Lead-Free Solder Micro-Ball Bumps for the Next Generation of Flip Chip Interconnection: Micro-Ball Materials, Bump Formation Process and Reliability

Micro-ball wafer bumping (MBB) technology, which has capability of fine pitch bumping such as 150-μm pad pitch and the advantages of adjusting the optimum material combinations of joints, was brought into practice. High productivity and yield were achieved by employing an inspection and the repair process with special equipment, and a void-less reflow process was established. Package-level reliability tests were performed for chips with Ti/NiV/Cu-UBM and Sn-Ag-Cu solder bumps using MBB technology with excellent results. An evaluation on reliability was also conducted with Sn-1.2Ag-0.5Cu-Ni solder and pure tin solder bumps. As a result of multiple reflow cycle tests for Ti/NiV/Cu-UBM and various lead-free solders, the shape of IMC and the spalling of IMC were influenced by the total amount of Cu and Ni in the solder and the UBM composition. Ti/NiV/Cu-UBM can be applied to various solders by changing the thickness of the surface Cu layer according to the composition of the solder.