Fundamental study of underfill void formation in flip chip assembly

Flip Chip in Package (FCIP) has been developed to achieve the assembly process with area array interconnects. Particularly, a high I/O count coupled with finer pitch area array interconnects structured FCIP can be achieved using no-flow underfill assembly process. Using the assembly process, a high, stable yield assembly process recently reported with eutectic lead-tin solder interconnections, 150 µm pitch, and I/O counts in excess of 3000. The assembly process reported created a large number of voids among solder interconnects in FCIP. The voids formed among solder interconnections can propagate, grow, and produce defects such as solder joint cracking and solder bridging. Moreover, these voids can severely reduce reliability performance. Indeed, many studies were conducted to examine the void formation in FCIP. Based on the studies, flip chip geometric design, process conditions, and material formulation have been considered as the potential causes of void formation. However, the present research won't be able to identify the mechanism of void formation, causing a lot of voids in assembly process without consideration of chemical reaction in the assembly process with a fine-pitch, high I/O density FCIP. Therefore, this research will present process technology necessary to achieve high yields in FCIP assemblies using no-flow underfills and investigate the underlying problem of underfill void formation in these assemblies. The plausible causes of void formation will be investigated using experimental techniques. The techniques will identify the primary source of the void formation. Besides, theoretical models will be established to predict the number of voids and to explain the growth behavior of voids in the FCIP. The established theoretical models will be verified by experiments. These models will validate with respect to the relationship between process parameters to achieve a high yield and to minimize voids in FCIP assemblies using no-flow underfill materials regarding process as well as material stand points. Eventually, this research provides design guideline achieving a high, stable yield and void-free assembly process.Ph.D.Committee Chair: Baldwin, Daniel; Committee Member: Colton, Jonathan; Committee Member: Ghiaasiaan, Mostafa; Committee Member: Moon, Jack; Committee Member: Tummala, Ra

A Study of the Morphology of Porosity in Sintered Uranium-Zirconium Alloys as a Function of Sintering Time

Uranium- 10 wt. % zirconium (U-10Zr) alloys were generated using powder metallurgy methods to create porous specimens with densities ranging from 70 to 98 % Theoretical Density (%T.D.). This was completed as part of a larger project funded by the U.S. Department of Energy designed to use computational and experimental methods to evaluate the sintering behavior in U-10Zr metallic fuel for advanced nuclear fuel simulations in the MOOSE/MARMOT simulation environment. Uranium microspheres (180 to 45 micron in diameter) produced in the Rotating Electrode System (RES) were mixed with purchased zirconium microspheres (<44 micron diameter). This powder was thoroughly mixed and pressed in a six millimeter die at 8,000 pounds force to form the green pellets. Subsequently, the pellets were measured, weighted, density calculated, and sintered at varying times from two to twelve hours. The resultant pellet was then re-measured for density, cut in a fashion that exposed the radial and axial center-line faces, polished, imaged in a Scanning Electron Microscope (SEM), and the image analyzed for porosity area fractions and morphology. As expected, longer sintering times result in more dense samples. However, due to deformation of the exterior of the pellet during pressing and sintering, alloying density changes, spring back, and pore migration, the change in density was far from linear. Additionally, pore sizes increased before finally decreasing as they migrated to uranium sphere boundaries. Pores converged into softer zirconium channels near the uranium sphere boundaries before dispersing as sintering time increased

Nuclear Fusion Programme: Annual Report of the Association Karlsruhe Institute of Technology/EURATOM ; January 2013 - December 2013 (KIT Scientific Reports ; 7671)

The Karlsruhe Institute of Technology (KIT) is working in the framework of the European Fusion Programme on key technologies in the areas of superconducting magnets, microwave heating systems (Electron-Cyclotron-Resonance-Heating, ECRH), the deuterium-tritium fuel cycle, He-cooled breeding blankets, a He-cooled divertor and structural materials, as well as refractory metals for high heat flux applications including a major participation in the preparation of the international IFMIF project

Evaluation of Aluminum-Boron Carbide Neutron Absorbing Materials for Interim Storage of Used Nuclear Fuel

