Narrow Band Random Vibration Reliability of a Doped Near Eutectic Tin-Bismuth-Based Alloy with a Large Fine-Pitch Ball Grid Array Device

This thesis investigates the vibration reliability and microstructure of two low temperature lead-free solder alloys. The experimental design involved a 2x2 factorial setup, with solder paste type and time above liquidus (TAL) as the primary factors. The solder pastes tested were Indalloy 281 and Indalloy 303, with TALs of two minutes and three minutes. Indalloy 281 is a eutectic Sn42/Bi58 solder and Indalloy 303 is a doped near eutectic Sn-Bi solder. The objective of the study is to identify how reliability changes between solders and the time above liquidous and to also examine the microstructure and the significant factors that impact vibration reliability. Vibration is a common failure mode for the automotive industry, however, there is limited published research on low temperature solder vibration reliability. The reliability of the solder joints is evaluated using Weibull analysis, linear regression is used to identify the significant factors, and cross-sectional failure analysis is used to evaluate the microstructure. Results indicated that Indalloy 303 exhibited superior vibration reliability compared to Indalloy 281 when a shorter TAL was used. The longer TAL generally improved reliability for both solder types, with a more pronounced effect on Indalloy 281. Microstructural analysis revealed that the dopants in Indalloy 303 resulted in Ag3Sn phases in grain structure, contributing to its enhanced performance. The Weibull analysis demonstrated that the failure modes for Indalloy 281 were primarily due to inherent material limitations, whereas Indalloy 303 showed improved resistance to vibration-induced fatigue. Linear regression analysis identified significant factors influencing solder joint reliability, including GRMS mean, board weight, and time since manufacturing. This study observes that Indalloy 303 presents a promising alternative to traditional eutectic solders, offering improved reliability and potential for broader application in the electronics industry. There are some concerns with the one test condition whose data did not appear like the other data which indicates there is possibly a manufacturing or vibration testing concern for that data. From this study there are many future research opportunities including analysis of this experiment that has not been done and running a large sample size experiment. Studies should explore other low-temperature solder alloys and their performance under various environmental conditions to further advance lead-free soldering technologies.