Mechanical Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2795
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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.Item RELIABILITY OF LEAD-FREE HIGH TEMPERATURE SURFACE MOUNT COMPONENT ATTACHES(2008) Oberc, Timothy James; McCluskey, F. P.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work investigates the relative reliabilities of SAC305, eutectic Au-Sn, and Ag-In transient liquid phase sintered (TLPS) solder joints subjected to high temperature passive thermal cycling. These solder materials were monitored for electrical resistance, mechanical pull strength, and microstructural changes during cycling. In fabricating the test assemblies, SAC305 and eutectic Au-Sn manufacturing parameters were gathered from the paste distributors while fabrication with Ag-In TLPS required in-house development. Work with the Ag-In TLPS paste revealed that reducing the additive (In) particle size led to statistically significant improvements in the solid volume fraction of the joints. Successful attachment of ceramic quadflat packs (CQFPs) to polyimide circuit boards using Ag-In TLPS demonstrated that surface mount joints with mechanical and electrical integrity could be manufactured from the material. Au-Sn was found to be the strongest of the materials while cracking in the SAC305 and Ag-In samples during cycling resulted in weaker joints.