Progresses in Fracture and Strength of Materials and Structures

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Authors: Jun Zhang, Xu Chen, Xin Li Wei, Yong Cheng Lin
Abstract: The environmental experiments of the thermal cycling (-40~125°C) and the high temperature/humidity (85°C, 85%RH) aging were used to evaluate the reliability of the specimens bonded with ACFs. It was found that the high temperature/humidity was the harshest condition to the ACFs bonding. The DSC testing and interfacial stresses analysis has been done under the high temperature/humidity condition. The mechanisms of the bonding strength decrease were investigated.
Authors: Qing Hua Li, Jian Hua Zhang
Abstract: Isotropic Conductive Adhesives (ICAs) were prepared using epoxy resin as matrix, latent curing agent as hardener, and silver particles as the conducting filler. The effects of nano-fillers (SiO2 nano-particles and carbon nanotubes) on the conductivity, adhension strength and reliability of ICAs were investigated experimentally in this paper. The results showed that these two nano fillers can improve both the conductivity and adhesion strength of ICAs, which maybe attributed to the nano-particles forming physico-chemical bonds with epoxy resin. These physico-chemical bonds increase the contact area and then minish the interspace of Ag particles, so it reduces electrical resistance and enables a high current flow. And the increasing contact area will improve the contact strength between Ag particles and epoxy resin. Under the reliability testing with the high temperature and high humidity (85°C/85RH), the SiO2 nano-particles can improve the reliability of ICAs apparently, while carbon nanotubes can not. This is because insulating material can prevent silver migration.
Authors: Guo Qin Chen, Gao Hui Wu, Long Tao Jiang, De Zhi Zhu, Dong Li Sun
Abstract: Microstructure and mechanical properties of the 55%, 60% and 67% Mo/Cu composites for electronic packaging application fabricated by a patent squeeze casting route have been investigated. The results show that Mo particles are homogeneously distributed in the matrix, and the Mo-Cu interfaces are clean, free from interfacial reaction products and amorphous layers. The densification of the Mo/Cu composites is higher than 99%. The as-received composites exhibit a Brinell hardness varying from HB178.1 to HB196.9 and an elastic modulus varying from 177GPa to 213 GPa. The tensile strength of the composites is higher than 480MPa. Moreover, the composites display favorable plasticity, while the elongation of the 55% Mo/Cu composite is as high as 5%. Obtaining high tensile strength and elongation in the composite is attributed to the high densification, as well as the clean and smooth Mo-Cu interfaces, both resulting from the cost-effective squeeze-casting technology.
Authors: Zi Yang Xiu, Gao Hui Wu, De Zhi Zhu
Abstract: Sip/4032Al composites for electronic packaging applications with high volume fraction of Si particles were fabricated by squeeze-casting technology. The microstructure observation showed that the composites were dense and Si particles distributed uniformly, The interfaces and the existance of the interface reaction were the important factors which affected the properties of the composites; The linear CTEs of Sip/4032Al composites was between (8.1~12) ×10-6°C-1, and they were decreased with the increasing content of Si particles as well as annealing treatment. Kerner model can predict the CTEs of Sip/4032Al composites moderately; the thermal conductivity can reach 103W/ (m·°C), which was decreased with the increasing contents of Si particles as well as annealing treatment. The thermal conductivity of composite calculated was larger than tested values. The composites had excellent mechanical properties and also could be recycled.
Authors: Hong Peng Li, Yu Ting He, Rong Shi, Heng Xi Zhang, Feng Li
Abstract: The mostly working time of airborne electronic equipment is under preliminary depletion failure phase, and inspection & maintenance at intervals can’t lower the failure probability. In this paper, the law of airborne electronic equipment failure is introduced firstly. Then, methods for failure prediction are summarized and analyzed. Finally, an example for predicting the airborne radar failure using the Auto-Regressive (AR) and Support Vector Regression (SVR) model is presented. On this basis, it is possible to achieve the goal that increases the reliability in working phase and establish a more scientific maintenance system and to assure the safety of airborne electronic equipment.
