Effect of thermal shock on lead-free solder reliability

The thermal shock resistance test of Sn-Ag-Cu-Bi-Ni(SACBN07), SAC305 and SAC0307 was conducted and compared in this study. The intermetallic compounds microstructure (IMC) and the mechanical properties of aged solder were investigated using nano-indentation and scanning electron microscopy. Results indicated that SACBN07 showed the best thermal shock resistance compared to the other two solder. The three types of solder exhibited different crack propagation paths during thermal shock test. The crack initiated and propagated in the bulk SAC305 solder. In the case of SACBN07, the crack propagated from the bulk solder to IMC layer. While the crack in SAC0307 was observed between IMC and copper pad. In addition, the addition of Bi and Ni elements into SnAgCu solder effectively suppresses the IMC growth. Under the same test condition, the layer thickness of IMCs for SACBN07 was the thinnest in the three solders. The hardness variation of SACBN07 subjected to thermal shock loading was the most slight. The hardness of SACBN07, SAC305 and SAC0307 decreased by 8.6%, 12.5% and 28.3% respectively after thermal shock test.The U71Mn G hot rolled rail from Wuhan Iron and Steel(Group) Company was welded by flash butt welding using weld machine of model# YHG-1200^TH. By analyzing the variation of welding current, voltages, displacement, pressure etc., in the welding process with respect to those factors including pre-flash, pulse flash, accelerating flash and upset forging, and combined with the hammer impact test, the study aimed to optimize the welding process parameters. Then analysis on the relations between welding heat input, upset forging and impact numbers was performed. The joint fractured surface and the microstructure were also observed. The study specifically approved that when welding heat input located between 11.5 to 12.5 MJ and upset forging length was inside 15~16 mm, the welded joint can perform well in the hammer impact tests,with good quality and consistency. The fractured surface of the joint welded in optimized parameters had no obvious defects. The microstructure of the weld the heat affected zone are pearlite with a small proportion of ferrite, No martensite, bainite or other defects was found in the weld structure.The resistance projection welding process was modeled in this work. The element of plane 223 was adopted to simulate thermal-electric-mechanical coupled projection welding simultaneously. The simulation result was compared with that of the experiment. The nugget size showed good agreement between simulation and experiment which vertified the model. The simulation result showed that the maximum von-mises stress and strain located around the projection and exceeds the yield stress of aluminum,forming a plastic strain zone. At welding period, the maximum temperature located in the faying interface between projection and seal cover. Along with the temperature rising, the projection collapsed rapidly and the nugget was formed in the later stage of welding period. The final depth of fusion was 1.42 mm. The direct molding of resistance projection welding provide a good reference for optimize the technology parameters.Because the stiffness of extra thin-plate welded joint or structure is very small, welding distortion is apt to generate after welding. Therefore, it is very meaningful to predict welding-induced deformation accurately in such welded joint. Inherent strain method is a practical approach which can be used to predict welding deformation in large and complex structures. However, this method is seldom employed to estimate welding deformation in extra thin-plate joints. In this study, the features of inherent strain distribution in bead-on joint with 1 mm thickness was investigated by means of thermal elastic plastic finite element (T-E-P FE) models. Meanwhile, the influence of weld length on the distribution of inherent strain was also clarified. Moreover, the welding deformation in extra thin-plate joints with different weld lengths was calculated by using inherent strain method. The comparison between the results obtained by inherent strain method and those computed by T-E-P FE models shows that when the weld length is up to a critical value, the inherent strain method can be used to predict welding deformation in the extra thin-plate joints.An approximate entropy (ApEn)-support vector machine (SVM) method of arc voltage was proposed to evaluate the stability of aluminum alloy twin-wire pulse metal insert gas (PMIG) welding process. A set of welding experiments were carried out and the ApEn of welding current and voltage signals was calculated. The results showed that the smaller the ApEn of current and voltage signals is the more stable, the welding process is. The application of ApEn on the welding current and the welding voltage was compared. It showed that the voltage based ApEn is sounder in measuring the stability of aluminum alloy twin-wire PMIG welding. Then a support vector machine (SVM) algorithm based on approximate entropy (ApEn) has been developed on voltage signals. And the results of the classification showed that the SVM algorithm based on ApEn can mark off the stable processes from the unstable ones. When the training data is more than 20%, the classification accuracy is more than 90%.This paper analysed the whole stress of the 3D packaging structure and the local copper cylinders stress in the process of chip heating. And the three-dimensional structure was optimized by using finite element simulation software ANSYS. The result showed that the maximum stress was distributed at the location between the outer corner and the bottom of the copper cylinder. The structural parameter was optimized taking the maximum stress of the copper cylinders as a response. The orthogonal optimization method including three factors and three levels was adopted, varied factors being copper cylinder diameter, the copper cylinder height and the copper cylinder pitch. The result showed that the copper cylinder diameter had the maximum effect on the stress, the copper cylinder height had the weakest influence, the effect of copper cylinder pitch was moderate. What's more, with the increase of the three factors mentioned above, the maximum equivalent stress between the outer corner and the bottom of the copper column decreased gradually.With the use of Pb in a variety of occasions prohibited, Lead-free technology becomes one of important research direction. For understanding the fatigue properties of lead-free solder, there is important significance to analyse fanalyse state of lead-free solders and to research on the method of testing. With the 0805 chip capacitor device package solder joints as the research object, Sn96.5/Ag3/Cu0.5 solder joints finite element model is established for multi period under temperature cycles. And shearing test is carried out. The value of Period-shearing stress to Sn96.5/Ag3/Cu0.5 and Sn63/Pb37 solders is obtained. Thermal fatigue fitting curves of solder in 1 500 periods is acquired, by using nonlinear least square method to fit curves. The results indicates that under the stipulated test condition, in limited 1 500 periods, thermal fatigue performance of Sn96.5/Ag₃/Cu0.5 solder joints' rate of thermal fatigue deterioration to 0805 capacitance is slightly slower than that of Sn63/Pb37 solder joints.The feasibility of ultrasonic welding process on carbon fiber reinforced polyphenylene sulfide (C_f/PPS) composites with thermal radiant preheating was investigated. The effect of preheating temperature and welding pressure on the formation of bonding interface and the mechanical strength of welded joint was focused on. It was shown that increasing preheating temperature improved the fusion of the resin at the bonding interface and 100% of bonding area was achieved with a preheating temperature of 110 ℃.The bonding area increased with the welding pressure and it reached 100% when the welding pressure exceeded 3 bars. The strength of the welded joint was enhanced with the welding pressure, but it declined at a welding pressure beyond 3 bars. The welded joint had a maximum strength of 20 MPa at a preheating temperature of 110 ℃ with a welding pressure of 3 bar.The processing parameter of titanium alloy honeycomb sandwich structure was studied, using filling foil of Ti-Zr-Ni-Cu based metal.The vacuum degree was not lower than 2×10^-3 Pa and the brazing temperature was 930 ℃with a holding time of 30 min. The ultrasonic testing(NDT) results showed an excellent brazing weld with no welding-off and faulty welding. The microstructure of the brazed joint was examined by means of scanning electron microscopy(SEM) and energy dispersive spectroscopy (EDS). The results showed that mutual diffusion was happened between the filler metal and the base metals resulting in the precipitation of new phases. Using the optimized parameters, the average tensile strength of joint was 12.8 MPa, the shear strength was 9.01 MPa. The fracture mode of the vacuum brazing joints belonged to a brittle type fracture