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Objectives: During Neuromuscular Electrical Stimulation (NMES), a real-time monitoring method is urgently needed to reduce the negative effect induced by muscle fatigue. Technology or Method: A novel method named electrical impedance myography (EIM) is proposed to evaluate muscle fatigue degree during NMES. The experiments were performed on the anterior tibialis muscle on several voluunteers. Two EIM parameters : impedance amplitude (|Z|) and phase (), were measured in real time, while applying six NMES parameter combinations. The mean power frequency (MPF) of the surface electromyography (sEMG) was selected for verification of the proposed method. Results: |Z| and of EIM signals decreased significantly after NMES (p < 0.05). They also both showed a linear downward trend during NMES, which was also observed in MPF of sEMG signals. At the measurement frequency of 20 kHz, steady- state fatigue was achieved when |Z| decreased to approximately 14% of the initial value. Clinical or Biological Impact: This study provides a method for monitoring muscle fatigue induced by NMES, which is beneficial to the application of NMES.

In order to alleviate the pressure of energy and environment on human life and social development, the development of electric vehicle industry is very rapid. Insulated Gate Bipolar Transistor ( IGBT ) module with superior performance has become the core component of electric vehicle converter. But limited heat dissipation space and complex packaging structure will cause excessive local temperature of the IGBT chip, and then the chip damaged. Therefore, the packaging structure of IGBT module for efficient heat dissipation is the key to ensure the safe and reliable operation of converters and even electric vehicles. Based on the double-sided forced liquid-cooled packaging structure of high-power IGBT module, a three-dimensional coupled model of heat conduction and coolant flow was established in this paper. Pressure distribution of cooling medium and temperature distribution of chips and the radiator at different inlet flow rates are calculated. The maximum temperature of chip surface and pressure difference between inlet and outlet under different inlet flow rates are analyzed. The results show that when the inlet flow rate is relatively small, the larger the inlet flow rate, the better the heat dissipation effect, but the greater the flow resistance; when the inlet flow rate reaches a certain value, the increase of flow rate can only greatly increase the flow resistance, but the heat dissipation is not obviously improved; the heat dissipation effect of liquid cooled radiator is non-uniform, the chip temperature near the inlet is lower, and the chip temperature near the outlet is higher. Finally, in order to alleviate the local high temperature of the chip near the outlet, graphene-based films (GBFs) were applied to the chips surface near the outlet in this model. The simulation results show that the maximum temperature of the outlet chip decreases to a certain extent with the same fluidity.

With the development of LED chip and packaging to the high power direction, improving the internal structure of the tube core and packaging, to solve the problem of heat dissipation, has become the mainstream direction of LED research. In this paper, a basic structure with sapphire epitaxial growth GaN flip-chip, film direct bonded copper substrate and array package was employed. Two-dimensional material graphene-based film with high thermal conductivity was applied into encapsulation structure of power LED to conduct transverse thermal diffusion of local hot spots, which would change the heat conduction path and improve the heat dissipation efficiency. Combined with the thermal resistance network of the power LED packaging structure and the simulation results of application in different ways of graphene-based film, the influence mechanism of graphene on the heat conduction of power devices was analyzed. It showed that the heat dissipation application of graphene in power LED packaging should be as close as possible to the GaN chip hot spots.

Al5052/Mg-9.5Li-2Al alloy clad plates were fabricated by cold rolling and the effect of annealing temperature on the microstructures and mechanical properties were investigated. Results show that no defects like cracks or voids are found at the bond interface in the annealed clad plates. Intermetallic layers are formed at the clad plate bond interface after annealing at and above 623 K. The main phases across the bond interface are α-Mg+β-Li, Mg 17 Al 12 , Li-dissolved Al 3 Mg 2 and α-Al in sequence from the Mg-9.5Li-2Al base plate to Al5052 cover plate. The bond strength increases with increasing of annealing temperature below 623 K. When annealed at 623 K, the interfacial normal bond strength of the clad plates attains its maximum 17.83 MPa, with excellent ductility of an elongation of 18.7%, and no debonding is observed in the tensile specimen. When annealed at 673 K, the tensile property of the clad plates worsens due to interface debonding.

