Design rule development for microwave flip-chip applications

This paper presents a novel experimental approach for the analysis of factors to be considered when designing a flip-chip package. It includes the design of an experiment and statistical analysis of the outputs and uses both test-structure measurements and full-wave simulation techniques in the 1-35-GHz frequency range. The most significant factors are found to be, from the most to least important, the length of the area where the device and substrate overlap (referred to as conductor overlap), the bump diameter, and the width of the coplanar-waveguide transmission-line launch. These results are valid for conductor overlaps between 300-500 μm. For a lower value (120 μm), the significance level of the overlap decreases and the bump height also becomes significant. Test-structure measurements in the 120-200-μm overlap range validate this result and demonstrate the decrease in the significance level. The substrate thickness in the 10-25-mil interval is found to be statistically insignificant, therefore, it can be eliminated from further analysis. This approach provides a foundation for development of a set of design rules for RF and microwave flip-chip similar to RF integrated-circuit design rules     

Design of experiments (DOE) technique for microwave/millimeter wave flip‐chip optimization

We present a design of experiments (DOE) technique for microwave/millimeter wave flip‐chip characterization and optimization. Two optimization approaches, signal bump misalignment and transmission line compensation, are combined together for optimal performance for high frequency operation. First, the design of experiments method is presented and its advantages are emphasized. Then, the two techniques are combined together in a factorial experiment with the purpose of optimizing the return loss to any desired frequency. The experiment is based on test structure fabrication and measurements. The one‐factor‐at‐a‐time strategy shows that return loss performance is increased with the misalignment values and decreased with compensation for the frequency range of interest. However, the statistical analysis revealed that the optimal performance is achieved for maximum compensation, and minimum misalignment. The optimal structure is measured from 1 to 75 GHz and shows return loss better than 17 dB. The method can be extended to include more optimization factors in different analysis intervals. Copyright © 2003 John Wiley & Sons, Ltd.     

Wideband scalable electrical model for microwave/millimeter waveflip chip interconnects

We present a method for developing fully scalable lumped element models for flip chip interconnects. Measurements of test structures and full wave simulations are used to generate circuit models for various single bump configurations. Furthermore, regression models are developed for scaling the values of the elements with the physical attributes of the circuit. First, the method is validated using only two factors, then the model is extended to more inputs related to the bump geometry and placement. The values of L and C in a simple π model have been scaled with the conductor overlap, the distance from the ground bump to the edge of the ground plane, the width of the CPW launch, the bump height and diameter. Explicit formulas are obtained for L and C as a function of those variables. It has been found that the value of the inductance varies with the conductor overlap, bump height and diameter, while the capacitance is mostly affected by conductor overlap. This paper presents the first fully scalable model for microwave flip chip technology     

The Role of Reactive Oxygen Species in Microvascular Remodeling

The microcirculation is a portion of the vascular circulatory system that consists of resistance arteries, arterioles, capillaries and venules. It is the place where gases and nutrients are exchanged between blood and tissues. In addition the microcirculation is the major contributor to blood flow resistance and consequently to regulation of blood pressure. Therefore, structural remodeling of this section of the vascular tree has profound implications on cardiovascular pathophysiology. This review is focused on the role that reactive oxygen species (ROS) play on changing the structural characteristics of vessels within the microcirculation. Particular attention is given to the resistance arteries and the functional pathways that are affected by ROS in these vessels and subsequently induce vascular remodeling. The primary sources of ROS in the microcirculation are identified and the effects of ROS on other microcirculatory remodeling phenomena such as rarefaction and collateralization are briefly reviewed.     

Modeling and sensitivity analysis of circuit parameters for flip-chip interconnects using neural networks

This paper presents a neural network-based technique for modeling and analyzing the electrical performance of flip-chip transitions. A lumped element model using a simple pi equivalent circuit is used to characterize the electrical properties of the flip-chip bond. Statistical experimental design is used to extract the electrical parameters for flip-chip characterization from measurements and full-wave simulations up to 35 GHz. The extracted data is used to train back-propagation neural networks to obtain an accurate model of the pi equivalent circuit components and s-parameters as a function of layout parameters. The prediction error of the models is less than 5%. The models are used to obtain response surfaces for the entire range of variation of layout parameters. The neural network models are subsequently used to perform sensitivity analysis. All electrical parameters are shown to be sensitive to conductor overlap. The inductance and capacitance of the pi equivalent circuit are sensitive to the bump height. However, the return loss (S₁₁) is insensitive to the change in bump height. The coplanar waveguide width has a significant impact on the s-parameters, as it affects the matching of flip-chip transitions     

Mechanical factors direct mouse aortic remodelling during early maturation

Numerous diseases have been linked to genetic mutations that lead to reduced amounts or disorganization of arterial elastic fibres. Previous work has shown that mice with reduced amounts of elastin (Eln+/−) are able to live a normal lifespan through cardiovascular adaptations, including changes in haemodynamic stresses, arterial geometry and arterial wall mechanics. It is not known if the timeline and presence of these adaptations are consistent in other mouse models of elastic fibre disease, such as those caused by the absence of fibulin-5 expression (Fbln5−/−). Adult Fbln5−/− mice have disorganized elastic fibres, decreased arterial compliance and high blood pressure. We examined mechanical behaviour of the aorta in Fbln5−/− mice through early maturation when the elastic fibres are being assembled. We found that the physiologic circumferential stretch, stress and modulus of Fbln5−/− aorta are maintained near wild-type levels. Constitutive modelling suggests that elastin contributions to the total stress are decreased, whereas collagen contributions are increased. Understanding how collagen fibre structure and mechanics compensate for defective elastic fibres to meet the mechanical requirements of the maturing aorta may help to better understand arterial remodelling in human elastinopathies.