Influence of top-side metal layers on the performance of gold, silver, and copper wire bonds on aluminum pads

This study analyzed the reliability of gold (Au), silver (Ag), and copper (Cu) wire bonds on aluminum (Al) pads coated with a multilayer Top-side metal (TSM) structure. The TSM structure was created by sequentially plating titanium (Ti), nickel-vanadium (NiV), and Ag on an Al pad, with Ag used as the surface contact layer for connection. The corrosion resistance of TSM -coated Al pads with Au, Ag, and Cu wire bonds was then examined through humidity testing, which involved pretreatment under moisture sensitivity level 3, and thermal aging at 200 degrees C for 5 h. The bonding interfaces of the pads were then investigated through scanning acoustic tomography, which indicated that all pads exhibited no wire bonding delamination. Testing results obtained for wire pull strength and ball shear strength indicated that the process capability index (CPK) values of the Cu wire bonds increased after thermal aging, which indicated the high thermal stability of these bonds; however, the CPK values of the Au and Ag bonds decreased marginally after thermal aging. Further analysis indicated that Au, Ag, and Cu formed solid solutions with the Ag layer of the TSM structure, and no intermetallic compound was generated; thus, the Au, Ag, and Cu wire bonds exhibited high stability and reliability even under high temperature and humidity. This study aids efforts to improve chip reliability and service life through appropriate wire material selection and TSM structure design.