Geometry effect on mechanical performance and fracture behavior of micro-scale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints

Solder joint integrity has long been recognized as a key issue affecting the reliability of integrated circuit packages. In this study, both experimental and finite element simulation methods were used to characterize the mechanical performance and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with different standoff heights (h, varying from 500 to 100 μm) and constant pad diameter (d, d = 480 μm) and contact angle under shear loading. With decreasing h (or the ratio of h/d), results show that the stiffness of BGA solder joints clearly increases with decreasing coefficient of stress state and torque. The stress triaxiality reflects the mechanical constraint effect on the mechanical strength of the solder joints and it is dependent on the loading mode and increases dramatically with decreasing h under tensile loading, while the change of h has very limited influence on the stress triaxiality under shear loading. Moreover, when h is decreased, the concentration of stress and plastic strain energy along the interface of solder and pad decreases, and the fracture location of BGA solder joints changes from near the interface to the middle of the solder. Both geometry and microstructure greatly affect the shear behavior of joints, the average shear strength shows a parabolic trend with decreasing standoff height. Furthermore, the brittle fracture of BGA solder joints after long-time isothermal aging was investigated. Results obtained show that, under the same shear force, the stress intensity factors, K_I and K_II, and the strain energy release rate, G_I, at the Sn–3.0Ag–0.5Cu/Cu₆Sn₅ interface and in the Cu₆Sn₅ layer obviously decrease with decreasing h, hence brittle fracture is more prone to occur in the joint with a large standoff height.     

Wear of die after drawing of pickled or reverse bent wire rod

The object of this paper was to evaluate the difference of die wear by using wire rods descaled by two different treatments; pickling or reversed bending. The paper gives a background of wear mechanism and describe a method to estimate die wear in wire drawing. The conclusions of the experiments were that the wire rod preparation seems to be of minor importance for the wear of die. A die in the sixth draft had a magnitude lower wear, compared to the die in the first draft. Abrasive wear is present from the WC grains, torn out in the adhesive wear, on both dies used on pickled wire rod and reverse bent and steel wool cleaned wire rod.     

The influence of a waveguiding structure on the excitonic luminescence of anatase thin films

Spectral and spatial properties of the excitonic luminescence of TiO₂ (anatase) waveguide layers grown by the atomic layer deposition on dielectric and metal substrates were investigated at low temperatures. Significant changes in self-trapped-excitonic (STE) spectra were observed in the direction nearly parallel to the film surface. The characteristic broad band STE emission spectrum of anatase peaking at ∼2.3 eV was transformed into directed spectrally narrow polarised bands. It was concluded that the leaky modes of the planar waveguide were responsible for this effect.     

Electrochemical Impedance Spectroscopy: Insights for fretting corrosion experiments

Using Electrochemical Impedance Spectroscopy (EIS), in the tribocorrosion field, especially in fretting corrosion, is new. The key point of this work is using EIS. The influence of ionic strength (I_c) and a model protein, albumin, on passive layer behavior was studied. At cathodic applied potential, E=−400 mV(SCE), fretting leads to an increase of corrosion current, without albumin. The current drop increases with the ionic strength. With albumin of 20 g L⁻¹, I is constant whatever the ionic strength: albumin acts as a corrosion inhibitor. Thanks to EIS, the degradation of passive layer due to fretting-corrosion is assessed by the fall of Polarization Resistance (R_p) and exponent of constant phase element (n), and the rise of constant phase element (Q).     

Soybean milk derived carbon intercalated with reduced graphene oxide as high efficient electrocatalysts for oxygen reduction reaction

Exploring high-performance and low-cost metal-free oxygen reduction reaction (ORR) catalysts from biomass-derived materials is vital to the development of novel energy conversion devices such as fuel cells, etc. Herein, nitrogen-enriched soybean milk derived carbon (BDC/rGO-HT-NH₃) intercalated with reduced graphene oxide (rGO) electrocatalyst is prepared via one-pot hydrothermal synthesis method followed with nitridation by NH₃. The resultant catalyst with high surface area, good conductivity and high content of N (9.4 at.%) shows high electrocatalytic activity towards ORR in alkaline medium, which mainly happens through the direct 4-electron pathway. The onset potential of BDC/rGO-HT-NH₃ catalyzed ORR is 0.96 V vs RHE, which is only 0.11 V lower than that of the commercial Pt/C (20 wt%) catalyst. In addition, the BDC/rGO-HT-NH₃ catalyst shows superior long-term running durability. The desirable catalytic performances enable the facile synthesis approach of BDC/rGO-HT-NH₃ to be a promising methodology for transforming other biomass materials to N-enriched carbon based materials as low-cost and environmental friendly catalysts for ORR.     

钛表面纳米管处理后在含白蛋白模拟唾液中的电化学性质(英文)

探讨了白蛋白对表面纳米管处理后的纯钛( nanotubular Ti,NT)中模拟唾液中电化学行为的影响,白蛋白浓度为5 g/L.与机械抛光的纯钛(mechanically polished Ti,MPT)相比,白蛋白导致NT的开路腐蚀电位向正方向偏移,而且更加有效地导致其阳极极化行为的变化与腐蚀电流密度的降低.取决于纳米管层性质的表面电容随着浸泡时间的增加而增大.结果表明,纯钛表面的纳米管有利于白蛋白的吸附.     

预变形程度和变形温度对CoCrFeMnNi高熵合金的变形机制及后续再结晶行为的影响

使用电子背向散射衍射技术研究了预变形程度和变形温度对CoCrFeMnNi高熵合金的变形机制和后续再结晶行为的影响。结果表明,在低应变量条件下,变形温度对CoCrFeMnNi高熵合金的形变微观组织没有显著的影响,形变机制均以位错滑移为主导;在室温下变形,随着应变量的增大位错滑移和孪生变形共同主导变形。在低温退火条件下预变形程度对再结晶行为也没有显著的影响,难以发生再结晶。但是在高温退火条件下,变形程度的提高使再结晶晶粒显著细化和∑3晶界的比例大幅度提高。