CF 3 I has been recognized as an attractive insulating medium for substituting SF 6 gas in high-voltage switchgear insulations, because it has low global warming potential (GWP) and an insulation capability that is 1.2 times greater than that of SF 6 . In this paper, the AC breakdown tests on CF 3 I/N 2 gas mixture have been completed in a sphere-plate geometry. We reveal the effect laws of mixture content, gas pressures, and gap distances. The results indicate that the insulation strength of the CF 3 I/N 2 gas mixture will be efficiently improved by prolonged insulation distance and higher gas pressure. And the insulation ability of the CF 3 I/N 2 gas mixture were demonstrated in a 12kV C-GIS designed for SF 6 gas when the gas is replaced with Alternative Gas.

In this study, a four-layer stacked chip simulation model is built under standard JEDEC environment, the heat dissipation path and temperature distribution of the stacked chip is analyzed. Based on linear superposition method, a method of estimating the temperature of stacked chip using thermal resistance matrix is proposed, and the function relationship between the power consumption and the element values of the thermal resistance matrix is established. The accuracy of the thermal resistance matrix is researched through simulation analysis, and the difference between the results of the thermal resistance matrix prediction and the simulation results is about 0.01%.

In order to improve the processing efficiency and processing quality of silicon rods, and to optimize the process parameters during the cutting process of silicon rods, the sawing force of wire saw is studied from the aspects of cutting deformation and friction. Meanwhile, the mathematic model is established between the sawing force and some cutting process parameters. Besides, the quadratic regression model is also established by Box-Behnken center combination experiment and the response surface methodology(RSM), which can reflect the wire saw speed, workpiece feed rate and wire saw radius of the interaction of three process parameters on the wire saw sawing force. The results show that the model can accurately predict the sawing force and optimize the process parameters during the cutting process as well.

The CuPc/buffer interlayer/C60heterojunction organic photovoltaic devices are fabricated by inserting a MoO3or RB interlayer and investigated the impact of buffer interlayer on the performance of heterojunction organic photovoltaic devices.The results suggest that OPV with the buffer interlayer has higher open-circuit voltage and power conversion efficiency,lower short-circuit current density and fill factor.The open-circuit voltage increases from 0.39Vto 0.58Vand 0.55V,respectively,and the power conversion efficiency reaches 0.44%,in comparison with a power conversion efficiency of 0.36%for OPV without interlayer.The short-circuit current density decreases from 1.92mA/cm2 to 1.77mA/cm2 and 1.81mA/cm2,and from 0.48to 0.43and 0.44in fill factor,respectively.Further research shows that the short-circuit current density strongly depends on the thickness of buffer layer.The short-circuit current density increases when the interlayer thickness is small,while it gradually decreases as the buffer layer thickness increasing.When the interlayer thickness is 10nm,the short-circuit current density decreases to 0.35mA/cm2.The open-circuit voltage enhances as the buffer layer thickness increasing,from 0.43V with 1nm interlayer to 0.63V10nm interlayer.Open-circuit voltage enhancement and the short-circuit current density decrease are studied according to the integer charge transfer model and interfacial energy level theory,which provide a research foundation for the performance improvement of organic solar cells.

The micro pore array with the feature of aspect ratio of more than 50 was fabricated on a 5-inch silicon wafer by means of photo-assisted electrochemical etching technique.After analyzing the factors that determine the morphology of pores,the following experiments were proceeded to study the relation of pore morphology to the etching voltage and electric current.When choosing a current by i-V curve,several different etching voltages were applied respectively and corresponding wafer was fabricated by adjusting experimental parameters according to the Lehmann′s model.It was found that the better pores could be produced under a voltage of 2 V.The results show that photo-assisted electrochemical etching technique can be more adopted to make the large area micro-pore array of high aspect-ratio on silicon wafer with low cost,being compared to the state of the art of micro-manufacturing technology.

Aerogels with densities in the range 40-175 mg·cm-3 were prepared using a tetraethyl orthosilicate(TEOS)ethanol-water solution as the precursor and hydrofluoric acid as the catalyst via a sol-gel process and CO 2 supercritical-fluid drying.The density-gradient aerogels were prepared using layer-by-layer gelation,sol co-gelation,and gradient-sol co-gelation methods and their gradient properties were studied systematically.The results show that aerogels with different densities all have a three-dimensional skeleton consisting of spherical particles of diameter about 40-90 nm.The lower the density is,the looser the skeleton and pore-size distributions are,and the larger the peak value of the pore size is.Gradient aerogels prepared via different methods exhibited graded,approximately gradient,or gradient distributions.Dynamic mechanical analysis indicates that the Young?s moduli of the aerogels at-100 and 25℃(changed from 4.6×10 5 to 1.9×10 5 Pa and from 5.0×10 5 to 2.1×10 5 Pa,respectively)tend to decrease with decreasing density.Thermal constants analysis shows that as the densities of the aerogels decrease,the thermal diffusion coefficients increase and the specific heat capacities decrease,but the thermal conductivities do not change monotonically.

