HAST - Highly Accelerated Stress Test

HAST (Highly Accelerated Stress Test) is an accelerated aging method designed to assess the reliability of electronic components when exposed to high humidity, elevated temperature, and pressure within a sealed environment.

Unlike traditional THB (Temperature Humidity Bias) tests that operate at atmospheric pressure and require longer durations (often 500 to 1000 hours), HAST leverages pressurized chambers to significantly reduce test time, completing evaluations in just 96 to 264 hours while maintaining equivalent or greater stress levels.

HAST can be conducted in:

  • Biased mode (electrical voltage applied) — most effective in detecting latent electrical failures.

  • Unbiased mode (no voltage applied) — often used to isolate packaging or environmental issues.

How is the HAST performed?

The test follows a standardized, precise procedure to ensure consistency and repeatability:

1. Device Preparation

  • DUTs (Devices Under Test) are selected based on batch, package type, and application.

  • Mounted onto test boards or sockets compatible with HAST chambers.

  • Connection points are verified and configured based on biased or unbiased testing modes.

2. Electrical Bias Application (if applicable)

  • A continuous or pulsed voltage is applied to selected pins, often:

    • Vcc vs GND

    • I/O pins under normal operating or stress conditions

    • Gate-to-source or drain-to-source in MOSFETs or similar devices

3. Chamber Conditions Setup

Devices are placed inside a sealed and pressurized HAST chamber. Standard parameters include:

Temperature: 110 °C to 130 °C

Relative Humidity: 85% to 100% (saturated conditions)

Internal Pressure: 2 to 3 atm (28–43 psi)

Duration: 96 h, 168 h, or 264 h, depending on spec

Note: Accelerated stress is achieved through the combined action of moisture saturation, high temperature, and elevated oxygen partial pressure.

4. Real-Time Monitoring (optional)

  • Devices may be monitored in situ for current leakage, breakdown voltage, or functional behavior.

  • Optional parametric testing can be performed periodically.

5. Post-Test Evaluation

After HAST exposure, devices are:

  • Functionally tested

  • Electrically analyzed (e.g., leakage current, threshold voltage shift)

  • Inspected via:

    • Acoustic microscopy (for delamination or voids)

    • X-ray and SEM (for microcracks, corrosion)

    • Chemical decapsulation and failure analysis

What types of failures does it detect?

HAST testing accelerates and uncovers failure modes associated with extreme environmental stress:

  • Internal corrosion due to moisture ingress combined with electric fields

  • Electrochemical migration (e.g., of Cu, Ag, or Au) between close metal traces

  • Contaminant-induced leakage paths, often invisible at room conditions

  • Increased leakage current or short-circuits across insulation gaps

  • Delamination between die, mold compound, and leadframe

  • Microcracks in epoxy, solder joints, or die attach regions

  • Dielectric breakdown due to field-assisted degradation

These failure mechanisms may remain dormant under standard conditions but emerge rapidly during HAST, making it invaluable for early detection.

Related standards

HAST testing is governed and standardized by multiple industry-recognized documents:

  • JEDEC JESD22-A110 – Biased Highly Accelerated Temperature and Humidity Stress Test

  • JEDEC JESD22-A118 – Unbiased HAST for general environmental reliability

  • AEC-Q100-008 – Automotive Electronics Council test specification for HAST

  • MIL-STD-883 Method 1004.7 – For military-grade microcircuits

  • IEC 60068-2-66 – Environmental testing for electronic devices

Manufacturers often tailor the stress profile according to customer specifications or end-application environments.

Final thoughts

The Highly Accelerated Stress Test (HAST) is a powerful tool that allows manufacturers to simulate years of field exposure within a matter of days. It is indispensable for:

  • Identifying latent defects early in production

  • Ensuring packaging reliability under severe humidity and pressure

  • Complying with industry reliability standards

  • Mitigating risk and improving product longevity

In high-stakes environments, reliability equals trust, and HAST provides the foundation for both.

Purpose of the test

The HAST test is utilized to:

  • Rapidly uncover latent defects related to moisture penetration, dielectric breakdown, corrosion, and material degradation.

  • Evaluate the robustness of device packaging and encapsulation, especially for components like sensors, MEMS, SoCs, and power ICs.

  • Simulate highly stressful field conditions, far beyond typical environmental standards.

  • Verify product reliability in harsh humidity/temperature combinations.

  • Accelerate time-to-failure predictions, reducing qualification time for high-reliability applications.

  • Ensure product conformity to stringent quality and lifetime expectations across multiple industries.

Why is it necessary?

HAST plays a critical role in product validation and qualification for high-reliability markets:

  1. Significant time savings over traditional THB or field life testing

  2. Accurately replicates extreme field environments in controlled lab conditions

  3. Enables early detection of systemic weaknesses in materials, layout, or design

  4. Helps optimize process parameters, encapsulation techniques, and material selection

  5. Works as a complementary tool to HTOL, ELFR, or PTC testing for complete coverage

  6. Confirms packaging integrity, particularly in ultra-fine pitch and 3D-packaged devices

  7. Supports predictive reliability modeling, lifetime estimation, and customer assurance

In industries like automotive or aerospace, failure of components due to moisture or contamination can result in life-threatening consequences, underscoring the test’s importance.

Who uses it?

HAST is widely adopted across sectors that demand high-reliability electronics:

  • Semiconductor manufacturers and OSATs (Outsourced Semiconductor Assembly and Test providers)

  • Automotive electronics suppliers – for ECUs, sensors, SoCs, and power modules

  • Aerospace and defense industries

  • Medical device companies – for implanted or external electronics exposed to moisture

  • Telecommunication manufacturers – antennas, RF front-ends, high-frequency ICs

  • Reliability labs and quality assurance units

Practical example

Case Study: Qualification of a QFN-packaged Microcontroller for Automotive Use

Component: 32-bit microcontroller in QFN package
Application: Engine Control Unit (ECU)
Test parameters:

  • Temperature: 130 °C

  • Humidity: 85% RH

  • Pressure: 2.5 atm

  • Bias: 5V applied between Vcc and GND

  • Duration: 96 hours

Observations:

  • 2 units exhibited abnormal leakage on I/O pins

  • Acoustic microscopy revealed interfacial delamination between mold and die

  • Further decapsulation showed corrosion at bond pad–wire interface due to ionic contaminants

Corrective Actions:

  • Switched to low-hygroscopic mold compound

  • Tightened process controls for die cleaning and pre-mold drying

  • Modified layout to reduce critical spacing between vulnerable nodes