Study on the interfacial reactions between In-Ag alloys and electroless nickel-immersion gold metallization

Purpose This paper aims to investigate the interfacial reaction mechanisms and microstructural evolution between In-Ag thermal interface materials (TIMs) and electroless nickel-immersion gold (ENIG) surface finishes during thermocompression bonding and subsequent solid-state aging. Design/methodology/approach Pure In, In-3Ag and In-10Ag foils were bonded to Cu substrates with electroplated Ni/Au or ENIG coatings. Cross-sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to analyze interfacial phases. The effects of Au layer thickness, Ag alloying and long-term annealing at 120°C up to 1000 h were systematically examined. Findings Electroplated Ni/Au finishes with a 0.3-µm-thick Au layers promoted the formation of brittle (Au,Ni)In2 intermetallic compounds (IMCs), whereas ENIG with a 0.05-µm-thick Au layer suppressed AuIn2 formation and favored Ni28In72 growth. Ag addition to In TIMs generated Ag-based IMCs (AgIn2, Ag2In), which partially transformed into Ag3In during aging, with Cu and Ni atoms substituting Ag lattice sites. The combined use of ENIG finishes and Ag alloying effectively reduced brittle AuIn2IMC formation and improved interfacial stability. Originality/value This work provides insights into interfacial phase evolution in In-Ag/ENIG systems and identifies practical strategies – Au layer thickness control and Ag alloying – for enhancing the reliability of metallic TIMs. The findings demonstrate the potential of ENIG/In-Ag joints for next-generation high-performance electronic packaging.