Faculty Publications
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Item Effect of cooling rate on joint shear strength of Sn-9Zn lead-free solder alloy reflowed on copper substrate(ASTM International, 2017) Tikale, S.; Sona, M.; Prabhu, K.Reliability of the solder joint largely depends on mechanical strength, fatigue resistance, coefficient of thermal expansion, and intermetallic compound formation. Cooling rate significantly affects the physical properties of an alloy and influences the mechanical behavior of solder joints. In the present study, Sn-9Zn lead-free solder alloy was solidified on Cu substrate under furnace cooling (0.04°C/s), air cooling (0.16°C/s), and water cooling (94°C/s) conditions. The effect of varying cooling rates on the intermetallic compound (IMC) formation at the interface and the resulting joint shear strength was studied. A microstructure study revealed the presence of Cu5Zn8 and CuZn5 intermetallic compounds at the solder-substrate interface. The IMC layer thickness at the interface increased with a decrease in the cooling rate. The joint shear strength increased with an increase in the cooling rate. The air and furnace cooling resulted in the formation of a thick IMC layer. The IMC obtained from the furnace cooling was associated with micro-cracks leading to a decrease in the joint shear strength. © Copyright 2017 by ASTM International.Item The effect of reflow temperature on time at the end of gravity zone (TGZ) of Sn-3.8Ag-0.7Cu solder alloy(ASTM International, 2020) Panikar, R.S.; Amogha Skanda, V.; Tikale, S.; Prabhu, K.N.The reflow time for solder until the end of the gravity zone (Tgz) is considered to be the optimum reflow time for obtaining high mechanical performance from lead-free solders. In the present work, the effect of reflow time and temperature on Tgz of Sn-3.8Ag-0.7Cu (SAC387) lead-free solder alloy reflowed on the copper substrate has been investigated. The evolution of interfacial microstructure and solder bond shear strength under different reflow temperatures and time was assessed. Solder balls weighing 0.08 ± 0.01 g were reflowed at 260°C, 280°C, and 300°C for reflow times of 30 s, 60 s, 120 s, and 240 s. Times at the end of the gravity zone for SAC387 solder were obtained as 110 ± 5 s, 55 ± 5 s, and 23 ± 3 s for reflow temperatures of 260°C, 280°C and 300°C, respectively. The contact angle for SAC387 solder on the copper substrate at Tgz was found to be 25.5° ± 0.2° for all reflow temperatures. Scanning electron microscopy revealed the formation of a Cu6Sn5 intermetallic compound (IMC) layer at the interface. The IMC layer thickness increased with increase in reflow temperature and time. Maximum solder joint strength was obtained at Tgz reflow times for all reflow temperatures. Microstructures of samples reflowed beyond the gravity zone showed secondary Cu6Sn5 precipitation in the solder bulk. The present investigation reveals a reduction in Tgz reflow time for SAC387 lead-free solder at higher operating reflow temperatures. © © 2020 by ASTM International