Printed Circuit Boards (PCBs) play a crucial role in supporting and connecting electronic components, while interference can significantly impact their performance. This guide explores anti-interference design principles for PCBs and microcontrollers (MCUs) to ensure reliable operation in high-noise environments.

Key Principles of PCB Anti-Interference Design

1. Ground Wire Layout

• Separate Digital and Analog Ground: Isolate digital and analog grounds to prevent mutual interference.
• Thicker Ground Wires: Use wires at least 2–3mm wide to handle 3× the allowable current on the PCB.
• Dead Loop Design: Create ground loops to reduce potential differences.

2. Power Line Design

• Adjust Wire Width: Ensure the power line width corresponds to the current size.
• Align with Data Flow: Maintain alignment of power and ground lines with data transmission direction.
• Add Decoupling Capacitors: Use 10–100μF capacitors at the power input to stabilize voltage.

Decoupling Capacitors: Configuration and Placement

• Short Leads: Avoid long leads for capacitors to minimize self-inductance.
• Capacitor Placement:
  • 10–100μF electrolytic capacitors across the power input.
  • 0.01–0.1μF ceramic capacitors between Vcc and GND for each IC.
  • Use 0.01μF capacitors on sensitive terminals like the MCU reset pin.

Device Placement and Circuit Routing

3. Device Configuration

• Clock Proximity: Place clock sources (e.g., oscillators) near the CPU and away from low-frequency components.
• Thermal Management: Position heat-generating components at the top of the chassis and away from sensitive devices.

4. Signal Line Separation

• Power vs. Signal Lines: Route power and AC lines separately from signal lines to minimize interference.

Advanced Anti-Interference Techniques

5. Noise Reduction Measures

• Clock Signal Isolation: Surround clock circuits with ground wires and keep them short.
• Vertical PCB Routing: Arrange perpendicular lines on both sides of the PCB to reduce crosstalk.
• 45° Angles: Use 45° fold lines in routing to minimize high-frequency signal coupling.

6. Shielding and Filtering

• Metal Covers: Shield circuits sensitive to high-frequency noise. Thin copper is effective for >500KHz signals.
• Shielded Cables: Ground both ends for high-frequency signals, or one end for low-frequency analog signals.

Digital Circuit and MCU Anti-Interference Design

7. Source Suppression

• Reduce du/dt and di/dt: Use capacitors, inductors, and freewheeling diodes to suppress transient noise.
• Relay Protection: Add spark suppression circuits (e.g., RC circuits) to relay contacts.

8. Propagation Path Control

• Power Supply Filters: Use π-shaped filters with magnetic beads and capacitors for clean power.
• Isolate Noisy Devices: Apply filters or optocouplers between noisy components (e.g., motors) and sensitive devices.

Improving MCU Resilience

9. Key Practices

• Idle Pin Management: Tie unused I/O pins to ground or Vcc.
• Watchdog Circuits: Integrate watchdog ICs for automatic reset during anomalies.
• Low-Speed Clocking: Opt for low-speed oscillators to reduce noise sensitivity.

10. Decoupling Optimization

• Use tantalum capacitors instead of electrolytic ones for better high-frequency performance.
• Minimize capacitor lead lengths to prevent resonance issues.

Software Anti-Interference Tips

1. Initialize Unused Memory: Clear unused code space to avoid execution errors.
2. Error Checking: Employ checksums or redundancy (e.g., 3-out-of-2 voting).
3. Software Watchdogs: Implement timers to reset the system during runaway conditions.

Effective anti-interference design in PCBs and MCUs involves combining hardware measures (e.g., grounding, decoupling) and software strategies (e.g., watchdogs, error-checking). By addressing interference sources, propagation paths, and sensitive devices, you can significantly enhance circuit reliability and performance.