In this article, the fatigue evolution of solder joints in a photovoltaic (PV) module at a hot climate under thermomechanical cycling was evaluated. The finite-element modeling (FEM) simulation results showed that the degradation evolution is very sensitive to the ambient temperature so that with an increase in ambient temperature from 25 °C to 75 °C, the fatigue life decreased by 34% for the solder joints. A handy equation was also given to predict fatigue life in the mentioned ambient temperature. The simulation outcomes also revealed that with an increase in solder layer thickness, the fatigue life improved, which is due to the lower accumulated strain energy per volume in the solder material. Moreover, SEM micrographs, from the experimental fatigue test, indicated that the damage evolution was accompanied by the appearance of elemental heterogeneity and void coalescence in the solder joints. The X-ray diffraction (XRD) test also showed that the decrease in solder thickness leads to the intensification of intermetallic compounds formation at the interface.

Thermomechanical Reliability Assessment of Solder Joints in a Photovoltaic Module Operated in a Hot Climate

This paper deals with the effects of electric current on the thermomechanical lifetime of solder joint as the most vulnerable part in electronic packages. The main focus of this paper is located on the Sn3.8Ag-0.5Cu based solder. Different current densities from 1 A/mm2 to 10 A/mm2 are under considered in two well-known solder ball joints, namely barrel- and hourglass-type, in the temperature cycling conditions. Electrical properties of the interested solder joints are experimentally extracted and applied to the finite element analysis in order to reveal the thermomechanical coupling effects of thermal cycling and electric current. Two most important phenomena including joule heating effects and induced triaxility play major roles in determination of solder joint types in the electronic packages. The results reveal that at the lower current density in which the joule heating effects are insignificant, the sharp triaxiality in the barrel-type solder joint is evident due to sharp tilting angle of solder joint. However, in the higher current densities in which the joule heating effects come into play, the number of cycle to failure of hourglass-type solder joint is lower in comparison with barrel-type solder joint. This event may be due to the lower diameter of hourglass-type solder joint in its neck so that more losses in the neck of hourglass-type solder joint, the more effective joule heating is occurred.

https://iopscience.iop.org/article/10.1088/2053-1591/ab366d/pdf

Interaction of thermal cycling and electric current on reliability of solder joints in different solder balls

This article deals with the reliability of a power semiconductor exposing to the severe thermal stresses. The importance of solder joint thickness on the power semiconductor's useful lifetime is demonstrated in this article. 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 article is concentrated on optimizing the solder layer thickness based on these two issues. The scanning electron microscope micrographs, the EDS maps and X-ray diffraction analysis were also taken to indicate the solder layer thickness effects on the number of voids and their propagations in the different solder layer thicknesses. The experimental tests validate the expected results in the extracted simulations.

Reliability Enhancement of a Power Semiconductor With Optimized Solder Layer Thickness

A competition between stress triaxiality and joule heating on microstructure evolution and degradation of SnAgCu solder joints


 The fabrication process of WLP (wafer-level packaging) has become more mature, and using the finite element method (FEM) to predict the reliability life of electronic packaging can shorten the WLP design cycles. This study adopted the NSMD (non-solder mask defined) solder joint structure in WLP and used an energy method to predict the solder joint geometry. A fixed mesh size will be determined for the critical region of the solder joint to evaluate the inelastic strain due to the thermal loading in finite element analysis. However, under the influence of the solder geometry of some tested vehicles, especially when the solder contact angle of the lower pad is less than 20 degrees, a shear locking phenomenon will occur at the solder joint. This phenomenon causes abnormal energy transfer. The excessive strain is concentrated on the upper part of the solder joint, resulting in an incorrect estimation of reliability life. Reduced integration can prevent shear locking and has improved strain results compared to full integration. The results of this research demonstrate that the FEM using proper mesh size control and the reduced integration point element in critical regions can deliver accurate reliability life prediction for WLP.

/pdf/study-of-shear-locking-effect-on-3d-solder-joint-reliability-1vkrbe6k.pdf

Study of shear locking effect on 3D solder joint reliability analysis

This paper demonstrates to what extent the number of thermal cycles affects the mechanical properties as well as the thermal conductivity of a porous solder joint in an insulated-gate bipolar transistor discrete. The blind mode voids were used for a finite-element method (FEM) simulation to obtain the results close to the actual conditions. The FEM results indicate that the concentration of creep strain at the interface of the solder/chip is in its maximum value, and it slightly decreases along with the depth of the solder layer. FEM also reveals that the boundaries of voids act as critical regions for strain concentration. An upward in the number of thermal cycles also leads to the void growth and coalescence process. The enhancement of void volume from 0 to 15 cycles is about 4% volume of the solder layer. Moreover, scanning electron microscope micrographs approve the FEM results and show the void growth and the damage accumulation during thermal cycling. The thermal analyses indicate that the increase in thermal cycles (creep strain) leads to a significant rise in thermal impedance. This event can be due to the increase in the void volume of the solder layer leading to the decrease in the effective area of heat path.

Effect of Thermal Cycle Loadings on Mechanical Properties and Thermal Conductivity of a Porous Lead-Free Solder Joint

Purpose: The paper deals with the optimization of the preparation of educational professional programs of higher education to the processes of accreditation and licensing.
Methodology: In this paper, we will consider technical tools that optimize the organization of the management of the university's educational process in the conditions of the “digitalization” of education.
Result: Since the verification of compliance of University educational programs with the requirements of Federal state educational standards is carried out in the process of accreditation examination, it is necessary to optimize the organization of management of the educational process of the University on the basis of computer equipment and software.
Applications: This research can be used for universities, teachers, and students.
Novelty/Originality: In this research, the model of the organization of the university educational process in terms of digitalization of education is presented in a comprehensive and complete manner.

https://giapjournals.com/hssr/article/download/hssr.2019.74156/1593

The organization of the university educational process in terms of digitalization of education

Purpose: The paper deals with the optimization of the preparation of educational professional programs of higher education to the processes of accreditation and licensing. 
Methodology: In this paper, we will consider technical tools that optimize the organization of the management of the university's educational process in the conditions of the “digitalization” of education. 
Result: Since the verification of compliance of University educational programs with the requirements of Federal state educational standards is carried out in the process of accreditation examination, it is necessary to optimize the organization of management of the educational process of the University on the basis of computer equipment and software. 
Applications: This research can be used for universities, teachers, and students. 
Novelty/Originality: In this research, the model of the organization of the university educational process in terms of digitalization of education is presented in a comprehensive and complete manner.

Linar G. Akhmetov

Papers

Effect of Thermal Cycle Loadings on Mechanical Properties and Thermal Conductivity of a Porous Lead-Free Solder Joint

The organization of the university educational process in terms of digitalization of education

The organization of the university educational process in terms of digitalization of education