Nanoindentation study on micromechanical behaviors of Au-Ni-Sn intermetallic layers in Au-20Sn/Ni solder joints

Micromechanical behavior of interfacial intermetallics is closely related to the reliability of micro solder joints. Nanoindentation was employed to investigate the micromechanical behavior of the (Au,Ni)Sn and (Ni,Au)3Sn2 intermetallic layers in Au-20Sn/Ni solder joints. The indentation size effect (ISE) of both intermetallics was quantitatively analyzed. Based on the ISE parameters, the average Burger's vectors of (Au,Ni)Sn and (Ni,Au)3Sn2 were determined to be 2.38×10−10 nm and 4.09×10−10 nm, respectively. The first pop-in event is associated with the elastic-plastic deformation transition and shows an obvious rate-dependent: both the first pop-in load and the maximum shear stress increased with the loading rate. The apparent activation volumes of pop-in were calculated to be 0.11b3 and 0.02b3 for (Au,Ni)Sn and (Ni,Au)3Sn2, respectively. The apparent activation volume determined from the stress relaxation increased with the loading rate because of the preferential activation of preexisting dislocations and the longer average distance that dislocations have to travel under high loading rate. From nanoindentation creep tests, the average stress exponent of (Au,Ni)Sn and (Ni,Au)3Sn2 were determined to be 0.86 and 1.42, respectively.