Screening effectiveness
Based on the accumulation of test data from previous product screenings, test projects that are effective in eliminating early failure products (higher elimination rate under non-destructive stress) are determined. Test projects with extremely low screening elimination rates or that cannot screen out defective products at all should not be included in the screening test. To evaluate whether a screening program is effective, it can be measured by indicators such as screening effect and screening elimination rate. The effectiveness of screening mainly depends on whether the selection of screening items and stress is reasonable. It is not easy to obtain a completely ideal screening effect. Similarly, to obtain data on the screening effect, a large number of preliminary experiments are required. People have accumulated rich experience through a large number of experiments. These practical experiences have now been summarized and formed into standards. Therefore, generally products are screened according to the screening requirements stipulated in their quality and reliability assurance levels. However, when a certain product often fails the quality consistency test after screening, you should consider whether the screening plan adopted is appropriate.
Determination principles for screening test stress
The stress conditions of the screening test are first of all non-destructive, that is, the quality and reliability of the product cannot be affected by screening, but the test stress cannot be too low, otherwise it will not play a screening role. In principle, the determination of screening items and stress conditions should be based on corresponding standards. For newly developed component products, the size of the screening test stress can be determined through bottom-up tests or on-site use information of similar products. The main principles for selecting screening stress are:
When screening stress types, stresses that can trigger early failure should be selected, which should be determined based on the information and failure mechanisms available for different products;
The screening stress should be aimed at stimulating early failure, so that various hidden dangers and defects of the product can be exposed as soon as possible;
Screening stress should not cause normal product failure;
After the screening stress is removed, the product should not leave residual stress or affect the service life of the product;
The duration of the stress screening test should be such that it can fully expose early failures.
The following table is a correlation analysis of common defects in integrated circuits and the main screening test items:
Screening test methods
Screening tests can be divided into conventional screening (such as sealing screening) and special environmental screening (such as radiation resistance, salt spray, etc.). We mainly introduce conventional screening methods. Conventional screening methods mainly include the following:
1. Check and filter
Inspection and screening can take the form of microscopic examination, infrared screening, or X-ray screening. Infrared screening can eliminate devices with serious thermal defects in the body or on the surface. X-ray screening is mainly used to check whether there are foreign objects in the tube shell, defects in the chip mounting, bonding or packaging process, and chip cracks.
2. Sealing screening (such as bubble method, helium mass spectrometer method, radioactive gas, tracer leak detection method), used to eliminate defects in the tube shell and sealing process (such as cracks, tiny leaks, pores and packaging alignment) Not good).
3. Environmental stress screening (such as vibration acceleration, impact acceleration, centrifugal acceleration, temperature cycle and thermal shock, etc.);
4. Lifespan screening (high temperature storage, low temperature storage, mature screening, precision screening, linear discrimination);
5. Electrical test screening (supplementary means for transistors).
In practice, a combination of physical screening (non-destructive) and aging screening (destructive) is often used. Laolian screening has good effect but high cost, while physical screening has low cost but poor effect.
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