Al surface morphology effect on flip-chip solder bump shear strength

This paper reports the result of a study on the effect of aluminum pad surface morphology on the flip-chip solder bump reliability. The influence of the Al surface morphology on the electroless zinc/nickel/gold UBM is presented. The reliability of the solder bump as measured by ball shear force is reported. Al pad were produced using two RF sputtering systems: CVC-601 and Varian-3180. The Al targets used in CVC and Varian system were 99%Al–1%Si and 98.95%Al–1%Si–0.05%Ti respectively. The surface of the CVC sputtered Al samples were smooth while the surface of the Varian sputtered Al samples were rough. All the samples were subjected to the electroless zinc/nickel/gold plating. The results suggest that after plating, the smooth Al surface resulted in a fine nickel UBM surface while the rough Al surface formed a coarse nickel UBM surface. Ball shear test was conducted after the solder balls were bumped on the UBM. Result shows that the fine UBM surface samples have twice the shear strength compared to the samples with coarse UBM surface samples. The analysis of the results indicates that shear surface occurred at the UBM and the solder interface for samples with rough UBM surface leading to the lower shear strength. Nickel bump shear test result shows that pretreatment of Al pad surface by sodium hydroxide and nitric acid created more zinc seeds this led to better electroless nickel plating. Nickel bump shear tests also shows that double zincated bumps had higher shear strength than single zincated bumps. To obtain reliable flip-chip solder bumps, it is essential to maintain good Al pad surface morphology, pretreatment of the Al pad and undergo second zincation.     

Process windows for low-temperature Au wire bonding

The process windows are presented for low-temperature Au wire bonding on Au/Ni/Cu bond pads of varying Au-layer thicknesses metallized on an organic FR-4 printed circuit board (PCB). Three different plating techniques were used to deposit the Au layers: electrolytic plating, immersion plating, and immersion plating followed by electrolytic plating. Wide ranges of wire bond force, bond power, and bond-pad temperature were used to identify the combination of these processing parameters that can produce good wire bonds, allowing the construction of process windows. The criterion for successful bonds is no peel off for all 20 wires tested. The wire pull strengths and wire deformation ratios are measured to evaluate the bond quality after a successful wire bond. Elemental and surface characterization techniques were used to evaluate the bond-pad surfaces and are correlated to wire bondability and wire pull strength. Based on the process windows along with the pull strength data, the bond-pad metallization and bonding conditions can be further optimized for improved wire bondability and product yields. The wire bondability of the electrolytic bond pad increased with Au-layer thickness. The bond pad with an Au-layer thickness of 0.7 μm displayed the highest bondability for all bonding conditions used. The bondability of immersion bond pads was comparable to electrolytic bond pads with a similar Au thickness. Although a high temperature was beneficial to wire bondability with a wide process window, it did not improve the bond quality as measured by wire pull strength.     

THE CURRENT DISTRIBUTION IN THROUGH-HOLE ELECTRODEPOSITION.II: TERTIARY CURRENT DISTRIBUTION

Tertiary current distribution was computed on both the inside and the outside surfaces of a through-hole during electrodeposition. Experiments were conducted in copper deposition at two different copper sulfate solutions. Results were compared with the theoretical calculation.     

On symmetric Runge-Kutta methods of high order

The usual characterization of symmetry for Runge-Kutta methods is that given by Stetter. In this paper an equivalent characterization of symmetry based on theW-transformation of Hairer and Wanner is proposed. Using this characterization it is simple to show symmetry for some well-known classes of high order Runge-Kutta methods which are based on quadrature formulae. It can also be used to construct a one-parameter family of symmetric and algebraically stable Runge-Kutta methods based on Lobatto quadrature. Methods constructed in this way and presented in this paper extend the known class of implicit Runge-Kutta methods of high order.     

Fault tolerance in Clos–Knockout multicast ATM switch

In this paper, we propose a new architecture for multicast ATM switches with fault tolerant capability based on the Clos–Knockout switch. In the new architecture, each stage has one more redundant switch module. If one switch module is faulty, the redundant module would replace the faulty one. On the other hand, under the fault‐free condition, the redundant modules in the second and third stages will provide additional alternative internal paths, and hence improve the performance. The performance analysis shows that the cell loss probability is lower than the original architecture when all modules are fault free, and the reliability of the original architecture is improved. Copyright © 2002 John Wiley & Sons, Ltd.     

