As the microelectronic industry moves toward stacking of dies to achieve greater performance and smaller footprint, there are several reliability concerns when assembling the stacked dies on current organic substrates. These concerns include excessive warpage, interconnect cracking, die cracking, and others. Silicon interposers are being developed to assemble the stacked dies, and then the silicon interposers are assembled on organic substrates. Although such an approach could address stacked-die to interposer reliability concerns, there are still reliability concerns between the silicon interposer and the organic substrate. This work examines the use of diced glass panel as an interposer, as glass provides intermediate coefficient of thermal expansion between silicon and organics, good mechanical rigidity, large-area panel processing for low cost, planarity, and better electrical properties. However, glass is brittle and low in thermal conductivity, and there is very little work in existing literature to examine glass as a potential interposer material. Starting with a 150 x 150 mm glass panel with a thickness of 100 µm, this work has built alternating layers of dielectric and copper on both sides of the panel. The panels have gone through typical cleanroom processes such as lithography, electroplating, etc. Upon fabrication, the panels are diced into individual substrates of 25 x 25 mm and a 10 x 10 mm flip chip with a solder bump pitch of 75 um is then reflow attached to the glass substrate followed by underfill dispensing and curing. The warpage of the flip-chip assembly is measured. In parallel to the experiments, numerical models have been developed. These models account for viscoplastic behavior of the solder. The models also mimic material addition and etching through element “birth-and-death” approach. The warpage from the models has been compared against experimental measurements for glass substrates with flip chip assembly. It is seen that the glass substrates provide significantly lower warpage compared to organic substrates, and thus could be a potential candidate for future 3D systems.

Over the past 50 years, electronics manufacturing industry has undergone revolutionary changes, which have provided consumers with a plethora of electronic products. The increase in functionality of electronic products and decrease in cost due to continuous miniaturization and lower manufacturing costs have evolved over time. As electronics manufacturing technology becomes more advanced, reliability of electronic products and devices have become more of a concern. Thermomechanical reliability in electronics is studied in this research. Thermomechanical failures are failures due to temperature loading conditions electronic products and devices experience during manufacturing and service. The thermomechanical issue studied in this research is the effect of convective solder reflow on the warpage of packaged electronic devices, bare boards and chip packages. A convective reflow-projection moir warpage measurement system is designed and implemented in this research. The system is the first available system capable of measuring warpage of printed wiring boards (PWBs) with and without electronic components during simulated convective reflow process. A finite element prediction tool is also developed to predict the warpage of PWBs populated with plastic ball grid array (PBGA) packages. The developed warpage measurement system as well as the developed finite element model is used to study various PWB assembly (PWBA) configurations during simulated convective reflow processes.

Das geometrische In-plane-Moireverfahren wird benutzt, um das Deformationsfeld um einen Riss in einem geschweißten Verbund zweier unterschiedlicher Metalle sowie in homogenen Proben dieser Materialien zu untersuchen. Konkret werden Vierpunktbiegeproben benutzt, wobei die Grenzflächen der Verbundproben durch Explosionsschweißen (Sprengplattieren) hergestellt werden. In Verbindung mit der digitalen Bildverarbeitung wird das Feld der Verschiebungen zum Zeitpunkt der Rissinitiierung als primäres Resultat aus den Isothetenfeldern ermittelt. Aus diesen Verschiebungsfeldern lassen sich mittels eines Approximationsverfahrens weitere Größen wie Verzerrungen und Spannungsgrößen an der Oberfläche ableiten. Zusätzlich werden dreidimensionale elastisch-plastische FEM-Berechnungen für die homogenen Proben und die Proben mit Grenzflächenriss durchgeführt. Das J-Integral wird aufgrund der experimentell und numerisch gewonnenen Daten für den Rissinitiierungszeitpunkt berechnet. Außerdem findet ein Vergleich mit J-Integralwerten statt, die mit Methoden der Materialprüfnormen bestimmt werden.

