Microstructure and shear behavior of Sn58Bi/Cu solder joint enhanced by SnAgCuBiNi bump

Abstract

In order to improve the mechanical behavior of the low-temperature [Formula: see text] (SnBi) lead-free solder joint, the [Formula: see text] (SACBN) solder ball with the diameter of 400 [Formula: see text]m was pre-soldered on Cu to obtain the SnBi/SACBN/Cu composite joint. The microstructure and shear behavior of the solder joints were investigated. Experimental results indicate that SnBi solder is well bonded on the SACBN bump due to the elemental diffusion and dissolution between the molten SnBi and solid SACBN bump during the soldering process. The addition of the SACBN bump shows a significant effect on the formation and growth of the [Formula: see text]-Sn grains in the SnBi bulk. Compared with the SnBi/Cu joint, the SnBi bulk in the composite joint shows enlarged [Formula: see text]-Sn dendritic grains. Meanwhile, the interfacial intermetallic compound (IMC) layer transforms from Cu6Sn5 into (Cu, Ni)6Sn5. Among these three solder joints, the shear strength of the SACBN/Cu joint is the highest, reaching 86.7 MPa. The shear strength of the SnBi/Cu solder joint is enhanced by the SACBN bump from 68.2 MPa to 75.2 MPa. Additionally, the addition of the SACBN bump shows a positive effect on suppressing the brittleness of the SnBi/Cu solder joint.