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What is HAST (highly accelerated stress test)?

A test that applies bias in pressurized steam at high humidity and temperatures above 100 °C to evaluate moisture resistance quickly. For example, 96 hours at 130 °C/85% RH is treated as equivalent to 1000 hours of temperature-humidity-bias testing (THB) at 85 °C/85% RH.

Japanese name: HAST(高度加速ストレス試験)

HAST (highly accelerated stress test) appears in 4 practice questions across 2 topics, including Reliability, Automotive Semiconductors and Functional Safety.

Field: Automotive Semiconductors and Functional Safety

Try it: questions about HAST (highly accelerated stress test)

In qualification of automotive ICs, what is the main reason HAST (a biased test in pressurized water vapor at around 130 °C and 85% RH) is sometimes used instead of the temperature humidity bias test (THB) run at 85 °C and 85% RH for 1000 hours?

  1. AIt accelerates failures such as corrosion caused by moisture ingress, shortening a 1000-hour test to around 100 hours
  2. BIt allows evaluation of soft errors caused by cosmic rays instead of moisture-induced failures
  3. CRaising the temperature drives out moisture, allowing lifetime to be evaluated in a dry state
Show answer and explanation

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.

Which failures are mainly evaluated by temperature-humidity-bias tests (THB and HAST)?

  1. ASoft errors caused by cosmic rays
  2. BClock delay
  3. CElectrode corrosion and increased leakage current due to moisture ingress
Show answer and explanation

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.

HAST (highly accelerated stress test) in the explanations

Questions that mention HAST (highly accelerated stress test) (4)

  1. In qualification of automotive ICs, what is the main reason HAST (a biased test in pressurized water vapor at around 130 °C and 85% RH) is sometimes used instead of the temperature humidity bias test (THB) run at 85 °C and 85% RH for 1000 hours?
  2. Which failures are mainly evaluated by temperature-humidity-bias tests (THB and HAST)?
  3. Among ESD (electrostatic discharge) test models, which pair correctly names "discharge when a charged person touches an IC pin" and "discharge when the IC itself is charged and a pin touches metal"?
  4. When estimating field lifetime from temperature-humidity test results, which model is commonly used to express the effect of humidity as a power of relative humidity?

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Related terms

ESD (electrostatic discharge) HBM TDDB (time-dependent dielectric breakdown) NBTI (negative bias temperature instability) Dennard scaling AEC-Q100 ASIL (Automotive Safety Integrity Level) CAN bus Diagnostic coverage ECU (electronic control unit)

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