The objective of this work was to understand the long-term corrosion behavior of Boral® and Bortec® neutron absorbers during deployment in a used nuclear fuel dry cask storage environment for several hundred years. Corrosion effects were accelerated by flowing humidified argon through an autoclave at temperatures between 300 and 570°C. Humidity levels ranged from 0.028 to 0.58 mass fraction with flow rates ranging from approximately 0.2 scfh to 1.5 scfh. Results from corrosion testing at temperatures between 300 and 570°C with varying humidity have shown that both Boral® and Bortec® develop new aluminum-boron-carbon phases. The phases formed are consistent at 300 and 400°C. Different formations were observed at 570°C. The samples also showed boron depletion at all temperatures. It is predicted that two mechanisms control the changes in Boral® and Bortec®. The phase changes observed result from the interaction of boron carbide with aluminum. These interactions result in boron and carbon diffusing into the aluminum matrix. The other series of interactions occurring between the sample and the water in the humidified argon. Boron on the surface rapidly reacts with the water to form B2O3 which can be volatilized. The loss of boron at the surface creates a concentration profile that can result in the continued diffusion of boron to the surface. The water will also react with the aluminum to form Al2O3. Aluminum oxide formed in humid conditions has some porosity and can degrade away and allow for continued oxidation of aluminum. Additional research is required to determine the suitability of these materials for use in dry cask storage. The new phase formation may affect mechanical properties and adversely affect the fuel baskets structural integrity. Boron redistribution may cause localized areas of boron depletion, additional testing needs to be conducted to determine boron diffusion in these materials in the absence of humidity. In the presence of humidity the boron will leach from the samples. Cask humidity levels need to be determined to be able to predict how much boron may be lost.PHDNuclear Engineering and Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111438/1/jonbrett_1.pd

DEFORMATION AND DAMAGE MECHANISMS IN SELECTED 2000 SERIES ALUMINUM ALLOYS UNDER BOTH QUASI-STATIC AND DYNAMIC IMPACT LOADING CONDITIONS

In recent times, application of aluminum alloys is favored in the transportation sectors such as the aerospace and automobile industries where reduced fuel consumption and greenhouse gas emission are major priorities. In these applications, these alloys can be exposed to dynamic shock loading conditions as in the case of car crash and birds’ collision during aircraft’s take-off or landing. This study therefore focused on the deformation and damage mechanisms in AA 2017, AA 2024 and AA 2624 aluminum alloys under both quasi-static and dynamic impact loading conditions. Cylindrical specimens of the selected aluminum alloys were investigated under both quasi-static loading at 3.2 x10-3 s-1 using an Instron R5500 mechanical testing machine and dynamic impact loading using the split Hopkinson pressure bar at strain rates ranging between 2000 and 8000 s-1. The effects of strain rate and temper condition on the microstructural evolution in the alloys during mechanical loading were studied. The electron backscatter diffraction (EBSD) technique was used to investigate the texture of the naturally-aged AA 2017 and AA 2624 alloys before and after dynamic shock loading. The contributions of the major alloying elements such as copper, magnesium and silicon to the microstructural evolution and deformation behavior of the alloys under the dynamic shock loading condition were also studied using the energy dispersive spectroscopy (EDS) technique. Results showed that the morphology and atomic distribution of particles in the investigated alloys are functions of the temper condition. The hardness of all the three alloys was higher in the age-hardened conditions than the annealed ones. Although deformation of the alloy under quasi-static compressive loading was dominated by strain hardening, flow softening leading to strain localization and formation of shear bands occurred once certain critical strain values were reached. Under both quasi-static and dynamic loading, the alloys with low Cu:Mg ratio (AA 2024 and AA 2624) showed higher mechanical strength in age-hardened condition than that with high Cu:Mg ratio (AA 2017). All the alloys in the annealed condition exhibited an enhanced plasticity and formability. Intense strain localization leading to formation of adiabatic shear bands (ASBs) was the principal contributor to failure in the alloys under dynamic impact loading. Both deformed and transformed bands were observed, with cracking occurring mainly along the transformed shear bands. The tendency for formation of adiabatic shear bands is observed to be a function of the alloy composition, temper condition, strain, strain rate and strain hardening rate. In the natural aging condition, AA 2024 showed the highest susceptibility to formation of ASBs followed by AA 2624 and AA 2017 in that order. On the other hand, AA 2024 has the least susceptibility in the artificially-aged condition. Occurrence of bifurcation of transformed bands in dynamic impacted specimens is dependent on temper condition, strain and strain rate. The mechanism of fracture of the precipitation hardened samples is typical of ductile fracture occurring sequentially by nucleation, growth, and coalescence of micro-voids processes within transformed band. Elongated grains were observed to arrest propagating shear band depending on the angle the band makes with elongated grains. The higher the angle of inclination of a shear band to the grain on its path, the higher the tendency of the grain to stop its propagation. Texture analysis of the impacted specimens of AA 2017-T451 and AA 2624-T351 shows that the former has a higher tendency for the evolution of ultra-fine DRX grains within the transformed shear band. High strain rate led to the development of CD// orientations at the expense of CD// orientations. Schmid factor calculations performed on few different orientations in the starting microstructure shows that CD// is less susceptible to slip deformation and consequently underwent rotation to CD//

