Papers by Abhay Maheshwari
MRS Proceedings, 1995
We have studied the surface morphology and wetting reaction of eutectic SnBi, eutectic SnPb, and ... more We have studied the surface morphology and wetting reaction of eutectic SnBi, eutectic SnPb, and pure Sn on Cu and Pd surfaces. In the case of Pd, the reactions were so fast that no quasiequilibrium wetting angle could be measured. The compound formation has changed not only the interfaces but also the surfaces. Due to the formation of a reaction band outside the solder cap, the SnPb solder is no longer wetting the Cu surface but rather the Cu-Sn compound surface. In the wetting interface between eutectic SnPb and Cu, the morphology of the scallop-like Cu-Sn compound grains shows that we may not apply the classical model of layered compound growth to analyze the rate of soldering reactions.
Physical Review Letters, 1993
The shapes of coherent misfitting Ni3A1 precipitates were systematically investigated using a par... more The shapes of coherent misfitting Ni3A1 precipitates were systematically investigated using a parameter g defined essentially by the ratio of particle sizes along &100) and &110&. The variation of (with size was measured in several alloys using electron microscopy. g does not depend uniquely on particle size; it is also strongly influenced by the volume fraction of Ni3AI. These results provide the first quantitative evidence that elastic interaction energy plays a major role not only in spatial correlations, but also in the morphological evolution of individual particles.
Acta Metallurgica et Materialia, 1995
Abstrac~Coherent equilibrium is investigated theoretically in alloys containing monodispersed sph... more Abstrac~Coherent equilibrium is investigated theoretically in alloys containing monodispersed spherical precipitates. The alloy system is subjected to a Dirichlet tessellation by constructing a Voronoi polyhedron around each particle, and for the purpose of calculation each polyhedron is approximated as a sphere. The basic unit of the microstructure is thus a cell consisting of concentric spheres, with the outer sphere occupied by the majority (matrix) phase. The stresses in each cell are derived analytically using as one of the boundary conditions the requirement that the displacements at the outer boundary vanish. Isotropic elasticity is assumed throughout. The equilibrium volume fraction and the coherent solubilities of the two phases are calculated as a function of the overall concentration of solute in the alloy. The relative importance of the lattice mismatch between the two phases, their elastic constants, and the curvatures of their free energies of mixing, is investigated theoretically. It is predicted that the equilibrium concentrations of both phases always increase with increasing volume fraction. The consequences of the theory on the Ni-Al and Cu-Co alloy phase diagrams are explored. Much larger effects are predicted for Ni-AI alloys than for CuzCo alloys, despite the fact that the lattice mismatch is over three times as large in the latter system. The reason is that the difference between the solute concentrations of the two phases is much bigger in CuzCo alloys. It is concluded that the influence of coherency effects will always be much greater for solid solutions in equilibrium with intermediate phases than for terminal solid solutions. Data on the solubility of Ni3AI in Ni-A1 alloys, which support the theory, are presented and discussed.
Acta Metallurgica et Materialia, 1992
The kinetics of coarsening of ?' precipitates in binary Ni AI alloys containing nominally 5.72, 5... more The kinetics of coarsening of ?' precipitates in binary Ni AI alloys containing nominally 5.72, 5.74 and 5.78 wt% A1 and aged at 630 C were investigated by transmission electron microscopy and magnetic analysis. The alloys were each pre-aged at a temperature just below its solvus prior to re-aging at 630uC. The volume fractions of 7' were low, between 0.02 and 0.03. The pre-aging treatment produced microstructures containing precipitates that nucleated heterogeneously on dislocations and grain boundaries, leaving empty matrix areas in which coherent 7' precipitates subsequently nucleated and coarsened. Measurements were made only on these precipitates. The coarsening kinetics are anomalous in that the rate constants decrease with increasing volume fraction, in contradiction with all the theories of this process. Furthermore, the increase is quite large, exceeding a factor of four over a range of volume fractions that increased by less than 40%, Additionally, the rate constants exceed the values expected from the literature by factors of 10~40. The distributions of particle sizes were measured, and with few exceptions were found to agree with those of earlier investigations. It is suggested that elastic interactions among the 7,' precipitates play a pivotal role in decelerating the kinetics of coarsening, overpowering the expected accelerating effect of increasing volume fraction.
