Mechanical Engineering
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Item MESOSCALE MICROSTRUCTURE EVOLUTION, RELIABILITY AND FAILURE ANALYSIS OF HIGH TEMPERATURE TRANSIENT LIQUID PHASE SINTERING JOINTS(2017) Moeini, Seyed Ali; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The continuous increase in application temperature of power electronic devices, due to the growing power density, miniaturization, and functionality in military and commercial applications, requires new packaging technologies with high temperature and reliability capabilities. Currently, the traditional maximum allowable temperature of power electronics (125°C) is a limiting factor for high temperature applications, such as space exploration, drilling, avionics, and electronic vehicles. Substitution of Silicon devices with wide bandgap (e.g., SiC) devices has extended the maximum allowable temperatures to 475 ̊C. However, this created the need for robust high temperature packaging materials, especially interconnects and attachments. High temperature solders are often too expensive, too brittle, or environmentally toxic to be used, leading to increased study of low temperature joining techniques, such as solid phase sintering and Transient Liquid Phase Sintering (TLPS), for producing high temperature stable attachments. TLPS is an emerging electronic interconnect technology enabling the formation of high temperature robust joints between metallic surfaces at low temperatures by the consumption of a transient, low temperature, liquid phase to form high temperature stable intermetallic compounds (IMCs). The performance and durability of these materials strongly depend on their microstructure, which is determined by their processing. The complicated process of IMC formation through eutectic solidification and the extensive number of parameters affecting the final microstructure make it impractical to experimentally study the effect of each factor. In this work, phase field modeling of the microstructure of TLPS materials fabricated by different processing methods will be conducted. Phase-field modeling (PFM) is a powerful thermodynamic consistent method in mesoscale modeling that simulates the evolution of intermetallic compounds during the solidification process, providing insight into the final microstructure. Application of this method facilitates the optimization of influential processing factors. Efforts will also be conducted to identify failure modes and mechanisms experimentally under dynamic, power and thermal cycling loads as a function of critical microstructural features, facilitating the optimization of joining parameters to obtain higher durability TLPS interconnections. The objective of this dissertation is to provide an insight into the processing of a reliable high temperature TLPS and facilitate their application in power electronic industries.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.