Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
12 results
Search Results
Item Effect of substrate surface roughness on wetting behaviour of vegetable oils(2009) Prabhu, K.N.; Fernades, P.; Kumar, G.Vegetable oils are mainly used in the heat treating industry due to their environmental friendliness. In the present work the effect of surface roughness on spreading of vegetable oils on stainless steel substrates was investigated. Spreading phenomenon was digitally recorded and analyzed. All of the oils under investigation exhibited power law spreading behaviour of the type: A = ktn, where A, t, k and n represent the drop base contact area, spreading time, constant and exponent, respectively. The coconut and sunflower oils exhibited accelerated kinetics owing to their lower viscosity as compared to palm and mineral oils while peanut oil showed intermediate behaviour. Viscous regime was dominant during spreading of mineral and palm oils as compared to that of coconut oil. All the oils took longer period of time on rough surfaces than on smooth surfaces to relax to the same degree of wetting. Oils spreading on rough surfaces had to overcome the additional barrier due to asperities of the rough surface. Contact angle decreased with increase in roughness supporting the Wenzel's proposition. The decrease was significant for increase in roughness from 0.25 ?m to 0.50 ?m for all oils. However, the effect was negligible with further increase in roughness particularly for high viscosity oils. A spread parameter (?) is proposed to account for the variation of contact angle with surface roughness of the substrate and momentum diffusivity of the spreading liquid. The result suggested that low viscosity liquids exhibit improved wetting characteristics during spreading on rough surfaces. A model is proposed to estimate dynamic contact angles on substrates having varying surface roughness. © 2008 Elsevier Ltd. All rights reserved.Item Thermal contact at solder/substrate interfaces during solidification(2009) Nyamannavar, S.; Prabhu, K.N.Heat flux transients at the solder/substrate interface during the solidification of Sn-37Pb and Sn-3.5Ag solder alloys against metallic substrates were estimated by the lumped heat capacitance model and the contact condition was assessed by scanning electronic microscopy (SEM). Copper substrates yielded maximum contact heat flux followed by brass and aluminium substrates. The SEM study in the solder/substrate interfacial region revealed the existence of a clear gap with the aluminium substrate. A conforming contact was obtained with copper and brass substrates. © 2009 Institute of Materials, Minerals and Mining.Item Wetting behaviour and evolution of microstructure of Sn-Ag-Zn solders on copper substrates with different surface textures(2010) Satyanarayan, S.; Prabhu, K.N.The effect of surface roughness on wetting behaviour and evolution of microstructure of two lead-free solders (Sn-2.625Ag-2.25Zn and Sn-1.75Ag-4.5Zn) on copper substrate was investigated. Both solders exhibited good wettability on copper substrates having rough surface and lower wettabilty on smooth surfaces. The contact angles of solders decreased linearly with increase in surface roughness of the substrate. The exponential power law, ?=exp(-K ?n), was used to model the relaxation behaviour of solders. A high intermetallic growth was observed at the interface particularly on copper substrates with rough surface texture. A thin continuous interface showing scallop intermetallic compounds (IMC) was obtained on smooth surfaces. With an increase in surface roughness, the IMC morphology changed from scallop shaped to needle type at the Sn-2.625Ag-2.25Zn solder/substrate interface and nodular to plate like IMCs for Sn-1.75Ag-4.5Zn solder matrix. Copyright © 2010 by ASTM International.Item Wetting behaviour and evolution of microstructure of Sn-Ag-Zn solders on copper substrates with different surface textures(ASTM International, 2011) Satyanarayan, S.; Prabhu, K.N.The effect of surface roughness on wetting behaviour and evolution of microstructure of two lead-free solders (Sn-2.625Ag-2.25Zn and Sn-1.75Ag-4.5Zn) on copper substrate was investigated. Both solders exhibited good wettability on copper substrates having rough surface and lower wettabilty on smooth surfaces. The contact angles of solders decreased linearly with increase in surface roughness of the substrate. The exponential power law, ?