An Accelerated life Test (ALT) applies to the type of test where failure times can be accelerated by applying higher “stress” to the component or semiconductor device.
Rather than test the device at normal use conditions, Accelerated Life Testing can test the device under circumstances that are more severe than normals. These severe conditions cause the device to break down faster and fail more suddenly. The results from the ALT test can be used to pass or fail the component. In addition, the accelerated failure data can be modeled to predict device reliability at normal use conditions.
ATE test conditions are typically controlled by an Automatic Test Equipment designed for ALT and is used with environmental chambers to measure and provide high levels of temperature, voltage, pressure, vibration, cyclic rate, etc.
In accelerated life testing, stress is classified into constant stress, step stress.
In constant stress testing, each test device is measured and provided with stimuli until it fails, keeping all the stress factors at constant levels. Examples of constant stress are temperature, voltage and current.
In step stress, a device is subjected to successively higher levels of stress. At first, it is subjected to a specified constant stress for a specified length of time. If it does no: fail, it is subjected to a higher stress level for a specified time.
ALT can both detect the possible failure modes and mechanisms and to quantitatively evaluate the characterization of the semiconductor that might lead to failures. If properly designed and the test is carefully conducted, Accelerated Life Tests provide a consistent basis for obtaining the ultimate information of the reliability of a product – the probability of failure.
Quantitive vs Qualitative
Qualitative accelerated tests (such as HALT) are used primarily to show probable failure modes for the device so that product engineers can improve the reliability of the product design.
Qualitative accelerated life tests are performed on devices put through an individual stress test, multiple stresses. In the event that device survives, it passes the test. Otherwise, appropriate actions will undoubtedly be taken to improve the product’s design in order to get rid of the cause of failure.
Quantitative accelerated life tests (QALT) are designed to produce the data required for accelerated life data analysis.
Quantitative accelerated life testing unlike the qualitative testing methods described earlier, consists of tests designed to quantify the life characteristics of the product, component or system under normal use conditions, and thereby provide reliability information. Reliability information can include the probability of failure of the product under use conditions, mean life under use conditions, and projected returns and warranty costs. It can also be used to assist in the performance of risk assessments, design comparisons, etc.