Fluxless wafer-level Cu-Sn bonding for micro- and nanosystems packaging

For wafers with integrated and released sensitive micro- and nanosystems a fluxless wafer-level hermetic packaging solution is required. By using a 1.5 μm thick Sn layer as oxidation barrier for 5.0 μm thick Cu bond frames, the surface does not require pre-cleaning or use of any flux agent prior to, or during Cu-Sn bonding. With a tailored temperature and pressure bonding profile, the amount of Sn squeeze-out is reduced. Both for Cu-Sn bonds performed with new and aged electroplated films the measured shear strength is above 30 MPa. Further temperature cycling of bonded dies does not result in any reduction in bonding yield or shear strength.