Metallic wafer bonding is becoming a key enabling technology in microelectromechanical systems packaging and heterogeneous integration. We realize the bonding of silicon (Si) wafers coated with aluminum (Al) film with thin tin (Sn) film as the intermediate layer. The bonding pressure is 0.25 MPa. The bonding is achieved at temperatures as low as 280°C after a short bonding time of 3 min. The average bonding strength is 9.9 MPa. The minimum variation of bonding layer thickness is about 0.2 μm within a large area. A fracture surface study and a cross-section analysis are conducted and the bond mechanism is investigated. It is found that the fracture mainly occurs at Al/Sn interface during the shear test. Two bonding conditions are compared and the results show that applying bonding pressure before heating is important to achieve a uniform bonding layer.