The solid-state, cross-interaction between the Ni layer on the component side and the Cu pad on the printed circuit board (PCB) side in ball grid array (BGA) solder joints was investigated by employing Ni(15 lm)/Sn(65 lm)/Cu ternary diffusion couples. The ternary diffusion couples were prepared by sequentially electroplating Sn and Ni on a Cu foil and were aged isothermally at 150, 180, and 200°C. The growth of the intermetallic compound (IMC) layer on the Ni side was coupled with that on the Cu side by the mass flux across the Sn layer that was caused by the difference in the Ni content between the (Cu 1-x Ni x ) 6 Sn 5 layer on the Ni side and the (Cu 1-y Ni y ) 6 Sn 5 layer on the Cu side. As the consequence of the coupling, the growth rate of the (Cu 1-x Ni x ) 6 Sn 5 layer on the Ni side was rapidly accelerated by decreasing Sn layer thickness and increasing aging temperature. Owing to the cross-interaction with the top Ni layer, the growth rate of the (Cu 1-y Ni y ) 6 Sn 5 layer on the Cu side was accelerated at 150°C and 180°C but was retarded at 200°C, while the growth rate of the Cu 3 Sn layer was always retarded. The growth kinetic model proposed in an attempt to interpret the experimental results was able to reproduce qualitatively all of the important experimental observations pertaining to the growth of the IMC layers in the Ni/Sn/Cu diffusion couple.
Abstract:The formation and morphological evolution of germanides formed in a ternary Ni/Ta-interlayer/Ge system were examined by ex situ and in situ annealing experiments. The Ni germanide film formed in the Ni/Ta-interlayer/Ge system maintained continuity up to 5508C, whereas agglomeration of the Ni germanide occurred in the Ni/Ge system without Ta-interlayer. Through microstructural and chemical analysis of the Ni/Ta-interlayer/Ge system during and after in situ annealing in a transmission electron microscope, it was confirmed that the Ta atoms remained uniformly on the top of the newly formed Ni germanide layer during the diffusion reaction. Consequently, the agglomeration of the Ni germanide film was retarded and the thermal stability was improved by the Ta incorporation.
Abstract:The oxidation mechanism and thermal stability of nickel oxide~NiO!/carbon nanotube~CNT! composites were investigated by examining composites with different NiO contents by thermogravimetric analysis and transmission electron microscopy~TEM!. NiO acts as a catalyst in the oxidation of CNT in the composite. CNTs can be oxidized, even in a vacuum, by reducing NiO to nickel at temperatures lower than the normal oxidation temperature of CNTs. This phase transition was confirmed directly by in situ heating TEM observations. In air, reduction by CNT occurs simultaneously with reoxidation by gaseous O 2 molecules, and NiO maintains its phase. The thermal stability decreased with increasing NiO content because of defects in the CNT generated by the NiO loading.
A very compact and frequency tunable Wilkinson power divider is suggested and demonstrated for the first time. By replacing k/ 4 section lines in a conventional Wilkinson power divider with varactor tunable, lumped-element synthetic transmission lines, dramatical size reduction and frequency tunability has been achieved. The prototype circuit fabricated shows excellent performance. For tunable frequencies from 0.71 to 0.99 GHz, the insertion loss is less than 3.52 dB, whereas the return loss and isolation are greater than 20 dB. Yet, the size of this voltage controllable Wilkinson power divider is only 4 mm by 8 mm, which occupies less than 3% area of original Wilkinson power divider structure.
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