Degradation Mechanism
Gradual damage caused by cyclic temperature fluctuations results in the initiation and propagation of cracks within electronic solder joints and packaging interfaces. The presence of thermal fatigue is particularly evident in power electronics where the device undergoes frequent heating and cooling during normal operation. As the materials expand and contract at different rates, the resulting strain weakens the metallic bonds.
Strain Accumulation
Each cycle adds a small amount of plastic deformation to the structure of the solder. Eventually, these tiny changes coalesce into a macroscopically visible fracture that interrupts the flow of electricity. Because thermal fatigue is a cumulative process, the time to failure depends on the temperature range and the frequency of the cycles.
Material Life
Engineers use the Coffin Manson equation to estimate the number of cycles a component can survive before breaking. This calculation accounts for the ductility of the material and the magnitude of the plastic strain.
Reliability Testing
Accelerated life tests in specialized chambers force the components through thousands of rapid temperature swings to validate the design. If a batch fails the test early, the alloy composition or the joint geometry must be revised to improve the resistance of the assembly.
