- 5. Environmental Stress Screening
- 5.1 The Environment
- 5.1.1 Temperature Tests
- 5.1.2 Atmospheric
- 5.1.3 Radiation
- 5.1.4 Dynamic Testing
- 5.2 The Objective of ESS
- 5.2.1 Burn-in
- 5.3 Application of ESS in Manufacturing flow
- 5.4 ESS Implementation:
- 5.4.1 Types of Failures detectable by various environments
- 5.4.2 Differences in the screening of components and equipment
- 5.4.3 Design of Screens:
- 5.4.4 Effect of Temperature and Humidity on some electronic components
- 5.4.5 Reduction or Elimination of ESS
- 5.5 Case study
- 5.6 Screening Effectiveness
5. Environmental Stress Screening
5.1. The Environment:
Reliability of all equipment produced depends upon the environment in which these are required to function and therefore the testing of equipment during design and production will have to take into account the environment in which the equipment are likely to function. Every product will have to go through the following environments.
1. Storage environment
2. Handling and shipping environment
3. Operating environment
Further, the environmental stresses may be due to
1. ”Natural” - i.e. determined by the general Geographic region and local climatic conditions.
2. ”Induced” - i.e. created by man either directly or indirectly such as the mechanical stresses experienced during handling and transportation environment.
Any product often needs to be stored before being issued to the customer (or the next stage of operation). Therefore, the environment, in which the product is stored has an impact on the reliability of the product. The storage environment is determined mainly by temperature, salt fog and humidity for most electronic components/products.
The service and transportation environment consists of Vibration, Shock, Bump and Acceleration which are mostly man made and many of which can be severe enough to damage the equipment. Given below are various types of environmental tests that a product can be tested against during development / manufacture.
Figure below gives some of the frequently used environmental tests on electronic products. However, the chart is not exhaustive.
5.1.1 Temperature tests:
Temperature tests are conducted using ‘Hot and Cold’ chamber. The temperature applied ranges from -500C to about 750C for electronic equipment. For electronic components the upper limit on temperature may be 1250C or even more depending on the type of component being tested e.g. Bipolar, CMOS etc. and the type of test being conducted, i.e. ALT, RET or ESS. However, the specific temperature limits are to be workedout depending upon the nature of the product being tested. The effects of temperature cycling on the test specimen are
1. Solder joint fatigue failure
2. CTE mismatch
3. Embrittlement of materials
4. Parameter changes
The corrective actions include use of better materials, components and improving the manufacturing process.