Experimental Determination of the Sn-Cu-Ni Phase Diagram for Pb-Free Solder Applications

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ON the 1st of July 2006, the European Union issued a directive prohibiting the use of Pb-containing solders in electronic devices and effectively banning such products from the market. Legislators in other jurisdictions, including Japan, China, and USA are considering regulations that would have a similar effect.[1–3] This is the reason that in recent decades, Pb-free solders have seen widespread use in the industry and there has been an increased stimulus for research. This research has included large multi-institution projects to develop thermodynamic databases for solder alloys; in the EU, this has been conducted within the COST project[4] and in the USA this has been led by NIST.[5] These efforts have resulted in the publication of an Atlas of Phase Diagrams for Lead-Free Soldering[6] and been the

HECTOR M. HENAO and JUAN P. SOLIS are with the Metallurgy and Materials Engineering Department, Technical University Federico Santa Marı´ a, Avenida Espan˜a, 2340000 Valparaı´ so, Chile. Contact e-mail: [email protected] CHINGSHUN CHU is with the School of Mechanical and Mining Engineering, The University of Queensland, St. Lucia, QLD 4072, Australia. KAZUHIRO NOGITA is with the Nihon Superior Centre for the Manufacture of Electronic Materials (NS CMEM), School of Mechanical and Mining Engineering, The University of Queensland, St. Lucia, QLD 4072, Australia and also with the School of Mechanical and Mining Engineering, The University of Queensland. Manuscript submitted October 25, 2017. Article published online December 20, 2018. 502—VOLUME 50B, FEBRUARY 2019

stimulus for commercial thermodynamic packages offering lead-free soldering databases including Thermo-Calc. (TCSLD2 database)[7] and MTDATA (MTSOLDERS database).[8] The projects mentioned above have been successful with many key ternary and higher order systems, notably Sn-Ag-Cu and Au-Ni-Sn, being characterized but, importantly, key systems remain that have not been fully studied which is an impediment to solder alloy design. An important example is the ternary Sn-Cu-Ni system, which while present in the Thermo-Calc. and MTDATA databases, relies on databases that have not been optimized for the full range of temperatures and compositions relevant to the soldering of electronic materials. A. Literature Review of the Associated Sn-Cu and Sn-Ni Binary Systems The Sn-Cu binary system is fundamental of various soldering alloys, such as Sn-Cu-Ag, Sn-Cu-Ni, and Sn-Ni-Cu-Ag and Sn-Ag-Co.[9,10] A summary of the reported phase equilibrium for the Sn-Cu system between liquid and Cu6Sn5 is displayed in Figure 1. Harding et al.,[11] Yu et al.,[12] Vuorinen et al.,[13] and Thermo-Calc[7] are all in reasonable agreement. On the other hand, the experimental results from Hanson et al.[14] only agree with results near to the eutectic temperature but show a large deviation as temperature is increased. In addition, the experimental result of

METALLURGICAL AND MATERIALS TRANSACTIONS B

Gourlay et al.[15] (draw in the Figure 1 for concentrations of Ni < 0.05 wt pct) indicated

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