Faculty Publications
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Item Wetting kinetics and joint strength of Sn-0.3Ag-0.7Cu lead-free solder alloy on copper substrate as a function of reflow time(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Sona, M.; Prabhu, K.Solder plays a vital role in the interconnection of electronic devices in electronic assemblies. As an interconnection material, the solder joint executes electrical, mechanical and thermal functions. The use of lead bearing solders in electronic products is banned due to the toxicity and environmental risks coupled with lead. In the present study, wetting kinetics, interfacial reactions and the formation of intermetallic compounds (IMCs) during solidification of Sn-0.3Ag- 0.7Cu solder alloy on Cu substrate and the corresponding joint strength were studied as a function of reflow time. Experiments were carried out at various reflow times of 10, 100, 300 and 500s. The reflow temperature was maintained at 270°C. The solder alloy showed enhanced wettability on the substrate at longer reflow times. The thickness of IMC layer formed during a reflow time of 10s was 1.67μm and the thickness increased to 2.20μm, 2.85μm, 2.91μm during 100s, 300s and 500s of reflow time respectively. The joint shear test was performed to assess the integrity of Sn-0.3Ag- 0.7Cu solder solidified on Cu substrates using Nordson DAGE 4000 Plus bond tester. The joint strength increased with the increase in reflow time up to 300s and the maximum joint strength was observed for samples reflowed for 300s. Although the samples reflowed for 500s samples showed good wettability, they exhibited lowest joint strength. © (2015) Trans Tech Publications, Switzerland.Item Wettability and bond shear strength of Sn-9Zn lead-free solder alloy reflowed on copper substrate(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Tikale, S.; Sona, M.; Prabhu, K.Lead-free solders are environment friendly and are in great demand for microelectronic applications. In the present study, Sn-9Zn lead free solder alloy was solidified on Cu substrate for different reflow times varying from 10 to 1000s. The influence of reflow time on wetting, bond shear strength and formation of intermetallic compounds (IMCs) was studied using dynamic contact angle analyzer, bond tester and scanning electron microscopy (SEM), respectively. The results indicate that, the wettability of the solder alloy increased with increase in reflow time. Microstructure study revealed the presence of Cu5Zn8 and CuZn5 IMCs at the interface. The thickness of an IMC increased with increase in the reflow time. A mean thickness of Cu5Zn8 IMC layer of about 11μm was obtained for a reflow time of 1000s. The thickness of CuZn5 layer increased up to a reflow time of 100s and decreased thereafter. The bond shear strength increased up to 100s and decreased with increase in reflow time. The decrease in shear strength at higher reflow time is mainly due to the formation of thick Cu5Zn8 IMC layer and diffusion of Sn from bulk solder towards the substrate. The thick IMC layer exhibited micro-cracks leading to the brittle failure of bond under the influence of shear stress. © (2015) Trans Tech Publications, Switzerland.Item Spreading Behaviour and Joint Reliability of Sn–0.3Ag–0.7Cu Lead-Free Solder Alloy on Nickel Coated Copper Substrate as a Function of Reflow Time(Springer India sanjiv.goswami@springer.co.in, 2015) Sona, M.; Prabhu, K.Solder joint directly interfaces electrically, mechanically and thermally with numerous electronic components in electronic assemblies. Sn–Ag–Cu lead-free solder alloys for electronic assembly are being driven by the environmental issues concerning the toxicity of lead. In the present study, spreading behaviour, evolution of intermetallic compounds during solidification of Sn–0.3Ag–0.7Cu solder alloy on Ni coated Cu substrate and the related joint strength were studied as a function of reflow time. Experiments were carried out for various reflow times of 10, 100, 300 and 500 s at a reflow temperature of 270 °C. The solder alloy exhibited improvement in wettability on the substrate at longer reflow times. An increase in the IMC (CuNi)6Sn5 thickness was observed for samples reflowed up to 300 s and the thickness decreased for samples reflowed for 500 s. IMC layer formed were about 0.3, 1.15, 2.03, 1.94 ?m during 10, 100, 300 and 500 s of reflow time respectively. The joint shear test was performed to assess the integrity of the Sn–0.3Ag–0.7Cu solder solidified on Cu substrates. The maximum joint strength was observed for samples reflowed for 100 s. © 2015, The Indian Institute of Metals - IIM.Item Assessment of Joint Reliability of Sn–2.5Ag–0.5Cu Solder/Cu as a Function of Reflow Time(Springer India sanjiv.goswami@springer.co.in, 2016) Sona, M.; Prabhu, K.N.Solder interconnect reliability is exceedingly influenced by the solder material properties, the intermetallics formed during soldering, and the environmentally imposed loads. The current study involves the study of the wetting behaviour, interfacial reactions and growth of intermetallic compounds (IMCs) in Sn–2.5Ag–0.5Cu lead free solder solidified on Cu substrate as function of reflow time. The reflow temperature was maintained at 270 °C and reflow time was varied from 10 to 10,000 s. The solder alloy showed better wettability on the substrate with the increase in reflow time. A growth in Cu6Sn5 IMC thickness was observed up to a reflow time of 500 s. IMC layer formed during a reflow time of 10 s was 3.09 ?m and its thickness increased to 4.40, 8.21, 10.96 ?m during 100, 300 and 500 s reflow time respectively. A decrease in the thickness of IMC was observed for samples reflowed for 1000 s. The IMC thickness increased with further increase in reflow time. The joint reliability of Sn–2.5Ag–0.5Cu solder solidified on copper substrate surfaces was assessed by performing bond shear test. The average shear strength decreased with an increase in reflow time after an optimum value. © 2015, The Indian Institute of Metals - IIM.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 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 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.