A Sn—Ag bonding and a method thereof are revealed. By means of a bonding layer formed by tin and silver between wafers, the stress released by diffusion and bonding between tin(Sn) and silver(Ag) is larger than the stress released by diffusion and bonding of conventional gold-silver bonding. Moreover, a Sn—Ag bonding method of the present invention forms Sn—Ag bonding at low temperature and releases more stress so as to reduce thermal stress generated during wafer bonding effectively. And after wafer bonding, the high temperature processes can be performed.