Artifact-Free Microstructures in the Interfacial Reaction between Eutectic In-48Sn and Cu Using Ion Milling

Abstract

Eutectic In-48Sn was considered a promising candidate for low-temperature solder due to its low melting point and excellent mechanical properties. Both Cu2(In,Sn) and Cu(In,Sn)2 formation were observed at the In-48Sn/Cu interface after 160 °C soldering. However, traditional mechanical polishing produces many defects at the In-48Sn/Cu interface, which may affect the accuracy of interfacial reaction investigations. In this study, cryogenic broad Ar+ beam ion milling was used to investigate the interfacial reaction between In-48Sn and Cu during soldering. The phase Cu6(Sn,In)5 was confirmed as the only intermetallic compound formed during 150 °C soldering, while Cu(In,Sn)2 formation was proven to be caused by room-temperature aging after soldering. Both the Cu6(Sn,In)5 and Cu(In,Sn)2 phases were confirmed by EPMA quantitative analysis and TEM selected area electron diffraction. The microstructure evolution and growth mechanism of Cu6(Sn,In)5 during soldering were proposed. In addition, the Young’s modulus and hardness of Cu6(Sn,In)5 were determined to be 119.04 ± 3.94 GPa and 6.28 ± 0.13 GPa, respectively, suggesting that the doping of In in Cu6(Sn,In)5 has almost no effect on Young’s modulus and hardness.

Identification and Evolution of Intermetallic Compounds Formed at the Interface between In-48Sn and Cu during Liquid Soldering Reactions

“…Although the Cu9(In,Sn)4 phase was not discovered in the ternary phase diagram of Liu et al [25] and Lin et al [26], it was universally observed in the Cu/In thin films [12,13] when the soldering temperature increased above 200 °C. Thus, during liquid-state aging, the Cu6(In,Sn)5 phase first nucleated and grew at the interface of the liquid solder/Cu sub- Although the Cu 9 (In,Sn) 4 phase was not discovered in the ternary phase diagram of Liu et al [25] and Lin et al [26], it was universally observed in the Cu/In thin films [12,13] when the soldering temperature increased above 200 • C. Thus, during liquid-state aging, the Cu 6 (In,Sn) 5 phase first nucleated and grew at the interface of the liquid solder/Cu substrate [32]. It is known that the melting point of the Cu 6 (In,Sn) 5 phase is higher than the soldering temperature (250 • C).…”