Faculty Publications
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Item Comparison of spreading behaviour and interfacial microstructure in Sn-0·7Cu, Sn-0·3Ag-0·7Cu and Sn-2·5Ag-0·5Cu lead free solder alloys on Fe-42Ni substrate(Maney Publishing michael.wagreich@univie.ac.at, 2013) Satyanarayan, S.; Prabhu, K.In the present work, spreading behaviour and development of interfacial microstructure in Sn- 0·7Cu, Sn-0·3Ag-0·7Cu and Sn-2·5Ag-0·5Cu lead free solder alloys on Fe-42Ni substrates having two different surface textures were investigated. Smooth textured surfaces yielded better wettability than rough surfaces particularly for Sn-0·7Cu solder alloy. Wettability of Sn-0·7Cu solder on rough textured surfaces was found to be poor compared to other solder alloys. Spreading of Sn-0·7Cu solder on substrate surface showed longer viscous regime, Sn-2·5Ag- 0·5Cu solder exhibited shortest viscous regime. Sn-0·3Ag-0·7 solder showed intermediate behaviour. Sn-Cu solder alloy exhibited needle and coarse shaped (Cu,Ni)6Sn5 intermetallics at the interface and in the matrix of the solder alloy on smooth substrate, whereas on rough substrate, formation of only coarse shaped (Cu,Ni)6Sn5 intermetallic compounds (IMCs) was observed. For Sn-0·3Ag-0·7Cu solder alloy, Fe-Ni-Sn and FeSn2 IMCs identified at the interface. (Cu,Ni)6/Sn5 IMCs were found to be less coarser than as observed at Sn-0·7Cu/substrate interface. Sn-2·5Ag-0·5Cu alloy exhibited (Cu,Ni) 3Sn4 and (Cu,Ni)6 Sn5 IMCs at the interface and in the bulk of solder alloy. © 2013 Institute of Materials, Minerals and Mining.Item Effect of purging gas on wetting behavior of Sn-3.5Ag lead-free solder on nickel-coated aluminum substrate(Springer Science and Business Media, LLC, 2013) Prabhu, K.; Varun, M.; Satyanarayan, S.The wetting characteristics of Sn-3.5Ag lead-free solder alloy on nickel-coated aluminum substrates in air (ambient), nitrogen, and argon atmospheres were investigated. The contact angles for the solder alloy obtained under air and argon atmospheres were in the range of 36 -38. With nitrogen atmosphere the contact angle was found to be significantly lower at about 26. Solder solidifying in air exhibited needle-shaped tin-rich dendrites surrounded by a eutectic matrix. The amount of tin dendrites decreased in argon atmosphere. However, the morphology of tin dendrites transformed from needle-shaped to nearly non-dendritic shape as the soldering atmosphere was changed from air to nitrogen. The interfacial microstructures revealed the presence of Ni 3Sn and Ni3Sn4 IMCs at the interface. The enhanced wettability observed under nitrogen atmosphere is attributed to the higher thermal conductivity of nitrogen gas and the formation of higher amount of Ni3Sn IMCs at the interface compared to air and argon atmospheres. © 2012 ASM International.Item Reactive wetting of Sn-2.5Ag-0.5Cu solder on copper and silver coated copper substrates(Springer Science and Business Media, LLC, 2013) Prabhu, K.In the present work, wetting characteristics and morphology of intermetallic compounds (IMCs) formed between Sn-2.5Ag-0.5Cu lead-free solder on copper (Cu) and silver (Ag) coated copper substrates were compared. It was found that, Ag coated Cu substrate improved the wettability of solder alloy. The average values of contact angles of solder alloy solidified on Ag coated Cu substrate were reduced to about 50 % as compared to contact angles obtained on Cu substrates. Flow restrictivity for spreading of solder on Ag coated Cu was found to be lower as compared to Cu substrate. The spreading of solder alloy on Ag coated Cu exhibited halo zone. Coarse needle shaped Cu6Sn 5 IMCs were observed at the solder/Cu substrate interface whereas at the solder/Ag coated Cu interface Cu6Sn5 IMCs showed scallop morphology. The formation of Cu3Sn IMC was observed for the spreading of solder alloy on both substrates. The solder/Ag coated Cu substrate interface exhibited more particulates of Ag3Sn precipitates as compared to solder/Cu substrate interface. The improved wettability of solder alloy on Ag coated Cu substrate is due to the formation of scallop IMCs at the interface. © Springer Science+Business Media New York 2012.Item The effect of the addition of strontium and cerium modifiers on microstructure and mechanical properties of hypereutectic Al-Si (LM30) alloy(ASTM International, 2013) Vijayan, V.; Ravi, M.; Prabhu, K.The present work deals with the melt treatment of LM30 hypereutectic Al-Si alloy using cerium and strontium and the assessment of its effect on microstructure and properties of the alloy. The addition of cerium simultaneously modified both primary and eutectic silicon, leading to an increase in ultimate tensile strength, as well as the wear resistance of the alloy. It was found that the coefficient of thermal expansion of the alloy decreased on modification of the microstructure. © 2013 by ASTM International.Item The Effect of Chilling and Ce Addition on the Microstructure and Mechanical Properties of Al-23Si Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Vijayan, V.; Prabhu, K.The present work involves the study of the effect of varying concentration of Ce addition on microstructure and mechanical properties of Al-23%Si alloys. Melt-treated alloys were solidified in copper, brass, stainless steel molds to assess the effect of cooling rate. The effect on microstructure was assessed by measuring the fineness of primary silicon and eutectic silicon particle characteristics. The Ce melt treatment transformed the coarse and irregular primary silicon into refined polyhedral silicon crystals, and the effect was more significant at higher cooling rates. Although the melt treatment had refined the eutectic silicon at lower cooling rates, it did not show any considerable effect on the eutectic silicon at higher cooling rates. The mechanical properties of the alloy increased significantly with increase in cooling rates and cerium concentration. Analysis of the results and literature reveals that the refined primary silicon was formed as a result of an invariant reaction between Ce compounds and primary silicon at higher temperatures. © 2016, ASM International.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.