Estudo da eletromigração em circuitos integrados na fase de projeto

Orientadores: Roberto Lacerda de Orio, Leandro Tiago ManeraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O dano por eletromigração nas interconexões é um gargalo bem conhecido dos circuitos integrados, pois causam problemas de confiabilidade. A operação em temperaturas e densidades de corrente elevadas acelera os danos, aumentando a resistência da interconexão e, portanto, reduzindo a vida útil do circuito. Este problema tem se acentuado com o escalonamento da tecnologia. Para garantir a confiabilidade da interconexão e, como consequência, a confiabilidade do circuito integrado, métodos tradicionais baseados no chamado Efeito Blech e numa densidade de corrente máxima permitida são implementados durante o projeto da interconexão. Esses métodos, no entanto, não levam em consideração o impacto da eletromigração no desempenho do circuito. Neste trabalho, a abordagem tradicional é estendida e um método para avaliar o efeito da eletromigração no desempenho de circuito integrado é desenvolvido. O método é implementado em uma ferramenta que identifica as interconexões críticas em um circuito integrado e sugere larguras adequadas com base em diferentes critérios para mitigar os danos à eletromigração e aumentar a confiabilidade. Além disso, é determinada a variação dos parâmetros de desempenho do circuito conforme a resistência das interconexões aumenta. A ferramenta é incorporada ao fluxo de projeto do circuito integrado e usa os dados dos kits de projeto e relatórios diretamente disponíveis no ambiente de projeto. Uma análise precisa da distribuição de temperatura na estrutura de interconexão é essencial para uma melhor avaliação da confiabilidade da interconexão. Portanto, é implementado um modelo para calcular a temperatura em cada nível de metalização da estrutura de interconexão. A distribuição de temperatura nas camadas de metalização de diferentes tecnologias é investigada. É mostrado que a temperatura no Metal 1 da tecnologia Intel 10 nm aumenta 75 K, 12 K mais alta que no Metal 2. Como esperado, as camadas mais próximas dos transistores sofrem um aumento de temperatura mais significativo. A ferramenta é aplicada para avaliar eletromigração nas interconexões e na robustez de diferentes circuitos, como um oscilador em anel, um circuito gerador de tensão de referência tipo bandgap e um amplificador operacional. O amplificador operacional, em particular, é cuidadosamente estudado. A metodologia proposta identifica interconexões críticas que quando danificadas por eletromigração causam grandes variações no desempenho do circuito. No pior cenário, a frequência de corte do circuito varia 65% em 5 anos de operação. Uma descoberta interessante é que a metodologia proposta identifica interconexões críticas que não seriam identificadas pelos critérios tradicionais. Essas interconexões operam com densidades de corrente abaixo do limite recomendado pelas regras de projeto. No entanto, uma dessas interconexões leva a uma variação de 30% no ganho do amplificador operacional. Em resumo, a ferramenta proposta verificou que dos 20% de caminhos com uma densidade crítica de corrente, apenas 3% degradam significativamente o desempenho do circuito. Este trabalho traz o estudo da confiabilidade das interconexões e de circuitos integrados para a fase de projeto, o que permite avaliar a degradação do desempenho do circuito antecipadamente durante o seu desenvolvimento. A ferramenta desenvolvida permite ao projetista identificar interconexões críticas que não seriam detectadas usando o critério de densidade máxima de corrente, levando a uma análise mais ampla e precisa da robustez de circuitos integradosAbstract: Electromigration damage in interconnects is a well-known bottleneck of integrated circuits, because it causes reliability problems. Operation at high temperatures and current densities accelerates the damage, increasing the interconnect resistance and, therefore, reducing the circuit lifetime. This issue has been accentuated with the technology downscaling. To guarantee the interconnect reliability and, as a consequence, the integrated circuit reliability, traditional methods based on the so-called Blech Effect and on the maximum allowed current density are implemented during interconnect design. These methods, however, do not take into account the impact of the electromigration on the circuit performance. In this work the traditional approach is extended and a method to evaluate the effect of the electromigration in an integrated circuit performance is developed. The method is implemented in a tool which identifies the critical interconnect lines of an integrated circuit and suggests the proper interconnect width based on different criteria to mitigate the electromigration damage and to increase the reliability. In addition, the variation of performance parameters of the circuit as an interconnect resistance changes is determined. The tool is incorporated into the design flow of the integrated circuit and uses the data from design kits and reports directly available from the design environment. An accurate analysis of the temperature distribution on the interconnect structure is essential to a better assessment of the interconnect reliability. Therefore, a model to compute the temperature on each metallization level of the interconnect structure is implemented. The temperature distribution on the metallization layers of different technologies is investigated. It is shown that the temperature in the Metal 1 of the Intel 10 nm can increase by 75 K, 12 K higher than in the Metal 2. As expected, the layers that are closer to the transistors undergo a more significant temperature increase. The tool is applied to evaluate the interconnects and the robustness of different circuits, namely a ring oscillator, a bandgap voltage reference circuit, and an operational amplifier, against electromigration. The operational amplifier, in particular, is thoroughly studied. The proposed methodology identifies critical interconnects which under electromigration cause large variations in the performance of the circuit. In a worst-case scenario, the cutoff frequency of the circuit varies by 65% in 5 years of operation. An interesting finding is that the proposed methodology identifies critical interconnects which would not be identified by the traditional criteria. These interconnects have current densities below the limit recommended by the design rules. Nevertheless, one of such an interconnect leads to a variation of 30% in the gain of the operational amplifier. In summary, the proposed tool verified that from the 20% paths with a critical current density, only 3% degrades significantly the circuit performance. This work brings the study of the reliability of the interconnects and of integrated circuits to the design phase, which provides the assessment of a circuit performance degradation at an early stage of development. The developed tool allows the designer to identify critical interconnects which would not be detected using the maximum current density criterion, leading to more accurate analysis of the robustness of integrated circuitsDoutoradoEletrônica, Microeletrônica e OptoeletrônicaDoutor em Engenharia Elétrica88882.329437/2019-01CAPE

