attributes control charts

**Attributes control charts** is the **SPC chart family for discrete count or proportion data such as defectives and defect counts** - they are used when continuous metrology is unavailable or impractical at required sampling volume. **What Is Attributes control charts?** - **Definition**: Charts that monitor binary outcomes or event counts rather than measured magnitudes. - **Common Types**: P chart, np chart, c chart, and u chart. - **Data Examples**: Pass-fail results, defect counts per wafer, and nonconforming lot proportions. - **Statistical Basis**: Uses binomial or Poisson assumptions with sample-size-aware limit calculation. **Why Attributes control charts Matters** - **Operational Practicality**: Supports high-throughput monitoring where detailed measurement is costly. - **Quality Visibility**: Provides direct signal of nonconformance trends and defect burden. - **Wide Applicability**: Useful across inspection stations and reliability screening stages. - **Decision Support**: Enables rapid containment actions on rising defective rates. - **Complementary Role**: Works with variables charts to provide fuller quality-control coverage. **How It Is Used in Practice** - **Chart-Type Matching**: Choose chart based on whether data represents defectives, defects, fixed sample size, or varying sample size. - **Limit Validation**: Recompute limits when sampling plan or baseline defect level changes. - **Response Planning**: Link attribute-chart alarms to containment and RCA workflows. Attributes control charts are **a core SPC option for discrete quality monitoring** - when configured correctly, they provide scalable detection of quality deterioration in production environments.