Meaning
Economic waste occurs when functional units are incorrectly rejected by automated test equipment due to measurement errors or overly tight guard bands. Within a production environment, false fail yield loss represents the percentage of total production that is scrapped or sent for unnecessary repair despite meeting all design specifications. This phenomenon increases the cost per good unit and can hide the actual performance of the fabrication process.
Economic Impact
Financial consequences of high rejection rates include the direct cost of materials and the indirect cost of technician time spent on re-testing. Manufacturers often find that false fail yield loss accounts for a significant portion of total production variance. Identifying these errors prevents the disposal of high value assemblies that are actually within tolerance.
Debugging Effort
Root cause analysis of a high failure rate begins with the calibration of the test probe and the verification of the software limits. If the test fixture introduces parasitic capacitance or inductance, the resulting measurements will deviate from the actual component values. Correcting these mechanical or electrical offsets allows the yield to return to its expected statistical baseline.
Engineers often use a golden unit with known properties to verify that the tester is not producing artificial errors.
Process Refinement
Adjusting the guard bands requires a balance between the risk of shipping a bad unit and the risk of rejecting a good one. Data from the test station is compared against laboratory benchmarks to ensure the production environment matches the design intent.
