The tracks of a Printed Circuit Board (PCB) have electrical currents travelling along with them as a voltage is applied or removed by control and signal circuits connected to them. Whenever there is an electrical current passing through a conductor such as a PCB track, there is also a magnetic field generated around this conductor. This magnetic field can couple onto other circuits and also has the potential to radiate from the PCB and interfere with the normal operation of nearby electronic equipment. This phenomenon is known as electromagnetic interference or EMI.
What is PBC EMC?
Electro-Magnetic Compatibility or EMC is the process of ensuring that electromagnetic emissions produced by a device do not cause interference to other external equipment. Similarly, it also applies to the ability of a device to operate in a known electromagnetic environment, without being susceptible to interference from this phenomenon.
What is PBC EMI?
PCB designers must consider EMI in order to ensure reliable operation and comply with mandatory EMC (Electro-Magnetic Compatibility) standards applicable to the end product.
It is not possible to eliminate electromagnetic emissions, as these emissions will be present whenever a modifying current passes through a conductor, however it is possible to limit the amplitude and frequency response of these emissions using PCB design techniques.
EMC Control Techniques
PCB designers use various measures to control EMI and comply with EMC compliance standards. A variety of shielding and filtering options are used by designers in the form of physical shields that cover all or part of the PCB. Some boards include lowpass filters for eliminating high-frequency noise.
While it’s all but impossible to design a PCB with no electromagnetic emissions, it is definitely a possibility to reduce those emissions to an extent that it complies with the applicable EMC standards. Here are a few design guidelines to assist with EMC compliance of your product:
1). Proper trace spacing and layout — The paths carrying current from the driver to the receiver are known as a trace. When these traces bend or cross, it leads to the formation of an antenna which may lead to EMI. This is why it is recommended to separate all the signals from other traces. It helps in reducing crosstalk.
2). Proper use of a ground plane — Make use of the entire ground plane to reduce or mitigate EMC problems.
3). Shielding – Shielding is commonly used to contain EMI. It is a closed conductive container that is connected to the ground and its role is to reduce the loop antenna size by reflecting and absorbing a part of the radiation.
4). Arrangement of layers — How the layers are arranged in a PCB also affects its EMC performance. If there are multiple layers, it is recommended to use an entire layer as a ground plane and the layer below it as a power plane. If you are using only a 2-layer board, it is recommended to use ground grids if you’re not able to use an entire layer as a ground plane.
5). Component segregation — In an ideal design, all the components should be grouped together based on the signals on which they operate such as high-speed signals, low-speed signals, power supply, digital or analogue.
6). Decoupling capacitor — The operation of integrated circuits generates high-frequency noise leading to EMI and decoupling capacitors should be placed close to the power pins of ICs to reduce EMI.
7). Controlled impedance – High-speed circuits often have an impedance mismatch problem leading to EMI issues. One of the ways to reduce EMI is to use matched signal termination strategies for mitigating signal reflection.
Electromagnetic emissions are generated by most electronic and electrical devices. PCB designers need to consider EMC compliance right from the initial design stage to ensure that the final product has the best chance of complying with the relevant EMC standards, and can be released onto the market without costly delays. A product cannot legally be sold if it is not compliant with all of the required EMC standards.
There are software packages available on the market that can assist with EMC by simulating signal integrity throughout the PCB before the product has even been manufactured. It is also highly recommended that pre-compliance EMC testing is performed on prototypes to give the highest confidence that your final product will comply when submitted for EMC testing the first time it is sent for testing.
High-Frequency PCB EMC Design Guidelines to Reduce EMI
Nearly every region in the world has mandatory EMC standards applicable to electronic products released in their market. In Australia, EMC standards are defined and implemented by Australian Communications and Media Authority (ACMA). These standards are imposed to ensure that the EMI generated by all the electronic and electrical products is within certain limits to ensure regular operation in the real-world environment
If a supplier or manufacturer wants to sell electronic products in the Australian market, they need to ensure the EMC compliance of the product with the appropriate EMC standards. Here is a quick breakdown of the process:
Identification of EMC standards applicable for the respective product as per the ACMA database
Conducting EMC testing through an accredited testing laboratory to demonstrate compliance
Signing a Declaration of Conformity which states that the product is in compliance with the appropriate standards
Registration on the national database
EMC Testing and Certification
Compliance Engineering operates an internationally accredited EMC testing laboratory and has decades of EMC compliance experience and can help you achieve compliance with appropriate EMC standards for products that are to be exported or sold locally. Our services include EMC testing and compliance, antenna calibrations, on-site EMC measurements, and EMC consultancy, among others.
Please call us today at Compliance Engineering on + 61 3 9763 3079 or request a quote.