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

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.