Not available / text

No description available.

No description available.

As the size of hybrid microelectronics is reduced, the power density increases and thermal interaction between heat-producing devices becomes significant. A nondimensional model is developed to investigate the effects of heat source interaction on a substrate. The results predict the maximum temperature created by a device for a wide range of device sizes, substrate thicknesses, device spacings, and external boundary conditions. They can be used to assess thermal interaction for preliminary design and layout of power devices on hybrid substrates. Previous work in this area typically deals with semi-infinite regions or finite regions with isothermal bases. In the present work, the substrate and all heat dissipating mechanisms below the substrate are modeled as two separate thermal resistances in series. The thermal resistance at the base of the substrate includes the bond to the heat sink, the heat sink, and convection to a cooling medium. Results show that including this external resistance in the model can significantly alter the heat flow path through the substrate and the spreading resistance of the substrate. Results also show an optimal thickness exists to minimize temperature rise when the Biot number is small and the device spacing is large. Tables are presented which list nondimensional values for maximum temperature and spreading resistance over a wide range of substrate geometries, device sizes, and boundary conditions. A design example is included to demonstrate an application of the results to a practical problem. The design example also shows the error that can result from assuming an isothermal boundary at the bottom of the substrate rather than a finite thermal resistance below the substrate. Several other models are developed and compared with the axisymmetric model. A one-dimensional model and two two-dimensional models are simpler than the axisymmetric model but prove to be inaccurate. The axisymmetric model is then compared with a full three-dimensional model for accuracy. The model proves to be accurate when sources are symmetrically spaced and when sources are asymmetrical under certain conditions. However, when the sources are asymmetrical the axisymmetric model does not always predict accurate results. / Master of Science

No description available.

No description available.

No description available.

An Underwater Digital Signal Processor (UDSP) multichip module (MCM) was designed and fabricated according to specifications outlined by the Naval Surface Warfare Center (NSWC), Dahlgren Division. Specifications indicated that low temperature cofired ceramic (L TCC) technology be used to fabricate the MCM with surface dimensions of 2"x2". The top surface of the module was to be designed to enclose mounted components and bare dice, and the bottom surface was to be equipped with a 144 pin grid array (PGA). The LTCC technology selected for this application incorporated DuPont's 951 Green Tape™ and compatible materials and pastes. A mixed metal system using inner silver system and outer surface gold system was used. Harris Corporation's FINESSE MCMTM, a computer-aided design (CAD) tool, was used to design the surface components and produce the circuit layout. FREESTYLE MCM™, an autorouter, was used to accomplish the routing of the signal layers. The design information provided by FINESSE MCM™ and FREESTYLE MCM™ was utilized to produce the artwork necessary for fabrication. Fabrication of the module was accomplished in part using thick film processes to produce the conducting areas on each layer. The layers were stacked in a press, laminated, and fired. Conducting areas were screen printed on the top surface of the module for wire bonding and on the bottom surface of the module for pin attachment. The main objectives of this thesis work were to convert silicon UDSP MCM to ceramic using LTCC, learn a new tool in CAD design that incorporates an autorouter, apply the tool to design a MCM-C module, and to develop criteria to evaluate the MCM. Future research work includes conducting line continuity testing, materials evaluation to determine reactions at interfaces and via filling, and resistance and electrical crosstalk measurements on the module. / Master of Science

<p dir="ltr">The integration of scientific machine learning with computational structural mechanics offers a range of opportunities to address some of the most significant challenges currently experienced by multiphysical simulations, design optimization, and inverse sensing problems. While traditional mesh-based numerical methods, such as the Finite Element Method (FEM), have proven to be very powerful when applied to complex and geometrically inhomogeneous domains, their performance deteriorates very rapidly when faced with simulation scenarios involving high-dimensional systems, high-frequency inputs and outputs, and highly irregular domains. All these elements contribute to increase in the overall computational cost, the mesh dependence, and the number of costly matrix operations that can rapidly render FEM inapplicable. In a similar way, traditional inverse solvers, including global optimization methods, also face important limitations when handling high-dimensional, dynamic design spaces, and multiphysics systems. Recent advances in machine learning (ML) and deep learning have opened new ways to develop alternative techniques for the simulation of complex engineering systems. However, most of the existing deep learning methods are data greedy, a property that strides with the typically limited availability of physical observations and data in scientific applications. This sharp contrast between needed and available data can lead to poor approximations and physically inconsistent solutions. An opportunity to overcome this problem is offered by the class of so-called physics-informed or scientific machine learning methods that leverage the knowledge of problem-specific governing physics to alleviate, or even completely eliminate, the dependence on data. As a result, this class of methods can leverage the advantages of ML algorithms without inheriting their data greediness. This dissertation aims to develop scientific ML methods for application to forward and inverse problems in acoustics and structural mechanics while simultaneously overcoming some of the most significant limitations of traditional computational mechanics methods. </p><p dir="ltr">This work develops fully physics-driven deep learning frameworks specifically conceived to perform forward <i>simulations</i> of mechanical systems that provide approximate, yet physically consistent, solutions without requiring labeled data. The proposed set of approaches is characterized by low discretization dependence and is conceived to support parallel computations in future developments. These characteristics make these methods efficient to handle high degrees of freedom systems, high-frequency simulations, and systems with irregular geometries. The proposed deep learning frameworks enforce the governing equations within the deep learning algorithm, therefore removing the need for costly training data generation while preserving the physical accuracy of the simulation results. Another noteworthy contribution consists in the development of a fully physics-driven deep learning framework capable of improving the computational time for simulating domains with irregular geometries by orders of magnitude in comparison to the traditional mesh-based methods. This novel framework is both geometry-aware and maintains physical consistency throughout the simulation process. The proposed framework displays the remarkable ability to simulate systems with different domain geometries without the need for a new model assembly or a training phase. This capability is in stark contrast with current numerical mesh-based methods, that require new model assembly, and with conventional ML models, that require new training.</p><p dir="ltr">In the second part of this dissertation, the work focuses on the development of ML-based approaches to solve inverse problems. A new deep reinforcement learning framework tailored for dynamic <i>design optimization</i> tasks in coupled-physics problems is presented. The framework effectively addresses key limitations of traditional methods by enabling the exploration of high-dimensional design spaces and supporting sequential decision-making in complex multiphysics systems. Maintaining the focus on the class of inverse problems, ML-based algorithms for <i>remote sensing</i> are also explored with particular reference to structural health monitoring applications. A modular neural network framework is formulated by integrating three essential modules: physics-based regularization, geometry-based regularization, and reduced-order representation. The concurrent use of these modules has shown remarkable performance when addressing the challenges associated with nonlinear, high-dimensional, and often ill-posed remote sensing problems. Finally, this dissertation illustrates the efficacy of deep learning approaches for experimental remote sensing. Results show the significant ability of these techniques when applied to learning inverse mappings based on high-dimensional and noisy experimental data. The proposed framework incorporates data augmentation and denoising techniques to handle limited and noisy experimental datasets, hence establishing a robust approach for training on experimental data.</p>