Low Cycle Thermo-Mechanical Fatigue Life of Solder Joints using Cohesive Zone Model

A temperature dependent cohesive zone model considering the thermo-mechanical fatigue loadings are used to simulate and predict the failure process of solder joint interface in power electronics modules. Cohesive Zone Models (CZMs) are gaining popularity for modeling the fracture and fatigue behavior in various class of materials such as metals, polymers, ceramics, and their composite materials. Unlike the traditional fracture mechanics which considers concept of infinitesimal crack, CZMs assume a fracture process zone in which external energy is distributed in vicinity to propagating crack. In order to predict the fatigue-fracture process under thermo-mechanical cyclic loading, a damage accumulation variable is utilized. The calculation of damage is performed using a progressive mechanism, and the cohesive zone model is updated to reflect the present level of damage. The existing cohesive forces are influenced by both the current damage status and the extent of separation. Consequently, the traction-separation relationships are non-reversible and contingent on prior events. The energy expended in the cohesive zone is compared against the selected critical energy based failure criteria. This work integrates the influence of temperature on the stiffness and the fatigue fracture energy, acknowledging the high operational temperatures that the solder material endures. A numerical simulation is performed in Finite element based software along with user defined functions to evaluate the cyclic life of solder joints in power electrical interfaces under coupled thermo-mechanical loadings. The current approach presents promising prospects for modeling the failure issues commonly observed in the interfacial solder joints of power modules. Keywords: Thermo-mechanical fatigue, Solder joint interface, Cohesive zone model, Damage criteria, Finite element analysis.