Silicon Carbide in EV Power Electronics: What It Means for EMI Shielding Design

The automotive industry's rapid adoption of silicon carbide semiconductors from Wolfspeed, Infineon, STMicroelectronics, and onsemi is delivering measurable gains in EV efficiency and range. But the same properties that make SiC MOSFETs attractive—faster switching speeds, higher operating temperatures, lower conduction losses—create an EMI profile that exposes weaknesses in shielding designs originally validated for silicon IGBT inverters.

Why Is There a Tradeoff Between SiC Efficiency and EMI?

Every improvement in SiC switching loss reduction comes from faster voltage and current transitions—and faster transitions mean higher-frequency EMI content that demands different shielding approaches. This tradeoff is fundamental to wide bandgap semiconductor physics.

SiC MOSFETs reduce switching losses by 50-80% compared to silicon IGBTs, enabling smaller heatsinks, lighter cooling systems, and higher switching frequencies that shrink passive components. Tesla's Model 3 traction inverter demonstrated these advantages in 2018, and today nearly every new EV platform—from Hyundai E-GMP to GM Ultium to BYD's latest architectures—specifies SiC for the main inverter.

But efficiency and EMI are coupled through dV/dt. A typical Infineon CoolSiC or Wolfspeed C3M MOSFET achieves 5-50 V/ns slew rates—an order of magnitude faster than the 1-5 V/ns typical of silicon IGBTs. The shielding implications are significant and cannot be addressed with incremental changes to existing designs.

How Does SiC Change the EMI Frequency Spectrum?

SiC generates significantly more EMI energy between 10 MHz and 500 MHz compared to IGBT-based designs, fundamentally shifting where shielding must be effective.

Switching Speed and Spectral Content

The frequency content of a switching waveform is determined by the speed of its transitions. A trapezoidal waveform has a spectral envelope that rolls off at -20 dB/decade above a corner frequency set by the rise/fall time:

• Silicon IGBT (200 ns rise time): corner frequency ≈ 1.6 MHz. Harmonics significant to ~5 MHz.
• SiC MOSFET (20 ns rise time): corner frequency ≈ 16 MHz. Harmonics significant to ~200 MHz.
• GaN HEMT (5 ns rise time): corner frequency ≈ 64 MHz. Harmonics significant to ~500 MHz+.

This means a SiC inverter produces meaningful EMI energy at frequencies where an IGBT inverter's emissions have already fallen below the noise floor—and where shield apertures that were electrically invisible become significant leakage paths.

What Causes Broadband Ringing Noise in SiC Circuits?

Parasitic inductance in the power loop—formed by the DC bus capacitors, power module, and PCB traces—creates a resonant circuit with the SiC device's output capacitance (Coss). Each switching event excites this LC resonance, producing RF bursts typically at 10-100 MHz depending on layout.

SiC's faster switching excites these parasitics more aggressively than IGBTs. Damping the ring with RC snubbers adds losses that partially defeat SiC's efficiency advantage, so engineers must instead minimize loop inductance through careful layout—and shield what remains. Rohde & Schwarz and Keysight EMI receivers routinely capture these ringing signatures during CISPR 25 pre-compliance testing.

IGBT vs SiC vs GaN: How Do Their EMI Profiles Compare?

| Parameter | Silicon IGBT | SiC MOSFET | GaN HEMT | |-----------|-------------|------------|----------| | Typical switching frequency | 5-20 kHz | 20-100 kHz | 100 kHz - 4 MHz | | Voltage slew rate (dV/dt) | 1-5 V/ns | 5-50 V/ns | 10-100+ V/ns | | Significant harmonics extend to | ~5 MHz | ~200 MHz | ~500 MHz+ | | Primary EMI concern | Conducted below 30 MHz | Conducted + radiated to 200 MHz | Radiated above 100 MHz | | Typical EV application | Legacy inverters | Traction inverters (100-300 kW) | OBC, DC-DC (1-10 kW) |

How Do SiC Frequencies Affect Shield Design Parameters?

