EMC Pre-Compliance Skill

Requirements

• Python 3.8+ — stdlib only, no pip dependencies
• Schematic analyzer JSON — from analyze_schematic.py --output
• PCB analyzer JSON — from analyze_pcb.py --full --output (recommended with --full)
• SPICE simulator (optional) — ngspice, LTspice, or Xyce for SPICE-enhanced PDN/filter checks. Auto-detected. Without one, analytical models run unchanged.

Workflow

Step 1: Run the analyzers

python3 <kicad-skill-path>/scripts/analyze_schematic.py design.kicad_sch --analysis-dir analysis/
python3 <kicad-skill-path>/scripts/analyze_pcb.py design.kicad_pcb --full --analysis-dir analysis/

Step 2: Run EMC analysis

Point --schematic and --pcb at the current run's JSONs and pass --analysis-dir analysis/ so emc.json co-locates with them and gets tracked in the manifest:

# Recommended: integrate into the current run
python3 <skill-path>/scripts/analyze_emc.py \
    --schematic analysis/<run_id>/schematic.json \
    --pcb analysis/<run_id>/pcb.json \
    --analysis-dir analysis/

# One-off JSON (bypasses the cache)
python3 <skill-path>/scripts/analyze_emc.py --schematic schematic.json --pcb pcb.json --output emc.json

# SPICE-enhanced (improved PDN and filter accuracy)
python3 <skill-path>/scripts/analyze_emc.py --schematic schematic.json --pcb pcb.json --spice-enhanced

# Select target standard
python3 <skill-path>/scripts/analyze_emc.py --schematic schematic.json --pcb pcb.json --standard cispr-class-b

# Select target market (sets all applicable standards)
python3 <skill-path>/scripts/analyze_emc.py --schematic schematic.json --pcb pcb.json --market eu

# Filter by severity
python3 <skill-path>/scripts/analyze_emc.py --schematic schematic.json --pcb pcb.json --severity high

# Human-readable text output
python3 <skill-path>/scripts/analyze_emc.py --schematic schematic.json --pcb pcb.json --text

Step 3: Interpret results

Read the JSON report and incorporate findings into the design review. Each finding has a severity, rule ID, description, and actionable recommendation. See "Interpreting Results" below.

What Gets Checked

44 rule IDs across 18 categories. Each rule has a specific threshold, rationale, and source citation — see references/pcb-emc-rules.md for full details.

Advisory outputs (not findings):

• Pre-compliance test plan — frequency band prioritization, interface risk ranking, near-field probe points
• Regulatory coverage — market-to-standards mapping, coverage matrix (what the tool checks vs what requires lab testing)

Output Format

{
  "summary": {
    "total_checks": 42,
    "critical": 2, "high": 5, "medium": 8, "low": 12, "info": 15,
    "emc_risk_score": 73
  },
  "target_standard": "fcc-class-b",
  "findings": [
    {
      "category": "ground_plane",
      "severity": "CRITICAL",
      "rule_id": "GP-001",
      "title": "Signal crosses ground plane void",
      "description": "Net SPI_CLK crosses a 3.2mm gap in GND on In1.Cu",
      "components": ["U3", "U7"],
      "nets": ["SPI_CLK"],
      "recommendation": "Route around the gap, or fill the void"
    }
  ],
  "per_net_scores": [
    {"net": "SPI_CLK", "score": 67, "finding_count": 3, "rules": ["GP-001", "CK-001", "BE-001"]}
  ],
  "test_plan": {
    "frequency_bands": [{"band": "30-88 MHz", "risk_level": "high", "source_count": 12}],
    "interface_risks": [{"connector": "J1", "protocol": "USB", "risk_score": 8}],
    "probe_points": [{"ref": "L1", "x": 45.2, "y": 32.1, "reason": "switching inductor"}]
  },
  "regulatory_coverage": {
    "market": "us",
    "applicable_standards": ["FCC Part 15 Class B"],
    "coverage_matrix": [{"standard": "...", "coverage": "partial", "note": "..."}]
  }
}

Severity Levels

Risk Score

Each rule ID contributes at most 3 findings to the score (worst severity first). This prevents per-net rules like GP-001 from saturating the score on 2-layer boards. All findings are still reported — only the score is capped.

penalty = sum(worst 3 per rule × severity weight), score = max(0, 100 - penalty). Scores below 50 indicate significant EMC risk.

Interpreting Results

Ground plane findings — Any CRITICAL finding (signal crossing a void) is almost always a real problem. Fix unconditionally.

Decoupling findings — Distance-based findings have moderate false positive rates. A cap at 6mm may be fine for a low-speed IC but problematic for a 100MHz clock buffer. Use frequency context to prioritize.

I/O filtering — Highly relevant for cable-connected products. For board-to-board connections inside an enclosure, the risk is lower.

Diff pair findings — Protocol-specific skew limits are well-defined. USB HS (25ps), PCIe (5ps), Ethernet (50ps). Findings exceeding these limits are real issues.

PDN findings — Anti-resonance peaks are real and cause voltage droop. SPICE-verified findings are more accurate than analytical. If a peak is flagged, add a capacitor with SRF near the peak frequency.

Emission estimates — Order-of-magnitude estimates (±10-20 dB). Use them to prioritize frequency bands for pre-compliance testing, not to predict pass/fail.

EMC Standards

The --market flag maps markets to all applicable standards: us, eu, automotive, medical, military.

Limitations

• Cannot predict absolute emission levels better than ±10-20 dB
• Cannot account for enclosure effects (shielding, apertures, seams)
• Cannot predict cable radiation without knowing external cable routing
• Cannot replace full-wave simulation for complex geometries
• Cannot guarantee compliance — only accredited lab measurement can