Journal of Alloys and Compounds 509 (2011) 7238–7246 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Structural and elastic properties of eutectic Sn–Cu lead-free solder alloy containing small amount of Ag and In A.A. El-Daly a,∗ , Farid El-Tantawy b , A.E. Hammad a , M.S. Gaafar c,1 , E.H. El-Mossalamy d , A.A. Al-Ghamdi e a Physics Department, Faculty of Science, Zagazig University, Zagazig, Egypt b Department of Physics, Faculty of Science, Suez Canal University, Ismailia, Egypt c Ultrasonic Laboratory, National Institute for Standards, Tersa Street, P.O. Box 136, El-Haram, El-Giza 12211, Egypt d Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, P.O. Box 80203, Jeddah 21569, Saudi Arabia e Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah, P.O. 80203, Jeddah 21569, Saudi Arabia article info Article history: Received 28 September 2010 Received in revised form 3 January 2011 Accepted 5 January 2011 Available online 14 January 2011 PACS: 62.20.Fe 61.82.Bg 61.66.Dk 43.35.Ae 62.20.Dc Keywords: Lead-free solder Sn–Cu alloys Microstructure Elastic properties Mechanical properties Pulse-echo technique abstract Sn–Cu alloys have been considered as a candidate for high temperature lead-free microelectronic sol- ders. In the present study, the change in microstructure, attenuation and elastic behavior associated with alloying of Ag and/or In into the eutectic Sn–Cu solder alloy system have been evaluated. The study involved measurements of longitudinal and shear wave velocities, attenuation, hardness, bulk and shear moduli, Young’s and Poisson’s ratio. The results of attenuation show that a clear attenuating effect in the ternary Sn–Cu–Ag and Sn–Cu–In alloys is realized, whereas the quaternary Sn–Cu–Ag–In solder displays an obscure attenuating effect. The obscure effect is mainly attributed to the competition for In between Sn and Ag, which results in weak interface formed between intermetallic compounds (IMCs) and -Sn matrix. Likewise, Poisson’s ratio results indicate that its value decreases with increasing the elastic mod- uli and ultrasonic velocities of Ag and In-containing alloys. The analyzed enhanced ductility of Sn–0.7Cu and Sn–0.7Cu–2In alloys and brittleness of Sn–0.7Cu–2Ag and Sn–0.7Cu–2Ag–2In alloys were rational- ized on the basis of Poisson’s ratio and the quotient of shear modulus to bulk modulus (Pugh’s ratio). Microstructural analysis revealed that the origin of change in the elastic properties of the ternary and quaternary alloys is ascribed to smaller -Sn dendrite grain dimensions and formation of new IMCs in the ternary and quaternary alloys. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Following the miniaturization of contemporary solder joints, the fraction of IMCs to the total volume of solder is increasing, and hence the elastic properties of IMCs formed during solder- ing reaction become crucial to the reliability of solder joints [1]. For Sn-based soldering system, it has been shown that Sn–0.7Cu alloy is considered as the most promising candidate lead-free sol- der materials to replace eutectic Sn–Pb solder for wave, dip, and iron soldering processes. It is environmentally benign, inexpen- sive and has good electrical conductivity. Sn–0.7Cu solder has a melting point equal to 227 ◦ C. Meanwhile, the primary interest is the lower cost compared with the other candidate lead-free sol- der alloys [2,3]. The presence of Cu in Sn-based materials leads to ∗ Corresponding author. Tel.: +20 552325030; fax: +20 552308213. E-mail address: dreldaly99@yahoo.com (A.A. El-Daly). 1 Current address: Physics Department, Faculty of Science, Al-Majmaah Univer- sity, Al-Zulfi, Saudi Arabia. an improvement in resistance to thermal cycle fatigue and wet- ting properties due to the formation of Cu 3 Sn and Cu 6 Sn 5 IMCs. It also plays an important role in decreasing the rate of dissolu- tion of Cu from the board [2,4]. However, its main disadvantage of high melting temperature, insufficient oxidation resistance charac- teristic and tin whiskers caused by the formation of Sn-rich phase prevents its wide practical application in microelectronic packag- ing industry, especially in the wave soldering applications, which are considerably forced nowadays [5–7]. Because of the technological interest, investigations of new Sn–Cu-based solder materials for electronic packaging products have never been stopped. Great achievement has been focused on developing the overall wetting and soldering properties of Sn–Cu solder and progress has been made by adding different alloying elements, such as Ag, In, Zn, and Ni [3,8–10]. The presence of the second phase has been shown to trigger the microstructural mech- anism that enhances the reliability of the solder joints. Recently, Wang and Shen [9] revealed that a small amount of Ni addition to the Sn–Cu solder could effectively improve the solder prop- erties, such as the mechanical strength and wettability. The Ni 0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.01.062