ESD) is a main source of EMI, and EMI can be transferred by several coupling mechanisms described above.
EMC Standards
Adhering to these international and national EMC standards is crucial for ensuring your product safety and market access.
Lists of EMC Standards in PCB
The following is a list of some of the more authoritative international EMC standards and some common standards.
| Standards | Geography | Content |
| FCC | More than 50 states, Colombia and US territories | Three common types of certification: Certification, DoC, and Verification(certified to a decreasing degree of stringency) |
| VDE | Mainly for the German and European markets. | Covering safety regulations, electromagnetic compatibility, chemical testing and analysis and many other aspects. |
| CISPR | Worldwide | 7 sub-committees, respectively responsible for radio interference measurement methods and statistical methods, industrial, scientific and medical radio frequency equipment, radio interference |
| IEC | Worldwide | Responsible for international standardization work related to the electrical and electronic fields |
| GB/T 17626 Series | China | Referring to the international standard IEC61000-4-X series, the latest current national standard GB/T 17626 has a total of 27 |
| MIL-STD-461 Series | USA (mainly for the US military) | Used for electromagnetic compatibility testing and evaluation of military equipment |
| EN 550XX Series | European Union Area | Equivalent to CISPR standard, applicable to different types of electrical and electronic equipment |
| AS/NZS CISPR Series | Australia and New Zealand | Based on the CISPR standard, it applies to electrical and electronic equipment marketed in Australia and New Zealand |
| Category | Common EMC Standard(s) |
| Healthcare and Life Sciences Medical Devices | IEC 60601-1-1 |
| Automobile | CISPR 12, ISO 7637, ISO 1145-1, ISO 1145-2 |
| Indoor Equipment | IEC EN 61000-6-6 |
| Power Stations | IEC EN 61000-6-5 |
| Industrial | IEC EN 61000-6-2, IEC EN 61000-6-4 |
| Commercial | IEC EN 61000-6-1, IEC EN 61000-6-8 |
| Residential | IEC EN 61000-6-1, IEC EN 61000-6-3 |
| Testing and Measurement | IEC EN 61000-4-2, IEC EN 61000-4-3 |
| Agriculture Equipment | ISO 14982 |
| Construction Machinery | EN 13309 |
Designing PCBs for EMC
Designing a PCB that is EMC compliant cuts across PCB schematic design, components selection, and PCB Layout Design.
Two key parts of EMC are emission, which is the unwanted generation and propagation of electromagnetic energy, and the susceptibility, receptance, and damaging effects of EMI on the system. The overall goal of EMC PCB is reducing(total elimination not so assured) the emission and susceptibility of the PCB.
Design Measures to Minimize EMI in PCB
Layout Design
- Power Plane Design: A well-designed power plane can reduce noise and improve signal integrity.
- Signal Layer Routing: Proper routing of signal layers is paramount. Use differential pair routing for high-speed signals to minimize crosstalk and radiation. Increase the distance between adjacent traces and avoid routing traces parallel to each other as much as possible. Move traces carrying fast digital signals away from the PCB edge to prevent radiating field emissions.
- Component Placement: Place components strategically to minimize coupling between signal traces and power planes, reducing EMI.
- Ground Planes: Ground planes minimize noise and signal deterioration by giving the current a low-impedance return path, thereby, minimizing the introduction of ground loops.
Component Selection
- Low-Emission Components: try choosing parts that are naturally quieter, like low-EMI integrated circuits, low-noise amplifiers, and low-noise voltage regulators. These will lower the overall PCB’s electromagnetic radiation emissions.
- Shielding: Use shielded components or put them in shielded enclosures if you have sensitive components. This will lessen their tendency to emit noise and shield them from outside electromagnetic interference.
- Filtering: Use filters, such as capacitors and ferrite beads. This will reduce high-frequency noise on signal and power supply lines, enhance the circuit’s overall noise immunity, and efficiently block undesired signals.
Shielding Methods
- Enclosure Shielding: With this technique, the PCB is enclosed in a conductive metal housing acting as a shield to prevent interference. Enclosing the PCB in a conductive enclosure will also significantly reduce radiated emissions.
- Cable Shielding: Signal cables in electrical systems are coated by a conductive layer and are grounded at either end. Shielding cables can prevent electromagnetic interference from propagating along the cable.
Power Supply Design
- Decoupling Capacitors: Decoupling capacitors are added to reduce noise in the power supply and improve system stability. To ensure effective decoupling, place capacitors as close as possible to the IC pins and keep leads short.
- Bypass Capacitors: Using bypass capacitors will filter out high-frequency noise from the power supply.
Additional Measures to Reduce Emissions
Reduce Switching Operation
- To the minimum and ensure necessary switching is done slowly as permissible.
Modular Design
- Modular design involves separating circuits that generate a lot of noise from the rest of the design and ensuring they are shielded appropriately.
PCB EMC in Electrical Systems
EMC Test and EMC Compliance
The first thing to do is preparation, which includes clarification with the customer on the PCB EMC standard they want and doing some preliminary checks on circuit layout, wiring, component selection, etc., of the PCB design for possible EMC problems.
Also, preparation of the PCB design drawings and other documents as well as the PCB samples should be made according to the production standards.
Then, determine the type of PCB EMC test, mainly including:
Radiation Emission Test
For example, in the 30MHz 1GHz band, in a semi-electrical wave darkroom, the PCB is put on a 0.8m high wooden table on the turntable, the antenna adjustable in height within 1-4m, measurement distance of 3m or 10m, etc., for carrying out vertical and horizontal polarization tests.
Anti-interference Test
Apply such interference as high-frequency electromagnetic field, electric fast transient pulse group to the PCB to observe its performance stability.
How to Read the PCB EMC Test Report?
Step 1:
Check Out the Entire Report
- View basic information about the PCB EMC test, such as the testing organization, test date, etc.
- Explain in detail the purpose of whether it is for radiation assessment, anti-interference, etc..
- Pay attention to the effects of the temperature and humidity of the test environment on the results, the accuracy of the equipment, etc. As it could be, the excessive rise in temperature may affect some parts within a PCB that consequently may affect test results.
Step 2:
Parameter Interpretation
Take the radiated emission test as an example:
- The “Freq” column represents the different frequency points of the test, like 30MHz, 50MHz, etc.
- The “Measurement” column gives the value of the radiation intensity of the PCB at that frequency, while the “Limit” column gives the maximum acceptable radiation intensity at the corresponding frequency.
- “Over” column is the subtract of Limit from Measurement. If “Over” is minus and smaller, it indicates that the smaller the radiation, the better the EMC performance. If Over is plus, such as at one frequency point Over=5dB, that means over the limit value 5 dB and probably does not meet the standard.
- “PK” represents the maximum amplitude of the signal, which is supposed to be the maximum value in each time unit. It fits electromagnetic nuisance level assessment in the worst situation, especially for transient or impulse events.
- “QP“ is the time average of the quantity to be measured, weighted by simulating the human ear’s perception of an interfering signal. Suitable for the quantification of the maximum level of electromagnetic nuisance of a device over brief periods, especially the disturbances that would affect the sense of hearing.
- AV represents the average amplitude of the signal at a certain time and is relevant for equipment working in a state of continuous operation or steady state regarding its electromagnetic disturbance.
Application of these parameters depends on the scenario during tests.
| Test Type | Frequency Range | Limit Requirement | Qualification Criteria |
| Conducted Emission Test | 9kHz ~ 30MHz | QP + AV | Both QP and AV data must be below standard limits |
| Disturbance Power Test | 30MHz ~ 300MHz | QP + AV | Both QP and AV data must be below standard limits *For 200MHz–300MHz: If PK value is 10dB below QP limit, radiation test exemption applies |
| Radiated Emission Test (Civil Standard) | 30MHz ~ 1000MHz | QP | QP data must be below standard limit |
| High-Freq. Radiation Test (Civil Standard) | 1000MHz ~ 40GHz | PK + AV | Both PK and AV data must be below standard limits |
| Military Standard (e.g., GJB151B) | Not specified | PK | PK data must be below standard limit (QP/AV evaluation not required) *Failure if PK exceeds limit (Ignore QP/AV data) |
Step 3:
Graphical Interpretation
Step 4:
Result Analysis
- In the graph of the results obtained from the radiation emission test, the abscissa is frequency, and the ordinate is radiation intensity. In case of exceeding the limit curve at some segment of the curve, the frequency point corresponding to that portion of the curve is the frequency point that will exceed the limit.
- For example, on the graph of the test report, when the curve is above the limit curve at 200 MHz, then this point in frequency needs concentration.
- Compare test results with the limit to see the general trend of, for example, whether the radiation intensity is changing regularly with the rising of frequency. If several frequency points are close to the limit though they have not exceeded the standard, there may be a potential risk.
- Determine whether the PCB meets the requirements of EMC. If not, indicate the direction for improvement, such as optimizing the wiring or adding shielding measures.
Conclusion
EMC is a critical consideration in PCB design. Thus, adhering to EMC standards is essential to ensure product reliability, prevent interference with other devices, and comply with regulatory requirements. By prioritizing EMC in your designs, you can safeguard your product’s functionality and market viability.
ELEPCB is a reliable PCB manufacturer that produces high quality PCB products, which has more than 10 years of manufacturing experience. Check out our quality control page to find out more. Contact us or leave a comment below to get a quote!
CONTACT US
English 
Italian 
Hungarian