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NTRODUCTION

SOLDERING is very important for the electronics industry. Step soldering refers to the circumstance that soldering is applied more than once in different stages during manufacturing processes. Solders with different melting points are necessary for step soldering, and SnSb alloys have been used as high melting point solders.[1–4] The Ag is frequently used in surface finishes in electronic products. Moreover, Sn-Sb-Ag(-x) alloys are being developed as possible high melting point solders used with Pb-free solders.[2–4] Knowledge of phase equilibria of the Sn-Sb-Ag ternary system is valuable for applications of Sn-Sb and Sn-Sb-Ag(-x) solders. There is very little phase equilibria information of the Sn-Sb-Ag ternary system.[1,5,6] Masson and Kirkpatrick[5] experimentally determined the Sn-Sb-Ag liquidus projection. Oh et al.[6] calculated the liquidus projection based on limited literature results. Chen et al.[1] determined the (Sn-5 wt pct Sb)-Ag isoplethal section by differential thermal analysis (DTA). All of the previous studies did not report the existence of any ternary compounds. Both Masson and Kirkpatrick[5] and Oh et al.[6] reported the formation of two continuous solid solutions, i.e., the e phase between e-Ag3Sn and e-Ag3Sb, and the f phase between f-Ag17Sb3 and f-Ag5Sn. The major difference between the two liquidus projections is that there are three invariant reactions in that SINN-WEN CHEN, Professor, and PO-YIN CHEN, CHEN-NAN CHIU, and YU-CHIH HUANG, Graduate Students, are with the Department of Chemical Engineering, National Tsing Hua University, Hsin-chu 300, Taiwan, R.O.C. Contact e-mail: [email protected]. edu.tw CHAO-HONG WANG, formerly Graduate Student, Department of Chemical Engineering, National Tsing Hua University, is Assistant Professor, Department of Chemical Engineering, National Chung Cheng University, Chia-yi 621, Taiwan, R.O.C. Manuscript submitted March 24, 2008. Article published online October 30, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A

proposed by Oh et al.,[6] while there are only two in that offered by Masson and Kirkpatrick.[5] This result is caused primarily by the discrepancy regarding the existence of the Sn3Sb2 phase.[5–8] A recent study[9] has confirmed the existence of the Sn3Sb2 phase, and the compositional differences between the b-SnSb and the Sn3Sb2 phases are small. In addition, the compositional regions of primary solidification phases in the two liquidus projections[5,6] are different, and their reported types of invariant reactions are not consistent, either. This study experimentally re-examines the liquidus projection and investigates the 250 °C isothermal section of the Sn-Sb-Ag system, because there is no isothermal section information available and the proposed liquidus projections[5,6] are not consistent. Ternary Sn-Sb-Ag ternary alloys were prepared, and their equilibrium phases at 250 °C and the primary solidification phases were determined. The phase transformation temperatures of Sn-Sb-Ag alloys were determined by using DTA. The ternary phase diagrams