Temperature Humidity Bias

Temperature Humidity Bias (THB) is a reliability stress test that simultaneously applies elevated temperature, high humidity, and electrical bias to semiconductor packages — accelerating moisture-driven corrosion and electrochemical failure mechanisms by creating conditions (85°C, 85% RH, with voltage applied) that force moisture into the package and provide the electrochemical driving force for metal corrosion, dendritic growth, and leakage current degradation over a standard 1000-hour test duration.

What Is THB?

• Definition: A JEDEC-standardized reliability test (JESD22-A101) that subjects packaged semiconductor devices to 85°C temperature, 85% relative humidity, and applied electrical bias (typically operating voltage) for 1000 hours — the combination of heat, moisture, and voltage accelerates corrosion mechanisms that would take years to manifest in normal field conditions.
• "85/85" Test: Industry shorthand for the 85°C/85% RH conditions — the temperature accelerates chemical reaction rates (Arrhenius), the humidity provides the moisture electrolyte, and the bias provides the electrochemical driving force for metal ion migration.
• Bias Purpose: The applied voltage creates an electric field between conductors — this field drives metal ions (Cu²⁺, Ag⁺) through the moisture film from anode to cathode, causing dendritic growth, electrochemical migration, and eventual short circuits between adjacent conductors.
• 1000-Hour Standard: The standard test duration of 1000 hours at 85/85 with bias is designed to represent 10+ years of field life in typical consumer electronics environments — the acceleration factor depends on the actual field conditions (temperature, humidity, duty cycle).

Why THB Matters

• Qualification Gate: THB is a mandatory qualification test for virtually all semiconductor packages — failure to pass THB blocks product release and requires design or material changes to improve moisture resistance.
• Corrosion Detection: THB reveals corrosion vulnerabilities in metallization, bond pads, wire bonds, and package interfaces — failures appear as increased leakage current, resistance shifts, or catastrophic opens/shorts.
• Package Integrity: THB tests the effectiveness of the package's moisture barrier — mold compound, die passivation, and hermetic seals must prevent moisture from reaching the active die surface where it can cause corrosion.
• Field Reliability Correlation: THB results correlate to field reliability in humid environments — products that pass 1000-hour THB typically demonstrate acceptable field reliability in tropical and coastal climates.

THB Test Conditions

THB Failure Mechanisms

• Aluminum Corrosion: Moisture + chloride ions + bias dissolves aluminum bond pads and metallization — creating open circuits as the metal is consumed.
• Dendritic Growth: Metal ions (silver, copper) dissolve at the anode, migrate through the moisture film, and plate out at the cathode as needle-like dendrites — eventually bridging conductors and causing short circuits.
• Leakage Current: Moisture on the die surface creates conductive paths between biased conductors — leakage current increases gradually as moisture penetrates deeper into the package.
• Delamination: Moisture absorption causes mold compound to swell and delaminate from the die or lead frame — creating voids that trap moisture and accelerate corrosion.

THB is the definitive moisture-corrosion reliability test for semiconductor packages — combining temperature, humidity, and electrical bias to accelerate the electrochemical failure mechanisms that threaten long-term reliability in humid environments, serving as the mandatory qualification gate that validates package integrity and corrosion resistance for field deployment.