RF, DC, and reliability characteristics of ALD HfO/sub 2/-Al/sub 2/O/sub 3/ laminate MIM capacitors for Si RF IC applications

High-performance metal-insulator-metal capacitors using atomic layer-deposited HfO/sub 2/-Al/sub 2/O/sub 3/ laminate are fabricated and characterized for RF and mixed-signal applications. The laminate capacitor can offer high capacitance density (12.8 fF//spl mu/m/sup 2/) up to 20 GHz, low leakage current of 4.9/spl times/10/sup -8/ A/cm/sup 2/ at 2 V and 125/spl deg/C, and small linear voltage coefficient of capacitance of 211 ppm/V at 1 MHz, which can easily satisfy RF capacitor requirements for year 2007 according to the International Technology Roadmap for Semiconductors. In addition, effects of constant voltage stress and temperature on leakage current and voltage linearity are comprehensively investigated, and dependences of quadratic voltage coefficient of capacitance (/spl alpha/) on frequency and thickness are also demonstrated. Meanwhile, the underlying mechanisms are also discussed.     

Thermo-Oxidative aging of a primary lightguide coating in films and dual-coated fibers

The thermo-oxidative aging of a polyether urethane lightguide primary coating has been studied in films and dual-coated fibers, In films, oxygen absorption is correlated with changes in modulus, yellowness, glass transition temperature, and sample weight. Thermal aging of fibers shows similar trends with regards to coating weight loss and discoloration as those observed with films. In addition, the force to mechanically strip the fiber follows the same patterns of change as the modulus of aged films. For both films and fibers, the time for onset of property changes varies inversely with temperature and can be delayed by the incorporation of an antioxidant.     

Effect of retained austenite on the hydrogen content and effective diffusivity of martensitic structure

In this work, the effects of retained austenite on the hydrogen content and the effective hydrogen diffusivity of an otherwise fully martensitic structure have been studied. In the electrochemical permeation experiment, the results on the first permeation transient indicate that high-carbon as-quenched specimens have a lower effective diffusivity than those with an additional subzero treatment. This was due to the presence of retained austenite in the former specimens, which afforded more sites for hydrogen trapping throughout the specimen membrane, hence lowering the hydrogen diffusion during the first transient. As the hydrogen traps were filled up, however, the second permeation transients gave similar effective diffusivity for both as-quenched and quenched + subzero-treated specimens. After hydrogen charging in hydrogen sulfide solution, the hydrogen contents of the specimens were determined using the vacuum hot extraction method. The results show that the hydrogen contents of as-quenched specimens were higher than those of the specimens subjected to quenched + subzero treatment. This again was due to the existence of retained austenite in as-quenched martensitic matrix, where the interfaces between the retained austenite and martensitic plates provided extra sites for hydrogen trapping. The hydrogen content of the presenting retained austenite in the martensite was independent of the carbon content of the specimen, but only depended on the hydrogen-charging period.     

Highly Packaged Terahertz Down-Converter Modules Using 3-D Integration

This letter describes the design of highly packaged heterodyne receivers for terahertz applications. The 3-D integration of a terahertz mixer with a low-noise intermediate frequency amplifier is implemented for the first time using off-the-shelf components. Thereby, an-order-of-magnitude volume and weight reduction are accomplished. We validate our packaging approach experimentally, demonstrating performance comparable to that of a similar receiver assembled with planar interconnects. These 3-D receivers can in principle constitute the basis of close-fitting, densely populated focal plane arrays.     

Image decomposition combining staircase reduction and texture extraction

This paper proposes a natural and efficient way to achieve staircase reduction in texture extraction models of image processing. Moreover, we propose a precise framework for this amalgamation. In a sense, we utilize the best of both worlds: (I) the use of higher order derivatives through a variant of the Chambolle–Lions inf convolution energy (an image decomposition model in itself) along with (II) approximations to Meyer’s G and E norms including the H⁻¹ negative norm for ameliorating staircasing in image decomposition and restoration problems.