The paper introduces the theory of gas concentration detection by infrared absorption spectrum and the modeling method of gas detection simulation system based on LabVIEW. On the basis of wavelength modulation technology, the second harmonic curve of the absorption spectrum is extracted by phase-locked algorithm and the concentration of the target gas can be obtained. By changing the parameters of the target gas concentration and modulation coefficients, the variation of the absorption curves and the second harmonic curves is acquired. It provides the reference for the design of gas detection system in practice.

This article fabricated the CuPc/C60 double-layer heterojunction organic photovoltaic devices,investigated the effects of different illumination intensity and temperature on device performance.The results showed that the illumination density directly determined the value of photocurrent under short circuit condition,while had little effect on the open circuit voltage.The short circuit density had little weak dependence on temperature.The device exhibited larger open circuit voltage with the reduction of temperature.According to the experimental data,This article theoretically analyzed the relationship of illumination intensity,tempe-rature short,circuit density and open circuit voltage,which provided a research foundation for the high performance of organic solar cells.

Novel nanoporous silicon was successfully converted from SiO2 aerogels by a template-confined magnesiothermic reduction at low temperature (650 °C) based on a gas-solid reaction. The composition, crystal structure, morphology, and pore structure of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett- Teller (BET) surface area analysis. Their optical and electrochemical properties were also investigated. The results indicated that the products consisted of nanocrystalline silicon, retained a morphology similar to that of the original templates, and possessed a specific surface area as high as 602 m 2 ·g - 1 . They also showed red photoluminescence at room temperature and had a high capacity and good Li-ion insertion/extraction properties for use in lithium ion batteries. (Article)

用提拉法成功生长出Nd：Sr 3 Gd 2 (BO 3 ) 4 晶体, 并对其光谱性能进行了研究. 测量了晶体在200~1000nm波段的吸收谱. 用808nm的波长激发, 测量了晶体的荧光光谱和荧光寿命, 计算得到晶体的发射截面. 根据J-O理论计算了晶体的光谱参数, 与其它Nd掺杂的晶体的光谱参数做了比较和分析.

Micro-interconnection copper pillar bumps are being widely used in the packaging areas of memory chip and high performance computer due to their high density, good conductivity and low noise. Studying the interfacial behavior of copper pillar bump is of great significance for understanding its failure mechanism and microstructure evolution in order to improve the reliability of flip chip package. The thermoelectric stress test, in-situ monitor, infrared thermography test, and microstructure analysis method are employed to study the interfacial reaction, life distribution, failure mechanism and their effect factors of Cu/Ni/SnAg1.8/Cu flip chip copper pillar interconnects under 9 groups of thermoelectric stresses including 2104-3104 A/cm2 and 100-150℃. Under thermoelectric stresses, the interfacial reaction of Cu pillar can be divided into three stages:Cu6Sn5 growth and Sn solder exhaustion; the Cu6Sn5 phase transformation, exhaustion and the Cu3Sn phase growth; voids formation and crack propagation. The rate of Cu6Sn5 phase transforming into Cu3Sn phase is positively correlated with the current density. There are four kinds of failure modes including Cu pad consumption, solder complete consumption and transformation into Cu3Sn, Ni plating layer erosion and strip voids. An obvious polar effect is observed during the dissolution of Cu pads on the substrate side and the Ni layer on the Cu pillar side. When Cu pad is located at the cathode, the direction of electron flow is the same as that of the heat flow, and it can accelerate the consumption of Cu pad and the growth of Cu3Sn. When Ni layer serves as the cathode, the electron flow can enhance the consumption of Ni layer. Under 150℃ and 2.5104 A/cm2, the local Ni barrier layer is eroded after 2.5 h, which results in the transformation of Cu pillar on the Ni side into (Cux, Niy)6Sn5 and Cu3Sn alloy. The life of Cu pillar interconnection complies well to the 2-parameter Weibull distribution with a shape parameter of 7.78, which is a typical characteristic of cumulative wear-out failure. The results show that the intermitallic growth behavior and failure mechanism at Cu pillar interconnects are significantly accelerated and changed under thermoelectric stresses compared with the scenario under the single high temperature stress.