=exp(-KT -1), was used to model the relaxation behaviour of solders. A high intermetallic growth was observed at the interface particularly on copper substrates with rough surface texture. A thin continuous interface showing scallop intermetallic compounds (IMC) was obtained on smooth surfaces. With an increase in surface roughness, the IMC morphology changed from scallop shaped to needle type at the Sn-2.625Ag-2.25Zn solder/ substrate interface and nodular to plate like IMCs for Sn-1.75Ag-4.5Zn solder matrix. Copyright © 2010 by ASTM International.Item Wetting behaviour and interfacial microstructure of Sn-Ag-Zn solder alloys on nickel coated aluminium substrates(2011) Satyanarayan, S.; Prabhu, K.N.Wetting behaviours of two lead free solders (Sn-2·625Ag- 2·25Zn and Sn-1·75Ag-4·5Zn) on nickel coated aluminium substrates were investigated. Sn-2·625Ag-2·25Zn exhibited better wettability compared to Sn-1·75Ag-4·5Zn solder. Contact angles of the solders increased with increasing roughness of the substrate. The Young-Dupre equation was used to evaluate the work of adhesion of solder on the substrate. Sn-2·625Ag-2·25Zn solder exhibited higher work of adhesion than Sn-1·75Ag-4·5Zn. A thin continuous layer of Ni 3Sn was detected at the interface between Sn-2·625Ag- 2·25Zn solder and nickel coated Al substrate. Sn-1·75Ag- 4·5Zn solder exhibited scallop intermetallic compounds (IMCs) growing into the solder field as well as a thin continuous IMC in some cases. Ni 3Sn and Ni3Sn4 IMCs were observed at the interface of Sn-1·75Ag-4·5Zn solder and nickel coated Al. © 2011 Institute of Materials, Minerals and Mining.Item Effect of temperature and substrate surface texture on wettability and morphology of IMCs between Sn-0.7Cu solder alloy and copper substrate(2012) Satyanarayan, S.; Prabhu, K.N.In the present work, the effect of soldering temperature (270 and 298 °C) and substrate surface texture (0.02 and 1.12 ?m) on wetting characteristics and morphology of intermetallic compounds (IMCs) between Sn-0.7Cu lead-free solder on copper substrates was investigated. It was found that increase in temperature and substrate surface roughness improved the wettability of solder alloy. However, the effect of surface roughness on wettability was significant as compared to that of temperature. The spreading of solder alloy was uniform on smooth substrate, whereas spreading of the alloy on rough substrate resulted in an oval shape. The morphology of IMCs transformed from long needle shaped to short and thick protrusions of IMCs with increase in surface roughness of the substrate. Needle shaped and thick protruded intermetallics formed at the solder/Cu interface were identified as Cu 6Sn 5 compounds. The formation of Cu 3Sn IMC was observed only for the spreading of solder alloy at 298 °C which contributed to improvement in the wettability of solder alloy on both smooth and rough substrate surfaces. © Springer Science+Business Media, LLC 2012.Item Effect of Reflow Time on Wetting Behavior, Microstructure Evolution, and Joint Strength of Sn-2.5Ag-0.5Cu Solder on Bare and Nickel-Coated Copper Substrates(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Sona, M.; Prabhu, K.N.The effect of reflow time on wetting behavior of Sn-2.5Ag-0.5Cu lead-free solder on bare and nickel-coated copper substrates has been investigated. The solder alloy was reflowed at 270°C for various reflow times of 10 s, 100 s, 300 s, and 500 s. On bare copper substrate, the intermetallic compound (IMC) thickness increased with increase in reflow time, whereas on Ni-coated Cu substrate, the IMC thickness increased up to 300 s followed by a drop for solder alloy reflowed for 500 s. The spreading behavior of the solder alloy was categorized into capillary, gravity (diffusion), and viscous zones. Gravity zone was obtained from 3.8 ± 0.43 s to 38.97 ± 3.38 s and from 5.99 ± 0.5 s to 77.82 ± 8.84 s for the Sn-2.5Ag-0.5Cu/Cu and Sn-2.5Ag-0.5Cu/Ni/Cu system, respectively. Sn-2.5Ag-0.5Cu solder alloy was also reflowed for the period corresponding to the end of the gravity zone (40 s and 80 s on bare and Ni-coated Cu, respectively). The joint strength was maximum at reflow time of 40 s and 80 s for the Sn-2.5Ag-0.5Cu/Cu and Sn-2.5Ag-0.5Cu/Ni/Cu system, respectively. The dynamic contact angle at the end of the gravity (diffusion) zone (?gz) was found to be a better parameter compared with the stabilized contact angle (?f) to assess the effect of the wettability of the liquid solder on the microstructure and joint strength. The present investigation reveals the significance of the gravity zone in assessment of optimum reflow time for lead-free solder alloys. © 2016, The Minerals, Metals & Materials Society.Item The Effect of Wetting Gravity Regime on Shear Strength of SAC and Sn-Pb Solder Lap Joints(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Sona, M.; Prabhu, K.N.The failure of solder joints due to imposed stresses in an electronic assembly is governed by shear bond strength. In the present study, the effect of wetting gravity regime on single-lap shear strength of Sn-0.3Ag-0.7Cu and Sn-2.5Ag-0.5Cu solder alloys reflowed between bare copper substrates as well as Ni-coated Cu substrates was investigated. Samples were reflowed for 10 s, Tgz (time corresponding to the end of gravity regime) and 100 s individually and tested for single-lap shear strength. The single-lap shear test was also carried out on eutectic Sn-Pb/Cu- and Sn-Pb/Ni-coated Cu specimens to compare the shear strength values obtained with those of lead-free alloys. The eutectic Sn-Pb showed