Overview
IEC 60749-33:2004 defines the unbiased autoclave method for accelerated moisture-resistance testing of non-hermetic semiconductor packages. The test uses a condensing, high-humidity, elevated-pressure and temperature environment to accelerate moisture ingress through encapsulants or along interfaces, exposing package weaknesses such as delamination and metallization corrosion. The method is destructive and intended for qualification, material or design change evaluation and failure-mode identification.
Key Topics
- Purpose and scope: Evaluates moisture-resistance integrity of non-hermetic solid-state devices using moisture-condensing or saturated steam environments. Not intended for laminate or tape-based packages.
- Test apparatus: Requires a pressure-capable chamber that maintains specified temperature and relative humidity under pressure. A permanent temperature profile record is recommended to verify stress conditions.
- Specimen placement and handling:
- Devices under stress shall be at least 30 mm from the internal chamber surface and not subjected to direct radiant heat.
- Hand coverings and contamination control are mandatory to avoid test artifacts.
- Water and contamination control: Distilled or deionized water must be used; ionic contamination of the chamber and fixtures must be controlled and frequent cleaning is recommended.
- Test conditions and duration: Test conditions combine temperature, relative humidity, vapor pressure and duration. A 96 h duration is typical, but the exact duration is specified by the relevant qualification or product specification. The test clock starts when set points are reached and stops at the start of ramp-down.
- Electrical measurements and timing:
- Electrical tests are performed no sooner than 2 h and no later than 48 h after ramp-down (room-temperature tests first).
- Use of sealed moisture-barrier bags can slow moisture loss and extend the allowable readout window (extensions are defined in the standard).
- Failure criteria: A device is a failure if parametric limits are exceeded or functionality cannot be demonstrated under nominal and worst-case conditions as defined in the relevant specification. Exclude failures due to external package damage that are artifacts of the test method.
- Safety and cautions: The standard warns that autoclave stress can produce failure mechanisms not representative of field use (e.g., plastic swelling, reduced glass transition temperature) and advises caution when extrapolating results.
Applications
- Qualification of new package designs and materials (mold compound, die passivation).
- Robustness testing after material or process changes.
- Root-cause analysis to identify moisture-induced internal failures.
Related Standards
- IEC 60749-24 - Accelerated moisture resistance: Unbiased HAST (referenced as an alternative test; unbiased HAST results take priority when both are applied).
- Other parts of the IEC 60749 series covering mechanical and climatic test methods for semiconductor devices.
This summary highlights practical elements from IEC 60749-33:2004 to support test planning, apparatus selection and interpretation of results. Consult the full standard for precise tables, tolerances and normative requirements before test execution.
Open preview (PDF)Semiconductor devices - Mechanical and climatic test methods - Part 33: Accelerated moisture resistance - Unbiased autoclave
