Introduction
The rollout of 5G networks and mmWave (millimeter wave) applications has introduced unprecedented electromagnetic interference (EMI) challenges for electronics designers. Operating at frequencies from 24 GHz to 100 GHz and beyond, these systems demand a fundamental rethinking of traditional shielding approaches. Copper-based EMI shielding solutions are proving essential in meeting the demanding requirements of next-generation wireless electronics.
The 5G EMI Challenge: Why Higher Frequencies Change Everything
At mmWave frequencies, several physical phenomena make EMI management substantially more difficult than at sub-6 GHz:
- Shorter wavelengths: At 28 GHz, the wavelength is approximately 10.7 mm — small enough that even minor shield gaps become effective slot ante
as, radiating or leaking energy
- Surface current effects: Skin depth in copper at 28 GHz is only 0.39 μm, meaning surface roughness and oxide layers significantly impact shielding performance
- Higher path loss: Free-space path loss increases by 20 dB when moving from 2.4 GHz to 24 GHz, making shielding effectiveness even more critical to preserve signal integrity
- Denser packaging: 5G ante
a arrays and beamforming ICs pack dozens of cha
els into compact modules, creating complex near-field coupling scenarios
Shielding Effectiveness at mmWave Frequencies
Shielding effectiveness (SE) combines reflection loss, absorption loss, and multiple-reflection correction. For copper shields at mmWave frequencies:
- Reflection loss decreases with increasing frequency because the impedance mismatch between air and copper becomes less pronounced for high-frequency plane waves
- Absorption loss increases with frequency due to the skin effect, but the practical shield thickness (typically 0.2–0.5 mm) limits total absorption
- The net result: achieving >60 dB SE at 28 GHz requires more careful design than at 2.4 GHz
Copper vs. Alternative Shielding Materials at High Frequency
| Material | Relative Conductivity | SE at 30 GHz (0.3 mm) | Key Advantage |
|---|---|---|---|
| Copper (C11000) | 1.00 | ~75 dB | Best conductivity |
| Aluminum | 0.61 | ~65 dB | Lower weight |
| Nickel Silver | 0.05–0.10 | ~40 dB | Corrosion resistance |
| Conductive Plastic | 0.001–0.01 | ~15–25 dB | Lightweight, molded |
Design Best Practices for Copper Shielding at mmWave
1. Minimize Aperture Dimensions
The maximum aperture dimension in any shield should not exceed λ/20 at the highest operating frequency. For 39 GHz (λ ≈ 7.7 mm), this means apertures must be <0.38 mm. This requires either solid copper enclosures or tightly-spaced via fences along seams.
2. Optimize Grounding and Seam Design
At mmWave frequencies, the contact resistance between shield and PCB ground is critical. Copper-to-copper contact with adequate pressure is ideal. Shield fences should use ground vias spaced no more than λ/10 apart — approximately 0.3 mm at 100 GHz.
3. Consider Surface Finish Impact
While bare copper provides the best conductivity, it oxidizes rapidly. For mmWave applications, a thin nickel underlayer (1–2 μm) with gold flash provides excellent corrosion protection without significantly degrading SE. Thick nickel plating should be avoided at mmWave frequencies due to nickel’s ferromagnetic properties and lower conductivity.
4. Compartmentalize High-Risk Zones
In 5G modules, separate shielding compartments for power amplifier sections, low-noise amplifier inputs, and digital control sections prevent coupling between high-power and sensitive circuits. Copper partition walls soldered to the PCB ground plane create effective isolation zones.
The Role of Copper Strips in 5G Shielding Assemblies
Precision-stamped copper strips form the backbone of 5G shielding solutions. They are used as:
- Shield fence rails soldered around RF sections to create compartment walls
- Spring finger contacts for removable shield lids that maintain consistent ground contact
- Integrated thermal-EMI solutions where copper strips serve dual functions as heat spreaders and shield elements
Conclusion
As 5G and mmWave technologies continue their rapid deployment, the importance of properly engineered copper EMI shielding ca
ot be overstated. The shorter wavelengths and tighter packaging demands of these systems reward careful material selection, precision manufacturing, and rigorous adherence to shielding design fundamentals. Copper — with its unmatched conductivity and established manufacturing infrastructure — remains the gold standard for high-frequency EMI control.
