trend detection

**Trend detection** is the **SPC analysis of sustained directional movement in process data over time** - it identifies gradual deterioration or drift before points exceed formal control limits. **What Is Trend detection?** - **Definition**: Detection of monotonic upward or downward sequences that indicate non-random process behavior. - **Signal Context**: Often appears as consecutive increases, consecutive decreases, or persistent slope in subgroup means. - **Typical Sources**: Tool wear, sensor aging, chemistry depletion, and thermal control drift. - **Rule Integration**: Implemented through Nelson or Western-style trend rules plus slope analytics. **Why Trend detection Matters** - **Early Warning**: Captures instability before out-of-control limit violations occur. - **Yield Protection**: Prevents gradual center shift from becoming large-scale specification failure. - **Maintenance Timing**: Trend slope gives practical lead time for planned intervention. - **Capacity Stability**: Reduces unplanned stops caused by late discovery of degrading conditions. - **Process Learning**: Longitudinal trends expose recurring degradation mechanisms by tool and chamber. **How It Is Used in Practice** - **Chart Segmentation**: Monitor trends by tool, chamber, product family, and shift to isolate true causes. - **Threshold Policy**: Define trigger criteria for consecutive movement or slope magnitude. - **Action Workflow**: Link trend alerts to inspection, recalibration, and preventive maintenance tasks. Trend detection is **a critical proactive control mechanism in SPC programs** - recognizing directional movement early turns slow failure patterns into manageable planned corrections.