Traceability is the ability to track every chip from raw wafer through fabrication, packaging, and test to the end customer, enabling quality investigation, failure analysis, and targeted recalls. Traceability levels: (1) Wafer-level—wafer ID, lot ID, process history (every tool, recipe, chamber, operator); (2) Die-level—wafer map position, probe test results, defect inspection data; (3) Package-level—package lot, assembly date, bond wire/solder type; (4) Unit-level—individual device serial number, test results, bin assignment; (5) Customer-level—ship date, destination, customer lot assignment. Traceability data flow: (1) Wafer fab—MES records every process step with tool ID, time, recipe; (2) Wafer sort—probe results linked to wafer map (x,y position); (3) Assembly—die-to-package mapping, assembly lot tracking; (4) Final test—test results per unit linked to package and die history; (5) Shipping—serialized tracking to customer. Key identifiers: (1) Lot ID—group of wafers processed together; (2) Wafer ID—unique per wafer (laser scribed); (3) Die ID—x,y coordinate on wafer; (4) Device serial—unique per packaged device (e-fuse or laser mark). Traceability systems: MES (manufacturing execution system), OCAP (out-of-control action plan), RMA (return material authorization) databases. Applications: (1) Failure analysis—trace field failure back to specific wafer, lot, process conditions; (2) Containment—when defect found, identify all potentially affected product; (3) Root cause—correlate failures with process excursions; (4) Continuous improvement—data-driven process optimization. Automotive requirements: IATF 16949 mandates full traceability, AEC-Q100 requires lot-level tracking. Recall capability: if systematic defect discovered, trace forward from process excursion to all affected chips in the field. Traceability is non-negotiable for quality-critical applications and provides the data foundation for zero-defect manufacturing programs.