ABSTRACT
The mechanical analysis techniques described in Chapter 4 explained the calculation of the stress and strain due to dynamic and static loads. Although in some cases the developed stress and strain could be compared to static material properties (see 4.8), usually fatigue is the governing factor in electronic packaging analysis. Fatigue is the "failure of a material by cracking resulting from repeated or cyclic stress" [48]. When the fatigue of the materials is compared to the cyclic loads expected in the operational, storage, and test environments, the expected life can be determined. Sources of these cyclic loads include the following:
• Vibration
• Repeated mechanical shock
• Acoustic noise
• Thermal cycling
• Temperature extremes
For electronic packaging configurations, much of the life analysis activity is concentrated on interconnections (solder joints, leads, plated-through holes, etc.), although concern must also be directed to chassis and other structural areas.
