Highly accelerated life testing (HALT) is a method used to test solid-state electronics and determine failure modes, operational limits, and destruct limits and design weaknesses over rapid test time. This test method differs significantly from reliability tests. HALT testing does not determine a statistical reliability or determine an estimated life. Reliability tests such as accelerated reliability testing or accelerated life testing are used to calculate reliability performance metrics such as mean time between failures.
The power of HALT testing is derived from a simple basic principle – if you wish to fatigue a component, semiconductor IC, subassembly or finished product you can stress it with lower levels of stress for a lot of cycles, or use a higher level of stress for a fewer number of cycles.
In a HALT test, every stimulus of potential value is used to find the weak links in the design and fabrication processes of a product during the design phase. These stimuli may include vibration, thermal cycling, burn-in, voltage, humidity, and whatever else will expose relevant weaknesses.
A HALT typically takes two or three days. Also, a HALT will identify several failure modes providing significant information for the design engineers to improve the product. Typical reliability tests will provide one or two failure modes, if the product fails at all.
Traditional reliability tests such as accelerated reliability testing (ART) and accelerated life testing (ALT) use environmental stresses applied uniformly and consistently to expose failures and to develop acceleration factors to equate the stresses applied in a test to reliability or to life in the actual customer use environment.
Rather than applying low stress levels over long durations, HALT testing applies high stress levels for short durations well beyond the expected field environment.
Highly Accelerated life testing is often used during the design phase of a system by applying increased stress to a product in incremental steps increasing variables until anomalies occur and fixing faults, if discovered, to improve the design. This process continues beyond the limits of normal shipping, storage and operational conditions normally encountered in the fields until the destruction limits of the material in the product are reached.
Because of the elevated temperature, the lifetime of the system is accelerated (hence the name) according to the Arrhenius equation, which calculates the speeding-up of chemical reactions under conditions of higher temperature. Unlike a traditional MTBF demonstration, which involves a basic grasp of statistics, a highly accelerated life test involves a very sophisticated understanding of the system under test and the specifics of running a valid HALT test.
With HALT, acceleration factors are difficult if not impossible to determine, and test time cannot be correlated to customer use time.
To consider the meaning of HALT from another angle, let’s analyze what HALT cannot do:
- HALT is not intended to find and fix all failures. The failures that affect product reliability should be resolved and an awareness developed of failure modes at stress conditions well beyond the design specification limits.
- HALT is not a qualification test.
- HALT has no pass/fail criteria