Various kinds of basic chemicals interact with dentin directly in different clinical conditions. However, owing to the lack of appropriate models and technology, it is still not known how the mineral components of dentin react to these chemicals. The technology of high-resolution X-ray microdiffraction, in combination with scanning electron microscopy, has been applied to study the microstructure and minor crystallographic changes in a longitudinal dentin section before and after chemical treatment. Phase analysis was performed; the crystal sizes at two dentin sections were calculated from the reflections (002) and (211), and the crystal orientations of reflections (222), (213) and (002) were compared before and after treatment. The results show an inhomogeneity of the microstructure in dentin between the coronal and the root regions and that they react differently to basic treatment. In particular, NaOH treatment causes a change in crystal sizes and disorder.

This paper deals with the synthesis of ultralow density silica aerogels using polyethoxydisiloxanes (PEDS) as the precursor via sol–gel process followed by supercritical drying using ethanol solvent extraction. Ultralow density silica aerogels with 5 mg/cc of density were made for the molar ratio by this method. A remarkable reduction in the gelation time was observed by the effect of the catalyst NH 4 OH at room temperature. The microstructure and morphology of the ultralow density silica aerogels were characterized by the specific surface area, S BET , SEM, TEM and the pore size distribution techniques. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is about several nm. The specific surface area of the silica aerogel is 339 m 2 /g and the specific surface area, pore volume and average pore diameter decrease with increasing density of the silica aerogel.

In this paper, parylene/SiO2 composite films were reported to protect KDP crystals, indispensable cells in ICF experiments, from moisture. FTIR, UV-NIR spectra and XPS were used to analyze the properties of films. Laser damage threshold of films was also measured. With porous silica coating on surface of parylene film, the transmittance of dual layers can be raised to more than 91%. KDP crystals with poly(p-xylylene)/SiO2 coating could work well in ambient atmosphere for more than half a year.

Nowadays, the solder layer failure between chip and metal frame is the most common failure mode of the power transistor. Accordingly, the optimization for solder layer thermal characteristics attracts more attention. In this paper, the optimization for solder layer thermal characteristics of the power transistor using a combined measurement and simulation approach is presented, and the approach is based on structure function. The transient temperature response of the tested package is measured by electrical method and structure function can be derived from transient temperature response. Then, a 3D numerical model consistent with the actual sample is established employing thermal CFD simulators. And different materials, thicknesses and areas of the solder layer of the model are simulated. Some valuable results are given in the simulation. Following conclusions can be drawn from these results: there is a non-linear relationship between the thermal conductivity of materials and the thermal resistance of solder layer, the thickness of the solder layer keeps a positive correlation with the thermal resistance and if the solder floor area is larger than the chip area, the additional area has no significant effect on the thermal resistance of the device. Compared with traditional methods, the test-simulation combined optimization is more effective and economic.

This article provides a method to perform finite element analysis (FEA) and theoretical evaluation on stress and strain characteristics of very-thin fine-pitch ball grid array (VFBGA) assembly under the random vibration environment. Solder ball diameter, ball pitch, ball joint height, PCB pad diameter, Intermetallic compounds (IMCS) between solder alloy and PCB pad, and IMCS thickness were selected as critical elements. By using an L 18 (37) orthogonal array, which combined of 18 configuration parameters, the mixed solder joints of VFBGA components were designed. FEA of the VFBGA packages under random vibration load were performed, then the distributions of stress and strain of VFBGA mixed solder joints was investigated. Based on the FEA results (stress value), range analysis and variance analysis was researched. In this study, the stress of mixed solder joints is affected by solder ball pitch, ball joints height, ball diameter, PCB pad diameter, IMC type, IMC thickness in a descending order and the best level combination of configuration parameters that results in the minimum stress and strain is the solder ball pitch of 0.7mm, the solder ball joint height of 0.25mm, the solder ball diameter of 0.56mm,the PCB pad diameter of 0.335mm, the IMC is Cu6Sn5, the IMC height is 1.4µm compared to other selected level in paper. With 90% confidence, the ball pitch and the ball joint height have significant effect on the stress of VFBGA solder joints whereas the other critical parameters have little effect on the strain of the mixed solder joints of VFBGA under random vibration load.

