A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item AN ANALYTICAL APPROACH FOR FATIGUE LIFE ESTIMATION OF COPPER TRACES FOR DESIGN OPTIMIZATION IN ELECTRONIC ASSEMBLIES(2015) Menon, Sandeep; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation investigates the durability of the copper traces using experimental results from a fully reversed four point bend test and finite element analysis. The durability data collected from the experiment was used in conjunction with the finite element based critical trace strain, to develop a set of compatible fatigue model constants that best fit the failure behavior observed in the tests. Experimental studies were also conducted in order to determine the impact of assembly variations on the trace fatigue failures including the presence of a surface finish, solder mask as well as the presence of assembled components. In order to validate the established fatigue life model constants further testing was conducted at a different load level. The model was able to predict the test out come with an error of less than 5 % Parametric studies using finite element analysis were also conducted in order to determine the relationship between the various geometric and loading conditions and the critical trace strain in the copper traces. Based on these relationships as well as the experiments to determine the impact of assembly variations of failure of the traces, an analytical model was developed in order to approximate the copper trace strain which is used as the input to the trace fatigue model. To understand the crack initiation and crack propagation process in copper traces, experiments were conducted where the crack growth was periodically monitored. Based on these experiments, the constants for the fatigue crack propagation in copper traces based on Paris’s Law were also determined in this study. Finally the analytical model for trace strain developed was also validated by comparing the copper trace strain evaluated using finite element modeling for the test vehicle used in the experiments. The strains estimated based on the analytical model match well with the strains based on the finite element modeling.Item THERMAL CYCLING RELIABILITY OF LEAD-FREE SOLDERS (SAC305 AND SN3.5AG) FOR HIGH TEMPERATURE APPLICATIONS(2010) George, Elviz; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutectic tin lead was the most widely used solder interconnect in the electronics industry before the adoption of lead-free legislation. But eutectic tin lead solder has a low melting point (183oC) and was not suited for some high temperature applications, such as oil and gas exploration, automotive, and defense. Hence, for these applications, the electronics industry had to rely on specialized solders. In this study, ball grid arrays (BGAs), quad flat packages (QFPs), and surface mount resistors assembled with SAC305 and Sn3.5Ag solder pastes were subjected to thermal cycling from -40oC to 185oC. Commercially available electroless nickel immersion gold (ENIG) board finish was compared to proprietary Sn-based board finish designed for high temperatures. The data analysis showed that the type of solder paste and board finish used did not have an impact on the reliability of BGAs. The failure site was on the package side of the solder joint. The morphology of intermetallic compounds (IMCs) formed after thermal cycling was analyzed.