Numerical simulation of reliability of single-sided/double-sided package interconnect structure under temperature cyclic load

Mechanical properties of Sn–Pb based solder joints and fatigue life prediction of PBGA package structure

Purpose As the solution to improve fatigue life and mechanical reliability of packaging structure, the material selection in PCB stack-up and partitioning design on PCB to eliminate the electromagnetic interference by keeping all circuit functions separate are suggested to be optimized from the mechanical stress point of view. Design/methodology/approach The present paper investigated the effect of RO4350B and RT5880 printed circuit board (PCB) laminates on fatigue life of the QFN (quad flat no-lead) packaging structure for high-frequency applications. During accelerated thermal cycling between −50 °C and 100 °C, the mismatched coefficients of thermal expansion (CTE) between packaging and PCB materials, initial PCB warping deformation and locally concentrated stress states significantly affected the fatigue life of the packaging structure. The intermetallics layer and mechanical strength of solder joints were examined to ensure the satisfactorily soldering quality prior to the thermal cycling process. The failure mechanism was investigated by the metallographic observations using a scanning electron microscope. Findings Typical fatigue behavior was revealed by grain coarsening due to cyclic stress, while at critical locations of packaging structures, the crack propagations were confirmed to be accompanied with coarsened grains by dye penetration tests. It is confirmed that the cyclic stress induced fatigue deformation is dominant in the deformation history of both PCB laminates. Due to the greater CTE differences in the RT5880 PCB laminate with those of the packaging materials, the thermally induced strains among different layered materials were more mismatched and led to the initiation and propagation of fatigue cracks in solder joints subjected to more severe stress states. Originality/value In addition to the electrical insulation and thermal dissipation, electronic packaging structures play a key role in mechanical connections between IC chips and PCB.

Perforating crease lines has been widely adopted as a practical method for achieving thickness accommodation in designing engineering origami structures. In a previous work, we proposed a perforated crease design with three rows of oblong holes that induces smooth folding behavior of thick origami sheets and improves their mechanical properties. Here we further investigate the effects of this configured crease design on the mechanical behavior and fatigue life of 3D origami tubular structures, including the Bellow, Yoshimura, horizontally-symmetric Kresling, and inclinedly-symmetric Kresling origami tubes. We utilize Rhino/Grasshopper to develop a parametric modeling framework for the studied origami structures based on their respective geometric relationships. An origami model with or without perforated creases can be efficiently established by adjusting input parameters in the modeling framework. Then, finite element analysis is adopted to assess folding behavior and mechanical properties of the structures, and to predict their fatigue life combined with FE-SAFE. The results show that the perforated crease can alleviate the issue of panel interference, resulting in smooth folding behavior of origami structures. Although the mechanical responses are weakened due to perforations, the fatigue life of the structures is significantly enhanced by an order of magnitude. We therefore expect that the perforated crease design with three rows of oblong holes can be applied to engineering origami structures.

Based on the typical aerospace frame structure, the fatigue life law of the structure under multi-axis correlation time-domain random excitation is studied. By constructing multi-axis time-domain random excitation with different correlation coefficients, multi-axial fatigue theory and structural vibration fatigue life time-domain method are used to calculate the fatigue life of the structure under different excitations; by constructing the structural finite element model in MSC. Pastran and nCode-DesignLife, and Co-simulation calculates the structural fatigue life. The results show that there is a negative correlation between the correlation coefficient of the applied multi-axis time-domain random excitation and the structural fatigue life, that is, the larger the correlation coefficient, the shorter the fatigue life.

Fatigue behavior of 3D stacked packaging structures under extreme thermal cycling condition

Mechanics-based acceleration for estimating thermal fatigue life of electronic packaging structure

Floating wind turbine structures are subjected to complex fatigue damage resources, such as wave dynamic, blade motion, turbine vibration, wind turbulence, structure vibration and so on. A study of a semi-submersible wind turbine structure has revealed that the load from wind turbine significantly affects the fatigue behavior of the structure. However, how the load is comprised and how impacts fatigue life is unknown. Lately developed fully coupled time domain global analysis are capable of getting the time history of wind turbine tower bottom load. A study is performed to analyze the load the get the components of the loads. To get fatigue life of the whole structure, a complete structure model instead of hydro model is required. Due to the complication of the fully coupled time domain structural analysis, it is required to develop a methodology for coupling wind and wave impact on the fatigue life of the structure. In this study, time domain wind turbine load is used to compute the fatigue life due to wind and spectral fatigue method is used to computer fatigue life caused by wave. Then the fatigue damages were combined and compared to give suggestions for the future floating wind turbine structures.

