Interfacial reaction between Au–Sn solder and Au/Ni-metallized Kovar

Abstract

Gold-tin (Au–Sn) solder and Kovar alloy have been widely used in many fields such as mechanical engineering, atomic energy industry, aerospace facility, and electronic devices. Solder bonds strongly to the metallized substrate by forming intermetallic compounds (IMCs) at the interface. The IMC layer may adversely affect the reliability of the joints due to excessive growth and thermal fatigue during storage and service. Therefore, knowledge of the interfacial reactions between the Au–Sn solder and Au/Ni-metallized Kovar in microelectronic and optoelectronic packaging is essential. In this study, the microstructural evolution and interfacial reactions between the Au–Sn solder and Au/Ni-plated Kovar substrate were studied during aging at 180 and 250 °C for up to 1,000 h. The microstructure of the Au–Sn/Ni/Kovar joint was stable during aging at 180 °C. The solid-state interfacial reaction was much faster at 250 °C than at 180 °C. The joints aged at 250 °C fractured along the interface, thereby demonstrating brittle failure possibly because of the brittle IMC layer at the interface. The complete consumption of the thin Ni layer significantly weakened the joint interface during aging at 250 °C and clearly demonstrated the need for a thicker Ni layer in order to ensure the high temperature reliability of the Au–Sn/Ni/Kovar joint above 250 °C.