What to Do If an EMC Test Fails: Root Causes and Effective Rectification Strategies
Published on: 2022-08-23
When your product fails an EMC (Electromagnetic Compatibility) test, it can feel like a major roadblock in product certification. EMC testing evaluates both a product’s electromagnetic interference (EMI) and its ability to resist external interference. It's a critical factor in product quality, safety, and compliance with regulatory standards like CE, FCC, and MIL-STD-461.
This guide provides a structured approach to EMC rectification, helping you understand common failure causes and practical solutions.
1. Understanding EMC Rectification
- Clarify Rectification Requirements: Avoid trial-and-error. Start with a rectification plan.
- Identify the Fault Source: Use intuitive judgment or data-driven comparative testing.
2. Common EMC Rectification Scenarios & Solutions
- Radiated Emissions (RE) Exceeding Limits: Shield components, reroute traces, add ferrites.
- Wire and Cable Radiation: Use shielded cables, ground properly, shorten routes.
- Signal Cable Interference: Add series resistors, impedance matching, rise-time control.
- Shielding Leakage: Improve contact, conductive gaskets, seal the enclosure.
3. Best Practices for EMC Rectification
Capacitor Filtering
Higher frequencies see lower impedance (Z) in capacitors, allowing them to divert noise to ground.
When Filtering Fails
Capacitors have self-inductance. After the resonant point, they behave like inductors.
LC Filter Advantages
LC filters attenuate at -40dB/decade vs. -20dB for single elements. Better suppression for high-frequency EMI.
4. Understanding PWM Frequency & EMI
PWM (e.g., 20kHz) signals generate wide EMI due to sharp edge transitions. Slower edge rates = better EMC.
5. PCB Layout Matters
Schematics are logical, but EMI behavior depends on physical routing and return paths.
- Verify ground return paths.
- Visualize current loops.
Summary: EMC Rectification Checklist
| Step | Action |
|---|---|
| 1 | Review the EMC report |
| 2 | Use tools or intuition to identify faults |
| 3 | Apply shielding, filtering, layout adjustments |
| 4 | Check component resonance |
| 5 | Validate PCB layout and return paths |
| 6 | Repeat EMC testing |
Recommended Components for EMC Fixes
- Feedthrough capacitors
- Screw-type EMI filters
- Solder-in EMI filters
- Miniature multilayer filters
For reliable EMI suppression solutions, explore LCA’s EMC product range.