Shield designs validated for IGBT inverters typically fail at SiC frequencies due to three factors: aperture leakage, inadequate seam treatment, and insufficient filtering bandwidth.

Skin Depth at SiC-Relevant Frequencies

Skin depth decreases with frequency, but at SiC frequencies the material itself is rarely the limiting factor:

• At 1 MHz (IGBT range): copper δ = 66 μm, aluminum δ = 84 μm
• At 100 MHz (SiC primary range): copper δ = 6.6 μm, aluminum δ = 8.5 μm
• At 500 MHz (upper SiC/GaN range): copper δ = 2.9 μm, aluminum δ = 3.8 μm

A standard 0.2 mm (200 μm) copper shield provides 30 skin depths at 100 MHz—far more than the 3 required for effective absorption. The material provides adequate attenuation; it's the apertures, seams, and penetrations that fail at higher frequencies.

Why Does the λ/20 Aperture Rule Matter More for SiC?

The λ/20 rule for maximum aperture size becomes dramatically more restrictive at SiC frequencies:

• At 10 MHz: maximum aperture ≈ 1.5 m (never a constraint)
• At 100 MHz: maximum aperture ≈ 15 cm (manageable)
• At 200 MHz: maximum aperture ≈ 7.5 cm (ventilation holes become a concern)
• At 500 MHz: maximum aperture ≈ 3 cm (connector cutouts need attention)
• At 1 GHz: maximum aperture ≈ 1.5 cm (every opening matters)

A ventilation pattern or connector cutout that was invisible at IGBT frequencies can be the dominant leakage path at SiC frequencies. Every opening in the shield enclosure must be re-evaluated.

What Materials Provide Broadband Attenuation for SiC?

SiC's wide EMI spectrum demands shields effective across multiple decades of frequency:

• Nickel silver (65% Cu, 18% Ni, 17% Zn) for board-level shield cans—provides both conductivity for reflection shielding and magnetic permeability for absorption at higher frequencies
• Mu-metal or nanocrystalline foil inner layers for low-frequency magnetic field attenuation near DC-DC converters
• Conductive elastomer gaskets (Parker Chomerics or Laird) at seams, selected for low transfer impedance through 500 MHz
• Composite enclosures with conductive outer coating and lossy inner layer for system-level broadband performance

What Are the Most Effective Shielding Approaches for SiC Systems?

Practical SiC EMI management combines source reduction (minimizing emissions at the inverter) with path blocking (shielding what remains).

Gate Driver Isolation and Local Shielding

The gate driver circuit is ground zero for SiC EMI—it delivers fast-switching signals and experiences full dV/dt stress. Board-level nickel silver shield cans (0.15-0.2 mm) over gate driver ICs from Silicon Labs, Broadcom, or Texas Instruments prevent high-frequency radiation from coupling to nearby sensitive electronics.

Select isolated gate drivers with common-mode transient immunity (CMTI) rated for SiC slew rates—minimum 100 V/ns per JEDEC standards. The Silicon Labs Si823x series and Texas Instruments UCC2152x family are designed specifically for SiC dV/dt environments.

How Does Power Loop Optimization Reduce SiC EMI?

Minimizing power loop inductance is the single most effective EMI reduction strategy for SiC, reducing emissions at the source before shielding is needed. Every nH of loop inductance directly increases ringing amplitude and duration.

• Laminated busbars with DC+ and DC- layers separated by thin Kapton dielectric achieve loop inductance below 5 nH
• PCB power planes in adjacent layers with 4-mil FR-4 dielectric provide similar benefits for lower-current stages
• Reducing loop inductance from 20 nH to 5 nH cuts ringing amplitude by ~6 dB—equivalent to doubling shielding effectiveness

Wolfspeed's CRD-06600FF065N reference design and Infineon's EvalM5-IMZ120R-SIC evaluation board both demonstrate optimized power loop layouts that engineers can reference.

