retest

**Retest** is **testing devices again after initial failure** — used to catch test equipment issues, marginal devices, or to verify rework effectiveness, with retest pass rates indicating overkill levels and test reliability. **What Is Retest?** - **Definition**: Re-running electrical test on previously failed devices. - **Purpose**: Catch test errors, verify rework, assess marginality. - **Retest Pass Rate**: Percentage of failures that pass on retest. - **Indicator**: High retest pass rate suggests test issues or overkill. **Why Retest Matters** - **Yield Recovery**: Recover devices that failed due to test issues. - **Overkill Detection**: High retest pass rate indicates false failures. - **Test Quality**: Measures test equipment reliability. - **Cost**: Adds test time and cost. **Retest Scenarios** - **Test Equipment Issue**: Tester malfunction causes false failures. - **Marginal Devices**: Barely fail limits, may pass on retest. - **Environmental**: Temperature or voltage variation during test. - **Post-Rework**: Verify rework was successful. **Analysis** ```python retest_pass_rate = (retest_pass / initial_fail) * 100 # High rate (>20%) suggests test issues or overkill # Low rate (<5%) suggests real failures ``` **Best Practice**: Investigate high retest pass rates to identify and fix test issues, reducing overkill and improving efficiency. Retest is **yield recovery and quality check** — recovering falsely failed devices while revealing test equipment and limit optimization opportunities.