Study of the bonding force at the Au-Ag bump/TiW interface in wire bonding

Purpose This paper aims to systematically investigate the interfacial bonding behavior and high-temperature reliability of Au–Ag alloy bumps with different Au contents (20%, 40% and 100%) against a TiW adhesion layer, verifying their feasibility as cost-effective alternative materials for wire bonding applications. Design/methodology/approach Three types of Au–Ag alloy bumps were fabricated via electrodeposition on an Si/TiW(420 nm)/Au(80 nm) substrate. The morphology, microstructure, crystallographic characteristics and strain distribution were systematically characterized using confocal laser scanning microscopy (CLSM), focused ion beam (FIB), transmission Kikuchi diffraction (TKD) and geometric phase analysis (GPA) via transmission electron microscopy. Interfacial bonding strength was evaluated by shear tests, and long-term reliability was assessed through 1,000-h high-temperature aging. Findings The 20% Au sample demonstrated the highest shear strength, while the 40% Au and pure Au samples showed comparable strength. CLSM measurements indicated a bump height of approximately 9 µm. FIB and TKD analyses revealed a decreasing grain size with increasing Ag content, a predominant (111) orientation in the Au–Ag bumps, a (101) orientation in the TiW layer and a reduction in lattice mismatch with higher Ag content. GPA results identified the most significant lattice distortion and local stress concentration in the 40% Au sample. All samples maintained high interfacial bonding strength after 1,000 h of aging. Originality/value This work systematically elucidates the composition–microstructure–property relationships at the Au–Ag/TiW interface for the first time. The multiscale characterization clarifies the competing effects of lattice mismatch and micro-strain on the interfacial bonding strength, providing theoretical foundation and practical guidance for implementing Au–Ag alloys in cost-effective, highly reliable interconnects.