Entwicklung eines Katalysators zur Abgasreinigung für Biomassekraftwerke

The integration of biomass based fuels is leading the way towards reliable energy supplies, but still high emission values are observed during the energy conversion (NOx, SOx, H3PO4 and soot), due to the Nitrogen, Sulphur and Phosphate contained in biomass [1]. Additionally, mineral content and heterogeneity of biofuels lead to high concentration of particles in exhaust gases, which can reach up to 60 mg/Nm3 [2]. To address this problem, robust exhaust gas treatments can be installed at firing systems, however for small and medium systems (<10 MW) economical and fitted solutions are still needed [3]. Previous approaches are based on catalytic coating of porous bodies, i.e. [4][5]. In this technique, the external surface of a filter body is coated with a catalytic solution. This method is also called impregnation [6]. Through this process, a particle filter and catalytic material are merged into one product. Although this technique has shown efficiencies of up to 80% at over 250°C in dusty conditions like biomass combustion, the impregnation method is limited by the porosity of the support [7]. On one hand, low porosity bodies efficiently retain particles, but at the same time this property limits the impregnation method because these bodies filter most of the catalytical particles. This inhibits the deposition of the catalyst in the internal bulky structure of the porous filter. On the other hand, supports with good porosity get easily coated, which also increases the amount of deposited catalyst [8]. However, these filters are clogged later under operational conditions. For instance, pores get plugged with dust particles, which increases the pressure drop and subsequently minimizes the catalytical effect [9]. An acceptable balance between porosity of the filter and activity of the catalyst calls for alternative fabrication methods. Besides, the active material should catalyze under dusty, wet and corrosive conditions. Moreover, other parameters such size, cost, mechanical stability and chemical resistance must be kept under the standard values [10]. Therefore, a new fabrication method for catalytic filters was developed and tested in this project to satisfy the requirement of small and medium firing plants, see figure below To achieve this, an organometallic compound based on copper was synthesized by a solvothermal process, see left side of previous figure. Stabilization of the active sites was achieved through addition of silicoaluminate precursors and an organic template as mesoporous structuring agent. This process encapsulated the catalytic material for upcoming steps. As illustrated in the middle part of the previous figure, integration of filter material and catalytic material was done by mixing and shaping the catalytic filter in a mold. Adjustment of the molding process and porosity were attained by addition of inorganic binder. Finally, the shaped body was calcinated and activated in a controlled atmosphere for the final operation in the SCR test stand. Validation of the process was linked to the NOx reduction capacity of the catalyst. Therefore, adjustment in the formulation was done by analysis of the NO conversion, depending on temperature. Additionally, a particle filtration test was run on the catalytic filter in order to analyze the simultaneous performance during dust filtration and NOx conversion. Lastly, the optimal formulation was tested under real exhaust gas and characterized based on temperature and pressure. Finally, to evaluate the synthesis, detailed spectroscopy measurements were implemented on the catalytic filter. By doing so, active centers and absorption sites of the catalyst were revealed by using several analytical techniques, such as STEM, XRD, TPR, TPO, EPR and NMR. Based on the analytical measurements, a catalytic mechanism is proposed.Die Entwicklung von biologischen Brennstoffen zeigt realistische Wege für erneuerbare Energien auf. Trotzdem gibt es