Interfacial thermal damage and fatigue between auxetic honeycomb sandwich and underneath substrate

Due to the random factors such as material properties,geometrical characteristic of structural member,load history and environmental condition,the fatigue life of structure often deviates from the design life. To reduce the scatter of fatigue life,a robust optimization model of structural fatigue life is presented. The model combines structural optimization theory and stochastic finite element method. Under the condition of considering the effects of variance of design variables and other random variables on the structural fatigue life,the problem is formulated as a multi-criteria optimization problem,in which both the mean structural fatigue life and the standard deviation of structural fatigue life are to be minimized. The relationship between the mean structural fatigue life and the standard deviation of structural fatigue life can be balanced by a weight factor. The structural fatigue life is limited between the low fatigue life and high fatigue life in the constrain functions. Fatigue life of the structure optimized by the proposed method has a relative small fluctuation at the mean value and keeps far away from the ultimate fatigue life. A numerical example is performed for a planar 10-bar truss. The result shows that the proposed method is feasible and applicable.

The structural integrity and the reliability of sheet structures, especially those of high risk like pressure vessels and pipes, is a relevant topic which has centered the attention of many researchers. This paper offers an engineering approach to determine the fatigue life of sheet structures under cyclic loading. The theoretical development presents a general method for calculating, by using a micro-computer, the initiation and fracture loci and the two-parameter crack growth paths as well as the integral value and therefore the fatigue life of the structure. This permits an evaluation of the influence of the different factors from the structural integrity point of view, and particularly of the material. The proposed method is applied to the computation of the fatigue life of a pressure vessel under cyclic loading produced by the thermal oscillations of the environment, allowing a study of leak before break.

Bolt tightening torque has an influence on the fatigue life of the multi-bolted joints which cannot be ignored, but there are few methods to predict the fatigue life of the multi-bolted composite structure by considering the bolt tightening torque. A fatigue life prediction method of the multi-bolted composite structure by considering the bolt tightening torque is proposed. It can take into account the various damages of bolts and laminates and accurately calculate fatigue life and damage evolution of multi-bolted composite structure. The multi-bolted composite structure being composed of T300/BMP-316 composite laminates and TC4 titanium alloy bolts is used to verify the present method. The logarithmic error between the predicted fatigue life and the experimental is 4.36%, and the failure mode is consistent with the experimental. Through the present method, the influence of the bolt tightening torque is explored, in which it is found that with the increasing of bolt tightening torque, the fatigue life increases firstly and decreases, and there is an optimal tightening torque. By observing the damage evolution diagram, it is found that when the tightening torque is below the optimal tightening torque, the damage propagation cannot be effectively restrained, which will lead to the reduction of fatigue life. On the contrary, when the tightening torque is more than the optimal tightening torque, it will cause the initial damage to the test piece, which will also lead to the reduction of fatigue life. In engineering, to choose the best tightening torque of the structure for assembly can effectively improve the fatigue life of the structure.

The hybrid method using the extended finite element method (XFEM) and the forward Euler approach is widely employed to predict the fatigue life of plate structures. Due to the accuracy of the forward Euler approach is determined by a small step size, the performance of fatigue life prediction of the hybrid method is not agreeable. Instead the forward Euler approach, a prediction method using midpoint method and support vector regression (SVR) is presented to evaluate the stress intensity factors (SIFs) and the fatigue life. Firstly, the XFEM is employed to calculate the SIFs with given crack sizes. Then use the history of SIFs as a function of either number of fatigue life cycles or crack sizes within the current cycle to build a prediction model. Finally, according to the prediction model predict the SIFs at different crack sizes or different cycles. Three numerical cases composed by a homogeneous plate with edge crack, a composite plate with edge crack and center crack are introduced to verify the performance of the proposed method. The results show that the proposed method enables large step sizes without sacrificing accuracy. The method is expected to predict the fatigue life of complex structures.

In this paper, the life reliability analysis of AL-AL repair structure is studied. Firstly, the fatigue life of the repair structure is predicted by finite element numerical modeling combined with Forman’s empirical formula, and the influence law of the variation of the repair structure parameters on the fatigue life is investigated. Secondly, the uncertain factors affecting the fatigue life of the structure are considered, the objective function of the structure is linearly fitted, and the fatigue reliability model of the repair structure is established, and the reliability of the structure is obtained by calculating the probability of predicting the fatigue life to be greater than the allowable life. Finally, the parameters of the repair plate that affect the life reliability are analyzed and studied. The results show that under the same fatigue life, the order of parameters affecting the reliability of the repair structure is: repair plate position x > repair plate width w > repair plate length l .

With Ceramic Quad Flat No-lead packaging structure as the research object, using finite element method on the distribution of stress and strain in the temperature cycle test simulation analysis, analyzed the thickness of the printed circuit board, the size of the Ceramic package, the form of the lead and the range of temperature change on the influence of solder joints reliability. Based on the simulation results, the fatigue life of CQFN packaging structure under temperature cyclic loading is calculated. Results show that by increasing the thickness of the PCB, reasonable selection of Ceramic package size and lead form and try to reduce the temperature change range, can effectively improve the thermal fatigue life of solder joint. It provides a reliable theoretical basis for the design of this kind of packaging structure. The problem such as the failure of welding spot after installation on PCB is avoided due to the unreasonable design of the structure. Reasonable structural design plays an important role in solving the failure problems in reliability test and improving the reliability of the device.

Robust optimization design for fatigue life