Influence of Zn addition on the microstructure, melt properties and creep behavior of low Ag-content Sn–Ag–Cu lead-free solders A.A. El-Daly a,n , A.E. Hammad a , G.S. Al-Ganainy b , M. Ragab a a Physics Department, Faculty of Science, Zagazig University, Zagazig, Egypt b Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt article info Article history: Received 2 March 2014 Received in revised form 14 April 2014 Accepted 17 April 2014 Available online 29 April 2014 Keywords: Lead-free solder Microstructure Thermal properties Creep properties abstract The effects of Zn addition on the microstructure, thermal behavior and tensile creep properties of Sn–1.0Ag–0.3Cu (SAC103) alloy were systematically investigated. Differential scanning calorimetry (DSC) reveals that the reductions of undercooling and pasty range are more significant for Zn-containing solders, although the solidus temperature remains the same or slightly changed. The creep life time of plain SAC103 alloy was remarkably enhanced two times with the addition of 3 wt% Zn. Moreover, significant improvement in creep resistance of 145% and 360% is realized with the addition of 2 wt% and 3wt% Zn into SAC(103) solder, respectively. The improvement of creep behavior is due to the microstructural change of Zn-containing solders, since the formation of new (Cu,Ag) 5 Zn 8 intermetallic compound (IMC) phase and fine fiber-like Ag 3 Sn precipitates at the surface of β-Sn matrix could provide more obstacles for dislocation pile-up, which enhanced the stress exponent values and improved the creep resistance and creep life time. These results show that the Garofalo model is suitable for describing the steady-state creep behavior of SAC(103) solders over the tested stress and temperature ranges. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Nowadays, Sn–Ag–Cu (SAC) solders have been regarded as the most promising solders that can replace Sn–Pb solders in the future [1,2]. Owing to their good temperature cycling reliability, the eutectic SAC alloy is widely used in surface mount technology (SMT), chip scale package (CSP) solder interconnects and ball grid array (BGA) applications [3]. The major challenge with the high Ag-content SAC solder alloys is the undesirable formation of large volume fraction of Ag 3 Sn IMCs [4]. These types of IMCs adversely affect the thermal fatigue life, mechanical properties and drop the lifetime of narrower solder joints in electronic circuits [5,6]. Therefore, efforts are ongoing to enhance the reliability of SAC solders. One approach to improve the mechanical performance is to reduce the Ag content in SAC alloys [7]. This means that the high cost of Ag associated with adopting lead-free soldering can also be suppressed. The second approach involves some metal additives, such as Ni, Zn, Fe, Co and rare-earth (RE) elements into SAC solders. Nevertheless, reducing the Ag content of SAC alloys, such as Sn–1.0Ag–0.5Cu (SAC105) alloy, gives rise to more primary β-Sn phase (large β-Sn grains). Hence, the elastic modulus and yield strength of SAC105 alloy are lower than that of high Ag-content SAC alloys. In the present study, the coupling effect of both minor alloying addition and reducing the amount of Ag phase have been proposed as an important strategy to improve the drop performance and reliability of eutectic SAC solder joints. Liu et al. [8] previously reported that the addition of small amounts of Mn or Ce to SAC105 solder greatly suppressed the coarsening of the bulk IMC particles, and significantly affected the grain-structure stability of bulk solder. These effects caused the bulk solder to exhibit stable mechanical properties during aging and thermal cycling. El-Daly et al. [7,9,10] studied the physical properties of SiC nanoparticles reinforced SAC105 solder. Mechanical property measurements indicated significant increase in mechanical strength, creep resistance and rupture time with reinforcing SiC nanoparticles. Moreover, the addition of SiC can decrease the undercooling and pasty range of SAC105 alloy. The authors suggested that the SiC particles could serve as additional nuclea- tion sites for the formation of primary β-Sn phase and Ag 3 Sn IMCs. The hard SiC particles and refined IMCs were found to obstruct the dislocation slipping and thus indicated a significant enhancement of the composite solder. Shnawah et al. [11,12] assessed the influence of different amounts of Fe on the drop reliability of SAC105 alloys. They found that the tensile strength, the elastic modulus and yield strength of solder joints decreased with increasing Fe content due to the formation of large FeSn 2 IMC Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2014.04.070 0921-5093/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. E-mail addresses: dreldaly11@yahoo.com, dreldaly@zu.edu.eg (A.A. El-Daly). Materials Science & Engineering A 608 (2014) 130–138