Effects of diamond nanoparticles reinforcement into lead-free Sn–3.0Ag–0.5Cu solder pastes on microstructure and mechanical properties after reflow soldering process Srivalli Chellvarajoo ⇑ , M.Z. Abdullah, C.Y. Khor Advanced Packaging and SMT Unit, School of Mechanical Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia article info Article history: Received 12 January 2015 Revised 18 May 2015 Accepted 29 May 2015 Keywords: Diamond nanoparticle Lead-free Sn–3.0Ag–0.5Cu Mechanical property Nanoindentation Reflow soldering process abstract This paper presents the effects of diamond nanoparticles reinforcement on lead-free SAC 305 solder paste after the reflow soldering process. Different diamond nanoparticles amounts (0.5, 1.5, and 2.5 wt.%) were mechanically mixed with SAC 305 to produce a new form of nanocomposite solder paste. The character- istics of the nanocomposite solder, such as melting point, morphology and thickness of the intermetallic compound (IMC), agglomeration of diamond nanoparticles, and hardness, were investigated. The exper- imental results revealed that the addition of diamond nanoparticles slightly decreases the melting point but significantly reduces the IMC thickness. The morphologies of the nano-reinforced solder paste showed the agglomeration of nanoparticles on the surface of the solder paste with increasing diamond nanoparticles percentage. The addition of 0.5 wt.% diamond nanoparticles was well embedded in the sol- der matrix after the reflow soldering process. The hardness of the nano-reinforced solder paste was eval- uated via nanoindentation technique. The addition of 0.5 wt.% diamond nanoparticles improved the hardness of SAC 305 by 77.5%. Increasing the nanoparticles amount by 1.5 and 2.5 wt.% in SAC 305 enhanced the hardness of SAC 305–0.5 wt.% by 6.3% and 17.8%, respectively. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Solder pastes that consist of tin (Sn), silver (Ag), and copper (Cu) elements (SAC) alloy compositions were recommended as a lead- ing current option for surface mount assemblies in the electronic packaging industries. SAC 305 was widely chosen as a dominant soldering material among the tin-based solders because of its cost and performance effectiveness [1,2]. Unfortunately, challenges were encountered when Sn-based solders containing binary or ternary alloys were used. Nowadays, researchers recognized the use of SAC 305 in electronic assemblies also attributed to fragility, void formation, wetting issues, process temperature issues, and fatigue issues, which were predominant failure mechanisms for solder joint reliability [3,4]. Solder joint failure could lead to elec- tronic product malfunction. Thus, researchers have been continu- ing investigations to further develop the efficiency of solder paste. Researchers reinforced various dopants such as Mn, Ti, Y, Bi, Ce, Ni, Co, Pt, Fe, Zn, Ni, Sb, Al and rare earth Yb into the SAC solder paste to enhance its interconnection reliability [5–8]. The addition of these alloying elements resulted in discernible changes in the state-of-the-art Pb-free composite solder paste, especially on the interfacial intermetallic compounds (IMCs) and solidification pro- cess [4]. Laurila et al. [9] classified the alloying elements to two dif- ferent categories based on the reactivity toward IMCs via thermodynamic–kinetic method. The elements in first group were Ni, Au, Sb, In, Co, Pt, Pd, and Zn which involved in the interfacial reaction mechanism. However, Bi, Ag, Fe, Al, P, rare-earth elements, Ti, and S were dropped in second group which act as ‘catalyst’ in the IMC formation scenario and do not involved themselves in the reaction process. Xia et al. [10] found that the addition of Ag, Bi and rare earth elements to pure Sn reduced the growth rate of IMCs and increased the tensile strength in the range of 40–50% respectively. Micro-sized particles, such as 0.2 wt.% of Zn, were added into Sn-based solder to reduce the void formation on the Cu 3 Sn layer between the Cu 6 Sn 5 /Cu substrate [4]. The addition of alloying elements should not exceed the limits to avoid reduction in reliability. There was failure in drop test performance if the rein- forcement of Ni and Co elements into SAC by more than 0.1 wt.% [9]. The overall consideration on IMCs, strength and failure of sol- der paste were very important for reliability issues. The homoge- neous particle size reinforcement as SAC alloy size into Sn-based solder required more energy and space in the reaction of IMC layer http://dx.doi.org/10.1016/j.matdes.2015.05.065 0264-1275/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: csrivalli_08@yahoo.com, sc12_mec040@student.usm.my (S. Chellvarajoo). Materials & Design 82 (2015) 206–215 Contents lists available at ScienceDirect Materials & Design journal homepage: www.elsevier.com/locate/matdes