weiterhin gefährliche Abgasemissionen während der energetischen Verwandlung. Diese Emissionen (NOx, SOx, HPO3 und Ruß) werden von Stickstoff, Schwefel und Phosphaten generiert, die in der Biomasse enthalten sind [1]. Noch dazu führen mineralische Inhaltsstoffe und chemische Heterogenität der Rohstoffe zu hohem Staubanteil in den Abgasen, welcher bis zu 60 mg/Nm3 erreicht [2]. Um diese Tatsache zu vermeiden, sind an Feuerungsanlagen robuste Abgasnachbehandlungssysteme installiert. Dennoch werden für mittelgroße sowie kleinere Anlagen (<10 MW) derzeit weiterhin ökonomische und angepasste Lösungen gesucht und erforscht [3]. Frühere Versuche basieren auf einer katalytischen Beschichtung poröser Köper, wie zum Beispiel in [4][5]. Bei dieser Technik wird die äußere Oberfläche eines Filters mit einer katalytischen Lösung beschichtet. Diese Methode wird auch als Imprägnierung bezeichnet [6]. Dadurch sind ein Partikelfilter und ein katalytisches Material in einem Produkt miteinander vereint. Diese Technik erzielt zwar eine Wirkungseffizienz von über 80% bei 250°C unter staubigen Bedingungen, wie bei der Verbrennung von Biomasse, aber die Imprägnierungsmethode ist durch die Porosität des Trägers begrenzt [7]. Einerseits filtrieren Köper mit niedriger Porosität Partikel effizient, doch behindert diese Eigenschaft gleichzeitig das Imprägnierungsverfahren, weil diese Träger auch die katalytischen Partikel filtrieren. Folglich behindert dieser Effekt die Aufladung des Katalysators in der inneren Struktur der porösen Filter. Andererseits steig die Beladung von den katalytischen Stoffen auf Köper mit hoher Porosität. Trotzdem verstopfen diese Filterköper später bei betrieblicher Bedienung[8]. Infolgedessen werden poröse Kanäle blockiert, indem der Druckverlust mit der folgenden Verminderung des katalytischen Effekts steigt [9]. Ein akzeptables Gleichgewicht zwischen Porosität und Aktivität des Katalysators macht neue Herstellungsmethoden erforderlich. Darüberhinaus sollten diese Methoden auch in staubigen, feuchten und korrosiven Umgebungen katalysieren. Noch dazu müssen andere Parameter wie Größe, Kosten, mechanische Stabilität und chemische Resistenz berücksichtigt werden [10]. Aus diesem Grund wurde im hier vorgelegten Projekt eine neue Herstellungsmethode für katalytische Filter entwickelt und getestet, damit die Anforderung an die kleinen und mittelgroßen Feuerungsanlagen erfüllt werden können, siehe untere Abbildung. Zur Herstellung eines Katalysators wurde eine organmetallische Verbindung, die auf Kupfer basiert, mittels eines Solvothermalverfahrens synthetisiert, siehe linke Seite der vorherigen Abbildung. Die Stabilisierung der katalytischen Zentren wurde mittels Ausgangstoffen aus Silizium und Aluminium und einer organischen Schablone erreicht, wobei die Schablone als mesoporöser Agent wirkt. Durch diesen Prozess wurden die katalytischen Zentren verkapselt. Wie in der Mitte der Abbildung illustriert ist, wurde die Integrierung von Träger und katalytischen Stoffen mittels Vermischung und Formung durchgeführt. Anpassung des Formungsverfahrens und der Porosität des Filters wurde durch Hinzufügung des organischen Binders erzielt. Anschließend wurde der geformte Köper kalziniert und mittels eines Gases im SCR-Prüfstand aktiviert. Die Validierung des Prozesses war mit der Entstickungswirkung verbunden. Deswegen wurde die Rezeptur des Katalysators durch die Stickoxidausbeute in Abhängigkeit von der Temperatur angepasst. Außerdem wurde ein Staubabscheidungstest zur Prüfung der simultanen NOx- und Staubabscheidung durchgeführt. Anschließend wurde die optimale Herstellungsmethode unter realen Abgasbedingungen getestet und eine auf Druck und Temperaturen basierte Charakterisierung ermittelt. Schließlich wurde eine detaillierte spektroskopische Messung am katalytischen Filter durchgeführt. Somit wurden die aktiven und Adsorptionszentren mittels Techniken, wie STEM, XRD, TPR, TPO, EPR und NMR, erkannt. Hinsichtlich der Ergebnisse wird ein katalytischer Mechanismus vorgeschlagen

