EMC in PCB design

CE marking? Electromagnetic Compatibility (EMC)? What is it about? How is EMC related to electronic design? Shall some rules be followed in the design of a product?

A lot of questions occur when you start designing a new product, such as ‘What kind of standards should be used?’, ‘What kind of tests are needed to be done?’ or ‘What kind of techniques should be applied to succeed in tests?’.

The CE marking is a symbol placed on products when they have been designed in concordance with some directives or requirements that allow to sell the product in the European Union market. The directives followed in order to get the CE marking, depends on the product manufactured.

In the PCB design, one of the directives is to take care of the Electromagnetic Compatibility (EMC) to limit the emissions and not generate electromagnetic disturbances which can generate problems in proximity devices.

There are several techniques that shall be implemented in the PCB design regarding electromagnetic compatibility, such as grounding methodologies (a ground plane for return currents to maintain the lowest impedance); decoupling capacitors (100nF) place close to the IC power pin (Figure 1 shows a comparative depends on the decoupling capacitor chosen), filter each signal entering and leaving the PCB, Y capacitors to remove noise from power and ground connected to the chassis ground; transients absorbers as ESD protection in each input signal to clamp transient voltages; keep high frequency and RF tracks as short as possible; use top and bottom layers for low speed signals and the middle layers for sensitive and high frequency signals, don´t place sensitive traces or power supply traces close to the edges in a PCB, select the most suitable layer stack up for demands of the design etc. These are only a few rules. The designer should consider thinking about which rules must follow when designing a PCB or a product to reach a successful EMC test.

In order to verify if the product has been designed properly, do not emit and receive any distortion that can damage the equipment or the equipment around it. Just do some tests in an accredited company such as Delta in Vasteras.

One of the standards used for this test is IEC 61000. IEC 61000 describes the testing techniques used in the EMC test. Examples of these tests, are tests done in the connector with a length cable less than 30 meters, the Electrostatic discharge (ESD) test (standard IEC 61000-4-2) and the Radiated Immunity test (standard IEC 61000-4-3). The tests in a connector with a length cable more than 30 meters are the tests described earlier and the burst test (standard 61000-4-4), surge test (standard 61000-4-5) and conductive immunity test (standard 61000-4-6).

Author: Tania Lazaro
Hardware Engineer at Addiva Software and Embedded Services

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