CuAg/Ni(P) bi-layered structure prepared via electrochemical process as an effective diffusion barrier in Sn/Cu interface

Electrodeposited Sn on Cu underlayers has numerous industrial applications; however, the reliability of the Sn/Cu system is limited by interdiffusion, which leads to the formation of Kirkendall voids (KVs) at the interface, Sn whisker growth, and surface passivation. To overcome these limitations, this study investigates a CuAg/Ni(P) bi-layered diffusion barrier. A multilayered Sn/CuAg (thickness: 0.1–0.5 μm)/Ni(P)/Cu structure was prepared via electroless deposition and electrodeposition. Experimental results showed that the diffusion of Cu into Sn was effectively delayed in the Sn/CuAg/Ni(P)/Cu structure, resulting in the formation of intermetallic compounds (IMCs) with a thickness of approximately 1 μm, compared to the 5 μm in conventional Sn/Cu and Sn/Cu/Ni(P)/Cu structures. This suppression of IMC growth prevented KV formation, surface passivation, and whisker growth after aging at 150 ℃ for 7 days. The sin²ψ X-ray diffraction method confirmed that the tensile residual stress in the CuAg underlayer influences the stress relaxation rate and whisker growth in the Sn layer. Consequently, whisker density was reduced by approximately 85.9% and 75.9% compared to Sn/Cu and Sn/Cu/Ni(P)/Cu, respectively. The improved reliability of the Sn/CuAg/Ni(P)/Cu structure was attributed to the high tensile residual stress of CuAg and the formation of Ag 3 Sn at the triple junctions, both of which effectively hinder Cu diffusion into Sn. By focusing on the synergistic effect of the CuAg layer in modulating stress and diffusion kinetics, this study demonstrates improved thermal and electrical reliability. This approach reduces the risk of electrical short circuits and offers a viable solution for semiconductor packaging and electric vehicle applications. • CuAg/Ni(P) bilayer as an effective diffusion barrier at the Sn/Cu interface • CuAg underlayer suppresses IMC growth, Kirkendall voids, and Sn whiskers • Residual stress in CuAg and Ag 3 Sn formation at triple junctions hinder Cu diffusion • Reduced compressive stress in Sn suppresses whisker growth