Feasibility of Solid State Bonding for Sn-Ag-Cu Solder Bumps in Ambient Air

The feasibility of solid state bonding for low-profiled Sn-3.0Ag-0.5Cu (wt%) solder bumps is confirmed at 25-200degC by thermo-compression bonding (TCB) and surface activated bonding (SAB) in ambient air. 100% bond yield was achieved. The bonding windows of the necessary bonding force and temperature were described. The composite percent on the bonding surfaces was analyzed quantitatively by X-ray photoelectron spectroscopy (XPS). The successful bonding of Sn-Ag-Cu solder bumps in solid state is benefited from dispersing contaminants and oxides. With the activated process to the bonding surfaces prior to the assembly, the thickness of contaminant and oxide layers in SAB is less than 2 nm, which is much smaller than that of TCB. SAB method is much helpful to reduce the necessary bonding force or temperature compared with TCB method.