This study reveals that film growth can be directly linked to traps density, and they are responsible for performance of solar cells. Defect states due to disorder have been obtained by the C-f characteristics.

The effect of Bi2O3 and MnO2 addition in [(Pb0.5Ca0.5)0.92La0.08](Fe0.5Nb0.5)O3 system on the sintering and dielectric properties have been investigated using X-ray diffractions and post-resonator measurement. Perovskite and pyrochlore phase exist in samples with MnO2 content ≤2 wt.% while specimens with Bi2O3 doping possessed the third unknown phase. The dielectric properties could be obviously adjusted as well as reducing the sintering temperature in both Bi2O3 and MnO2 addition system. It was found that Bi2O3 and MnO2 co-doping could reduce the sintering temperature more effectively by 100–140 °C while improve the microwave dielectric properties. Microwave dielectric properties of ɛr = 91.1, Qf = 4870 GHz and τf = 18.5 ppm/°C could be obtained in [(Pb0.5Ca0.5)0.92La0.08](Fe0.5Nb0.5)O3 system when k = 1, w = 1 wt.% and sintered at 1050 °C for 4 h.

With the development of lead-free in electronic products, mixed soldering of lead-free component with lead solder is inevitable in high reliability electronic assembly. For the mixed assemblies, the primary task is to ensure the reliability of mixed solder joints. This study is aimed at finding out the harmonic vibration fatigue properties of plastic ball grid array (PBGA) mixed solder joints under 1st natural frequency and getting the relation curve between equivalent stress and number of fatigue cycles of the mixed solder joints. A specified PBGA assembly was designed with a piece of daisy-chained printed circuit board (PCB). Modal test and harmonic vibration test were implemented. The PCB strain was measured by strain gages, and the time to failure of solder joints was monitored by an event detector. After comparing natural frequencies, modal shapes and PCB strain with the simulation corresponding results, finite element model (FEM) was validated. Then, the volume averaged equivalent stress of mixed solder joints was discovered with modified model. Finally, S-N curve of mixed solder joints was fitted with Basquin power law relation. In the hopeful future, combining the fitted S-N curve with other methodologies, the vibration fatigue life of mixed solder joints could be estimated.

In this study, the formation mechanisms of Kirkendall voids in Sn3Ag0.5Cu/Cu and Ni/Sn3Ag0.5Cu/Cu joints were investigation, and the coupling effect of joint size and Kirkendall voids on the fracture features of Ni/SnAgCu/Cu joints were also studied. It was found that the size effect had a significant influence on the formation of Kirkendall voids at Cu side in Sn3Ag0.5Cu/Cu and Ni/Sn3Ag0.5Cu/Cu joint, the ratio of Kirkendall voids to the total area of Cu 3 Sn layer increased with solder volume irrespective of the structure of joint. The coupling effect of Ni and Cu inhibited the growth of Cu 3 Sn significantly and increased the ratio of Kirkendall voids to the total area of Cu 3 Sn layer. However, the Kirkendall effect seems to have no obvious influence on the fracture features of Ni/ Sn3Ag0.5Cu /Cu joints compared with Cu/Sn3Ag0.5Cu/Cu joint by using lap-shear test method.

In this study, the effect of series Pb content on shear performance of SnAgCu-xSnPb/Cu solder joint was investigated. It was found that Pb content influenced the BGA solder joint shear strength significantly. The shear strength as a function of Pb content shows a parabola trend. The shear strength increased with Pb content increased from 0% to 9.22%. Then the shear strength value kept at a high level from 9.22% to 26.49%. However, this trend stopped when Pb content is 29.42% and the shear strength began to decrease. The failure mode is strongly associated with fracture energy. When Pb was imported into Sn3.0Ag0.5Cu/Cu solder joint, the fracture energy (shear work) of solder joint shear test decreased. When Pb content ranges from 4.67% to 37% the fracture energy seemed no obvious difference. Pb content influenced the solidification sequence when the solder joint was cooling down. The solidification sequence is closely related to the microstructure of mixed solder joint.