Out-of-plane displacement (warpage) is one of the major thermomechanical reliability concerns for board-level electronic packaging. Printed wiring board (PWB) and component warpage results from CTE mismatch among the materials that make up the PWB assembly (PWBA). Warpage occurring during surface-mount assembly reflow processes and normal operations may cause serious reliability problems. In this research, a convective reflow and projection moire warpage measurement system was developed. The system is the first real-time, non-contact, and full-field measurement system capable of measuring PWB/PWBA/chip package warpage with the projection moire technique during different thermal reflow processes. In order to accurately simulate the reflow process and to achieve the ideal heating rate, a convective heating system was designed and integrated with the projection moire system. An advanced feedback controller was implemented to obtain the optimum heating responses. The developed system has the advantages of simulating different types of reflow processes, and reducing the temperature gradients through the PWBA thickness to ensure that the projection moire system can provide more accurate measurements. Automatic package detection and segmentation algorithms were developed for the projection moire system. The algorithms are used for automatic segmentation of the PWB and assembled packages so that the warpage of the PWB and chip packages can be determined individually. The effect of initial PWB warpage on the fatigue reliability of solder bumps on board assemblies was investigated using finite element modeling (FEM) and the projection moire system. The 3-D models of PWBAs with varying board warpage were used to estimate the solder bump fatigue life for different chip packages mounted on PWBs. The simulation results were validated and correlated with the experimental results obtained using the projection moire system and accelerated thermal cycling tests. Design of experiments and an advanced prediction model were generated to predict solder bump fatigue life based on the initial PWB warpage, package dimensions and locations, and solder bump materials. This study led to a better understanding of the correlation between PWB warpage and solder bump thermomechanical reliability on board assemblies.

This thesis describes the problem of fiber gratings, focusing primarily on the use of Bragg's grids in the sensor. It describes the types of fiber mesh production, especially the method of writing with a phase mask. The next part deals with the possibilities of using apodization in fiber optic systems. It deals with the various functions that can be used to describe apodization. The following part describes the moire principle, especially the method of overlapping two phase masks with a different period.

Laser beams can be manipulated by volume diffractive elements in addition to conventional optical elements like mirrors, lenses, and beam splitters. Conventional optical elements can be described by applying the basic laws of reflection and refraction at the surfaces of the elements. Even diffraction by surface gratings utilizes relatively simple mathematics. This is to be contrasted with the volume diffraction, which requires coupled wave theory in the slowly varying envelope approximation (SVEA) to obtain accurate results. Efficient spatially distributed diffraction of laser beams is possible due to the high coherence of laser light, and it occurs at specific resonant Bragg conditions. This research work is inspired and driven by the successful development of recording technology for robust, high-efficiency volume Bragg gratings (VBGs) in photo-thermo-refractive (PTR) glass. Mostly VBGs of the reflective type are discussed in this dissertation. Starting with an analysis of electro-magnetic wave propagation in layered media, we have reformulated Fresnel and volume reflection phenomena in terms of a convenient parameter – strength of reflection. The influence that the different non-uniformities inside a VBG have on its spectral properties has been examined. One important result of this work is the proposal of moiré VBG and the derivation of an analytical expression for its bandwidth. A multiplexed VBG used as a coherent combiner is discussed as well. Beam distortion via transmission through and/or reflection by a heated VBG due to residual absorption is analyzed.

This thesis, submitted to the University of Manchester, covers a range of topics related to current research in two-dimensional materials under the title: 'Investigations into the interfacial interaction of graphene with hexagonal boron nitride.'In the last decade, two-dimensional materials have become a rich source of original research and potential applications. The main advantage lies in the ability to produce novel composite structures, so-called 'layered heterostructures', which are only a few atomic layers thick. One can utilise the unique properties of several species of crystal separately, or how they interact to realise a diverse range of uses. Two such crystals are graphene and hexagonal boron nitride. Hexagonal boron nitride has, so far, been used primarily as a substrate for graphene, allowing researchers to get the most out of graphene's impressive individual properties. However, in this thesis, the non-trivial van der Waals interaction between graphene and hexagonal boron nitride is examined. The interface potential reveals itself as a relatively large-scale, orientation-dependant superlattice, which is described in chapters 1 and 2.I In Chapter 4, the effect of this superlattice is examined by measurement of its effect upon the electrons in graphene, where its modulation leads to the creation of second and third generation Dirac points, revealing Hofstadter's Butterfly. As well as an excellent example of the physics possible with graphene, it also presents a new tool with which to create novel devices possessing tailored electronic properties. II In chapter 5, the consequential effect of the superlattice potential on the structure of graphene is studied. Results are discussed within the framework of the Frenkel-Kontorova model for a chain of atoms on a static background potential. Results are consistent with relaxation of the graphene structure leading to the formation of a commensurate ground state. This has exciting consequences for the production of heterostructures by demonstrating that alignment angle can have large effects upon the physical properties of the crystals. III In chapter 6, the van der Waals potential is shown to be responsible for the self-alignment of the two crystals. This effect is important for the fabrication of perfectly aligned devices and may lead to new applications based on nanoscale motion.

