Quasi-transient liquid-phase bonding by eutectic reaction of Sn-plated Zn on Cu substrate for high-temperature die attachment

•We demonstrate a novel Pb-free die-attachment structure using Sn-plated Zn solder.•The bonded microstructure can be controlled by the process time.•The current bonding structure shows high bonding strength above 30MP.•The fracture of current bonding system occurred in the β-Sn matrix soldered layer.•The β-Sn phase in the fracture layer can be expected to reduce the brittleness of Zn. A novel die-attachment method is demonstrated through quasi-transient liquid-phase bonding using Sn-plated Zn sheets. The bonding temperature can be decreased to 250°C, which is ∼100°C lower than that for typical Zn–Sn high-temperature solders. The bonded interface consists of primary α-Zn and Sn–Zn eutectic phases, and the microstructure can be controlled according to the diffusion velocities of metals. The high die-shear strength exceeding 30MPa from the controlled microstructure is superior to typical Pb–5Sn solders strength around 20MPa.