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In the actual production process, soldering is a key step in the flip-chip packaging process. The reliability of the interconnection interface of flip-chip LED chips is considered to be one of the most important reliability issues. This paper studies the influence of different soldering temperatures on the microstructure and shear behavior of the Au/Sn-3.0Ag-0.5Cu/Cu solder joints of flip-chip LED chips. The lead-free solder Sn-3.0Ag-0.5Cu was selected as the solder. The microstructure of the intermetallic compound (IMC) interface and the inferred surface of the solder joint is observed, and the microstructure evolution of the solder joint is analyzed. The void ratio of the solder joints at 250°C, 260°C, 270°C, 280°C, and 290°C soldering temperature was tested to characterize the influence of the contact area between the chip and the solder joint on the shear stress. In addition, the solder joints were aged for 1000 hours in an environment with a relative humidity of 85°C/85%, and a shear test was performed to evaluate the influence of the interface reaction on the mechanical reliability of the solder joints during the isothermal aging process. The research show that when the soldering temperature is 270°C, the Au on the bottom of the chip, and the solder and Cu on the substrate have fully reacted, and the solder joints have high shear resistance. The shear strength of the aging solder joints increases first and then decreases, because the high temperature repairs the defects in the solder layer caused by the low soldering temperature to a certain extent. With the extension of aging, cracks and voids gradually appear at the fracture interface, and the effective contact area decreases. The shear strength of the solder joint decreases, and the fracture mode becomes brittle. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of two different welding methods, direct welding (DW) and vacuum furnace welding (VFW), on flip-chip light-emitting diode (FC-LED) filament properties. Shearing force, SEM, steady-state voltage, steady-state luminous flux, and change of photoelectric performance with aging time were employed to characterize the differences in filament properties between the two welding methods. The shearing test revealed that the average shearing force of the VFW group was higher than that of the DW group, but the two groups followed the standard. Furthermore, the microstructure of the VFW group fault was more smoother, and the voids were fewer and smaller based on the SEM test results. The steady-state voltage and luminous flux revealed that the VFW group had a more concentrated voltage and a higher luminous flux. The aging data revealed that the steady-state voltage change rate of both groups was not very different, and both luminous flux maintenance rates of the VFW group were higher than those of the DW group, but all were within the standard range. In conclusion, if there is a higher requirement for filament in a practical application, such as the filament is connected in series or in parallel and needs a higher luminous flux, it can be welded using vacuum furnace welding. If the focus is on production efficiency and the high performance of filaments is not required, direct welding can be used. [ABSTRACT FROM AUTHOR]

We realized a facile chromaticity tuning for the YAG:Ce3+ phosphor-in-glass (PiG) based WLEDs (white light-emitting diodes) by tape casting CaAlSiN3:Eu2+ red film layer on PiG plate and then encapsulated to a remote-type stacking configuration. Experimental results indicated that the color converting material realized a tunable chromaticity quality and yield high luminous efficiency. Microstructures were investigated to reveal the state of phosphor dispersion, as well as interaction of PiG substrate with red film layer. Besides, the thickness of red films was discussed in detail to illustrate its influence on the luminous properties. The optimized WLED exhibits excellent optical performance with a luminous efficiency of 95.76 lm/W, a correlated color temperature of 3949 K, a color rendering index of 82.2, and a color shift deviation from Planckian locus in Duv of 0.0043. The color converter with good heat-resistance performance is expected to be a promising indoor high-quality general lighting source. [ABSTRACT FROM AUTHOR]

The composition, microstructure and corrosion behavior of Al Mg Ga In Sn alloy in cast and heat-treatment were investigated by XRD (X-ray diffraction), SEM (scanning electron microscope) and EDS (energy dispersive spectrometer). The hydrogen evolution parameters, and the electrochemical properties based on different heat-treatment parameters conditions and immersion temperature were also tested. As the heat-treated temperature increased, the second phases were found to be spheroidizing or ellipsoidal shape due to the diffusion and solid solution. The reaction can be divided into three stages: i) the amalgamation initial stage; ii) the micro-galvanic reaction for propagation corrosion; iii) the dissolution-precipitation reaction for uniform corrosion. The hydrolysis rate reached the maximum value when the sample was annealed at temperature of 500 °C for 9 h. The hydrogen generation rate and the open electrochemical potential of the activated aluminum under water are both depending on heat treatment time, heat treatment temperature, and reaction temperature. A corrosion mechanism was also proposed in which Mg 2 Sn and eutectic phase acted as the induction reaction stage during hydrolysis reaction. [ABSTRACT FROM AUTHOR]

The white LED was fabricated using a mixture of phosphors (LuAG: Ce and CaAlSiN 3 : Eu) in bismuthate glass as converted materials. The phosphors (LuAG: Ce and CaAlSiN 3 : Eu) in glass was prepared by low-temperature co-sintering. The microstructure and luminescent mechanism of a mixture of phosphors (LuAG: Ce and CaAlSiN 3 : Eu) in glass was investigated, the results showed that phosphors (LuAG: Ce and CaAlSiN 3 : Eu) not only exist in the glass matrix without noticeable reaction, but also can be effectively excited by blue light. After simply varying the weight ratio of bismuthate glass to phosphors (LuAG: Ce and CaAlSiN 3 : Eu) as well as the ratio of LuAG: Ce to CaAlSiN 3 : Eu, the CIE chromaticity tuning in the fabricated LED has been achieved. It has revealed that the fabricated white LED has excellent developing potential for different lighting applications. [ABSTRACT FROM AUTHOR]