Knowing EMI/EMC for Product Designing

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Knowing EMI/EMC for Product Designing

The World is Revolutionizing with Technological advancement. Since the past decade, IoT is be becoming need of the hour in all the sector, be it Manufacturing, Entertainment, Travel or Food & Beverages, IoT is Everywhere. All of these are driven by Hardware / Software based IoT. The Hardware is nothing but a bundle of Electronic Components assembled on the board called PCB and these PCBs should be able to work without any electronic interferences from other devices.

Understanding EMI/EMC :

EMI Stands for Electro Magnetic Interference and EMC Stands for Electro Magnetic Compliance. Sometimes, the Product we design can be a source or victim of Radio Frequency Waves due to various sources. The Amount of radiation that an electronic product can radiate or amount of radiation an electronic product should withstand without any permanent failure.

With Increased use of electronics in our daily life, compliance to these standards ensure users are safe and products don’t pollute and affects the products in the vicinity. While each country has its own standards, they do not vary much in values.

The Main design objective for compliance to EMC requirements will be to minimize the size and number of openings and to name few:

  1. Displays (LED/CRT)
  2. Keypads or Membrane Switches
  3. Status Indicators
  4. Cooling Apertures
  5. Box Assembly Seams
  6. Cable or Connector Openings

Designers think EMC/EMI problems are due to enclosures alone. This is a myth every designer should be aware. For a successful compliance entire product design has to be designed to meet the standards. PCBAs are the major culprit and they need careful EMC/EMI design in addition to enclosures.

EMC Standards:

Military Standards:

In solving an EMC problem, both the emitter noise level and susceptor’s noise threshold must be considered. If the susceptor’s lowest signal threshold level can be made greater by at least two times the highest emitter (noise) level (for a 6dB safety margin) then the emitter and the susceptor are considered to be compatible with each other. One way of achieving this type of compatibility is to define not only the maximum allowable emissions level but also the minimum allowable susceptibility threshold level.

The most commonly used military standard for both emissions and susceptibility is MIL-STD-461. There are more than one emission and susceptibility level defined in MILL-STD-461 since the requirement applications vary.

Commercial Standards:

The most common commercial standards are FCC (Federal Communications Commission) as USA based standard and VDE (Verband Der Elektrotechnik) as Germany based standard.

How We can Solve this Problem:

One Challenge that designers will face in electronic packaging very often is that Solution to one problem will become a problem to another area (Example EMI/EMC and Thermal Design).

Sheetmetal enclosures lend themselves to EMC/EMI Problem in a natural way, while plastic enclosure poses a big challenge for EMI/EMC and to make them meet the standards, they need to be conductive. Most Popular and expensive solution is to coat a conductive paint inside the plastic enclosure or make the plastic conductive by adding additives in plastic manufacturing method. Other processes for coating are Electroless Plating and Metal Foil Lining. Both these processes are expensive and delicate.

PCB Design and Layout – where RF and Digital Designers will design the PCBAs to reduce or eliminate noise and susceptibility.

Power Supply Design and Layout – where Power Supply Designers will design the power supplies to reduce or eliminate noise and susceptibility.

Internal Wiring – where the above Designers and Mechanical Designers will work to design interconnects between PCBAs and to enclosure which will not pick-up or induce EMI internally (self-jamming) or externally (violate FCC/CISPR/VDE/Military regulations).

Enclosure Design – where Mechanical Designers will Design a continuously closed conductive envelope in order to prevent outside fields from penetrating the equipment and to prevent internally generated noises from escaping the enclosure.

The enclosure should be the continuous metal surface where PCBA grounds are attached at specific locations. This continuous metal surface can be either “actual” metal (like aluminium, magnesium, or steel) or it can be a conductive coating that has been put onto a non-conductive material (like plastic). Note that, when considering “actual” metal as an enclosure, the designer must take into account that the surface finish on the metal must be conductive. Several common surface finishes for metal are not conductive (enough) to serve as a “continuous metal surface”. Any finish chosen to be conductive, must remain so during the environment (corrosion) and wear (say, due to vibration) that the product will undergo during its expected life.