"Internal Cracking in Cu6Sn5 Intermetallic Layer in Lead-Free Solder Joints" 

Lijia Xie, MSE PhD Candidate 

Advisors: Professors Carol Handwerker, Ganesh Subbarayan-Shastri, and John Blendell

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ABSTRACT

Solder alloys provide good mechanical and electronic connections for circuit boards. In recent decades, researchers have been turning their attention to lead-free solder alloys for advanced packaging applications. The intermetallic layer formed between the lead-free solder and the substrate is crucial for the mechanical performance of the solder joint. Because of the phase transformation, the internal crack appears in the intermetallic layer, which can degrade the mechanical performance of the solder. Adding Ni content is a feasible method, but its efficacy also highly depends on the composition of the solder alloy. Changing the reflow profile is another way to eliminate the internal crack, where the proper temperatures and time range are still under investigation. In this document, there is a focus on comparing the Innolot (Sn-3.8wt%Ag-0.7wt%Cu-3wt%Bi-1.4wt%Sb-0.15wt%Ni) alloy and SAC305 (Sn-3wt%Ag-0.5wt%Cu) alloy, aiming at figuring out the suitable reflow profiles to suppress the formation of internal cracks, and how each element works together to affect the thermal and mechanical properties of the solder alloy.