Study on Sn–Ag Oxidation and Feasibility of Room Temperature Bonding of Sn–Ag–Cu Solder

A method for room temperature bonding of lead-free solders in different environments (vacuum, N2, air) was developed to avoid the problems caused by the high melting temperature of lead-free alloys. The method is called as surface activated bonding (SAB) method. In order to understand the influence of oxidation of Sn–Ag alloy on the bonding characteristics, the surface oxides were removed by argon fast atom beam (Ar-FAB) irradiation and then the growth of the oxides on the alloy surfaces in air was investigated by using X-ray photoelectron spectroscopy (XPS). The oxidation of Sn–Ag alloy appeared a logarithm law at room temperature. The information gathered in the investigation was applied to flip chip bonding, using Sn–Ag–Cu solder bumps at room temperature. The bond strength in different bonding environments was compared, and the results showed that the bond strength depended on the oxide thickness, and by controlling the oxidation process, a room temperature bonding might be possible even in non-vacuum conditions.