Improving PCBA Design for EMI and EMC Compliance: A Case Study
Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC) compliance is critical in electronic product development. Recently, we undertook the task of redesigning a Printed Circuit Board Assembly (PCBA) for a variable speed control system of a DC brushed motor, complete with an LCD user interface.Â
While the initial design met functional expectations, the product owner requested a revision to accommodate assembly changes and support a more powerful motor. Here’s an outline of the key updates we implemented to achieve enhanced EMI and EMC compliance, improving both performance and reliability.
Understanding the Challenge
Our customer faced significant challenges with EMI and EMC compliance, struggling to meet the standards with their existing resources. Achieving EMI and EMC compliance is inherently iterative and requires deep experience and a thorough understanding of root causes. It involves extensive testing, including pre-compliance testing, which, although less expensive than full compliance testing, demands access to a well-equipped testing lab for multiple iterations. The crux of the issue often lies in the layout design, emphasizing the need for experienced engineers to mitigate compliance issues effectively.
Key Updates for Improved EMI and EMC Compliance
- Ground Planes Isolation: We separated the ground planes to prevent interference and reduce electrical noise from the motor.
- Noise Filter Addition: We added a noise filter circuit to cut down on electrical noise around the motor control chip. This included a specific circuit to match the motor control frequency, placed near the motor control area.
- Connector Upgrade: We swapped out the Dupont pin header for a more compact connector like FPC. This change saves space and reduces the impact of electrical noise on downstream devices like the LCD.
- Flyback Diode Addition: We added a flyback diode to the motor output to protect against voltage spikes.
- Thicker Substrate: To prevent mechanical bending of the assembly, we made the substrate thicker.
- Enhanced Power Traces: We increased the number of connections on power traces, especially those leading to the motor output, to improve current handling and heat management.
- Thermal Pad Addition: A thermal pad was added underneath a key component to help with heat dissipation.
- Buzzer Circuit Update: We redesigned the circuit around the buzzer to reduce noise interference.
- Mounting Holes Adjustment: We removed unnecessary electrical connections around the mounting holes.
- Smaller Ground Area: To reduce noise reception, we made the ground area on the top layer smaller.
- Robust Motor and Power Connectors: We upgraded the motor and power connectors to more durable, quick-connect types, avoiding the use of spring terminals.
Addressing EMI/EMC Proximity Issues
Given the proximity of the assembly to the motor, the PCBA was subjected to significant EMI, particularly during speed changes and high loads. To mitigate this:
- We adjusted the mounting orientation.
- Added internal layer copper pours to better guide EMI.
- Combined a noise filter circuit with copper pours for enhanced EMI management.
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Our experience and methodical approach ensured that the new version not only met but exceeded the compliance requirements, resulting in a more robust and reliable product. We have 70+ engineers in SrushtyES to work on electronic systems to achieve the best results.
