A reliability test that applies voltage in a hot, humid environment, typically 85 °C/85% RH, to evaluate corrosion and increased leakage caused by moisture entering the package. It is also called the 85/85 test.
Japanese name: 高温高湿バイアス試験(THB)
THB (temperature-humidity-bias test) appears in 3 practice questions across 2 topics, including Reliability, Automotive Semiconductors and Functional Safety.
Field: Reliability
THB stands for temperature humidity bias. Products are placed in a temperature-humidity chamber at atmospheric pressure, typically at 85 °C and 85% RH, and held for about 1000 hours with voltage applied. Plastic packages sealed with mold compound are not hermetic, so moisture slowly reaches the die through the mold compound and along the interfaces between the compound and the lead frame. When voltage is present there, electrochemical reactions proceed and failures are accelerated. Electrical characteristics are measured before, during and after the test to check for rising leakage current or functional failures.
The main target is corrosion of aluminum bond pads and interconnects. When chloride or other ionic contaminants dissolve in the moisture, corrosion progresses much faster. Between adjacent biased conductors, ion migration can also occur: metal dissolves as ions, migrates and deposits as dendrites that cause shorts. Cracks and defects in the passivation film become paths for moisture, and delamination between mold compound and the die or lead frame speeds its entry. Increased leakage current along the die surface or package surface is also evaluated.
HAST (highly accelerated stress test) uses unsaturated steam at about 110 to 130 °C in a pressure vessel, accelerating humidity-driven failures more strongly than THB. The commonly used HAST at 130 °C/85% RH for 96 hours serves as a substitute for THB at 85 °C/85% RH for 1000 hours. HAST gives results quickly, but its higher temperature can change mold compound properties and cause failures that would not occur in service. THB runs at a lower temperature closer to real environments, so it takes longer. Which one is used depends on the applicable standard and agreements with the customer.
Bias is applied so that as much voltage as possible appears between adjacent pins while power dissipation stays low. If the die heats up, its surface temperature rises and the local relative humidity falls, making moisture-driven failures less likely. Methods such as alternating supply and ground across the pins or applying voltage intermittently are therefore used. To estimate field life from the results, models such as Peck's model are used, expressing the humidity term as a power of relative humidity (exponent around 3) and the temperature term in Arrhenius form.
Answer: A. It accelerates failures such as corrosion caused by moisture ingress, shortening a 1000-hour test to around 100 hours
HAST (Highly Accelerated Stress Test) is a method that tests at temperatures above 100 °C under pressure while maintaining high humidity. Raising the temperature and water vapor pressure speeds the movement of moisture through the package mold compound to the chip, accelerating electrode corrosion, increased leakage current and similar failures. For example, it is common to run about 96 hours at 130 °C and 85% RH as an evaluation equivalent to 1000 hours at 85 °C and 85% RH. It has nothing to do with evaluating soft errors or dry conditions.
Answer: C. Electrode corrosion and increased leakage current due to moisture ingress
Applying bias in hot, humid conditions lets moisture and ionic impurities that penetrate the package corrode aluminum pads and drive ion migration, increasing leakage or causing opens. THB runs at 85 °C/85% RH for about 1,000 hours, while HAST uses pressurized steam around 130 °C to accelerate moisture ingress, evaluating humidity resistance in roughly 100 hours. Soft errors and clock delays are targets of other tests.
It refers to test conditions of 85 °C and 85% relative humidity. THB is often run for about 1000 hours under these conditions with voltage applied, which is why it is also called the 85/85 test.
Both apply voltage at high temperature and humidity, but THB runs at 85 °C and atmospheric pressure for about 1000 hours, while HAST uses pressurized steam at about 110 to 130 °C to reach a comparable evaluation in about 100 to 300 hours.
If the die heats up, it drives moisture away and lowers the relative humidity at its surface, making humidity-driven corrosion and ion migration less likely. Bias conditions are chosen to apply voltage while keeping self-heating small.
THB runs at 85 °C/85% RH for about 1,000 hours, while HAST uses pressurized steam around 130 °C to accelerate moisture ingress, evaluating humidity resistance in roughly 100 hours.
Which failures are mainly evaluated by temperature-humidity…The test that applies humidity and voltage together is the temperature-humidity-bias test (THB).
Which stress is applied in HTOL but not in a high-temperatu…As an Amazon Associate I earn from qualifying purchases.
HAST (highly accelerated stress test) HTOL (high-temperature operating life test) High-temperature storage test (HTS) TDDB (time-dependent dielectric breakdown) Electromigration Nonvolatile memory Arrhenius model Bathtub curve ESD (electrostatic discharge) FIT rate