From Wikipedia, the free encyclopedia - View original article
|This article needs additional citations for verification. (August 2008)|
A highly accelerated life test (HALT), is a stress testing methodology for accelerating product reliability during the engineering development process. It is commonly applied to electronic equipment and is performed to identify design weaknesses. The methodology greatly reduces the probability of in-service failures (that is, it increases the product's reliability), and decreases both monetary costs and design time.
Environmental stresses are progressively applied in a HALT procedure, eventually reaching a level significantly beyond that expected during use. Using this method, weaknesses can be identified using a small number of samples (usually between one and five.) A second function of HALT testing is to characterize the equipment under test; that is, identify the equipment's safe operating limits and design margins.
Failure rate data used to characterize any device in a product must correlate with the stress levels in the product or application.
Temperature cycling and repetitive shock, power margining and power cycling are the most common forms of failure acceleration for electronic equipment. HALT does not measure or determine equipment reliability or life expectancy but it does serve to improve the robustness of a product. It is an empirical method used across industry to identify the limiting failure modes of a product and the stresses at which these failures occur.
Once these fundamental limits of the technology have been ascertained by use of a HALT/HASS chamber and the concepts of accelerated life testing, manufacturers and design engineers can cost-effectively improve the robustness of their product for the target customer and environment in which it shall be used.*
An environmental chamber is required for successful HALT testing. A temperature ramp rate of at least 45 degrees Celsius per minute is required. Some HALT chambers can achieve closer to 60 degrees Celsius per minute. To achieve these high ramp-rates, cooling evaporation of liquid nitrogen is generally required.
A suitable chamber also has to be capable of applying vibration with a suitable profile in relation to frequency. It has to be capable of doing this at the same time that it applies temperature cycling so a chamber that can perform both is essential.
Test fixtures must transmitt random vibration to the item under test such that all areas and components are stressed to the same degree as nearly as possible. Thus a successful fixture minimizes resonance at specific frequencies. It must also be open in design or that uses forced air circulation to maximize ramp rates.
The equipment under test must operate and be monitored so that if the equipment fails under test, the failure is detected.
On military technology, HALT is conducted before qualification testing. By catching failures early, flaws are found earlier in the acceptance process, eliminating repetitive later-stage reviews.