6 Reliability of Electronic Packaging

Electronic packages and assemblies are designed and manufactured with specific objectives with regard to their performance in the user environment. Product expected life is selected at the design stage depending on the use/application environment in which it will operate and the consumer. It also determines the materials' choices and the system robustness. The materials and the processes are selected on the basis of these. Electronic products are categorized on the basis of the industry segments they serve. Table 6.1 gives typical environments and expected product lives for different product categories.

As can be seen from Table 6.1, it contains only the temperature extremities. Temperature is not the only stress to which a product is subjected to in its life cycle. Stress is defined as an applied force or forces that tend to produce deformation or degradation. The deformation thus produced is called a strain. Again, there are deformations that are reversible and irreversible after the removal of the imposed stress. Strains that do not revert to their original state are termed inelastic or plastic strains and those that revert are called elastic strains.