Highly Accelerated Life Test

A Highly Accelerated Life Test (English for highly accelerated life cycle test ', abbreviated as STOP ) or accelerated aging test is a method with the aim preferably electronic and electromechanical assemblies or suspend the development stage of accelerated aging in order to discover vulnerabilities and design errors.

Target

The objective of HALT is primarily the finding vulnerabilities in device design and manufacturing process within a very short time and by a small number of prototypes. This is accomplished by an extreme acceleration of the aging process and damage by changes in temperature and vibration, making failures occur early and weaknesses are made ​​recognizable. The thermal and mechanical stress here ranges far beyond the limits specified in the product to be tested out. It is assumed that the error patterns that occur in the STOP are the same as those observed in the field later. Any such uncovered vulnerability thus offers the opportunity to improve the device design or the production process. In this way the robustness of the product is increased, and thus its reliability. Furthermore, shortening development time by the STOP and ultimately reduce costs.

Equipment

For a special HALT HALT test chambers are used, in which the DUT can be fixed to a vibrating table. The inspection table can be excited by means of compressed air-operated hammers in six degrees of freedom. The chambers have a temperature range of -100 to 250 ° C, with possible temperature gradient from 2 to 80 K / min. This is accomplished with strong electric heating elements and a nitrogen cooling. So that the thermal energy as efficiently as possible to act on the test piece, this is passed by means Luftleitschläuchen. In Table 1, typical technical parameters of a HALT chamber are given.

Specimens

The specimens to be used in HALT must be prepared before the test so that their operation and monitoring function from outside the HALT chamber is possible. In addition, temperature and acceleration sensors can be attached to the prototypes used to document the applied stress can. In the specimens implemented protection mechanisms need to be put out of function because otherwise protect the specimens themselves and fault patterns can not be excited for the HALT if necessary.

Method

The individual tests are described in the HALT. Occurring during the tests damage must be documented and fix, so that the test can be continued. A defect is not a termination criterion, but represents a desired intermediate result

Cold stages exam

The HALT is started with the cold stages exam because these are usually the least damaging effect on the DUT. It starts at an ambient temperature of 20 ° C, which is reduced in 10 K increments until the lower limit function ( Lower operating limit ) is achieved for the temperature. Thereafter, the lower limit destruction ( Lower Destruct limit ) is determined when this is possible. The corresponding residence time in each stage is about 10 minutes. This time is needed so that the test piece settles thermally and the function can be checked.

Heat levels exam

The heat stage testing is begun ambient temperature at 20 ° C, which is increased in 10 K increments until the upper limit function ( Upper operating limit ) the temperature is reached. Thereafter, the upper limit destruction ( Upper Destruct limit ) is determined when this is possible. The corresponding residence time in each stage is about 10 minutes. This time is needed so that the test piece settles thermally and the function can be checked.

Temperature cycling test

At the temperature cycling test is cyclically compared with the maximum possible heating and cooling power between two cutoff temperatures back and forth. The cutoff temperatures that are used in this test, based on the determined function limits ( Lower and Upper Operating Limit) the temperature levels exams. The candidate must be constantly monitored and checked for function here. Additionally it can be turned off and at the cutoff temperatures of the device under test to generate additional stress.

Vibration test

The vibration test starts at about 5 grm per step and is increased by 5 grm, to the functional and destruction limit is reached. The function of the examinee needs to be monitored throughout the test, in addition, held by a vibration acceleration sensor of the applied stress. The holding time of each stage is about 10 minutes. If a vibration level of 30 grm and higher achieved without an error image occurs, the function of the test specimen should be re- tested at lower stress levels. There is the possibility that error patterns caused by high vibration level, can only be detected at lower vibration levels.

Combined stress test

After the individual stress tests are completed, the combined stress test, which is composed of the superposition of vibration and thermal shock test, can be performed. The reason for the importance of this combined stress test is based on the fact that this will change the vibration behavior of many products with the change of temperature.

Test result and the end

A HALT provides the following parameters, based on thermal and mechanical stress, for a product:

• Lower limit function ( Lower Operating Limit)
• Upper limit function ( Upper Operating Limit)
• Lower limit destruction ( Lower Destruct Limit)
• Upper destruction limit ( Upper Destruct Limit)
• Fundamental technological limitations (Fundamental limit of Technology)

Functional and destruction limits are schematically shown in Figure 1. However, it is not always possible to identify all boundaries. In such a case, the test shall be such that any existing vulnerabilities should have been apparent.

Criticism

• There is in this method there is no match between the test loads and the subsequent real stresses of the components.
• Unlike other test methods, this testing is not standardized, so the test conditions are not independently reproducible.
• A scientific basis for the method is only conditionally.