What Cable Shielding Does a SiC Drivetrain Require?

High-voltage cables in SiC systems carry sharper current transients than IGBT systems, requiring enhanced shielding:

• Braid coverage >95% with supplemental aluminum/mylar foil wrap for >120 dB shielding effectiveness per MIL-STD-1344
• 360-degree connector termination using Amphenol, TE Connectivity, or APTIV HV connectors—pigtail grounds create inductance that defeats shielding above a few MHz
• Transfer impedance <50 mΩ/m through 200 MHz per SAE J1939 requirements
• Minimum 100 mm separation from ADAS sensor and CAN/LIN communication harnesses per typical OEM routing specifications

Filter Design for SiC Switching Profiles

SiC filters must address a wider bandwidth than IGBT filters:

• Common-mode chokes: Nanocrystalline cores (Vacuumschmelze VITROPERM) for 10 kHz - 10 MHz, NiZn ferrite (TDK/EPCOS) for 10 - 300 MHz
• Y-capacitors: Low-ESL ceramic capacitors (Murata, TDK) maintaining effectiveness through 500 MHz
• Multi-stage topology: First stage for differential-mode below 10 MHz, second stage for common-mode 10-300 MHz, rather than a single broadband attempt

Frequently Asked Questions

Why does silicon carbide create more EMI than silicon IGBTs?

SiC MOSFETs switch at voltage slew rates of 5-50 V/ns compared to 1-5 V/ns for silicon IGBTs. Faster voltage transitions contain more high-frequency spectral content. While IGBT harmonics roll off above a few MHz, SiC switching harmonics extend to 200 MHz and beyond with significant amplitude, requiring shielding effective at much higher frequencies.

Do I need to redesign my EMI shield when switching from IGBT to SiC?

In most cases, yes. A shield validated for an IGBT inverter likely has apertures and seams adequate at lower frequencies but that become leakage paths at SiC-relevant frequencies above 100 MHz. Re-evaluate aperture sizing against the λ/20 rule, gasket impedance at higher frequencies, and material thickness relative to skin depth at the new frequency range.

How does 800V architecture compound SiC EMI challenges?

Higher bus voltage means larger voltage swings during switching events. An 800V SiC MOSFET switching at 10 V/ns produces twice the peak dV/dt of a 400V device at the same slew rate, increasing both conducted and radiated emissions proportionally. Cable shielding, connector designs, and enclosure integrity all require re-evaluation for 800V platforms.

What is the difference between SiC and GaN EMI profiles?

GaN HEMTs switch even faster than SiC (up to 100+ V/ns) at frequencies up to 4 MHz, pushing EMI energy above 500 MHz. However, GaN is currently used mainly in lower-power EV applications like onboard chargers and DC-DC converters (typically under 10 kW), while SiC MOSFETs dominate traction inverters at 100-300 kW.

What shield materials work best for SiC frequency ranges?

Nickel silver is effective for board-level shield cans because it provides both conductivity for reflection-based shielding and magnetic loss for absorption at higher frequencies. For system-level enclosures, composite approaches using conductive outer layers with lossy inner materials provide broadband attenuation across the full SiC harmonic range from 100 kHz to 500 MHz.

What Does the 800V SiC Future Mean for Shielding?

The transition from 400V to 800V architectures—led by Hyundai E-GMP, Porsche PPE, and Kia EV6—doubles voltage stress during switching events. Combined with SiC's fast slew rates, 800V systems produce proportionally higher radiated emissions that push shield requirements even further.

Engineers designing for next-generation 800V SiC platforms should plan for EMI energy extending to 500 MHz and above. Shield designs validated at 400V require re-evaluation—the jump to 800V is not just voltage scaling. Engaging shielding suppliers like POCONS during the architecture phase, rather than after the first failed CISPR 25 pre-compliance scan, saves both design iterations and time to market.

---

Designing shielding for SiC-based EV systems? Contact POCONS USA to discuss your requirements with our engineering team.