A-Series 22×80 LTS SSD: LI 4523 Failure Analysis from MLCC Damage to SMT Calibration Drift

Overview

During LI, a late-stage label attachment and interface test process, 14 A-Series 22×80 LTS (Low Temperature Solder) SSD units failed with 4523 (LINK PM FAIL), an internal LI failure code related to link power-management behavior. Hardware confirmation showed MLCC (multilayer ceramic capacitor) short and visible MLCC damage, which indicated a true process-induced defect rather than a test false-fail. The investigation traced the defect back to SMT underfill calibration, where residual calibration liquid on the sensor surface created a height mismatch between the laser sensing reference and the nozzle contact reference.

Problem

LI testing reported a repeated 4523-class failure pattern that initially could have been interpreted as a test program issue, interface or power-management behavior, contact instability, false failure, or isolated component defect. Hardware confirmation narrowed the issue to MLCC short and visible MLCC damage, so the investigation moved upstream from LI testing into the SMT assembly process.

Data Used

• LI-stage 4523 (LINK PM FAIL) failure records
• Affected-unit list and failure distribution
• Hardware confirmation feedback
• MLCC short and visible damage observations
• SMT underfill and nozzle calibration review
• Laser sensing and nozzle contact reference-height comparison
• Follow-up defect-rate monitoring

Review Scope

• The case needed to separate a true process-induced defect from common SSD test false-fail patterns.
• The abnormality appeared downstream during LI testing, while the root cause was upstream in SMT underfill calibration.
• Manual inspection alone was not enough to prevent recurrence.
• The corrective action needed to be practical for production operators and equipment teams.
• Sensitive internal product names, customer names, line identifiers, equipment IDs, raw logs, and exact internal records cannot be published.

Approach

Connected downstream electrical symptoms with upstream process conditions by reviewing LI-stage failure behavior, confirming the issue was not a simple test interruption, tracing MLCC damage to the SMT underfill and nozzle calibration process, and supporting cross-functional discussion with quality, production, test, and equipment stakeholders.

Investigation Focus

• Reviewed LI-stage 4523 failure symptoms and hardware confirmation results.
• Confirmed that the failures were not simple test interruptions or false-fail cases.
• Traced MLCC damage back to the SMT underfill and nozzle calibration process.
• Identified residual calibration liquid on the sensor surface as the trigger for reference-height mismatch.
• Compared the laser sensing reference and nozzle contact reference logic.
• Proposed and coordinated a visualization/alarm requirement for laser/nozzle height difference as a process-control signal.
• Supported follow-up monitoring until the defect rate recovered to the normal level.

Key Investigation Choices

Methods & Tools

• Manufacturing Quality
• Root Cause Analysis
• Process Control
• Defect Prevention
• Corrective Action
• Quality Risk Reduction

Result & Impact

• Recovered to normal level
  Defect rate
• Calibration cleaning SOP reinforced and shift-level residue inspection added
  Process control
• Laser/nozzle height-difference visualization and alarm requirement proposed and coordinated
  Prevention signal

Defect rate recovered to the normal level after SOP reinforcement, shift-level residue inspection, and laser/nozzle height-difference visualization requirements. The case also moved the control point upstream from LI failure detection to SMT calibration monitoring.

Notes

• A downstream test failure can be the first visible signal of an upstream process-control problem.
• Hardware confirmation is critical when separating test false-fails from true process-induced defects.
• SOP reinforcement is useful, but hidden calibration drift needs visual or alarm-based control.
• The most valuable quality improvements often move detection upstream, before the defect reaches final test.
• Manufacturing digitalization is most useful when it turns hard-to-see process variation into visible control points.