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My team is responsible for designing industrial electrical devices. We had successfully designed several devices before. Recently, we are designing products that have to meet IEC 61000-4-4 class A standard. We got ourselves EFT generator for testing. But most prototypes have failed and we need to redesign the PCB then test again. This process costs us time and money a lot until we pass the test.

I assume our design team lack of knowledge in this field.

  1. How to design PCB to pass the EFT and EMC testing?
  2. How to debug or troubleshoot?
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A few suggestions to start:

No slots in ground planes that current flows.

Grounds connected to single point ground with no loops.

Current carrying tracks run above ground plane or directly above ground return tracks.

Decoupling caps with minimum inductance path to ground at every IC power pin
(ie any pin that is liable to source/sink more than signal current).

Larger filter caps occasionally.

Limit pin slew rates where possible and not harmful to application.

Dither / semi-randomise clock periods or half periods where acceptable to spread energy bandwidth and thus lower amplitudes.

Limit FET gate drive currents to lowest acceptable rate.

Spread rectifier power diode conduction angles with series resistors.

Any shielding slots to NOT look like a slot radiator at any conceivable frequencies involved including harmonics.

Ferrite ring/clamp filters on wiring with suitable adjacent bypass caps to enhance low pass nature of ferrite-inductor / capacitor combination

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Critique and/or comment on any of these suggestions is welcome.

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Use a GROUND plane. Have 1Kohm resistors in every signal wire that connects off the PCB.

To prevent long PCB traces becoming antennas, insert 10Kohm resistors near the load end. Thus between a MCU and an analog-digital-converter, place 10Kohm resistors in the SPI (3 wires).

And many more methods.

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  • Continuous grounds are best (if you need digital and analog separation, this can be done with layout and physical separation and keeping track of return currents)

  • Use X2Y caps to short out unwanted high frequency voltages at the source

  • Use good cable EMC control, twist wires and shield cables that may potentially radiate.

  • Use ferrites to block high frequency currents on cables

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