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With the increase in the power density of power semiconductor chips, the lateral temperature gradient over the chip surface becomes more pronounced. Temperature gradients play an important role in reliability evaluation of IGBTs and have attracted great attentions. In this paper, the influence of IGBT chip temperature gradients on the crack initiation site and propagation path of the solder layer is investigated by finite-element analysis (FEA). Results indicated that the temperature gradient could influence the mechanism of solder layer fatigue. With the temperature gradient increasing, the crack initiation site shifts from the edge of solder layer to the center. The crack propagation path also changed. The fatigue mechanism of the solder layer under high temperature gradients is investigated by FEA. The inelastic strain energy density per cycle (ΔW) is found to be unequal at crack initiation and crack propagation stages. Accordingly, a novel energy-based lifetime prediction model based on Darveaux's model for solder layer fatigue of IGBTs is proposed, which takes into account the variation of ΔW within these two stages and can better characterize the processes of crack initiation and propagation in the solder layer. Subsequently, two lifetimes of IGBT modules under accelerated aging tests from the existing publications are used to verify the effectiveness of the proposed model. Finally, the accelerated aging tests were carried out to support the theoretical analysis on the direction of crack propagation under high temperature gradients. • The influence of temperature gradient on crack initiation site and propagation path is investigated by FEA • The fatigue mechanism under high temperature gradients is investigated by adding solder layer cracks with different lengths • An energy-based lifetime prediction model for solder layers of IGBT modules under high temperature gradients is proposed • ΔW is inequality in crack initiation and propagation stage [ABSTRACT FROM AUTHOR]

Reliability of bond wires in power modules has been a main subject of interest in both industry and academia. Until now, analytical modeling of thermo-mechanical stress mainly focuses on the loop height variation of bond wires instead of plastic strain, which is the key factor causing the fatigue failure. In this paper, an analytical model for analyzing plastic strain of bond wires in IGBT modules is proposed. Using a laser displacement sensor, the dynamic loop height variations of bond wires under different heating currents are experimentally measured, based on which the finite element analysis (FEA) simulation is calibrated and verified to reveal the actual thermo-mechanical stress. In this way, the usefulness of our proposed method is verified by comparing its simulation results with those from the multi-physics fields FEA method. Finally, the relationship between the bonding angle and the plastic strain at the heel of bond wires is established. This study would provide new perspectives into further research on thermo-mechanical fatigue analysis and optimal design of bond wires in power modules. • An analytical model for analyzing plastic strain of bond wires in IGBT modules is proposed. • The FEA simulation is calibrated based on the experimental results of loop top displacement. • The relationship between the bonding angle and the plastic strain at the heel of bond wires is established. • The models have been compared with FEA simulation results with good agreements. [ABSTRACT FROM AUTHOR]

Physical lifetime prediction methods based on inelastic strain energy density (energy-based lifetime prediction) have been proven to be effective in producing reliable results on small solder joints (ball-grid arrays or chip-scale package) due to their capabilities to represent physical characteristics of soldering materials and loading history. However, in the existing energy-based lifetime models for solder layer failure the inelastic strain energy density is usually assumed to unchanged during aging, which is untrue particularly for large-area solder joints when crack propagation is considered. In this paper, an energy-based lifetime prediction method is proposed for failure of IGBT modules by explicit emulation of solder layer degradation. Inelastic strain energy density variances with respect to aging are meticulously modeled. The large-area solder layer is evenly divided into meshed elements, birth and death technique in finite element analysis (FEA) is used to successively emulate crack propagation. In this way, the increment of thermal resistance due to the solder layer degradation can be predicted. The lifetime prediction results by our proposed method show nice agreement with the experiment under different aging conditions. • An energy-based lifetime prediction method is proposed for failure of IGBT modules • Birth and death technique in FEA is used to successively emulate crack propagation • The increment of thermal resistance due to the solder layer degradation can be predicted • ΔW will change with different aging stage [ABSTRACT FROM AUTHOR]