Low-Temperature Solid-State Bonding Using Hydrogen Radical Treated Solder for Optoelectronic and MEMS Packaging

Low temperature hermetic sealing methods that are tolerant to surface roughness are required for optoelectronic and MEMS devices. In this paper, a new bonding process based on a solid-state interdiffusion between Sn and Au at a bonding temperature lower than 200 degrees C using hydrogen radical treated Sn-3.0Ag-0.5Cu (wt%) solder was developed. This is a fluxless bonding technique. The Sn-Ag-Cu solder patterns using hydrogen radical reflow process were exposed to air and bonded with Au thin films without flux at temperatures below the melting point. Successful bonding was obtained at a bonding temperature above 150 degrees C for 10 min. The samples bonded at a bonding temperature of 170 degrees C under the application of a bonding pressure of 150 MPa showed leakage rates of less than 1.0 x 10(-9) Pa m(3) s(-1).