Study on the time dependence of bond strength in room temperature bonding

The time dependence of bond strength between Au wire and Au film produced by the room temperature bonding was investigated. The bonding tests were carried out under an ultra high vacuum condition (1.0×10-8 Pa). The bonding surfaces of the specimens were cleaned by Ar+ ion sputter system (Ar+ irradiation: 2 kV×30 min) before bonding. The bonding pressure σB was from 5 to 20 MPa and the bonding time tB was 1 min. The peel strength increased with time after bonding. It was found that the bonded area did not increase with time by SEM observation. Therefore, it was suggested that the stress situation on the bond interface could be changed with time. Bonding process was also analyzed using a two-dimensional numerical model. Calculated results suggested that the stress distribution on the bond-interface was changed with time even at room temperature. It follows that the time dependence of the bond strength is caused by the relaxation of residual stress on the bond-interface.