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

Eutectic In-48Sn was considered a promising candidate for low-temperature solder due to its low melting point and excellent mechanical properties. Both Cu-2(In,Sn) and Cu(In,Sn)(2) formation were observed at the In-48Sn/Cu interface after 160 degrees 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 Cu-6(Sn,In)(5) was confirmed as the only intermetallic compound formed during 150 degrees C soldering, while Cu(In,Sn)(2) formation was proven to be caused by room-temperature aging after soldering. Both the Cu-6(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 Cu-6(Sn,In)(5) during soldering were proposed. In addition, the Young's modulus and hardness of Cu-6(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 Cu-6(Sn,In)(5) has almost no effect on Young's modulus and hardness.

Automated summary

In this study, cryogenic broad Ar+ beam ion milling was used to investigate the interfacial reaction between In-48Sn and Cu during soldering. Cu-6(Sn,In)5 and Cu(In,Sn)2 were confirmed as the main intermetallic compounds formed. The microstructure evolution and growth mechanism of Cu-6(Sn,In)5 during soldering were proposed. Additionally, the Young's modulus and hardness of Cu-6(Sn,In)5 were determined.