The Microgravity Research Experiments (MICREX) Data Base

An electronic data base identifying over 800 fluids and materials processing experiments performed in a low-gravity environment has been created at NASA Marshall Space Flight Center. The compilation, called MICREX (MICrogravity Research Experiments) was designed to document all such experimental efforts performed (1) on U.S. manned space vehicles, (2) on payloads deployed from U.S. manned space vehicles, and (3) on all domestic and international sounding rockets (excluding those of China and the former U.S.S.R.). Data available on most experiments include (1) principal and co-investigator (2) low-gravity mission, (3) processing facility, (4) experimental objectives and results, (5) identifying key words, (6) sample materials, (7) applications of the processed materials/research area, (8) experiment descriptive publications, and (9) contacts for more information concerning the experiment. This technical memorandum (1) summarizes the historical interest in reduced-gravity fluid dynamics, (2) describes the importance of a low-gravity fluids and materials processing data base, (4) describes thE MICREX data base format and computational World Wide Web access procedures, and (5) documents (in hard-copy form) the descriptions of the first 600 fluids and materials processing experiments entered into MICREX

Nuclear Fusion Programme: Annual Report of the Association Karlsruhe Institute of Technology/EURATOM ; January 2011 - December 2011 (KIT Scientific Reports ; 7621)

The Karlsruhe Institute of Technology (KIT) is working in the framework of the European Fusion Programme on key technologies in the areas of superconducting magnets, microwave heating systems (Electron-Cyclotron-Resonance-Heating, ECRH), the deuterium-tritium fuel cycle, He-cooled breeding blankets, a He-cooled divertor and structural materials, as well as refractory metals for high heat flux applications including a major participation in the preparation of the international IFMIF project