Navegando por Autor "Spinelli, José Eduardo"

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Interface evaluation of a Bi–Zn eutectic solder alloy : effects of different substrate materials on thermal contact conductance.
(2021) Azeredo, Rudimylla Septimio; Cruz, Clarissa Barros da; Xavier, Marcella Gautê Cavalcante; Lima, Thiago Soares; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
Industry is searching for ways of improving the process control required for the manufacture of electronic circuitry. In this respect, a numerical mathematical model for thermal contact conductance of solder/substrate couples is developed based on an inverse heat conduction problem. The intention of this research is combining the model results and wetting experiments in order to determine if there is a compromise between them in the matter of the Bi–Zn eutectic alloy. Substrate materials considered as priority for the electronics industry were tested. It was found that the heat transfer coefficients (h) and the contact angles (θ) might be related to each other. The Bi–Zn/copper, Bi–Zn/nickel, Bi–Zn/Invar and Bi–Zn/steel couples, in this order, generated θ varying from the smallest to the largest as well as h from the largest to the smallest. Microstructural coarsening effect has been realized with higher spacing between Zn fibers (λZn) referring to a condition of worse heat extraction imposed by an alloy/substrate couple during solidification.
Interfacial heat transfer and microstructural analyses of a Bi- 5% Sb lead- free alloy solidified against Cu, Ni and low-C steel substrates.
(2021) Lima, Thiago Soares; Cruz, Clarissa Barros da; Xavier, Marcella Gautê Cavalcante; Reyes, Rodrigo André Valenzuela; Bertelli, Felipe; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
Bi-Sb system alloys demonstrate high corrosion resistance and good wettability, becoming promising for use as lead-free solder alloys. The simplicity of the phase diagram is also a characteristic of this system, which is isomorphous forming the (Bi,Sb) phase. While extensive research has been performed on heat flow in couples of microelectronics surfaces with eutectic and peritectic alloys, literature regarding the issues of interfacial heat transfer between isomorphous alloys and microelectronics substrates is nonexistent. In this regard, the present research work demonstrates not only the application of a numerical mathematical model for thermal interface conductance but also wetting and interfacial reaction layer results in the formation of phases for the Bi- 5 wt% Sb alloy in different substrate materials. After carrying out the mentioned analyzes in three different conditions, Bi-Sb/copper, Bi-Sb/nickel and Bi-Sb/low-C steel, the wetting angle is shown not to be the predominant factor in controlling the interfacial heat transfer. Instead, the phases forming the interfacial layer from each of the tested substrates have a role in the heat transfer coefficients (h). In the case of the steel substrate, there is no layer formation, which allows greater contact conductance, whereas Bi-Sb/copper and Bi-Sb/nickel couples generate smaller h, being reasonably similar to each other.
Interplay of wettability, interfacial reaction and interfacial thermal conductance in Sn-0.7Cu solder alloy/substrate couples.
(2020) Lima, Thiago Soares; Cruz, Clarissa Barros da; Silva, Bismarck Luiz; Brito, Crystopher Cardoso de; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
Directional solidification experiments coupled with mathematical modelling, drop shape analyses and evaluation of the reaction layers were performed for three different types of joints produced with the Sn-0.7 wt.%Cu solder alloy. The association of such findings allowed understanding the mechanisms affecting the heat transfer efficiency between this alloy and substrates of interest. Nickel (Ni) and copper (Cu) were tested since they are considered work piece materials of importance in electronic soldering. Moreover, low carbon steel was tested as a matter of comparison. For each tested case, wetting angles, integrity and nature of the interfaces and transient heat transfer coefficients, ‘h’, were determined. Even though the copper has a thermal conductivity greater than nickel, it is demonstrated that the occurrence of voids at the copper interface during alloy soldering may decrease the heat transfer efficiency, i.e., ‘h’. Oppositely, a more stable and less defective reaction layer was formed for the alloy/nickel couple. This is due to the sup-pression of the undesirable thermal contraction since the hexagonal Cu6Sn5 intermetallics is stable at temperatures below 186C in the presence of nickel.
Microstructural and segregation efects afecting the corrosion behavior of a high‐temperature Bi‐Ag solder alloy in dilute chloride solution.
(2021) Azeredo, Rudimylla Septimio; Cruz, Clarissa Barros da; Silva, Bismarck Luiz; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
In electronic devices the solder joint is exposed not only to the air but also to moistures and other corrosive media such as chlorine and sulfur compounds. Bi–Ag alloys meet the melting temperature requirement to be classifed as high-temperature solders, therefore, knowledge of corrosion behavior is important for a long-term reliability of Bi–Ag solder connections. However, corrosion studies of Bi–Ag alloys are quite restricted in the literature. In this study, the role of the representative length scale of the microstructure as well as of the efects of Ag segregation on the resulting corrosion behavior of Bi–4 wt% Ag alloy samples are investigated. Cyclic potentiodynamic polarization and electrochemical impedance spectroscopy measurements were performed, and an equivalent circuit was also proposed to simulate the electrochemical corrosion behavior. All the used techniques indicated a tendency of better corrosion resistance associated with the sample having coarser microstructure and less Ag content.
Thermal conductance at Sn‐0.5mass%Al solder alloy/substrate interface as a factor for tailoring cellular/dendritic growth.
(2022) Oliveira Junior, Ricardo; Cruz, Clarissa Barros da; Barros, André dos Santos; Bertelli, Felipe; Spinelli, José Eduardo; Garcia, Amauri; Cheung, Noé
The use of Al for replacing high-cost alloying metals, like Ag, Bi, and Cu, as the second major element in Sn-based alloys, arises as a promising alternative for the development of low-cost Pb-free solder alloys. To date, however, the interfacial characteristics of Sn–Al solder joints in electronic substrates remain barely explored. Thus, the present study focuses on an understanding of the mechanisms afecting the heat transfer efciency between a Sn–Al eutectic alloy and two types of substrates, establishing correlations with the microstructure evolution. Results of solidifcation experiments coupled with mathematical modeling demonstrate an interfacial thermal conductance between the Ni substrate and the Sn-0.5mass%Al alloy higher than that observed for the Sn–Al/Cu couple. Furthermore, Al-rich intermetallics are shown to occur at the interfacial reaction layers for both tested conditions. While dendritic and dendritic/cellular morphologies predominate in the solidifcation of the Sn–Al eutectic alloy in a Cu substrate, the better heat extraction through the Ni substrate induces the growth of refned high-cooling rate cells. Then, growth laws relating the length scale of the Sn-matrix, represented by cellular or primary dendritic spacings, to solidifcation thermal parameters such as cooling rate and growth rate are proposed.