Influence of nickel plating on the welding metallurgical mechanism, microstructure, and shear performance of C101/80Au20Sn/C101 solder joints

Abstract

Herein, electroplated and electroless plating processes were used to plate nickel (Ni) on the surface of C101 alloy, which is a low-carbon steel with a carbon content of approximately 0.1% and Fe primarily contributing to the rest of the content and which is commonly used in metal packaging, and electroplated Ni and electroless Ni C101/80Au20Sn/C101 solder joints were prepared. The welding metallurgical mechanisms, microstructures, and shear performances of the two types of solder joints were investigated through experimental observation, material characterization, shear testing, and finite-element analysis (FEA). The diffusion of Ni atoms within the two platings was evaluated using first-principles calculation. Results indicated that the atomic arrangement of the electroplated Ni layer was polycrystalline, whereas that of the electroless Ni layer was primarily amorphous. The orientation of Ni grains in the electroplated-Ni joints affected the growth of (Ni,Au)3Sn2 throughout the welding metallurgical process. The [111] orientation suppressed the growth of (Ni,Au)3Sn2, resulting in a discontinuous distribution of (Ni,Au)3Sn2 at the Ni/solder interface and considerable variations in the thickness of (Ni,Au)3Sn2. Amorphous Ni in the electroless Ni layer promoted the growth of (Ni,Au)3Sn2, resulting in a continuous (Ni,Au)3Sn2 layer having a relatively uniform thickness. The shear strength of the electroplated-Ni joints was considerably lower than that of the electroless-Ni joints. FEA results demonstrated that the locations of stress concentration in the electroplated- and electroless-Ni joints were at the (Ni,Au)3Sn2/solder interface and within the solder matrix, respectively. First-principles calculations showed that the diffusion performance of Ni atoms in the electroless Ni layer was considerably superior to that of Ni atoms in the electroplated Ni layer.