Investigating effect of aging time on microstructure and mechanical properties of lead-free Sn-Ag-Cu/Co composite solder on copper substrate

Composite solders are widely used in various electronic applications, especially in high-current-density environments. In this study, solder foils were created by adding ۰.۲ weight percent of cobalt to a low-silver lead-free, Sn-۰.۳Ag-۰.۷Cu (SAC۰۳۰۷) solder, using a casting alloying method followed by accumulative roll bonding. These solder foils were then subjected to aging heat treatment at ۷۵°C for various durations: ۵۰, ۱۵۰, ۴۵۰, and ۱۰۰۰ hours. After aging, the microstructural and mechanical properties of the solder and solder joint were carefully analyzed. To evaluate the mechanical properties, shear-tensile tests were conducted on the heat-treated solders. Additionally, the joint characteristics, including the microstructure of the solder matrix and the intermetallic compounds (IMCs) at the interface, were examined using scanning electron microscope (SEM). The findings revealed that adding cobalt led to an increase in the thickness of the intermetallic compounds after ۱۰۰۰ hours of aging. The IMC thickness increased by ⁓۴۰% for SAC۰۳۰۷ and ⁓۲۳% for SAC۰۳۰۷+۰.۲Co. As the aging time increased, the size and thickness of the intermetallic compounds also increased. The diffusion-controlled growth coefficient (k) for both SAC۰۳۰۷ and SAC۰۳۰۷+۰.۲Co at ۷۵°C was calculated to be ۳.۲۶۸×۱۰-۱۹ and ۳.۰۴۴×۱۰-۱۹ m²/s, respectively. Moreover, the morphology of the interfacial intermetallic compounds became flatter over time. The shear tensile test results showed that after ۱۰۰۰ hours of aging, the shear-strength of the joints decreased by ⁓۲۶% for SAC۰۳۰۷ and ⁓۴ % for SAC۰۳۰۷+۰.۲Co. These results highlighted the impact of cobalt addition and aging time on the micro structural and mechanical behavior of the solder.

کلیدواژه ها:

Lead-free Solder ، SAC۰۳۰۷ ، SAC۰۳۰۷+۰.۲Co ، Intermetallic Compound (IMC) ، Aging Treatment