We report a highly efficient and high power self-starting femtosecond Cr:forsterite laser pumped by a 1064-nm Yb doped fibre laser. Five chirped mirrors are used to compensate for the intra-cavity group-delay dispersion, and the mode-locking is initiated by a semiconductor saturable absorber mirror (SESAM). Under pump power of 7.9 W, stable femtosecond laser pulses with average power of 760mW are obtained, yielding a pump power slope efficiency of 12.3%. The measured pulse duration and spectral bandwidth (FWHM) are 46 fs and 45nm; the repetition rate is 82 MHz.

The influence of different Pb content on solidification behavior, formation and evolution of microstructure in mixed solder alloy were investigated. It has been shown that the onset temperature of DSC cooling curve decreased with increasing of Pb content or decreasing of solder ball's volume. When Pb content in solder alloy reached 21.90wt.%, the solidification behavior of mixed solder alloy was dominated by eutectic Sn-Pb alloy. The addition of Pb resulted in the coarsening of dentritic β-Sn in solder matrix significantly, and the addition of Pb resulted in the formation of a low melting temperature Sn-Ag-Pb ternary eutectic alloy easily.

Five group thermal resistance test samples of the power devices were performed high temperature aging at 150°C for 0h, 24h, 48h, 72h, 96h respectively, then the maximum thermal test current without device self-heating temperature rise of 5mA was determined, and the transient thermal resistance test method was employed to obtain the heat transient response curves containing the thermal resistance and heat capacity parameters respectively. Numerical convolution method and structure function analysis techniques were used to acquire total junction-case thermal resistances of power devices, and the internal thermal resistance of each layer's package structure of the chip, the adhesive and the case was separated from the total junction-case thermal resistances. Finally, the scanning acoustic test was performed on the five group samples to validate the package defect and the effect of typical package defect on internal thermal resistance of device was analyzed. The results show that the structure function analysis method can effectively separate the thermal resistance of internal each layer package structure. The excursion of structure function and die attachment delamination of tested sample were found after 96 hours aging. The excursion of structure function compared with the original curve can reflect the internal package quality of power device. Generally, the package defect, such as voids, delamination, etc. could induce the increase of internal thermal resistance. The structure function analysis method provides a favorable reference to thermal reliability design and analysis of power devices. Reducing the thermal resistance of the adhesive layer is the key to improving the overall heat dissipation of the device.

To study the tin whisker growth behavior of different lead substrates, five kinds of lead frames were designed as plating substrates and the pure tin were electroplated onto the substrates respectively, then the thermal shock, high temperature/humidity storage, and the ambient temperature/humidity storage test were performed under the annealing and un-annealing conditions, and the effect of lead substrates on the crystal structures of Sn plating was analyzed and the influence of environment condition, crystal structure, annealing process on the tin whisker growth was studied. The results showed that the Sn plating of brass frame was easier to grow tin whisker than other lead frames because of bigger crystal sizes and smaller boundary interspaces of grains, The temperature change condition was the best external driving force, The capability of anti-tin whisker was excellent for Sn plating of C7025 substrate plating, and the external environment had a great impact to the tin whisker growth of 42 alloy substrate plating. At last, the annealing process was available to slow down the growth of tin whisker under isothermal condition.

The Pb contamination on the solidification behaviors and shear properties of Backward Compatible solder joints were investigated. The solidification behavior of solder and joint examined by using a DSC instrument, and it was found that the addition of Pb in Sn3.0Ag0.5Cu would change the primary phase during solidification and change the microstructure of backward compatible solder and joint, meantime, it is easy form a low melting temperature Sn-Ag-Pb ternary eutectic alloy, and the pasty rang between two endothermic(or exothermic) peak decreases with the increasing of Pb content in solder matrix. The discrepancy in solidification behavior results in different microstructures significantly. The average sizes of β-Sn and IMC particles(Ag3Sn and Cu6Sn5) in solder matrix are larger than those in Sn3.0Ag0.5Cu solder relatively. However, the shear force of backward compatible mixed joints is higher than SAC/Cu joint independent of Pb content when Pb content in solder matrix is less than 30 wt.% by using ball shear test, it seems that the low melting temperature Sn-Ag-Pb has little influence on the shear properties of mixed joints with a single interface in as-solidified condition. The addition of Pb in Sn3.0Ag0.5Cu solder apparently facilitated the slip of β-Sn and stress release under shear stress to some extent.