A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Integrated Measurement Technique To Measure Curing Process-dependent Mechanical And Thermal Properties Of Polymeric Materials Using Fiber Bragg Grating Sensors(2009) Wang, Yong; Han, Bongtae; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An innovative technique based on a fiber Bragg grating (FBG) sensor is proposed to measure the critical mechanical and thermal properties of polymeric materials. The properties include (1) chemical shrinkage evolution during curing, (2) modulus evolution during curing, (3) glass transition temperature (4) coefficient of thermal expansion (CTE), and (5) visco-elastic properties. Optimum specimen configurations are proposed from the theoretical analysis. Then an efficient numerical procedure is established to determine the material properties from the measured Bragg wavelength (BW) shift. The technique is implemented with various polymeric materials. The measured quantities are verified through a self-consistency test as well as the existing testing methods such as a warpage measurement of a bi-material strip, and a TMA measurement. The evolution properties obtained at a curing temperature are extended further by combining them with the conventional isothermal DSC experiments. Based on the existing theories, the evolution properties can be predicted at any temperatures. The proposed technique greatly enhances the capability to characterize the mechanical properties and behavior of polymeric materials. Since the specimen preparation is very straightforward, the proposed method can be routinely practiced and the measurement can be completely automated. It will provide a much-needed tool for rapid but accurate assessment of polymer properties, which, in turn, will enhance the accuracy of predictive modeling for design optimization of a microelectronics product at the conceptual stage of product development.Item End-of-Life and Constant Rate Reliability Modeling for Semiconductor Packages Using Knowledge-Based Test Approaches(2009) Yang, Liyu; Bernstein, Joseph B; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)End-of-life and constant rate reliability modeling for semiconductor packages are the focuses of this dissertation. Knowledge-based testing approaches are applied and the test-to-failure approach is approved to be a reliable approach. First of all, the end-of-life AF models for solder joint reliability are studied. The research results show using one universal AF model for all packages is flawed approach. An assessment matrix is generated to guide the application of AF models. The AF models chosen should be either assessed based on available data or validated through accelerated stress tests. A common model can be applied if the packages have similar structures and materials. The studies show that different AF models will be required for SnPb solder joints and SAC lead-free solder joints. Second, solder bumps under power cycling conditions are found to follow constant rate reliability models due to variations of the operating conditions. Case studies demonstrate that a constant rate reliability model is appropriate to describe non solder joint related semiconductor package failures as well. Third, the dissertation describes the rate models using Chi-square approach cannot correlate well with the expected failure mechanisms in field applications. The estimation of the upper bound using a Chi-square value from zero failure is flawed. The dissertation emphasizes that the failure data is required for the failure rate estimation. A simple but tighter approach is proposed and provides much tighter bounds in comparison of other approaches available. Last, the reliability of solder bumps in flip chip packages under power cycling conditions is studied. The bump materials and underfill materials will significantly influence the reliability of the solder bumps. A set of comparable bump materials and the underfill materials will dramatically improve the end-of-life solder bumps under power cycling loads, and bump materials are one of the most significant factors. Comparing to the field failure data obtained, the end-of-life model does not predict the failures in the field, which is more close to an approximately constant failure rate. In addition, the studies find an improper underfill material could change the failure location from solder bump cracking to ILD cracking or BGA solder joint failures.Item Evaluation of Environmental Tests for Tin Whisker Assessment(2009) Panashchenko, Lyudmyla; Osterman, Michael D; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tin whiskers are electrically conductive crystalline structures of tin that over time may grow outward from tin-rich surfaces and present a reliability hazard to electronic systems. While the problem has been known for decades, no satisfactory explanation of whisker growth mechanisms exists, leaving the industry to create whisker-assessment tests based on empirical data gathered under various environmental storage conditions controlled for temperature, humidity and temperature cycling. The long-term predictability of these environmental storage tests has not been addressed and the accuracy of these tests in foreseeing whisker growth is unclear. In this thesis, different tin finishes are assessed for whisker growth in accordance with existing environmental test standards and compared to growth seen in ambient storage conditions. The results indicate that environmental tests may over-predict, under-predict, or show little distinguishable growth as compared to ambient-stored tin finishes. In conclusion, environmental tests are not a reliable method of assessing future whisker growth.Item PROGNOSTICS OF SOLDER JOINT RELIABILITY UNDER VIBRATION LOADING USING PHYSICS OF FAILURE APPROACH(2009) Gu, Jie; Pecht, Michael G; Barker, Donald; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Physics-of-failure (PoF) is an approach that utilizes knowledge of a product's life cycle loading and failure mechanisms to perform reliability modeling, design, and assessment. Prognostics is the process of predicting the future reliability of a system by assessing the extent of deviation or degradation of a product from its expected normal operating states. When prognostics is combined with physics-of-failure models, it is possible to make continuously updated reliability predictions based on the monitoring of the actual environmental and operational conditions of each individual product. A literature review showed that the research on prognostics of solder joint reliability under vibration loading is