UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item SPECTRAL METHODS FOR MODELING AND ESTIMATING VIBRATION FATIGUE DAMAGE IN ELECTRONIC INTERCONNECTS(2023) Welch, Jacob Adam; Dasgupta, Abhijit; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this thesis is to explore the accuracy of fatigue damage estimation in printedwiring assembly (PWA) interconnects, using purely frequency-domain (also known as spectral) information such as the power spectral density (PSD) of the input excitation. The test case used in this study is the estimation of fatigue damage accumulation rate in the critical interconnects of low profile quad flat-pack (LQFP) components on a PWA, under broad-band random vibration excitation. this study examines whether the fatigue predictions made with this frequency-domain approach are consistent with those obtained from a direct time-domain approach. The frequency-domain response modeling is achieved using a two-stage global-local modeling process using a finite element model (in ABAQUS©), where the dominant modal participation factors for the dynamic response is obtained using a dynamic global simplified dynamic finite element model consisting of shell elements to represent the entire PWA. The PSD of the input excitation is applied as a boundary condition and the PSD of the PWA strain response is recorded at the base of critical components. The corresponding PSD for the dynamic strain response at critical interconnects is estimated with strain-transfer functions (STFs) for each dominant mode, obtained from detailed 3D quasi-static nonlinear local models of the component, adjacent PWB, and the interconnects. The global-local STF provides a relationship between the level of equivalent strain in the critical interconnects and the flexural strain at the adjacent surface of the PWB. The STF for each of the dominant vibration modes is obtained by imposing the corresponding mode-shape predicted by the dynamic global model on the PWB, in the quasistatic local model, using multi-point constraint equations. The PSD of the equivalent strain in the critical interconnect is then estimated via linear modal superposition. A deterministic estimate of the cyclic fatigue damage accumulation rate in the critical interconnect is then conducted with the Basquin high cycle fatigue (HCF) model and linear damage superposition approach, by using three different spectral approaches for representing the strain severity with estimated probability density functions (PDFs). The three approaches include: (i) Raleigh method; (ii) Dirlik method and (iii) Range distribution function created with the Rainflow cycle counting method. Methods (ii) and (iii) are derived from a pseudo time-history created with an inverse Fourier transform. These frequency-domain results are compared to corresponding fatigue damage estimates from a multi-modal time-domain analysis method, to assess the consistency of the two approaches.Item Methods and Models for Assessing Solder Interconnect Reliability of Control Boards in Power Electronic Systems(2013) Squiller, David; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over the past 20 years, power electronic systems have been increasingly required to operate in harsh environments including automotive, deep-well drilling and aerospace applications. In parallel, the higher power densities and miniaturization of the power switching module result in elevated stress levels on the control circuitry. The objective of this study was to develop methods and models for assessing the interconnect reliability of components used in the control circuitry for power electronic systems. Physics-of-Failure modeling and a series of thermal and reliability simulations were conducted on a 2.2 kW variable-frequency drive to evaluate the susceptibility of system level and component level failure mechanisms. Assessment methods consisted of developing CalcePWA simulation models of the primary sub-assemblies and constructing a power cycling apparatus to perform accelerated testing of the drive.Item A Physics of Failure Based Qualification Process for Flexible Display Interconnect Materials(2011) Martin, Thomas; Christou, Aris; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The next paradigm shift in display technology involves making them flexible, bringing with it many challenges with respect to product reliability. To compound the problem, industry is continuously introducing novel materials and experimenting with device geometries to improve flexibility and optical performance. Hence, a method to rapidly qualify these new designs for high reliability applications is imperative. This dissertation involves the development of a qualification process for gate line interconnects used in flexible displays. The process starts with the observed failure mode of permanent horizontal lines in the displays, followed by the identification of the underlying failure mechanism. Finite element analyses are developed to determine the relationship between the physical flexing and the mechanical stress imposed on the traces. The design of an accelerated life test is performed based on the known agent of failure being cyclic bending that induces a tensile strain. A versatile dedicated test system is designed and integrated in order to rapidly capture changes in resistance of multiple traces during test. Dedicated test structures are also designed and fabricated to facilitate in-situ electrical measurements and direct observations. Since the test structures were consumed during the integration of the test system, random failure times are used in the process of determining a life-stress model. Different models are compared with respect to their applicability to the underlying failure mechanism as well as parameter estimation techniques. This methodology may be applied towards the rapid qualification of other novel materials, process conditions, and device geometries prior to their widespread use in future display systems.Item ELECTROMAGNETIC MODELING WITH A NEW 3D ALTERNATING-DIRECTION-IMPLICIT (ADI) MAXWELL EQUATION SOLVER(2004-08-10) Shao, Xi; Goldsman, Neil; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We introduce a time-domain method to simulate the digital signal propagation along on-chip interconnects, aperture radiation, and indoor-communication by solving the Maxwell equation with the Alternating-Direction-Implicit (ADI) method. With this method, we are able to resolve the large scale (i.e. electromagnetic wave propagation) and fine scale (i.e. metal skin depth, substrate current, coating material) structure in the same simulation, and the simulation time step is not limited by the Courant condition. The simulations allow us to calculate in detail parasitic current flow inside the substrate; propagation losses, skin-depth and dispersion of digital signals on non-ideal interconnects; detailed surface current and standing wave pattern in aperture radiation problem; signal power map and propagation delay in complicated in-door communication scenarios