What is HALT testing?
HALT, Highly Accelerated Life Testing, is a discovery test, not a pass/fail one. Temperature, vibration and the two combined are stepped well beyond the product's specification until it stops working, to find its operating and destruct limits. The weaknesses that surface are then designed out. HALT produces no reliability prediction and no MTBF figure.
What actually happens in a HALT
A HALT runs five stress steps, in this order. The methodology guide gives the full procedure.
- Cold step stress. Temperature is lowered from ambient in steps, typically 10 °C, with a dwell and a functional test at each, until the unit stops working and then until it is damaged.
- Hot step stress. The same, upward.
- Rapid thermal transitions. The product cycles between temperatures inside the limits just found, at the fastest rate the chamber can deliver, to attack differential expansion between materials.
- Vibration step stress. Six-degree-of-freedom repetitive shock vibration starts at about 5 GRMS and rises in 5 GRMS steps, with a dwell and a functional test at each level.
- Combined environment. Rapid thermal cycling and stepped vibration together, which finds failures neither stress finds alone.
Every relevant failure then gets root-cause analysis and a corrective action, and a verification HALT confirms that the margins improved.
What comes out of it: operating and destruct limits
A HALT measures two kinds of limit, for cold, heat and vibration. At an operating limit the product stops working correctly but recovers when the stress is reduced. At a destruct limit it is permanently damaged. Each fix moves the limits outward, and the gap between them and the environment the product will see in service is design margin, the real deliverable of a HALT program. Operating limit vs destruct limit explains both.
What HALT is not
- Not a qualification test. MIL-STD-810H and IEC 60068 are qualification standards: defined profiles, representative of the service environment, with a pass/fail outcome. HALT is a discovery method. Its stresses are deliberately unrepresentative, and it produces no pass. Qualification asks “does it meet the spec?”; HALT asks “how much better than the spec is it?”
- Not a reliability prediction. No acceleration factor is calculated, so HALT gives no MTBF or service-life figure. It gives measured limits and a list of weak links.
- Not a production screen. Screening every unit built is HASS, which runs inside the limits HALT finds: see What is HASS testing?
In the standards
- IPC-9592B makes HALT a requirement for power conversion devices.
- GMW8287 is GM’s guideline for HALT and HASS/HASA.
- IEST-RP-PR003 is the Institute of Environmental Sciences and Technology’s recommended practice for HALT and HASS.
The standards guide gives each one’s revision and issuer, and what it asks for.
The short answer
What is HALT testing?
Highly Accelerated Life Testing: a design-stage discovery test that steps temperature, vibration and combined stress far beyond the specification to find the product's operating and destruct limits and the weak links behind them, so they can be fixed before release. It is not a pass/fail test and does not predict MTBF.