Behavior of surface oxide and intermetallic compounds in interconnections of micro Sn-Ag solder bumps

A flip-chip technology was put into practical use by interconnecting a chip-on-chip (CoC) with several thousands of micro-solder bumps with a diameter of 30 mum. Using this technology, the signal transmission rate between chips became comparable to system on chip (SOC) technology. This success with interconnects owes much to the characterization and control of the surface oxidation behavior of solder bumps and the growth of intermetallic compounds (IMCs), which influences the yield and reliability of solder bump interconnections. We clarified the growth behavior of solder oxide film and IMCs at the bonded interface of Sn 3.5 wt.% Ag solder bumps on Ni electrodes in the present research. As a result, we found an oxide film of solder with an initial thickness of 3 to 4 nm saturated at around 5 nm demonstrating an excellent solder interconnect. Although the interface between the solder and Sn-Ni IMCs roughens as they grow, the smoothness can be recovered by annealing at 100degC for 100 hr, resulting in a decrease in the fraction of the defect failure mode from 6% to about 0 to 3%