With the dramatic advances that have taken place in microelectronics over the past three decades, ball-grid array (BGA) packages are increasingly being used in microsystems applications. BGA packages with area-array configuration have several advantages: smaller footprint, faster signal transmission, testability, reworkability, handling easiness, etc. Although ceramic ball grid array (CBGA) packages have been used extensively in the microsystems industry, the use of plastic ball grid array (PBGA) packages is relatively new, especially for automotive and aerospace applications where harsh thermal conditions prevail. This thesis work has developed an experimental and a theoretical modeling program to study the reliability of two PBGA packages. The physics-based theoretical models take into consideration the time-dependent creep behavior through power law creep and time-independent plastic behavior through multi-linear kinematic hardening. In addition, unified viscoplastic constitutive models are also taken into consideration. The models employ two damage-metrics, namely inelastic strain and inelastic strain energy density, to predict the solder joint fatigue life. The theoretical predictions have been validated through air-to-air in-house thermal cycling tests carried out between 55 and #61616;C and 125 and #61616;C. In addition, laser-moir interferometry has been used to determine the displacement contours in a cross-section of the package at various temperatures. These contours measured through moir interferometry have also been used to validate the thermally-induced displacement contours, predicted by the models. Excellent agreement is seen between the experimental data and the theoretical predictions. In addition to life prediction, the models have been extended to map the field-use conditions with the accelerated thermal cycling conditions. Both linear and non-linear mapping techniques have been developed employing inelastic strain and strain energy density as the damage metric. It is shown through this research that the symmetric MIL-STD accelerated thermal cycles, currently in practice in industry, have to be modified to account for the higher percentage of creep deformation experienced by the solder joints in the field-use conditions. Design guidelines have been developed for such modifications in the accelerated thermal cycles.

Title from PDF of title page. / Document formatted into pages; contains 87 pages. / Thesis (M.S.M.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: As technology progresses towards smaller electronic packages, thermo-mechanical considerations pose a challenge to package designers. One area of difficulty is the ability to predict the fatigue life of the solder connections. To do this one must be able to accurately model the thermo-mechanical performance of the electronic package. As the solder ball size decreases, it becomes difficult to determine the performance of the package with traditional methods such as the use of strain gages. This is due to the fact that strain gages become limited in size and resolution and lack the ability to measure discreet strain fields as the solder ball size decreases. A solution to the limitations exhibited in strain gages is the use of Moiré interferometry. Moiré interferometry utilizes optical interferometry to measure small, in-plane relative displacements and strains with high sensitivity. / ABSTRACT: Moiré interferometry is a full field technique over the application area, whereas a strain gage gives an average strain for the area encompassed by the gage. This ability to measure full field strains is useful in the analysis of electronic package interconnections; especially when used to measure strains in the solder ball corners, where failure is known to originate. While the improved resolution of the data yielded by the method of Moiré interferometry results in the ability to develop more accurate models, that is not to say the process is simple and without difficulties of it's own. Moiré interferometry is inherently susceptible to error due to experimental and environmental effects; therefore, it is vital to generate a reliable experimental procedure that provides repeatable results. This was achieved in this study by emulating and modifying established procedures to meet our specific application. / ABSTRACT: The developed procedure includes the preparation of the specimen, the replication and transfer of the grids, the use of the PEMI, interpretation of results, and validation of data by finite element analysis using ANSYS software. The data obtained maintained uniformity to the extent required by the scope of this study, and potential sources of error have been identified and should be the subject of further research. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

This research aims to understand the reliability of Sn-Ag-Cu solder interconnects used in plastic ball grid array (PBGA) packages using microstructure evolution, laser moiré interferometry and finite-element modeling. A particle coarsening based microstructure evolution of the solder joint material during thermal excursions was studied for extended periods of time lasting for several months. The microstructure evolution and particle coarsening was quantified, and acceleration factors were determined between benign field-use conditions and accelerated thermal cycling (ATC) conditions for PBGA packages with different form factors and for two different lead-free solder alloys. A new technique using laser moiré interferometry was developed to assess the deformation behavior of Sn-Ag-Cu based solder joints during thermal excursions. This technique can used to estimate the fatigue life of solder joints quickly in a matter of few days instead of months and can be extended to cover a wide range of temperature regimes. Finite-element analysis (FEA) in conjunction with experimental data from the ATC for different lead-free PBGA packages was used to develop a fatigue life model that can be used to predict solder joint fatigue life for any PBGA package. The proposed model will be able to predict the mean number of cycles required for crack initiation and crack growth rate in a solder joint.