Although the high and low temperature test chamber environmental test and reliability test are closely related, they are different in the test purpose, the amount of environmental stress used, the selection criteria of environmental force value, the test type, the test time, and the test termination criterion.
1. High and low temperature test chamber test purpose
The environmental test examines the adaptability of the product to the environment, determines whether the design of the product's environmental adaptability meets the contract requirements, and provides decision-making basis for acceptance and rejection. The reliability test is to quantitatively evaluate the reliability of the product, that is, the probability of the product to complete the specified function within the specified time under specified environmental conditions.
2. The amount of environmental stress used in the high and low temperature test chamber
As far as environmental tests are concerned, 19 test items are specified in GJB 150, 20 items are specified in MIL-STD-810 D, and 810F has increased to 24 test items, including the more important environmental impact on products. Such as: temperature, humidity, salt spray, vibration, shock, pressure, solar radiation, sand, rain, etc.
The test items should be selected according to their future use environmental conditions and the degree of impact, and generally more than 10 environmental stresses should be investigated. The reliability test only combines the comprehensive environmental stress (temperature, humidity, vibration) with the electrical stress due to the comprehensive simulation. It can be seen that the number of environmental stresses selected for the high and low temperature test chamber reliability test is much less than that of the environmental test.
3. Selection criteria for environmental stress value of high and low temperature test chamber
The environmental test basically adopts extreme conditions, and replaces mild with harsh, that is, the slightly extreme environmental conditions that the product may encounter in the life cycle are used as test conditions. Many tests are destructive and generally do not need to simulate the working state of the product during the test.
The reliability test adopts the actual effect test, that is, the main environmental conditions and their dynamic change process encountered in the process of storage, transportation and use are realistically simulated. GJB-889 and the corresponding MIL-STD-781D stipulate a set of methods to determine the environmental profile according to the task profile, and then simplify the environmental profile into a test profile to conduct long-term reliability assessment of the product.
The high and low temperature test chamber reliability test generally does not cause damage to the product. It needs to simulate the working state of the product. Most of the test conditions used simulate the milder stress environments often encountered in operation. Therefore its value is much lower than the environmental test.
4. Test type of high and low temperature test chamber
Environmental tests usually use single-factor tests and multi-factor combination tests, which act on the product in a certain order. Reliability tests mostly use comprehensive stress tests. Multiple environmental stresses are applied to the sample in the same space and at the same time, which more realistically simulates the impact of environmental conditions.
In order to improve the accuracy and reliability of the test results, environmental testing has also begun to focus on the development of comprehensive testing, and actively develop large-scale multi-functional environmental testing equipment that can simultaneously apply temperature, humidity, vibration, radiation, sand, wind, rain and other stresses.
5. Test time of high and low temperature test chamber
In the environmental test, the time of each test basically depends on the selected test and the specific test procedure, but there are some differences due to the different time required for performance testing at each stage, and the test time is much shorter than that of the reliability test. The reliability test time of the high and low temperature test chamber depends on the reliability index value to be verified and the selected statistical test scheme, as well as the quality of the product itself. The time cannot be determined. If the total number of hours of the tested product reaches the specified value or the acceptance can be made, the judgment of rejection is.
6. Test termination criterion for high and low temperature test chamber
Failures are not allowed in the environmental test. Once the product fails, it is considered that it cannot pass the test, the test is stopped and the failure analysis is carried out, and corrective measures are taken to improve the design. This is the TAAF process for environmental testing.
The reliability test is a test that expresses the result with a certain statistical probability, and the allowable number of failures is determined according to the quantitative reliability index required by the contract and the selected statistical scheme. The test must be carried out until the specified total number of hours is reached before it can be stopped. A Failure Reporting, Analysis and Corrective Action System (FRACAS) shall be established throughout the test.