Sujuan Zhong

Properties and Microstructures of Sn-Bi-X Lead-Free Solders

The Sn-Bi base lead-free solders are proposed as one of the most popular alloys due to the low melting temperature (eutectic point: 139°C) and low cost. However, they are not widely used because of the lower wettability, fatigue resistance, and elongation compared to traditional Sn-Pb solders. So the alloying is considered as an effective way to improve the properties of Sn-Bi solders with the addition of elements (Al, Cu, Zn, Ga, Ag, In, Sb, and rare earth) and nanoparticles. In this paper, the development of Sn-Bi lead-free solders bearing elements and nanoparticles was reviewed. The variation of wettability, melting characteristic, electromigration, mechanical properties, microstructures, intermetallic compounds reaction, and creep behaviors was analyzed systematically, which can provide a reference for investigation of Sn-Bi base solders.

Cu/SnAgCu/Cu TLP with different thicknesses for 3D IC

Purpose This paper aims to investigate Cu/SnAgCu/Cu transient liquid phase (TLP) bonding with different thicknesses for three-dimensional (3D) integrated circuit (IC). Design/methodology/approach This paper includes experiments and finite element simulation. Findings The growth rate of the intermetallic compound layer during TLP soldering was calculated to be 0.6 μm/s, and the small scallop-type morphology Cu6Sn5 grains can be observed. With the decrease in thickness in solder joint, the thickness of intermetallic compounds represents the same size and morphology, but the size of eutectic particles (Ag3Sn, Cu6Sn5) in the matrix microstructure decrease obviously. It is found that with the increase in thickness, the tensile strength drops obviously. Based on finite element simulation, the smaller value of von Mises demonstrated that the more reliability of lead-free solder joints in 3D IC. Originality/value The Cu/SnAgCu/CuTLPbondingwithdifferentthicknessesfor3D IC was investigated.

Cu6Sn5 Whiskers Precipitated in Sn3.0Ag0.5Cu/Cu Interconnection in Concentrator Silicon Solar Cells Solder Layer

Cu6Sn5 whiskers precipitated in Sn3.0Ag0.5Cu/Cu interconnection in concentrator silicon solar cells solder layer were found and investigated after reflow soldering and during aging. Ag3Sn fibers can be observed around Cu6Sn5 whiskers in the matrix microstructure, which can play an active effect on the reliability of interconnection. Different morphologies of Cu6Sn5 whiskers can be observed, and hexagonal rod structure is the main morphology of Cu6Sn5 whiskers. A hollow structure can be observed in hexagonal Cu6Sn5 whiskers, and a screw dislocation mechanism was used to represent the Cu6Sn5 growth. Based on mechanical property testing and finite element simulation, Cu6Sn5 whiskers were regarded as having a negative effect on the durability of Sn3.0Ag0.5Cu/Cu interconnection in concentrator silicon solar cells solder layer.

Effects of PEG1000 and Sol Concentration on the Structural and Optical Properties of Sol–Gel ZnO Porous Thin Films

ZnO porous thin films were synthesized as antireflection coatings via a sol–gel dip-coating method with polyethylene glycol (PEG1000) utilized as a polymeric porogen on alumina transparent ceramics. The pore formation mechanism of the ZnO porous thin films was proposed through thermal and Fourier transformation infrared spectrometer (FTIR) analyses. The effect of sol concentrations on crystal structure, microstructure, and optical properties was also discussed. The experiment results indicated that all the ZnO thin films exhibited a hexagonal wurtzite structure with their preferred orientation along a (0 0 2) plane by X-ray diffraction (XRD) patterns. The grain size of the films increased from 30.5 to 37.4 nm with the sol concentration ranging from 0.2 to 1.0 M. Furthermore, scanning electron microscopy (SEM) images show that the pores on the surface were observed to first decrease as the sol concentration increased and then to disappear as the sol concentration continued to increase. The UV spectrum presents a maximum transmittance of 93.5% at a wavelength of 600 nm at a concentration of 0.6 M, which will be helpful in the practical applications of ZnO porous film on alumina transparent ceramic substrates. The pore formation mechanism of ZnO porous thin films can be ascribed to ring-like network structures between the PEG1000 and zinc oligomers under the phase separation effect.

Microstructural and electrical characteristics of rare earth oxides doped ZnO varistor films

ZnO-Bi2O3 varistor films doped with two kinds of rare earth element oxides (Lu2O3 and Yb2O3) were prepared by the sol-gel method. The effects of Lu2O3/Yb2O3 doping on the microstructure and electrical characteristics of ZnO-Bi2O3 varistor films were investigated. All samples show a homogenized morphology and an improved nonlinear relationship between the electric field (E) and current density (I). Both Yb2O3 and Lu2O3 doping can decrease the grain size of ZnO-Bi2O3 varistor films and improve the electrical properties, which have a positive effect on the development of ZnO varistor ceramics. Yb2O3 doping significantly increases the dielectric constant at low frequency. 0.2 mol. % Yb2O3 doped ZnO-Bi2O3 varistor films exhibit the highest nonlinear coefficient (2.5) and the lowest leakage current (328 μA) among Lu2O3/Yb2O3 doped ZnO-Bi2O3 varistor films. Similarly, 0.1 mol. % Lu2O3 doping increases the nonlinear coefficient to 1.9 and decrease the leakage current to 462 μA.ZnO-Bi2O3 varistor films doped with two kinds of rare earth element oxides (Lu2O3 and Yb2O3) were prepared by the sol-gel method. The effects of Lu2O3/Yb2O3 doping on the microstructure and electrical characteristics of ZnO-Bi2O3 varistor films were investigated. All samples show a homogenized morphology and an improved nonlinear relationship between the electric field (E) and current density (I). Both Yb2O3 and Lu2O3 doping can decrease the grain size of ZnO-Bi2O3 varistor films and improve the electrical properties, which have a positive effect on the development of ZnO varistor ceramics. Yb2O3 doping significantly increases the dielectric constant at low frequency. 0.2 mol. % Yb2O3 doped ZnO-Bi2O3 varistor films exhibit the highest nonlinear coefficient (2.5) and the lowest leakage current (328 μA) among Lu2O3/Yb2O3 doped ZnO-Bi2O3 varistor films. Similarly, 0.1 mol. % Lu2O3 doping increases the nonlinear coefficient to 1.9 and decrease the leakage current to 462 μA.

Reliability of Pb-free solder joints in FCBGA using finite element simulation and Taguchi method

Thermo-mechanical reliability of containing Pb and Pb-free solder joints in FCBGA device subjected to an accelerated thermal cyclic loading was investigated based on finite element simulation and Taguchi method. Effects of different control factors on the reliability of the lead-free solder joints were anlyzed and calculated. The corner solder joint is the most critical solder joints in the ball array, the top surface of the solder joint is the crack propagated location. The optimal combination in FCBGA assembly show obvious enhancement effect on fatigue life of solder joints. Moreover, the solder material is the most important factor among the control factors in the FCBGA device.