Mechanical Deformation Behavior of Sn-Ag-Cu Solders with Minor Addition of 0.05 wt.% Ni A.E. HAMMAD 1,2,3 and A.M. EL-TAHER 1 1.—Physics Department, Faculty of Science, Zagazig University, Zagazig, Egypt. 2.—e-mail: a_hammad_82@yahoo.com. 3.—e-mail: a_hammad@zu.edu.eg The aim of the present work is to develop a comparative evaluation of the microstructural and mechanical deformation behavior of Sn-Ag-Cu (SAC) solders with the minor addition of 0.05 wt.% Ni. Test results showed that, by adding 0.05Ni element into SAC solders, generated mainly small rod-shaped (Cu,Ni) 6 Sn 5 intermetallic compounds (IMCs) inside the b-Sn phase. Moreover, increasing the Ag content and adding Ni could result in the change of the shape and size of the IMC precipitate. Hence, a significant improvement is observed in the mechanical properties of SAC solders with increasing Ag content and Ni addition. On the other hand, the tensile results of Ni-doped SAC solders showed that both the yield stress and ultimate tensile strengths decrease with increasing temperature and with decreasing strain rate. This behavior was attributed to the competing effects of work hardening and dynamic recovery processes. The Sn-2.0Ag-0.5Cu-0.05Ni solder displayed the highest mechanical properties due to the formation of hard (Cu,Ni) 6 Sn 5 IMCs. Based on the obtained stress exponents and activation energies, it is suggested that the dominant deformation mechanism in SAC (205)-, SAC (0505)- and SAC (0505)-0.05Ni solders is pipe diffusion, and lattice self-diffusion in SAC (205)-0.05Ni solder. In view of these results, the Sn-2.0Ag-0.5Cu-0.05Ni alloy is a more reliable solder alloy with improved properties compared with other solder alloys tested in the present work. Key words: Lead-free solders, Sn-Ag-Cu alloy, microstructure, mechanical properties INTRODUCTION In recent years, the increasing demand for por- table electronics has led to the shrinking in size of electronic components and solder joint dimensions. 1 Furthermore, driven by government legislation, the electronics industry has advanced to lead-free sol- ders due to environmental and health concerns emanating from the use of Pb-based solders. 2–5 To date, several types of lead-free solders have been developed such as Sn-Ag, Sn-Cu, Sn-Bi and Sn-Ag- Cu alloys. 6,7 Sn-Ag-Cu (SAC) alloy has good mechanical properties and wettability, making it the most widely used lead-free solder. 8,9 However, according to the literature, 10,11 SAC solder alloys with high Ag content are more brittle in nature than Sn-Pb solders due to the intermetallic compounds (IMC) Cu 6 Sn 5 and Cu 3 Sn formed at the SAC solder/ Cu interface; Ag 3 Sn IMC formed at the SAC solder/ Ag interface. In addition, the high Ag content increases the relative cost for the products. Thus, it is almost mandatory to shift to low-Ag-content SAC alloys. Reducing the Ag content can improve the reliability of SAC solder joints in dynamic environ- ments. 12 It has been proved that, to further enhance the properties of SAC solder alloys, alloying ele- ments such as Bi, Ni, P and Ce have been added to these alloys. 13–15 Among them, the Ni element is usually an effective additive because adding the Ni element cannot improve the wettability and anti- oxidization of the Sn-3.0Ag-0.5Cu (SAC305) solder alloy, but it can depress the interfacial IMC growth due to the high temperature aging and it then (Received March 24, 2014; accepted July 5, 2014; published online July 26, 2014) Journal of ELECTRONIC MATERIALS, Vol. 43, No. 11, 2014 DOI: 10.1007/s11664-014-3323-y Ó 2014 The Minerals, Metals & Materials Society 4146