Enhancement of Cu pillar bumps by electroless Ni plating

Cu pillar bumps were mechanically enhanced using electroless Ni plating for fine-pitch electronic packaging applications. The interfacial reaction and mechanical properties of the Ni-plated Cu pillar bump joints were evaluated. After reflowing, the plated Ni layer dissolved into the Sn-Ag solder caps. The Ni was incorporated into the interfacial reactions, forming a (Cu,Ni) 6 Sn 5 intermetallic compound on the Cu pillar bumps. Adding Ni to the Cu pillar bumps significantly affected the mechanical properties of the joint and increased the bump shear strength of the solder cap.