Complex sentence: Under thermal cycling stresses are generated in the solder due to coefficient of thermal expansion mismatch this causes the solder joints to experience non-recoverable deformation via creep and plasticity that accumulates and leads to degradation and eventual fracture.
Split into simpler sentences: Under thermal cycling, stresses are generated in the solder due to coefficient of thermal expansion mismatch. This causes the solder joints to experience non-recoverable deformation via creep and plasticity that accumulates and leads to degradation and eventual fracture.