Quality Metric
Statistical measurements represent the number of defective units that bypass inspection processes and reach the end customer for every million units produced. A parts per million escape rate acts as a performance indicator for the effectiveness of an automated optical inspection or X-ray system. A low value indicates that the screening process is successfully identifying solder bridges and missing components.
Calculating this figure requires accurate data from both the factory floor and field return reports.
Calculation Method
Dividing the number of faulty items found by the customer by the total quantity shipped provides the basis for the score. Because the parts per million escape rate focuses on what was missed, it highlights gaps in the test coverage or human error in manual review stations. If a factory ships one hundred thousand boards and the customer finds two defects, the rate is twenty.
This data forces a review of the inspection limits.
Process Improvement
Analysis of the specific defects that escaped leads to adjustments in the lighting or algorithms of the inspection machines. Reducing the parts per million escape rate often involves tightening the criteria for false calls or adding redundant test steps like functional verification. The value provides a measure of the risk inherent in the current manufacturing flow.
Stable processes maintain a consistent rate over time. Suppliers use these figures to demonstrate their reliability during contract negotiations.