very limited. However, personal portable electronic products are no longer used exclusively in a benign office environment. For example, any electronic component (throttles, brakes, or steering) in an automobile should be able to survive in a vibration environment. In this thesis, a methodology was developed for monitoring, recording, and analyzing the life-cycle vibration loads for remaining-life prognostics of solder joints. The responses of printed circuit boards (PCB) to vibration loading were monitored using strain gauges and accelerometers, and they were further transferred to solder strain and stress for damage assessment using a failure fatigue model. Damage estimates were accumulated using Miner's rule after every mission and then used to predict the life consumed and the remaining life. The results were verified by experimentally measuring component lives through real-time daisy-chain resistance measurements. This thesis also presents an uncertainty assessment method for remaining life prognostics of solder joints under vibration loading. Basic steps include uncertainty source categorization, sensitivity analysis, uncertainty propagation, and remaining life probability calculation. Five types of uncertainties were categorized, including measurement uncertainty, parameter uncertainty, model uncertainty, failure criteria uncertainty, and future usage uncertainty. Sensitivity analysis was then used to identify the dominant input variables that influence model output. After that, a Monte Carlo simulation was used for uncertainty propagation and to provide a distribution of accumulated damage. From the accumulated damage distributions, the remaining life was then able to be predicted with confidence intervals. The results showed that the experimentally measured failure time was within the bounds of the uncertainty analysis prediction.Item Electromagnetic Interference Reduction using Electromagnetic Bandgap Structures in Packages, Enclosures, Cavities, and Antennas(2007-11-26) Mohajer Iravani, Baharak; Ramahi, Omar M.; Granatstein, Victor L.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electromagnetic interference (EMI) is a source of noise problems in electronic devices. The EMI is attributed to coupling between sources of radiation and components placed in the same media such as package or chassis. This coupling can be either through conducting currents or through radiation. The radiation of electromagnetic (EM) fields is supported by surface currents. Thus, minimizing these surface currents is considered a major and critical step to suppress EMI. In this work, we present novel strategies to confine surface currents in different applications including packages, enclosures, cavities, and antennas. The efficiency of present methods of EM noise suppression is limited due to different drawbacks. For example, the traditional use of lossy materials and absorbers suffers from considerable disadvantages including mechanical and thermal reliability leading to limited life time, cost, volume, and weight. In this work, we consider the use of Electromagnetic Band Gap (EBG) structures. These structures are suitable for suppressing surface currents within a frequency band denoted as the bandgap. Their design is straight forward, they are inexpensive to implement, and they do not suffer from the limitations of the previous methods. A new method of EM noise suppression in enclosures and cavity-backed antennas using mushroom-type EBG structures is introduced. The effectiveness of the EBG as an EMI suppresser is demonstrated using numerical simulations and experimental measurements. To allow integration of EBGs in printed circuit boards and packages, novel miniaturized simple planar EBG structures based on use of high-k dielectric material (r > 100) are proposed. The design consists of meander lines and patches. The inductive meander lines serve to provide current continuity bridges between the capacitive patches. The high-k dielectric material increases the effective capacitive load substantially in comparison to commonly used material with much lower dielectric constant. Meander lines can increase the effective inductive load which pushes down the lower edge of bandgap, thus resulting in a wider bandgap. Simulation results are included to show that the proposed EBG structures provide very wide bandgap (~10GHz) covering the multiple harmonics of of currently available microprocessors and its harmonics. To speed up the design procedure, a model based on combination of lumped elements and transmission lines is proposed. The derived model predicts accurately the starting edge of bandgap. This result is verified with full-wave analysis. Finally, another novel compact wide band mushroom-type EBG structure using magneto-dielectric materials is designed. Numerical simulations show that the proposed EBG structure provides in-phase reflection bandgap which is several times greater than the one obtained from a conventional EBG operating at the same frequency while its cell size is smaller. This type of EBG structure can be used efficiently as a ground plane for low-profile wideband antennas.Item Development of an Advanced Adhesion Test for Polymer Interfaces(2007-11-19) Vickey, Nathan Andrew; Han, Bongtae; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The bond strength of polymer interfaces within packaged microelectronic devices significantly influences their reliability. In the interest of predictive modeling and to facilitate materials selection during the design process, it is highly desirable to be able to distinguish between the adhesive performances of multiple polymer interfaces. However, typical adhesion testing is normally plagued by large deviations in its test results which make drawing statistical conclusions from adhesion strength data difficult. To remedy this, an investigation into the primary sources of variance associated with the pull test was performed. Four primary factors were identified, load alignment, loading rate, bond thickness, and the edge condition. The control of each of these four parameters was targeted during the development of an improved adhesion test technique. The results are an adhesion measurement method which has successfully reduced the scatter in test results from a standard deviation of 50% to approximately 10%.Item PROGNOSTICS DEMONSTRATION OF ELECTRONIC COMPONENTS SUBJECTED TO VIBRATION ENVIRONMENT OF A LIGHT MILITARY TACTICAL VEHICLE(2007-11-05) Yu, Alan; Barker, Donald B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A demonstration of the Prognostics and Health Management (PHM) method in a military vehicle environment was performed. The purpose of the demonstration is to show rapid and cost effective means to increase reliability and effectiveness of in-cabin equipment through PHM implementation. The PHM method allows for prediction of damage accumulation in a system while in its operating environment. Prediction is achieved by monitoring and assessing appropriate product parameters. An experimental setup to perform in-cabin accelerated testing on printed circuit boards (PCB) was developed. Strain, acceleration, continuity, and GPS data were recorded during testing. Using recorded data, life prediction with cycle counting and PSD load blocking techniques was demonstrated for BGA components. A limited set of terrain and loading conditions was characterized using Root Mean Square (RMS) and Power Spectral Density (PSD).Item Investigation of PDA LCD Screen Failures Under Humidity Cycling and Bending Loads(2006-12-08) Johnson, Morrigan Lynn; Barker, Donald B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Liquid crystal displays are commonly used in various applications and subjected to numerous environmental and handling conditions that can especially affect the performance and life of these devices. In addition to humidity and temperature exposure, cyclic loadings and handling conditions (bending, repetitive shock, and drop loading) have been shown to cause failures in LCDs. Due to the large number of variable failure modes and use conditions, the question arises: how long can a LCD survive before a failure occurs? Characterizing these failures, along with providing information and techniques to help assess the life expectancy of an LCD are addressed here. The effects of cyclic humidity exposure and biaxial bending were studied. The resulting failures were analyzed and compared to previous studies to determine common failure modes and relationships that would be useful in providing a rapid product life assessment. Conclusions were made concerning appropriate methodology and testing that can be consistently and efficiently be used to assess LCD assemblies, thus saving time and money in the manufacturing process.Item Rapid Assessment of BGA Fatigue Life Under Vibration Loading(2006-08-31) Wu, Mei-Ling; Barker, Donald; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ball Grid Array (BGA) packages are a relatively new package type and have rapidly become the package style of choice. Much high density, high I/O count semiconductor devices are now only offered in this package style. Designers are naturally concerned about the robustness of BGA packages in a vibration environment when their experience base is with products using more traditional compliant gull or J leaded surface mount packages. Because designers simply do not have the experience, tools are needed to assess the vibration fatigue life of BGA packages during early design stages and not have to wait for product qualification testing, or field returns, to determine if a problem exists. This dissertation emphasizes a rapid assessment methodology to determine fatigue life of BGA components. If time and money were not an issue, clearly one would use a general-purpose finite element program to determine the dynamic response of the printed wiring board in the vibration environment. Once the response of the board was determined, one would determine the location and value of the critical stress in the component of interest. Knowing the critical stress, one would estimate the fatigue life from a damage model. The time required building the FEA model, conducting the analysis, and post-process the results would take at least a few days to weeks. This is too time-consuming, except in the most critical applications. It is not a process that can be used in everyday design and what-if simulations. The rapid assessment approach proposed in this research focuses on a physics of failure type approach to damage analysis and involves global and local modeling to determine the critical stress in the component of interest. A fatigue damage model then estimates the life. Once implemented in software, i.e. the new version of CALCE_PWA, the entire fatigue life assessment is anticipated to be executed by an average engineer in real time and take only minutes to generate accurate results.Item Thermo-mechanical Analysis of Encapsulated Ball-Wedge Wire Bonds in Microelectronics, using Raleigh-Ritz Modeling(2006-08-16) Jinka, Krishna Kumar; Dastupta, Abhijit; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study addresses encapsulated wire bonds in chip-on-board (CoB) multi chip modules, which provide a low cost option for dealing with the current trend towards compact microelectronic packages with increased I/O, higher reliability and lower cost. The focus is on thermomechanical stresses caused in the bond wires when the encapsulant is cooled from high curing temperatures and subsequently subjected to thermal cycling loading. The stresses generated in bond wires due to thermal expansion mismatches, in an encapsulated CoB are very complex and are driven by both global and local thermal expansion mismatches between: (i) glob-top encapsulant and the silicon die, (ii) encapsulant and the wire, and (iii) encapsulant and the substrate assembly. A 2D stress analysis model based on the variational Raleigh-Ritz (RR) method is developed, to estimate thermomechanical stresses in the bond wire, based on elastic analysis. The study focuses on detailed parametric investigation of different encapsulated CoB configurations. The initial wire profile, before encapsulation, is first modeled with RR 2-D trial functions based on cubic splines. This predicted geometry is then used for the subsequent thermomechanical stress analysis after encapsulation, based on trial functions composed of polynomials and exponential functions. The results are calibrated with Finite Element Analysis. Plastic deformations are ignored in the current analysis, as a first-order approximation. This model is therefore suitable for parametric design sensitivity studies and qualitative ranking of design options, but not for quantitative predictions of thermal cycling durability. The results show that the region above the ball bond is the predominant failure site. The RR 2-D model has a well-defined range of validity for CoB Ball-Wedge wire bond configurations with stiff encapsulants (E¬ >= 3 GPa) and thin wires (dia <= 2 mils). Also, the trend of maximum elastic strains obtained from the RR 2-D model is found to be in qualitative agreement with thermal cycling fatigue test data obtained from the literature.