Finite element modeling and characterization of lead-free solder joints fatigue life during power cycling of surface mounting power devices

In this work it is developed a numerical model for thermo-mechanical fatigue of SMD chip solder joints in power converters that can be useful for reliability prediction. By this model the thermo-mechanical stress–strain distribution in the structure is studied by means of Finite Elements (FE) method and operational life of the solder joints can be calculated. As a case study the estimation of the fatigue life of lead-free solder joints in SO8-packaged power MOSFETs is investigated. A stress bench for power cycling was set up to tune the developed FE model by experimental results and dynamic thermal measurements are reported. Results obtained by either simply applying the Coffin–Manson law or also accounting for creep, depending on cycle period, are discussed.