This paper deals with the reliability of a power semiconductor exposing to the sever thermal stresses. The importance of solder joint thickness on the power semiconductor's useful lifetime is demonstrated in this study. Solder layer thickness has knock on effects both on the creep accumulated strain and thermal characteristics of the power semiconductors. Since, these effects are in contradictory of each other, a trade-off seems to be essential to optimize the solder layer thickness. Thereby, thermo-mechanical behavior of a discrete power semiconductor under the thermal mission profile was simulated and the results were integrated to the actual conditions. The simulation results reveal that after thermal cycling, some creep strain is produced in the solder layer especially at the corners. The thinner the solder joint was, the greater accumulated creep strain was observed leading to the faster degradation. On the contrary, the thicker the solder layer was, the larger thermal resistance was observed leading to the higher junction temperature. Accordingly, the paper is concentrated on optimizing the solder layer thickness based on this two issues. The SEM micrographs, the EDS maps and XRD analysis also were taken to indicate the solder layer thickness effects on the number of voids and their propagations in the different solder layer thicknesses.

Costly and time-consuming approaches for solder joint lifetime estimation in electronic systems along with the limited availability and incoherency of data challenge the reliability considerations to be among the primary design criteria of electronic devices. In this article, an iterative machine learning framework is designed to predict the useful lifetime of the solder joint using a set of self-healing data that reinforce the machine learning predictive model with thermal loading specifications, material properties, and geometry of the solder joint. The self-healing dataset is iteratively injected through a correlation-driven neural network (CDNN) to fulfill the data diversity. Outcomes show a very significant enhancement in lifetime prediction accuracy of the solder joint within a very short time. The effects of solder alloy and solder layer geometry are separately evaluated on the creep-fatigue damage evolution of the solder joint. The results reveal that Sn–Ag–Cu-based solder alloy generally has a better performance. Moreover, the creep and fatigue damage evolutions are found dominant, respectively, in Sn–Pb- and Sn–Ag–Cu-based solder alloys. The proposed framework offers a tool allowing for the reliability-driven design of electronic devices in the early stage of fabrication.

In this work, the combination of vibration loading and thermal cycle effects on the fatigue properties of a solder joint in a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) discrete was investigated. The fatigue mechanism under each loading mode was individually analyzed, and then according to the incremental damage superposition approach, the simultaneous effects were thoroughly studied. Under thermal cycling, the creep behavior of the solder is linked to the fatigue life. In fact, the creep accumulated strain in each thermal cycle has a straight relation to the failure time of solder joint. The origin of stress/strain in the assembly is owing to the sharp difference between coefficients of thermal expansions of the components in the electronic package. Regarding the vibration loading, the root mean square of peeling stress as a widely acceptable failure indicator was used to evaluate the vibration effects on the fatigue life. It is determined that the maximum stress is concentrated at the corner of solder layer. This result was similar to the outcomes of thermal cycling. The results also indicated that the combination of thermal and mechanical loadings accelerates the failure of the solder joint of the power MOSFET. Furthermore, the experimental and simulation studies showed similar results and approved the crack initiation at the corner of solder layer.

This paper demonstrates the feasibility of low cycle fatigue effects on the thermo-mechanical fatigue evolution in the solder joints of a power module. To achieve this goal, FEM simulation and experimental studies have been carried out. One of the prepared samples was exposed to the sole thermal cycling while another one underwent frequent drop impacts, as indicator of low cycle fatigue event, during the thermal cycling. The FEM results indicate that the thermal cycling leads to the accumulated creep strain in the solder joints. The amount of creep strain considerably increases when the drop impacts are coupled to the thermal cycling. This phenomenon is due to the additional peeling stress applied by drop impacts to the solder joints. It is also revealed that with an increase in the number of drop impacts, the rate of strain accumulation declines which may be due to the restriction of changes led by stress triaxiality. The fractography also validates that the sample exposed to both drop and thermal loadings shows an entire brittle fracture mode. Moreover, the EDS map shows that the elemental distribution heterogeneity and intermetallic growth were created under mutual effects of drop impacts and thermal cycle fatigue.