http://hdl.handle.net/10136/17 Publications of Materials and Metallurgical Engineering Department Search the Channel search http://dspace.nmt.edu/dspace/simple-search http://hdl.handle.net/10136/22 Title: Smart Lead-Free Solders Via Shape-Memory Alloy Reinforcement <br/> <br/>Authors: Dutta, I.; Majumdar, B.S.; Chen, T.; Chung, C.; Ye, B. <br/> <br/>Abstract: Microelectronic solder joints are exposed to aggressive thermo-mechanical cycling (TMC) during service, resulting in strain localization near solder / bond-pad interfaces, which eventually leads to low-cycle fatigue (LCF) failure of the joint. In order to mitigate these strain concentrations and thereby improve LCF life, a 'smart solder' reinforced with a martensitic NiTi based shape memory alloy (SMA) is being developed. This paper presents an overview of processing, characterization and modeling of these composite solders, and articulates the role of NiTi particles on strain evolution in composite solders. Based on finite element modeling and experiments on model single fiber composites, it is shown that NiTi pariculate reinforcements can reduce inelastic strain levels in the solder via shape recovery associated with the B19'®B2 transformation. In situ TMC studies in the SEM, in conjunction with strain analysis via digital image correlation, show evidence of reverse deformation in the solder commensurate with the NiTi phase transformation, demonstrating the conceptual viability of the smart solder approach. Details of processing and joint formation, and the resultant microstructures of smart solder are discussed. Finally, results of TMC experiments on monolithic solder and NiTi/solder composite joints are reported, highlighting the beneficial effect of shape-memory transformation in reducing inelastic strain range, and hence enhancing the LCF life, of solders.