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HALT (Highly Accelerated Life Test) is a process that exposes reliability defects early in the product development cycle and can result in mature, robust products at introduction. Traditional design verification methods are ineffective compared to HALT. HALT employs combined thermal and 6 Degree of Freedom vibration stresses that quickly uncover design flaws and latent defects that would later appear as field failures and warranty problems. Products under test are powered-up and monitored throughout the process. HALT is an engineering tool that identifies the operational and destruct limits of designs, enabling improvement.
HASS (Highly Accelerated Stress Screening) precipitates latent defects in manufacturing and dramatically reduces associated field failures. Some companies have also used HASS to reduce manufacturing cycle times and improve inventory turns by eliminating "Burn In". HASS can identify problems caused by substituting components on an existing design. Development of a HASS profile requires previous HALT results, other product-specific information and a validation exercise. Products under test are powered-up and monitored throughout the process. HASS is a manufacturing process that utilizes similar equipment to HALT.
HALT has been successfully applied to a wide variety of electrical and electro-mechanical products in many different industries. HALT can be used to determine the operating and destruct limits of most electronic and electro-mechanical assemblies. Root cause identification of the failure modes and elimination of those modes will always result in a more robust, reliable product.
Every product has a set of failure modes built into the design and determined by the manufacturing process. These failure modes will all eventually appear in the field. HALT stresses only accelerate the onset of these same failures. Some new ESPEC Qualmark customers have "explained away" HALT failures only to have the same failure modes appear later as high field returns. HALT is an engineering tool and engineers determine which stresses to apply to a product in order to avoid the application of stresses that would never occur in use.
Companies with ESPEC Qualmark chambers at their facilities, test all stages: Alpha, beta, and final production. The earlier in the development cycle that a failure mode can be identified, the better.
Stop the test.
Record the failure mode and stress level.
Use isolation techniques to identify failure location.
Document failure location. Perform root cause analysis. Repair/replace the failed component or create a "work around" for the failure mode. Resume testing to induce additional failures and to widen the operating margins of the product until the fundamental limit of the technology is reached.
HALT is a life extension process, not a life prediction mechanism. Other methods must be used to predict product life.
Several companies have specifications in place that allow the use of HALT in lieu of other tests. However, if such a specification is not appropriate, HALT still reduces the time required to perform other testing and typically reduces the time to market. HALT eliminates failure modes resulting in a more robust product earlier.
If humidity testing is a requirement for a product design, it should be performed separately. Humidity is considered to be a very weak stress for electronic and electro-mechanical systems. Humidity testing is also a longer-term test and may only begin a process that results in defects occurring much later. Humidity testing is only practical at temperatures above 0 degrees C.
Certain failures will only occur during operation. HALT and HASS stresses can precipitate intermittent failures that can only be detected if the unit is operating and monitored. Part of the HALT process is to identify the operating limits of thermal, vibration and other stresses. These limits can only be accurately determined when an monitored operating unit begins to malfunction.
HALT stresses products beyond their specifications, significantly accelerating the time to failure for existing product failure modes. Tests take about 3-5 days. Traditional methods simulate field environments and test products within their specifications.
- Generally, products are unpowered and unmonitored.
- Take weeks to months to perform.
- May or may not identify latent failure modes.
The overstress applied during HALT accelerates the onset of failure modes that may occur infrequently in a large population of units operating within specified limits. Testing beyond the specifications identifies the operating and destruct margins of the product or component. A product with inadequate operating margin beyond the specification will experience excessive field returns.
It is usually advantageous to test the complete system. However, in some cases, the operating and destruct limits of individual components or subassemblies may be so different that the weaker stresses must be isolated for a successful HALT on the others.
HALT uses combined step stresses to identify failure modes and find operating/destruct limits. The product must be powered up and monitored throughout testing. When a failure mode or operating limit is identified, the engineer must determine root cause.
Your product should be stressed, in a stepwise fashion, until you reach the "Fundamental Limit of the Technology". Component level - The fundamental limit of technology is the operating or destruct limit. System Level - The point at which the system is so far outside its operating limits that it fails catastrophically or cannot be operated, even when stresses are reduced or removed.
HALT eliminates failure modes that would have reduced the MTBF. Therefore, HALT directly improves product MTBF in most cases. However, other tools and methods are required to make an estimate of MTBF.
HALT is not a test that is designed to replace traditional design verification testing. However, we recommend that companies perform a complete assessment of their design assurance test program after HALT has been successfully integrated in the development process. At that time, it will become apparent if there are other tests that may be modified or eliminated.