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Gold-Tin eutectic bonding was studied to get hermetic packaging at wafer level. Scanning Electron Microscopy cross section images showed the sealing joint morphology at different stages including before bonding and after bonding with or without thermal treatment at 400°C. Electron Dispersive X-ray Spectrometry enabled to get chemical information of observed phases. The Ni layer which was used as diffusion barrier reacts with the solder to form a nearly void free joint. Shear strength was in the range of 70 MPa before and after thermal treatment at 400°C. Hermeticity was assessed by measurement of membrane deflection caused by He overpressure. The air standard leak rate was lower than 2.6×10-11 atm.cm3/s. After Through Silicon Via (TSV) process, low contact resistances in the range of 10 mΩ were obtained for the joint as for the TSV.