%0 Journal Article
%T The Effects of Gallium Additions on Microstructures and Thermal and Mechanical Properties of Sn-9Zn Solder Alloys
%A Kang I. Chen
%A Shou C. Cheng
%A Chin H. Cheng
%A Sean Wu
%A Yeu-L. Jiang
%A Tsung-C. Cheng
%J Advances in Materials Science and Engineering
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/606814
%X The effects of gallium additions on microstructures and thermal and mechanical properties of the Sn-9Zn solder alloys are investigated in this study. The results show that the melting temperature of the alloys decreases with the increase in the Ga concentration, while the pasty ranges of the alloys are simultaneously enlarged. By adding a 0.25每0.5ˋwt.% Ga element, the Sn-matrix region is slightly increased and the Zn-rich phase becomes slightly coarser; however, the overall microstructure is still very similar to that of the Sn-9Zn alloy. It is found that, when the Ga concentration is less than 0.50ˋwt.%, the ultimate tensile strength and elongation are maintained at the same values. The addition of a 0.25每0.50ˋwt.% Ga to the Sn-9Zn alloy also leads to small cup and cone fracture surfaces which exhibit near-complete ductile fracturing. With the addition being increased to 0.75ˋwt.%, larger cup and cone fractures are observed. The 1.00ˋwt.% Ga alloy has lower strength and ductility due to the coarser and nonuniform microstructures. However, the fracture surfaces of the 1.00ˋwt.% Ga alloy show partial cleavage and a partially dimpled fracture. 1. Introduction Conventional Sn-Pb solders have commonly been used as the interconnection materials for soldering electronic components and devices. However, the use of Pb is restricted due to health and environmental issues. On the other hand, an alloy of Sn-Ag-Cu has been recognized as a potential lead-free solder even though Sn-Ag alloy systems have higher melting points (say, 216 to 221∼C), as compared to an eutectic Sn-Pb alloy [1, 2]. A high melting point is accompanied by high soldering temperatures, which may give rise to substrate instability problems. Recently, the Sn-9Zn alloy system has received increased interest since it features low cost, great mechanical properties, and a low eutectic temperature (198∼C), close to that of the Sn-Pb alloy [2, 3]. The eutectic structure of the Sn-9Zn alloy system consists of two phases: a body centered tetragonal Sn matrix phase and a secondary phase of hexagonal Zn containing less than 0.039ˋat.% Sn in solid solution [3, 4]. However, the tendency of oxidation and poor wetting ability of this alloy system limits its application [5, 6]. In recent years, to overcome the shortfalls in the Sn-9Zn alloy, some authors have tried to add a third element, such as In [7], Ga [8], Bi [9每13], Al [14每18], Ag [19每22], Cr [23], Cu [24], and Ce/La [25每27], to the Sn-Zn binary system to improve the melting temperature, wettability, oxidation resistance, corrosion, and mechanical
%U http://www.hindawi.com/journals/amse/2014/606814/