Browsing by Author "Kumarasiri, A."

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    A contact angle based approach to improve the lead-free solder compatibility on nichrome alloy
    (4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Kumarasiri, A.; Attygalle, D.; Amarasinghe, D. A. S.
    Nichrome (Ni/Cr) alloys are using in many industrial applications due to their high corrosion resistance and thermal stability. It is a known fact that a passivation layer tends to form on these alloy surfaces in ambient conditions. This passivation layer is consisting of chromium oxide. This layer alters the surface energy of the nichrome surface, thereby decreases the wettability and work of adhesion on the nichrome surface. Surface free energy is the work required to increase the surface area of a solid phase. Wettability measurements can be done by calculating the contact angles of sessile droplets formed on nichrome surface. The contact angle �� is related to wettability through Young’s Equation. The contact angle of a sessile droplet on a solid surface is measured through the liquid, where a liquid-vapor interface meets the solid surface. Geometrical basis of young’s equation is showed below, γs=γsl+γl Cosθ Whereas the contact angle θ relates with surface free energy of the fluids (���� ), Solid phase free energy ( γs) and solid-liquid interface energy (γsl). Work of adhesion (Wa) can be represented by, Wa=γs+γl-γsl From young’s equation, Wa=γl[Cosθ+1] Lower wettability affects the quality of soldering and thereby the performance of electrical and electronic components. Because poor wettability on the nichrome surfaces leads to poor solderability. Poor soldering can cause a various problem in connecting wires such as resistance variations with time. In this study, a liquid salt solution was used in an acidic environment (ZnCl2/HCl) to remove the oxide passivation layer and, to enhance the wettability of solder on the nichrome surface. Lead-free industrial solder alloy, SN100C (Sn / Cu 0.70% / Ni 0.06% / Ge 0.005%.) was used as the soldering material. Shapes of the solder drop formed on the pre-treated and non-treated Nichrome surface at 325-350 °C were analyzed by image processing. An image processing software was developed to process the images of the solder droplets and to find the contact angles on the nichrome surface. Polynomial and ellipse fittings were applied to analyze the drop shape. Validation of the algorithm implemented in the software was done by conducting a comparison test with known contact angles of droplets. The validation process showed mean absolute error lower than 1%, confirming that the method of image analysis of a sessile droplet is accurate. Results of the study show that the contact angles of solder droplets were reduced by more than 50 % after the treatment.
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    Development of an electrodeposition method to enhance the solderability of lead-free solder on nichrome alloy
    (Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Kumarasiri, A.; Amarasinghe, D.A.S.; Attygalle, D.
    Nichrome (Ni/Cr) alloy is used in many industrial applications due to its unique electrical properties and marketability. These alloys consist of passive surfaces due to the chromium oxide layers formed on the nichrome surface. This passive oxide layer forms when exposed to the ambient environment and tends to change the alloy surface's energy. It also decreases the wettability of common soldering materials, which seriously affects the electrical and electronic manufacturing industry, as the low surface wettability leads to poor solderability. Poorly soldered wires can cause problems such as fluctuating resistance and short-circuiting. In this study, a novel passivity breakdown strategy is introduced to enhance the solderability on nichrome. Solderability was assessed by analyzing solder droplets on the nichrome alloy surface. The potential of nickel electroplating was investigated as a method to improve solderability. Simple electroplating will not give a stable nickel layer on the alloy. Therefore, the conditions and pre-treatments required to achieve a stable electroplated layer on the nichrome surface were studied. A nichrome tape with a thickness of 20 µm was used as the cathode electrode. One side of the nichrome tape was electrolytically polished, and a non-conductive polymer was coated on the other side. A nickel metal plate was used as the anode electrode. An acidic bath containing NiCl2 was used to breakdown the passivity of nichrome. Next, a Watt's type bath was used to electrodeposit nickel on the pre-treated nichrome tape. The electroplating parameters such as plating time, pH, and current density of the Watt's bath were investigated, and the effects of these parameters on the quality of soldering were analyzed. An image processing software and contact angle measuring instrument were developed for the solder droplet analysis. The investigation was carried out by droplet shape analysis, and it was done by employing polynomial and ellipse fitting methods. After nickel electroplating, the contact angles of solder droplets were reduced, which in turn improved the solderability. The optimal conditions for obtaining a better solderability are pH of 4.0, current density of 400 A m2 ⁄ , and plating time of 3 minutes.
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