significantly higher ultimate shear strength on bare Cu substrates when compared to Sn-Ag-Cu alloys. However, SAC alloys reflowed on nickel-coated copper substrate exhibited higher shear strength when compared to eutectic Sn-Pb/Ni-coated Cu specimens. All the substrate/solder/substrate lap joint specimens that were reflowed for the time corresponding to the end of gravity regime exhibited maximum ultimate shear strength. © 2017, ASM International.Item Development of low-silver content SAC0307 solder alloy with Al2O3 nanoparticles(Elsevier Ltd, 2020) Tikale, S.; Prabhu, K.N.The present study is focused on the development of low Ag content 99Sn-0.3Ag-0.7Cu (SAC0307) solder alloy with Al2O3 nanoparticles reinforcement. The effects of multiple reflow cycles and the addition of Al2O3 nanoparticles in 0.01, 0.05, 0.1, 0.3 and 0.5 percentages by weight on microstructure development and mechanical strength of the solcder joint were first investigated. The addition of ceramic nanoparticles in 0.01-0.5 wt% range resulted in 15-40% increase in the wetting area and about 10-55% increase in the microhardness of the solder. The shear strength of nanoparticles reinforced SAC0307 solder joint increased by 11-53% under multiple reflow conditions. Nano-composite solder joints containing 0.01 and 0.05 wt% Al2O3 nanoparticles showed superior shear strength and improved ductility for two reflow cycles. Hence, these nano-composites were selected and tested for their performance and joint reliability. The surface mount 2220 capacitor joint assemblies with the selected nano-composites reflowed on bare copper and Ni–P coated Cu substrates were investigated. The reliability of the solder joint was assessed by determining the joint shear strength under varying temperature environments. The nano-composite with 0.05 wt% nanoparticles addition resulted in maximum joint reliability compared to monolithic solder. The Ni–P coating on the Cu substrate significantly hindered the IMC growth at the joint interface under different thermal conditions. The joint strength improved by about 26% for samples reflowed on Ni–P surface finish compared to that on bare Cu metallization. The Weibull analysis of the joint shear strength under all thermal conditions suggest that the addition of Al2O3 nanoparticles in very small amounts to SAC0307 solder and the presence of Ni–P surface finish on Cu substrate significantly enhances the performance and reliability of solder joints. In terms of both quality and reliability, the newly developed low-silver content SAC0307+0.05Al2O3 nano-composite is an effective alternate lead-free solder that can be used in microelectronics industry in place of high-silver content Sn–Ag–Cu solders. © 2020 Elsevier B.V.Item Performance and reliability of Al2O3 nanoparticles doped multicomponent Sn-3.0Ag-0.5Cu-Ni-Ge solder alloy(Elsevier Ltd, 2020) Tikale, S.; Prabhu, K.N.The effect of Al2O3 nanoparticles addition on melting, microhardness, microstructural, and mechanical properties of multicomponent Sn-3Ag-0.5Cu-0.06Ni-0.01Ge (SACNiGe) solder alloy was investigated. The shear strength of the capacitor assemblies under varying high-temperature environments for different nanocomposites was assessed and the reliability of the joint was determined using Weibull analysis. The SACNiGe solder doped with 0.01 and 0.05 wt% Al2O3 nanoparticles to prepare nanocomposites and tested on the solder joints for their performance and reliability under different thermal conditions. Plain copper and Ni[sbnd]P layer coated substrates were used to investigate the effect of different surface finish on the joint reliability. The addition of ceramic nanoparticles in small amounts did not affect the melting parameters of the solder. In comparison with the bare solder alloy, nanocomposites yielded about 20% increase in tin-climb height and 14% higher microhardness. The dispersion of ceramic nanoparticles in the matrix and presence of Ni and Ge elements in the solder resulted in substantial microstructure refinement and about 24% supression in intermetallic compounds (IMCs) growth at the joint interface. In comparison with the bare Cu substrate, the Ni[sbnd]P coating on the substrate provided a strong diffusion barrier, promoted thin and complex (Cu, Ni)6Sn5 IMC layer formation at the interface, and significantly retarded the IMC growth kinetics under elevated temperature conditions. Under varying thermal conditions, nanoparticles doped solder compositions showed about 20% increase in the joint shear strength value. The reliability of joints improved appreciably with the addition of 0.05 wt% Al2O3 nanoparticles in the solder. Samples with SACNiGe+0.05Al2O3 nanocomposite reflowed on Ni[sbnd]P coating showed about 32% higher reliability than that on the uncoated-copper substrate. The SACNiGe solder joint performance and reliability could be significantly improved by minor weight percent addition of Al2O3 nanoparticles in the presence of Ni[sbnd]P coating on the substrate. © 2020 Elsevier Ltd