Surface evolution and bonding properties of electroplated Au/Sn/Au

Sandwich-structural multilayer films Au (4.0 mum)/Sn (2.0 mum)/Au (x mum) with x = 0.1, 0.3 have been electroplated on metalized silicon wafers. Interdiffusion of thin film Au in metallic Sn at room temperature is observed by light microscope on fresh electroplated multilayer surface. For the multilayer films with Au thickness x = 0.1, 0.3 mum, the Sn surface concentration on surface are roughly increased from 0 to 20(at)% after 1 and 4 days aging, respectively. The sandwich structure is bonded to wafers with x mum layer of electroplated Au. The bonding experiments are performed at 280degC, in atmosphere without flux. Scanning Electron Microscope (SEM) cross-section images show the formation of gold-tin alloy in bonded region and shear testing results indicate that the bonding strength reaches more than 11 MPa.