Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers.
Among them, Zn–Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn–Al–Mg–Ga
solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment
was performed in a forming gas environment at temperature ranging from 370 to 400 °C. At the interface with Cu lead-frame,
CuZn4, Cu5Zn8 and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al3Ni2 IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn3 IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with
a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about
45 wt% Al). Zn–Al–Mg–Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the
Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 °C. Die shear strength
was found within the acceptable limit (21.8–29.4 MPa) for all the die attach temperatures. Die shear strength of standard
Pb–Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output
voltage after 1,000 thermal cycles was found 12.1%. 相似文献
The present study numerically explores the mixed convection phenomena in a differentially heated ventilated square cavity with active flow modulation via a rotating plate. Forced convection flow in the cavity is attained by maintaining external fluid flow through an opening at the bottom of the left cavity wall while leaving it through another opening at the right cavity wall. A counter-clockwise rotating plate at the center of the cavity acts as an active flow modulator. Moving mesh approach is used for the rotation of the plate and the numerical solution is achieved using arbitrary Lagrangian-Eulerian finite element formulation with a quadrilateral discretization scheme. Transient parametric simulations have been performed for various frequency of the rotating plate for a fixed Reynolds number (Re) of 100 based on maximum inlet flow velocity while the Richardson number (Ri) is maintained at unity. Heat transfer performance has been evaluated in terms of spatially averaged Nusselt number and time-averaged Nusselt number along the heated wall. Power spectrum analysis in the frequency domain obtained from the fast Fourier transform analysis indicates that thermal frequency and plate frequency start to deviate from each other at higher values of velocity ratio (>4). 相似文献
The Libyan economy is dominated by the oil and the gas industry which are considered as the primary energy sources for the generating power plants. With the increased energy demands in the near future, Libya will be forced to burn more oil and gas. This, in turn will result in reducing the country revenue, threatening the economy and increasing the CO2 emission. This triggers the alarm for Libya to an urgent plan to diversify the energy sources through using sustainable energy. The sun showers Libya every day by a huge amount of sunshine, especially during the peaks in the summer days. Recently, the country has been struggling to satisfy its escalating energy demands. The residential and street lighting loads constitute more than 50% of the electricity demands in Libya. Street lighting consumes more than 3.996 TW h, which is around one fifth of the energy demands in Libya. Energy conservation and transition from fossil fuel to renewable energy could have significant profit on the energy sector in Libya. For example, Libya is still relying on the old-fashioned, inefficient and unsustainable street lighting systems. Replacing the old technology lighting systems with up-to-date solar powered lighting system can achieve energy saving and sustainability. In this paper, improving the energy situation in Libya through replacing the high pressure sodium street lighting systems with solar powered LED street lighting systems is investigated. A four km road is chosen as a case study. Four alternatives are analyzed; grid-powered high pressure sodium lamp street lighting system, grid-powered LED lamp street lighting system, stand-alone solar powered LED street lighting system and grid-connected solar powered LED street lighting system. The four options are compared in terms of the capital cost, maintenance cost, total cost, fuel cost and the CO2 emission. Replacing the high pressure sodium lamp system with LED lamp system saves 75% of energy and reduces the CO2 emission by 75%. The stand-alone solar powered LED lighting system cuts the CO2 emission, saves the fuel and is economically feasible. Furthermore, improvement is attained if the solar powered lighting system is connected to the grid where the excess energy is fed to the grid. The two solar powered options are economically feasible and sustainable. 相似文献
Superconductivity has been improved by partial substitution of slightly higher electronegative (M=Bi, Hg) elements at Tl sites in (Cu0.5Tl0.5?xMx)Ba2O4??? (x=0,0.25) charge reservoir layer of (Cu0.5Tl0.5?xMx)Ba2Ca2Cu3O10??? superconductor. These samples were characterized by X-ray diffractometry, dc-resistivity, ac-susceptibility, FTIR absorption spectroscopy, and fluctuation-induced conductivity (FIC) analysis. The FIC analysis has been carried out in the light of Aslamasov?CLarkin (AL) theory on the resistivity versus temperature curves of (Cu0.5Tl0.5?xMx)Ba2Ca2Cu3O10??? superconductor. The microscopic parameters such as cross-over temperature (To), zero-temperature coherence length ??c(0), inter-layer coupling (J), and critical exponents (??2D and ??3D) have been determined from FIC analysis of these samples and tried to correlate them to the superconductivity order parameters. A?direct correlation between the cross-over temperatures (To) and zero resistivity critical temperature {Tc(R=0)} and carrier concentration in these samples has been observed. The improvement in Tc(R=0) and the shift of 3D AL region to higher temperature values with the doping of Bi and Hg have also been observed. 相似文献
Dithiacarbamates reacted with malononitrile dimer to give 1,4-dihydropyridine-2-thiols. The structures of the obtained products were proven by IR, mass, and NMR spectra and elemental analyses. The reaction mechanism is also discussed. 相似文献
Heat and mass transfer effects in three-dimensional mixed convection flow of viscoelastic fluid over a stretching surface with convective boundary conditions are investigated. The fluid is electrically conducting in the presence of constant applied magnetic field. Conservation laws of energy and concentration are based upon the Soret and Dufour effects. First order chemical reaction effects are also taken into account. By using the similarity transformations, the governing boundary layer equations are reduced into the ordinary differential equations. The transformed boundary layer equations are computed for the series solutions. Dimensionless velocity, temperature, and concentration distributions are shown graphically for different values of involved parameters. Numerical values of local Nusselt and Sherwood numbers are computed and analyzed. It is found that the behaviors of viscoelastic, mixed convection, and concentration buoyancy parameters on the Nusselt and Sherwood numbers are similar. However, the Nusselt and Sherwood numbers have qualitative opposite effects for Biot number, thermophoretic parameter, and Soret-Dufour parameters.
Multimedia Tools and Applications - Enhancing the degree of learner productivity, one of the major challenges in E-Learning systems, may be catered through effective personalization, adaptivity and... 相似文献