Effect of nano Al 2 O 3 additions on the microstructure, hardness and shear strength of eutectic Sn–9Zn solder on Au/Ni metallized Cu pads Tama Fouzder a , Asit Kumar Gain a , Y.C. Chan a, * , A. Sharif b , Winco K.C. Yung c a Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong b Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh c Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong article info Article history: Received 7 March 2010 Received in revised form 20 June 2010 Available online 27 July 2010 abstract Nano-sized, nonreacting, noncoarsening Al 2 O 3 particles have been incorporated into eutectic Sn–Zn sol- der alloys to investigate the microstructure, hardness and shear strength on Au/Ni metallized Cu pads ball grid array substrate (BGA). In the plain Sn–Zn solder joint and solder joints containing Al 2 O 3 nano-parti- cles, a scallop-shaped AuZn 3 intermetallic compound layer was found at the interfaces. In the solder joints containing Al 2 O 3 nano-particles, a fine acicular-shaped Zn-rich phase and Al 2 O 3 nano-particles were found to be homogeneously distributed in the b-Sn matrix. The shear strengths and hardness of sol- der joints containing higher percentage of Al 2 O 3 nano-particles exhibited consistently higher value than those of plain solder joint and solder joints containing lower percentage of Al 2 O 3 nano-particles due to control the fine microstructure as well as homogeneous distribution of Al 2 O 3 nano-particles acting as a second phase dispersion strengthening mechanism. The fracture surfaces of plain Sn–Zn solder joints exhibited a brittle fracture mode with smooth surfaces while Sn–Zn solder joints containing Al 2 O 3 nano-particles showed a typical ductile failure with very rough dimpled surfaces. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Owing to the realization of the harmful influence of lead and lead containing alloys on the environment and human health, increasing efforts have been conducted to search for suitable lead-free solders as replacement for the conventional Sn–Pb eutec- tic alloy [1–4]. Therefore, many research groups are concerned with the development of new lead-free solders and their compos- ites. A further factor is the continual miniaturization of integrated circuits and the quest for better performance and reliability from interconnection joints [5]. In general, new lead-free solders must meet an expected level of mechanical and electrical performance, have a suitable melting temperature, be corrosion resistant, relatively harmless to health and the environment and have a low material cost [6–8]. Reliability of a solder joint plays an important role in determining the lifetime of electronic devices. It is mainly dependent on matching the coeffi- cient of thermal expansion, having a high elastic modulus, yield strength and shear strength together with resistance to fatigue and creep [9–11]. Studies have shown that a potentially viable and economically affordable approach to improve the mechanical prop- erties of a solder is to add appropriate second phase particles, of ceramic, metallic or intermetallic, to a solder matrix so as to form a composite. The formation, presence and growth of the second phase have been proposed as a potential mechanism controlling sol- derability, a fine microstructure and improved reliability of solder joints [12]. Lin et al. studied the influence of reinforcing TiO 2 and Cu nano-particles on microstructural development and hardness of eutectic Sn–Pb solders, and the measured microhardness re- vealed that the addition of TiO 2 and Cu nano-particles enhanced the overall strength of the eutectic solder [13,14]. Mavoori and Jin [15] used 5 nm TiO 2 and 10 nm Al 2 O 3 particles as reinforcement for a conventional 63Sn–37Pb solder and reported significant enhancement in creep resistance and other mechanical properties. Mohan et al. [16] prepared Sn–Pb composite solders by the addition of single wall carbon nano-tubes (SWCNT) as a reinforcing agent and their mechanical properties such as hardness, yield strength and ultimate tensile strength were shown to be superior to the unrein- forced solder, while the melting point was not appreciably altered. Shen et al. [17] successfully prepared a ZrO 2 reinforced composite solder by mechanically dispersing ZrO 2 particles into a eutectic Sn–3.5Ag solder paste and the composite solders had an improved microhardness and a refined microstructure. Li and Gupta [18] re- ported that nano Al 2 O 3 reinforced 91.4Sn–4In–4.1Ag–0.5Cu alloy significantly improved the hardness, yield strength and ultimate tensile strength. However, the result of a literature search revealed that no stud- ies have been reported so far to develop lead-free Sn–Zn solder joints containing Al 2 O 3 nano-particles on Au/Ni metallized Cu 0026-2714/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2010.06.013 * Corresponding author. Tel.: +852 2788 7130; fax: +852 2788 7579. E-mail address: eeycchan@cityu.edu.hk (Y.C. Chan). Microelectronics Reliability 50 (2010) 2051–2058 Contents lists available at ScienceDirect Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel