Temperature-Humidity-Bias Failure Analysis (THB FA) is the systematic investigation of semiconductor package failures that occur during or after THB/HAST reliability testing — using optical microscopy, SEM/EDS, cross-sectioning, and chemical analysis to identify the specific corrosion products, migration paths, and failure locations that caused electrical failure, enabling root cause determination and corrective action to improve package moisture reliability.

What Is THB Failure Analysis?

• Definition: The post-test examination of semiconductor packages that failed THB or HAST testing — combining non-destructive techniques (X-ray, C-SAM) with destructive analysis (decapsulation, cross-sectioning, SEM/EDS) to identify the physical and chemical evidence of moisture-induced failure mechanisms.
• Corrosion Product Identification: THB FA identifies the specific corrosion products present — green/black deposits indicate copper corrosion (Cu₂O, CuCl₂), white deposits indicate aluminum corrosion (Al(OH)₃, AlCl₃), and metallic dendrites indicate electrochemical migration.
• Migration Path Tracing: For dendritic growth failures, FA traces the dendrite path from cathode to anode — identifying the moisture ingress route, the contamination source that provided mobile ions, and the conductor spacing that allowed bridging.
• Root Cause Chain: THB FA establishes the complete failure chain: moisture ingress path → contamination source → electrochemical mechanism → failure location → electrical symptom — enabling targeted corrective action.

Why THB FA Matters

• Corrective Action: Without FA, a THB failure provides no guidance for improvement — FA identifies whether the failure is due to passivation cracks, mold compound delamination, ionic contamination, or inadequate conductor spacing, each requiring different corrective actions.
• Process Improvement: FA often reveals manufacturing process issues — residual flux contamination, incomplete plasma cleaning, passivation pinholes, or mold compound voids that allowed moisture to reach the die surface.
• Material Qualification: FA results guide material selection — identifying which mold compounds, underfills, or passivation layers provide adequate moisture protection and which allow premature corrosion.
• Design Rules: FA findings feed back into design rules — establishing minimum conductor spacing, passivation thickness, and guard ring requirements to prevent moisture-induced failures in future designs.

THB FA Techniques

Common THB FA Findings

• Aluminum Bond Pad Corrosion: Green/white deposits on bond pads — caused by moisture + chloride ions penetrating through passivation cracks or mold compound delamination.
• Copper Trace Corrosion: Dark discoloration and thinning of copper traces — anodic dissolution under bias in the presence of moisture and halide contamination.
• Silver Dendrites: Metallic tree-like growths bridging conductors — silver migrates fastest of common metals, requiring careful control of silver-containing materials near biased conductors.
• Delamination-Enabled Corrosion: Corrosion concentrated at delaminated interfaces — moisture accumulates in delamination voids, creating localized corrosion cells.

THB failure analysis is the diagnostic discipline that transforms reliability test failures into actionable improvements — identifying the specific corrosion mechanisms, contamination sources, and moisture ingress paths that caused failure, enabling targeted corrective actions in package design, materials, and manufacturing processes to achieve robust moisture reliability.