Structure de lentille de concentrateur à large surface et procédé
L'invention concerne un module solaire comprenant un element substrat, une pluralite de bande... more L'invention concerne un module solaire comprenant un element substrat, une pluralite de bandes photovoltaiques disposees en une configuration de reseau chevauchant l'element substrat, et une structure de concentrateur comprenant un materiau en verre extrude couple fonctionnellement a la pluralite de bandes photovoltaiques. Une pluralite de regions convexes allongees est configuree dans la structure du concentrateur. Les regions convexes allongees sont respectivement couplees aux bandes photovoltaiques. Chacune des regions convexes allongees comprend une longueur et une region de surface convexe caracterisee par un rayon de courbure, chacune des regions convexes allongees etant concue de facon a avoir un grossissement compris entre environ 1,5 et environ 5. Un materiau de revetement rendant le verre auto-nettoyant recouvre la pluralite de regions convexes allongees.
Large Area Concentrator Lens Structure and Method Configured for Stress Relief
Method and apparatus for cleaning and removing flux from an electronic component package
Method and system for manufacturing integrated molded concentrator photovoltaic device
Solar Cell Concentrator Structure Including A Plurality of Glass Concentrator Elements With A Notch Design
Solder Replacement by Conductive Tape Material
System and Method for Laminating Photovoltaic Structures
System and Module for Solar Module with Integrated Glass Concentrator
Photovoltaic Devices Having Shaped Concentrator Members
High Impact and Load Bearing Solar Glass for a Concentrated Large Area Solar Module and Method
Backside encapsulation of tape automated bonding device
Elastic interactions and their effect on gamma prime precipitate shapes in aged dilute Ni-Al alloys
Scripta Metallurgica et Materialia
ABSTRACT
Anomalous coarsening of small volume fractions of Ni3Al precipitates: An explanation of inhomogeneous dispersions observed at small undercoolings
Elastic interactions and their effect on γ' precipitate shapes in aged dilute Ni-Al alloys
The shape of coherent gamma prime precipitates in aged Ni-Al alloys was investigated experimental... more The shape of coherent gamma prime precipitates in aged Ni-Al alloys was investigated experimentally using transmission electron microscopy. It is found that the shape of the gamma prime precipitates depends not only on their size but also on their volume fraction. The higher the volume fraction of gamma prime precipitates, the greater is the tendency for their elastic strain fields to overlap and to become cuboidal in shape, with the individual precipitates acquiring convex interfaces. In the case of small volume fractions, the gamma prime precipitates become nearly perfectly cubic as they grow to a certain size. 13 refs.
The Effect of Volume Fraction on γ’ (Ni3Si) Precipitate Coarsening In Ni-Si Alloys
NATO ASI Series, 1994
During precipitate coarsening large particles grow at the expense of smaller ones such that the a... more During precipitate coarsening large particles grow at the expense of smaller ones such that the average particle size increases with increasing aging time. Lifshitz and Slyozov1, and Wagner2 published one of the earliest theories of diffusion-controlled coarsening, now known as the LSW theory, wherein the rate of solute transfer from the smaller to the larger particles is controlled by the rate of solute diffusion in the matrix. One of its predictions is the familiar asymptotic rate law 〈r〉3 ≈ kt, where 〈r〉 is the average particle radius and t is the aging time. The rate constant k is related to the material constants of the alloy system.
… , 2002. Proceedings. 52nd, 2002
Innovative MPM (Multi Package Module) BGA (Ball Grid Array) packages have been developed at Xilin... more Innovative MPM (Multi Package Module) BGA (Ball Grid Array) packages have been developed at Xilinx to satisfy the needs for space-efficient, pre-engineered, high-density systemlevel multiple IC solution. MPM BGA package takes advantage of the miniaturization trends in electronic packaging industry, avoiding known good die (KGD) testinmandling issues and improves the system performance by bridging the gap between current packaging technology and advanced IC technology. This paper focuses on MPM BGA package structure, assembly flow, package performance and one example of the application.
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Papers by Abhay Maheshwari