Authors: Yu Ting He, Hong Peng Li, Feng Li, Chao Hua Fan
Abstract: Based on the analyses of reliability and life characteristics in electronic equipment, a new concept of Electronic Equipment Life Envelope (EELE) is presented. The basic approach to EELE establishment is investigated in detail. The interrelationship between storage life and working life of electronic equipment is demonstrated by virtue of EELE, which validates its preliminary application and advantages. The new philosophy can be further applied to accelerated experiments and service life prediction for electronic equipments.
Authors: Hong Peng Li, Rong Shi, Yu Ting He, Heng Xi Zhang, Feng Li
Abstract: Passivation cracking is one of the main failures of Integrated circuits (ICs). A major cause for these failures is due to the mismatch of Coefficients of Thermal Expansion (CTE), Young’s modulus, Poisson’s ratios of package materials. In this paper, in order to analysis the stress distribution around the passivation layer corner, the finite element simulations and simplified analytical solutions are both applied. Then the comparison of stress values is made between the FEM result and simplified analytical solution, which shows that there is a good agreement. Based on these analyses, a conclusion can be drawn out that the simplified analytical model can be used to analyze the maximum stress around the passivation layer corner fast when design a chip preliminarily.
Authors: Kuo Jun Xie, Chang Shun Jiang, Lin Zhu, Hai Feng Xu
Abstract: With the increasing of packaging integration the power and the quantity of heat of integrate circuit will increase, it will bring more and more temperature distributions and problems about thermal stresses in package. In this paper a finite element thermal stress model of substrate-adhesive-chip is established, thermal stress distribution of substrate-chip interfaces and the affects of geometrical structure on thermal stresses are analyzed by finite element method, especially discuss interfacial thermal stresses distributions on chip-adhesive interface and adhesinve-substrate interface.
Authors: Ning Bai, Xu Chen, Xin Li
Abstract: A series of torsional fatigue tests were conducted on 63Sn-37Pb and Sn-0.7Cu solders. A continuous load drop was observed during the test. It was found that the load drop percentage had little effect on the elastic strain-life curve but strong effect on the plastic strain-life curve. The fatigue strength coefficient, fatigue strength exponent and fatigue ductility exponent had no great changes with the load drop. However, fatigue ductility coefficient showed a great difference and was linearly varying with load drop. A fatigue criterion of Coffin-Manson type was proposed in relation to load drop. The descending curve of the stress range with cycle was observed to consist of transient, steady state and tertiary regions. The percentage of load drop corresponding to the turning point from the steady state to the tertiary region was about 25% for all strain ranges of 63Sn-37Pb, and 30% for all strain ranges of Sn-0.7Cu. The torsional fatigue lives were correlated with von Mises equivalent strain amplitudes well. The fatigue behavior of Sn-0.7Cu is better than that of 63Sn-37Pb.
Authors: Ke Ke Zhang, Yao Li Wang, Yan Li Fan, Jie Yiang, Yan Fu Yan, Xin Zhang
Abstract: Creep property of solder alloys is one of the important factors to effect the reliability of surface mount technology (SMT) soldered joints. The creep behavior and its rupture life of Sn2.5Ag0.7CuXRE lead-free soldered joints were separately investigated and predicted under constant temperature by a single shear lap creep specimen with a 1mm2 cross sectional area and finite element method (FEM) in this paper. Results show that the creep property of Sn2.5Ag0.7Cu0.1RE is superior to that of the commercial employed lead-free solder Sn3.8Ag0.7Cu and the creep rupture life of its soldered joints is 8.4 times more than that of Sn2.5Ag0.7Cu solder. The creep rupture life of Sn2.5Ag0.7CuXRE lead-free soldered joints indirectly predicted by FEM is better in accord with that of actual testing results, which are important to design the reliability of lead-free soldered joints for SMT.

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