8.16 Root Cause Analysis (RCA) & CAPA

The management of Non-Conforming Material (NCM) and the Corrective and Preventive Action (CAPA) system form the "immune system" of the factory.

8.16.1 The Fishbone (Ishikawa) Diagram

When a defect occurs, the investigation must look at six distinct categories ("The 6 Ms") to avoid blaming the operator.

1. Man (People): Training, fatigue.
2. Machine: Calibration, wear, settings.
3. Material: Component vendors, shelf life.
4. Method: Work instructions, routing.
5. Measurement: Gauge error, lighting.
6. Mother Nature (Environment): Humidity, temperature.

8.16.2 The 5 Whys

Drill down from the symptom to the systemic root cause.

• Problem: Solder bridge.
• Why? Paste volume too high.
• Why? Stencil aperture too large.
• Why? Designed 1:1 with pad.
• Why (Root)? DFM Guidelines did not specify aperture reduction for this pitch.

8.16.3 CAPA (Corrective & Preventive Action)

• Correction: Fix the immediate problem (rework).
• Corrective Action: Eliminate the root cause to prevent recurrence (fix the stencil).
• Verification of Effectiveness: Audit the process 30-60 days later. If the problem returned, the CAPA failed.

Final Checklist