Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

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 give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Filters

2008 - 200922010 - 20161

Settings

Subject: search.filters.subject.lead free

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    EFFECT OF ISOTHERMAL AGING ON SAC305 HARMONIC VIBRATION DURABILITY
    (2016) Lin, Elaine; Dasgupta, Abhijit; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The effect of isothermal aging on the harmonic vibration durability of Sn3.0Ag0.5Cu solder interconnects is examined. Printed wiring assemblies with daisy-chained leadless chip resistors (LCRs) are aged at 125°C for 0, 100, and 500 hours. These assemblies are instrumented with accelerometers and strain gages to maintain the same harmonic vibration profile in-test, and to characterize PWB behavior. The tested assemblies are excited at their first natural frequencies until LCRs show a resistance increase of 20%. Dynamic finite element models are employed to generate strain transfer functions, which relate board strain levels observed in-test to respective solder strain levels. The transfer functions are based on locally averaged values of strains in critical regions of the solder and in appropriate regions of the PWB. The vibration test data and the solder strains from FEA are used to estimate lower-bound material fatigue curves for SAC305 solder materials, as a function of isothermal pre-aging.
  • Thumbnail Image
    Item
    EVOLUTION OF THE MICROSTRUCTURE AND VISCOPLASTIC BEHAVIOR OF MICROSCALE SAC305 SOLDER JOINTS AS A FUNCTION OF MECHANICAL FATIGUE DAMAGE
    (2009) Cuddalorepatta, Gayatri; Dasgupta, Abhijit; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The effect of mechanical cycling fatigue damage and isothermal aging histories on the evolution of the constitutive and fatigue responses, and microstructure of microscale SAC305 solder joints is investigated. In particular, the study examines if joint dependent behavior should be expected from as-fabricated and cycled microscale SAC305 joints that exhibit an initial non-homogenous coarse-grained Sn microstructure. In addition, the ability of traditionally used macroscale constitutive models based on continuum mechanics to represent the viscoplastic constitutive behavior of the non-homogenous as-fabricated microscale SAC305 specimens is explored. Insights into the effect of key microstructural features and dominant creep mechanisms influencing the measured viscoplastic behavior of SAC305 are provided using a multi-scale mechanistic modeling framework. Modified lap-shear microscale SAC305 specimens are characterized using the thermomechanical microscale test setup (TMM). Microscale SAC305 solder specimens show significant piece-to-piece variability in the viscoplastic constitutive properties under identical loading histories in the as-fabricated state. The mechanical response is strongly influenced by the grain microstructure across the entire joint, which is non-repeatable and comprises of very few highly anisotropic Sn grains. The statistical non-homogeneity in the microstructure and the associated variability in the mechanical properties in the microscale SAC305 test specimen are far more significant than in similar Sn37Pb specimens, and are consistent with those reported for functional microelectronics solder interconnects. In spite of the scatter, as-fabricated SAC305 specimens exhibit superior creep-resistance (and lower stress relaxation) than Sn37Pb. Macroscale creep model constants represent the non-homogeneous behavior of microscale joints in an average sense. Macroscale modeling results show that the range of scatter measured from macroscale creep model constants is within the range of scatter obtained from the stress relaxation predictions. Stress relaxation predictions are strongly sensitive to the inclusion or exclusion of primary creep models. The proposed multiscale framework effectively captures the dominant creep deformation mechanisms and the influence of key microstructural features on the measured secondary creep response of microscale as-fabricated SAC305 solder specimens. The multiscale model predictions for the effect of alloy composition on SAC solders provide good agreement with test measurements. The multiscale model can be extended to understand the effects of other parameters such as aging and manufacturing profiles, thereby aiding in the effective design and optimization of the viscoplastic behavior of SAC alloys. Accumulated fatigue damage and isothermal aging are found to degrade the constitutive and mechanical fatigue properties of the solder. The scatter gradually decreases with an increasing state of solder damage. Compared to the elastic-plastic and creep measurements, the variability in the fatigue life of these non-homogenous solder joints under mechanical fatigue tests is negligible. Recrystallization is evident under creep and mechanical fatigue loads. Gradual homogenization of the Sn grain microstructure with damage is a possible reason for the observed evolution of scatter in the isothermal mechanical fatigue curves. The yield stress measurements suggest that SAC305 obeys a hardening rule different from that of isotropic or kinematic hardening. The measured degradation in elastic, plastic and yield properties is captured reasonably well with a continuum damage mechanics model from the literature.
  • Thumbnail Image
    Item
    Development of a Shifting Melting Point Ag-In Paste Via Transient Liquid Phase Sintering for High Temperature Environments
    (2008-07-18) Quintero, Pedro; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The increasing demand for electronic devices capable of operating at temperatures above the traditional 125°C limit is driving major efforts in research and development. Devices based on wide band gap semiconductors have been demonstrated to operate at temperatures up to 500°C, but packaging still remains a major hurdle for product development. Recent regulations, such as RoHS and WEEE, increase the complexity of the packaging task as they prohibit the use of certain materials in electronic products such as lead (Pb), which has traditionally been used in high temperature solder attach. The successful development of new attach materials and manufacturing processes will enable the realization of next generation products capable of operating reliably at elevated temperatures. In this investigation a shifting melting point silver (Ag) - indium (In) solder paste that uses a Transient Liquid Phase Sintering (TLPS) process was developed. This novel material and manufacturing process constitutes a major advancement over the conventional soldering process temperature hierarchy, in which the maximum allowable application temperature is limited by the melting point of the attach material. By virtue of a shifting melting temperature, which results from isothermal solidification during the TLPS process, this attach material can be processed at a relatively low temperature while being capable of sustaining much higher temperatures in use, limited only by its new melting point. In order to develop an empirical kinetics model of the Ag-In TLPS process, a design of experiments (DOE) was used to study the effect of multiple factors on the solidification reaction. These factors include particle size, weight fraction of solute, heating rate, holding time, and processing temperature. The physical implications of the empirical model were confirmed by constructing a diffusion based mechanistic model. Pivotal microstructural information was obtained from metallographic analysis where a transition from an In-rich matrix to an Ag-rich solid solution was observed. The metallographic characteristics, mechanical strength, and electrical conductivity of the resulting Ag-In TLPS material were assessed. This study has resulted in the creation of a novel attach material and method that will enable future development of electronic packaging for high temperature environments. The quantitative description of the reaction kinetics during the TLPS process provided a valuable tool for future development and an optimization of this system.