Journal of Alloys and Compounds 505 (2010) 793–800 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Elastic properties and thermal behavior of Sn–Zn based lead-free solder alloys A.A. El-Daly ∗ , A.E. Hammad Physics Department, Faculty of Science, Zagazig University, Zagazig, Egypt article info Article history: Received 1 May 2010 Received in revised form 17 June 2010 Accepted 22 June 2010 Available online 1 July 2010 PACS: 62.20.Fe 61.82.Bg 61.66.Dk Keywords: Lead-free solder Sn–Zn alloy Microstructure Ultrasonic velocity Thermal properties Elastic properties abstract In this study, the effects of separate and dual additions of small amount of Cu, In and Ag on the microstructure and elastic properties as well as thermal behavior of the eutectic Sn–9Zn solder alloy were investigated. The elastic properties of the newly developed ternary and quaternary alloys have been investigated using sound wave velocity measurements at 4 MHz and T = 25 ◦ C. In particular, the hardness, the attenuation coefficient, the bulk and shear moduli, Young’s and Poisson’s ratio have been established for a range of alloy compositions. Results showed that alloying of Cu, In and Ag resulted in reducing fusion heat, solidus temperature and broadening the pasty range. Moreover, the presence of additional elements in Sn–Zn alloy system allows many complex intermetallic (IMC) phases to form. Both the hardness and reduced modulus increase as the Poisson’s ratio of the alloy decreases. The elastic properties can be correlated with the formation of the new IMC phases. By analyzing the quotient of shear modulus to bulk modulus, we can assume that the Sn–9Zn, Sn–9Zn–1.5Ag and Sn–9Zn–0.7Cu alloys are ductile solders whereas, the Sn–9Zn–1.5In and Sn–9Zn–1.5Ag–0.7Cu alloys are brittle in nature. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Increased health concerns over the toxicity of Pb in eutectic Sn–Pb solders have promoted the development of new lead-free solder alloys for electronic packaging [1]. Among the various lead- free solders, eutectic Sn–Zn solder alloy has so far received much attention and emerged as possible replacements for Sn–Pb solders because of its low melting point, excellent mechanical properties and low cost. However, its main disadvantage of poor oxidation resistance and wetting properties caused by the high activity and corrosion susceptibility of Zn prevents its wide practical applica- tions, especially in the critical part of electronic packaging products. Studies on the improvement of their overall wetting and mechani- cal properties have been widely investigated and progress has been made by adding different alloying elements, such as Ag, Cu, Bi, In, Ge and ZrO 2 nanoparticles [2–7]. Previous studies showed that the proper addition of Cu in Sn–Zn solders is effective way to avoid the formation of Au–Zn IMCs between the interface with Sn–Zn and Au and improve the wetting properties [2,3]. Recently, Wang et al. [4] reported that the addi- tion of Ge could effectively improve the anti-oxidation capability, electrical resistance, thermal expansion behavior and mechani- ∗ Corresponding author. Tel.: +20 552325030; fax: +20 552308213. E-mail address: dreldaly99@yahoo.com (A.A. El-Daly). cal strength of Sn 84 Zn 13 Bi 3 solder alloys. Our previous works [5,6] indicate that the addition of small amount of Bi could effec- tively improve the overall thermal and mechanical properties of the eutectic Sn–Zn solder alloy. On the other hand, the effects of separate and dual addition of small amount of Ag and Cu on the microstructure and mechanical properties of the eutectic Sn–9Zn solder alloy were also investigated. It was found that the proper additions of Ag and/or Cu in Sn–Zn solders are beneficial to encour- age the formation of new Ag–Zn, Cu–Zn and Cu–Sn IMCs. These IMCs play an important role in mechanical properties of the Sn–9Zn solder alloy. For example, single addition of Ag led to formation of AgZn, Ag 5 Zn 8 and -AgZn 3 IMCs, which results in significant increase in both ultimate tensile strength (UTS) and ductility, while, the flower shaped and rod shaped Cu 6 Sn 5 , -Cu 5 Zn 8 and -CuZn 5 IMCs produced by Cu alloying, results in small increase in UTS and ductility. Moreover, the dual addition of Ag and Cu suppressed the appearance of Ag–Zn IMCs due to the competition for Zn between Cu and Ag, which results in slight decrease in UTS and ductility of Sn–9Zn–1.5Ag solder. Efforts are still needed to further improve the overall mechanical properties of this type of alloys and to discover the determining factors that control the reliability of the Sn–9Zn solder. However, the elastic constants are one such material property that builds a foundation for a better understanding of various other properties such as mechanical, physical or even electronic. Lately, elastic constants have been correlated to properties like hardness, 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.06.142