For example, a device might fail due to an electrical mechanism caused by mechanical stress. The common failure mechanisms for semiconductors can be broken down into several main categories. Encapsulation failure . Mechanical or thermal stress and differences in the coefficient of thermal expansion between the encapsulation material and metal used for leads can cause the cracks to form. These openings let moisture enter the package when humidity is high or when the device gets exposed to flux, cleaning agents, and so on.
Chemical action can degrade the device and cause it to fail.
Improper contact between the die and substrate decreases thermal conductivity between the two. As a result, the die can overheat, which leads to stressing and cracking, and thus device failure. Thermal overstress due to high current flow, mechanical stress in the bond wire due to improper bonding, cracks at the interface between bond wire and die, electromigration of silicon, and excessive bonding pressure can each cause wire-bond failures. When a bond fails, so does the device, because one of its conductors no longer exists. Bulk-silicon defects .