EMC Design Optimization for MCU & OBC: From Rework Failure to First-Pass Compliance

n electric vehicle (EV) power electronics development, the Motor Control Unit (MCU) and On-Board Charger (OBC) are among the most EMI-challenged subsystems. As high-voltage platforms, fast switching frequencies, and compact packaging become standard, electromagnetic compatibility (EMC) issues are no longer exceptions—they are predictable outcomes of early design decisions.

Yet many projects still rely on a reactive workflow:
prototype → EMC test failure → rework → retest.
This loop consumes time, inflates cost, and often reaches a dead end once mechanical structures are frozen.

Based on multiple real MCU and OBC co-design projects, this article outlines a proven path from repeated EMC rework failure to first-pass compliance, demonstrating why EMC is fundamentally a design problem, not a post-test fix.

Why EMC Rework Fails: Lessons from Real MCU & OBC Projects

Case 1: MCU Radiated Emissions Exceed Limit by 12 dB

Issue
Radiated emissions exceeded limits by up to 12 dB in the 30–200 MHz range.

Original approach
Standard conductive fabric applied to shield the MCU control board, with large mechanical gaps.

Root causes

• Poor rebound of conductive fabric increased contact impedance over time

• No chamfering at mating edges, breaking shielding continuity

• Incompatible with SMT processes, leading to unstable grounding

Optimized solution

• Replaced with SMT gasket (SMD-G-KLD series)

• Structural chamfer optimization

• Controlled compression ratio of 25–30%

Result
Radiated emissions reduced by 15 dB, passing CISPR 25 Class 3 in a single test cycle.

Key takeaway
Shielding materials must match structure, process, and lifecycle reliability—not just conductivity.

Case 2: OBC Conducted Emissions Fail at 150 kHz

Issue
Conducted emissions exceeded limits by 8 dB at 150 kHz; input and output filtering ineffective.

Original approach
Standard π-filter used, but filter housing left floating.

Root causes

• Floating metal housing enabled capacitive noise coupling

• Ground path exceeded 20 mm, increasing inductive impedance

• No low-impedance material for coplanar grounding

Optimized solution

• Conductive silicone rubber gasket directly bonding filter housing to enclosure

• Ground path shortened to <10 mm

• Aluminum foil shielding tape enabling 360° cable termination

Result
Conducted emissions reduced by 18 dB, fully compliant with GB 34660.

Key takeaway
Filter performance depends more on grounding quality than on component values alone.

From Failure to First-Pass Compliance: A Four-Step EMC Design Method

Step 1: Early EMC Risk Identification

Key checks during the design phase:

• Power and control zones isolated (recommended spacing ≥5 mm)

• Filters placed close to interfaces with grounding paths <10 mm

• Shielding structures support 360° termination

• Materials meet automotive reliability standards

Related reference:
PCB EMI Shielding: From Point Protection to System-Level Isolation

Step 2: Material–Structure Co-Design

Shielding material selection principles

Structural optimization guidelines

• Add chamfers to ensure uniform compression

• Avoid “pigtail” cable grounding—use full 360° termination

• Filter housings must be directly bonded, never via flying leads

For SMT-compatible solutions, see:
SMT Gaskets｜Compact Yet Powerful EMI Protection for Electronic Devices

Step 3: Simulation + Measurement Verification

• Near-field simulation using HFSS or CST to predict impedance paths

• Pre-compliance testing in customer labs to identify risks early

• All optimizations validated by measured data, not assumptions

Step 4: Closed-Loop Collaboration

• Build a traceable loop: issue → solution → validation → standardization

• Convert successful fixes into internal EMC design rules

• Apply proven solutions upfront in new projects to achieve first-pass success

Our Role: Collaborative EMC Design Partner

We do not replace system architects. Instead, we define the feasible boundaries of material and grounding performance within real manufacturing constraints.

Our contribution includes:

• Material definition: TDS, simulation models, process parameters

• Early EMC risk warnings during structural design

• Data-driven rework recommendations

• Support for SMT assembly and mass-production consistency

To understand long-term material reliability risks, refer to:
Hidden Corrosion of Conductive Silicone Rubber: How Micro-Scale Electrochemistry Undermines EMI Reliability

From Rework Thinking to Design Thinking

EMC issues in MCU and OBC systems should never be “found and fixed” after testing—they should be designed out from the beginning.

Rework is a cost.
Design is an investment.
Collaboration is the path.
First-pass compliance is the result.

Konlida does not offer universal shortcuts. We provide verifiable, repeatable, and production-ready EMC solutions, grounded in material science, system logic, and automotive manufacturing reality.

If your MCU or OBC project is facing persistent EMC challenges, we are ready to collaborate—until the problem is resolved at its root.